tornadic supercell storms: Topics by Science.gov

Sample records for tornadic supercell storms

Stalled Pulsing Inertial Oscillation Model for a Tornadic Cyclone

NASA Technical Reports Server (NTRS)

Costen, Robert C.

2005-01-01

A supercell storm is a tall, rotating thunderstorm that can generate hail and tornadoes. Two models exist for the development of the storm's rotation or mesocyclone - the conventional splitting-storm model, and the more recent pulsing inertial oscillation (PIO) model, in which a nonlinear pulse represents the supercell. Although data support both models and both could operate in the same supercell, neither model has satisfactorily explained the tornadic cyclone. A tornadic cyclone is an elevated vorticity concentration of Rossby number approximately 1000 that develops within the contracting mesocyclone shortly before a major tornado appears at the surface. We now show that if the internal temperature excess due to latent energy release is limited to the realistic range of -12 K to +12 K, the PIO model can stall part way through the pulse in a state of contraction and spin-up. Should this happen, the stalled-PIO model can evolve into a tornadic cyclone with a central pressure deficit that exceeds 40 mb, which is greater than the largest measured value. This simulation uses data from a major tornadic supercell that occurred over Oklahoma City, Oklahoma, USA, on May 3, 1999. The stalled-PIO mechanism also provides a strategy for human intervention to retard or reverse the development of a tornadic cyclone and its pendant tornado.
Tornadogenesis in Simulated Supercells from VORTEX2 Environments

NASA Astrophysics Data System (ADS)

Coffer, Brice Evan

Despite an increased understanding of the environments that favor tornado formation, a high false-alarmrate for tornado warnings still exists. The composite near-stormenvironments of nontornadic and tornadic supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms' tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong supercells with robust mid-level mesocyclones and hook echoes, though the tornadic supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic supercell only produces shallow vortices, which never reach the EF0 wind speed threshold. Even though the nontornadic supercell readily produces subtornadic surface vortices, these vortices fail to be stretched by the low-level updraft. This is due to a disorganized low-level mesocyclone caused by predominately crosswise vorticity in the lowest few hundred meters above ground level within the nontornadic environment. In contrast, the tornadic supercell ingests predominately streamwise horizontal vorticity, which promotes a strong low-level mesocyclone with enhanced dynamic lifting and stretching of surface vertical vorticity. These results support the idea that larger streamwise vorticity leads to a more intense low-level mesocyclone, whereas predominately crosswise vorticity yields a less favorable configuration of the low-level mesocyclone for tornadogenesis. Since it is known that not every stormin seemingly favorable environments is tornadic, either our knowledge of environmental controls on tornadoes is incomplete, or there are factors beyond the environment that determine whether a supercell produces a tornado or not. In other words, tornado formation could be a volatile process that is largely internal to each storm. To assess this, an ensemble of thirty supercell simulations was constructed based on small variations to the nontornadic and tornadic environmental profiles composited from VORTEX2. All simulations produce distinct supercells despite occurring in similar environments. Both the tornadic and nontornadic ensemble members possess ample subtornadic surface vertical vorticity; the determinative factor is whether this vorticity can be converged and stretched by the low-level updraft. Each of the fifteen members in the tornadic VORTEX2 ensemble produces a long-track, intense tornado. Although there are notable differences in the precipitation and near-surface buoyancy fields, each stormfeatures strong dynamic lifting of surface air with vertical vorticity. This lifting is due to a steady low-level mesocyclone, which is linked to the ingestion of predominately streamwise environmental vorticity. In contrast, each nontornadic VORTEX2 simulation features a supercell with a disorganized low-level mesocyclone, due to crosswise vorticity in the lowest few hundred meters in the nontornadic environment. This generally leads to insufficient dynamic lifting and stretching to accomplish tornadogenesis. Even so, forty percent of the nontornadic VORTEX2 ensemble members becomeweakly tornadic. This implies that chaotic within-stormdetails can still play a role, and occasionally lead to marginally tornadic vortices in suboptimal storms. It is also unclear whether systematically varying the lower-tropospheric horizontal vorticity will yield a "tipping point" between nontornadic and tornadic supercells. Additional simulations have been conducted where the environment is systematically varied between the nontornadic and tornadic VORTEX2 composite profiles. The low-level wind profiles are linearly interpolated between the two composites (20/40/60/80%). The interpolated VORTEX2 simulations show that increasing lower tropospheric SRH leads to progressively more organized low-level mesocyclones and a higher probability of tornadic supercells, regardless of the upper-level winds or thermodynamic profile. The mean 0 - 500mSRH value where supercells are consistently tornadic for all the VORTEX2 interpolated simulations is 110m2 s-2. Supercells transitioned from nontornadic to tornadic when at least 40% of the tornadic low-level wind profile was introduced. This transition could not be attributed to warmer outflow temperatures nor the availability of subtornadic vertical vorticity within the hook echo. Instead, the low-level updraft was once again the discriminating factor, as a robust updraft is present directly overtop of the hook echo in each of the tornadic supercells. The fundamental feature of the nontornadic supercells is the low-level updrafts are generally disorganized, with pockets of descent present in the weak echo region. (Abstract shortened by ProQuest.).
Doppler Radar and Lightning Network Observations of a Severe Outbreak of Tropical Cyclone Tornadoes

NASA Technical Reports Server (NTRS)

McCaul, Eugene W., Jr.; Buechler, Dennis; Goodman, Steven; Cammarata, Michael

2003-01-01

Data from a single WSR-88D Doppler radar and the National Lightning Detection Network are used to examine in detail the characteristics of the convective storms that produced a severe tornado outbreak within Tropical Storm Beryl's remnants on 16 August 1994. Comparison of the radar data with reports of tornadoes suggests that only 13 cells produced the 29 tornadoes that were documented in Georgia and the Carolinas on that date. Six of these cells spawned multiple tornadoes, and the radar data confirm the presence of miniature supercells. One of the cells was identifiable on radar for 11 hours, spawning tornadoes over a time period spanning approximately 6.5 hours. Several other tornadic cells also exhibited great longevity, with cell lifetimes greater than ever previously documented in a landfalling tropical cyclone tornado event, and comparable to those found in major midlatitude tornadic supercell outbreaks. Time-height analyses of the three strongest tornadic supercells are presented in order to document storm kinematic structure and to show how these storms appear at different ranges from a WSR-88D radar. In addition, cloud-to-ground (CG) lightning data are examined for the outbreak, the most intense tropical cyclone tornado event studied thus far. Although the tornadic cells were responsible for most of Beryl's CG lightning, flash rates were only weak to moderate, even in the most intense supercells, and in all the tornadic storms the lightning flashes were almost entirely negative in polarity. A few of the single-tornado storms produced no detectable CG lightning at all. In the stronger cells, there is some evidence that CG lightning rates decreased during tornadogenesis, as has been documented before in some midlatitude tornadic storms. A number of the storms spawned tornadoes just after producing their final CG lightning flashes. Surprisingly, both peak currents and positive flash percentages were larger in Beryl s nontornadic storms than in the tornadic ones. Despite some intriguing patterns, the CG lightning behavior in this outbreak remains mostly inconsistent and ambiguous, and offers only secondary value for warning guidance. The present findings argue in favor of the implementation of observing systems capable of continuous monitoring of total lightning activity in storms.
Cloud-to-Ground Lightning Characteristics of a Major Tropical Cyclone Tornado Outbreak

NASA Technical Reports Server (NTRS)

McCaul, Eugene W., Jr.; Buechler, Dennis; Goodman, Steven J.

1999-01-01

A comprehensive analysis has been conducted of the cloud-to-ground lightning activity occurring within a landfalling tropical cyclone that produced an outbreak of strong and damaging tornadoes. Radar data indicate that 12 convective cells were responsible for 29 tornadoes, several of which received an F3 intensity rating, in the southeastern United States on 16 August 1994 within the remnants of Tropical Storm Beryl. Of these 12 tornadic storms, the most active cell produced 315 flashes over a 5.5 hour period, while the other storms were less active. Three tornadic storms failed to produce any CG lightning at all. In general, the tornadic storms were more active electrically than other non-tornadic cells within Beryl's remnants, although the flash rates were rather modest by comparison with significant midlatitude severe storm events. Very few positive polarity flashes were found in the Beryl outbreak. During some of the stronger tornadoes, CG flash rates in the parent storms showed sharp transient decreases. Doppler radar data suggest the stronger tornadic storms were small supercells, and the lightning data indicate these storms exhibited lightning characteristics similar to those found in heavy-precipitation supercell storms.
Doppler Radar and Cloud-to-Ground Lightning Observations of a Severe Outbreak of Tropical Cyclone Tornadoes

NASA Technical Reports Server (NTRS)

McCaul, Eugene W., Jr.; Buechler, Dennis; Cammarata, Michael; Arnold, James E. (Technical Monitor)

2002-01-01

Data from a single WSR-88D Doppler radar and the National Lightning Detection Network are used to examine the characteristics of the convective storms that produced a severe tornado outbreak within Tropical Storm Beryl's remnants on 16 August 1994. Comparison of the radar data with reports of tornadoes suggests that only 12 cells produced the 29 tornadoes that were documented in Georgia and the Carolinas on that date. Six of these cells spawned multiple tornadoes, and the radar data confirm the presence of miniature supercells. One of the cells was identifiable on radar for 11 hours, spawning tornadoes over a time period spanning approximately 6.5 hours. Time-height analyses of the three strongest supercells are presented in order to document storm kinematic structure and evolution. These Beryl mini-supercells were comparable in radar-observed intensity but much more persistent than other tropical cyclone-spawned tornadic cells documented thus far with Doppler radars. Cloud-to-ground lightning data are also examined for all the tornadic cells in this severe swarm-type tornado outbreak. These data show many of the characteristics of previously reported heavy-precipitation supercells. Lightning rates were weak to moderate, even in the more intense supercells, and in all the storms the lightning flashes were almost entirely negative in polarity. No lightning at all was detected in some of the single-tornado storms. In the stronger cells, there is some evidence that lightning rates can decrease during tornadogenesis, as has been documented before in some midlatitude tornadic storms. A number of the storms spawned tornadoes just after producing their final cloud-to-ground lightning flashes. These findings suggest possible benefits from implementation of observing systems capable of monitoring intracloud as well as cloud-to-ground lightning activity.
Cloud-to-ground lightning in a tornadic storm on 8 May 1986

NASA Technical Reports Server (NTRS)

Macgorman, Donald R.; Nielsen, Kurt E.

1991-01-01

The National Severe Storms Laboratory (NSSL) gathered Doppler radar and lightning ground strike data on a supercell storm that produced three tornadoes, including an F3 tornado in Edmond, Oklahoma, approximately 40 km north of NSSL. The Edmond storm formed 30 km ahead of a storm complex and developed its first and most damaging tornado just as the storm complex started to overtake it from the west. Lightning strike locations tended to concentrate just north of the mesocyclone, close to and inside a 50 dBZ reflectivity core. Positive ground flashes began just prior to the storm becoming tornadic, and positive flash rates peaked during the tornadic stage of the storm.
Proximity sounding analysis for derechos and supercells: an assessment of similarities and differences

NASA Astrophysics Data System (ADS)

Doswell, Charles A.; Evans, Jeffry S.

Proximity soundings (within 2 h and 167 km) of derechos (long-lived, widespread damaging convective windstorms) and supercells have been obtained. More than 65 derechos, accompanied by 115 proximity soundings, are identified during the years 1983 to 1993. The derechos have been divided into categories according to the synoptic situation: strong forcing (SF), weak forcing (WF), and "hybrid" cases (which are neither weakly nor strongly forced). Nearly 100 supercell proximity soundings have been found for the period 1998 to 2001, subdivided into nontornadic and tornadic supercells; tornadic supercells were further subdivided into those producing significant (>F1 rating) tornadoes and weak tornadoes (F0-F1 rating). WF derecho situations typically are characterized by warm, moist soundings with large convective available potential instability (CAPE) and relatively weak vertical wind shear. SF derechos usually have stronger wind shears, and cooler and less moist soundings with lower CAPE than the weakly forced cases. Most derechos exhibit strong storm-relative inflow at low levels. In WF derechos, this is usually the result of rapid convective system movement, whereas in SF derechos, storm-relative inflow at low levels is heavily influenced by relatively strong low-level windspeeds. "Hybrid" cases collectively are similar to an average of the SF and WF cases. Supercells occur in environments that are not all that dissimilar from those that produce SF derechos. It appears that some parameter combining instability and deep layer shear, such as the Energy-Helicity Index (EHI), can help discriminate between tornadic and nontornadic supercell situations. Soundings with significant tornadoes (F2 and greater) typically show high 0-1 km relative humidities, and strong 0-1 km shear. Results suggest it may not be easy to forecast the mode of severe thunderstorm activity (i.e., derecho versus supercell) on any particular day, given conditions that favor severe thunderstorm activity in general. It is possible that the convective initiation mechanism is an important factor, with linear initiation favoring derechos, whereas nonlinear forcing might favor supercells. Upper-level storm-relative flow in supercells tends to be rear-to-front, whereas for derechos, storm-relative flow tends to be front-to-rear through a deep surface-based layer. However, knowing the storm-relative hodograph requires knowledge of storm motion, which can be a challenge to predict. These results generally imply that probabilistic forecasts of convective mode could be a successful strategy.
Doppler Radar and Lightning Network Observations of a Severe Outbreak of Tropical Cyclone Tornadoes

NASA Technical Reports Server (NTRS)

Mccaul, Eugene W., Jr.; Buechler, Dennis E.; Goodman, Steven J.; Cammarata, Michael

2004-01-01

Data from a single Weather Surveillance Radar-1988 Doppler (WSR-88D) and the National Lightning Detection Network are used to examine the characteristics of the convective storms that produced a severe tornado outbreak, including three tornadoes that reached F3 intensity, within Tropical Storm Beryl s remnants on 16 August 1994. Comparison of the radar data with reports of tornadoes suggests that only 13 cells produced the 29 tornadoes that were documented in Georgia and the Carolinas on that date. Six of these cells spawned multiple tornadoes, and the radar data confirm the presence of miniature supercells. One of the cells was identifiable on radar for 11 h. spawning tornadoes over a time period spanning approximately 6.5 h. Several other tornadic cells also exhibited great longevity, with cell lifetimes longer than ever previously documented in a landfalling tropical cyclone (TC) tornado event. This event is easily the most intense TC tornado outbreak yet documented with WSR-88Ds. Time-height analyses of the three strongest tornadic supercells are presented in order to document storm kinematic structure and to show how these storms appear at different ranges from a WSR-88D. In addition, cloud-to-ground (CG) lightning data are examined in Beryl s remnants. Although the tornadic cells were responsible for most of Beryl's CG lightning, their flash rates were only weak to moderate, and in all the tornadic storms the lightning flashes were almost entirely negative in polarity. A few of the single-tornado storms produced no detectable CG lightning at all. There is evidence that CG lightning rates decreased during the tornadoes, compared to 30-min periods before the tornadoes. A number of the storms spawned tornadoes just after producing their final CG lightning flashes. Contrary to the findings for flash rates, both peak currents and positive flash percentages were larger in Beryl's nontornadic storms than in the tornadic ones.
Observational analysis of the interaction between a baroclinic boundary and supercell storms on 27 April 2011

NASA Astrophysics Data System (ADS)

Sherrer, Adam Thomas

A thermal boundary developed during the morning to early afternoon hours on 27 April as a result of rainfall evaporation and shading from reoccurring deep convection. This boundary propagated to the north during the late afternoon to evening hours. The presence of the boundary produced an area more conducive for the formation of strong violent tornadoes through several processes. These processes included the production of horizontally generated baroclinic vorticity, increased values in storm-relative helicity, and decreasing lifting condensation level heights. Five supercell storms formed near and/or propagated alongside this boundary. Supercells that interacted with this boundary typically produced significant tornadic damage over long distances. Two of these supercells formed to the south (warm) side of the boundary and produced a tornado prior to crossing to the north (cool) side of the boundary. These two storms exhibited changes in appearance, intensity, and structure. Two other supercells formed well south of the boundary. These two storms remained relatively weak until they interacted with the boundary. These storms then rapidly intensified and produced tornadoes. Supercells that formed well into the cool side of the boundary either did not produce tornadoes or the tornadoes were determined to be weak in nature.
Analyses and forecasts of a tornadic supercell outbreak using a 3DVAR system ensemble

NASA Astrophysics Data System (ADS)

Zhuang, Zhaorong; Yussouf, Nusrat; Gao, Jidong

2016-05-01

As part of NOAA's "Warn-On-Forecast" initiative, a convective-scale data assimilation and prediction system was developed using the WRF-ARW model and ARPS 3DVAR data assimilation technique. The system was then evaluated using retrospective short-range ensemble analyses and probabilistic forecasts of the tornadic supercell outbreak event that occurred on 24 May 2011 in Oklahoma, USA. A 36-member multi-physics ensemble system provided the initial and boundary conditions for a 3-km convective-scale ensemble system. Radial velocity and reflectivity observations from four WSR-88Ds were assimilated into the ensemble using the ARPS 3DVAR technique. Five data assimilation and forecast experiments were conducted to evaluate the sensitivity of the system to data assimilation frequencies, in-cloud temperature adjustment schemes, and fixed- and mixed-microphysics ensembles. The results indicated that the experiment with 5-min assimilation frequency quickly built up the storm and produced a more accurate analysis compared with the 10-min assimilation frequency experiment. The predicted vertical vorticity from the moist-adiabatic in-cloud temperature adjustment scheme was larger in magnitude than that from the latent heat scheme. Cycled data assimilation yielded good forecasts, where the ensemble probability of high vertical vorticity matched reasonably well with the observed tornado damage path. Overall, the results of the study suggest that the 3DVAR analysis and forecast system can provide reasonable forecasts of tornadic supercell storms.
The terminal area simulation system. Volume 2: Verification cases

NASA Technical Reports Server (NTRS)

Proctor, F. H.

1987-01-01

The numerical simulation of five case studies are presented and are compared with available data in order to verify the three-dimensional version of the Terminal Area Simulation System (TASS). A spectrum of convective storm types are selected for the case studies. Included are: a High-Plains supercell hailstorm, a small and relatively short-lived High-Plains cumulonimbus, a convective storm which produced the 2 August 1985 DFW microburst, a South Florida convective complex, and a tornadic Oklahoma thunderstorm. For each of the cases the model results compared reasonably well with observed data. In the simulations of the supercell storms many of their characteristic features were modeled, such as the hook echo, BWER, mesocyclone, gust fronts, giant persistent updraft, wall cloud, flanking-line towers, anvil and radar reflectivity overhang, and rightward veering in the storm propagation. In the simulation of the tornadic storm a horseshoe-shaped updraft configuration and cyclic changes in storm intensity and structure were noted. The simulation of the DFW microburst agreed remarkably well with sparse observed data. The simulated outflow rapidly expanded in a nearly symmetrical pattern and was associated with a ringvortex. A South Florida convective complex was simulated and contained updrafts and downdrafts in the form of discrete bubbles. The numerical simulations, in all cases, always remained stable and bounded with no anomalous trends.
An investigation of the environment surrounding supercell thunderstorms using wind profiler data

NASA Astrophysics Data System (ADS)

Thornhill, Kenneth Lee, II

1998-12-01

One of the cornerstones of severe thunderstorm research has been quantifying the relationship between the ambient vertical wind profile and the environment of a supercell thunderstorm. Continual refinement of that understanding will lead to the ability to distinguish between tornadic and non-tornadic supercells. Recently, studies have begun to show the importance of the mid-level winds (about 3-6 km), in addition to the normally analyzed 0-3 km inflow layer winds. The 32 wind profilers of the NOAA Profiler Network provide a new source of wind field data that is of higher temporal and spatial resolution that the normally used radiosonde soundings. Continuous raw wind field data (u, v, and w) is now available every 6 minutes, with a quality controlled hourly averaged wind field data set also available. In this work, a 6-minute quality control algorithm is presented and utilized. This 6-minute quality controlled wind data can be used to calculate predictive parameters such as storm relative environmental helicity, Bulk Richardson Number shear, and positive mean shear, indices that are normally calculated only for the inflow layer. In addition, the time series evolution of the mean midlevel winds and the mean vertical winds can also be examined. This present work concentrates on the 1994 and 1995 spring tornado seasons in the central plains of the United States. Combining the data from the NOAA Profiler Network with the data collected from the Verification of the Origins of Rotation in Tornadoes Experiment, the time series evolution of the several indices mentioned above are examined for the winds above the inflow layer in an attempt to add to the current understanding of the relationship between the vertical wind profile and the environment of tornadic and non-tornadic supercell thunderstorms.
The application of UAS towards tornado research and forecasting

NASA Astrophysics Data System (ADS)

Houston, A. L.; Argrow, B. M.; Frew, E.; Weiss, C.

2014-12-01

UAS hold significant potential to advance the understanding of tornadoes and improve tornado warning skill. While the current regulatory environment places limits on the application of UAS towards these ends, demonstrated success targeting tornadic and non-tornadic supercells proves the general feasibility of this work. In this presentation we will summarize the successes using UAS to collect data in the vicinity of supercell thunderstorms and discuss ways that these data, along with additional data collected in future field campaigns, can be used answer basic research questions concerning tornado formation and applied research questions concerning the value of UAS in the tornado warning decision process. The associative relationship between the rear-flank downdraft (RFD) and tornadogenesis has long been recognized. Yet, despite decades of research focused on tornadoes, the causal relationship between the RFD and tornadogenesis remains unresolved. In the presentation, we will describe ways that UAS could be used to test hypotheses posed to explain this causal relationship. We will also present a strategy to quantify the impact of UAS on tornado warning skill. Through controlled forecast experiments conducted using data collected through small field campaigns that leverage prior success targeting supercell thunderstorms with UAS, the value of targeted surveillance of potentially tornadic storms using UAS can be assessed. Significant changes to the existing regulatory environment are likely required for UAS, operated in a targeted surveillance mode, to contribute to improving tornado warning skill, but progress can be made today towards quantifying the impact that UAS could make.
The 2008 Super Tuesday Tornado Outbreak: Synthetic Dual Doppler Analysis of Contrasting Tornadic Storm Types

NASA Technical Reports Server (NTRS)

Knupp, Kevin R.; Coleman, Timothy; Carey, Larry; Peterson, Walt; Elkins, Calvin

2008-01-01

During the Super Tuesday Tornado Outbreak on 5-6 February, a significant number of storms passed within about 40 km of WSR-88D radars. This distance, combined with the significant motion vector (from the southwest at 20-25 m per second) of relatively steady storms, is amenable to a synthetic dual Doppler analysis during the times when the storms passed the WSR-88D locations. Nine storms will be analyzed using the SDD technique. The following table provides their general characteristics and nearest approach to the 88D radars. For this data set, storm structure ranges from isolated supercell to QLCS. Each storm will be analyzed for a 40-60 min period during passage by the WSR-88D radar to determine general storm properties. Analysis of high-resolution single Doppler data around the time of passage (plus or minus 30 min), combined with 1-2 SDD analyses, will be used to examine the kinematic structure of low-level circulations (e.g., mesocyclone, downdraft) and the relation to the parent storm. This analysis may provide insights on the fundamental differences between cyclonic circulations in supercell storms and those within QCLS's.
Semi-Autonomous Small Unmanned Aircraft Systems for Sampling Tornadic Supercell Thunderstorms

NASA Astrophysics Data System (ADS)

Elston, Jack S.

This work describes the development of a network-centric unmanned aircraft system (UAS) for in situ sampling of supercell thunderstorms. UAS have been identified as a well-suited platform for meteorological observations given their portability, endurance, and ability to mitigate atmospheric disturbances. They represent a unique tool for performing targeted sampling in regions of a supercell thunderstorm previously unreachable through other methods. Doppler radar can provide unique measurements of the wind field in and around supercell thunderstorms. In order to exploit this capability, a planner was developed that can optimize ingress trajectories for severe storm penetration. The resulting trajectories were examined to determine the feasibility of such a mission, and to optimize ingress in terms of flight time and exposure to precipitation. A network-centric architecture was developed to handle the large amount of distributed data produced during a storm sampling mission. Creation of this architecture was performed through a bottom-up design approach which reflects and enhances the interplay between networked communication and autonomous aircraft operation. The advantages of the approach are demonstrated through several field and hardware-in-the-loop experiments containing different hardware, networking protocols, and objectives. Results are provided from field experiments involving the resulting network-centric architecture. An airmass boundary was sampled in the Collaborative Colorado Nebraska Unmanned Aircraft Experiment (CoCoNUE). Utilizing lessons learned from CoCoNUE, a new concept of operations (CONOPS) and UAS were developed to perform in situ sampling of supercell thunderstorms. Deployment during the Verification of the Origins of Rotation in Tornadoes Experiment 2 (VORTEX2) resulted in the first ever sampling of the airmass associated with the rear flank downdraft of a tornadic supercell thunderstorm by a UAS. Hardware-in-the-loop simulation capability was added to the UAS to enable further assessment of the system and CONOPS. The simulation combines a full six degree-of-freedom aircraft dynamic model with wind and precipitation data from simulations of severe convective storms. Interfaces were written to involve as much of the system's field hardware as possible, including the creation of a simulated radar product server. A variety of simulations were conducted to evaluate different aspects of the CONOPS used for the 2010 VORTEX2 field campaign.
Use of Dual-Polarization Radar Variables to Assess Low-Level Wind Shear in Severe Thunderstorm Near-storm Environments in the Tennessee Valley

NASA Technical Reports Server (NTRS)

Crowe, Christina C.; Schultz, Christopher J.; Kumjian, Matthew; Carey, Lawerence D.; Petersen, Walter A.

2011-01-01

The upgrade of the National Weather Service (NWS) network of S ]band dual-polarization radars is currently underway, and the incorporation of polarimetric information into the real ]time forecasting process will enhance the forecaster fs ability to assess thunderstorms and their near ]storm environments. Recent research has suggested that the combination of polarimetric variables differential reflectivity (ZDR) and specific differential phase (KDP) can be useful in the assessment of low level wind shear within a thunderstorm. In an environment with strong low ]level veering of the wind, ZDR values will be largest along the right inflow edge of the thunderstorm near a large gradient in horizontal reflectivity (indicative of large raindrops falling with a relative lack of smaller drops), and take the shape of an arc. Meanwhile, KDP values, which are proportional to liquid water content and indicative of a large number of smaller drops, are maximized deeper into the forward flank precipitation shield than the ZDR arc as the smaller drops are being advected further from the updraft core by the low level winds than the larger raindrops. Using findings from previous work, three severe weather events that occurred in North Alabama were examined in order to assess the utility of these signatures in determining the potential for tornadic activity. The first case is from October 26, 2010, where a large number of storms indicated tornadic potential from a standard reflectivity and velocity analysis but very few storms actually produced tornadoes. The second event is from February 28, 2011, where tornadic storms were present early on in the event, but as the day progressed, the tornado threat transitioned to a high wind threat. The third case is from April 27, 2011, where multiple rounds of tornadic storms ransacked the Tennessee Valley. This event provides a dataset including multiple modes of tornadic development, including QLCS and supercell structures. The overarching goal of examining these three events is to compare dual ]polarization features from this larger dataset to previous work and to determine if these signatures can be a useful indication of the potential for tornadic activity associated with the amount of low ]level wind shear in the near ]storm environment.
Large charge moment change lightning on 31 May to 1 June 2013, including the El Reno tornadic storm

NASA Astrophysics Data System (ADS)

Lang, Timothy J.; Cummer, Steven A.; Petersen, Danyal; Flores-Rivera, Lizxandra; Lyons, Walter A.; MacGorman, Donald; Beasley, William

2015-04-01

On 31 May 2013, a line of severe tornadic thunderstorms (the El Reno event) developed during the local afternoon in central Oklahoma, USA. Within range of the Oklahoma Lightning Mapping Array, the evolution of the event can be separated into three distinct periods: an Early period (before 02:00 UTC on 1 June) when the storm consisted of discrete supercells, a Middle period (02:00-05:00 UTC) when the convection began merging into a linear feature and stratiform precipitation developed, and a Late period (after 05:00 UTC) featuring a mature mesoscale convective system (MCS). Each of these periods demonstrated distinct patterns in the large (>100 C km) charge moment change (CMC) lightning that was produced. During the Early period, large-CMC positive cloud-to-ground (+CG) lightning was produced in the convective cores of supercells. These flashes were small in area (typically <500 km2) and were commonly associated with a sloping midlevel positive charge region in the echo overhang on the storm's forward flank. The Middle period featured a population of larger +CMCs (>500 km2, >300 C km) in the developing stratiform, similar to typical sprite-parent lightning in MCSs. During the Late period, convective large CMC +CGs ceased and instead large-CMC negative CGs were produced in and near the MCS convection. These flashes neutralized charge both in convection as well as in adjacent stratiform and anvil precipitation. The results suggest that the CMC metric has potential applications for studying tropospheric weather.
A Comparison of Cloud-to-Ground Lightning Characteristics and Observations from Multiple Networks and Videos during the 31 May 2013 El Reno, OK Tornadic Supercell Storm

NASA Astrophysics Data System (ADS)

Kuhlman, K. M.; Coy, J.; Seimon, A.

2015-12-01

Cloud-to-ground (CG) lightning flashes recorded by both the National Lightning Detection Network (NLDN) and Earth Networks Total Lightning Network (ENTLN) are compared with three-dimensional lightning mapping observations from the Oklahoma Lightning Mapping Array (OKLMA) and storm chaser video recorded of the 31 May 2013 El Reno tornadic supercell. The El Reno Survey Project (El-Reno-Survey.net) was created to crowd-source the abundance of storm chaser video from this event and provide open-access to the scientific community of the data. An initial comparison of CG lightning flashes captured on these videos with CG data from NLDN revealed a disagreement on the total number of flashes, with NLDN recording many negative CG flashes at lower peak amplitude not apparent in any of the videos. For this study, the area of the comparison was expanded to include the entire storm and data from both the ENTLN and LMA were added to compare the observations from each network in terms of timestamp, location detection, peak current, and polarity of each flash in the period 2230-2330 UTC. An initial comparison of 557 matched NLDN and ENLTN CG flashes, indicated predominately negative polairy CG flashes (58% NLDN/77% ENI) throughout the storm during this period. However, after a 15 kA peak current filter was applied, the NLDN indicated primarily positive polarity (84% +CG) while ENTLN still indicated primarily negative polarity (77% -CG) for the 264 remaining matched flashes. Before the filter was applied, the average distance between the two networks for the same flash was more than 2 km, but improved to approximately 1 km after the 15 kA filter was applied, likely removing some misidentified cloud flashes of uncertain location. This misclassification of IC flashes as CG at low peak current amplitudes for both networks is further evident when compared to video and the OKLMA data. Additionally, the charge analysis of OKLMA flashes revealed the NLDN-determined positive-polarity as correct every time the NLDN and ENTLN disagreed. For the 2013 El Reno supercell storm, there appears to be a major flaw in the ENTLN's ability to determine the polarity of CG flashes despite having roughly similar peak current magnitudes and location for most CG flash occurrences as the NLDN.
An Analysis of Total Lightning Characteristics in Tornadic Storms: Preparing for the Capabilities of the GLM

NASA Astrophysics Data System (ADS)

Reimel, Karly Jackson

Numerous studies have found that severe weather is often preceded by a rapid increase in the total lightning flash rate. This rapid increase results from numerous intra-cloud flashes forming around the periphery of an intensifying updraft. The relationship between flash rates and updraft intensity is extremely useful to forecasters in severe weather warning decision making processes, but total lightning data has not always been widely available. The Geostationary Lightning Mapper (GLM) will be the first instrument to detect lightning from geostationary orbit, where it will provide a continuous view of lightning over the entire western hemisphere. To prepare for the capabilities of this new instrument, this thesis analyzes the relationship between total lightning trends and tornadogenesis. Four supercellular and two non-supercellular tornadic storms are analyzed and compared to determine how total lightning characteristics differ between dynamically different tornadic storms. Supercellular tornadoes require a downdraft to form while landspout tornadoes form within an intensifying updraft acting on pre-existing vertical vorticity. Results of this analysis suggest that the supercellular tornadoes we studied show a decrease in flash rate and a decrease in lightning mapping array (LMA) source density heights prior to the tornado. This decrease may indicate the formation of a downdraft. In contrast, lightning flash rates increase during landspout formation in conjunction with an intensifying updraft. The total lightning trends appear to follow the evolution of an updraft rather than directly responding to tornadogenesis. To further understand how storm microphysics and dynamics impact the relationship between lightning behavior and tornadogenesis, two of the tornadic supercells were analyzed over Colorado and two were analyzed over Alabama. Colorado storms typically exhibit higher flash rates and anomalous charge structures in comparison to the environmentally different Alabama storms that are typically normal polarity and produce fewer flashes. The difference in microphysical characteristics does not appear to affect the relationship between total lightning trends and tornadogenesis. The capabilities of GLM are yet to be determined because the instrument is still in its calibration/validation stages. However, as part of the GLM cal/val team, we were in a unique position to examine the first-light GLM data and contribute to the assessment of its performance for noteworthy thunderstorm events during the Spring/Summer seasons of 2017. The final chapter of this thesis displays a preliminary analysis of GLM data. A first look into GLM performance is established by comparing GLM data with data from other lightning detecting instruments. Overall, GLM appears to detect fewer flashes than other lightning detecting networks and instruments in Colorado storms, more so for intense storms compared to weaker storms.
Multiple cyclic tornado production modes in the 5 May 2007 Greensburg, Kansas supercell storm

NASA Astrophysics Data System (ADS)

Tanamachi, Robin Lynn

Long-track, violent tornadoes are rare events, but are responsible for a disproportionate majority of tornado fatalities, injuries, and property damage. It has been observed that such tornadoes are often generated as part of a series produced by one supercell, and preceded by one or more smaller tornadoes. At some point, a transition in the tornado production mode occurs, from short-track, cyclic tornado production (mode I), to long-track, single (plus satellite) tornado production (mode II). This transition has been documented only a few times at close range by Doppler weather radars. A cyclic, tornadic supercell ("the Greensburg storm") generated at least 22 tornadoes in southwest Kansas on 5 May 2007. One of these was the first documented EF-5 tornado ("the Greensburg tornado"), which destroyed 95% of the buildings in Greensburg, Kansas and caused 11 fatalities. The University of Massachusetts X-band, polarimetric, mobile Doppler radar (UMass X-Pol), which was operating in the area as part of a severe storms research project, collected data in the Greensburg storm for over an hour, including its transition from tornado production mode I to mode II. The first 10 tornadoes produced by the Greensburg storm can be seen in this UMass X-Pol data set. In this study, the UMass X-Pol data (as well as contemporaneous data from the WSR-88D at Dodge City, Kansas, or KDDC) are analyzed with the aim of diagnosing whether this transition occurred as a result of changes in the environmental wind profile, interaction of tornadoes with the storm's cold pool, or a combination of the two. These efforts met with limited success, largely because of the relative scarcity of observations of low-level flow in the inflow sector of the Greensburg storm. However, in the process, features of the Greensburg storm related to tornado production (such as vortices, updrafts, and polarimetric signatures) are documented, and relationships among them before, during, and after this transition are diagnosed. In particular, it is found that: (1) The horizontal motions of the earlier tornadoes (mode I) tracked to the left with respect to the updraft motion, while the motion of the Greensburg tornado and its satellites (mode II) more closely matched that of the updraft. (2) The vortex signatures in the UMass X-Pol data matched with the surveyed damage tracks. In addition, several non-tornadic circulations were documented. (4) A forward surge and retreat of a RFGF was documented a few minutes before the development of the Greensburg tornado. (4) At least two cyclonic-anticyclonic pairs of satellite tornadoes (of the Greensburg tornado) occurred, possibly indicating the upward arching of low-level horizontal vortex lines over bulges in the RFGF. (5) Weak-echo holes are documented in several tornadoes, and found to be consistently collocated with corresponding vortex signatures in azimuth but biased slightly far from the radar in range. (6) A polarimetric tornadic debris signature is found near the surface in the mature Greensburg tornado. In addition, a ZDR arc is documented whose presence corroborates increasing low-level vertical wind shear in the inflow sector. Other polarimetric supercell features are consistent with those found in previous studies. In an attempt to retrieve in-storm variables not observed by radar, KDDC and UMass X-Pol radar data were assimilated into a numerical weather prediction model using the ensemble Kalman filter (EnKF) technique. Two sets of experiments were performed, one in which UMass X-Pol data were either included or withheld from assimilation with KDDC data, and another in which the 0 -- 3 km AGL initial environmental wind profile was modified to include a low-level jet, or not. Assimilation of UMass X-Pol data results in more pronounced changes to the analyses than the addition of a low-level jet, although both changes result in nearsurface vortices that are stronger, deeper, and longer-lived than in experiments without. When UMass X-Pol data are assimilated, vortices appear in the analyses that correspond to mode I tornadoes, and the southward-spreading, surface cold pool from the Greensburg storm (which likely results from the use of a relatively simple microphysical parameterization scheme) deflects around the assimilated observations of southerly flow at the UMass X-Pol deployment site. Neither of these features appear when UMass X-Pol data are withheld. I close by discussing the implications of these results for future avenues of research involving analysis and assimilation of data from mobile Doppler radars, including storm-scale prediction.

Vertically homogeneous stationary tornado-type vortex

NASA Astrophysics Data System (ADS)

Rutkevich, P. B.; Rutkevych, P. P.

2010-05-01

Tornado is regarded as one of the most dangerous atmosphere phenomena. The tornado phenomenon has been intensively studied so far, however, there is still no established and accepted theory of how tornadoes form, an uncertainty still exists concerning extreme winds and pressure drops in tornadoes. It is commonly accepted that it is possible to describe tornado from the set of nonlinear hydrodynamical equations, however, it is still unclear which non-linear processes are responsible for its formation. Nonlinear terms in the system are associated with either centrifugal force, or entropy transport, or transport of humidity. It appears that the amount and spatial distribution of precipitation with the convection are important indicators of the weather phenomena associated with a particular storm. The low-precipitation supercells that produce relatively little precipitation and yet show clear visual signs of rotation. Low-precipitation supercells occur most often near the surface dryline and, owing to the sparse precipitation and relatively dry environments with little cloudiness. Low-precipitation storms are frequently non-tornadic and many are non-severe despite exhibiting persistent rotation. On the other hand, the so-called high-precipitation storms are characterized by substantial precipitation within their mesocyclonic circulations. When high-precipitation storms have a recognizable hook radar echo, reflectivity in the hook is comparable to those in the precipitation core. High-precipitation supercells are probably the most common form of supercell and produce severe weather of all types including tornadoes. Therefore, in this work we consider a hydrodynamic system with only one nonlinear term associated with atmosphere humidity, which yields energy to the system. The tornado vortex is usually to a good approximation cylindrical so we use cylindrical geometry and homogeneity in vertical direction. In this case the problem reduces to a system of ordinary differential equations. Rotation in the vortex is associated with compressibility so we also take into account the compressibility of the gas. Under certain approximations the problem reduces to a single high-order nonlinear equation. Numerical solution of the obtained high-order equation describes all three velocity components and all thermodynamic parameters in the system. The system exhibits high rotation and strong vertical air flow in the middle part of the vortex.
Lightning rates relative to tornadic storm evolution on 22 May 1981

NASA Technical Reports Server (NTRS)

Macgorman, Donald R.; Burgess, Donald W.; Mazur, Vladislav; Rust, W. David; Taylor, William L.

1989-01-01

Lightning and Doppler radar data for two tornadic storms in Oklahoma on May 22, 1981 are used to analyze ground flash rates relative to the time of tornadoes. It is found that the ground flash rates had no obvious relationship with the tornado times, although the stroke rate in both storms was greatest after the tornadic stage ended. The variations in the cyclone shear and the intracloud flash rates within 10 km of the mesocyclone region are examined. The results suggest that most tornadic storms have an increase in total flash rates near the time of the tornado and that this increase is often dominated by intracloud flashes.
A review of supercell and tornado dynamics

NASA Astrophysics Data System (ADS)

Davies-Jones, Robert

2015-05-01

Thunderstorms that form in strong vertical wind shear often evolve into supercell storms. Supercells are well-organized, monolithic units of vigorous long-lasting convection. A classic supercell in its mature stage consists of a rotating updraft (mid-altitude mesocyclone) and a downdraft that coexists symbiotically with the updraft in an almost steady state. Doppler-radar and visual observations along with computer simulations reveal that tornadic supercells evolve through three stages. Firstly, the updraft starts rotating and a mesocyclone forms aloft, secondly a narrower vortex develops near the ground (thus completing a rotating column that extends from the ground to upper levels), and lastly a tornado forms from contraction of the near-ground cyclone. The updraft tilts environmental horizontal vorticity upwards. The updraft rotates cyclonically as a whole if this vorticity is streamwise in the updrafts' reference frame (i.e., in the direction of the storm-relative wind). Updraft rotation and motion are linked so a complete theory of mid-altitude mesocyclones requires an understanding of how supercells propagate. There are two principle propagation mechanisms; one is linear and the other is nonlinear. The process whereby rotation develops in rising air cannot explain how cyclonic rotation starts near the ground where updrafts and background vertical vorticity are normally weak. A near-ground cyclone does not form without a downdraft. In computer simulations, low-altitude air parcels with cyclonic vorticity have previously subsided in horizontal gradients of buoyancy that generate horizontal vorticity. During an air parcel's descent, its horizontal vorticity is first tipped downward into anticyclonic vorticity, but then upwards into cyclonic vorticity before it reaches the nadir of its trajectory because the vorticity vector is inclined upward relative to the velocity vector. The parcel then flows close to the ground into the updraft where its cyclonic vorticity is greatly amplified as it is stretched vertically. In simulations, this near-ground cyclone collapses into a tornado only if the model includes surface friction, which paradoxically causes the extreme upward and rotary winds. With friction, inflowing air parcels near the ground penetrate much closer to the rotation axis and revolve much faster despite some loss of angular momentum to the ground. Their extra kinetic energy comes from a further loss in their enthalpy.
High-Resolution Analysis Products to Support Severe Weather and Cloud-to-Ground Lightning Threat Assessments over Florida

NASA Technical Reports Server (NTRS)

Case, Jonathan; Spratt, Scott; Sharp, David

2006-01-01

The Applied Meteorology Unit (AMU) located at the Kennedy Space Center (KSC)/Cape Canaveral Air Force Station (CCAFS) implemented an operational configuration of the Advanced Regional Prediction System (ARPS) Data Analysis System (ADAS), as well as the ARPS numerical weather prediction (NWP) model. Operational, high-resolution ADAS analyses have been produced from this configuration at the National Weather Service in Melbourne, FL (NWS MLB) and the Spaceflight Meteorology Group (SMG) over the past several years. Since that time, ADAS fields have become an integral part of forecast operations at both NWS MLB and SMG. To continue providing additional utility, the AMU has been tasked to implement visualization products to assess the potential for supercell thunderstorms and significant tornadoes, and to improve assessments of short-term cloud-to-ground (CG) lightning potential. This paper and presentation focuses on the visualization products developed by the AMU for the operational high-resolution ADAS and AR.PS at the NWS MLB and SMG. The two severe weather threat graphics implemented within ADAS/ARPS are the Supercell Composite Parameter (SCP) and Significant Tornado Parameter (SIP). The SCP was designed to identify areas with supercell thunderstorm potential through a combination of several instability and shear parameters. The SIP was designed to identify areas that favor supercells producing significant tornadoes (F2 or greater intensity) versus non-tornadic supercells. Both indices were developed by the NOAAINWS Storm Prediction Center (SPC) and were normalized by key threshold values based on previous studies. The indices apply only to discrete storms, not other convective modes. In a post-analysis mode, the AMU calculated SCP and SIP for graphical output using an ADAS configuration similar to the operational set-ups at NWS MLB and SMG. Graphical images from ADAS were generated every 15 minutes for 13 August 2004, the day that Hurricane Charley approached and made landfall on the Florida peninsula. Several tornadoes struck the interior of the Florida peninsula in advance of Hurricane Charley's landfall during the daylight hours of 13 August. Since SPC had previously examined this case using SCP and SIP graphics generated from output of the Rapid Update Cycle (RUC) model, this day served as a good benchmark to compare and validate the high-resolution ADAS graphics against the smoother RUC analyses, which serves as background fields to the ADAS analyses. The ADAS-generated SCP and STP graphics have been integrated into the suite of products examined operationally by NWS MLB forecasters and are used to provide additional guidance for assessment of the near-storm environment during convective situations.
Aerosol Effects on Microphysical Processes, Storm Structure, and Cold Pool Strength in Simulated Supercell Thunderstorms from VORTEX-2 and VORTEX-SE

NASA Astrophysics Data System (ADS)

Guo, M.; Dawson, D. T., II; Baldwin, M. E.; Mansell, E. R.

2017-12-01

The cloud condensation nuclei (CCN) concentration has been found to strongly affect microphysical, dynamical and thermodynamical processes in supercells and other deep convective storms. Moreover, recent simulation studies have shown aerosols effects differ between higher- and lower-CAPE environments. Owing to the known sensitivity of severe storms to microphysical differences, studying the impact of aerosols supercell storms different environments is of clear societal importance. Tornadic environments in the southwastern U.S. are generally characterized by lower magnitudes CAPE and deeper tropospheric moisture than those in the Great Plains. These two regions were the focus of Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)-2 and VORTEX-Southeast (SE) field campaigns, respectively. In our study, we simulate several cases from VORTEX-2 and -SE with the Advanced Regional Prediction System (ARPS) Model at 6 different CCN concentrations (100-3000 cm-3). We use NSSL 3-moment microphysics parameterization schemeto explicitly predict precipitation particle size distributions and microphysirocess rates. Overall, storms under the higher-CAPE VORTEX-2 environments are more sensitiveto the change of CCN than those under the lower-CAPE VORTEX-SE environments. Updraft volume decreases as CCN increases for the VORTEX-2 cases, whereas the opposite is true but with a much weaker trend for the VORTEX-SE cases. Moreover, the cold pool strength drops dramatically as CCN surpasses 1000 cm-3n the VORTEX-2 cases but barely changes for the VORTEX-SE cases. Through a microphysics budget analysis, we show the change of the importance of ice processes is key to the differing sensitivities. in the VORTEX-2 cases, deposition to ice nuclei, cloud drop freezing and rain drop freezing in the upper levels (5-11km) contribute more to latent heating since more rain and cloud drops are lifted above the freezing level due to stronger updrafts. For CCN concentration over 1000cm-3, the drops become too small for efficient accretion by graupel and hail, leading to considerable decrease of latent heating and thus updraft volume. Finally, the decrease in cold pool strength in the VORTEX-2 cases at higher CCN is due to the rapid decrease of graupel melting at lower levels (<2km).
A long-lived tornado on 7 December 2010 in mainland Portugal

NASA Astrophysics Data System (ADS)

Belo-Pereira, Margarida; Andrade, Cristina; Pinto, Paulo

2017-03-01

On 7 December 2010 a long lived convective storm formed southwest of Lisbon in an instability line that developed in a very moist and unstable airmass, in the circulation of an extra-tropical cyclone propagating north-eastwards. This storm crossed the Lisbon district and spawned an F3 tornado a few dozens of kilometers to the northeast. Several parameters evaluating buoyancy, available moisture and vertical wind shear, were derived from Lisbon rawinsonde and ECMWF analyses, highlighting an environment that is favourable for tornadic development. The tornado touchdown occurred by 14:15 UTC, lasting for about 45 min and producing an exceptionally long damage path of around 54 km, according to the damage survey. It caused about 18 million Euros damage, > 40 injured people, but no fatalities. This storm had a very long lifetime of at least 5 h, intensified inland, sustained strong updrafts during, at least, 1 h and hold large hail cores as observed on radar. Exhibiting several supercell like features, it also produced intense lightning, with a predominance of cloud-to-ground flashes before the tornado touchdown and intra-cloud flashes during the tornado lifetime. Furthermore, in high resolution visible satellite imagery, a pattern of feeder clouds was identified one hour before tornadogenesis. This pattern has been associated to storm intensification and the onset of severe weather.
The life cycle of a tornadic cloud as seen from a geosynchronous satellite

NASA Technical Reports Server (NTRS)

Hung, R. J.; Dodge, J. C.; Smith, R. E.

1983-01-01

The life span of a severe storm is on the order of a few hours. Rapid-scan infrared and visible observations from geosynchronous satellites can be useful for studying the life cycle of a severe convective storm. By using artificial colors for pixels representing blackbody temperatures of the cloud top, convective storms can be observed throughout their life cycles. In this paper clouds associated with a tornadic storm, the Ringwood, OK tornado on May 29, 1977, are compared with those without a tornadic storm to illustrate how the infrared and visible observations from a geosynchronous satellite can be used to study the differences in their life cycles. The instability of the air mass and the meteorological background are discussed based on balloon observations.
On the measurement of wind speeds in tornadoes with a portable CW/FM-CW Doppler radar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bluestein, H.B.; Unruh, W.P.

1991-01-01

Both the formation mechanism and structure of tornadoes are not yet well understood. The Doppler radar is probably the best remote-sensing instrument at present for determining the wind field in tornadoes. Although much has been learned about the non-supercell tornado from relatively close range using Doppler radars at fixed sites, close-range measurements in supercell tornadoes are relatively few. Doppler radar can increase significantly the number of high-resolution, sub-cloud base measurements of both the tornado vortex and its parent vortex in supercells, with simultaneous visual documentation. The design details and operation of the CW/FM-CW Doppler radar developed at the Los Alamosmore » National Laboratory and used by storm-intercept teams at the Univ. of Oklahoma are described elsewhere. The radar transmits 1 W at 3 cm, and can be switched back and forth between CW and FM-CW modes. In the FM-CW mode the sweep repetition frequency is 15.575 kHz and the sweep width 1.9 MHz; the corresponding maximum unambiguous range and velocity, and range resolution are 5 km, {plus minus} 115 m s{sup {minus}1}, and 78 m respectively. The bistatic antennas, which have half-power beamwidths of 5{degree}, are easily pointed wit the aid of a boresighted VCR. FM-CW Data are recorded on the VCR, while voice documentation is recorded on the audio tape; video is recorded on another VCR. The radar and antennas are easily mounted on a tripod, and can be set up by three people in a minute or two. The purpose of this paper is to describe the signal processing techniques used to determine the Doppler spectrum in the FM-CW mode and a method of its interpretation in real time, and to present data gathered in a tornadic storm in 1990. 15 refs., 7 figs.« less
Lightning activity related to satellite and radar observations of a mesoscale convective system over Texas on 7 8 April 2002

NASA Astrophysics Data System (ADS)

Dotzek, Nikolai; Rabin, Robert M.; Carey, Lawrence D.; MacGorman, Donald R.; McCormick, Tracy L.; Demetriades, Nicholas W.; Murphy, Martin J.; Holle, Ronald L.

2005-07-01

A multi-sensor study of the leading-line, trailing-stratiform (LLTS) mesoscale convective system (MCS) that developed over Texas in the afternoon of 7 April 2002 is presented. The analysis relies mainly on operationally available data sources such as GOES East satellite imagery, WSR-88D radar data and NLDN cloud-to-ground flash data. In addition, total lightning information in three dimensions from the LDAR II network in the Dallas-Ft. Worth region is used. GOES East satellite imagery revealed several ring-like cloud top structures with a diameter of about 100 km during MCS formation. The Throckmorton tornadic supercell, which had formed just ahead of the developing linear MCS, was characterized by a high CG+ percentage below a V-shaped cloud top overshoot north of the tornado swath. There were indications of the presence of a tilted electrical dipole in this storm. Also this supercell had low average CG- first stroke currents and flash multiplicities. Interestingly, especially the average CG+ flash multiplicity in the Throckmorton storm showed oscillations with an estimated period of about 15 min. Later on, in the mature LLTS MCS, the radar versus lightning activity comparison revealed two dominant discharge regions at the back of the convective leading edge and a gentle descent of the upper intracloud lightning region into the trailing stratiform region, apparently coupled to hydrometeor sedimentation. There was evidence for an inverted dipole in the stratiform region of the LLTS MCS, and CG+ flashes from the stratiform region had high first return stroke peak currents.
An index of anomalous convective instability to detect tornadic and hail storms

NASA Astrophysics Data System (ADS)

Qian, Weihong; Leung, Jeremy Cheuk-Hin; Luo, Weimeng; Du, Jun; Gao, Jidong

2017-12-01

In this article, the synoptic-scale spatial structures for raising tornadic and hail storms are compared by analyzing the total and anomalous variable fields from the troposphere to the stratosphere. 15 cases of tornado outbreaks and 20 cases of hail storms that occurred in the central United States during 1980-2011 were studied. The anomalous temperature-height field shows that a tornadic or hail storm usually occurs at the boundary of anomalous warm and cold air masses horizontally in the troposphere. In one side, an anomalous warm air mass in the mid-low troposphere and an anomalous cold air mass in the stratosphere are vertically separated by a positive center of height anomalies at the upper troposphere. In another side, an opposite vertical pattern shows that an anomalous cold air mass in the mid-low troposphere and an anomalous warm air mass in the stratosphere are separated by a negative center of height anomalies at the upper troposphere. Therefore, two pairs of adjacent anomalous warm/cold centers and one pair of anomalous high/low centers combining together form a major tornadic or hail storm paradigm, which can be physically considered as the storage of anomalous potential energy (APE) to generate severe weather. To quantitatively measure the APE, we define an index of anomalous convective instability (ACI) which is a difference of integrating temperature anomalies based on two vertically opposite anomalous air masses. The APE transformation to anomalous kinetic energy, which reduces horizontal and vertical gradients of temperature anomalies, produces anomalous rising and sinking flows in the lower-layer anomalous warm and cold air mass sides, respectively. The intensity of ACI index for tornadic storm cases is 1.5 times larger than that of hail storm cases in average. Thus, this expression of anomalous variables is better than total variables used in the traditional synoptic chart and the ACI index is better than other indices to detect potential tornadic and hail storms in order to understand the environmental conditions affecting severe weather in analytical and model output datasets.
A Low Precipitation Supercell over the Southeast US: A Case Study

NASA Technical Reports Server (NTRS)

Robert, Barry C.; Knupp, Kevin R.; Buechler, Dennis

1998-01-01

On 28 March 1997 a low precipitation supercell storm was observed 125 km east of Memphis, TN. The storm exhibited a visual appearance similar to that of Great Plains low precipitation (LP) supercells while it was being video typed for 35 min. beginning at 2335 UTC. While the storm produced hailstones up to 4.5 cm in diameter, and had a 4 hour lifetime, tornadoes were absent. However, over 20 tornadoes were produced in Kentucky and Tennessee (TN) by other thunderstorms during that afternoon and evening. The purpose of this paper is to document this LP supercell that occurred in the Southeastern US. To the authors' knowledge an LP storm has not yet been documented in the Southeastern US. This paper presents a detailed overview of the LP supercell, including synoptic conditions, radar observations, lightning data and visual observations of the storm.
A study of severe storm electricity via storm intercept

NASA Technical Reports Server (NTRS)

Arnold, Roy T.; Horsburgh, Steven D.; Rust, W. David; Burgess, Don

1985-01-01

Storm electricity data, radar data, and visual observations were used both to present a case study for a supercell thunderstorm that occurred in the Texas Panhandle on 19 June 1980 and to search for insight into how lightning to ground might be related to storm dynamics in the updraft/downdraft couplet in supercell storms. It was observed that two-thirds of the lightning ground-strike points in the developing and maturing stages of a supercell thunderstorm occurred within the region surrounding the wall cloud (a cloud feature often characteristic of a supercell updraft) and on the southern flank of the precipitation. Electrical activity in the 19 June 1980 storm was atypical in that it was a right-mover. Lightning to ground reached a peak rate of 18/min and intracloud flashes were as frequent as 176/min in the final stages of the storm's life.
An investigation of the detection of tornadic thunderstorms by observing storm top features using geosynchronous satellite imagery

NASA Technical Reports Server (NTRS)

Anderson, Charles E.

1991-01-01

The number of tornado outbreak cases studied in detail was increased from the original 8. Detailed ground and aerial studies were carried out of two outbreak cases of considerable importance. It was demonstrated that multiple regression was able to predict the tornadic potential of a given thunderstorm cell by its cirrus anvil plume characteristics. It was also shown that the plume outflow intensity and the deviation of the plume alignment from storm relative winds at anvil altitude could account for the variance in tornadic potential for a given cell ranging from 0.37 to 0.82 for linear to values near 0.9 for quadratic regression. Several predictors were used in various discriminant analysis models and in censored regression models to obtain forecasts of whether a cell is tornadic and how strong tornadic it could be potentially. The experiments were performed with the synoptic scale vertical shear in the horizontal wind and with synoptic scale surface vorticity in the proximity of the cell.
Numerical simulation of intense multi-scale vortices generated by supercell thunderstorms

NASA Astrophysics Data System (ADS)

Finley, Catherine Ann

1998-11-01

A nested grid primitive equation model (RAMS version 3b) is used to study various aspects of tornadoes and the thunderstorms that produce them. A unique aspect of these simulations is that the model was initialized with synoptic data, and telescoping grids allow atmospheric flows ranging from the synoptic-scale down to sub- tornado-scale vortices to be represented in the model. Two different case studies were simulated in this study: June 30, 1993, and May 15, 1991. The June 30, 1993, simulation produced a classical supercell storm which developed at the intersection between a stationary front and an outflow boundary generated by previous convection. As the simulation progressed, additional storms developed west of the main storm along the stationary front. One of these storms interacted with the main storm to produce a single supercell storm. This storm had many characteristics of a high-precipitation (HP) supercell, and eventually evolved into a bow-echo. The transition of the storm into a bow-echo is discussed and possible physical processes responsible for the transition are presented. The June 30, 1993, simulated supercell produced two weak tornadoes. The first tornado developed along the flanking line of the storm to the southeast of the mesocyclone. The second tornado developed along a strong horizontal shear zone beneath the rotating comma-head structure of the HP supercell. Neither tornado was clearly linked to the mesocyclone in the parent storm, and both tornadoes formed first near the surface and then developed upward with time. Circulation and vorticity analyses were used to investigate the tornadogenesis process in this case. Results from these analyses indicated that the circulation associated with both tornadoes was already present at low-levels in the storm environment 15-20 minutes before the tornadoes developed. Although the baroclinic term associated with the downdraft air made a negligible contribution to the circulation in this case, the downdraft played an important role in tilting horizontal vorticity into the vertical just above the surface in the near tornado environment where horizontal convergence could then act to amplify it. A comparison with the proposed tornadogenesis process(es) in classical supercells is also presented. The May 15, 1991, simulation produced a classical supercell which developed along the dryline in the Texas panhandle. This supercell in turn produced a tornado which lasted for 50 minutes in the simulation. During a ten minute period toward the end of the simulation, six secondary vortices developed within the main tornado vortex. The simulated secondary vortices had many features in common with multiple-vortex tornadoes and secondary vortices produced in laboratory vortices. The evolution and structure of the simulated secondary vortices is presented, and physical mechanisms responsible for their development and dissipation are discussed.
The Severe Weather Outbreak of 10 November 2002: Lightning and Radar Analysis of Storms in the Deep South

NASA Technical Reports Server (NTRS)

Buechler, D. E.; McCaul, E. W., Jr.; Goodman, S. J.; Blakeslee, R. J.; Bailey, J. C.; Gatlin, P.

2004-01-01

On the afternoon and evening of 10 November 2002, the Midwest and Deep South were struck by a major outbreak of severe storms that produced some 80 tornadoes. In terms of number of tornadoes, this was the largest outbreak in the United States since November 1992. Some 32 of the tornadoes occurred in Tennessee, Mississippi, Alabama and Georgia, including several long-track killers. We use the North Alabama Lightning Mapping Array (LMA) and other data sources to perform a comprehensive analysis of the structure and evolution of the outbreak. Most of the Southern tornadoes occurred in isolated, fast-moving supercell storms that formed in warm, moist air ahead of a major cold front. Storms tended to form in lines parallel to storm cell motion, resulting in many communities being hit multiple times by severe storms that evening. Supercells in Tennessee produced numerous strong tornadoes with short to medium-length track paths, while the supercells further south produced several very long-track tornadoes. Radar data indicate that the Tennessee storms tended to split frequently, apparently limiting their ability to sustain long-lived tornadoes, while storms further south split at most one time. The differences between these storms appear to be related to the presence of stronger jetstream winds in Tennessee relative to those present in Mississippi, Alabama and Georgia. LMA-derived flash rates associated with most of the supercell storm cores were about 1-2 flashes per second. Rapid increases in lightning rates (or "jumps") occurred prior to tornado touchdown in many instances. Lightning "holes" (lightning-free regions associated with the echo-free vault) occurred in two of the Tennessee supercells. The complexity of the relationship between lightning and storm severity is revealed by the behavior of one Alabama supercell, which produced a peak flash rate of nearly 14 flashes per second, well after the end of its long-track tornado, while interacting and ultimately merging with a daughter supercell on its southwest flank. Close examination of this powerful storm indicates that its prodigious flash rate was the result of strong flash activity over an unusually large area, rather than a concentrated core of extremely high flash rate activity.
Observations of lightning in convective supercells within tropical storms and hurricanes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyons, W.A.; Keen, C.S.

1994-08-01

Cloud-to-ground (CG) lightning observations from land-based lightning detection networks now allow monitoring this component of the electrical structure of tropical storms and hurricanes within a few hundred kilometers of the United States coastline. Several case studies confirm the long-held opinion that lightning is rather common within the outer rainbands. The general absence of CG lightning within the interior of mature tropical cyclones is also apparent. On the other hand, bursts of CG lightning near the circulation center of developing storms appear to precede periods of further deepening. The CG events are associated with convective supercells, whose anvil canopies can oftenmore » obscure much of the underlying storm. Near-eyewall CG bursts preceding periods of intensification were noted in Hurricanes Diana (1984) and Florence (1988). A detailed case study of the 1987 unnamed tropical storm that struck the Texas-Louisiana coastline reveals that lightning was associated with two large supercells. These supercells appeared to be the trigger for the development of a closed circulation that formed several hours after the apparent low pressure center made landfall. Further studies of lightning may provide additional insight into the role of convective supercells in tropical storm intensification. It may also provide a useful diagnostic of impending deepening.« less
Cloud-to-Ground Lightning Characteristics of a Major Tropical Cyclone Tornado Outbreak

NASA Technical Reports Server (NTRS)

McCaul, Eugene W., Jr.; Buechler, Dennis; Goodman, Steven J.

1999-01-01

It is well known that most tropical cyclones (TCs) that make landfall along the Gulf coast of the United States spawn at least a few tornadoes. Although most landfalling TCs generate fewer than a dozen such tornadoes, a small proportion produce large swarm outbreaks, with as many as 25 or more tornadoes. Usually, these major outbreaks occur in large, intense hurricane-strength TCs, but on 15-17 August 1994 Tropical Storm Beryl spun off 37 tornadoes along its path from the Florida panhandle through the mid-Atlantic states. Some 32 of these tornadoes occurred on 16 August 1994 from eastern Georgia to southern Virginia, with most of these taking place in South Carolina. Beryl's 37 tornadoes moved it into what was at that time fifth place historically in terms of TC tornado productivity. The Beryl outbreak is especially noteworthy in that at least three of the tornadoes achieved peak intensity of F3 on the Fujita damage intensity scale. Although no fatalities resulted from the Beryl outbreak, at least 50 persons suffered injuries, and property damages totalled more than $50 million . The Beryl outbreak is a good example of a TC whose greatest danger to the public is its post-landfall severe weather. In this respect, and in the character of its swarm outbreak of tornadoes, it resembles another large tornado outbreak spawned by a relatively weak TC, Hurricane Danny of 1985). In the Danny outbreak, numerous shallow mini-supercell storms were found to have occurred, and it was noted that, because of the storms' relatively shallow depth, cloud-to-ground (CG) lightning was negligible. Better observations of future TC tornado outbreaks, especially with modern surveillance tools such as Doppler radars and the National Lightning Detection Network (NLDN), were recommended. Although the Beryl tornado outbreak is not the first set of TC-spawned tornado storms to be observed with the NLDN, it is one of the largest and likely the most intense such outbreak. The purpose of this paper is to document the NLDN-derived CG lightning characteristics of Beryl's tornadic storms, and to see how they compare with observations of CG lightning activity in other types of severe storms. In particular, we attempt to quantify the CG flash rates of TC tornadic cells, and to discover if there are any characteristics of their CG activity that may be useful to operational forecasters seeking to distinguish which cells are most likely to produce severe weather.
Terminal Area Simulation System User's Guide - Version 10.0

NASA Technical Reports Server (NTRS)

Switzer, George F.; Proctor, Fred H.

2014-01-01

The Terminal Area Simulation System (TASS) is a three-dimensional, time-dependent, large eddy simulation model that has been developed for studies of wake vortex and weather hazards to aviation, along with other atmospheric turbulence, and cloud-scale weather phenomenology. This document describes the source code for TASS version 10.0 and provides users with needed documentation to run the model. The source code is programed in Fortran language and is formulated to take advantage of vector and efficient multi-processor scaling for execution on massively-parallel supercomputer clusters. The code contains different initialization modules allowing the study of aircraft wake vortex interaction with the atmosphere and ground, atmospheric turbulence, atmospheric boundary layers, precipitating convective clouds, hail storms, gust fronts, microburst windshear, supercell and mesoscale convective systems, tornadic storms, and ring vortices. The model is able to operate in either two- or three-dimensions with equations numerically formulated on a Cartesian grid. The primary output from the TASS is time-dependent domain fields generated by the prognostic equations and diagnosed variables. This document will enable a user to understand the general logic of TASS, and will show how to configure and initialize the model domain. Also described are the formats of the input and output files, as well as the parameters that control the input and output.
Environmental risk perception from visual cues: the psychophysics of tornado risk perception

NASA Astrophysics Data System (ADS)

Dewitt, Barry; Fischhoff, Baruch; Davis, Alexander; Broomell, Stephen B.

2015-12-01

Lay judgments of environmental risks are central to both immediate decisions (e.g., taking shelter from a storm) and long-term ones (e.g., building in locations subject to storm surges). Using methods from quantitative psychology, we provide a general approach to studying lay perceptions of environmental risks. As a first application of these methods, we investigate a setting where lay decisions have not taken full advantage of advances in natural science understanding: tornado forecasts in the US and Canada. Because official forecasts are imperfect, members of the public must often evaluate the risks on their own, by checking environmental cues (such as cloud formations) before deciding whether to take protective action. We study lay perceptions of cloud formations, demonstrating an approach that could be applied to other environmental judgments. We use signal detection theory to analyse how well people can distinguish tornadic from non-tornadic clouds, and multidimensional scaling to determine how people make these judgments. We find that participants (N = 400 recruited from Amazon Mechanical Turk) have heuristics that generally serve them well, helping participants to separate tornadic from non-tornadic clouds, but which also lead them to misjudge the tornado risk of certain cloud types. The signal detection task revealed confusion regarding shelf clouds, mammatus clouds, and clouds with upper- and mid-level tornadic features, which the multidimensional scaling task suggested was the result of participants focusing on the darkness of the weather scene and the ease of discerning its features. We recommend procedures for training (e.g., for storm spotters) and communications (e.g., tornado warnings) that will reduce systematic misclassifications of tornadicity arising from observers’ reliance on otherwise useful heuristics.
An isolated tornadic supercell of 14 July 2012 in Poland - A prediction technique within the use of coarse-grid WRF simulation

NASA Astrophysics Data System (ADS)

Taszarek, Mateusz; Czernecki, Bartosz; Walczakiewicz, Szymon; Mazur, Andrzej; Kolendowicz, Leszek

2016-09-01

On 14 July 2012 a shortwave trough with a cold front passed through Poland. A few tornadoes were reported in the north central part of the country within an isolated cyclic supercell. The cell moved along the thermal and moisture horizontal gradients and the support of a synoptic scale lift. An analysis allowed for setting up four tornado damage tracks in a distance of 100 km and with a total length of 60 km. Tornadoes damaged 105 buildings with predominant intensity of F1-F2/T3-T4 (maximum F3/T6) in Fujita/TORRO scale, caused 1 fatality, 10 injures and felled 500 hectares of Bory Tucholskie forest. The main aim of this article was to analyze this event and assess the possibilities of its short-term prediction. In order to achieve this, a model forecast data derived from WRF-ARW simulation with a spatial resolution of 15 km and initial conditions extracted from 0000 UTC GFS was used. An analysis yielded that the cell moved in the environment of a low lifting condensation level, rich boundary layer's moisture content and a steepening vertical lapse rates that provided the presence of a thermodynamic instability. A wind vectors tilting with height and an increased vertical wind shear occurred as well. A forecasting method that combined a Universal Tornadic Index composite parameter with a convective precipitation filter showed that convective cells at 1500 UTC in the north central Poland had a potential to become tornadic. Within the use of a proposed methodology, it was possible to issue a tornado forecast for the areas where an index pointed the risk.

Numerical Simulation of a Tornado Generating Supercell

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.

2012-01-01

The development of tornadoes from a tornado generating supercell is investigated with a large eddy simulation weather model. Numerical simulations are initialized with a sounding representing the environment of a tornado producing supercell that affected North Carolina and Virginia during the Spring of 2011. The structure of the simulated storm was very similar to that of a classic supercell, and compared favorably to the storm that affected the vicinity of Raleigh, North Carolina. The presence of mid-level moisture was found to be important in determining whether a supercell would generate tornadoes. The simulations generated multiple tornadoes, including cyclonic-anticyclonic pairs. The structure and the evolution of these tornadoes are examined during their lifecycle.
Lightning Behavior and its Dependence on Storm Kinematic and Precipitation Processes in Northern Alabama

NASA Technical Reports Server (NTRS)

Johnson, Elsie V.; Petersen, W. A,

2009-01-01

Numerous case studies and recent modeling studies have found that various metrics of updraft intensity appear to be reasonably well correlated to lightning production in thunderstorms, particularly severe thunderstorms. Indeed, the relationship between updraft and lightning flash rate is hypothesized to be the physical connection between a lightning "jump" signature and manifestations of severe weather such as tornadic activity. This study further examines this connection using a combination of dual Doppler wind retrievals made with the UAH ARMOR dual polarimetric and KHTX WSR 88D Doppler radar pair, together with northern Alabama Lightning Mapping Array (LMA) data. The dual Doppler data were used to construct three dimensional wind fields and the retrieved vertical velocity fields were subsequently compared to collocated total lightning flash rates observed by the LMA. Particular attention was paid to the timing of updraft pulses relative to changes in the flash rate, with the goal of assessing impacts on warning decision lead time. Results from the analysis of severe and non severe thunderstorms in Northern Alabama will be presented including the EF 4 tornado producing supercell on 6 February 2008.
Advection of Microphysical Scalars in Terminal Area Simulation System (TASS)

NASA Technical Reports Server (NTRS)

Ahmad, Nashat N.; Proctor, Fred H.

2011-01-01

The Terminal Area Simulation System (TASS) is a large eddy scale atmospheric flow model with extensive turbulence and microphysics packages. It has been applied successfully in the past to a diverse set of problems ranging from prediction of severe convective events (Proctor et al. 2002), tracking storms and for simulating weapons effects such as the dispersion and fallout of fission debris (Bacon and Sarma 1991), etc. More recently, TASS has been used for predicting the transport and decay of wake vortices behind aircraft (Proctor 2009). An essential part of the TASS model is its comprehensive microphysics package, which relies on the accurate computation of microphysical scalar transport. This paper describes an evaluation of the Leonard scheme implemented in the TASS model for transporting microphysical scalars. The scheme is validated against benchmark cases with exact solutions and compared with two other schemes - a Monotone Upstream-centered Scheme for Conservation Laws (MUSCL)-type scheme after van Leer and LeVeque's high-resolution wave propagation method. Finally, a comparison between the schemes is made against an incident of severe tornadic super-cell convection near Del City, Oklahoma.
Observed and Simulated Supercell Demise Depicted by VORTEX2 Observations

NASA Astrophysics Data System (ADS)

Letkewicz, Casey Elizabeth

Over the past several decades, supercell thunderstorms have been the subject of much research, aimed at understanding their governing dynamics and better forecasting their potential hazards. While focus has been placed on understanding supercells' developing and mature stages, fewer studies have examined the conditions and processes associated with supercell demise. The current gaps in our understanding of supercell demise in turn suggest that we do not yet fully understand supercell maintenance. On 9 June 2009, the Verification of the Origins of Rotation in Tornadoes Experiment 2009-2010 (VORTEX2) captured a unique dataset of dense observations throughout the lifetime of an isolated supercell, including its demise. The storm formed just to the cool side of a quasi-stationary synoptic boundary, initially exhibiting strong low-level rotation. Over time, however, the storm moved deeper into the cool air and completely dissipated. Three near-inflow soundings launched over the lifetime of the supercell illustrated an increase in low-level convective inhibition (CIN) over time. However, an elevated layer containing sufficient instability and modest inhibition was also present, and the near-storm environment demonstrated a notable decrease in bulk vertical wind shear and storm-relative helicity over the lifetime of the storm. While the likely impact of an increasingly stable near-storm environment is seemingly straightforward, the possible contributions from the elevated layer of instability, the extent to which the evolving kinematic profile influenced storm dissipation, and the relevant processes at work, are less certain. Such details are not easily extracted from the observations. Thus, an idealized modeling approach was adopted to isolate the trends in the thermodynamic and kinematic profiles and understand their relative contributions to storm demise, and also assess the relevant processes. Based on the evolving near-storm environment on 9 June 2009, a new modeling technique deemed base-state substitution (BSS) was developed to incorporate a varying base-state while maintaining a degree of experimental control. BSS was designed to test the impact of a new horizontally homogeneous base-state environment on storm morphology while maintaining storm-induced perturbations. The thermodynamic and kinematic environment can be independently altered, with modifications incorporated slowly (gradual BSS) or all at once (instant BSS). Trial simulations demonstrated that model stability was maintained and domain-integrated fields were well-behaved. The simulations of the 9 June 2009 supercell were designed to isolate the effects of the changing wind profile from those of the increasingly stable boundary layer. The observed environmental modifications, when gradually incorporated into the model via BSS, were able to reasonably reproduce the observed storm morphology. Overall, the experiments demonstrated that the demise of the supercell was ultimately the result of depleting the updraft's buoyancy. The increasingly stable low-level environment predominately contributed to demise; however, changes to the wind profile also acted to notably impact storm strength and morphology. Analysis of updraft parcels in each experiment demonstrated that the mean source region became elevated over time as the low-level environment stabilized and/or shear and helicity weakened. Consequently, updraft buoyancy was eventually depleted since the drier elevated parcels (with less instability) were more negatively impacted by entrainment. The diagnostic pressure equation was utilized to examine the evolution of vertical accelerations within the simulated storm updraft and explore how storm dynamics evolved as the environment evolved. It was found that changes to nonlinear dynamic acceleration primarily influenced the evolution in total vertical acceleration, though these changes were interconnected with shifts in buoyancy and updraft strength and rotation. The findings of this study suggest that a shifting updraft parcel source region can significantly impact storm maintenance; importantly, such a shift can result from either thermodynamic or kinematic changes in the environment. To anticipate whether environmental heterogeneities will have a negative impact on storm maintenance, it is recommended that vertical profiles of instability, convective inhibition, and humidity be examined to identify any unfavorable layers. Additionally, it is recommended that future studies utilize BSS to gain further understanding of the impact of environmental heterogeneities on storm evolution.
The North Alabama Lightning Mapping Array: Recent Results and Future Prospects

NASA Technical Reports Server (NTRS)

Goodman, S. J.; Blakeslee, R.; Christian, H.; Boccippio, D.; Koshak, W.; Bailey, J.; Hall, J.; Bateman, M.; McCaul, E.; Buechler, D.

2002-01-01

The North Alabama Lightning Mapping Array became operational in November 2001 as a principal component of a severe weather test bed to infuse new science and technologies into the short-term forecasting of severe and hazardous weather and the warning decision-making process. The LMA project is a collaboration among NASA scientists, National Weather Service (NWS) weather forecast offices (WFOs), emergency managers, and other partners. The time rate-of-change of storm characteristics and life-cycle trending are accomplished in real-time through the second generation Lightning Imaging Sensor Data Applications Display (LISDAD II) system, initially developed in T997 through a collaboration among NASA/MSFC, MIT/Lincoln Lab and the Melbourne, FL WFO. LISDAD II is now a distributed decision support system with a JAVA-based display application that allows anyone, anywhere to track individual storm histories within the Tennessee Valley region of the southeastern U.S. Since the inauguration of the LMA there has been an abundance of severe weather. During 23-24 November 2001, a major tornado outbreak was monitored by LMA in its first data acquisition effort (36 tornadoes in Alabama). Since that time the LMA has collected a vast amount of data on hailstorms and damaging wind events, non-tornadic supercells, and ordinary non-severe thunderstorms. In this paper we provide an overview of LMA observations and discuss future prospects for improving the short-term forecasting of convective weather.
Lightning location relative to storm structure in a supercell storm and a multicell storm

NASA Technical Reports Server (NTRS)

Ray, Peter S.; Macgorman, Donald R.; Rust, W. David; Taylor, William L.; Rasmussen, Lisa Walters

1987-01-01

Relationships between lightning location and storm structure are examined for one radar volume scan in each of two mature, severe storms. One of these storms had characteristics of a supercell storm, and the other was a multicell storm. Data were analyzed from dual-Doppler radar and dual-VHF lightning-mapping systems. The distributions of VHF impulse sources were compared with radar reflectivity, vertical air velocity, and their respective gradients. In the supercell storm, lightning tended to occur along streamlines above and down-shear of the updraft and reflectivity cores; VHF impulse sources were most concentrated in reflectivities between 30 and 40 dBZ and were distributed uniformly with respect to updraft speed. In the multicell storm, on the other hand, lightning tended to coincide with the vertical reflectivity and updraft core and with the diverging streamlines near the top of the storm. The results suggest that the location of lightning in these severe storms were most directly associated with the wind field structure relative to updraft and reflectivity cores. Since the magnitude and vertical shear of the environmental wind are fundamental in determining the reflectivity and wind field structure of a storm, it is suggested that these environmental parameters are also fundamental in determining lightning location.
Tornadic storm avoidance behavior in breeding songbirds

USGS Publications Warehouse

Streby, Henry M.; Kramer, Gunnar R.; Peterson, Sean M.; Lehman, Justin A.; Buehler, David A.; Andersen, David E.

2015-01-01

Migration is a common behavior used by animals of many taxa to occupy different habitats during different periods. Migrant birds are categorized as either facultative (i.e., those that are forced to migrate by some proximal cue, often weather) or obligate (i.e., those that migrate on a regular cycle). During migration, obligate migrants can curtail or delay flights in response to inclement weather or until favorable winds prevail, and they can temporarily reorient or reverse direction when ecological or meteorological obstacles are encountered. However, it is not known whether obligate migrants undertake facultative migrations and make large-scale movements in response to proximal cues outside of their regular migration periods. Here, we present the first documentation of obligate long-distance migrant birds undertaking a facultative migration, wherein breeding golden-winged warblers (Vermivora chrysoptera) carrying light-level geolocators performed a >1,500 km 5-day circumvention of a severe tornadic storm. The birds evacuated their breeding territories >24 hr before the arrival of the storm and atmospheric variation associated with it. The probable cue, radiating >1,000 km from tornadic storms, perceived by birds and influencing bird behavior and movements, is infrasound (i.e., sound below the range of human hearing). With the predicted increase in severity and frequency of similar storms as anthropogenic climate change progresses, understanding large-scale behavioral responses of animals to such events will be an important objective of future research.
The medical impact of tornadoes in North America.

PubMed

Bohonos, J J; Hogan, D E

1999-01-01

North America suffers some of the most severe tornado disasters of any location on the planet. Significant injury and economic impact may result from these storms, particularly in rural areas. Tornadic storms present unique problems for prehospital and Emergency Department personnel. Soft tissue injuries seen after tornadoes are contaminated with polymicrobial flora and may require delayed primary closure. Fractures are a frequent cause of hospital admission and head injury is a frequent cause of death. Advanced warning and proper sheltering actions by a population are the most significant factors in reducing morbidity and mortality. This article reviews the pertinent literature on the medical impact of tornadoes and details the mechanisms of injury, nature of injuries, pre-hospital and ED planning points associated with tornadic storms.
Detection of Storm Damage Tracks with EOS Data

NASA Technical Reports Server (NTRS)

Jedlovec, Gary J.; Nair, Udaysankar; Haines, Stephanie L.

2006-01-01

The damage surveys conducted by the NWS in the aftermath of a reported tornadic event are used to document the location of the tornado ground damage track (pathlength and width) and an estimation of the tornado intensity. This study explores the possibility of using near-real-time medium and high spatial resolution satellite imagery from the NASA Earth Observing System satellites to provide additional information for the surveys. Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were used to study the damage tracks from three tornadic storms: the La Plata, Maryland, storm of 28 April 2002 and the Ellsinore and Marquand, Missouri, storms of 24 April 2002. These storms varied in intensity and occurred over regions with significantly different land cover. It was found that, depending on the nature of the land cover, tornado damage tracks from intense storms (F1 or greater) and hail storms may be evident in ASTER, Landsat, and MODIS satellite imagery. In areas where the land cover is dominated by forests, the scar patterns can show up very clearly, while in areas of grassland and regions with few trees, scar patterns are not as obvious or cannot be seen at all in the satellite imagery. The detection of previously unidentified segments of a damage track caused by the 24 April 2002 Marquand, Missouri, tornado demonstrates the utility of satellite imagery for damage surveys. However, the capability to detect tornado tracks in satellite imagery depends on the ability to observe the ground without obstruction from space and appears to be as much dependent on the nature of the underlying surface and land cover as on the severity of the tornadic storm.
Pulsing Inertial Oscillation, Supercell Storms, and Surface Mesonetwork Data

NASA Technical Reports Server (NTRS)

Costen, R. C.; Miller, L. J.

1998-01-01

The pulsing inertial oscillation (PIO) model is a nonlinear, time-dependent, translating vortex solution of the inviscid, compressible fluid dynamic equations in the middle troposphere. The translation of this vortex during a pulse is strikingly similar to that of a supercell storm -- a rotating thunderstorm that can generate tornadoes and hail. Two studies were performed to test the hypothesis that some supercell storms are manifestations of a PIO pulse. The first study applied the model to an intense interior draft whose buoyancy was bounded by a temperature excess of +/- 12 K. The peak updraft speed achieved was 41.5 m/ s and the peak Rossby number was 92.9. The study also pointed to an advanced concept for attaining higher values. The second study applied the PIO model to a supercell storm as a whole and succeeded in replicating its bulk properties, such as mesocyclonic circulation, net mass and moisture influxes, and time track. This study also identified a critical feature of the PIO model that could be tested against storm data: The average vertical draft is downward before the turn in the storm track and upward afterwards. In the conventional theory, the average vertical draft is upward from storm inception until dissipation. These differing draft predictions were compared with the best available data, which are surface mesonetwork data. These data were found to support the PIO model. However, surface data alone are not conclusive, and further measurements are warranted.
The 2008 Super Tuesday Tornado Outbreak: Overview of the Tornadoes and their Parent Storms

NASA Technical Reports Server (NTRS)

Knupp, Kevin R.; Coleman, Tim; Carey, Larry; Petersen, Walt

2008-01-01

The cold-season Tornado outbreak that occurred over the Southeast on 5-6 February 2008 was significant for the following reasons: about 84 tornadoes were documented over a 15 h period between late afternoon on 5 February and early morning on 6 February 2008; a wide variety of parent storms were associated with the tornadoes; a total of five EF-4 tornadoes occurred, with two forming over Alabama during the early morning hours prior to sunrise; there was a significant lull period between the initial convective and the early morning activity over Alabama 10 hours later; and, a wide spectrum of storm types, ranging from isolated supercell storms to QLCS bow echoes, accompanied the tornadoes. The goal of this paper is to provide a general description of the outbreak including the distribution of tornadoes and supercell storms over the region, a detailed map of the tornado tracks, time series of tornadoes and parent storms, and general characteristics of all parent tornado storms. The total number of major storms (duration greater than 3 h, at least three tornadoes produced) was seven. Several noteworthy storms are described: a long track (198 km long) tornado and its parent storm over Arkansas; a prolific supercell storm persisted for 7-8 hours and produced 16 tornadoes from north-central Mississippi to southern KY; and, bow echo storms (QLCS's) were simultaneous over KY and produced 16 tornadoes.
Tornadic storm avoidance behavior in breeding songbirds.

PubMed

Streby, Henry M; Kramer, Gunnar R; Peterson, Sean M; Lehman, Justin A; Buehler, David A; Andersen, David E

2015-01-05

Migration is a common behavior used by animals of many taxa to occupy different habitats during different periods. Migrant birds are categorized as either facultative (i.e., those that are forced to migrate by some proximal cue, often weather) or obligate (i.e., those that migrate on a regular cycle). During migration, obligate migrants can curtail or delay flights in response to inclement weather or until favorable winds prevail, and they can temporarily reorient or reverse direction when ecological or meteorological obstacles are encountered. However, it is not known whether obligate migrants undertake facultative migrations and make large-scale movements in response to proximal cues outside of their regular migration periods. Here, we present the first documentation of obligate long-distance migrant birds undertaking a facultative migration, wherein breeding golden-winged warblers (Vermivora chrysoptera) carrying light-level geolocators performed a >1,500 km 5-day circumvention of a severe tornadic storm. The birds evacuated their breeding territories >24 hr before the arrival of the storm and atmospheric variation associated with it. The probable cue, radiating >1,000 km from tornadic storms, perceived by birds and influencing bird behavior and movements, is infrasound (i.e., sound below the range of human hearing). With the predicted increase in severity and frequency of similar storms as anthropogenic climate change progresses, understanding large-scale behavioral responses of animals to such events will be an important objective of future research. Copyright © 2015 Elsevier Ltd. All rights reserved.
Supercell and tornado roles

Science.gov Websites

where C is the storm motion vector, and k is the unit vector in the vertical (Davies-Jones et al. 1990 mutually interacting perspectives, each addressing different aspects of the supercell storms most directly marked by low clouds, extending to the left. Photograph Â© 2005 C. Doswell 4. Developing a conceptual
Inertial Oscillation of a Vertical Rotating Draft with Application to a Supercell Storm: Video Supplement to NASA-TP-3230

NASA Technical Reports Server (NTRS)

Costen, Robert C.; Stock, Larry V.

1992-01-01

In this video (8 min., color, sound, VHS), animation depicts the inertial oscillation of a new mathematical model ('vertical rotating draft') for spinning up a single supercell storm. The oscillation consists of a long quiescent phase when the draft is large in diameter and rotates anticyclonically and a short intense phase when the draft is small and cyclonic. During the intense phase, the rotating draft resembles a supercell. The physical basis for the oscillation is depicted by tracking air parcels in the draft as they move along inertial circles (projected on a horizontal plane), where the horizontal pressure gradient is zero and the Coriolis force balances the centrifugal force. A side view of the oscillation shows that contraction and expansion are linked, respectively, to buoyantly driven compressible downdraft and updraft. An aerial view tracks the draft as it moves above the surface of the Earth and turns to the right during the intense phase. Radar echoes from a supercell storm are superimposed for comparison. The data appear to support only the intense phase. A critical experiment would measure the predominantly downward flow that theoretically occurs before the right turn in a supercell track and causes contraction and spin-up.
Detection Of Tornado Damage Tracks With EOS Data

NASA Technical Reports Server (NTRS)

Jedlovec, Gary J.; Nair, Udaysankar; Haines, Stephanie L.

2005-01-01

The damage surveys conducted by the NWS in the aftermath of a reported tornadic event are used to document the location of the tornado ground damage track (path length and width) and an estimation of the tornado intensity. This study explored the possibility of using near real-time medium and high-resolution satellite imagery from the NASA EOS satellites to provide additional information for the surveys. MODIS and ASTER data were used to study the damage tracks from three tornadic storms; the La Plata, Maryland storm of 28 April 2002 and the Carter-Butler Counties and Madison County Missouri storms of 24 April 2002. These storms varied in intensity (from F0-F4) and occurred over regions with different land use. It was found that, depending on the nature of land use, tornado damage tracks from intense storms (F2 or greater) may be evident in both ASTER and MODIS satellite imagery. In areas of dense vegetation the scar patterns show up very clearly, while in areas of grassland and regions with few trees, scar patterns are not at all obvious in the satellite imagery. The detection of previously unidentified segments of a damage track caused by the 24 April 2004 Madison County, Missouri tornado demonstrates the utility of satellite imagery for damage surveys. However, the capability to detect tornado tracks in satellite imagery appears to be as much dependent on the nature of the underlying surface and land use as on the severity of the tornadic storm. The imaging sensors on the NPOESS operational satellites to be launched in 2006 will continue the unique observing capabilities of the EOS instruments.
Inertial oscillation of a vertical rotating draft with application to a supercell storm

NASA Technical Reports Server (NTRS)

Costen, Robert C.; Stock, Larry V.

1992-01-01

An analytic model (vertical rotating draft) which includes the gross features of a supercell storm on an f-plane, undergoes an inertial oscillation that appears to have been overlooked in previous analytic and numerical models. The oscillation is nonlinear and consists of a long quiescent phase and a short intense phase. During the intense phase, the rotating draft has the following features of a supercell: the diameter of the core contracts as it spins up and expands as it spins down; if vertical wind shear is included, the track of the rotating draft turns to the right (an anticyclonic rotating draft turns to the left); this turning point is followed by a predominantly upward flow; and the horizontal pressure gradient is very small (a property of most tornadoless supercells). The rapid spin-up during the intense phase and the high Rossby numbers obtainable establish the ability of the Coriolis force to spin up single cyclonic or anticyclonic supercells by means of this inertial oscillation. This surprising result has implications for numerical supercell simulations, which generally do not rely on the Coriolis force as a source of rotation. The physics and mathematics of the inertial oscillation are given, and the solution is applied to a documented supercell.
Synoptic Regulation of The 3 May 1999 Oklahoma Tornado Outbreak

NASA Astrophysics Data System (ADS)

Schultz, D. M.; Roebber, P. J.; Romero, R.

Despite the relatively successful long-lead-time forecasts of the storms during the 3 May 1999 tornadic outbreak in Oklahoma and Kansas, forecasters were unable to predict with confidence details concerning convective initiation and convective mode. The forecasters identified three synoptic processes they were monitoring for clues as to how the event would unfold. These elements were (a) the absence of strong surface convergence along a dryline in western Oklahoma and the Texas panhandle, (b) the presence of a cirrus shield that was hypothesized to limit surface heating, and (c) the arrival into Oklahoma of an upper-level wind-speed maximum (associated with the so- called southern PV anomaly) that was responsible for favorable synoptic-scale ascent and the cirrus shield. The Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model Version 5 (MM5) is used in forecast mode (using the operational AVN run data to provide initial and lateral boundary conditions) to explore the sen- sitivity of the outbreak to these features using simulations down to 2-km horizontal grid spacing. A 30-h control simulation is compared to the available observations and captures important qualitative characteristics of the event, including convective initi- ation east of the dryline and organization of mesoscale convective systems into long lived, long-track supercells. Additional simulations in which the initial strength of the southern PV anomaly is altered suggest that synoptic regulation of the 3 May 1999 event was imposed by the effects of the southern PV anomaly. The model results in- dicate that: (1) convective initiation in the weakly forced environment was achieved through modification of the existing cap through both surface heating and synoptic- scale ascent associated with the southern PV anomaly; (2) supercellular organization was supported regardless of the strength of the southern PV anomaly, although weak- to-moderate forcing from this feature was most conducive to the production of long lived supercells and strong forcing resulted in a trend toward linear mesoscale convec- tive systems; (3) the cirrus shield was important in limiting development of convection and reducing competition between storms.
Kinematic, dynamic, and thermodynamic impacts of hook-echo hydrometeors, including explorations into the utilization of polarimetric radar data

NASA Astrophysics Data System (ADS)

Askelson, Mark Anthony

Recent studies have revealed that the thermodynamic properties of the rear flank downdraft (RFD) may dictate whether or not a supercell becomes tornadic. Since hydrometeors are thought to be an important driving force for the RFD, it is postulated that they may be important to its thermodynamic properties and, possibly, to tornadogenesis. The role hook-echo hydrometeors play in driving RFDs is investigated by estimating hook-echo hydrometeor types and amounts from polarimetric radar data and by using that information to drive a relatively simple downdraft model. Soundings for the individual cases are used to initialize the downdraft model in order to replicate the environments of the storms as closely as possible. Since this effort and others like it require the quantitative utilization of radar data, issues pertaining to this are explored. In addition to analyses of coordinate transformation equations and an innovative objective analysis technique for weather radar data, the difficult problem of response functions for arbitrary weight functions and data distributions was considered. A novel approach to this problem revealed that the local response function for distance dependent weighted averaging schemes is the complex conjugate of the normalized Fourier transform of the effective weight function. This facilitates new research avenues, especially regarding analyses of irregularly spaced data. Simulations of hydrometeor driven RFDs show that hydrometeor fields inferred from radar data are able to drive significant downdrafts without the influence of vertical perturbation pressure gradients. Moreover, they reveal that above the boundary layer supercell environments are relatively resistant to downdrafts whereas within the boundary layer they are generally supportive of downdrafts. It appears that in many supercell environments relatively large hail (≥1 cm in diameter) or vertical perturbation pressure gradients may be needed to drive deep midlevel downdrafts that penetrate into the boundary layer. Because the boundary layer is an important downdraft generation/intensification layer, its thetae profile appears to be important to the surface RFD thetae deficit and, consequently, to tornadogenesis. To further examine these issues, analyses using idealized soundings that represent multiple possible RFD environments and analyses of the complete set of VORTEX cases are planned.
Case study of the 9 May 2003 windstorm in southwestern Slovakia

NASA Astrophysics Data System (ADS)

Kaňák, Ján; Benko, Martin; Simon, André; Sokol, Alois

2007-02-01

May 9, 2003 thunderstorm in southwest Slovakia is considered one of the most severe convective events to have happened in Slovakia during the past ten years. The majority of the reported damage was caused by very strong outflowing winds and hail. The downburst (macroburst) nature of the event was confirmed by a damage survey carried out in the area hit by the thunderstorm. The supercell nature of the storm was inferred from radar measurements, with the fields of radar reflectivity and radial Doppler velocity showing typical supercell features (e.g. BWER echo). The satellite imagery (from METEOSAT 7) indicated a large-scale dry air intrusion as a possible factor of downdraft enhancement. Aspects of the storm environment were inferred from soundings, numerical analysis of the ALADIN model and Velocity Azimuth Display data from radar. The results enable comparison of the outputs of several instability indices, such as CAPE, DCAPE and Storm to Relative Environmental Helicity (SREH). It was concluded based on structure and development that the storm showed many similarities to the so called High Precipitation (HP) supercell type.
Lightning Mapping Observations: What we are learning.

NASA Astrophysics Data System (ADS)

Krehbiel, P.

2001-12-01

The use of radio frequency time-of-arrival techniques for accurately mapping lightning discharges is revolutionizing our ability to study lightning discharge processes and to investigate thunderstorms. Different types of discharges are being observed that we have not been able to study before or knew existed. Included are a variety of inverted and normal polarity intracloud and cloud-to-ground discharges, frequent short-duration discharges at high altitude in storms and in overshooting convective tops, highly energetic impulsive discharge events, and horizontally extensive `spider' lightning discharges in large mesoscale convective systems. High time resolution measurements valuably complement interferometric observations and are starting to exceed the ability of interferometers to provide detailed pictures of flash development. Mapping observations can be used to infer the polarity of the breakdown channels and hence the location and sign of charge regions in the storm. The lightning activity in large, severe storms is found to be essentially continuous and volume-filling, with substantially more lightning inside the storm than between the cloud and ground. Spectacular dendritic structures are observed in many flashes. The lightning observations can be used to infer the electrical structure of a storm and therefore to study the electrification processes. The results are raising fundamental questions about how storms become electrified and how the electrification evolves with time. Supercell storms are commonly observed to electrify in an inverted or anomalous manner, raising questions about how these storms are different from normal storms, and even what is `normal'. The high lightning rates in severe storms raises the distinct possibility that the discharges themselves might be sustaining or enhancing the electrification. Correlated observations with radar, instrumented balloons and aircraft, and ground-based measurements are leading to greatly improved understanding of the electrical processes in storms. The mapping observations also provide possible diagnostics of storm type and severity. Lightning `holes' are observed as storms intensify and are robust indicators of strong updrafts and precursors of tornadic activity. Lightning in overshooting convective tops provides another indicator of strong convective surges and a valuable precursor of severity. The lightning observations show the locations of convective cores in storms and can be obtained in real time to monitor and track convective activity, much like meteorological radar. Mapping systems are able to passively detect and track aircraft flying through ice crystal clouds, as well as airborne or ground-based instruments or vehicles carrying active transmitters. Finally, the mapping techniques could readily be adapted to monitor noise and detect faults on power transmission lines.

Meso-beta scale perturbations of the wind field by thunderstorm cells

NASA Technical Reports Server (NTRS)

Ulanski, S. L.; Heymsfield, G. M.

1986-01-01

Data from the high density storm-scale rawinsonde network of the Severe Environmental Storms and Mesoscale Experiment revealed temporal and spatial changes in the divergence fields of the troposphere in response to severe storm evolution on May 2, 1979; these changes were detectable on the meso-beta scale. This unique set of data was subsequently used to study the evolution of the wind, divergence and vertical motion fields in the presence of intense convection. Mid- and upper-tropospheric divergence was superimposed over low-level convergence. The divergence, which has a maximum value of .0004/s, occurred 75 to 100 km upwind as well as over the tornadic cells. To the south of the storm cells, the kinematic pattern was in reverse, upper level convergence was superimposed over low-level divergence. A vertical motion doublet was found to ascend over the squall line and descend about 70 km south of the squall line. It is suggested that the following effects are accountable for the nature of the kinematic fields: (1) blocking of tropospheric environmental flow by the storm cells, (2) anvil outflows, particularly from the tornadic cells, and (3) divergence from the exit region of the jet stream.
Vertical wind shear characteristics that promote supercell-to-MCS transitions

NASA Astrophysics Data System (ADS)

Peters, J. M.

2017-12-01

What causes supercells to transition into MCSs in some situations, but not others? To explore this question, I first examined observed environmental characteristics of supercell events when MCSs formed, and compared them to the analogous environmental characteristics of supercell events when MCSs did not form. During events when MCS growth occurred, 0-1 km (low-level) vertical wind shear was stronger and 0-10 km (deep-layer) vertical wind shear was weaker than the wind shear during events when MCS growth did not occur. Next, I used idealized simulations of supercell thunderstorms to understand the connections between low-level and deep-layer shear and MCS growth. Compared to simulations with strong deep-layer shear, the simulations with weak deep-layer shear had rain in the storm's forward-flank downdraft (FFD) that fell closer to the updraft, fell through storm-moistened air and evaporated less, and produced a more intense FFD. Compared to simulations with weak low-level shear, the simulations with stronger low-level shear showed enhanced northward low-level hydrometeor transport into the FFD. Environments with strong low-level shear and weak deep-layer shear therefore conspired to produce a storm with a more intense FFD cold pool, when compared to environments with weak low-level shear and/or strong deep-layer shear. This strong FFD periodically disrupted the supercells' mesocyclones, and favorably interacted with westerly wind shear to produce widespread linear convection initiation, which drove MCS growth. These results suggest that increasing low-level wind shear after dark - while commonly assumed to enhance tornado potential - may in fact drive MCS growth and reduce tornado potential, unless it is combined with sufficiently strong deep layer shear.
A Mediterranean nocturnal heavy rainfall and tornadic event. Part I: Overview, damage survey and radar analysis

NASA Astrophysics Data System (ADS)

Bech, Joan; Pineda, Nicolau; Rigo, Tomeu; Aran, Montserrat; Amaro, Jéssica; Gayà, Miquel; Arús, Joan; Montanyà, Joan; der Velde, Oscar van

2011-06-01

This study presents an analysis of a severe weather case that took place during the early morning of the 2nd of November 2008, when intense convective activity associated with a rapidly evolving low pressure system affected the southern coast of Catalonia (NE Spain). The synoptic framework was dominated by an upper level trough and an associated cold front extending from Gibraltar along the Mediterranean coast of the Iberian Peninsula to SE France, which moved north-eastward. South easterly winds in the north of the Balearic Islands and the coast of Catalonia favoured high values of 0-3 km storm relative helicity which combined with moderate MLCAPE values and high shear favoured the conditions for organized convection. A number of multicell storms and others exhibiting supercell features, as indicated by Doppler radar observations, clustered later in a mesoscale convective system, and moved north-eastwards across Catalonia. They produced ground-level strong damaging wind gusts, an F2 tornado, hail and heavy rainfall. Total lightning activity (intra-cloud and cloud to ground flashes) was also relevant, exhibiting several classical features such as a sudden increased rate before ground level severe damage, as discussed in a companion study. Remarkable surface observations of this event include 24 h precipitation accumulations exceeding 100 mm in four different observatories and 30 minute rainfall amounts up to 40 mm which caused local flash floods. As the convective system evolved northward later that day it also affected SE France causing large hail, ground level damaging wind gusts and heavy rainfall.
DSD Characteristics of a Mid-Winter Tornadic Storm Using C-Band Polarimetric Radar and Two 2D-Video Disdrometers

NASA Technical Reports Server (NTRS)

Thurai, M.; Petersen, W. A.; Carey, L. A.

2010-01-01

Drop size distributions in an evolving tornadic storm are examined using C-band polarimetric radar observations and two 2D-video disdrometers. The E-F2 storm occurred in mid-winter (21 January 2010) in northern Alabama, USA, and caused widespread damage. The evolution of the storm occurred within the C-band radar coverage and moreover, several minutes prior to touch down, the storm passed over a site where several disdrometers including two 2D video disdrometers (2DVD) had been installed. One of the 2DVDs is a low profile unit and the other is a new next generation compact unit currently undergoing performance evaluation. Analyses of the radar data indicate that the main region of precipitation should be treated as a "big-drop" regime case. Even the measured differential reflectivity values (i.e. without attenuation correction) were as high as 6-7 dB within regions of high reflectivity. Standard attenuation-correction methods using differential propagation phase have been "fine tuned" to be applicable to the "big drop" regime. The corrected reflectivity and differential reflectivity data are combined with the co-polar correlation coefficient and specific differential phase to determine the mass-weighted mean diameter, Dm, and the width of the mass spectrum, (sigma)M, as well as the intercept parameter , Nw. Significant areas of high Dm (3-4 mm) were retrieved within the main precipitation areas of the tornadic storm. The "big drop" regime assumption is substantiated by the two sets of 2DVD measurements. The Dm values calculated from 1-minute drop size distributions reached nearly 4 mm, whilst the maximum drop diameters were over 6 mm. The fall velocity measurements from the 2DVD indicate almost all hydrometeors to be fully melted at ground level. Drop shapes for this event are also being investigated from the 2DVD camera data.
Total Lightning and Radar Storm Characteristics Associated with Severe Storms in Central Florida

NASA Technical Reports Server (NTRS)

Goodman, Steven J.; Raghavan, Ravi; Ramachandran, Rahul; Buechler, Dennis; Hodanish, Stephen; Sharp, David; Williams, Earle; Boldi, Bob; Matlin, Anne; Weber, Mark

1998-01-01

A number of prior studies have examined the association of lightning activity with the occurrence of severe weather and tornadoes, in particular. High flash rates are often observed in tornadic storms (Taylor, 1973; Johnson, 1980; Goodman and Knupp, 1993) but not always. Taylor found that 23% of nontornadic storms and 1% of non-severe storms had sferics rates comparable to the tornadic storms. MacGorman (1993) found that storms with mesocyclones produced more frequent intracloud (IC) lightning than cloud-to-ground (CG) lightning. MacGorman (1993) and others suggest that the lightning activity accompanying tomadic storms will be dominated by intracloud lightning-with an increase in intracloud and total flash rates as the updraft increases in depth, size, and velocity. In a recent study, Perez et al. (1998) found that CG flash rates alone are too variable to be a useful predictor of (F4, F5) tornado formation. Studies of non-tomadic storms have also shown that total lightning flash rates track the updraft, with rates increasing as the updraft intensities and decreasing rapidly with cessation of vertical growth or downburst onset (Goodman et al., 1988; Williams et al., 1989). Such relationships result from the development of mixed phase precipitation and increased hydrometer collisions that lead to the efficient separation of charge. Correlations between updraft strength and other variables such as cloud-top height, cloud water mass, and hail size have also been observed.
The North Alabama Lightning Mapping Array: Recent Severe Storm Observations and Future Prospects

NASA Technical Reports Server (NTRS)

Goodman, S. J.; Blakeslee, R.; Christian, H.; Koshak, W.; Bailey, J.; Hall, J.; McCaul, E.; Buechler, D.; Darden, C.; Burks, J.

2004-01-01

The North Alabama Lightning Mapping Array became operational in November 2001 as a principal component of a severe weather test bed to infuse new science and technology into the short-term forecasting of severe and hazardous weather, principally within nearby National Weather Service forecast offices. Since the installation of the LMA, it has measured the total lightning activity of a large number of severe weather events, including three supercell tornado outbreaks, two supercell hailstorm events, and numerous microburst-producing storms and ordinary non-severe thunderstorms. The key components of evolving storm morphology examined are the time rate-of-change (temporal trending) of storm convective and precipitation characteristics that can be diagnosed in real-time using NEXRAD WSR-88D Doppler radar (echo growth and decay, precipitation structures and velocity features, outflow boundaries), LMA (total lightning flash rate and its trend) and National Lightning Detection Network (cloud-to- ground lightning, its polarity and trends). For example, in a transitional season supercell tornado outbreak, peak total flash rates for typical supercells in Tennessee reached 70-100/min, and increases in the total flash rate occurred during storm intensification as much as 20-25 min prior to at least some of the tornadoes. The most intense total flash rate measured during this outbreak (over 800 flashes/min) occurred in a storm in Alabama. In the case of a severe summertime pulse thunderstorm in North Alabama, the peak total flash rate reached 300/min, with a strong increase in total lightning evident some 9 min before damaging winds were observed at the surface. In this paper we provide a sampling of LMA observations and products during severe weather events to illustrate the capability of the system, and discuss the prospects for improving the short-term forecasting of convective weather using total lightning data.
A pseudo-dual-Doppler analysis of cyclic tornadogenesis

NASA Astrophysics Data System (ADS)

Dowell, David Collin

2000-06-01

Several tornadic storms formed in the Texas Panhandle on 8 June 1995, the date of the last mission of VORTEX (Verification of the Origins of Rotation in Tornadoes EXperiment). The southernmost storm in this severe weather outbreak produced a family of at least five tornadoes near the town of McLean. Airborne Doppler radar scans of this storm by the ELDORA (ELectra DOppler RAdar) offer the most detailed look to date at a storm producing a family of tornadoes. The goals of this study were twofold. The first was to determine a pseudo-dual-Doppler wind synthesis method in Cartesian coordinates appropriate for the analysis of the ELDORA data. Unique aspects of this part of the study include a comparison of wind synthesis methods based on variational formulations and the use of a non-uniform moving reference frame for the syntheses. A dual-Doppler formulation in which the radial velocity and continuity equations are all satisfied as weak constraints (Gamache 1997, Shapiro and Mewes 1999) yields a more accurate wind field than traditional (and variational) methods in which the radial velocity equations are satisfied exactly. The second goal of this study was to diagnose both the cyclic process and the formation of individual tornadoes. The McLean storm produced three large tornadoes at 18 min intervals. The last of these then lasted much longer (over one hour) and was stronger than the previous tornadoes. New pre-tornadic vortices formed on the east side of the updraft by tilting of strong environmental low-level horizontal vorticity into the vertical and then stretching of the vertical vorticity within the updraft. The vortices did not mature at low levels until they migrated to the west side of the updraft. Indirect evidence indicates that both baroclinic generation of horizontal vorticity and the rear downdraft may have played roles in tornado formation at this stage. The tornadic potential of a storm appears-to be related to the relative strength of low-level storm outflow and inflow beneath the west side of updraft. Cyclic tornadogenesis modes may be possible both when the inflow slightly dominates and when the outflow slightly dominates. The description of an inflow-dominated cyclic mode like that observed in the McLean storm is original. Internal cell interactions within the McLean storm appear to have helped the transition from the cyclic phase to a more steady phase.
Characteristics of flash initiations in a supercell cluster with tornadoes

NASA Astrophysics Data System (ADS)

Zheng, Dong; MacGorman, Donald R.

2016-01-01

Flash initiations within a supercell cluster during 10-11 May 2010 in Oklahoma were investigated based on observations from the Oklahoma Lightning Mapping Array and the Norman, Oklahoma, polarimetric radar (KOUN). The flash initiations at positions dominated by graupel, dry snow, small hail and crystals accounted for 44.3%, 44.1%, 8.0% and 3.0% of the total flashes, respectively. During the tornadic stage of the southern supercell in the cluster, flash initiations associated with graupel occupied the main body, the right flank and the forward flank of the supercell, while those associated with dry snow dominated the outskirts of the adjacent forward anvil, right anvil and rear anvil. The flash initiations associated with small hail were concentrated around the main updraft, particularly toward its front side. Highly dense flash initiations were located in the regions overlying the differential reflectivity (ZDR) arc and right anvil. The average initial height of the flashes decreased gradually from the rear to the front and from the right to the left flanks, while the height range over which initiations occurred reached a maximum at the front of the updraft. The flashes that were initiated in the adjacent forward anvils were largest on average, followed by those in the regions ahead of the updraft and near the ZDR arc. This study supports the concept of charge pockets and further deduces that the pockets in the right anvil are the most abundant and compact due to the frequent flash initiations, small-sized flashes and thin layers including flash initiations.
The Meteorological Setting of Narrow Bipolar Events

NASA Astrophysics Data System (ADS)

Stanley, M. A.; Suszcynsky, D. M.; Heavner, M. J.

2003-12-01

Narrow Bipolar Events (NBEs) are an impulsive form of electrical breakdown in storms which emits strong VHF radiation. It is well known that these events can be readily detected by VHF receivers in orbit and thus may provide a highly practical means to globally monitor storm activity. However, relatively little is known about how NBEs relate to the convective phase of storms and of how good a predictor they are of severe weather events such as large hail, damaging winds, and tornadoes. On June 10, 2002, numerous energetic NBEs were detected over Kansas by the Los Alamos National Laboratory Edot array, which is primarily located in Florida. These NBEs were also detected by a VHF receiver on-board the SVN 54 GPS satellite. The NBEs were associated with severe thunderstorms which produced softball size hail exceeding 11 centimeters in diameter and a weak F0 tornado. In another case study, several F2 tornadic Florida storms were analyzed for March, 2001. Unlike the Kansas storms, the NBEs of the Florida tornadic storms were spread out over a much wider area and exhibited considerable variability in both frequency of occurrence and predominant polarity of vertical charge transfer. To further explore the significance of the NBE rate variability, we will analyze NEXRAD radar volume scans in conjunction with Edot 3-dimensional locations to better understand how NBEs correlate with the thunderstorm life-cycle.
The Dynamical Core Model Intercomparison Project (DCMIP-2016): Results of the Supercell Test Case

NASA Astrophysics Data System (ADS)

Zarzycki, C. M.; Reed, K. A.; Jablonowski, C.; Ullrich, P. A.; Kent, J.; Lauritzen, P. H.; Nair, R. D.

2016-12-01

The 2016 Dynamical Core Model Intercomparison Project (DCMIP-2016) assesses the modeling techniques for global climate and weather models and was recently held at the National Center for Atmospheric Research (NCAR) in conjunction with a two-week summer school. Over 12 different international modeling groups participated in DCMIP-2016 and focused on the evaluation of the newest non-hydrostatic dynamical core designs for future high-resolution weather and climate models. The paper highlights the results of the third DCMIP-2016 test case, which is an idealized supercell storm on a reduced-radius Earth. The supercell storm test permits the study of a non-hydrostatic moist flow field with strong vertical velocities and associated precipitation. This test assesses the behavior of global modeling systems at extremely high spatial resolution and is used in the development of next-generation numerical weather prediction capabilities. In this regime the effective grid spacing is very similar to the horizontal scale of convective plumes, emphasizing resolved non-hydrostatic dynamics. The supercell test case sheds light on the physics-dynamics interplay and highlights the impact of diffusion on model solutions.
Satellite-observed cloud-top height changes in tornadic thunderstorms

NASA Technical Reports Server (NTRS)

Adler, R. F.; Fenn, D. D.

1981-01-01

Eleven tornadic storms are evaluated with respect to cloud top temperature changes relative to tornado touchdown. Digital IR data from the SMS/GOES geosynchronous satellites were employed for 10 F2 and one F1 tornadoes. A rapid ascent of the cloud tops 30-45 min before tornado touchdown, a temperature decrease of 0.4 K/min, and an ascent rate of about 3 m/sec were observed. The presence of an operating Doppler radar for three of the sample storms allowed detection of a mesocyclone coincident with the rapid cloud top ascent. The intensification and descent of the vortex to form a tornado is concluded to be due to a weakening of the updraft, the formation of a downdraft, and a shift of the vortex to the updraft-downdraft boundary, leading to dominance of the tilting term in the generation of vorticity.
Perceptions and Expected Immediate Reactions to Severe Storm Displays.

PubMed

Jon, Ihnji; Huang, Shih-Kai; Lindell, Michael K

2017-11-09

The National Weather Service has adopted warning polygons that more specifically indicate the risk area than its previous county-wide warnings. However, these polygons are not defined in terms of numerical strike probabilities (p s ). To better understand people's interpretations of warning polygons, 167 participants were shown 23 hypothetical scenarios in one of three information conditions-polygon-only (Condition A), polygon + tornadic storm cell (Condition B), and polygon + tornadic storm cell + flanking nontornadic storm cells (Condition C). Participants judged each polygon's p s and reported the likelihood of taking nine different response actions. The polygon-only condition replicated the results of previous studies; p s was highest at the polygon's centroid and declined in all directions from there. The two conditions displaying storm cells differed from the polygon-only condition only in having p s just as high at the polygon's edge nearest the storm cell as at its centroid. Overall, p s values were positively correlated with expectations of continuing normal activities, seeking information from social sources, seeking shelter, and evacuating by car. These results indicate that participants make more appropriate p s judgments when polygons are presented in their natural context of radar displays than when they are presented in isolation. However, the fact that p s judgments had moderately positive correlations with both sheltering (a generally appropriate response) and evacuation (a generally inappropriate response) suggests that experiment participants experience the same ambivalence about these two protective actions as people threatened by actual tornadoes. © 2017 Society for Risk Analysis.
Progress of research to identify rotating thunderstorms using satellite imagery

NASA Technical Reports Server (NTRS)

Anderson, Charles E.

1988-01-01

The possibility of detecting potentially tornadic thunderstorm cells from geosynchronous satelite imagery is determined. During the life of the contract, we examined eight tornado outbreak cases which had a total of 124 individual thunderstorm cells, 37 of which were tornadic.These 37 cells produced a total of 119 tornadoes. The outflow characteristics of all the cells were measured. Through the use of a 2-D flow field model, we were able to simulate the downstream developmemt of an anvil cloud plume which was emitted by the storm updraft at or near the tropopause. We used two parameters to characterize the anvil plume behavior: its speed of downstream propagation (U max) and the clockwise deviation of the centerline of the anvil plume from the storm relative ambient wind at the anvil plume outflow level (MDA). U max was the maximum U-component of the anvil wind parameter required to successfully maintain an envelope of translating particles at the tip of the expanding anvil cloud. MDA was the measured deviation angle acquired from McIDAS, between the storm relative ambient wind direction and the storm relative anvil plume outflow direction; tha latter being manipulated by controlling a tangential wind component to force the envelope of particles to maintain their position of surrounding the expanding outflow cloud.
A Total Lightning Perspective of the 20 May 2013 Moore, Oklahoma Supercell

NASA Technical Reports Server (NTRS)

Stano, Geoffrey T.; Schultz, Christopher J.; Carey, Lawrence D.; MacGorman, Don R.; Calhoun, Kristin M.

2014-01-01

In the early afternoon of 20 May 2013, a storm initiated to the west-southwest of Newcastle, Oklahoma. This storm would rapidly intensify into the parent supercell of the tornado that struck the city of Moore, Oklahoma. This article describes what contributions total lightning observations from the Oklahoma Lightning Mapping Array could provide to operational forecasters had these observations been available in real-time. This effort includes a focus on the GOES-R pseudo-geostationary lightning mapper demonstration product as well as the NASA SPoRT / Meteorological Development Laboratory's total lightning tracking tool. These observations and tools identified several contributions. Two distinct lightning jumps at 1908 and 1928 UTC provided a lead time of 19 minutes ahead of severe hail and 26 minutes ahead of the Moore, Oklahoma tornado's touchdown. These observations provide strong situational awareness to forecasters, as the lightning jumps are related to the rapid strengthening of the storm's updraft and mesocyclone and serve as a precursor to the stretching of the storm vortex ahead severe weather.
Passive microwave structure of severe tornadic storms on 16 November 1987

NASA Technical Reports Server (NTRS)

Heymsfield, Gerald M.; Fulton, Richard

1994-01-01

Passive microwave observations using the Special Sensor Microwave/Imager (SSM/I) are presented for severe tornadic storms in the lower midwestern United States on 16 November 1987. These measurements are compared with Geostationary Operational Environmental Satellite infrared (IR) measurements for the same case. The IR observations had a classic 'V' cold feature commonly associated with severe Midwest thunderstorms. The minimum microwave brightness temperatures at 86 GHz, which primarily respond to ice scattering by larger ice particles, were located in the convective region and the warm interior of the anvil top, between the arms of the IR V feature. The interior warm region was the only portion of the entire anvil region that had high 86-GHz polarization difference temperatures. Microphysical implications of these multispectral observations are discussed. The observations suggest that there are large variations of ice microphysical characteristics spatially and vertically in the anvil region. These observations are discussed in the context of previous dynamical and microphysical hypotheses on the IR V feature.
Interactions Between Convective Storms and Their Environment

NASA Technical Reports Server (NTRS)

Maddox, R. A.; Hoxit, L. R.; Chappell, C. F.

1979-01-01

The ways in which intense convective storms interact with their environment are considered for a number of specific severe storm situations. A physical model of subcloud wind fields and vertical wind profiles was developed to explain the often observed intensification of convective storms that move along or across thermal boundaries. A number of special, unusually dense, data sets were used to substantiate features of the model. GOES imagery was used in conjunction with objectively analyzed surface wind data to develop a nowcast technique that might be used to identify specific storm cells likely to become tornadic. It was shown that circulations associated with organized meso-alpha and meso-beta scale storm complexes may, on occasion, strongly modify tropospheric thermodynamic patterns and flow fields.
The annual amount of lightning in just 20 minutes: the October 25th, 2015 super-cell thunderstorm over central Israel

NASA Astrophysics Data System (ADS)

Yair, Y.; Ziv, B.; Lynn, B. H.; Evgeni, K.

2016-12-01

An exceptionally rare Eastern Mediterranean super-cell thunderstorm occurred during the morning hours of October 25th 2015. The storm developed within the northern tip of a Red-Sea trough (extending from Sudan to the Southeastern Mediterranean Sea) off the Egyptian coastline near Alexandria and moved north-west, crossing the Israeli coast just north of Tel-Aviv at 0900 local time. Deep convective cells developed rapidly over the sea, with thunderclouds exhibiting cloud top temperatures colder than -70°C (18 km) and radar reflectivity cores > 65 dBz at 10 km. The storms were accompanied by intensive lightning activity, severe hail, downbursts, and intense rain. The super-cell subsided upon reaching the Jordan rift in eastern Israel. The super-cell caused 1 fatality, extensive flooding and agricultural damages. It also impacted the national electrical network with power outages lasting for 3 days in central Israel. More than 17,000 cloud-to-ground lightning strokes were registered by the lightning detection system of the Israeli Electrical Corporation, exceeding the annual average for the entire country. The average cloud-to-ground flash rates between 0940-0950 and 0950-1000 (local time) were greater than 436 and 430 strokes per minute respectively, exceeding the global record flash rates found in the Argentina-Paraguay border (Zipser et al., 2006). This was the most powerful thunderstorm ever observed in Israel since lightning detection became operational in 1997. Medium-range forecast models such as ECMWF and the GFS missed the timing and severity of this unusual storm. We will present a mesoscale and microphysical analysis of this event to better understand the origins and severity of this rare super-cell. WRF high-resolution simulations with lightning assimilation (Fierro et al., 2012; Lynn et al., 2015) coupled with the Dynamic Lightning Scheme (Lynn et al., 2012) will be used in order to evaluate the performance of the WRF for accurately nowcasting such events.
An Ionospheric Response to the 2013 Moore EF5 Tornad, Detected By High-Resolution GPS-TEC Observations

NASA Astrophysics Data System (ADS)

Kubota, M.; Nishioka, M.; Tsugawa, T.; Ishii, M.

2014-12-01

We observed clear concentric waves and short-period oscillations in the ionosphere after the EF5 tornado hit Moore, Oklahoma, USA, on 20 May 2013 using a dense wide-coverage ionospheric total electron content (TEC) observation in North America. These concentric waves were non-dispersive waves with a horizontal wavelength of ~120 km and a period of ~13 minutes. They were observed for more than seven hours throughout North America. TEC oscillations with a period of ~4 minutes were also observed in the south of Moore for more than eight hours. Comparison between the TEC observation and the infrared cloud image from the GOES satellite indicates that the concentric waves were caused by supercells rather than the tornados themselves. Backward ray-tracing analysis suggests that the leaking of atmospheric waves in a thermal duct excited AGWs in the ionosphere. The short-period TEC oscillation could be explained by the acoustic resonance triggered by strong long-lasting supercells. This observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere.
Total Lightning and Radar Storm Characteristics Associated with Severe Storms in Central Florida

NASA Technical Reports Server (NTRS)

Goodman, Steven J; Raghavan, R.; Buechler, Dennis; Hodanish, S.; Sharp, D.; Williams, E.; Boldi, B.; Matlin, A.; Weber, M.

1998-01-01

This paper examines the three dimensional characteristics of lightning flashes and severe storms observed in Central Florida during 1997-1998. The lightning time history of severe and tornadic storms were captured during the on-going ground validation campaign supporting the Lightning Imaging Sensor (LIS) experiment on the Tropical Rainfall Measuring Mission (TRMM). The ground validation campaign is a collaborative experiment that began in 1997 and involves scientists at the Global Hydrology and Climate Center, MIT/Lincoln Laboratories, and the NWS Forecast Office at Melbourne, FL. Lightning signatures that may provide potential early warning of severe storms are being evaluated by the forecasters at the NWS/MLB office. Severe storms with extreme flash rates sometimes exceeding 300 per minute and accompanying rapid increases in flash rate prior to the onset of the severe weather (hall, damaging winds, tornadoes) have been reported by Hodanish et al. and Williams et al. (1998-this conference). We examine the co-evolving changes in storm structure (mass, echo top, shear, latent heat release) and kinematics associated with these extreme and rapid flash rate changes over time. The flash frequency and density are compared with the three dimensional radar reflectivity structure of the storm to help interpret the possible mechanisms producing the extreme and rapidly increasing flash rates. For two tornadic storms examined thus far, we find the burst of lightning is associated with the development of upper level rotation in the storm. In one case, the lightning burst follows the formation of a bounded weak echo region (BWER). The flash rates diminish with time as the rotation develops to the ground in conjunction with the decent of the reflectivity core. Our initial findings suggest the dramatic increase of flash rates is associated with a sudden and dramatic increase in storm updraft intensity which we hypothesize is stretching vertical vorticity as well as enhancing the development of the mixed phase region of the storm. We discuss the importance of these factors in producing both the observed extreme flash rates and the severe weather that follows in these storms and others to be presented.
Numerical modeling of severe convective storms occurring in the Carpathian Basin

NASA Astrophysics Data System (ADS)

Horváth, Á.; Geresdi, I.; Németh, P.; Csirmaz, K.; Dombai, F.

Squall lines often cause serious damages due to the strong surface outflow, hail, or heavy precipitation in Hungary every summer. Squall lines in the Carpathian Basin can be classified into two main categories: pre-frontal squall-lines and frontal convective lines. In this paper, these two types of severe mesoscale phenomena are investigated using the high resolution numerical weather prediction model, the MM5. The case study for the first type of convective systems occurred on 18th May 2005 when two main convective lines with their embedded severe storms formed daytime and caused high-velocity wind events and extensive damages in the eastern part of Hungary. The second case study is a frontal squall line that hit Budapest on 20th August 2006 and the associated high precipitation (HP) supercells reached the capital of Hungary at same time when the traditional Constitution Day firework began. The consequences were catastrophic: five people were killed and more than one thousand were injured due to the extreme weather. The non-hydrostatic high resolution MM5 model was able to simulate and catch the severe weather events occurred on the days under discussion. Moreover, the model was able to compute the detailed structure of the supercells embedded in thunderstorm lines. By studying the equivalent potential temperature (EPT) fields at lower levels, we state that in the prefrontal case, there is a competition between the supercell thunderstorms for the wet and warm air. A thunderstorm that can collect the wet and warm air from larger area will have longer lifetime and more intense updraft. In the second case, the frontal squall lines, the movement and the behavior of the supercell storms embedded in the line was highly determined by the synoptic-scale motions and less affected by the EPT field of the prefrontal masses.

Microphysical and Kinematic Characteristics of Regions of Flash Initiation in a Supercell Storm and a Multicell Storm Observed During the DC3 Field Program

NASA Astrophysics Data System (ADS)

DiGangi, E.; MacGorman, D. R.; Ziegler, C.; Betten, D.; Biggerstaff, M. I.

2017-12-01

Lightning initiation in thunderstorms requires that the local electric field magnitude exceed breakdown values somewhere, and this tends to occur between regions of positive and negative charge, where the largest electric field magnitudes tend to occur. Past studies have demonstrated that, near updrafts, storms with very strong updrafts tend to elevate regions of charge and of flash initiations higher, as well as to have more flashes initiated by small pockets of charge, than in storms with much weaker updrafts. In all thunderstorms, the source of these charge regions is generally thought to be microscopic charge separation via the relative growth rate noninductive mechanism, followed by macroscopic charge separation via sedimentation, although other charge generation mechanisms can contribute to charge in some regions. Charge generation and lightning initiation are therefore inherently dependent on the microphysical and kinematic characteristics of a given storm. This study compares the results of a hydrometeor classification algorithm applied to C-band mobile radar data with mixing ratios calculated by a diabatic Lagrangian analysis retrieval from the dual-Doppler wind fields for two storms, the 29-30 May 2012 supercell storm and the 21 June 2012 multicell storm, observed during the Deep Convective Clouds and Chemistry experiment. Using these data, we then compare the inferred microphysical and kinematic characteristics of regions in which the Oklahoma Lightning Mapping Array indicated that flashes were initiated in these two very different storms.
Features of the Raleigh Tornadic Storm Based on Analysis of Damage

DTIC Science & Technology

1990-01-01

studies have shown that a smaller scale microburst may occur within a larger downburst, or macroburst (Fujita and Wakimoto, 1981, Sinclair et a&, 1988...downburst: microburst and macroburst . SMRP Res. Paper No. 210, Univ. of Chicago, 82 PP. Fujita, T. T., 1989: The Teton-Yellowstone tornado of 21 July 1987
NASA/NOAA/AMS Earth Science Electronic Theater

NASA Technical Reports Server (NTRS)

Hasler, Fritz

1999-01-01

Selections from the following very large Earth science observed & simulated datasets shown from: Historical: GOES-10 & AVHRR, SeaWIFS, TRMM, Meteosat, GMS, FY2, and ADEOS. and Simulated: EOS-AM1, Landsat 7, Astrovision, and 3D numerical storm model. Also highlights of the 1998 Hurricane & Severe Storm Seasons will be reviewed. A spectacular animations of La Nina season hurricanes: Bonnie, Georges, etc. 5000 frame 5-min GOES 10 continuous 28 day animation of the'98 Spring tornadic thunderstorm season and other special GOES test datasets will be shown.
Effects of resolved boundary layer turbulence on near-ground rotation in simulated quasi-linear convective systems (QLCSs)

NASA Astrophysics Data System (ADS)

Nowotarski, C. J.

2017-12-01

Though most strong to violent tornadoes are associated with supercell thunderstorms, quasi-linear convective systems (QLCSs) pose a risk of tornadoes, often at times and locations where supercell tornadoes are less common. Because QLCS low-level mesocyclones and tornado signatures tend to be less coherent, forecasting such tornadoes remains particularly difficult. The majority of simulations of such storms rely on horizontally homogeneous base states lacking resolved boundary layer turbulence and surface fluxes. Previous work has suggested that heterogeneities associated with boundary layer turbulence in the form of horizontal convective rolls can influence the evolution and characteristics of low-level mesocyclones in supercell thunderstorms. This study extends methods for generating boundary layer convection to idealized simulations of QLCSs. QLCS simulations with resolved boundary layer turbulence will be compared against a control simulation with a laminar boundary layer. Effects of turbulence, the resultant heterogeneity in the near-storm environment, and surface friction on bulk storm characteristics and the intensity, morphology, and evolution of low-level rotation will be presented. Although maximum surface vertical vorticity values are similar, when boundary layer turbulence is included, a greater number of miso- and meso-scale vortices develop along the QLCS gust front. The source of this vorticity is analyzed using Eulerian decomposition of vorticity tendency terms and trajectory analysis to delineate the relative importance of surface friction and baroclinicity in generating QLCS vortices. The role of anvil shading in suppressing boundary layer turbulence in the near-storm environment and subsequent effects on QLCS vortices will also be presented. Finally, implications of the results regarding inclusion of more realistic boundary layers in future idealized simulations of deep convection will be discussed.
Overshooting top behavior of three tornado-producing thunderstorms

NASA Technical Reports Server (NTRS)

Umenhofer, T. A.

1975-01-01

The behavior of overshooting tops and jumping cirrus observed in three tornado-producing thunderstorms during the 1974 Learjet Cloud-Truth experiment is discussed. An investigation of temporal changes in the heights of overshooting domes (conglomerations of overshooting tops with diameters less than 1 km) reveals several distinctive features associated with tornadic events. There is a gradual decrease in dome height prior to tornado touchdown. Minimum dome activity occurred 5 min after, 5.5 min before, and at approximately the same time as the tornadic event in the storms observed. In all cases, dramatic dome growth at a rate of 17 to 23 m/sec immediately followed the occurrence of the minimum dome heights. There is evidence that tornado production is insensitive to the pre-touchdown maximum dome heights between 1 and 3 km.
Statistical Examination of Tornado Report and Warning Near-Storm Environments

NASA Astrophysics Data System (ADS)

Anderson-Frey, Alexandra K.

This study makes use of a 13-year dataset of 14,814 tornado events and 44,961 tornado warnings in the continental United States, along with near-storm environmental data associated with each of those tornado events and warnings, to build a methodology that can be used to create nuanced climatologies of near-storm environmental data. Two key parameter spaces are identified as being particularly useful in this endeavor: mixed-layer convective available potential energy (MLCAPE) versus 0-6-km vector shear magnitude (SHR6) and mixed-layer lifting condensation level (MLLCL) versus 0-1-km storm-relative helicity (SRH1). In addition, the Significant Tornado Parameter (STP) is identified as a useful composite parameter that can highlight near-storm environments that are particularly favorable for the development of significant tornadoes. Two particular statistical methods for the analysis and characterization of near-storm environments are described and applied: Kernel Density Estimation (KDE), which is applied to bulk (proximity soundinglike) parameter values associated with each event or warning, and Self-Organizing Maps (SOMs), which are applied to fully two-dimensional plots of STP in an area surrounding each event or warning. The KDE approach characterizes and identifies differences in the environments of tornadoes forming in quasi-linear convective systems versus those forming in right-moving supercells; specific environmental traits are also identified for different geographical regions, seasons, and times of day. Tornado warning performance is found to be best in environments with particularly large values of MLCAPE and SHR6. The early evening transition (EET) period is of particular interest: MLCAPE and MLLCL heights are in the process of falling, and SHR6 and SRH1 are in the process of increasing. Accordingly, tornadoes rated 2 or greater on the enhanced Fujita scale (EF2+) are also most common during the EET, probability of detection (POD) is relatively high, and false-alarm ratio (FAR) is relatively low. Overall, when comparing the distribution of environments for events versus those for warnings, there is no "smoking gun" indicating a systematic problem with forecasting that explains the high overall false-alarm ratio, which instead seems to stem from the inability to know which storms in a given environment will be tornadic. The SOM approach establishes nine statistically distinct clusters of spatial distributions of STP values in the 480 km x 480 km region surrounding each tornado event or warning. For tornado events, distinct patterns are associated more with particular times of day, geographical locations, and times of year, and the use of two-dimensional data rather than point proximity sounding information means that these patterns can be identified and characterized with still more detail; for instance, the archetypal springtime dryline environment in the Great Plains emerges readily from the data. Although high values of STP tend to be associated with relatively high POD and relatively low FAR, the majority of tornado events occur within a pattern of low STP, with relatively high FAR and low POD. The two-dimensional plots produced by the SOM approach provide an intuitive way to create distinct climatologies of tornadic near-storm environments. Having established a methodology through the use of KDE and SOM, this research then examines the topic of tornado outbreaks [defined as ten or more (E)F1+ tornadoes that occur with no more than 6 h or 2,000 km between subsequent tornadoes]. Outbreak tornadoes in a given geographical region have greater SRH1 and SHR6 than isolated tornadoes in the same region, and also have considerably higher POD than isolated tornadoes. When SOMs are created for all (E)F1+ tornadoes, the percentage of outbreak tornadoes in a given node is found to depend more strongly on the magnitude of the STP value surrounding the tornado than its orientation. For the SOM of outbreak tornadoes, outbreaks occurring in environments with higher magnitudes of STP will generally also have the highest casualty rates, regardless of the specific two-dimensional pattern of STP. Two specific tornado outbreaks are then examined through this methodology, which allows the events to be placed into their climatological context with more nuance than typical proximity sounding-based approaches would allow.
Spatial-temporal characteristics of lightning flash size in a supercell storm

NASA Astrophysics Data System (ADS)

Zhang, Zhixiao; Zheng, Dong; Zhang, Yijun; Lu, Gaopeng

2017-11-01

The flash sizes of a supercell storm, in New Mexico on October 5, 2004, are studied using the observations from the New Mexico Lightning Mapping Array and the Albuquerque, New Mexico, Doppler radar (KABX). First, during the temporal evolution of the supercell, the mean flash size is anti-correlated with the flash rate, following a unary power function, with a correlation coefficient of - 0.87. In addition, the mean flash size is linearly correlated with the area of reflectivity > 30 dBZ at 5 km normalized by the flash rate, with a correlation coefficient of 0.88. Second, in the horizontal, flash size increases along the direction from the region near the convection zone to the adjacent forward anvil. The region of minimum flash size usually corresponds to the region of maximum flash initiation and extent density. The horizontal correspondence between the mean flash size and the flash extent density can also be fitted by a unary power function, and the correlation coefficient is > 0.5 in 50% of the radar volume scans. Furthermore, the quality of fit is positively correlated to the convective intensity. Third, in the vertical direction, the height of the maximum flash initiation density is close to the height of maximum flash extent density, but corresponds to the height where the mean flash size is relatively small. In the discussion, the distribution of the small and dense charge regions when and where convection is vigorous in the storm, is deduced to be responsible for the relationship that flash size is temporally and spatially anti-correlated with flash rate and density, and the convective intensity.
Deep convection over Northern Italy: synoptic and thermodynamic analysis

NASA Astrophysics Data System (ADS)

Costa, S.; Mezzasalma, P.; Levizzani, V.; Alberoni, P. P.; Nanni, S.

Synoptic and thermodynamic characteristics of severe storm outbreaks, including supercells, over northern Italy's Po valley are examined over a 3-year period. Storms are divided into three main categories according to the most relevant associated ground phenomenon: tornado-like, hailfall and heavy rain. For each category, the most common synoptic characteristics are investigated. Sounding data are used to calculate stability indices that help define the storm's environment. Results indicate that the interaction between the synoptic flow and the steep Alpine orography is the key factor responsible for building up the mesoscale circulation that leads to different kinds of severe storms. Some of the stability indices can be regarded as predictors of intense convection.
Infrared Data for Storm Analysis

NASA Technical Reports Server (NTRS)

Adler, R.

1982-01-01

The papers in this section include: 1) 'Thunderstorm Top Structure Observed by Aircraft Overflights with an Infrared Radiometer'; 2) 'Thunderstorm Intensity as Determined from Satellite Data'; 3) 'Relation of Satellite-Based Thunderstorm Intensity to Radar-Estimated Rainfall'; 4) 'A Simple Physical Basis for Relating Geosynchronous Satellite Infrared Observations to Thunderstorm Rainfall'; 5) 'Satellite-Observed Cloud-Top Height Changes in Tornadic Thunderstorms'; 6) 'Predicting Tropical Cyclone Intensity Using Satellite-Measured Equivalent Blackbody Temperatures of Cloud Tops'.
Investigation into the Formation, Structure, and Evolution of an EF4 Tornado in East China Using a High-Resolution Numerical Simulation

NASA Astrophysics Data System (ADS)

Yao, Dan; Xue, Haile; Yin, Jinfang; Sun, Jisong; Liang, Xudong; Guo, Jianping

2018-04-01

Devastating tornadoes in China have received growing attention in recent years, but little is known about their formation, structure, and evolution on the tornadic scale. Most of these tornadoes develop within the East Asian monsoon regime, in an environment quite different from tornadoes in the U.S. In this study, we used an idealized, highresolution (25-m grid spacing) numerical simulation to investigate the deadly EF4 (Enhanced Fujita scale category 4) tornado that occurred on 23 June 2016 and claimed 99 lives in Yancheng, Jiangsu Province. A tornadic supercell developed in the simulation that had striking similarities to radar observations. The violent tornado in Funing County was reproduced, exceeding EF4 (74 m s-1), consistent with the on-site damage survey. It was accompanied by a funnel cloud that extended to the surface, and exhibited a double-helix vorticity structure. The signal of tornado genesis was found first at the cloud base in the pressure perturbation field, and then developed both upward and downward in terms of maximum vertical velocity overlapping with the intense vertical vorticity centers. The tornado's demise was found to accompany strong downdrafts overlapping with the intense vorticity centers. One of the interesting findings of this work is that a violent surface vortex was able to be generated and maintained, even though the simulation employed a free-slip lower boundary condition. The success of this simulation, despite using an idealized numerical approach, provides a means to investigate more historical tornadoes in China.
Severe storm electricity

NASA Technical Reports Server (NTRS)

Rust, W. D.; Macgorman, D. R.

1985-01-01

During FY-85, Researchers conducted a field program and analyzed data. The field program incorporated coordinated measurements made with a NASA U2. Results include the following: (1) ground truth measurements of lightning for comparison with those obtained by the U2; (2) analysis of dual-Doppler radar and dual-VHF lightning mapping data from a supercell storm; (3) analysis of synoptic conditions during three simultaneous storm systems on 13 May 1983 when unusually large numbers of positive cloud-to-ground (+CG) flashes occurred; (4) analysis of extremely low frequency (ELF) wave forms; and (5) an assessment of a cloud -ground strike location system using a combination of mobile laboratory and fixed-base TV video data.
Flash Location, Size, and Rates Relative to the Evolving Kinematics and Microphysics of the 29 May 2012 DC3 Supercell Storm

NASA Astrophysics Data System (ADS)

MacGorman, D. R.; DiGangi, E.; Ziegler, C.; Biggerstaff, M. I.; Betten, D.; Bruning, E. C.

2014-12-01

A supercell thunderstorm was observed on 29 May 2012 during the Deep Convective Clouds and Chemistry (DC3) experiment. This storm was part of a cluster of severe storms and produced 5" hail, an EF-1 tornado, and copious lightning over the course of a few hours. During a period in which flash rates were increasing rapidly, observations were obtained from mobile polarimetric radars and a balloon-borne electric field meter (EFM) and particle imager, while aircraft sampled the chemistry of the inflow and anvil. In addition, the storm was within the domain of the 3-dimensional Oklahoma Lightning Mapping Array (LMA) and the S-band KTLX WSR-88D radar. The focus of this paper is the evolution of flash rates, the location of flash initiations, and the distribution of flash size and flash extent density as they relate to the evolving kinematics and microphysics of the storm for the approximately 30-minute period in which triple-Doppler coverage was available. Besides analyzing reflectivity structure and three-dimensional winds for the entire period, we examine mixing ratios of cloud water, cloud ice, rain, and graupel/hail that have been retrieved by a Lagrangian analysis for three select times, one each at the beginning, middle, and end of the period. Flashes in an around the updraft of this storm were typically small. Flash size tended to increase, and flash rates tended to decrease as distance from the updraft increased. Although flash initiations were most frequent near the updraft, some flashes were initiated near the edge of 30 dBZ cores and propagated into the anvil. Later, some flashes were initiated in the anvil itself, in vertical cells that formed and became electrified tens of kilometers downshear of the main body of the storm. Considerable lightning structure was inferred to be in regions dominated by cloud ice in the upper part of the storm. The continual small discharges in the overshooting top of the storm tended to be near or within 15 dBZ contours, although occasional discharges appeared to extend above the storm.
Total Lightning Characteristics with Respect to Radar-Derived Mesocyclone Strength

NASA Technical Reports Server (NTRS)

Stough, Sarah M.; Carey, Lawrence D.; Schultz, Christopher J.

2015-01-01

Recent work investigating the microphysical and kinematic relationship between a storm's updraft, its total lightning production, and manifestations of severe weather has resulted in development of tools for improved nowcasting of storm intensity. The total lightning jump algorithm, which identifies rapid increases in total lightning flash rate that often precede severe events, has shown particular potential to benefit warning operations. Maximizing this capability of total lightning and its operational implementation via the lightning jump may best be done through its fusion with radar and radar-derived intensity metrics. Identification of a mesocyclone, or quasi-steady rotating updraft, in Doppler velocity is the predominant radar-inferred early indicator of severe potential in a convective storm. Fused lightning-radar tools that capitalize on the most robust intensity indicators would allow enhanced situational awareness for increased warning confidence. A foundational step toward such tools comes from a better understanding of the updraft-centric relationship between intensification of total lightning production and mesocyclone development and strength. The work presented here utilizes a sample of supercell case studies representing a spectrum of severity. These storms are analyzed with respect to total lightning flash rate and the lightning jump alongside mesocyclone strength derived objectively from the National Severe Storms Laboratory (NSSL) Mesocyclone Detection Algorithm (MDA) and maximum azimuthal shear through a layer. Early results indicate that temporal similarities exist in the trends between total lightning flash rate and low- to mid-level rotation in supercells. Other characteristics such as polarimetric signatures of rotation, flash size, and cloud-to-ground flash ratio are explored for added insight into the significance of these trends with respect to the updraft and related processes of severe weather production.
Radar characteristics of tornadic and non-tornadic quasi-linear convective systems over the central United States

NASA Astrophysics Data System (ADS)

Grana, Sarah

Quasi-Linear Convective Systems (QLCS) are linear convective systems known to produce a variety of severe weather threats including damaging winds, hail, flooding, and even tornadoes. Previous studies have found that QLCSs are most common in the Ohio and Mississippi River Valleys and produce roughly 18% of tornadoes across the United States. In addition, it has been shown that QLCS tornadoes spawn from low-level circulations called mesovortices. Mesovortices build quickly from the ground up making it very difficult to accurately identify them on radar, especially at long distances. Therefore, it is imperative that more research be done to distinguish between QLCSs that produce tornadoes and those that do not. Fifty-seven QLCS events were selected to investigate how radar parameters differ between tornadic and non-tornadic QLCSs. These events were broken into the following categories: warm season tornadic, warm season non-tornadic, cold season tornadic, and cold season non-tornadic. Tornadic cases produced one or more tornadoes, while non-tornadic cases had tornado warnings issued without a tornado actually being produced. These events were chosen based on their geographical location and the data available. The goal was to find radar parameters that were statistically significantly different between tornadic events and non-tornadic events.
Seismic detection of tornadoes

USGS Publications Warehouse

Tatom, F. B.

1993-01-01

Tornadoes represent the most violent of all forms of atmospheric storms, each year resulting in hundreds of millions of dollars in property damage and approximately one hundred fatalities. In recent years, considerable success has been achieved in detecting tornadic storms by means of Doppler radar. However, radar systems cannot determine when a tornado is actually in contact with the ground, expect possibly at extremely close range. At the present time, human observation is the only truly reliable way of knowing that a tornado is actually on the ground. However, considerable evidence exists indicating that a tornado in contact with the ground produces a significant seismic signal. If such signals are generated, the seismic detection and warning of an imminent tornado can become a distinct possibility.
Techniques used to identify tornado producing thunderstorms using geosynchronous satellite data

NASA Technical Reports Server (NTRS)

Schrab, Kevin J.; Anderson, Charles E.; Monahan, John F.

1992-01-01

Satellite imagery in the outbreak region in the time prior to and during tornado occurrence was examined in detail to obtain descriptive characteristics of the anvil plume. These characteristics include outflow strength (UMAX), departure of anvil centerline from the storm relative ambient wind (MDA), storm relative ambient wind (SRAW), and maximum surface vorticity (SFCVOR). It is shown that by using satellite derived parameters which characterize the flow field in the anvil region, the occurrence and intensity of tornadoes, which the parent thunderstorm produces, can be identified. Analysis of the censored regression models revealed that the five explanatory variables (UMAX, MDA, SRAW, UMAX-2, and SFCVOR) were all significant predictors in the identification of tornadic intensity of a particular thunderstorm.
Severe storm identification with satellite microwave radiometry: An initial investigation with Nimbus-7 SMMR data

NASA Technical Reports Server (NTRS)

Spencer, R. W.; Howland, M. R.

1984-01-01

The severe weather characteristics of convective storms as observed by the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) are investigated. Low 37 GHz brightness temperatures (due to scattering of upwelling radiation by precipitation size ice) are related to the occurrence of severe weather (large hail, strong winds or wind damage, tornadoes and funnel clouds) within one hour of the satellite observation time. During 1979 and 1980 over the United States there were 263 storms which had very cold 37 GHz signatures. Of these storms 15% were severe. The SMMR detected hail, wind, and tornadic storms equally well. Critical Success Indices (CSI's) of 0.32, 0.48, and 0.38 are achieved for the thresholding of severe vs. nonsevere low brightness temperature events during 1979, 1980, and the two years combined, respectively. Such scores are comparable to skill scores for early radar detection methods. These results suggest that a future geostationary passive microwave imaging capability at 37 GHz, with sufficient spatial and temporal resolution, would allow the detection of severe convective storms. This capability would provide a useful complement to radar, especially in areas not covered by radar.
Comparisons Between Total Lightning Data, Mesocyclone Strength, and Storm Damage Associated with the Florida Tornado Outbreak of February 23, 1998

NASA Technical Reports Server (NTRS)

Hodanish, S; Sharp, D.; Williams, E.; Boldi, B.; Goodman, Steven J.; Raghavan, R.; Matlin, A.; Weber, M.

1998-01-01

During the early morning hours of February 23 1998, the worst tornado outbreak ever recorded occurred over the central Florida peninsula. At least 7 confirmed tornadoes, associated with 4 supercells, developed, with 3 of the tornadoes reaching F3 intensity. Many of the tornadoes where on the ground for tens of miles, uncommon for the state of Florida. A total of 42 people were killed, with over 250 people injured. During the outbreak, National Weather Service Melbourne, in collaboration with the National Aeronautics and Space Administration and the Massachusetts Institute of Technology was collecting data from a unique lightning observing system called Lightning Imaging Sensor Data Applications Display (LISDAD, Boldi et.al., this conference). This system marries radar data collected from the KMLB WSR-88D, cloud to ground data collected from the National Lightning Detection Network, and total lightning data collected from NASKs Lightning Detection And Ranging system. This poster will display, concurrently, total lightning data (displayed in 1 minute increments), time/height storm relative velocity products from the KMLB WSR-88D, and damage information (tornado/hail/wind) from each of the supercell thunderstorms. The primary objective of this poster presentation is to observe how total lightning activity changes as the convective storm intensifies, and how the lightning activity changes with respect to mesocyclone strength (vortex stretching) and damaging weather on the ground.
Simulating southwestern U.S. desert dust influences on supercell thunderstorms

NASA Astrophysics Data System (ADS)

Lerach, David G.; Cotton, William R.

2018-05-01

Three-dimensional numerical simulations were performed to evaluate potential southwestern U.S. dust indirect microphysical and direct radiative impacts on a real severe storms outbreak. Increased solar absorption within the dust plume led to modest increases in pre-storm atmospheric stability at low levels, resulting in weaker convective updrafts and less widespread precipitation. Dust microphysical impacts on convection were minor in comparison, due in part to the lofted dust concentrations being relatively few in number when compared to the background (non-dust) aerosol population. While dust preferentially serving as cloud condensation nuclei (CCN) versus giant CCN had opposing effects on warm rain production, both scenarios resulted in ample supercooled water and subsequent glaciation aloft, yielding larger graupel and hail. Associated latent heating from condensation and freezing contributed little to overall updraft invigoration. With reduced rain production overall, the simulations that included dust effects experienced slightly reduced grid-cumulative precipitation and notably warmer and spatially smaller cold pools. Dust serving as ice nucleating particles did not appear to play a significant role. The presence of dust ultimately reduced the number of supercells produced but allowed for supercell evolution characterized by consistently higher values of relative vertical vorticity within simulated mesocyclones. Dust radiative and microphysical effects were relatively small in magnitude when compared to those from altering the background convective available potential energy and vertical wind shear. It is difficult to generalize such findings from a single event, however, due to a number of case-specific environmental factors. These include the nature of the low-level moisture advection and characteristics of the background aerosol distribution.
Case study: An isolated severe storm with giant hail hit Slovenian capital city Ljubljana on May 25th 2009

NASA Astrophysics Data System (ADS)

Korosec, M.

2009-09-01

Introduction A quite unusual weather pattern for month of May with first and early season heat wave of year 2009 resulted in several days of active severe storms across central Europe and Alpine region. Synoptic situation On May 25th 2009, an omega block pattern with strong upper-level subtropical ridge extending over Mediterranean and Balkan Peninsula brought stable and warm conditions into Southern Europe. Elsewhere, two large-scale troughs were located over Western and Eastern Europe with very unstable environment. On the nose of the Mediterranean ridge a jet streak with moderate shear was placed while over the Southern Alpine region only weak shear was placed over Slovenia. Rich boundary layer moisture and steep lapse rates within an elevated mixed layer favored extreme amounts of CAPE. After strong diurnal heating and surface wind convergence along the local topography a few convective cells were triggered in the mountainous terrain while deep moist convection over the rest of Slovenia was trapped by the strong capping inversion. In late afternoon several cells from the mountainous terrain interfered with each other and explosive convective cell was initiated along their outflow boundaries. Increasing near surface southeasterly wind flow supported enhanced low-level shear and storm relative helicity which caused this cell to very rapidly grown into an organized supercell storm on the flat terrain in northern Slovenia. This supercell then started racing southeastwards towards Ljubljana, a capital city of Slovenia. It caused extensive hail damage with very large to giant hailstones up to 7cm in diameter falling over parts of Ljubljana and areas north and southeast of the city. Presentation of research This case study will go through a research of this very damaging hailstorm, throughout a detailed analysis of the synoptic situation including analysis of satellite, radar and surface observations. At first, forecasting models did not suggest organized convection and severe storms to occur given the only weak wind shear forecasted, while there was extreme amount of instability with CAPE exceeding 2500 J/kg expected. But then, according to the closest modified 12 UTC skew-t diagrams from Udine and unfolding evolution, better instability with CAPE values over 3000 J/kg and moderate near 20m/s 0-6km bulk shear were favorable enough for rapid organization of this isolated storm into such a dangerous severe hailstorm. This paper will also present a visual analysis of this storm as classic textbook supercell structure with accompanied features was documented by many storm chasers from nearby. References - EARS/ARSO radar, satellite and surface observation data (www.arso.gov.si) - GFS/ALADIN forecasting model maps (wetterzentrale.de, www.arso.gov.si) - ESTOFEX convective outlook for May 25th 2009 (www.estofex.org) - EUMETSAT satellite images (www.eumetsat.int) - Administration of Civil Protection and Disaster Relief (www.sos112.si) - EARS/ARSO article: "Porocilo o neurjih 25. maja 2009" (www.arso.gov.si) - Skywarn Slovenia article: "Analiza supercelične nevihte z debelo točo nad Ljubljano 25. maja, 2009" (www.skywarn.si) - ESSL/ESWD database storm reports

Medicolegal aspects of tornadic storms in Kansas, U.S.A.

PubMed

Eckert, W G

1991-12-01

Kansas is known for its fierce whether, including tornados in the spring and fall and blizzards in the winter. A recent series of tornados cut a path of destruction a mile wide for greater than 40 miles (64 km), killed 20 people, and caused several hundred casualities on the evening of April 26, 1991, in Tornado Alley, which runs from the northern border of Oklahoma through southern Kansas past Wichita toward Emporium, Kansas. The wind velocity was greater than 200 mph. Twenty people were killed, 17 of these in Andover, Kansas, a small town east of Wichita. Injuries caused by the tornados and the excellent emergency response and care provided by medical, law-enforcement, and volunteer personnel in the wake of the storms are described here.
Developing Empirical Lightning Cessation Forecast Guidance for the Cape Canaveral Air Force Station and Kennedy Space Center

DTIC Science & Technology

2010-01-01

345th Weather Squadron, Patrick Air Force Base, Cocoa Beach, Florida, USA. Copyright 2010 by the American Geophysical Union. 0148‐0227/10/2009JD013034...V. Mazur, W. D. Rust, W. L. Taylor, and B. C. Johnson (1989), Lightning rates relative to tornadic storm evolution on 22 May 1981, J. Atmos. Sci...Marshall, T. C., M. Stolzenburg, P. R. Krehbiel, N. R. Lund, and C. R. Maggio (2009), Electrical evolution during the decay stage of New Mexico thunderstorms
Ionospsheric observation of enhanced convection-initiated gravity waves during tornadic storms

NASA Technical Reports Server (NTRS)

Hung, R. J.

1981-01-01

Atmospheric gravity waves associated with tornadoes, with locally severe storms occuring with tornadoes, and with hurricanes were studied through the coupling between the ionosphere and the troposphere. Reverse group ray tracing computations of gravity waves observed by an ionospheric Doppler sounder array were analyzed. The results of ray tracing computations and comparisons between the computed location of the wave sources and with conventional meteorological data indicate that the computed sources of the waves were near the touchdown of the tornadoes, near the eye of the hurricanes, and directly on the squall line of the severe thunderstorms. The signals excited occurred one hour in advance of the tornadoes and three hours in advance of the hurricanes. Satellite photographs show convective overshooting turrets occurring at the same locations and times the gravity waves were being excited. It is suggested that gravity wave observations, conventional meteorological data, and satellite photographs be combined to develop a remote sensing technique for detecting severe storms.
Large Charge Moment Change Lightning in an Oklahoma Mesoscale Convective System

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Cummer, Steven; Petersen, Danyal; Flores-Rivera, Lizxandra; Lyons, Walt; MacGorman, Donald; Beasley, William

2014-01-01

On 31 May 2013, a line of severe thunderstorms developed during the local afternoon in central Oklahoma, USA. One of the supercells produced the El Reno tornado, which caused significant damage and killed several people. During the 2300 UTC hour (during the mature supercell stage and just after the tornado began), the storm produced several positive cloud-to-ground (+CG) lightning strokes that featured large (> 100 C km) impulse charge moment changes (iCMCs; charge moment during the first 2 ms after the return stroke). These discharges occurred mainly in convection, in contrast to the typical pattern of large-CMC and sprite-parent +CGs occurring mainly in stratiform precipitation regions. After this time, the line of thunderstorms evolved over several hours into a large mesoscale convective system (MCS). By the 0700 UTC hour on 1 June 2013, the large-CMC pattern had changed markedly. Large-CMC negative CGs, which were absent early in the storm's lifetime, occurred frequently within convection. Meanwhile, large-CMC +CGs had switched to occurring mainly within the broad stratiform region that had developed during the intervening period. The evolution of the large-CMC lightning in this case will be examined using a mix of national mosaics of radar reflectivity, the Oklahoma Lightning Mapping Array (OKLMA), the Charge Moment Change Network (CMCN), and the National Lightning Detection Network (NLDN). A major goal of this study is understanding how storm structure and evolution affected the production of large-CMC lightning. It is anticipated that this will lead to further insight into how and why storms produce the powerful lightning that commonly causes sprites in the upper atmosphere.
Large Charge Moment Change Lightning in an Oklahoma Mesoscale Convective System

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Cummer, Steven; Beasley, William; Flores-Rivera, Lizxandra; Lyons, Walt; MacGorman, Donald

2014-01-01

On 31 May 2013, a line of severe thunderstorms developed during the local afternoon in central Oklahoma, USA. One of the supercells produced the El Reno tornado, which caused significant damage and killed several people. During the 2300 UTC hour (during the mature supercell stage and just after the tornado began), the storm produced several positive cloud-to-ground (+CG) lightning strokes that featured large (> 75 C km) impulse charge moment changes (iCMCs - charge moment during the first 2 ms after the return stroke). These discharges occurred mainly in convection, in contrast to the typical pattern of large-CMC and sprite-parent +CGs occurring mainly in stratiform precipitation regions. After this time, the line of thunderstorms evolved over several hours into a large mesoscale convective system (MCS). By the 0700 UTC hour on 1 June 2013, the large- CMC pattern had changed markedly. Large-CMC negative CGs, which were absent early in the storm's lifetime, occurred frequently within convection. Meanwhile, large- CMC +CGs had switched to occurring mainly within the broad stratiform region that had developed during the intervening period. The evolution of the large-CMC lightning in this case will be examined using a mix of polarimetric data from individual radars, national mosaics of radar reflectivity, the Oklahoma Lightning Mapping Array (OKLMA), the Charge Moment Change Network (CMCN), and the National Lightning Detection Network (NLDN). A major goal of this study is understanding how storm structure and evolution affected the production of large-CMC lightning. It is anticipated that this will lead to further insight into how and why storms produce the powerful lightning that commonly causes sprites in the upper atmosphere.
An Observational Study on Quantifying the Distance of Supercell-Boundary Interaction in the Great Plains

NASA Astrophysics Data System (ADS)

Magee, Kathleen Marie

Several case studies and numerical simulations have confirmed that baroclinic boundaries provide enhanced horizontal and vertical vorticity, wind shear, helicity, and moisture that induce stronger updrafts, higher reflectivity, and stronger low-level rotation in supercells. However, the distance at which a boundary will provide such enhancement is less well-defined. Previous studies have identified distances ranging from 5 km to 200 km, and only focused on tornadogenesis rather than all forms of severe weather. To better aid short-term forecasts, the actual distances at which supercells produce severe weather in proximity to a boundary needs to be assessed. In this study, the distance between a large number of supercells and nearby surface boundaries (including warm fronts, stationary fronts, and outflow boundaries) is measured throughout the lifetime of each storm; the distance at which associated reports of large hail, strong winds, and tornadoes is also collected. Data is gathered from SPC storm reports, WPC surface analyses, ASOS archives, and NCDC radar archives. The Integrated Data Viewer (IDV) from Unidata is used to analyze the distance of the supercell from the boundary every twenty minutes. These distances are then used to interpolate the distance at which severe and significantly severe reports occurred; reports are grouped by severe type (tornado, hail, or wind), then by boundary type (warm front, stationary front, or outflow). Using these distributions, the range from the boundary at which each type of severe weather is produced is identified per boundary type to assist forecasters. Overall, the range at which tornadoes are more likely to be produced is generally closer to the boundary than hail and wind reports for all three boundary types, likely owing to the enhanced helicity present near a boundary. Statistical analyses are used to assess the sensitivity of report distributions to report type, boundary type, distance from the boundary, and boundary strength. The distance of different report types near the same boundary surprisingly did not test as statistically different, except for warm fronts; however, when comparing the distances of the same report type associated with different boundaries, statistically significant differences were found for different boundaries in which different report types are maximally produced. Temperature gradients are not as statistically different between boundaries, but the temperature gradient within the same boundary is statistically significant for the occurrence of tornadoes vs. hail. Additional analyses were conducted to complement the distributions of severe report distances. Previous research has demonstrated that the angle at which supercells interact with boundaries impacts tornado production; in the present dataset, supercells interacting at an angle less than 45° are not only more likely to produce tornadoes, but also more likely to produce significantly severe tornadoes. Additionally, other studies have suggested that the temperature gradient of a boundary is of minimal importance with regards to tornado production. Interestingly, the tornadoes in this study were associated with stronger temperature gradients than for hail or wind production, thus v implying that a stronger amount of baroclinically-generated horizontal vorticity is required for tornadogenesis, likely due to the enhanced low-level rotation.
Severe Storm Identification with Satellite Microwave Radiometry: An Initial Investigation with Nimbus-7 SMMR Data.

NASA Astrophysics Data System (ADS)

Spencer, Roy W.; Howland, Michael R.; Santek, David A.

1987-06-01

In an attempt to determine the feasibility of detecting and monitoring severe weather with future satellite passive microwave observations, the severe weather characteristics of convective storms as observed by the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) are investigated. Low 37 GHz brightness temperatures (due to scattering of upwelling radiation by precipitation size ice) were related to the occurrence of severe weather (large hail, strong winds or wind damage, tornados and funnel clouds) within one hour of the satellite observation time. During 1979 and 1980 over the study area within the United States, there were 263 storms that had cold 37 GHz signatures. Of these storms, 15 percent were reported as severe. The relative number of storms falling in hail, wind, or tornadic categories did not differ from those expected climatologically. Critical Success Indices (CSIs) of 0.32, 0.48 and 0.38 were achieved for the low brightness temperature thresholding of severe versus nonsevere storms during 1979, 1980 and the two years combined, respectively. The preliminary indication is that a future geostationary passive microwave imaging capability at 37 GHz (or possibly higher frequencies), with sufficient spatial and temporal resolution, would facilitate the detection and monitoring of severe convective storms. This capability would provide a useful complement to radar, especially over most of the globe which is not covered by radar.
Eliminating the major tornado threat in Tornado Alley

NASA Astrophysics Data System (ADS)

Tao, R.

2014-06-01

The 2013 devastating tornadoes in Oklahoma, Illinois and other states in Tornado Alley raise an important question: Can we do something to eliminate the major tornado threats in Tornado Alley? Violent tornadoes in Tornado Alley start from the clash-between northbound warm air flow and southbound cold air flow. As there is no mountain in Tornado Alley ranging from west to east to weaken or block the air flows, some clashes are violent, creating vortex turbulence called supercells. These supercells are initially in horizontal spinning motion at the lower atmosphere and then tilt as the air turns to rise in the storm's updraft, creating a component of spin around a vertical axis. About 30% of supercells develop into tornadoes, causing tremendous damages. Here we show that if we build three east-west great walls in the American Midwest, 300 m high and 50 m wide, one in North Dakota, one passing Oklahoma to east and the third one in the south Texas and Louisiana, we will weaken or block such air mass clashes and therefore diminish the major tornado threat in the Tornado Alley forever. We may also first build such great walls locally at some areas with frequent devastating tornado outbreaks and then gradually extend them.
Remote sensing of tornadic storms from geosynchronous satellite infrared digital data

NASA Technical Reports Server (NTRS)

Hung, R. J.; Smith, R. E.

1982-01-01

Two cases of GOES digital infrared data were analyzed during the three-hour period immediately prior to the tornado touchdown times. Clouds associated with tornadoes were compared to those without tornadoes using a combination of satellite infrared and rawinsonde data. On the basis of this limited data sample, it appears as if the altitude to which the overshooting cloud top penetrated above the tropopause is the factor which determines whether or not a tornado is formed. In these cases, the overshooting cloud top collapsed about 15 to 30 min before the tornado touchdown.
Precipitation Field and Intrastorm Flow of Supercell Convective Storms.

DTIC Science & Technology

1981-08-01

1978: Observations of radome transmission losses at 5 cm wavelengths. Preprints 18th Conf. on Radar Meteor., Atlanta, Amer. Meteor. Soc., 288-291. , and...La, and Lr are loss factors (dimensionless) for the radome, the transmission path, and atmospheric gaseous absorp- tion. Typical values are Lc - 2dB...surface fields. Objectively analyzed maps of streamflow , wind com- ponents, temperature, dew point, pressure, divergence, vorticity, mix- ing ratio, and
On the Possible Role of Gently Sloping Topography in Influencing the Nature of Convective Storms: A Case Study on the High Plains of the U. S.

NASA Astrophysics Data System (ADS)

Bluestein, H. B.; Weiss, C.; Rotunno, R.; Reif, D. W.; Romine, G. S.

2016-12-01

On 27 May 2015 a quasi-stationary supercell in the northern Texas Panhandle produced several tornadoes, before it evolved into a mesoscale convective system. The pre-storm environment was characterized by relatively weak midlevel winds from the west and surface winds from the south/southwest, such that the 0 - 6 km vertical shear was too weak for supercells to have evolved. There was, however, an increase in speed and backing of the surface wind to the easterly/southeasterly direction during the afternoon, so that the 0 - 6 km shear exceeded 20 m s-1, the approximate threshold for supercell formation. The approximate motion of a convective storm without taking into account shear-related or gust-front propagation is the mean wind in the lowest 6 km. With an increase in the easterly component of the surface winds, the mean wind in the lowest 6 km, in the absence of any increase in westerlies at 6 km, decreased. Some physical mechanisms that could be responsible for the backing and increase in easterly component of the surface wind are as follows: (a) the approach of a synoptic-scale, upper-level trough, with its attendant pre-trough, quasi-geostrophic-induced ascent accompanied by surface convergence, an increase in surface vorticity, and concomitant drop in surface pressure, so that east of the region of ascent a westward-directed pressure-gradient forced develops; (b) surface heating on a surface that slopes upward to the west, such that a westward-directed pressure-gradient force develops; (c) the westward movement of a low-level cold pool that had developed in pre-existing, upstream convective storms; (d) the downward mixing of easterly momentum aloft; and (e) the diurnal inertial oscillation in boundary-layer wind due to the diurnal change in vertical mixing of momentum. It is hypothesized that for this case the primary mechanism was (b). A WRF forecast is described in which evidence is presented in favor of our hypothesis. An estimate will also be given of how much backing and increase in surface wind could be explained by heating on the sloping terrain and also climatological changes in wind speed and direction during the afternoon based on surface mesonet data will be shown. The results of this study could have applications to the study of convection anywhere around the globe where there is gently sloping terrain.
An intense, quasi-steady thunderstorm over mountainous terrain. I - Evolution of the storm-initiating mesoscale circulation

NASA Technical Reports Server (NTRS)

Cotton, W. R.; George, R. L.; Knupp, K. R.

1982-01-01

The evolution of mesoscale systems that eventually lead to the formation of large quasi-steady storm systems is investigated. The morphological and turbulent structure of the quasi-steady storm is described. Data obtained during the South Park Area Cumulus Experiment from surface meteorological stations, rawinsondes and tethered balloons, conventional and Doppler radars, powered aircraft, and satellites, indicate that on July 19, 1977, a north-south oriented line of intense convective cells formed and remained within South Park. Elevated surface heating created a region of low-level convergence, importing Pacific moisture from west of the Rockies. The mesoscale thunderstorm line formed over this convergence zone, and a single large convective cell was observed to grow on the southern end of the mesoscale line, exhibiting supercell characteristics and substantial modifications of the environmental flow.
Tornadogensis within Hurricanes Based on the Orientation of the Rainband to the Coast after Landfall

NASA Astrophysics Data System (ADS)

Etten-Bohm, M.

2015-12-01

The focus of this study is to investigate the development of tornadoes within the rainband of a hurricane for various orientations of the rainband when a hurricane makes landfall. The rainband of a hurricane is a common area where tornadogenesis is found depending on the size, intensity, and orientation of the rain band when the storm makes landfall. As a hurricane approaches a coast line, land-surface roughness contributes to surface friction, which can contribute in tornadogenesis. The orientation of the rainband may play a part in the type of supercells that are formed in that rainband and the number and intensity of the tornadoes produced. This study will investigate if the orientation of the rainband leads to the direction in which the supercells rotate, whether clockwise or counter-clockwise, and the scale and intensity of the tornadoes produced.
Tornadogenesis via squall line and supercell interaction revisited - The 15 November 1989 Huntsville tornado

NASA Technical Reports Server (NTRS)

Goodman, Steven J.; Knupp, Kevin R.

1990-01-01

A case study analyzing the environmental setting and storm system morphology that provides observational evidence of a mechanism involving the interaction of a gust front with a preexisting mesocyclone is presented. This case serves to reemphasize the existence of a high conditional probability of tornado occurrence, given the merger of a gust front (or storm outflow) with a moderate to strong thunderstorm ahead of it. The resultant data serve to illustrate some important unresolved issues relevant to the severe weather warning system that involve the present and planned local warning and network radars, and future algorithms that might intelligently integrate other data sources and models with the radar data.
U.S. preparedness for severe storms questioned

NASA Astrophysics Data System (ADS)

Showstack, Randy

Doug Hill, chief meteorologist for WJLA-TV in Washington, D.C., recalled the broadcast news coverage of two supercell thunderstorms that swept through the region on September 24, producing three tornadoes and causing two fatalities. Hill said that only one local radio station which airs his forecasts activated the federal emergency alert system to immediately notify the public about the tornadoes, and added that there should be some changes in requirements. “Somehow, broadcast stations have to get the idea that these warnings and requests to activate [the alerts] are not done [just] for fun,” he said.Hill was among several experts appearing at an October 11 congressional hearing, “Weatherproofing the U.S.: Are We Prepared for Severe Storms?” The hearing, which was held by the U.S. House of Representatives' Science Committee, included testimony about the nation's emergency preparedness in dealing with several types of severe weather: tornadoes, hurricanes, and wind storms.
Total Lightning as a Severe Weather Diagnostic in Strongly Baroclinic Systems in Central Florida

NASA Technical Reports Server (NTRS)

Williams, E.; Boldi, B.; Matlin, A.; Weber, M.; Hodanish, S.; Sharp, D.; Goodman, Steven J.; Raghavan, R.; Buechler, Dennis

1998-01-01

The establishment of a consistent behavior of total lightning activity in severe convective storms has been challenged historically by the relative scarcity of these storms combined with the difficulties inherent in documenting the (dominant) intracloud component of total lightning. This situation has changed recently with the abundance of severe weather in central Florida during 1997-98, including the tornado outbreak of February 23, 1998, and with the development of the operational LISDAD system (Boldi et al, this conference) to document these cases. This paper is concerned primarily with the behavior of total lightning in severe weather during the dry season when the Florida atmosphere is most strongly baroclinic. It has been found that all three manifestations of severe weather (ie., hall, wind, tornadoes) are consistently preceded by rapid increases in total flash rate with values often in excess of 100 flashes/minute. Preliminary analysis suggests that this systematic electrical behavior observed in summertime 'pulse severe' storms (Hodanish et al, this conference) also pertains to the more strongly baroclinic, long-track tornadic storms (more common in Oklahoma), as evidenced by the February 23, 1998 outbreak case in central Florida exhibiting two long-tracking F3 tornadoes. The largest flash rates in severe weather anywhere occur in baroclinic conditions at midlatitude. The physical plausibility of flash rates in excess of 100 per minute will be assessed. We will also consider the differences in storm structure for high flash rate storms that are non-severe.
Surface wind, pressure and temperature fields near tornadic and non-tornadic narrow cold-frontal rainbands

NASA Astrophysics Data System (ADS)

Clark, Matthew; Parker, Douglas

2014-05-01

Narrow cold frontal rainbands (NCFRs) occur frequently in the UK and other parts of northwest Europe. At the surface, the passage of an NCFR is often marked by a sharp wind veer, abrupt pressure increase and a rapid temperature decrease. Tornadoes and other instances of localised wind damage sometimes occur in association with meso-gamma-scale vortices (sometimes called misocyclones) that form along the zone of abrupt horizontal wind veer (and associated vertical vorticity) at the leading edge of the NCFR. Using one-minute-resolution data from a mesoscale network of automatic weather stations, surface pressure, wind and temperature fields in the vicinity of 12 NCFRs (five of which were tornadic) have been investigated. High-resolution surface analyses were obtained by mapping temporal variations in the observed parameters to equivalent spatial variations, using a system velocity determined by analysis of the radar-observed movement of NCFR precipitation segments. Substantial differences were found in the structure of surface wind and pressure fields close to tornadic and non-tornadic NCFRs. Tornadic NCFRs exhibited a large wind veer (near 90°) and strong pre- and post-frontal winds. These attributes were associated with large vertical vorticity and horizontal convergence across the front. Tornadoes typically occurred where vertical vorticity and horizontal convergence were increasing. Here, we present surface analyses from selected cases, and draw comparisons between the tornadic and non-tornadic NCFRs. Some Doppler radar observations will be presented, illustrating the development of misocyclones along parts of the NCFR that exhibit strong, and increasing, vertical vorticity stretching. The influence of the stability of the pre-frontal air on the likelihood of tornadoes will also be discussed.
Modes of isolated, severe convective storm formation along the dryline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bluestein, H.B.; Parker, S.S.

1993-05-01

Patterns of the formation of isolated, severe convective storms along the dryline in the Southern plains of the United States during the spring over a 16-year period were determined from an examination of the evolution of radar echoes as depicted by WSR-57 microfilm data. It was found that in the first 30 min after the first echo, more than half of the radar echoes evolved into isolated storms as isolated cells from the start; others developed either from a pair of cells, from a line segment, from a cluster of cells, from the merger of mature cells, or from amore » squall line. Proximity soundings were constructed from both standard and special soundings, and from standard surface data. It was found that the estimated convective available potential energy and vertical shear are characteristic of the environment of supercell storms. The average time lag between the first echo and the first occurrence of severe weather of any type, or tornadoes alone, was approximately 2 h. There were no significant differences in the environmental parameters for the different modes of storm formation. 49 refs., 15 figs., 3 tabs.« less
The environment associated with significant tornadoes in Bangladesh

NASA Astrophysics Data System (ADS)

Bikos, Dan; Finch, Jonathan; Case, Jonathan L.

2016-01-01

This paper investigates the environmental parameters favoring significant tornadoes in Bangladesh through a simulation of ten high-impact events. A climatological perspective is first presented on classifying significant tornadoes in Bangladesh, noting the challenges since reports of tornadoes are not documented in a formal manner. The statistical relationship between United States and Bangladesh tornado-related deaths suggests that significant tornadoes do occur in Bangladesh so this paper identifies the most significant tornadic events and analyzes the environmental conditions associated with these events. Given the scarcity of observational data to assess the near-storm environment in this region, high-resolution (3-km horizontal grid spacing) numerical weather prediction simulations are performed for events identified to be associated with a significant tornado. In comparison to similar events over the United States, significant tornado environments in Bangladesh are characterized by relatively high convective available potential energy, sufficient deep-layer vertical shear, and a propensity for deviant (i.e., well to the right of the mean flow) storm motion along a low-level convergence boundary.
Understanding How Climate Change Could Affect Tornadoes

NASA Astrophysics Data System (ADS)

Elsner, James; Guishard, Mark

2014-11-01

Current understanding of how tornadoes might change with global warming is limited. Incomplete data sets and the small-scale nature of tornadic events make it difficult to draw definitive conclusions. A consensus report on the climate of extreme storms found little evidence of trends in tornado frequency in the United States. However new research suggests a potential climate change footprint on tornadoes. Some of this research was presented at the First International Summit on Tornadoes and Climate Change, hosted by Aegean Conferences. The summit took place at the Minoa Palace in Chania, Greece, from 25 to 30 May 2014. Thirty delegates from eight countries—Greece, the United States, Germany, the United Kingdom, China, Japan, Israel, and Taiwan—participated.

Observations of Two Sprite-Producing Storms in Colorado

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Lyons, Walter A.; Cummer, Steven A.; Fuchs, Brody R.; Dolan, Brenda; Rutledge, Steven A.; Krehbiel, Paul; Rison, William; Stanley, Mark; Ashcraft, Thomas

2016-01-01

Two sprite-producing thunderstorms were observed on 8 and 25 June 2012 in northeastern Colorado by a combination of low-light cameras, a lightning mapping array, polarimetric and Doppler radars, the National Lightning Detection Network, and charge moment change measurements. The 8 June event evolved from a tornadic hailstorm to a larger multicellular system that produced 21 observed positive sprites in 2 h. The majority of sprites occurred during a lull in convective strength, as measured by total flash rate, flash energy, and radar echo volume. Mean flash area spiked multiple times during this period; however, total flash rates still exceeded 60 min(sup 1), and portions of the storm featured a complex anomalous charge structure, with midlevel positive charge near 20degC. The storm produced predominantly positive cloud-to-ground lightning. All sprite-parent flashes occurred on the northeastern flank of the storm, where strong westerly upper level flow was consistent with advection of charged precipitation away from convection, providing a pathway for stratiform lightning. The 25 June event was another multicellular hailstorm with an anomalous charge structure that produced 26 positive sprites in less than 1 h. The sprites again occurred during a convective lull, with relatively weaker reflectivity and lower total flash rate but relatively larger mean flash area. However, all sprite parents occurred in or near convection and tapped charge layers in adjacent anvil cloud. The results demonstrate the sprite production by convective ground strokes in anomalously charged storms and also indicate that sprite production and convective vigor are inversely related in mature storms.
Dual-Polarimetric Radar-Based Tornado Debris Paths Associated with EF-4 and EF-5 Tornadoes over Northern Alabama During the Historic Outbreak of 27 April 2011

NASA Technical Reports Server (NTRS)

Carey, Lawrence D.; Schultz, Christopher J.; Schultz, Elise V.; Petersen, Walter A.; Gatlin, Patrick N.; Knupp, Kevin R.; Molthan, Andrew L.; Darden, Christopher B.

2011-01-01

An historic tornado and severe weather outbreak devastated much of the southeastern United States between 25 and 28 April 2011. On 27 April 2011, northern Alabama was particularly hard hit by a large number of tornadoes, including several that reached EF-4 and EF-5 on the Enhanced Fujita damage scale. In northern Alabama alone, there were approximately 100 fatalities and hundreds of more people who were injured or lost their homes during the havoc caused by these violent tornadic storms. Two long-track and violent (EF-4 and EF-5) tornadoes occurred within range of the University of Alabama in Huntsville (UAHuntsville) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). A unique capability of dual-polarimetric radar is the near-real time identification of lofted debris associated with ongoing tornadoes on the ground. The focus of this paper is to analyze the dual-polarimetric radar-inferred tornado debris signatures and identify the associated debris paths of the long-track EF-4 and EF-5 tornadoes near ARMOR. The relative locations of the debris and damage paths for each tornado will be ascertained by careful comparison of the ARMOR analysis with NASA MODIS (Moderate Resolution Imaging Spectroradiometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite imagery of the tornado damage scenes and the National Weather Service tornado damage surveys. With the ongoing upgrade of the WSR-88D (Weather Surveillance Radar - 1988 Doppler) operational network to dual-polarimetry and a similar process having already taken place or ongoing for many private sector radars, dual-polarimetric radar signatures of tornado debris promise the potential to assist in the situational awareness of government and private sector forecasters and emergency managers during tornadic events. As such, a companion abstract (Schultz et al.) also submitted to this conference explores "The use of dual-polarimetric tornadic debris signatures in an operational setting."
Dual-Polarimetric Radar-Based Tornado Debris Paths Associated with EF-4 and EF-5 Tornadoes over Northern Alabama During the Historic Outbreak of 27 April 2011

NASA Technical Reports Server (NTRS)

Carey, Lawrence D.; Schultz, Chrstopher J.; Schultz, Elise V.; Petersen, Walter A.; Gatlin, Patrick N.; Knupp, Kevin R.; Molthan, Andrew L.; Jedlovec, Gary J.; Darden, Christopher B.

2012-01-01

An historic tornado and severe weather outbreak devastated much of the southeastern United States between 25 and 28 April 2011. On 27 April 2011, northern Alabama was particularly hard hit by a large number of tornadoes, including several that reached EF-4 and EF-5 on the Enhanced Fujita damage scale. In northern Alabama alone, there were approximately 100 fatalities and hundreds of more people who were injured or lost their homes during the havoc caused by these violent tornadic storms. Two long-track and violent (EF-4 and EF-5) tornadoes occurred within range of the University of Alabama in Huntsville (UAHuntsville) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). A unique capability of dual-polarimetric radar is the near-real time identification of lofted debris associated with ongoing tornadoes on the ground. The focus of this paper is to analyze the dual-polarimetric radar-inferred tornado debris signatures and identify the associated debris paths of the long-track EF-4 and EF-5 tornadoes near ARMOR. The relative locations of the debris and damage paths for each tornado will be ascertained by careful comparison of the ARMOR analysis with NASA MODIS (Moderate Resolution Imaging Spectroradiometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite imagery of the tornado damage scenes and the National Weather Service tornado damage surveys. With the ongoing upgrade of the WSR-88D (Weather Surveillance Radar 1988 Doppler) operational network to dual-polarimetry and a similar process having already taken place or ongoing for many private sector radars, dual-polarimetric radar signatures of tornado debris promise the potential to assist in the situational awareness of government and private sector forecasters and emergency managers during tornadic events. As such, a companion abstract (Schultz et al.) also submitted to this conference explores The use of dual-polarimetric tornadic debris signatures in an operational setting.
Simulation of Tornado over Brahmanbaria on 22 March 2013 using Doppler Weather Radar and WRF Model

NASA Astrophysics Data System (ADS)

Das, M. K.; Chowdhury, M.; Das, S.

2013-12-01

A tornado accompanied with thunderstorm, rainfall and hailstorm affected Brahmanbaria of Bangladesh in the afternoon of 22 March 2013. The tornadic storms are studied based on field survey, ground and radar observations. Low level moisture influx by southerly flow from the Bay of Bengal coupled with upper level westerly jet stream causing intense instability and shear in the wind fields triggered a series of storms for the day. The exact time and locations of the storms are investigated by using the Agartala and Cox's Bazar Doppler Weather Radar (DWR). Subsequently, the storms are simulated by using the WRF-ARW model at 1 km horizontal resolution based on 6 hourly analyses and boundary conditions of NCEP-FNL. Among the typical characteristics of the storms, the CAPE, surface wind speed, flow patterns, T-Φ gram, rainfall, sea level pressure, vorticity and vertical velocity are studied. Results show that while there are differences of 2-3 hours between the observed and simulated time of the storms, the distances between observed and simulated locations of the storms are several tens of kilometers. The maximum CAPE was generally above 2400 J kg-1 in the case. The maximum intensity of surface wind speed simulated by the model was only 38 m sec-1. This seems to be underestimated. The highest vertical velocity (updraft) simulated by the model was 250 m sec-1 around 800-950 hPa. The updraft reached up to 150 hPa. It seems that the funnel vortex reached the ground, and might have passed some places a few meters above the surface. According to the Fujita Pearson scale, this tornado can be classified as F-2 with estimated wind speed of 50-70 ms-1. Keywords: Tornado, DWR, NCEP-FNL, T-Φ gram, CAPE.
On the reliability of hook echoes as tornado indicators

NASA Technical Reports Server (NTRS)

Forbes, G. S.

1981-01-01

A study of radar echoes associated with the tornadoes of the 3 April 1974 outbreak was performed to evaluate the usefulness of echo shape as an indicator of tornadic thunderstorms. The hook shape was usually successful in characterizing an echo as tornadic, with a false alarm rate of 16%. Because hook echoes were relatively rare, however, a less restrictive shape called distinctive was more successful at detecting tornadic thunderstorms, identifying 65% of the tornadic echoes. An echo had a distinctive shape if it possessed a marked appendage on its right rear flank or was in the shape of a spiral, comma or line echo wave pattern (LEWP). Characteristics of the distinctive echo are given.
Green Thunderstorms Observed.

NASA Astrophysics Data System (ADS)

Gallagher, Frank W., III; Beasley, William H.; Bohren, Craig F.

1996-12-01

Green thunderstorms have been observed from time to time in association with deep convection or severe weather events. Often the green coloration has been attributed to hail or to reflections of light from green foliage on the ground. Some skeptics who have not personally observed a green thunderstorm do not believe that green thunderstorms exist. They suggest that the green storms may be fabrications by excited observers. The authors have demonstrated the existence of green thunderstorms objectively using a spectrophotometer. During the spring and summer of 1995 the authors observed numerous storms and recorded hundreds of spectra of the light emanating corn these storms. It was found that the subjective judgment of colors can vary somewhat between observers, but the variation is usually in the shade of green. The authors recorded spectra of green and nongreen thunderstorms and recorded spectral measurements as a storm changed its appearance from dark blue to a bluish green. The change in color is gradual when observed from a stationary position. Also, as the light from a storm becomes greener, the luminance decreases. The authors also observed and recorded the spectrum of a thunderstorm during a period of several hours as they flew in an aircraft close to a supercell that appeared somewhat green. The authors' observations refute the ground reflection hypothesis and raise questions about explanations that require the presence of hail.
National Weather Service Warning Performance Based on the WSR-88D.

NASA Astrophysics Data System (ADS)

Polger, Paul D.; Goldsmith, Barry S.; Przywarty, Richard C.; Bocchieri, Joseph R.

1994-02-01

The National Weather Service (NWS) began operational use of the Weather Surveillance Radar-1988 Doppler (WSR-88D) system in March 1991 at Norman, Oklahoma. WSR-88D data have been available to forecasters at five additional offices: Melbourne, Florida, and sterling, Virginia (since January 1992); St. Louis, Missouri, and Dodge City, Kansas (since March 1992); and Houston, Texas (since April 1992). The performance of the severe local storm and flash flood warning programs at the six offices before and after the availability of the WSR-88D was measured quantitatively. The verification procedures and statistical measures used in the quantitative evaluation were those used operationally by the NWS.The statistics show that the warnings improved dramatically when the WSR-88D was in operation. Specifically, the probability of detection of severe weather events increased and the number of false alarms decreased. There was also a marked improvement in the lead time for all severe local storm and flash flood events. These improvements were evident throughout the effective range of the radar. Stratification of severe local storm data by severe thunderstorms versus tornadoes revealed an improvement in the NWS's ability to differentiate between tornadic and nontornadic storms when the WSR-88D was in operation. Four individual cases are examined to illustrate how forecasters used the WSR-88D to achieve the improved results. These cases focus on the unique features of the WSR-88D that provide an advantage over conventional NWS radars.
The Impact on Simulated Storm Structure and Intensity of Variations in the Lifted Condensation Level and the Level of Free Convection

NASA Technical Reports Server (NTRS)

McCaul, Eugene W., Jr.; Cohen, Charles; Arnold, James E. (Technical Monitor)

2001-01-01

The sensitivities of convective storm structure and intensity to changes in the altitudes of the prestorm environmental lifted condensation level and level of free convection axe studied using a full-physics three-dimensional cloud model. Matrices of simulations are conducted for a range of LCL=LFC altitudes, using a single moderately-sheared curved hodograph trace in conjunction with 1 convective available potential energy values of either 800 or 2000 J/kg, with the matrices consisting of all four combinations of two distinct choices of buoyancy and shear profile shape. For each value of CAPE, the LCL=LFC altitudes are also allowed to vary in a series of simulations based on the most highly compressed buoyancy and shear profiles for that CAPE, with the environmental buoyancy profile shape, subcloud equivalent potential temperature, subcloud lapse rates of temperature and moisture, and wind profile held fixed. For each CAPE, one final simulation is conducted using a near optimal LFC, but a lowered LCL, with a neutrally buoyant environmental thermal profile specified in between. Results show that, for the buoyancy-starved small-CAPE environments, the simulated storms are supercells and are generally largest and most intense when LCL=LFC altitudes lie in the approximate range 1.5-2.5 km above the surface. The simulations show similar trends for the shear-starved large-CAPE environments, except that conversion from supercell to multicell morphology frequently occurs when the LCL is high. For choices of LCL=LFC height within the optimal 1.5-2.5 km range, peak storm updraft overturning efficiency may approaches unity relative to parcel theory, while for lower LCL=LFC heights, overturning efficiency is reduced significantly. The enhancements of overturning efficiency and updraft diameter with increasing LFC height are shown to be the result of systematic increases in the mean equivalent potential temperature of the updraft at cloud base. For the shear-starved environments, the tendency for outflow dominance is eliminated, but a large overturning efficiency maintained, when a low LCL is used in conjunction with a high LFC. The result regarding outflow dominance at high LCL is consistent with expectations, but the beneficial effect of a high LFC on convective overturning efficiency has not previously been widely recognized. The simulation findings here also appear to be consistent with statistics from previous severe storm environment climatologies, but provide a new framework for interpreting those statistics.
Investigation and Characterization of Acoustic Emissions of Tornadoes Using Arrays of Infrasound Sensors

NASA Astrophysics Data System (ADS)

Frazier, W. G.; Talmadge, C. L.; Waxler, R.; Knupp, K. R.; Goudeau, B.; Hetzer, C. H.

2017-12-01

Working in co-ordination with the NOAA Vortex Southeast (Vortex SE) research program, 9 infrasound sensor arrays were deployed at fixed sites across North Alabama, South-central Tennessee, and Northwest Georgia during March and April of 2017, to investigate the emission and characterization of infrasonic acoustic energy from tornadoes and related phenomena. Each array consisted of seven broadband acoustic sensors with calibrated frequency response from 0.02 Hz to 200 Hz. The arrays were configured in a pattern such that accurate bearings to acoustic sources could be obtained over a broad range of frequencies (nominally from 1 Hz to 100 Hz). Data were collected synchronously at a rate of 1000 samples per second. On 22 April 2017 a line of strong storms passed directly through the area being monitored producing at least three verified tornadoes. Two of these were rated at EF0 and the other an EF1. Subsequent processing of the data from several of the arrays revealed acoustic emissions from the tornadic storms ranging in frequencies below 1 Hz to frequencies greater than 10 Hz. Accurate bearings to the storms have been calculated from distances greater than 60 km. Preliminary analysis has revealed that continuous emissions occurred prior to the estimated touchdown times, while the storms were on the ground, and for short periods after the tornadoes lifted; however, the strongest emissions appeared to occur while the storms were on the ground. One of the storms passed near two arrays simultaneously, and therefore accurate an accurate track of the storm as it moved has been obtained only using the infrasound measurements. Initial results from the analysis of the infrasound data will be presented. Under Vortex SE meteorological data was collected on a large suite of sensors. Correlations between the infrasound data and the meteorological data will be investigated and discussed.
The severe hailstorm in Germany on 28 July 2013: Characteristics and meteorological conditions

NASA Astrophysics Data System (ADS)

Kunz, Michael; Blahak, Ulrich; Handwerker, Jan; Schmidberger, Manuel; Mohr, Susanna; Jürgen Punge, Heinz; Fluck, Elody; Mühr, Bernhard

2015-04-01

At the end of July 2013, a series of violent thunderstorms with large hail, severe gusts and heavy rain affected several parts of Germany. These storms were triggered by pre-frontal convergence zones that formed within unstable air masses ahead of a low pressure system named Andreas. They marked the end of a short, but intense heat wave with temperatures up to 38°C. On 28 July, two supercell thunderstorms formed in the Rhine valley upstream of the Black Forest Mountains and moved almost parallel over the Swabian Jura and Bavaria. While the northern cell was weaker, the southern cell substantially intensified in the first hours and created hailstones with diameters of up to 8 cm. The hail fell mainly over a heavily populated region between the cities of Reutlingen and Tübingen with a high concentration of exposed assets. The track of that supercell ended in the north of Czech Republic and had a length of 500 km. Approximately 80,000 buildings were severely damaged by this major hailstorm. In total, insured loss was estimated to amount around 2 bn EURO, which is even higher than that related to the June flood in Germany in the same year. In this paper we investigate the temporal evolution and the characteristics of the most damaging supercell on 28 July by combining different data from remote sensing instruments such as radar, satellite, and lightning detection systems with ground-based observations and reports from eye-witnesses and a crop insurance company. Additional simulations with the Consortium for Small Scale Modelling COSMO-DE model with different setups reveal the important role of the cold pool for the triggering of the most severe hail cell. It will be shown that a major problem for simulating the storm was its initiation, while, once triggered artificially by 'warm bubbles', its track could be simulated rather well over several hours. Moreover, the operational COSMO version has some problems to simulate the observed reflectivity structure of the hailstorm, while a two-moment microphysical scheme yields results in very good agreement to the observations. Finally, a historical context is provided by comparing that event with other severe hailstorms that occurred over recent decades in Germany.
Validation of satellite-based CI detection of convective storms via backward trajectories

NASA Astrophysics Data System (ADS)

Dietzsch, Felix; Senf, Fabian; Deneke, Hartwig

2013-04-01

Within this study, the rapid development and evolution of several severe convective events is investigated based on geostationary satellite images, and is related to previous findings on suitable detection thresholds for convective initiation. Nine severe events have been selected that occurred over Central Europe in summer 2012, and have been classified into the categories supercell, mesoscale convective system, frontal system and orographic convection. The cases are traced backward starting from the fully developed convective systems to its very beginning initial state using ECMWF data with 0.5 degree spatial resolution and 3h temporal resolution. For every case the storm life cycle was quantified through the storm's infrared (IR) brightness temperatures obtained from Meteosat Second Generation SEVIRI with 5 min temporal resolution and 4.5 km spatial resolution. In addition, cloud products including cloud optical thickness, cloud phase and effective droplet radius have been taken into account. A semi-automatic adjustment of the tracks within a search box was necessary to improve the tracking accuracy and thus the quality of the derived life-cycles. The combination of IR brightness temperatures, IR temperature time trends and satellite-based cloud products revealed different stages of storm development such as updraft intensification and glaciation well in most casesconfirming previously developed CI criteria from other studies. The vertical temperature gradient between 850 and 500 hPa, the Total-Totals-Index and the storm-relative helicity have been derived from ECMWF data and were used to characterize the storm synoptic environment. The results suggest that the storm-relative helicity also influences the life time of convective storms over Central Europe confirming previous studies. Tracking accuracy has shown to be a crucial issue in our study and a fully automated approach is required to enlarge the number of cases for significant statistics.
Physical Patterns Associated with 27 April 2011 Tornado Outbreak

NASA Astrophysics Data System (ADS)

Ramos, Fernanda; Salem, Thomas

2012-02-01

The National Weather Service office in Memphis, Tennessee has aimed their efforts to improve severe tornado forecasting. Everything is not known about tornadogenesis, but one thing is: tornadoes tend to form within supercell thunderstorms. Hence, 27 April 2011 and 25 May 2011 were days when a Tornado Outbreak was expected to arise. Although 22 tornadoes struck the region on 27 April 2011, only 1 impacted the area on 25 May 2011. In order to understand both events, comparisons of their physical features were made. These parameters were studied using the Weather Event Simulator system and the NOAA/NWS Storm Prediction database. This research concentrated on the Surface Frontal Analysis, NAM40 700mb Dew-Points, NAM80 250mb Wind Speed and NAM20 500mb Vorticity images as well as 0-6 km Shear, MUCAPE and VGP mesoscale patterns. As result of this research a Dry-Line ahead of a Cold Front, Dew-points 5C and higher, and high Vorticity values^ were synoptic patterns that influenced to the formation of supercell tornadoes. Finally, MUCAPE and VGP favored the possibility of tornadoes occurrence on 25 May 2011, but shear was the factor that made 27 April 2011 a day for a Tornado Outbreak weather event.
Mature Thunderstorm Cloud-Top Structure and Dynamics: A Three-Dimensional Numerical Simulation Study.

NASA Astrophysics Data System (ADS)

Schlesinger, Robert E.

1984-05-01

An anelastic three-dimensional model is used to investigate the effects of vertical wind shear regime on cloud-top structure and internal properties of mature isolated midlatitude thunderstorms. Four comparative experiments, designated A through D, are performed with varying shear profiles in otherwise identical initializations. Cases A-C assume strong shear, differing only in the veering of the low-level hodograph: moderate in A, strong in B and none in C. Weak shear, everywhere 40% as great as in C, is assumed in case D.The strong-shear cases A-C show moderately vigorous quasi-steady mature updrafts with strong midlevel mesovortex couplets, and marked anvil elongation along the net vertical shear vector. Differences are modest, especially at cloud top, though with low-level hodograph curvature the updraft is enhanced and skewed toward the cyclonic right flank. The weak-shear case D shows a weaker and less persistent mature updraft than A-C, along with weaker midlevel rotation and a much more newly circular anvil.In the strong-shear experiments, the cloud top considerably resembles geostationary satellite observations of tornadic storms (Negri, 1982), even though the model storm interiors lack the significant low-level mesocyclone and very strong concentrated updraft typical of observed tornadic storms. Both model and observations show a persistent cloud-top temperature pattern featuring a cold area slightly upshear of the cloud summit, with a warm area downshear in the absence of a local height minimum, though in the model the thermal couplet is smaller-scale with lower amplitude and lacks the well-developed `V' shape seen in the observations. The thermal couplet is also present with weak shear, but is only about half as strong, largely due to a much weaker cold area.Several dynamic features of the cloud-top thermal couplet are revealed by backward and forward parcel trajectory analyses for Case B: 1) The cold and warm areas at cloud top result from ascent and descent, respectively, of stratospheric air from upshear. 2) Only slightly below cloud top, shallow downward extensions of the warm and cold areas consist of air that originates from downshear in the lower troposphere, traverses' the updraft core and overshoots the tropopause. 3) Strong turbulent mixing between these contrasting airflow branches takes place astride the cloud top. 4) Parcels intercepting the cold region subside subsequently into the warm region. 5) The perturbation vertical pressure gradient force is an important factor in the trajectories.
Cloud-top structure of tornadic storms on 10 April 1979 from rapid scan and stereo satellite observations

NASA Technical Reports Server (NTRS)

Negri, A. J.

1982-01-01

Stereoscopic data from near-synchronous eastern and western GOES satellite 3 min interval visible and IR measurements and ground-based radar are used to examine the Wichita Falls, TX tornado of April, 1979. The visible wavelength scan was at 0.6 micron, while the IR was at 11 microns, and additional IR blackbody temperatures were acquired from the Tiros-N spacecraft. A minimum cloud top temperature of 208 K located the point of tornadogenesis. The cloud top cooling rate was determined to be 7 K/21 min above the tropopause preceding the tornado, while a warm area at 221 K developed downwind at the same time. It was found that temperature differences of 10 K can exist between GOES and Tiros-N anvil top measurements, and reach 20 K in the case of a young thunderstorm.
Toward better assessment of tornado potential in typhoons: Significance of considering entrainment effects for CAPE

NASA Astrophysics Data System (ADS)

Sueki, Kenta; Niino, Hiroshi

2016-12-01

The characteristics of typhoons that spawned tornadoes (tornadic typhoons: TTs) in Japan from 1991 to 2013 were investigated by composite analysis using the Japanese 55 year Reanalysis and compared with those of typhoons that did not spawn tornadoes (nontornadic typhoons: NTs). We found that convective available potential energy (CAPE), which considers the effects of entrainment (entraining CAPE: E-CAPE), and storm-relative environmental helicity (SREH) are significantly large in the northeast quadrant of TTs where tornadoes frequently occur and that E-CAPE and SREH in that quadrant for TTs are larger than those for NTs. On the other hand, ordinary CAPE without entrainment does not account for the spatial distribution of tornado occurrences nor does it distinguish TTs from NTs. E-CAPE is sensitive to humidity in the midtroposphere; thus, it is effective for detecting a conditionally unstable layer up to about 550 hPa, which is distinctive of TTs.
Raindrop fall velocities from an optical array probe and 2-D video disdrometer

NASA Astrophysics Data System (ADS)

Bringi, Viswanathan; Thurai, Merhala; Baumgardner, Darrel

2018-03-01

We report on fall speed measurements of raindrops in light-to-heavy rain events from two climatically different regimes (Greeley, Colorado, and Huntsville, Alabama) using the high-resolution (50 µm) Meteorological Particle Spectrometer (MPS) and a third-generation (170 µm resolution) 2-D video disdrometer (2DVD). To mitigate wind effects, especially for the small drops, both instruments were installed within a 2/3-scale Double Fence Intercomparison Reference (DFIR) enclosure. Two cases involved light-to-moderate wind speeds/gusts while the third case was a tornadic supercell and several squall lines that passed over the site with high wind speeds/gusts. As a proxy for turbulent intensity, maximum wind speeds from 10 m height at the instrumented site recorded every 3 s were differenced with the 5 min average wind speeds and then squared. The fall speeds vs. size from 0.1 to 2 and > 0.7 mm were derived from the MPS and the 2DVD, respectively. Consistency of fall speeds from the two instruments in the overlap region (0.7-2 mm) gave confidence in the data quality and processing methodologies. Our results indicate that under low turbulence, the mean fall speeds agree well with fits to the terminal velocity measured in the laboratory by Gunn and Kinzer from 100 µm up to precipitation sizes. The histograms of fall speeds for 0.5, 0.7, 1 and 1.5 mm sizes were examined in detail under the same conditions. The histogram shapes for the 1 and 1.5 mm sizes were symmetric and in good agreement between the two instruments with no evidence of skewness or of sub- or super-terminal fall speeds. The histograms of the smaller 0.5 and 0.7 mm drops from MPS, while generally symmetric, showed that occasional occurrences of sub- and super-terminal fall speeds could not be ruled out. In the supercell case, the very strong gusts and inferred high turbulence intensity caused a significant broadening of the fall speed distributions with negative skewness (for drops of 1.3, 2 and 3 mm). The mean fall speeds were also found to decrease nearly linearly with increasing turbulent intensity attaining values about 25-30 % less than the terminal velocity of Gunn-Kinzer, i.e., sub-terminal fall speeds.
A database about the tornadic activity in Catalonia (NE Spain) since 1994

NASA Astrophysics Data System (ADS)

Morales, M. E.; Arús, J.; Llasat, M. C.; Castán, S.

2009-09-01

Although tornadic activity is not the most important hazard in Spain, the damages that tornadoes and downburst generate are considerable in urban areas, giving place in some occasions to casualties. In Spain, the oldest systematic works collecting data about tornadoes, refer to the Balearic Islands, although some series about tornadoes in Spain have also been collected and analysed (Gayà, 2005). These series shows a positive increase that is probably more related to a change in the perception level of the population than to climatic change. In some occasions it is difficult to separate the damages produced by the tornado itself from those produced by other associated hazards like heavy rains, hail or a wind storms. It was the case of the September 2006 event, in which flash floods and tornadoes were recorded. In the same sense in some occasions, damages produced by a downsburt are confused with those that produced by a tornado. Having in mind all these facts, having a good systematic data base about tornadoes is necessary, before to obtain some conclusions not enough justified. This kind of database is not easy to obtain, because of it requires to have detailed information about damages, meteorological observations and testimonies that has to be filtered by a good quality control. After a general presentation about tornadoes and downsbursts in Mediterranean Region, this contribution presents the database that have affected Catalonia during the period 1994-2009, starting with the tornado recorded on the Espluga de Francolí the 31 August 1994.This database has been built in basis to the AEMET information, the Consorcio de Compensación de Seguros (the insurance company of Spain for natural disasters), the newspapers and field visits to the affected places.
The October 25th 2015 super-cell storm over central Israel: numerical simulations with the WRF model

NASA Astrophysics Data System (ADS)

Lynn, Barry; Yair, Yoav

2017-04-01

We present high-resolution WRF simulations with lightning assimilation (Fierro et al., 2012; Lynn et al., 2015) coupled with the Dynamic Lightning Scheme (Lynn et al., 2012) of the October 25th 2015 super-cell event in the eastern Mediterranean. That storm developed within the northern tip of a Red-Sea trough off the Egyptian coastline near Alexandria, with deep convective cells rapidly growing over the sea, exhibiting cloud top temperatures colder than -70°C ( 18 km) and radar reflectivity cores > 65 dBz at 10 km. As the cells crossed the Israeli coast-line north of Tel-Aviv, they exhibited intensive lightning activity, severe hail, downbursts, and intense rain. The lightning detection system of the Israeli Electrical Corporation registered a total of over 17,000 CGs, and for 20 minutes at the peak of the event recorded CG flash-rates greater than 430 strokes per minute (if including IC strokes, it was likely higher). The results of the simulations properly reconstruct the rapid growth of vertically extensive high-reflectivity cores, with significant amounts of graupel, ice and supercooled water within the charging zone below -20C. This guaranteed the effectiveness of non-inductive charge separation processes leading to the exceptional flash rates that were observed. Fierro, A. O, E. R. Mansell, C. L. Ziegler, and D. R. MacGorman, 2012: Application of a Lightning Data Assimilation Technique in the WRF-ARW Model at Cloud-Resolving Scales for the Tornado Outbreak of 24 May 2011. Mon. Wea. Rev., 140, 2609-2627. Lynn, B. H., G. Kelman, and G. Ellrod, 2015: An Evaluation of the Efficacy of Using Observed Lightning to Improve Convective Lightning Forecasts. Wea. Forecasting, 30, 405-423. Lynn, B. H., Y. Yair, C. Price, G. Kelman, and A. J. Clark, 2012: Predicting cloud-to-ground and intracloud lightning in weather forecast models.Wea. Forecasting, 27, 1470-1488, doi:10.1175/WAF-D-11-00144.1.
Causes and behavior of a tornadic fire-whirlwind

Treesearch

Arthur R. Pirsko; Leo M. Sergius; Carl W. Hickerson

1965-01-01

A destructive whirlwind of tornadic force was formed in a 600-acre brush fire burning on the lee side of a ridge near Santa Barbara on March 7, 1964. The fire whirlwind, formed in a post-frontal unstable air mass, cut a mile long path, injured 4 people, destroyed 2 houses, a barn, and 4 automobiles, and wrecked a 100-tree avocado orchard.[higher-...
Revisiting the latent heat nudging scheme for the rainfall assimilation of a simulated convective storm

NASA Astrophysics Data System (ADS)

Leuenberger, D.; Rossa, A.

2007-12-01

Next-generation, operational, high-resolution numerical weather prediction models require economical assimilation schemes for radar data. In the present study we evaluate and characterise the latent heat nudging (LHN) rainfall assimilation scheme within a meso-γ scale NWP model in the framework of identical twin simulations of an idealised supercell storm. Consideration is given to the model’s dynamical response to the forcing as well as to the sensitivity of the LHN scheme to uncertainty in the observations and the environment. The results indicate that the LHN scheme is well able to capture the dynamical structure and the right rainfall amount of the storm in a perfect environment. This holds true even in degraded environments but a number of important issues arise. In particular, changes in the low-level humidity field are found to affect mainly the precipitation amplitude during the assimilation with a fast adaptation of the storm to the system dynamics determined by the environment during the free forecast. A constant bias in the environmental wind field, on the other hand, has the potential to render a successful assimilation with the LHN scheme difficult, as the velocity of the forcing is not consistent with the system propagation speed determined by the wind. If the rainfall forcing moves too fast, the system propagation is supported and the assimilated storm and forecasts initialised therefrom develop properly. A too slow forcing, on the other hand, can decelerate the system and eventually disturb the system dynamics by decoupling the low-level moisture inflow from the main updrafts during the assimilation. This distortion is sustained in the free forecast. It has further been found that a sufficient temporal resolution of the rainfall input is crucial for the successful assimilation of a fast moving, coherent convective storm and that the LHN scheme, when applied to a convective storm, appears to necessitate a careful tuning.

Very large hail occurrence in Poland from 2007 to 2015

NASA Astrophysics Data System (ADS)

Pilorz, Wojciech

2015-10-01

Very large hail is known as a presence of a hailstone greater or equal to 5 cm in diameter. This phenomenon is rare but its significant consequences, not only to agriculture but also to automobiles, households and people outdoor makes it essential thing to examine. Hail appearance is strictly connected with storms frequency and its kind. The most hail-endangered kind of storm is supercell storm. Geographical distribution of hailstorms was compared with geographical distribution of storms in Poland. Similarities were found. The area of the largest number of storms is southeastern Poland. Analyzed European Severe Weather Database (ESWD) data showed that most of very large hail reports occurred in this part of Poland. The probable reason for this situation is the longest period of lasting tropical airmasses in southeastern Poland. Spatial distribution analysis shows also more hail incidents over Upper Silesia, Lesser Poland, Subcarpathia and Świętokrzyskie regions. The information source about hail occurrence was ESWD - open database, where everyone can add report and find reports which meet given search criteria. 69 hailstorms in the period of 2007 - 2015 were examined. They caused 121 very large hail reports. It was found that there is large disproportion in number of hailstorms and hail reports between individual years. Very large hail season in Poland begins in May and ends in September with cumulation in July. Most of hail occurs between 12:00 and 17:00 UTC, but there were some cases of very large (one extremely large) hail at night and early morning hours. However very large hail is a spectacular phenomenon, its local character determines potentially high information loss rate and it is the most significant problem in hail research.
On forecasting severe storms in Alberta using environmental sounding data

NASA Astrophysics Data System (ADS)

Dupilka, Maxwell L.

Thermodynamic and dynamic parameters computed from observed sounding data are examined to determine whether they can aid in forecasting the potential for severe weather in Alberta. The primary focus is to investigate which sounding parameters can provide probabilistic guidance to distinguish between Significant Tornadoes (F2 to F4), Weak Tornadoes (F0 and F1), and Non-Tornado severe hail storms (≥ 3 cm diameter hail but no reported tornado). The observational data set contains 87 thunderstorm events from 1967 to 2000 within 200 km of Stony Plain, Alberta. Three tornadic thunderstorms with F-scale ratings of F3 and F4 are examined in more detail. A secondary focus is to determine whether sounding data can be used to predict 24 hour snowfall amounts (specifically amounts ≥ 10 cm). Snowfall data covered all of Alberta east of the mountains from October 1990 to April 1993. The major findings were: (a) Significant Tornadoes tended to have stronger environmental bulk wind shear values than Weak Tornadoes or Non-Tornado storms, with a shear magnitude in the 900-500 mb layer exceeding 3 m s-1 km-1. Combining the 900-500 mb shear with the 900-800 mb shear increased the probabilistic guidance for the likelihood of Significant Tornado occurrence. (b) Values of storm-relative helicity showed skill in distinguishing Significant Tornadoes from both Weak Tornadoes and Non-Tornadoes. Significant Tornadoes tended to occur with 0-3 km storm-relative helicity >140 m2 s-2 whereas Weak Tornadoes were typically formed with values between 30 and 150 m 2 s-2. (c) The amount of precipitable water showed statistically significant differences between Significant Tornadoes and the other two groups. Significant Tornadoes had values exceeding 21 mm. Combining precipitable water values with the 900-500 mb shear increased the probabilistic guidance for the potential of Significant Tornadoes. (d) Values of thermal buoyancy, storm convergence, and height of the lifted condensation level provided no skill in discriminating between the three storm categories. (e) The Edmonton tornado case, unlike the Holden and Pine Lake cases, did not feature a prominent synoptic scale moisture front. (f) Observed snowfall amounts showed a roughly linear dependence on the 850 mb temperature, supporting a moisture conservation theory.
On the Environment of Supercells That Produce Anticyclonic-Cyclonic Tornado Pairs

NASA Astrophysics Data System (ADS)

Bluestein, H. B.; Snyder, J.; Houser, J.

2015-12-01

Anticyclonic tornadoes in supercells are very rare events, which have been documented in anticyclonically rotating, left-moving supercells in the Northern Hemisphere. It is well known that anticyclonic supercells, which can spawn anticyclonic tornadoes, form in an environment in which the vertical shear vector turns in a counterclockwise manner with height. Less rare, however, are anticyclonic tornadoes that appear in cyclonically rotating, right-moving supercells. When these anticyclonic tornadoes have been documented, they have occurred in tandem with a cyclonic tornado or intense mesocyclone. In this talk we will present Doppler radar documentation and photographs and videos of anticyclonic-cyclonic tornado pairs. We will then describe the environmental conditions under which they occur, with emphasis on any special conditions that observationally seem to favor their development.
Progress and challenges with Warn-on-Forecast

NASA Astrophysics Data System (ADS)

Stensrud, David J.; Wicker, Louis J.; Xue, Ming; Dawson, Daniel T.; Yussouf, Nusrat; Wheatley, Dustan M.; Thompson, Therese E.; Snook, Nathan A.; Smith, Travis M.; Schenkman, Alexander D.; Potvin, Corey K.; Mansell, Edward R.; Lei, Ting; Kuhlman, Kristin M.; Jung, Youngsun; Jones, Thomas A.; Gao, Jidong; Coniglio, Michael C.; Brooks, Harold E.; Brewster, Keith A.

2013-04-01

The current status and challenges associated with two aspects of Warn-on-Forecast-a National Oceanic and Atmospheric Administration research project exploring the use of a convective-scale ensemble analysis and forecast system to support hazardous weather warning operations-are outlined. These two project aspects are the production of a rapidly-updating assimilation system to incorporate data from multiple radars into a single analysis, and the ability of short-range ensemble forecasts of hazardous convective weather events to provide guidance that could be used to extend warning lead times for tornadoes, hailstorms, damaging windstorms and flash floods. Results indicate that a three-dimensional variational assimilation system, that blends observations from multiple radars into a single analysis, shows utility when evaluated by forecasters in the Hazardous Weather Testbed and may help increase confidence in a warning decision. The ability of short-range convective-scale ensemble forecasts to provide guidance that could be used in warning operations is explored for five events: two tornadic supercell thunderstorms, a macroburst, a damaging windstorm and a flash flood. Results show that the ensemble forecasts of the three individual severe thunderstorm events are very good, while the forecasts from the damaging windstorm and flash flood events, associated with mesoscale convective systems, are mixed. Important interactions between mesoscale and convective-scale features occur for the mesoscale convective system events that strongly influence the quality of the convective-scale forecasts. The development of a successful Warn-on-Forecast system will take many years and require the collaborative efforts of researchers and operational forecasters to succeed.
Preliminary Results form the Japanese Total Lightning Network

NASA Astrophysics Data System (ADS)

Hobara, Y.; Ishii, H.; Kumagai, Y.; Liu, C.; Heckman, S.; Price, C. G.; Williams, E. R.

2015-12-01

We report on the initial observational results from the first Japanese Total Lightning Detection Network (JTLN) in relation to severe weather phenomena. The University of Electro-Communications (UEC) has deployed the Earth Networks (EN) Total Lightning System over Japan to carry out research on the relationship between thunderstorm activity and severe weather phenomena since 2013. In this paper we first demonstrate the current status of our new network followed by the initial scientific results. The lightning jump algorithm was applied to our total lightning data to study the relationship between total lighting activity and hazardous weather events such as gust fronts and tornadoes over land reported by the JMA (Japanese Meteorological Agency) in 2014. As a result, a clear increase in total lighting flash rate as well as lightning jumps are observed prior to most hazardous weather events (~20 min) indicating potential usefulness for early warning in Japan. Furthermore we are going to demonstrate the relationship of total lightning activities with meteorological radar data focusing particularly on Japanese Tornadic storms.
A preliminary look at the impact of warming Mediterranean Sea temperatures on some aspects of extreme thunderstorm events in Italy

NASA Astrophysics Data System (ADS)

Gallus, William; Parodi, Antonio; Miglietta, Marcello; Maugeri, Maurizio

2017-04-01

As the global climate has warmed in recent decades, interest has grown in the impacts on extreme events associated with thunderstorms such as tornadoes and intense rainfall that can cause flash flooding. Because warmer temperatures allow the atmosphere to contain larger values of water vapor, it is generally accepted that short-term rainfall may become more intense in a future warmer climate. Regarding tornadoes, it is more difficult to say what might happen since although increased temperatures and humidity in the lowest part of the troposphere should increase thermodynamic instability, allowing for stronger thunderstorm updrafts, vertical wind shear necessary for storm-scale rotation may decrease as the pole to equator temperature gradient weakens. The Mediterranean Sea is an important source for moisture that fuels thunderstorms in Italy, and it has been warming faster than most water bodies in recent decades. The present study uses three methods to gain preliminary insight into the role that the warming Mediterranean may have on tornadoes and thunderstorms with intense rainfall in Italy. First, a historical archive of Italian tornadoes has been updated for the 1990s, and it will be used along with other data from the European Severe Weather Database to discuss possible trends in tornado occurrence. Second, convection-allowing Weather Research and Forecasting (WRF) model simulations have been performed for three extreme events to examine sensitivity to both the sea surface temperatures and other model parameters. These events include a flash flood-producing storm event near Milan, a non-tornadic severe hail event in far northeastern Italy, and the Mira EF-4 tornado of July 2015. Sensitivities in rainfall amount, radar reflectivity and storm structure, and storm rotation will be discussed. Finally, changes in the frequency of intense mesoscale convective system events in and near the Ligurian Sea, inferred from the presence of strong convergence lines in EXPRESS-Hydro regional climate model output, will be examined.
Dual-Polarimetric Radar-Based Tornado Debris Signatures and Paths Associated with Tornadoes Over Northern Alabama During the Historic Outbreak of 27 April 2011

NASA Technical Reports Server (NTRS)

Carey, Lawrence D.; Schultz, Christopher J.; Schultz, Elise V.; Petersen, Walter A.; Gatlin, Patrick N.; Knupp, Kevin R.; Molthan, Andrew L.; Jedloved, Gary J.; Carcione, Brian C.; Darden, Christopher B.;

2012-01-01

A historic tornado and severe weather outbreak devastated much of the southeastern United States between 25 and 28 April 2011. On 27 April 2011, northern Alabama was particularly hard hit by 40 tornadoes, including 6 that reached EF-4 to EF-5 on the Enhanced Fujita damage scale. In northern Alabama alone, there were approximately 100 fatalities and hundreds of people who were injured or lost their homes during the havoc caused by these violent tornadic storms. Many of these tornadoes occurred within range of the University of Alabama in Huntsville (UAHuntsville) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). A unique capability of dual-polarimetric radar is the near-real time identification of lofted debris associated with ongoing tornadoes. The focus of this paper is to analyze the dual-polarimetric radar-inferred tornado debris signatures in 6 tornadoes in North Alabama on April 27, 2011. Several of these debris signatures were disseminated in real-time to the NWS Huntsville and local media to confirm storm spotter reports, confidence to enhance wording within warnings, and accurately pinpoint the locations of tornadoes for residents downstream of the storm. Also, the debris signature locations were used in post-event storm surveys to help locate areas of damage in regions where damage went unreported, or to help separate tornado tracks that were in close proximity to each other. Furthermore, the relative locations of the debris and damage paths for long track EF-4 and EF-5 tornadoes will be ascertained by careful comparison of the ARMOR analysis with NASA MODIS (Moderate Resolution Imaging Spectroradiometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite imagery of the tornado damage scenes and the National Weather Service tornado damage surveys.

Using Model Helicopters for Meteorological Observations in Support of Tornado Forecasting

NASA Astrophysics Data System (ADS)

Harrison, William; Roscoe, Bryan; Schafer, David; Bluestein, Howard; Lary, David

2012-10-01

In order to gain a better understanding of the physical factors involved in tornadogenesis, a complete 3-D profile of winds, temperature, and humidity in the forward-flank and rear-flank gust front regions in supercells is required. Conventional methods of making comparative measurements in and around storms are very limited. Measurements that comprehensively profile the boundary layer winds and thermodynamics are valuable but rare. A better understanding of the physical properties in these boundary layers will improve forecasts and increase warning times in affected areas. Remote-controlled model helicopters are a uniquely qualified platform for this application, allowing us to fully profile these boundary layers. Our system will consist of a swarm of autonomous acrobatic helicopters, each outfitted with temperature, pressure, humidity, and wind speed sensors.
The Effects of Lightning NO(x) Production during the July 21 EULINOX Storm studied with a 3-D Cloud-scale Chemical Transport Model

NASA Technical Reports Server (NTRS)

Ott, Lesley E.; Pickering, Kenneth E.; Stenchikov, Georgiy L.; Huntrieser, Heidi; Schumann, Ulrich

2006-01-01

The July 21,1998 thunderstonn observed during the European Lightning Nitrogen Oxides Project (EULINOX) project was simulated using the three-dimensional Goddard Cumulus Ensemble (GCE) model. The simulation successfully reproduced a number of observed storm features including the splitting of the original cell into a southern cell which developed supercell characteristics, and a northern cell which became multicellular. Output from the GCE simulation was used to drive an offline cloud-scale chemical transport model which calculates tracer transport and includes a parameterization of lightning NO(x) production which uses observed flash rates as input. Estimates of lightning NO(x) production were deduced by assuming various values of production per intracloud and production per cloud-to-ground flash and comparing the results with in-cloud aircraft observations. The assumption that both types of flashes produce 360 moles of NO per flash on average compared most favorably with column mass and probability distribution functions calculated from observations. This assumed production per flash corresponds to a global annual lightning NOx source of 7 Tg N per yr. Chemical reactions were included in the model to evaluate the impact of lightning NO(x), on ozone. During the storm, the inclusion of lightning NOx in the model results in a small loss of ozone (on average less than 4 ppbv) at all model levels. Simulations of the chemical environment in the 24 hours following the storm show on average a small increase in the net production of ozone at most levels resulting from lightning NO(x), maximizing at approximately 5 ppbv per day at 5.5 km. Between 8 and 10.5 km, lightning NO(x) causes decreased net ozone production.
Kinematic and Microphysical Control of Lightning Flash Rate over Northern Alabama

NASA Technical Reports Server (NTRS)

Carey, Lawrence D.; Bain, Anthony L.; Matthee, Retha; Schultz, Christopher J.; Schultz, Elise V.; Deierling, Wiebke; Petersen, Walter A.

2015-01-01

The Deep Convective Clouds and Chemistry (DC3) experiment seeks to examine the relationship between deep convection and the production of nitrogen oxides (NO (sub x)) via lightning (LNO (sub x)). A critical step in estimating LNO (sub x) production in a cloud-resolving model (CRM) without explicit lightning is to estimate the flash rate from available model parameters that are statistically and physically correlated. As such, the objective of this study is to develop, improve and evaluate lightning flash rate parameterizations in a variety of meteorological environments and storm types using radar and lightning mapping array (LMA) observations taken over Northern Alabama from 2005-2012, including during DC3. UAH's Advanced Radar for Meteorological and Operational Research (ARMOR) and the Weather Surveillance Radar - 1988 Doppler (WSR 88D) located at Hytop (KHTX) comprises the dual-Doppler and polarimetric radar network, which has been in operation since 2004. The northern Alabama LMA (NA LMA) in conjunction with Vaisala's National Lightning Detection Network (NLDN) allow for a detailed depiction of total lightning during this period. This study will integrate ARMOR-KHTX dual Doppler/polarimetric radar and NA LMA lightning observations from past and ongoing studies, including the more recent DC3 results, over northern Alabama to form a large data set of 15-20 case days and over 20 individual storms, including both ordinary multicell and supercell convection. Several flash rate parameterizations will be developed and tested, including those based on 1) graupel/small hail volume; 2) graupel/small hail mass, and 3) convective updraft volume. Sensitivity of the flash rate parameterizations to storm intensity, storm morphology and environmental conditions will be explored.
Effects of lightning NOx production during the 21 July European Lightning Nitrogen Oxides Project storm studied with a three-dimensional cloud-scale chemical transport model

NASA Astrophysics Data System (ADS)

Ott, Lesley E.; Pickering, Kenneth E.; Stenchikov, Georgiy L.; Huntrieser, Heidi; Schumann, Ulrich

2007-03-01

The 21 July 1998 thunderstorm observed during the European Lightning Nitrogen Oxides Project (EULINOX) project was simulated using the three-dimensional Goddard Cumulus Ensemble (GCE) model. The simulation successfully reproduced a number of observed storm features including the splitting of the original cell into a southern cell which developed supercell characteristics and a northern cell which became multicellular. Output from the GCE simulation was used to drive an offline cloud-scale chemical transport model which calculates tracer transport and includes a parameterization of lightning NOx production which uses observed flash rates as input. Estimates of lightning NOx production were deduced by assuming various values of production per intracloud and production per cloud-to-ground flash and comparing the results with in-cloud aircraft observations. The assumption that both types of flashes produce 360 moles of NO per flash on average compared most favorably with column mass and probability distribution functions calculated from observations. This assumed production per flash corresponds to a global annual lightning NOx source of 7 Tg N yr-1. Chemical reactions were included in the model to evaluate the impact of lightning NOx on ozone. During the storm, the inclusion of lightning NOx in the model results in a small loss of ozone (on average less than 4 ppbv) at all model levels. Simulations of the chemical environment in the 24 hours following the storm show on average a small increase in the net production of ozone at most levels resulting from lightning NOx, maximizing at approximately 5 ppbv day-1 at 5.5 km. Between 8 and 10.5 km, lightning NOx causes decreased net ozone production.
Investigation of the passage of a derecho in Belgium

NASA Astrophysics Data System (ADS)

Hamid, Karim

2012-04-01

From the 7th July, 2010 until 14th July, 2010, a heat wave dominated the weather in Belgium. Three major storm situations occurred during this period and all three caused severe damage. In this paper, we discuss the last storm case of 14th July. That day, a quasi-linear convective system (QLCS) crossed parts of France, Belgium and the Netherlands and caused very important wind damages and at least 2 people were killed. Most of the damage was caused by straight-line wind but at least one tornado was observed over the north of the Netherlands. This complex was induced in a very favorable synoptic configuration for severe weather and also the timing of the storm was favorable. In the frame of the Supercell project at the RMI, a damage survey was made of one of the most affected regions, which yielded useful information about the origin of the losses. Careful examination of the radar imagery revealed some connections between internal mesovortices and tracks of enhanced damage. As far as known, this paper is the first description of a derecho in Belgium. It is also the first time a connection is shown between some mesovortices and several damage tracks over the country. During the evolution of the QLCS, several examples of successive vortices were found in front of the system. Several of the vortices were accompanied by a tornado or a funnel cloud and the damage was typically concentrated along elongated tracks.
Convective Radio Occultations Final Campaign Summary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biondi, R.

2016-03-01

Deep convective systems are destructive weather phenomena that annually cause many deaths and injuries as well as much damage, thereby accounting for major economic losses in several countries. The number and intensity of such phenomena have increased over the last decades in some areas of the globe. Damage is mostly caused by strong winds and heavy rain parameters that are strongly connected to the structure of the particular storm. Convection over land is usually stronger and deeper than over the ocean and some convective systems, known as supercells, also develop tornadoes through processes that remain mostly unclear. The intensity forecastmore » and monitoring of convective systems is one of the major challenges for meteorology because in situ measurements during extreme events are too sparse or unreliable and most ongoing satellite missions do not provide suitable time/space coverage.« less
Characterization of Mediterranean hail-bearing storms using an operational polarimetric X-band radar

NASA Astrophysics Data System (ADS)

Vulpiani, G.; Baldini, L.; Roberto, N.

2015-07-01

This work documents the fruitul use of X-band radar observations for the monitoring of severe storms in an operational framework. More specifically, a couple of severe hail-bearing Mediterranean storms occurred in 2013 in southern Italy, flooding two important cities of Sicily, are described in terms of their polarimetric radar signatures and retrieved rainfall fields. It is used the X-band dual-polarization radar operating inside the Catania airport (Sicily, Italy), managed by the Italian Department of Civil Protection. A suitable processing is applied to X-band radar measurements. The crucial procedural step relies on the differential phase processing based on an iterative approach that uses a very short-length (1 km) moving window allowing to properly catch the observed high radial gradients of the differential phase. The parameterization of the attenuation correction algorithm, which use the reconstructed differential phase shift, is derived from electromagnetic simulations based on 3 years of DSD observations collected in Rome (Italy). A Fuzzy Logic hydrometeor classification algorithm was also adopted to support the analysis of the storm characteristics. The precipitation fields amount were reconstructed using a combined polarimetric rainfall algorithm based on reflectivity and specific differential phase. The first considered storm was observed on the 21 February, when a winter convective system, originated in the Tyrrhenian sea, hit only marginally the central-eastern coastline of Sicily causing the flash-flood of Catania. Due to the optimal radar location (the system is located at just few kilometers from the city center), it was possible to well retrieve the storm characteristics, including the amount of rainfall field at ground. Extemporaneous signal extinction, caused by close-range hail core causing significant differential phase shift in very short range path, is documented. The second storm, occurred on 21 August 2013, is a summer mesoscale convective system originated by the temperature gradient between sea and land surface, lasted a few hours and eventually flooded the city of Siracusa. The undergoing physical process, including the storm dynamics, is inferred by analysing the vertical sections of the polarimetric radar measurements. The high registered precipitation amount was fairly well reconstructed even though with a trend to underestimation at increasing distances. Several episodes of signal extinction clearly manifested during the mature stage of the observed supercell.
Characterization of Mediterranean hail-bearing storms using an operational polarimetric X-band radar

NASA Astrophysics Data System (ADS)

Vulpiani, G.; Baldini, L.; Roberto, N.

2015-11-01

This work documents the effective use of X-band radar observations for monitoring severe storms in an operational framework. Two severe hail-bearing Mediterranean storms that occurred in 2013 in southern Italy, flooding two important Sicilian cities, are described in terms of their polarimetric radar signatures and retrieved rainfall fields. The X-band dual-polarization radar operating inside the Catania airport (Sicily, Italy), managed by the Italian Department of Civil Protection, is considered here. A suitable processing is applied to X-band radar measurements. The crucial procedural step relies on the differential phase processing, being preparatory for attenuation correction and rainfall estimation. It is based on an iterative approach that uses a very short-length (1 km) moving window, allowing proper capture of the observed high radial gradients of the differential phase. The parameterization of the attenuation correction algorithm, which uses the reconstructed differential phase shift, is derived from electromagnetic simulations based on 3 years of drop size distribution (DSD) observations collected in Rome (Italy). A fuzzy logic hydrometeor classification algorithm was also adopted to support the analysis of the storm characteristics. The precipitation field amounts were reconstructed using a combined polarimetric rainfall algorithm based on reflectivity and specific differential phase. The first storm was observed on 21 February when a winter convective system that originated in the Tyrrhenian Sea, marginally hit the central-eastern coastline of Sicily, causing a flash flood in Catania. Due to an optimal location (the system is located a few kilometers from the city center), it was possible to retrieve the storm characteristics fairly well, including the amount of rainfall field at the ground. Extemporaneous signal extinction, caused by close-range hail core causing significant differential phase shift in a very short-range path, is documented. The second storm, on 21 August 2013, was a summer mesoscale convective system that originated from a Mediterranean low pressure system lasting a few hours that eventually flooded the city of Syracuse. The undergoing physical process, including the storm dynamics, is inferred by analyzing the vertical sections of the polarimetric radar measurements. The high registered amount of precipitation was fairly well reconstructed, although with a trend toward underestimation at increasing distances. Several episodes of signal extinction were clearly manifested during the mature stage of the observed supercells.
First-principles supercell calculations of small polarons with proper account for long-range polarization effects

NASA Astrophysics Data System (ADS)

Kokott, Sebastian; Levchenko, Sergey V.; Rinke, Patrick; Scheffler, Matthias

2018-03-01

We present a density functional theory (DFT) based supercell approach for modeling small polarons with proper account for the long-range elastic response of the material. Our analysis of the supercell dependence of the polaron properties (e.g., atomic structure, binding energy, and the polaron level) reveals long-range electrostatic effects and the electron–phonon (el–ph) interaction as the two main contributors. We develop a correction scheme for DFT polaron calculations that significantly reduces the dependence of polaron properties on the DFT exchange-correlation functional and the size of the supercell in the limit of strong el–ph coupling. Using our correction approach, we present accurate all-electron full-potential DFT results for small polarons in rocksalt MgO and rutile TiO2.
JPSS Data Product Applications for Monitoring Severe Weather and Environmental Hazards

NASA Astrophysics Data System (ADS)

Liu, X.; Zhou, L.; Divakarla, M. G.; Atkins, T.

2016-12-01

The Joint Polar Satellite System (JPSS) is the National Oceanic and Atmospheric Administration's (NOAA's) next-generation polar-orbiting operational environmental satellite system. The Suomi National Polar-orbiting Partnership (S-NPP) is the first satellite in the JPSS series. One of the JPSS supported key mission areas is to reduce the loss of life from high-impact weather events while improving efficient economies through environmental information. Combining with the sensors on other polar and geostationary satellite platforms, JPSS observations provided much enhanced capabilities for the Nation's essential products and services, including forecasting severe weather like hurricanes, potential tornadic outbreaks, and blizzards days in advance, and assessing environmental hazards such as droughts, floods, forest fires, poor air quality and harmful coastal waters. Sensor and Environmental Data Records (SDRs/EDRs) derived from S-NPP and follow-on JPSS satellites provide critical data for environmental assessments, forecasts and warnings. This paper demonstrates the use of S-NPP science data products towards analysis events of severe weather and environmental hazards, such as Paraguay Flooding, Hurricane Iselle, the record-breaking winter storm system that impacted the US East Coast area early this year, and Fort McMurray wildfire. A brief description of these examples and a detailed discussion of the winter storm event are presented in this paper. VIIRS (Visible Infrared Imaging Radiometer Suite) and ATMS (Advanced Technology Microwave Sounder) SDR/EDR products collected from multiple days of S-NPP observations are analyzed to study the progression of the winter storm and illustrate how JPSS products captured the storm system. The products used for this study included VIIRS day/night band (DNB) and true color images, ocean turbidity images, snow cover fraction, and the multi-sensor snowfall rates. Quantitative evaluation of the ATMS derived snowfall rates with the radar estimates revealed good agreement. Use of STAR JPSS product monitoring and visualization tools to evaluate these events, and applications of these tools for anomaly detection, mitigation, and science maintenance of the long-term stability of the data products is also presented in this paper.
image1goes5117.jpg

NASA Image and Video Library

2017-12-08

NASA Sees Severe Weather from Central to Eastern US A vigorous weather system has generated severe weather over the mid-section of the U.S. and satellites are providing a look at it as it is moving toward the East Coast. NASA and NOAA satellites have been tracking a storm system that has generated flooding and tornadic thunderstorms in the central U.S. and is expected bring severe weather to the U.S. Mid-Atlantic region. At NASA's Goddard Space Flight Center in Greenbelt, Maryland, data from NOAA's GOES-East satellite were used to create images and an animation of the movement of the powerful storm. On April 30, the Moderate Resolution Imaging Spectroradiometer, or MODIS, instrument aboard NASA's Aqua satellite captured a visible image of the storms moving over eastern Texas and Louisiana. Tornadoes in eastern Texas killed four people. The system generated heavy rainfall and caused additional fatalities and damages in Arkansas, Missouri, Mississippi, Alabama and Tennessee. On Monday, May 1, NOAA's National Weather Service noted, "Major to record flooding continues over portions of the central U.S. Severe thunderstorms are possible from the Mid-Atlantic to the northeastern U.S. "Major to record flooding will continue over portions of eastern Oklahoma, northern Arkansas, Missouri, Illinois and Indiana. Rivers will gradually recede over the next several days. Additional strong to severe thunderstorms will be possible Monday afternoon and evening over portions of the Mid-Atlantic and Northeast U.S. Damaging winds, large hail, and isolated tornadoes will be possible." Image caption: On May 1, 2017, at 10:37 a.m. EDT (1437 UTC) NOAA's GOES-East satellite captured this visible image of the storm system centered over Iowa with an associated cold front that stretches into the Gulf of Mexico. Credits: NASA/NOAA GOES Project NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram
Doppler-radar wind-speed measurements in tornadoes: A comparison of real and simulated spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bluestein, H.B.; LaDue, J.G.; Stein, H.

1993-03-01

Bluestein and Unruh have discussed the advantages of using a portable doppler radar to map the wind field in tornadoes. during the spring of 1991 a storm-intercept team from the University of Oklahoma (OU) collected data near five supercell tornadoes in Oklahoma and Kansas. Details about the 1-W, 3-cm, 5-deg half-power beamwidth, CW/FM-CW Doppler radar we used and the methods of data collection and analysis are found in Bluestein and Unruh and Bluestein et al. Using the portable radar, we approximately doubled in only one year the number of tornado spectra that had been collected over a period of almostmore » 20 years by NSSL`s fixed-site Doppler radar. In this paper we will compare observed tornado wind spectra with simulated wind spectra (Zmic and Doviak 1975) in order to learn more about tornado structure.« less
Doppler-radar wind-speed measurements in tornadoes: A comparison of real and simulated spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bluestein, H.B.; LaDue, J.G.; Stein, H.

1993-01-01

Bluestein and Unruh have discussed the advantages of using a portable doppler radar to map the wind field in tornadoes. during the spring of 1991 a storm-intercept team from the University of Oklahoma (OU) collected data near five supercell tornadoes in Oklahoma and Kansas. Details about the 1-W, 3-cm, 5-deg half-power beamwidth, CW/FM-CW Doppler radar we used and the methods of data collection and analysis are found in Bluestein and Unruh and Bluestein et al. Using the portable radar, we approximately doubled in only one year the number of tornado spectra that had been collected over a period of almostmore » 20 years by NSSL's fixed-site Doppler radar. In this paper we will compare observed tornado wind spectra with simulated wind spectra (Zmic and Doviak 1975) in order to learn more about tornado structure.« less

Nuclear and magnetic supercells in the multiferroic candidate: Pb 3TeMn 3P 2O 14

DOE PAGES

Silverstein, Harlyn J.; Huq, Ashfia; Lee, Minseong; ...

2014-10-18

Here we report that the dugganites, Te 6+-containing members of the langasite series, have attracted recent interest due to their complex low-temperature magnetic unit cells, magnetodielectric, and potentially multiferroic properties. For Pb 2+-containing dugganites, a large monoclinic supercell was reported and was found to have a profound effect on the low temperature magnetism and spin excitation spectra. Pb 3TeMn 3P 2O 14 is another dugganite previously shown to distort away from the canonical P321 langasite unit cell, although this supercell was never fully solved. We report the full crystal and magnetic structure solution of Pb 3TeMn 3P 2O 14 usingmore » synchrotron x-ray and neutron diffraction data: a large trigonal supercell is observed in this material, which is believed to be the first supercell of its kind in the langasite family. Here, the magnetic structure, high-magnetic field behavior, and dielectric properties of Pb 3TeMn 3P 2O 14 are presented. In addition to showing weak magnetoelectric behavior similar to other langasites, it was found that a phase transition occurs at 3 T near the antiferromagnetic transition temperature.« less
A study of tornadic thunderstorm interactions with thermal boundaries

NASA Technical Reports Server (NTRS)

Maddox, R. A.; Hoxit, L. R.; Chappell, C. F.

1980-01-01

A study of tornadic thunderstorm interactions with thermal boundaries using a model of subcloud wind profiles is presented. Within a hot, moist, and conditionally unstable air mass, warm thermal advection and surface friction cause the winds to veer and increase with height, while within a cool, moist air mass cool thermal advection and friction combine to produce a wind profile that has maximum speeds near the surface and veers little with height. The spatial distribution of different wind profiles and moisture contents within the boundary layer may act together to maximize mesoscale moisture contents, convergence, and cyclonic vorticity within a narrow mixing zone along the thermal boundary.
ARMOR Dual-Polarimetric Radar Observations of Tornadic Debris Signatures

NASA Technical Reports Server (NTRS)

Petersen, W. A,; Carey, L. D.; Knupp, K. R.; Schultz, C.; Johnson, E.

2008-01-01

During the Super-Tuesday tornado outbreak of 5-6 February 2008, two EF-4 tornadoes occurred in Northern Alabama within 75 km range of the University of Alabama in Huntsville (UAH) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). This study will present an analysis of ARMOR radar-indicated dual-polarimetric tornadic debris signatures. The debris signatures were associated with spatially-confined large decreases in the copolar correlation coefficient (rho(hv)hv) that were embedded within broader mesocyclone "hook" signatures. These debris signatures were most obviously manifest during the F-3 to F-4 intensity stages of the tornado(s) and extended to altitudes of approximately 3 km. The rho(hv) signatures of the tornadic debris were the most easily distinguished relative to other polarimetric and radial velocity parameters (e.g., associated with large hail and/or the incipient mesocyclone). Based on our analysis, and consistent with the small number of studies found in the literature, we conclude that dual-polarimetric radar data offer at least the possibility for enhancing specificity and confidence in the process of issuing tornado warnings based only on radar detection of threatening circulation features.
Geostationary Lightning Mapper for GOES-R

NASA Technical Reports Server (NTRS)

Goodman, Steven; Blakeslee, Richard; Koshak, William

2007-01-01

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR optical detector, used to detect, locate and measure total lightning activity over the full-disk as part of a 3-axis stabilized, geostationary weather satellite system. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series with a planned launch in 2014 will carry a GLM that will provide continuous day and night observations of lightning from the west coast of Africa (GOES-E) to New Zealand (GOES-W) when the constellation is fully operational. The mission objectives for the GLM are to 1) provide continuous, full-disk lightning measurements for storm warning and Nowcasting, 2) provide early warning of tornadic activity, and 3) accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997-Present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 11 year data record of global lightning activity. Instrument formulation studies begun in January 2006 will be completed in March 2007, with implementation expected to begin in September 2007. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite, airborne science missions (e.g., African Monsoon Multi-disciplinary Analysis, AMMA), and regional test beds (e.g, Lightning Mapping Arrays) are being used to develop the pre-launch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution. Real time lightning mapping data now being provided to selected forecast offices will lead to improved understanding of the application of these data in the severe storm warning process and accelerate the development of the pre-launch algorithms and Nowcasting applications. Proxy data combined with MODIS and Meteosat Second Generation SEVERI observations will also lead to new applications (e.g., multi-sensor precipitation algorithms blending the GLM with the Advanced Baseline Imager, convective cloud initiation and identification, early warnings of lightning threat, storm tracking, and data assimilation).
Characteristics and Impacts of the severe Hailstorm on 28 July 2013

NASA Astrophysics Data System (ADS)

Kunz, Michael; Jürgen Punge, Heinz; Fluck, Elody; Schmidberger, Manuel; Blahak, Ulrich; Handwerker, Jan; Mohr, Susanna; Mühr, Bernhard

2015-04-01

On 27/28 July, two severe supercell thunderstorms in Germany caused unexpected extreme losses of 3.1 bn EUR(insured) and 4.0 bn EUR(economic), respectively. According to the recently published damage statistics of Munich Re for the year 2013, these hail events were the costliest natural catastrophe in worldwide for that year ranked by insured losses. This example exemplifies the large damage potential related to hail events, which is still underestimated both by the public and the insurance industry. On 27 July, the first supercell moved over the federal states of North Rhine-Westphalia and Lower Saxony. Large hail with diameters of up to 7.5 cm according to observations archived in the European Severe Weather Database (ESWD) caused severe damage especially over the Volkswagen factory in Wolfsburg. One day later, on 28 July, another supercell formed upstream of the Black Forest Mountains and moved almost parallel over the Swabian Jura and Bavaria. Hail with diameters of up to 8 cm fell over a heavily populated region between the cities of Reutlingen and Tübingen. In this area, exposed assets are extremely high, which partly explain the high total loss. Approximately 100,000 buildings and 50,000 automobiles (not considered are the damaged automobiles at the parking lot in Wolfsburg) were severely damaged by these two events. Considering the single event definition over a 72-hr period, which is usually applied in the insurance industry, these hailstorms were one of the most expensive loss events in Germany. In this paper, we investigate the severe hailstorm on 28 July from different views. By using and combining available observational data sets, the objective is to reconstruct the whole events at a very high resolution and to examine the conditions that are most relevant for convective initiation and the further development of the organized convective cell. Using a series of photos of damaged objects the aim is to relate different object classes and hail stone sizes. Relations between radar-derived intensity and damage frequency are derived on the basis of insurance loss data provided by a special crop insurer. These analyses also reveal to what extent past hailstorms, where observations are usually scarce, can be reconstructed reliably from insurance data. Using a radar-derived event set of past hailstorms in Germany over a 9-year period, the hail storm is put in the historic context.
Charged dopants in neutral supercells through substitutional donor (acceptor): nitrogen donor charging of the nitrogen-vacancy center in diamond

NASA Astrophysics Data System (ADS)

Löfgren, Robin; Pawar, Ravinder; Öberg, Sven; Larsson, J. Andreas

2018-02-01

Charged defects are traditionally computed by adding (subtracting) electrons for negative (positive) impurities. When using periodic boundary conditions this results in artificially charged supercells that also require a compensating background charge of the opposite sign, which makes slab supercells problematic because of an arbitrary dependence on the vacuum thickness. In this work, we test the method of using neutral supercells through the use of a substitutional electron donor (acceptor) to describe charged systems. We use density functional theory (DFT) to compare the effects of charging the well-studied NV-center in diamond by a substitutional donor nitrogen. We investigate the influence of the donor-N on the NV-center properties as a function of the distance between them, and find that they converge toward those obtained when adding an electron. We analyze the spin density and conclude that the donor-N has a zero magnetic moment, and thus, will not be seen in electron spin resonance. We validate our DFT energies through comparison to GW simulations. Charging the NV-center with a substitutional donor-N enables accurate calculations of slabs, without the ambiguity of using charged supercells. Implantation of donor-N atoms opens up the possibility to engineer NV-centers with the desired charge state for future ICT and sensor applications.
Chromatography of blood-clotting factors and serum proteins on columns of diatomaceous earth.

PubMed

MILSTONE, J H

1955-07-20

1. In batch adsorptions with prothrombin solutions, hyflo was the weakest adsorbent, standard super-cel intermediate, and filter-cel strongest. Of these three grades of diatomaceous earth, hyflo has the smallest surface area per gram and filter-cel the largest. In parallel breakthrough experiments, a column of standard super-cel had a capacity almost six times that of a hyflo column. 2. After partial removal of impurities by diatomaceous earth, prothrombin preparations contained less thrombokinase, were more stable, and displayed less tendency to form thrombin "spontaneously." Thrombokinase (or its precursor) was removed from a preparation of prothrombin by passage through a filter cake of standard super-cel. The specific activity of the prothrombin was increased; and 62 per cent of the activity was recovered. 3. Prothrombin was adsorbed from an ammonium sulfate solution at pH 5.26 by columns of hyflo or standard super-cel. When eluted by phosphate solutions, the protein moved down the columns more readily at higher pH and higher concentration of phosphate salts, within the pH range 5.0 to 6.6, and within the phosphate range 0.1 to 1.0 M. 4. Thrombin was adsorbed on a column of standard super-cel at pH 5.11. As successive eluents passed through the column, the thrombin emerged between two bands of impurities. The specific activity of the thrombin was raised; and 83 per cent of the activity was recovered. 5. With a column of standard super-cel, and with a series of eluents within the pH range 5.1 to 6.3, total serum proteins were separated into four major bands. About 94 per cent of the protein was recovered.
CHROMATOGRAPHY OF BLOOD-CLOTTING FACTORS AND SERUM PROTEINS ON COLUMNS OF DIATOMACEOUS EARTH

PubMed Central

Milstone, J. H.

1955-01-01

1. In batch adsorptions with prothrombin solutions, hyflo was the weakest adsorbent, standard super-cel intermediate, and filter-cel strongest. Of these three grades of diatomaceous earth, hyflo has the smallest surface area per gram and filter-cel the largest. In parallel breakthrough experiments, a column of standard super-cel had a capacity almost six times that of a hyflo column. 2. After partial removal of impurities by diatomaceous earth, prothrombin preparations contained less thrombokinase, were more stable, and displayed less tendency to form thrombin "spontaneously." Thrombokinase (or its precursor) was removed from a preparation of prothrombin by passage through a filter cake of standard super-cel. The specific activity of the prothrombin was increased; and 62 per cent of the activity was recovered. 3. Prothrombin was adsorbed from an ammonium sulfate solution at pH 5.26 by columns of hyflo or standard super-cel. When eluted by phosphate solutions, the protein moved down the columns more readily at higher pH and higher concentration of phosphate salts, within the pH range 5.0 to 6.6, and within the phosphate range 0.1 to 1.0 M. 4. Thrombin was adsorbed on a column of standard super-cel at pH 5.11. As successive eluents passed through the column, the thrombin emerged between two bands of impurities. The specific activity of the thrombin was raised; and 83 per cent of the activity was recovered. 5. With a column of standard super-cel, and with a series of eluents within the pH range 5.1 to 6.3, total serum proteins were separated into four major bands. About 94 per cent of the protein was recovered. PMID:13242761
Lightning NOx Production and Transport in the 29 May 2012 DC3 case: A Modeling Study Using Radar Data Assimilation and a Branched Lightning Simulation.

NASA Astrophysics Data System (ADS)

Allen, B. J.; Mansell, E. R.; Betten, D.

2014-12-01

Open questions exist regarding chemical transport by convection and the sensitivity of Lightning Nitrogen Oxide (LNOx) production to flash type (IC vs. CG), channel height, and channel length. To help answer these and other questions, the Deep Convective Clouds and Chemistry (DC3) field project was conducted during the spring of 2012. On 29 May 2012, observations of an Oklahoma supercell were collected by two mobile SMART-R radars, the mobile NOXP radar, multiple NEXRAD radars, the Oklahoma Lightning Mapping Array (LMA), and the NSF/NCAR HIAPER and NASA DC-8 aircraft. In this study, data from the mobile and NEXRAD radars are assimilated into the NSSL COMMAS model using the Ensemble Kalman Filter, beginning shortly after initiation of convection and ending when the aircraft made their final measurements of the storm's outflow. The model analyses produce a realistic representation of the kinematic character of the storm throughout this time period. COMMAS includes the NSSL multimoment microphysics, explicit cloud electrification, and a branched lightning discharge scheme, which is used to produce LNOx within the model via a method dependent upon air pressure and lightning channel length. Model results will be presented and compared to radar, lightning, and aircraft observations. Of particular importance, the vertical distribution of lightning, channel length of lightning, and LNOx production and transport in the model will be analyzed and compared to LMA observations and anvil-level outflow observations from the aircraft. In addition, to examine entrainment and detrainment of air by the storm and to provide a check on LNOx production and transport, trajectory analyses will be presented and the transport of inert trace gases such as carbon monoxide in the model will be analyzed and compared to aircraft measurements.
The Interaction between Very Deep Convection and Biomass Burning Plumes during DC3 and the Impact on the UTLS Region over The North Atlantic

NASA Astrophysics Data System (ADS)

Huntrieser, H.; Lichtenstern, M.; Scheibe, M.; Aufmhoff, H.; Schlager, H.; Heimerl, K.; Pucik, T.; Minikin, A.; Weinzierl, B.; Fütterer, D.; Pollack, I. B.; Peischl, J.; Ryerson, T. B.; Honomichl, S.; Hair, J. W.; Butler, C. F.; Schwartz, M. J.; Rappenglück, B.; Ackermann, L.; Pickering, K. E.; Cummings, K.; Biggerstaff, M. I.; Betten, D.; Barth, M. C.

2016-12-01

The Central United States is known to be a region where intense thunderstorms develop. During the Deep Convective Cloud and Chemistry Experiment (DC3) in summer 2012 a number of these imposing storms were investigated by airborne and ground-based measurements focusing on the chemistry, microphysics and dynamics in these unique storms. Here we report on aircraft penetrations of the anvil outflow of isolated supercells and organized mesoscale convective systems and the distribution of different trace species as e.g. CO, O3, and NOx. Conspicuously, the burning of several extended wildfires in New Mexico and Colorado, which emitted huge amounts of SO2 and black carbon (BC), significantly impacted the chemical composition within and nearby the probed thunderstorms. In several cases, overshooting thunderstorms developed that injected considerable amounts of pollutants into the lower stratosphere. Both in the lofted biomass burning plumes and in the thunderstorm outflow, O3 mixing ratios were frequently enhanced due to photochemical production and downward transport from the stratosphere; however, the latter process dominated the measured O3 enhancements in the storms. Here we present results from the local flights over Colorado, Oklahoma and Texas along with transit flights over the North Atlantic conducted by the German DLR Falcon research aircraft. In addition, microphysical measurements from radar, and remote trace species measurements (lidar and satellites) are used to demonstrate the strong air mass exchange in the UTLS region caused by the frequent occurrence of very deep convection over the Central U.S. The more general impact of these widespread, aged, and more or less invisible anvil outflows on the UTLS region downwind of the U.S. continent (North Atlantic) is discussed regarding chemistry, new particle formation, and radiation.
Atmospheric structure prior to tornadoes as derived from proximity and precedent upper-air soundings, covering the period April 1977-June 1979

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, G.E.; Darkow, G.L.

1982-05-01

The uniqueness of the thermodynamic and dynamic structure of the atmosphere in the area of imminent tornado bearing storm development is analyzed by comparing 115 tornado proximity soundings with upper air soundings made at the same location 6 and 12 hours earlier (precedent soundings) and with soundings made simultaneously at neighboring upper air stations. The comparisons suggest that both the proximity station and the neighboring station upstream with respect to the mean flow in the low level moist air display very similar degrees of hydrostatic and potential-convective instability by late afternoon. The principal difference is in the wind profiles atmore » the two locations. The tornado proximity station displays significantly stronger wind speeds above 1 km with the most striking difference being in the vertical shear of the wind in the layer from 1 to 3 km above ground level. In this layer the winds at the proximity station show an average increase of about 3 m sec/sup -1/ while the upstream, non-tornadic, station shows a slight decrease of wind speed with height.« less
Discriminating a deep gallium antisite defect from shallow acceptors in GaAs using supercell calculations

DOE PAGES

Schultz, Peter A.

2016-03-01

For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as B As. Thismore » systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. Lastly, the properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.« less
Design and analysis of gradient index metamaterial-based cloak with wide bandwidth and physically realizable material parameters

NASA Astrophysics Data System (ADS)

Bisht, Mahesh Singh; Rajput, Archana; Srivastava, Kumar Vaibhav

2018-04-01

A cloak based on gradient index metamaterial (GIM) is proposed. Here, the GIM is used, for conversion of propagating waves into surface waves and vice versa, to get the cloaking effect. The cloak is made of metamaterial consisting of four supercells with each supercell possessing the linear spatial variation of permittivity and permeability. The spatial variation of material parameters in supercells allows the conversion of propagating waves into surface waves and vice versa, hence results in reduction of electromagnetic signature of the object. To facilitate the practical implementation of the cloak, continuous spatial variation of permittivity and/or permeability, in each supercell, is discretized into seven segments and it is shown that there is not much deviation in cloaking performance of discretized cloak as compared to its continuous counterpart. The crucial advantage, of the proposed cloaks, is that the material parameters are isotropic and in physically realizable range. Furthermore, the proposed cloaks have been shown to possess bandwidth of the order of 190% which is a significantly improved performance compared to the recently published literature.
Validation of updated neutronic calculation models proposed for Atucha-II PHWR. Part I: Benchmark comparisons of WIMS-D5 and DRAGON cell and control rod parameters with MCNP5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mollerach, R.; Leszczynski, F.; Fink, J.

2006-07-01

In 2005 the Argentine Government took the decision to complete the construction of the Atucha-II nuclear power plant, which has been progressing slowly during the last ten years. Atucha-II is a 745 MWe nuclear station moderated and cooled with heavy water, of German (Siemens) design located in Argentina. It has a pressure-vessel design with 451 vertical coolant channels, and the fuel assemblies (FA) are clusters of 37 natural UO{sub 2} rods with an active length of 530 cm. For the reactor physics area, a revision and update calculation methods and models (cell, supercell and reactor) was recently carried out coveringmore » cell, supercell (control rod) and core calculations. As a validation of the new models some benchmark comparisons were done with Monte Carlo calculations with MCNP5. This paper presents comparisons of cell and supercell benchmark problems based on a slightly idealized model of the Atucha-I core obtained with the WIMS-D5 and DRAGON codes with MCNP5 results. The Atucha-I core was selected because it is smaller, similar from a neutronic point of view, and more symmetric than Atucha-II Cell parameters compared include cell k-infinity, relative power levels of the different rings of fuel rods, and some two-group macroscopic cross sections. Supercell comparisons include supercell k-infinity changes due to the control rods (tubes) of steel and hafnium. (authors)« less
Monitoring System for Atmospheric Water Vapor with a Ground-Based Multi-Band Radiometer: Meteorological Application of Radio Astronomy Technologies

NASA Astrophysics Data System (ADS)

Nagasaki, T.; Araki, K.; Ishimoto, H.; Kominami, K.; Tajima, O.

2016-08-01

High-resolution estimation of thermodynamic properties in the atmosphere can help to predict and mitigate meteorological disasters, such as local heavy rainfall and tornadic storms. For the purposes of short-term forecasting and nowcasting of severe storms, we propose a novel ground-based measurement system, which observes the intensity of atmospheric radiation in the microwave range. Our multi-band receiver system is designed to identify a rapid increase in water vapor before clouds are generated. At frequencies between 20 and 30 GHz, our system simultaneously measures water vapor as a broad absorption peak at 22 GHz as well as cloud liquid water. Another band at 50-60 GHz provides supplementary information from oxygen radiation to give vertical profiles of physical temperature. For the construction of this cold receiver system, novel technologies originally developed for observations of cosmic microwave background radiation were applied. The input atmospheric signal is amplified by a cold low-noise amplifier maintained below 10 K, while the spectrum of this amplified signal is measured using a signal analyzer under ambient conditions. The cryostat also contains a cold black body at 40 K to act as a calibration signal. This calibration signal is transported to each of the receivers via a wire grid. We can select either the atmospheric signal or the calibration signal by changing the orientation of this wire. Each receiver can be calibrated using this setup. Our system is designed to be compact (<1 m3), with low power consumption (˜ 1.5 kW). Therefore, it is easy to deploy on top of high buildings, mountains, and ship decks.
Preliminary Development and Evaluation of Lightning Jump Algorithms for the Real-Time Detection of Severe Weather

NASA Technical Reports Server (NTRS)

Schultz, Christopher J.; Petersen, Walter A.; Carey, Lawrence D.

2009-01-01

Previous studies have demonstrated that rapid increases in total lightning activity (intracloud + cloud-to-ground) are often observed tens of minutes in advance of the occurrence of severe weather at the ground. These rapid increases in lightning activity have been termed "lightning jumps." Herein, we document a positive correlation between lightning jumps and the manifestation of severe weather in thunderstorms occurring across the Tennessee Valley and Washington D.C. A total of 107 thunderstorms were examined in this study, with 69 of the 107 thunderstorms falling into the category of non-severe, and 38 into the category of severe. From the dataset of 69 isolated non-severe thunderstorms, an average peak 1 minute flash rate of 10 flashes/min was determined. A variety of severe thunderstorm types were examined for this study including an MCS, MCV, tornadic outer rainbands of tropical remnants, supercells, and pulse severe thunderstorms. Of the 107 thunderstorms, 85 thunderstorms (47 non-severe, 38 severe) from the Tennessee Valley and Washington D.C tested 6 lightning jump algorithm configurations (Gatlin, Gatlin 45, 2(sigma), 3(sigma), Threshold 10, and Threshold 8). Performance metrics for each algorithm were then calculated, yielding encouraging results from the limited sample of 85 thunderstorms. The 2(sigma) lightning jump algorithm had a high probability of detection (POD; 87%), a modest false alarm rate (FAR; 33%), and a solid Heidke Skill Score (HSS; 0.75). A second and more simplistic lightning jump algorithm named the Threshold 8 lightning jump algorithm also shows promise, with a POD of 81% and a FAR of 41%. Average lead times to severe weather occurrence for these two algorithms were 23 minutes and 20 minutes, respectively. The overall goal of this study is to advance the development of an operationally-applicable jump algorithm that can be used with either total lightning observations made from the ground, or in the near future from space using the GOES-R Geostationary Lightning Mapper.
Relationship between tornadoes and hook echoes on April 3, 1974

NASA Technical Reports Server (NTRS)

Forbes, G. S.

1975-01-01

Radar observations of tornado families occurring on April 3, 1974 are discussed. Of the 93 tornadoes included in the sample, 81% were associated with hook-like echoes with appendages at least 40 deg to the south of the echo movement. At least one tornado was associated with 62% of the hook-like echoes observed. All of the tornadoes with intensities of F 4 and F 5 were produced by hook-like echoes; the mean intensity of all tornadoes associated with this type of echo was F 3, while the mean intensity of the remaining tornadoes was F1. The tornadic hook-like echoes moved to the right of the non-tornadic echoes forming a tornado line in advance of the squall line. Some tornadoes were associated with 'spiral' echoes.
Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTi O 3

DOE PAGES

Silverstein, Harlyn J.; Skoropata, Elizabeth; Sarte, Paul M.; ...

2016-02-19

In the last few years the magnetoelectric behavior of MnTiO 3 has been observed even though its been studied for many decades. We use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiOmore » 3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Moreover, the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO 3 is likely more important than previously thought.« less
Density functional theory calculations of magnetocrystalline anisotropy energies for (Fe(1-x)Co(x))(2)B.

PubMed

Däne, Markus; Kim, Soo Kyung; Surh, Michael P; Åberg, Daniel; Benedict, Lorin X

2015-07-08

We present and discuss density functional theory calculations of magnetic properties of the family of ferromagnetic compounds, (Fe(1-x)Co(x))(2)B, focusing specifically on the magnetocrystalline anisotropy energy (MAE). Using periodic supercells of various sizes (up to 96 atoms), it is shown that the general qualitative features of the composition dependence of the MAE is in agreement with experimental findings, while our predicted magnitudes are larger than those of experiment. We find that the use of small supercells (6 and 12-atom) favors larger MAE values relative to a statistical sample of configurations constructed with 96-atom supercells. The effect of lattice relaxations is shown to be small. Calculations of the Curie temperature for this alloy are also presented.
Radar observations of a tornado-spawning storm complex in Southeast Brazil and Meso-Eta forecasts of this extreme event

NASA Astrophysics Data System (ADS)

Held, Gerhard; Gomes, Jorge Luis; Gomes, Ana Maria

2014-05-01

During the early afternoon of 22 September 2013, severe storms, accompanied by large hail, damaging winds, heavy precipitation and intense lightning activity, devastated a region in the southeast State of São Paulo. Several extremely intense storm cells moved at up to 80 km/h east-southeastwards, ahead of a strong cold front approaching through Paraná, which created extremely unstable conditions that led to deep convection and overshooting towers up to 18 km. At least one of theses cells spawned a tornado when it reached the town of Taquarituba. The tornado traversed the town from south-southwest to north-northeast and was responsible for 63 people injured and two fatalities. Based on the damage reported, it was at least an F3 according to the Fujita scale. The objective of the present study is to characterize this severe thunderstorm event, using different types of data, and to evaluate the forecasts provided by the Meso-Eta model centered over Bauru. The pre-frontal and frontal convective cells were tracked throughout their life-time by IPMet's Doppler radars, which cover the western and central regions of the State São Paulo, as well as northern Paraná State. Radar volume scans, generated every 7,5 min, were processed with the TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting) Software, yielding the following preliminary results: as the storm complex traversed the Paranapanema River, which forms the border between the two states, the cells intensified drastically and shortly before reaching the town of Taquarituba, that particular cell displayed extremely strong radial shear just above the cloud base (about -20 to +35 m/s), which led to the formation of a deep meso-cyclone, from which the tornado spawned and touched down at around 14:30 LT (LT=UT-3h). Cell properties calculated by TITAN showed a drastic increase of VIL (Vertically Integrated Liquid water content) from 13:52 LT (7,9 kg/m2) to a maximum of 61,8 kg/m2 at 14:15 LT. From 14:22 LT to 14:45 LT the VIL dropped to 14,2 kg/m2, indicative of destructive winds reaching the ground, coincident with the tornado touch-down. Simultaneously, the accumulated hail mass aloft increased from 0 to 802 ktons at 14:22 LT, which subsequently dropped to the ground, confirmed by the likewise decrease of VIL. Furthermore, the fact that the 40 dBZ radar reflectivity reached up to 16,6 km at the time of the tornado occurrence was also outstanding, while maximum reflectivities varied between 50 and 60 dBZ during 90 min. The Meso-Eta model is initiated twice daily (00 and 12 UT) for a domain, which amply covers the State of São Paulo at a resolution of 10x10km horizontally and 38 levels from 1000 to 50 hPa. It also computes additional convective parameters (Storm Relative Helicity (SRH), BRN Shear, supercell index, etc), as well as vertical profiles (Skew-T-Log-P) at any specified grid point. Furthermore, each run of the model is executed twice, using the convection parameterization of Betts & Miller and Kain-Fritsch, respectively. Based on the forecast from the 21Sept2013-12UT and 22Sept2013-00UT model runs (+27h & +30h and +15h & +18h, respectively), a warning for very severe storms to occur in the region from Ourinhos to Taquarituba could be emitted during the night before the extreme event. Some of the indicators were: CAPE 3000-4000 J/kg; K Index 38-42; strong wind shear between 500 hPa and 250 hPa (northwest at ±20 m/s to west at 30m/s); Omega at 500 hPa -1,0 to -1,4 Pa/s; Supercell Parameter -1 and SRH 150-200 m2/s2. The time window ranged from 12:00 to 18:00 LT. The Skew-T diagram at 09:00LT at Taquarituba indicated relatively dry air between 600-200hPa, which was quickly moistened as the cold front approached.

Towards evaluating the intensity of convective systems by using GPS radio occultation profiles

NASA Astrophysics Data System (ADS)

Biondi, Riccardo; Steiner, Andrea K.; Kirchengast, Gottfried

2015-04-01

Deep convective systems, also more casually often just called storms, are destructive weather phenomena causing every year many deaths, injuries and damages and accounting for major economic losses in several countries. The number and intensity of such phenomena increased over the last decades in some areas of the globe, including Europe. Damages are mostly caused by strong winds and heavy rain and these parameters are strongly connected to the structure of the storm. Convection over land is usually stronger and deeper than over the ocean and some convective systems, known as supercells, also develop tornadoes through processes which are still mostly unclear. The intensity forecast and monitoring of convective systems is one of the major challenges for meteorology because in-situ measurements during extreme events are too sparse or not reliable and most ongoing satellite missions do not provide suitable time/space coverage. With this study we propose a new method for detecting the convection intensity in terms of rain rate and surface wind speed by using meteorological surface measurements in combination with atmospheric profiles from Global Positioning System (GPS) radio occultation observations, which are available in essentially all weather conditions and with global coverage. The analysis of models indicated a relationship between the cloud top altitude and the intensity of a storm. We thus use GPS radio occultation bending angle profiles for detecting the storm's cloud top altitude and we correlate this value to the rain rate and wind speed measured by meteorological station networks in two different regions, the WegenerNet climate station network (South-Eastern Styria, Austria) and the Atmospheric Radiation Measurement site (ARM, Southern Great Plains, USA), respectively. The results show a good correlation between the cloud top altitude and the maximum rain rate in the monitored areas, while this is not found for maximum wind speed. We conclude from this initial study that for land convective systems the cloud top altitude is strongly connected to the rain intensity and that GPS radio occultation observations show encouraging potential to improve the intensity nowcasting and detection of such kind of severe weather phenomena.
Potential Vorticity Analysis of Low Level Thunderstorm Dynamics in an Idealized Supercell Simulation

DTIC Science & Technology

2009-03-01

Severe Weather, Supercell, Weather Research and Forecasting Model , Advanced WRF 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT...27 A. ADVANCED RESEARCH WRF MODEL .................................................27 1. Data, Model Setup, and Methodology...03/11/2006 GFS model run. Top row: 11/12Z initialization. Middle row: 12 hour forecast valid at 12/00Z. Bottom row: 24 hour forecast valid at
Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions

NASA Astrophysics Data System (ADS)

Rubel, O.; Bokhanchuk, A.; Ahmed, S. J.; Assmann, E.

2014-09-01

Supercells are often used in ab initio calculations to model compound alloys, surfaces, and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include formation of donorlike states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.
Properties of single-layer graphene with supercell doped by one defect only

NASA Astrophysics Data System (ADS)

Wang, Zongguo; Qin, Shaojing; Wang, Chuilin

2017-10-01

Graphene has vast promising applications in nanoelectronics and spintronics because of its unique magnetic and electronic properties. Making use of an ab initio spin-polarized density functional theory, implemented by the method of the Heyd-Scuseria-Ernzerhof 06 (HSE06) hybrid functional, the properties of various defect dopants in a supercell of a semi-metal monolayer graphene were investigated. We found from our calculation that introducing one defect dopant in a supercell would break the spin sublattice symmetry, and will induce a magnetic state at some appropriate doping concentrations. This paper systematically analyzes the magnetic effects of three types of defects on graphene, that is, vacancy, substitutional dopant and adatoms. Different types of defects will induce various new properties in graphene. The energies and electronic properties of these three types of defects were also calculated.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Chanana, Anuja; Mahapatra, Santanu, E-mail: santanu@dese.iisc.ernet.in

Investigation of a transition metal dichalcogenide (TMD)-metal interface is essential for the effective functioning of monolayer TMD based field effect transistors. In this work, we employ the Density Functional Theory calculations to analyze the modulation of the electronic structure of monolayer WS{sub 2} with chlorine doping and the relative changes in the contact properties when interfaced with gold and palladium. We initially examine the atomic and electronic structures of pure and doped monolayer WS{sub 2} supercell and explore the formation of midgap states with band splitting near the conduction band edge. Further, we analyze the contact nature of the puremore » supercell with Au and Pd. We find that while Au is physiosorbed and forms n-type contact, Pd is chemisorped and forms p-type contact with a higher valence electron density. Next, we study the interface formed between the Cl-doped supercell and metals and observe a reduction in the Schottky barrier height (SBH) in comparison to the pure supercell. This reduction found is higher for Pd in comparison to Au, which is further validated by examining the charge transfer occurring at the interface. Our study confirms that Cl doping is an efficient mechanism to reduce the n-SBH for both Au and Pd, which form different types of contact with WS{sub 2}.« less
Three-dimensional nonhydrostatic simulations of summer thunderstorms in the humid subtropics versus High Plains

NASA Astrophysics Data System (ADS)

Lin, Hsin-mu; Wang, Pao K.; Schlesinger, Robert E.

2005-11-01

This article presents a detailed comparison of cloud microphysical evolution among six warm-season thunderstorm simulations using a time-dependent three-dimensional model WISCDYMM. The six thunderstorms chosen for this study consist of three apiece from two contrasting climate zones, the US High Plains (one supercell and two multicells) and the humid subtropics (two in Florida, US and one in Taipei, Taiwan, all multicells). The primary goal of this study is to investigate the differences among thunderstorms in different climate regimes in terms of their microphysical structures and how differently these structures evolve in time. A subtropical case is used as an example to illustrate the general contents of a simulated storm, and two examples of the simulated storms, one humid subtropical and one northern High Plains case, are used to describe in detail the microphysical histories. The simulation results are compared with the available observational data, and the agreement between the two is shown to be at least fairly close overall. The analysis, synthesis and implications of the simulation results are then presented. The microphysical histories of the six simulated storms in terms of the domain-integrated masses of all five hydrometeor classes (cloud water, cloud ice, rain, snow, graupel/hail), along with the individual sources (and sinks) of the three precipitating hydrometeor classes (rain, snow, graupel/hail) are analyzed in detail. These analyses encompass both the absolute magnitudes and their percentage contributions to the totals, for the condensate mass and their precipitation production (and depletion) rates, respectively. Comparisons between the hydrometeor mass partitionings for the High Plains versus subtropical thunderstorms show that, in a time-averaged sense, ice hydrometeors (cloud ice, snow, graupel/hail) account for ˜ 70-80% of the total hydrometeor mass for the High Plains storms but only ˜ 50% for the subtropical storms, after the systems have reached quasi-steady mature states. This demonstrates that ice processes are highly important even in thunderstorms occurring in warm climatic regimes. The dominant rain sources are two of the graupel/hail sinks, shedding and melting, in both High Plains and subtropical storms, while the main rain sinks are accretion by hail and evaporation. The dominant graupel/hail sources are accretion of rain, snow and cloud water, while its main sinks are shedding and melting. The dominant snow sources are the Bergeron-Findeisen process and accretion of cloud water, while the main sinks are accretion by graupel/hail and sublimation. However, the rankings of the leading production and depletion mechanisms differ somewhat in different storm cases, especially for graupel/hail. The model results indicate that the same hydrometeor types in the different climates have their favored microphysical sources and sinks. These findings not only prove that thunderstorm structure depends on local dynamic and thermodynamic atmospheric conditions that are generally climate-dependent, but also provide information about the partitioning of hydrometeors in the storms. Such information is potentially useful for convective parameterization in large-scale models.
Severe Weather Environments in Atmospheric Reanalyses

NASA Astrophysics Data System (ADS)

King, A. T.; Kennedy, A. D.

2017-12-01

Atmospheric reanalyses combine historical observation data using a fixed assimilation scheme to achieve a dynamically coherent representation of the atmosphere. How well these reanalyses represent severe weather environments via proxies is poorly defined. To quantify the performance of reanalyses, a database of proximity soundings near severe storms from the Rapid Update Cycle 2 (RUC-2) model will be compared to a suite of reanalyses including: North American Reanalysis (NARR), European Interim Reanalysis (ERA-Interim), 2nd Modern-Era Retrospective Reanalysis for Research and Applications (MERRA-2), Japanese 55-year Reanalysis (JRA-55), 20th Century Reanalysis (20CR), and Climate Forecast System Reanalysis (CFSR). A variety of severe weather parameters will be calculated from these soundings including: convective available potential energy (CAPE), storm relative helicity (SRH), supercell composite parameter (SCP), and significant tornado parameter (STP). These soundings will be generated using the SHARPpy python module, which is an open source tool used to calculate severe weather parameters. Preliminary results indicate that the NARR and JRA55 are significantly more skilled at producing accurate severe weather environments than the other reanalyses. The primary difference between these two reanalyses and the remaining reanalyses is a significant negative bias for thermodynamic parameters. To facilitate climatological studies, the scope of work will be expanded to compute these parameters for the entire domain and duration of select renalyses. Preliminary results from this effort will be presented and compared to observations at select locations. This dataset will be made pubically available to the larger scientific community, and details of this product will be provided.
Multiple Convective Cell Identification and Tracking Algorithm for documenting time-height evolution of measured polarimetric radar and lightning properties

NASA Astrophysics Data System (ADS)

Rosenfeld, D.; Hu, J.; Zhang, P.; Snyder, J.; Orville, R. E.; Ryzhkov, A.; Zrnic, D.; Williams, E.; Zhang, R.

2017-12-01

A methodology to track the evolution of the hydrometeors and electrification of convective cells is presented and applied to various convective clouds from warm showers to super-cells. The input radar data are obtained from the polarimetric NEXRAD weather radars, The information on cloud electrification is obtained from Lightning Mapping Arrays (LMA). The development time and height of the hydrometeors and electrification requires tracking the evolution and lifecycle of convective cells. A new methodology for Multi-Cell Identification and Tracking (MCIT) is presented in this study. This new algorithm is applied to time series of radar volume scans. A cell is defined as a local maximum in the Vertical Integrated Liquid (VIL), and the echo area is divided between cells using a watershed algorithm. The tracking of the cells between radar volume scans is done by identifying the two cells in consecutive radar scans that have maximum common VIL. The vertical profile of the polarimetric radar properties are used for constructing the time-height cross section of the cell properties around the peak reflectivity as a function of height. The LMA sources that occur within the cell area are integrated as a function of height as well for each time step, as determined by the radar volume scans. The result of the tracking can provide insights to the evolution of storms, hydrometer types, precipitation initiation and cloud electrification under different thermodynamic, aerosol and geographic conditions. The details of the MCIT algorithm, its products and their performance for different types of storm are described in this poster.
Multi-scale evolution of a derecho-producing MCS

NASA Astrophysics Data System (ADS)

Bernardet, Ligia Ribeiro

1997-12-01

In this dissertation we address one type of severe weather: strong straight-line winds. In particular, we focus on derechos, a type of wind storm caused by a convective system and characterized by its long duration and by the large area it covers. One interesting characteristic of these storms is that they develop at night, on the cold side of a thermal boundary. This region is not characterized by large convective instability. In fact, surface parcels are generally stable with respect to vertical displacements. To gain understanding of the physical processes involved in these storms, we focused on the case of a MCS that developed in eastern Colorado on 12-13 May, 1985. The system formed in the afternoon, was active until early morning, and caused strong winds during the night. A multi-scale full physics simulation of this case was performed using a non-hydrostatic mesoscale model. Four telescopically nested grids covering from the synoptic scale down to cloud scale circulations were used. A Lagrangian model was used to follow trajectories of parcels that took part in the updraft and in the downdraft, and balance of forces were computed along the trajectories. Our results show that the synoptic and mesoscale environment of the storm largely influences convective organization and cloud-scale circulations. During the day, when the boundary layer is well mixed, the source of air for the clouds is located within the boundary layer. At night, when the boundary layer becomes stable, the source of air shifts to the top of the boundary layer. It is composed of warm, moist air that is brought by the nocturnal low-level jet. The downdraft structure also changes from day to night. During the day, parcels acquire negative buoyancy because of cooling due to evaporation and melting. As they sink, they remain colder than the environment, and end up at the surface constituting the cold pool. During the night, downdrafts are stronger, generating the strong surface winds. The most important branch of the downdraft has an 'up-down' trajectory. Parcels start close to the ground, are lifted up by a strong pressure gradient force, and become colder than their surroundings as they ascend in a stable environment. Then, as they go through the precipitation shaft, they sink due to negative buoyancy enhanced by condensate loading. The upward pressure gradient force is partially related to mid-level rotation in the storm, which has characteristics of a high-precipitation supercell.
EHD Approach to Tornadic Thunderstorms and Methods of Their Destruction

NASA Astrophysics Data System (ADS)

Kikuchi, H.

2005-05-01

In many cases, tornadoes are accompanied or involved by lightning discharges and are thought to be com- posed of uncharged and charged components different from each other in terms of velocity, vorticity, heli- city, and appearance (shape and luminosity). Their visible dark portion may correspond to uncharged tor- nadoes, while luminous or bright part may involve charged tornadoes with return strokes. Usually, un- charged tornadoes have been considered to be ascending hot streams of thermohydrodynamic origin. This is the conventional theory of tornadoes, based on hydrodynamics (HD) or thermohydrodynamics (THD) but does not consider electrical effects that are really significant in tornadic thunderstorms..It has been shown, however, that a new electrohydrodynamics (EHD) established and developed over the last more than a decade is applicable to tornadic thunderstorms with lightning. This paper summarizes such an EHD approach and proposes the methods of tornado destruction based on EHD. Space charge and electric field configurations in tornadic thunderstorms are considered to be quadrupole-like, taking into account the cloud-charge images onto the ground. Accordingly, dynamics of particles and EHD flows in an electric quadrupole forming an electric cusp and mirror can straightly apply to those circumstances. When the gas pressure is below the breakdown threshold, there occur helical motion of particles, not only charged but also even uncharged, and/or vortex generation. While for gases whose pressure is beyond the breakdown threshold, the following basic processes succeed one after another. When the grain is uncharged, a dis- charge channel is formed towards each pole as a result of X-type reconnection. For a negatively or posi- tively charged grain, I-type reconnection occurs between the grain and positive or negative poles, respect- ively. For uncharged two grains, O-type reconnection between both grains could be involved in addition to X-type between each pole, while for oppositely charged two grains, F-type reconnection could be in- volved between grains in addition to I-type between each grain and a pole with opposite polarity. Thus one can say that the uncharged component of tornadic thunderstorms is composed of conventional ascending hot streams of thermohydrodynamic origin and particle flows of new EHD origin produced by a quadru- pole-like cloud-base, funnel-top charge distributions, while the charged component is a bunch of return strokes including charged flows due to dust-related electric reconnection and EHD vortices in large-scale generated by EHD helical turbulence where there may occur self-organization to coalescence of fluid vor- tex and electric displacement field lines at least in an initial stage of return stroke (rise time of some ms), since earth's magnetic field could be ignored. This also indicates that fluid vortex breakdown points also tend to merge electric cusps, X-type and O-type. Then the principle of dust-related electric reconnection could be replaced by dust cluster injection into electric cusps (X-type and O-type) in several ways just mentioned above. Thus a variety of such dust cluster injection could cause additional cloud-to-dust cluster discharges, expending electrostatic energy accumulated in thunderclouds considerably and destructing tornadoes consequently.
The Tornado.

ERIC Educational Resources Information Center

Snow, John T.

1984-01-01

Although tornadoes have been one of the most elusive phenomena in meteorology, new observation techniques are now revealing how they are spawned by thunderstorms. Tornado structure and formation, thunderstorms, tornadic thunderstorms, and the evolution and structure of such thunderstorms are considered. Why the Midwest has frequent tornadoes is…
The Next Generation of Airborne Polarimetric Doppler Weather Radar: NCAR/EOL Airborne Phased Array Radar (APAR) Development

NASA Astrophysics Data System (ADS)

Moore, James; Lee, Wen-Chau; Loew, Eric; Vivekanandan, Jothiram; Grubišić, Vanda; Tsai, Peisang; Dixon, Mike; Emmett, Jonathan; Lord, Mark; Lussier, Louis; Hwang, Kyuil; Ranson, James

2017-04-01

The National Center for Atmospheric Research (NCAR) Earth observing Laboratory (EOL) is entering the third year of preliminary system design studies, engineering prototype testing and project management plan preparation for the development of a novel Airborne Phased Array Radar (APAR). This system being designed by NCAR/EOL will be installed and operated on the NSF/NCAR C-130 aircraft. The APAR system will consist of four removable C-band Active Electronically Scanned Arrays (AESA) strategically placed on the fuselage of the aircraft. Each AESA measures approximately 1.5 x 1.9 m and is composed of 3000 active radiating elements arranged in an array of line replaceable units (LRU) to simplify maintenance. APAR will provide unprecedented observations, and in conjunction with the advanced radar data assimilation schema, will be able to address the key science questions to improve understanding and predictability of significant and high-impact weather APAR, operating at C-band, allows the measurement of 3-D kinematics of the more intense portions of storms (e.g. thunderstorm dynamics and tornadic development, tropical cyclone rainband structure and evolution) with less attenuation compared with current airborne Doppler radar systems. Polarimetric measurements are not available from current airborne tail Doppler radars. However, APAR, with dual-Doppler and dual polarization diversity at a lesser attenuating C-band wavelength, will further advance the understanding of the microphysical processes within a variety of precipitation systems. The radar is sensitive enough to provide high resolution measurements of winter storm dynamics and microphysics. The planned APAR development that would bring the system to operational readiness for research community use aboard the C-130 is expected to take 8 years once major funding support is realized. The authors will review the overall APAR design and provide new details of the system based on our Technical Requirements Document, airflow studies and antenna aperture simulations We will further outline the next steps needed to bring this exceptional tool into full operation.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Schultz, Peter A.

For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as B As. Thismore » systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. Lastly, the properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.« less
Spin asymmetric band gap opening in graphene by Fe adsorption

NASA Astrophysics Data System (ADS)

del Castillo, E.; Cargnoni, F.; Achilli, S.; Tantardini, G. F.; Trioni, M. I.

2015-04-01

The adsorption of Fe atom on graphene is studied by first-principles Density Functional Theory. The structural, electronic, and magnetic properties are analyzed at different coverages, all preserving C6v symmetry for the Fe adatom. We observed that binding energies, magnetic moments, and adsorption distances rapidly converge as the size of the supercell increases. Among the considered supercells, those constituted by 3n graphene unit cells show a very peculiar behavior: the adsorption of a Fe atom induces the opening of a spin-dependent gap in the band structure. In particular, the gap amounts to tenths of eV in the majority spin component, while in the minority one it has a width of about 1 eV for the 3 × 3 supercell and remains significant even at very low coverages (0.25 eV for θ ≃ 2%). The charge redistribution upon Fe adsorption has also been analyzed according to state of the art formalisms indicating an appreciable charge transfer from Fe to the graphene layer.
A supercell approach to the doping effect on the thermoelectric properties of SnSe.

PubMed

Suzuki, Yasumitsu; Nakamura, Hisao

2015-11-28

We study the thermoelectric properties of tin selenide (SnSe) by using first-principles calculations coupled with the Boltzmann transport theory. A recent experimental study showed that SnSe gives an unprecedented thermoelectric figure of merit ZT of 2.6 ± 0.3 in the high-temperature (>750 K) phase, while ZT in the low-temperature phase (<750 K) is much smaller than that of the high-temperature phase. Here we explore the possibility of increasing ZT in the low-temperature regime by carrier doping. For this purpose, we adopt a supercell approach to model the doped systems. We first examine the validity of the conventional rigid-band approximation (RBA), and then investigate the thermoelectric properties of Ag or Bi doped SnSe as p- or n-type doped materials using our supercell method. We found that both types of doping improve ZT and/or the power factor of the low-temperature phase SnSe, but only after the adjustment of the appropriate doping level is achieved.
Lattice dynamics and electron-phonon coupling calculations using nondiagonal supercells

NASA Astrophysics Data System (ADS)

Lloyd-Williams, Jonathan; Monserrat, Bartomeu

Quantities derived from electron-phonon coupling matrix elements require a fine sampling of the vibrational Brillouin zone. Converged results are typically not obtainable using the direct method, in which a perturbation is frozen into the system and the total energy derivatives are calculated using a finite difference approach, because the size of simulation cell needed is prohibitively large. We show that it is possible to determine the response of a periodic system to a perturbation characterized by a wave vector with reduced fractional coordinates (m1 /n1 ,m2 /n2 ,m3 /n3) using a supercell containing a number of primitive cells equal to the least common multiple of n1, n2, and n3. This is accomplished by utilizing supercell matrices containing nonzero off-diagonal elements. We present the results of electron-phonon coupling calculations using the direct method to sample the vibrational Brillouin zone with grids of unprecedented size for a range of systems, including the canonical example of diamond. We also demonstrate that the use of nondiagonal supercells reduces by over an order of magnitude the computational cost of obtaining converged vibrational densities of states and phonon dispersion curves. J.L.-W. is supported by the Engineering and Physical Sciences Research Council (EPSRC). B.M. is supported by Robinson College, Cambridge, and the Cambridge Philosophical Society. This work was supported by EPSRC Grants EP/J017639/1 and EP/K013564/1.
Numerical simulation of severe convective phenomena over Croatian and Hungarian territory

NASA Astrophysics Data System (ADS)

Mahović, Nataša Strelec; Horvath, Akos; Csirmaz, Kalman

2007-02-01

Squall lines and supercells cause severe weather and huge damages in the territory of Croatia and Hungary. These long living events can be recognised by radar very well, but the problem of early warning, especially successful numerical forecast of these phenomena, has not yet been solved in this region. Two case studies are presented here in which dynamical modelling approach gives promising results: a squall line preceding a cold front and a single supercell generated because of a prefrontal instability. The numerical simulation is performed using the PSU/NCAR meso-scale model MM5, with horizontal resolution of 3 km. Lateral boundary conditions are taken from the ECMWF model. The moist processes are resolved by Reisner mixed-phase explicit moisture scheme and for the radiation scheme a rapid radiative transfer model is applied. The analysis nudging technique is applied for the first two hours of the model run. The results of the simulation are very promising. The MM5 model reconstructed the appearance of the convective phenomena and showed the development of thunderstorm into the supercell phase. The model results give very detailed insight into wind changes showing the rotation of supercells, clearly distinguish warm core of the cell and give rather good precipitation estimate. The successful simulation of convective phenomena by a high-resolution MM5 model showed that even smaller scale conditions are contained in synoptic scale patterns, represented in this case by the ECMWF model.
Thunderstorms and flooding of August 17, 2007, with a context provided by a history of other large storm and flood events in the Black Hills area of South Dakota

USGS Publications Warehouse

Driscoll, Daniel G.; Bunkers, Matthew J.; Carter, Janet M.; Stamm, John F.; Williamson, Joyce E.

2010-01-01

The Black Hills area of western South Dakota has a history of damaging flash floods that have resulted primarily from exceptionally strong rain-producing thunderstorms. The best known example is the catastrophic storm system of June 9-10, 1972, which caused severe flooding in several major drainages near Rapid City and resulted in 238 deaths. More recently, severe thunderstorms caused flash flooding near Piedmont and Hermosa on August 17, 2007. Obtaining a thorough understanding of peak-flow characteristics for low-probability floods will require a comprehensive long-term approach involving (1) documentation of scientific information for extreme events such as these; (2) long-term collection of systematic peak-flow records; and (3) regional assessments of a wide variety of peak-flow information. To that end, the U.S. Geological Survey cooperated with the South Dakota Department of Transportation and National Weather Service to produce this report, which provides documentation regarding the August 17, 2007, storm and associated flooding and provides a context through examination of other large storm and flood events in the Black Hills area. The area affected by the August 17, 2007, storms and associated flooding generally was within the area affected by the larger storm of June 9-10, 1972. The maximum observed 2007 precipitation totals of between 10.00 and 10.50 inches occurred within about 2-3 hours in a small area about 5 miles west of Hermosa. The maximum documented precipitation amount in 1972 was 15.0 inches, and precipitation totals of 10.0 inches or more were documented for 34 locations within an area of about 76 square miles. A peak flow of less than 1 cubic foot per second occurred upstream from the 2007 storm extent for streamflow-gaging station 06404000 (Battle Creek near Keystone); whereas, the 1972 peak flow of 26,200 cubic feet per second was large, relative to the drainage area of only 58.6 square miles. Farther downstream along Battle Creek, a 2007 flow of 26,000 cubic feet per second was generated entirely within an intervening drainage area of only 44.4 square miles. An especially large flow of 44,100 cubic feet per second was documented for this location in 1972. The 2007 peak flow of 18,600 cubic feet per second for Battle Creek at Hermosa (station 06406000) was only slightly smaller than the 1972 peak flow of 21,400 cubic feet per second. Peak-flow values from 2007 for three sites with small drainage areas (less than 1.0 square mile) plot close to a regional envelope curve, indicating exceptionally large flow values, relative to drainage area. Physiographic factors that affect flooding in the area were examined. The limestone headwater hydrogeologic setting (within and near the Limestone Plateau area on the western flank of the Black Hills) has distinctively suppressed peak-flow characteristics for small recurrence intervals. Uncertainty is large, however, regarding characteristics for large recurrence intervals (low-probability floods) because of a dearth of information regarding the potential for generation of exceptionally strong rain-producing thunderstorms. In contrast, the greatest potential for exceptionally damaging floods is around the flanks of the rest of the Black Hills area because of steep topography and limited potential for attenuation of flood peaks in narrow canyons. Climatological factors that affect area flooding also were examined. Area thunderstorms are largely terrain-driven, especially with respect to their requisite upward motion, which can be initiated by orographic lifting effects, thermally enhanced circulations, and obstacle effects. Several other meteorological processes are influential in the development of especially heavy precipitation for the area, including storm cell training, storm anchoring or regeneration, storm mergers, supercell development, and weak upper-level air flow. A composite of storm total precipitation amounts for 13 recent individual storm events indicates
Local environment effects in the magnetic properties and electronic structure of disordered FePt

NASA Astrophysics Data System (ADS)

Khan, Saleem Ayaz; Minár, Ján; Ebert, Hubert; Blaha, Peter; Šipr, Ondřej

2017-01-01

Local aspects of magnetism of disordered FePt are investigated by ab initio fully relativistic full-potential calculations, employing the supercell approach and the coherent potential approximation (CPA). The focus is on trends of the spin and orbital magnetic moments with chemical composition and with bond lengths around the Fe and Pt atoms. A small but distinct difference between average magnetic moments obtained when using the supercells and when relying on the CPA is identified and linked to the neglect of the Madelung potential in the CPA.
Local Energies and Energy Fluctuations — Applied to the High Entropy Alloy CrFeCoNi

NASA Astrophysics Data System (ADS)

Fukushima, Tetsuya; Katayama-Yoshida, Hiroshi; Sato, Kazunori; Ogura, Masako; Zeller, Rudolf; Dederichs, Peter H.

2017-11-01

High entropy alloys show a variety of fascinating properties like high hardness, wear resistance, corrosion resistance, etc. They are random solid solutions of many components with rather high concentrations. We perform ab-initio calculations for the high entropy alloy CrFeCoNi, which equal concentration of 25% for each element. By the KKRnano program package, which is based on an order-N screened Korringa-Kohn-Rostoker Green's function method, we consider a face-centered cubic (FCC) supercell with 1372 randomly distributed elements, and in addition also smaller supercells with 500 and 256 atoms. It is found from our calculations that the local moments of the Cr atoms show a large environmental variation, ranging from -1.70 μB to +1.01 μB with an average of about -0.51 μB. We present a new method to calculate "local energies" of all atoms. This is based on the partitioning of the whole space into Voronoi cells and allows to calculate the energetic contribution of each atomic cell to the total energy of the supercell. The supercell calculations show very large variations of the local energies, analogous to the variations of the local moments. This shows that the random solid solution is not stable and has a tendency to form an L12-structure with the Cr-atoms ordered at the corner of the cube and the elements Fe, Co, and Ni randomly distributed on the three other FCC sublattices. For this structure the variation of the local moments are much smaller.

Crystal structures of η''-Cu3+xSi and η'''-Cu3+xSi.

PubMed

Corrêa, Cinthia Antunes; Perez, Olivier; Kopeček, Jaromír; Brázda, Petr; Klementová, Mariana; Palatinus, Lukáš

2017-08-01

The binary phase diagram of Cu-Si is unexpectedly complex in the vicinity of Cu 3+x Si. The low-temperature region contains three closely related incommensurately modulated phases denoted, in order of increasing temperature of stability, η''', η'' and η'. The structure analysis of η' has been reported previously [Palatinus et al. (2011). Inorg. Chem. 50, 3743]. Here the structure model for the phases η'' and η''' is reported. The structures could be solved in superspace, but no superspace structure model could be constructed due to the complexity of the modulation functions. Therefore, the structures were described in a supercell approximation, which involved a 4 × 4 × 3 supercell for the η'' phase and a 14 × 14 × 3 supercell for the η''' phase. Both structures are very similar and differ only by a subtle symmetry lowering from η'' to η'''. A comparison of the structure models of η'' and η''' with the reported structure of η' suggests that the reported structure model of η' contains an incorrect assignment of atomic types.
Novel Layered Supercell Structure from Bi 2AlMnO 6 for Multifunctionalities

DOE PAGES

Li, Leigang; Boullay, Philippe; Lu, Ping; ...

2017-10-02

Layered materials, e.g., graphene and transition metal (di)chalcogenides, holding great promises in nanoscale device applications have been extensively studied in fundamental chemistry, solid state physics and materials research areas. In parallel, layered oxides (e.g., Aurivillius and Ruddlesden–Popper phases) present an attractive class of materials both because of their rich physics behind and potential device applications. In this work, we report a novel layered oxide material with self-assembled layered supercell structure consisting of two mismatch-layered sublattices of [Bi 3O 3+δ] and [MO 2] 1.84 (M = Al/Mn, simply named BAMO), i.e., alternative layered stacking of two mutually incommensurate sublattices made ofmore » a three-layer-thick Bi–O slab and a one-layer-thick Al/Mn–O octahedra slab in the out-of-plane direction. Strong room-temperature ferromagnetic and piezoelectric responses as well as anisotropic optical property have been demonstrated with great potentials in various device applications. Furthermore, the realization of the novel BAMO layered supercell structure in this work has paved an avenue toward exploring and designing new materials with multifunctionalities.« less
Impact of aluminum doping on the thermo-physical properties of refractory medium-entropy alloys

NASA Astrophysics Data System (ADS)

Tian, Fuyang; Wang, Yang; Vitos, Levente

2017-01-01

We investigate the elastic moduli, ideal tensile strength, and thermodynamic properties of TiVNb and AlTiVNb refractory medium-entropy alloys (HEAs) by using ab initio alloy theories: the coherent potential approximation (CPA), the special quasi-random supercell (SQS), and a 432-atom supercell (SC). We find that with increasing number of alloy components, the SQS elastic constants become sensitive to the supercell size. The predicted elastic moduli are consistent with the available experiments. Aluminum doping decreases the stability of the body centered cubic phase. The ideal tensile strength calculation indicates that adding equiatomic Al to TiVNb random solid solution increases the intrinsic strength (ideal strain increase from 9.6% to 11.8%) and decreases the intrinsic strength (from 9.6 to 5.7 GPa). Based on the equation of states calculated by the CPA and SC methods, the thermodynamic properties obtained by the two ab initio methods are assessed. The L21 AlTiVNb (Ti-Al-V-Nb) alloy is predicted to be thermodynamically and dynamically stable with respect to the solid solution.
Case study: A severe hailstorm and strong downbursts over northeastern Slovenia on June 16th 2009

NASA Astrophysics Data System (ADS)

Korosec, M.

2009-09-01

Introduction A strong isolated storm complex with bow echo feature crossed northeastern Slovenia in the late afternoon hours and caused extensive damage due to severe wind gusts near 30m/s, excessive rainfalls and large hail. Synoptic situation On June 16th 2009, an upper-level ridge persists over southern Europe while a positively tilted short-wave trough, connected to a complex deep trough over northern Europe, crosses central Europe. Accompanied by this trough, a cold front is extending southwestwards towards the Alps. A relatively strong jet steak wraps around the trough axis and creates strong shear environment which overlaps with a narrow band of unstable airmass present ahead of the coming frontal boundary. Behind this trough/front over central Europe, a high pressure area is developing with stable conditions. Over Slovenia, strong surface heating was on going through the day but lack of near-surface convergence zones, limited moisture and strong capping inversion surpressed any storm initiation in the afternoon. Presentation of research This case study will go through a research of damaging bow echo which caused extensive damage due to severe winds, excessive rainfalls and large hail over much of northeastern Slovenia. Numerous trees were down or uprooted and numerous roofs were blown off or were seriously damaged due to severe wind gusts near or exceeding 30m/s. At first stages, when an isolated severe storm entered Slovenia, it had classic high precipitation supercell features while it transformed into a powerful bow echo later on. Very large hail up to 6cm in diameter was first observed in southeast Austria and near the border with Slovenia, while later on the main threat was very strong wind gusts and intense rainfalls. This research paper will show a detailed analysis of the synoptic situation including analysis of satellite, radar and surface observations. Radar imagery clearly showed isolated storm trailing along the near-surface frontal boundary as a bow echo and also satellite imagery showed signs of extremely severe storm as overshooting tops, "cold ring" and "U-shape" features were observed. References - Skywarn Austria forum: (http://www.skywarn.at/forum/) - EARS radar and SFC observations archive (http://www.arso.gov.si) - EARS article: Porocilo o neurjih 16. junija 2009 - OSMER FVG (http://www.meteo.fvg.it) - ESSL/ESWD database (www.essl.org) - ESTOFEX convective maps (www.estofex.org) - EUMETSAT satellite imagery (www.eumetsat.int) - 24ur.com/RTVSLO web portal (www.24ur.com, www.rtvslo.si) - Sobota Info web portal (www.sobotainfo.com) - Pomurje web portal (www.pomurje.si) - Administration of the Republic of Slovenia for Civil Protection and Disaster Relief, www.sos112.si - Worldwide Skew-t diagrams (http://weather.uwyo.edu/upperair/europe.html)
Three scales of motions associated with tornadoes. [Cyclones, tornadoes, and suction vortexs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbes, G.S.

1978-03-01

This dissertation explores three scales of motion commonly associated with tornadoes, and the interaction of these scales: the tornado cyclone, the tornado, and the suction vortex. The goal of the research is to specify in detail the character and interaction of these scales of motion to explain tornadic phenomena.
A Modeling Study of the Spring 2011 Extreme US Weather Activity

NASA Technical Reports Server (NTRS)

Schubert, S.; Suarez, M.; Chang, Y.

2012-01-01

The spring of 2011 was characterized by record-breaking tornadic activity with substantial loss of life and destruction of property. While a waning La Nina and other atmospheric teleconnections have been implicated in the development of these extreme weather events, a quantitative assessment of their causes is still lacking. This study uses high resolution (1/4 lat/lon) GEOS-5 AGCM experiments to quantify the role of SSTs and soil moisture in the development of the extreme weather activity with a focus on April - the month of peak tornadic activity. The simulations, consisting of 22-member ensembles of three-month long simulations (initialized March 1st) reproduce the main features of the observed large-scale changes including the below-normal temperature and above-normal precipitation in the Central US, and the hot and dry conditions to the south. Various sensitivity experiments are conducted to separate the roles of the SST, soil moisture and the initial atmospheric conditions in the development and predictability of the atmospheric conditions (wind shear, moisture, etc.) favoring the severe weather activity and flooding.
The Electronic Properties of O-Doped Pure and Sulfur Vacancy-Defect Monolayer WS₂: A First-Principles Study.

PubMed

Wang, Weidong; Bai, Liwen; Yang, Chenguang; Fan, Kangqi; Xie, Yong; Li, Minglin

2018-01-31

Based on the density functional theory (DFT), the electronic properties of O-doped pure and sulfur vacancy-defect monolayer WS₂ are investigated by using the first-principles method. For the O-doped pure monolayer WS₂, four sizes (2 × 2 × 1, 3 × 3 × 1, 4 × 4 × 1 and 5 × 5 × 1) of supercell are discussed to probe the effects of O doping concentration on the electronic structure. For the 2 × 2 × 1 supercell with 12.5% O doping concentration, the band gap of O-doped pure WS₂ is reduced by 8.9% displaying an indirect band gap. The band gaps in 3 × 3 × 1 and 4 × 4 × 1 supercells are both opened to some extent, respectively, for 5.55% and 3.13% O doping concentrations, while the band gap in 5 × 5 × 1 supercell with 2.0% O doping concentration is quite close to that of the pure monolayer WS₂. Then, two typical point defects, including sulfur single-vacancy (V S ) and sulfur divacancy (V 2S ), are introduced to probe the influences of O doping on the electronic properties of WS₂ monolayers. The observations from DFT calculations show that O doping can broaden the band gap of monolayer WS₂ with V S defect to a certain degree, but weaken the band gap of monolayer WS₂ with V 2S defect. Doping O element into either pure or sulfur vacancy-defect monolayer WS₂ cannot change their band gaps significantly, however, it still can be regarded as a potential method to slightly tune the electronic properties of monolayer WS₂.
Importance of elastic finite-size effects: Neutral defects in ionic compounds

DOE PAGES

Burr, P. A.; Cooper, M. W. D.

2017-09-15

Small system sizes are a well known source of error in DFT calculations, yet computational constraints frequently dictate the use of small supercells, often as small as 96 atoms in oxides and compound semiconductors. In ionic compounds, electrostatic finite size effects have been well characterised, but self-interaction of charge neutral defects is often discounted or assumed to follow an asymptotic behaviour and thus easily corrected with linear elastic theory. Here we show that elastic effect are also important in the description of defects in ionic compounds and can lead to qualitatively incorrect conclusions if inadequatly small supercells are used; moreover,more » the spurious self-interaction does not follow the behaviour predicted by linear elastic theory. Considering the exemplar cases of metal oxides with fluorite structure, we show that numerous previous studies, employing 96-atom supercells, misidentify the ground state structure of (charge neutral) Schottky defects. We show that the error is eliminated by employing larger cells (324, 768 and 1500 atoms), and careful analysis determines that elastic effects, not electrostatic, are responsible. The spurious self-interaction was also observed in non-oxide ionic compounds and irrespective of the computational method used, thereby resolving long standing discrepancies between DFT and force-field methods, previously attributed to the level of theory. The surprising magnitude of the elastic effects are a cautionary tale for defect calculations in ionic materials, particularly when employing computationally expensive methods (e.g. hybrid functionals) or when modelling large defect clusters. We propose two computationally practicable methods to test the magnitude of the elastic self-interaction in any ionic system. In commonly studies oxides, where electrostatic effects would be expected to be dominant, it is the elastic effects that dictate the need for larger supercells | greater than 96 atoms.« less
Importance of elastic finite-size effects: Neutral defects in ionic compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burr, P. A.; Cooper, M. W. D.

Small system sizes are a well known source of error in DFT calculations, yet computational constraints frequently dictate the use of small supercells, often as small as 96 atoms in oxides and compound semiconductors. In ionic compounds, electrostatic finite size effects have been well characterised, but self-interaction of charge neutral defects is often discounted or assumed to follow an asymptotic behaviour and thus easily corrected with linear elastic theory. Here we show that elastic effect are also important in the description of defects in ionic compounds and can lead to qualitatively incorrect conclusions if inadequatly small supercells are used; moreover,more » the spurious self-interaction does not follow the behaviour predicted by linear elastic theory. Considering the exemplar cases of metal oxides with fluorite structure, we show that numerous previous studies, employing 96-atom supercells, misidentify the ground state structure of (charge neutral) Schottky defects. We show that the error is eliminated by employing larger cells (324, 768 and 1500 atoms), and careful analysis determines that elastic effects, not electrostatic, are responsible. The spurious self-interaction was also observed in non-oxide ionic compounds and irrespective of the computational method used, thereby resolving long standing discrepancies between DFT and force-field methods, previously attributed to the level of theory. The surprising magnitude of the elastic effects are a cautionary tale for defect calculations in ionic materials, particularly when employing computationally expensive methods (e.g. hybrid functionals) or when modelling large defect clusters. We propose two computationally practicable methods to test the magnitude of the elastic self-interaction in any ionic system. In commonly studies oxides, where electrostatic effects would be expected to be dominant, it is the elastic effects that dictate the need for larger supercells | greater than 96 atoms.« less
Importance of elastic finite-size effects: Neutral defects in ionic compounds

NASA Astrophysics Data System (ADS)

Burr, P. A.; Cooper, M. W. D.

2017-09-01

Small system sizes are a well-known source of error in density functional theory (DFT) calculations, yet computational constraints frequently dictate the use of small supercells, often as small as 96 atoms in oxides and compound semiconductors. In ionic compounds, electrostatic finite-size effects have been well characterized, but self-interaction of charge-neutral defects is often discounted or assumed to follow an asymptotic behavior and thus easily corrected with linear elastic theory. Here we show that elastic effects are also important in the description of defects in ionic compounds and can lead to qualitatively incorrect conclusions if inadequately small supercells are used; moreover, the spurious self-interaction does not follow the behavior predicted by linear elastic theory. Considering the exemplar cases of metal oxides with fluorite structure, we show that numerous previous studies, employing 96-atom supercells, misidentify the ground-state structure of (charge-neutral) Schottky defects. We show that the error is eliminated by employing larger cells (324, 768, and 1500 atoms), and careful analysis determines that elastic, not electrostatic, effects are responsible. The spurious self-interaction was also observed in nonoxide ionic compounds irrespective of the computational method used, thereby resolving long-standing discrepancies between DFT and force-field methods, previously attributed to the level of theory. The surprising magnitude of the elastic effects is a cautionary tale for defect calculations in ionic materials, particularly when employing computationally expensive methods (e.g., hybrid functionals) or when modeling large defect clusters. We propose two computationally practicable methods to test the magnitude of the elastic self-interaction in any ionic system. In commonly studied oxides, where electrostatic effects would be expected to be dominant, it is the elastic effects that dictate the need for larger supercells: greater than 96 atoms.
Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection.

PubMed

Liu, Bingyi; Zhao, Wenyu; Jiang, Yongyuan

2016-12-05

As the two dimensional version of the functional wavefront manipulation metamaterial, metasurface has become a research hot spot for engineering the wavefront at will with a subwavelength thickness. The wave scattered by the gradient metasurface, which is composed by the periodic supercells, is governed by the generalized Snell's law. However, the critical angle that derived from the generalized Snell's law circles the domain of the incident angles that allow the occurrence of the anomalous reflection and refraction, and no free space scattering waves could exist when the incident angle is beyond the critical angle. Here we theoretically demonstrate that apparent negative reflection can be realized by a gradient acoustic metasurface when the incident angle is beyond the critical angle. The underlying mechanism of the apparent negative reflection is understood as the higher order diffraction arising from the interaction between the local phase modulation and the non-local effects introduced by the supercell periodicity. The apparent negative reflection phenomena has been perfectly verified by the calculated scattered acoustic waves of the reflected gradient acoustic metasurface. This work may provide new freedom in designing functional acoustic signal modulation devices, such as acoustic isolator and acoustic illusion device.
Discriminating a deep defect from shallow acceptors in supercell calculations: gallium antisite in GaAs

NASA Astrophysics Data System (ADS)

Schultz, Peter

To make reliable first principles predictions of defect energies in semiconductors, it is crucial to discriminate between effective-mass-like defects--for which existing supercell methods fail--and deep defects--for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a framework of level occupation patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BAs. This systematic analysis determines that the gallium antisite is inconsistent with a shallow state, and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, predicting that the Ga antisite is a deep double acceptor and has two donor states, one of which might be accidentally shallow. -- Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
A new DFT approach to model small polarons in oxides with proper account for long-range polarization

NASA Astrophysics Data System (ADS)

Kokott, Sebastian; Levchenko, Sergey V.; Scheffler, Matthias; Theory Department Team

In this work, we address two important challenges in the DFT description of small polarons (excess charges localized within one unit cell): sensitivity to the errors in exchange-correlation (XC) treatment and finite-size effects in supercell calculations. The polaron properties are obtained using a modified neutral potential-energy surface (PES). Using the hybrid HSE functional and considering the whole range 0 <= α <= 1 , we show that the modified PES model significantly reduces the dependence of the polaron level and binding energy in MgO and TiO2 on the XC functional. It does not eliminate the dependence on supercell size. Based on Pekar's model, we derive the proper long-range behavior of the polaron and a finite-size correction that allows to obtain the polaron properties in the dilute limit (tested for supercells containing up to 1,000 atoms). The developed approach reduces drastically the computational time for exploring the polaron PES, and gives a consistent description of polarons for the whole range of α. It allowed us to find a self-trapped hole in MgO that is noticeably more stable than reported previously. partially supported by UniCat (Deutsche Forschungsgemeinschaft).
Pre-Launch Algorithms and Risk Reduction in Support of the Geostationary Lightning Mapper for GOES-R and Beyond

NASA Technical Reports Server (NTRS)

Goodman, Steven; Blakeslee, Richard; Koshak, William; Petersen, Walt; Buechler, Dennis; Krehbiel, Paul; Gatlin, Patrick; Zubrick, Steven

2008-01-01

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk as part of a 3-axis stabilized, geostationary weather satellite system. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series with a planned launch in 2014 will carry a GLM that will provide continuous day and night observations of lightning from the west coast of Africa (GOES-E) to New Zealand (GOES-W) when the constellation is fully operational.The mission objectives for the GLM are to 1) provide continuous,full-disk lightning measurements for storm warning and Nowcasting, 2) provide early warning of tornadic activity, and 3) accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997-Present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. Instrument formulation studies were completed in March 2007 and the implementation phase to develop a prototype model and up to four flight units is expected to begin in latter part of the year. In parallel with the instrument development, a GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2B algorithms and applications. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) sate]lite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama and the Washington DC Metropolitan area) are being used to develop the pre-launch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution. Real time lightning mapping data provided to selected National Weather Service forecast offices in Southern and Eastern Region are also improving our understanding of the application of these data in the severe storm warning process and help to accelerate the development of the pre-launch algorithms and Nowcasting applications. Abstract for the 3 rd Conference on Meteorological
WRF-Chem Simulations of Lightning-NOx Production and Transport in Oklahoma and Colorado Thunderstorms Observed During DC3

NASA Technical Reports Server (NTRS)

Cummings, Kristin A.; Pickering, Kenneth E.; Barth, M.; Bela, M.; Li, Y.; Allen, D.; Bruning, E.; MacGorman, D.; Rutledge, S.; Basarab, B.;

2016-01-01

The focus of this analysis is on lightning-generated nitrogen oxides (LNOx) and their distribution for two thunderstorms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign in May-June 2012. The Weather Research and Forecasting Chemistry (WRF-Chem) model is used to perform cloud-resolved simulations for the May 29-30 Oklahoma severe convection, which contained one supercell, and the June 6-7 Colorado squall line. Aircraft and ground-based observations (e.g., trace gases, lightning and radar) collected during DC3 are used in comparisons against the model-simulated lightning flashes generated by the flash rate parameterization schemes (FRPSs) incorporated into the model, as well as the model-simulated LNOx predicted in the anvil outflow. Newly generated FRPSs based on DC3 radar observations and Lightning Mapping Array data are implemented in the model, along with previously developed schemes from the literature. The results of these analyses will also be compared between storms to investigate which FRPSs were most appropriate for the two types of convection and to examine the variation in the LNOx production. The simulated LNOx results from WRF-Chem will also be compared against other previously studied mid-latitude thunderstorms.

Tornadoes and other atmospheric vortices

NASA Technical Reports Server (NTRS)

Deissler, R. G.

1976-01-01

The growth of random vortices in an atmosphere with buoyant instability and vertical wind shear is studied along with the velocities in a single gravity-driven vortex; a frictionless adiabatic model which is supported by laboratory experiments is first considered. The effects of axial drag, heat transfer, and precipitation-induced downdrafts are then calculated. Heat transfer and axial drag tend to have stabilizing effects; they reduce the downdrafts of updrafts due to buoyancy. It is found that downdrafts or tornadic magnitude might occur in negatively-buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. Conditions under which radial-inflow velocities become sufficiently large to produce tangential velocities of tornadic magnitude are determined. The radial velocities in the outer regions, as well as the tangential velocities in the inner regions may be large enough to cause damage. The surface boundary layer, which is a region where large radial inflows can occur, is studied, and the thickness of the radial-inflow friction layer is estimated. A tornado model which involves a rotating parent cloud, as well as buoyancy and precipitation effects, is discussed.
Examining Rotational Ground Motion Induced by Tornados

NASA Astrophysics Data System (ADS)

Kessler, Elijah; Dunn, Robert

2016-03-01

Ring lasers are well known for their ability to detect rotation and to serve as replacements for mechanical gyroscopes. The sensitivity of large ring lasers to various forms of ground motion is less familiar. Since ring lasers preferentially measure rotational ground motion and a standard seismograph is designed to measure translational and vertical ground motion, each device responds to different aspects of ground movement. Therefore, the two instruments will be used to explore responses to microseisms, earthquake generated shear waves, and in particular tornado generated ground movement. On April 27, 2014 an EF4 tornado devastated Vilonia, AR a small town ~ 21 km from the Hendrix College ring laser. The proximity of the tornado's path to the ring laser interferometer and to a seismograph located in Vilonia provided the opportunity to examine the response of these instruments to tornadic generated ground motion. Our measurements suggest tornadic weather systems can produce both rotational and lateral ground motion. This contention is supported by an after the fact damage survey which found that the tornado flattened a forest in which trees were uprooted and laid down in a pair of converging arcs with the centerline pointed in the direction of the tornado's path.
Strain field of the monovacancy in silicene: First-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Rui, E-mail: rli-lynu@163.com; Liu, Zhongli; Ma, Wenqiang

The in-plane strain fields of single-vacancy silicene with different monovacancy (MV) concentrations, as well as the corresponding electronic band structures, are investigated by using the first-principle calculations. Firstly the self-healing MV is found to be the most stable ground structure in silicene, which is different from the other 2D hexagonal honeycomb materials, e.g. graphene, h-BN. In the isolated MV center, the bonds along the pentagons are compressed, creating a compress field, and those close to the distorted hexagons are stretched, creating a stretch field. As the MV concentration increasing, the interacted compress field tends to corrugate the defected silicene, whilemore » the interacted stretch field impacts little on the low-buckled structure. Especially, the corrugation presents in those supercells with small MV concentration, just as the (4, 5), (4, 6), (4, 7), (4, 8) supercells. The corrugations approach zero at both low and high MV concentrations, and the (4, 6) supercell with a MV concentration of about 0.021, has a peak value of 3.23Å. The electronic calculations show that the linear dispersion at Γ point in pristine silicene is broken by the lower lattice symmetry of the self-healing MV reconstruction, which translates it into metal as well.« less
Steering elastic SH waves in an anomalous way by metasurface

NASA Astrophysics Data System (ADS)

Cao, Liyun; Yang, Zhichun; Xu, Yanlong

2018-03-01

Metasurface, which does not exist in nature, has exhibited exotic essence on the manipulation of both electromagnetic and acoustic waves. In this paper, the concept of metasurface is extended to the field of elastic SH waves, and the anomalous refractions of SH waves across the designed elastic SH wave metasurfaces (SHWMs) are demonstrated numerically. Firstly, a SHWM is designed with supercells, each supercell is composed of four subunits. It is demonstrated that this configuration has the ability of deflecting the vertical and oblique incident waves in an arbitrary desired direction. Then, a unique SHWM with supercell composed of only two subunits is designed. Numerical simulation shows its ability of splitting the vertical and oblique incident waves into two tunable transmitted wave beams, respectively. In the process of steering SH waves, it is also found that two kinds of leakages of transmitted waves across the designed SHWM will occur in some particular situations, which will affect the desired transmitted wave. The mechanisms of the leakages, which are different from that of the common high-order diffraction mentioned in existing literatures, are revealed. The current study can offer theoretical guidance not only for designing devices of directional ultrasonic detection and splitting SH waves but also for steering other kinds of classical waves.
System-size convergence of point defect properties: The case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Corsetti, Fabiano; Mostofi, Arash A.

2011-07-01

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Γ-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Γ-point quickly converges to a fixed value which correctly describes the bonding at the defect center. Our calculated transition levels with 1000-atom supercells and Γ-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect center that verifies the canonical Watkins model.

Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection

PubMed Central

Liu, Bingyi; Zhao, Wenyu; Jiang, Yongyuan

2016-01-01

As the two dimensional version of the functional wavefront manipulation metamaterial, metasurface has become a research hot spot for engineering the wavefront at will with a subwavelength thickness. The wave scattered by the gradient metasurface, which is composed by the periodic supercells, is governed by the generalized Snell’s law. However, the critical angle that derived from the generalized Snell’s law circles the domain of the incident angles that allow the occurrence of the anomalous reflection and refraction, and no free space scattering waves could exist when the incident angle is beyond the critical angle. Here we theoretically demonstrate that apparent negative reflection can be realized by a gradient acoustic metasurface when the incident angle is beyond the critical angle. The underlying mechanism of the apparent negative reflection is understood as the higher order diffraction arising from the interaction between the local phase modulation and the non-local effects introduced by the supercell periodicity. The apparent negative reflection phenomena has been perfectly verified by the calculated scattered acoustic waves of the reflected gradient acoustic metasurface. This work may provide new freedom in designing functional acoustic signal modulation devices, such as acoustic isolator and acoustic illusion device. PMID:27917909
a Numerical Simulation of a Tornado-Scale Vortex in a Three-Dimensional Cloud Model

NASA Astrophysics Data System (ADS)

Wicker, Louis John

1990-01-01

One of the more spectacular and elusive events of nature is the tornado. Usually spawned by a highly organized, lasting, and rotating thunderstorm called a "supercell", tornadoes are one of the most destructive atmospheric phenomena. Tornadoes almost always have length and time scales smaller than the measurable scales within the observing network of surface stations, conventional radar, Doppler radar and satellites. Therefore direct observations of tornadoes and their parent features are rarely obtained. Consequently, understanding of these phenomena will generally have to come from theoretical work, laboratory experiments, and numerical simulations. In this thesis we seek to understand the process of tornadogenesis within the context of a fully three-dimensional cloud model. Very high horizontal and vertical resolution is used to capture a developing tornado-scale vortex during the simulation of a strongly rotating supercell storm simulated within the 3 April 1964 environment from Witchita Fall, Texas. To better represent the influence of surface friction on the vortex flow, a simple surface layer parametrization of the vertical fluxes of horizontal momentum is added to the model. Results from the simulation show that a tornado -scale vortex forms along the western edge of the mesocyclone, intensifies and rotates cyclonically around the center of the mesocyclone over a several minute period. The inclusion of the surface layer parameterization increases the low -level velocity convergence. Surface vertical vorticity is greater than 0.43 s^{-1} for thirty seconds and greater than 0.3 s^ {-1} for several minutes. During tornadogenesis, pressures at the surface fall 3-4 mb in thirty seconds and a pressure gradient develops of over 7 mb from the outer edge of the tornado to the center. A vortex tube extends from the surface to over 2.5 km aloft and tilts to the northwest. Analyses show that tornadogenesis occurs when the vertical velocity gradients along the western side of the mesocyclone increase and that the principle mechanism for intensifying the vertical vorticity is convergence. Analyses also show that the development of the occlusion updraft along the western edge of the mesocyclone is related to advection of warm air southwestward over the gust front and the lowering of pressure aloft within the mesocyclone core.
Investigations of severe/tornadic thunderstorm development and evolution based on satellite and AVE/SESAME/VAS data

NASA Technical Reports Server (NTRS)

Vonderhaar, T. H.; Purdom, J. F. W.

1984-01-01

The use of rapid scan satellite imagery to investigate the local environment of severe thunderstorms is discussed. Mesoscale cloud tracking and vertical wind shear as it affects thunderstorm relative flow are mentioned. The role of pre-existing low level cloud cover in the outbreak of tornadoes was investigated. Applying visible atmospheric sounding imagery to mesoscale phenomena is also addressed.
Visions of Our Planet's Atmosphere, Land & Oceans - ETheater Presentation

NASA Technical Reports Server (NTRS)

Hasler, F.

2000-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to Florida and the KSC Visitor's Center. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer hurricanes & tornadic thunderstorms. See the latest spectacular images from NASA and NOAA remote sensing missions like GOES, NOAA, TRMM, SeaWiFS, Landsat7, & new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran and Linda. See visualizations featured on covers of ma'gazines like Newsweek, TIME, National Geographic, Popular Science and on National & International Network TV. New Digital Earth visualization tools allow us to roam & zoom through massive global images including a Landsat tour of the US, with drill-downs into major cities using 1 m resolution spy-satellite technology from the Space Imaging IKONOS satellite. Spectacular new visualizations of the global atmosphere & oceans are shown. See massive dust storms sweeping across Africa. See ocean vortexes and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUS, 5 Gigabytes of RAM and Terabyte disk using two projectors across the super sized Universe Theater panoramic screen.
In search of discernible infrasound emitted by numerically simulated tornadoes

NASA Astrophysics Data System (ADS)

Schecter, David A.

2012-09-01

The comprehensive observational study of Bedard (2005) provisionally found that the infrasound of a tornado is discernible from the infrasound of generic cloud processes in a convective storm. This paper discusses an attempt to corroborate the reported observations of distinct tornado infrasound with numerical simulations. Specifically, this paper investigates the infrasound of an ordinary tornado in a numerical experiment with the Regional Atmospheric Modeling System, customized to simulate acoustic phenomena. The simulation has no explicit parameterization of microphysical cloud processes, but creates an unsteady tornado of moderate strength by constant thermal forcing in a rotational environment. Despite strong fluctuations in the lower corner flow and upper outflow regions, a surprisingly low level of infrasound is radiated by the vortex. Infrasonic pressure waves in the 0.1 Hz frequency regime are less intense than those which could be generated by core-scale vortex Rossby (VR) waves of modest amplitude in similar vortices. Higher frequency infrasound is at least an order of magnitude weaker than expected based on infrasonic observations of tornadic thunderstorms. Suppression of VR waves (and their infrasound) is explained by the gradual decay of axial vorticity with increasing radius from the center of the vortex core. Such non-Rankine wind-structure is known to enable the rapid damping of VR waves by inviscid mechanisms, including resonant wave-mean flow interaction and "spiral wind-up" of vorticity. Insignificant levels of higher frequency infrasound may be due to oversimplifications in the computational setup, such as the neglect of thermal fluctuations caused by phase transitions of moisture in vigorous cloud turbulence.
GOES-R Geostationary Lightning Mapper Performance Specifications and Algorithms

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Goodman, Steven J.; Blakeslee, Richard J.; Koshak, William J.; Petersen, William A.; Boldi, Robert A.; Carey, Lawrence D.; Bateman, Monte G.; Buchler, Dennis E.; McCaul, E. William, Jr.

2008-01-01

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR imager/optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series will carry a GLM that will provide continuous day and night observations of lightning. The mission objectives for the GLM are to: (1) Provide continuous, full-disk lightning measurements for storm warning and nowcasting, (2) Provide early warning of tornadic activity, and (2) Accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997- present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2 algorithms and applications. The science data will consist of lightning "events", "groups", and "flashes". The algorithm is being designed to be an efficient user of the computational resources. This may include parallelization of the code and the concept of sub-dividing the GLM FOV into regions to be processed in parallel. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama, Oklahoma, Central Florida, and the Washington DC Metropolitan area) are being used to develop the prelaunch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution.
A Presentation of Spectracular Visualizations

NASA Technical Reports Server (NTRS)

Hasler, Fritz; Pierce, Hal; Einaudi, Franco (Technical Monitor)

2000-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to Florida and the KSC Visitor's Center. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer hurricanes & tornadic thunderstorms. See the latest spectacular images from NASA and NOAA remote sensing missions like GOES, NOAA, TRMM, SeaWiFS, Landsat7, & new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran and Linda. See visualizations featured on covers of magazines like Newsweek, TIME, National Geographic, Popular Science and on National & International Network TV. New Digital Earth visualization tools allow us to roam & zoom through massive global images including a Landsat tour of the US, with drill-downs into major cities using I m resolution spy-satellite technology from the Space Imaging IKONOS satellite. Spectacular new visualizations of the global atmosphere & oceans are shown. See massive dust storms sweeping across Africa. See ocean vortexes and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUs, 5 Gigabytes of RAM and Terabyte disk using two projectors across the super sized Universe Theater panoramic screen.
Visions of Our Planet's Atmosphere, Land and Oceans: Electronic-Theater 2000

NASA Technical Reports Server (NTRS)

Hasler, A. F.

2000-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to the Delaware Bay and Philadelphia area. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer tropical cyclones & tornadic thunderstorms. See the latest spectacular images from NASA, NOAA & UMETSAT remote sensing missions like GOES, Meteosat, NOAA, TRMM, SeaWiFS, Landsat7, & new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran and Linda. see visualizations featured on covers of magazines like Newsweek, TIME, National Geographic, Popular Science and on National & International Network TV. New Digital Earth visualization tools allow us to roam & zoom through massive global images including Landsat tours of the US, and Africa with drill downs of major global cities using 1 m resolution commercialized spy-satellite technology from the Space Imaging IKONOS satellite. Spectacular new visualizations of the global atmosphere & oceans are shown. See massive dust storms sweeping across Africa. see ocean vortexes and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUs, 5 Gigabytes of RAM and Terabyte disk using two projectors across a super sized panoramic screen.
NASA/NOAA/AMS Earth Science Electronic Theatre

NASA Technical Reports Server (NTRS)

Hasler, Fritz; Pierce, Hal; Einaudi, Franco (Technical Monitor)

2001-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to Florida and the KSC Visitor's Center. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer hurricanes & tornadic thunderstorms. See the latest spectacular images from NASA and NOAA remote sensing missions like GOES, NOAA, TRMM, SeaWiFS, Landsat 7, & new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran and Linda. See visualizations featured on covers of magazines like Newsweek, TIME, National Geographic, Popular Science and on National & International Network TV. New Digital Earth visualization tools allow us to roam & zoom through massive global images including a Landsat tour of the US, with drill-downs into major cities using 1 m resolution spy-satellite technology from the Space Imaging IKONOS satellite, Spectacular new visualizations of the global atmosphere & oceans are shown. See massive dust storms sweeping across Africa. See ocean vortexes and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUs, 5 Gigabytes of RAM and Terabyte disk using two projectors across the super sized Universe Theater panoramic screen.
A Presentation of Spectacular Visualizations. Visions of Our Planet's Atmosphere, Land and Oceans: ETheater Presentation

NASA Technical Reports Server (NTRS)

Hasler, Fritz; Pierce, Hal; Einaudi, Franco (Technical Monitor)

2000-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to Florida and the KSC Visitor's Center. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer hurricanes & tornadic thunderstorms. See the latest spectacular images from NASA and NOAA remote sensing missions like GOES, NOAA, TRMM, SeaWiFS, Landsat7, & new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran and Linda. See visualizations featured on covers of magazines like Newsweek, TIME, National Geographic, Popular Science and on National & International Network TV. New Digital Earth visualization tools allow us to roam & zoom through massive global images including a Landsat tour of the US, with drill-downs into major cities using 1 m resolution spy-satellite technology from the Space Imaging IKONOS satellite. Spectacular new visualizations of the global atmosphere & oceans are shown. See massive dust storms sweeping across Africa. See ocean vortices and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUs, 5 Gigabytes of RAM and Terabyte disk using two projectors across the super sized Universe Theater panoramic screen.
Cross-Plane Seebeck Coefficient Measurement of Misfit Layered Compounds (SnSe)n(TiSe2)n (n = 1,3,4,5).

PubMed

Li, Zhen; Bauers, Sage R; Poudel, Nirakar; Hamann, Danielle; Wang, Xiaoming; Choi, David S; Esfarjani, Keivan; Shi, Li; Johnson, David C; Cronin, Stephen B

2017-03-08

We report cross-plane thermoelectric measurements of misfit layered compounds (SnSe) n (TiSe 2 ) n (n = 1,3,4,5), approximately 50 nm thick. Metal resistance thermometers are fabricated on the top and bottom of the (SnSe) n (TiSe 2 ) n material to measure the temperature difference and heat transport through the material directly. By varying the number of layers in a supercell, n, we vary the interface density while maintaining a constant global stoichiometry. The Seebeck coefficient measured across the (SnSe) n (TiSe 2 ) n samples was found to depend strongly on the number of layers in the supercell (n). When n decreases from 5 to 1, the cross-plane Seebeck coefficient decreases from -31 to -2.5 μV/K, while the cross-plane effective thermal conductivity decreases by a factor of 2, due to increased interfacial phonon scattering. The cross-plane Seebeck coefficients of the (SnSe) n (TiSe 2 ) n are very different from the in-plane Seebeck coefficients, which are higher in magnitude and less sensitive to the number of layers in a supercell, n. We believe this difference is due to the different carrier types in the n-SnSe and p-TiSe 2 layers and the effect of tunneling on the cross-plane transport.
Catastrophic wind damage to North American forests and the potential impact of climate change.

PubMed

Peterson, C J

2000-11-15

Catastrophic winds from tornadoes and downbursts are a major cause of natural disturbance in forests of eastern North America, accounting for thousands of hectares of disturbed area annually. Wind disturbance shows substantial regional variation, decreasing from the mid-west to the east and from the south-east to New England. In terms of the relative importance among these types of storms, more forest damage results from tornadoes in the south-east and mid-west, while downbursts are the most important type of wind disturbance in the Great Lakes area. Downbursts vary widely in size, but large ones can damage thousands of hectares, while tornadoes are much smaller, seldom affecting more than several hundred hectares. Tornadoes cause the most severe wind disturbances. Site characteristics such as physiography, soil moisture, and soil depth; stand characteristics like density and canopy roughness; and tree characteristics such as size, species, rooting depth, and wood strength, are the factors most recognized as influencing damage patterns. The consequences of wind damage to forests, such as change in environmental conditions, density, size structure, species composition, and successional status, occur on both immediate (hours-to-days) and long-term (months-to-decades) time scales. Most wind disturbances result in the post-disturbance vegetation being comprised of surviving canopy trees, and varying amounts of sprouts, released understory stems, and new seedlings. Stand size structure is usually reduced, and successional status of a forest is often advanced. Diversity can be either increased or decreased, depending on the measure of abundance used to calculate diversity. Because tornadoes and downbursts are in part products of thermodynamic climatic circumstances, they may be affected by anticipated changes in climatic conditions as the 21st century progresses. However, the current understanding of tornado and downburst formation from supercell storms is very incomplete, and climate-change model predictions sufficiently coarse, that predictions of changes in frequency, size, intensity, or timing of these extreme events must be regarded as highly uncertain. Moreover, retrospective approaches that employ tree demography and dendrochronology require prohibitively large sample sizes to resolve details of the relationship between climate fluctuations and characteristics of these storms. To improve predictions of changes in the climatology of these storms, we need improved understanding of the genesis of tornadoes and downbursts within thunderstorms, and greater resolution in global climate models. To improve coping strategies, forest scientists can contribute by giving more attention to how various silvicultural actions influence stand and tree vulnerability. Finally, increased focus on the dynamics of forest recovery and regrowth may suggest management actions that can facilitate desired objectives after one of these unpredictable wind disturbances.
Low-Level Outflow Potential of Non-Tornadic Thunderstorms Inferred from Single-Doppler Radar

DTIC Science & Technology

1988-01-01

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Ab initio investigation of competing antiferromagnetic structures in low Si-content FeMn(PSi) alloy

NASA Astrophysics Data System (ADS)

Li, Guijiang; Eriksson, Olle; Johansson, Börje; Vitos, Levente

2016-06-01

The antiferromagnetic structures of a low Si-content FeMn(PSi) alloy were investigated by first principles calculations. One possible antiferromagnetic structure in supercell along the c-axis was revealed in FeMnP0.75Si0.25 alloy. It was found that atomic disorder occupation between Fe atom on 3f and Mn atoms on 3g sites is responsible for the formation of antiferromagnetic structures. Furthermore the magnetic competition and the coupling between possible AFM supercells along the c and a-axis can promote a non-collinear antiferromagnetic structure. These theoretical investigations help to deeply understand the magnetic order in FeMn(PSi) alloys and benefit to explore the potential magnetocaloric materials in Fe2P-type alloys.
Simultaneous Estimation of Microphysical Parameters and Atmospheric State Variables With Radar Data and Ensemble Square-root Kalman Filter

NASA Astrophysics Data System (ADS)

Tong, M.; Xue, M.

2006-12-01

An important source of model error for convective-scale data assimilation and prediction is microphysical parameterization. This study investigates the possibility of estimating up to five fundamental microphysical parameters, which are closely involved in the definition of drop size distribution of microphysical species in a commonly used single-moment ice microphysics scheme, using radar observations and the ensemble Kalman filter method. The five parameters include the intercept parameters for rain, snow and hail/graupel, and the bulk densities of hail/graupel and snow. Parameter sensitivity and identifiability are first examined. The ensemble square-root Kalman filter (EnSRF) is employed for simultaneous state and parameter estimation. OSS experiments are performed for a model-simulated supercell storm, in which the five microphysical parameters are estimated individually or in different combinations starting from different initial guesses. When error exists in only one of the microphysical parameters, the parameter can be successfully estimated without exception. The estimation of multiple parameters is found to be less robust, with end results of estimation being sensitive to the realization of the initial parameter perturbation. This is believed to be because of the reduced parameter identifiability and the existence of non-unique solutions. The results of state estimation are, however, always improved when simultaneous parameter estimation is performed, even when the estimated parameters values are not accurate.
Novel optical properties of CdS:Zn rocksalt system (a theoretical study)

NASA Astrophysics Data System (ADS)

Khan, M. Junaid Iqbal; Nauman Usmani, M.; Kanwal, Zarfishan

2017-11-01

In present computational study, we focus on optical properties of Zn doped CdS for 1 × 1 × 2 and 2 × 2 × 2 supercell configurations. Cd atoms are substituted with Zn atoms and results for optical properties demonstrate different trends due to interaction of Zn with S atoms. The study has been performed by PBE-GGA approach using Wien2K within framework of DFT. TDOS and PDOS represent that S-3p states are responsible for conduction. For large supercell configuration, a tremendous change in optical properties has been observed due to different bonding. Optical absorption tends to increase in visible range which supports candidacy of Zn doped CdS for enhanced optoelectronic and nanotechnology applications.
Cation disorder in MgX2O4 (X = Al, Ga, In) spinels from first principles

NASA Astrophysics Data System (ADS)

Jiang, Chao; Sickafus, Kurt E.; Stanek, Christopher R.; Rudin, Sven P.; Uberuaga, Blas P.

2012-07-01

We have performed first-principles density functional theory calculations to investigate the possible physical origins of the discrepancies between the existing theoretical and experimental studies on cation distribution in MgX2O4 (X = Al, Ga, In) spinel oxides. We show that for MgGa2O4 and MgIn2O4, it is crucial to consider the effects of lattice vibrations to achieve agreement between theory and experiment. For MgAl2O4, we find that neglecting short-range order effects in thermodynamic modeling can lead to significant underestimation of the degree of inversion. Furthermore, we demonstrate that the common practice of representing disordered structures by randomly exchanging atoms within a small periodic supercell can incur large computational error due to either insufficient statistical sampling or finite supercell size effects.
Random Combinatorial Gradient Metasurface for Broadband, Wide-Angle and Polarization-Independent Diffusion Scattering.

PubMed

Zhuang, Yaqiang; Wang, Guangming; Liang, Jiangang; Cai, Tong; Tang, Xiao-Lan; Guo, Tongfeng; Zhang, Qingfeng

2017-11-29

This paper proposes an easy, efficient strategy for designing broadband, wide-angle and polarization-independent diffusion metasurface for radar cross section (RCS) reduction. A dual-resonance unit cell, composed of a cross wire and cross loop (CWCL), is employed to enhance the phase bandwidth covering the 2π range. Both oblique-gradient and horizontal-gradient phase supercells are designed for illustration. The numerical results agree well with the theoretical ones. To significantly reduce backward scattering, the random combinatorial gradient metasurface (RCGM) is subsequently constructed by collecting eight supercells with randomly distributed gradient directions. The proposed metasurface features an enhanced specular RCS reduction performance and less design complexity compared to other candidates. Both simulated and measured results show that the proposed RCGM can significantly suppress RCS and exhibits broadband, wide-angle and polarization independence features.
Recent Advances in the Tempest UAS for In-Situ Measurements in Highly-Dynamic Environments

NASA Astrophysics Data System (ADS)

Argrow, B. M.; Frew, E.; Houston, A. L.; Weiss, C.

2014-12-01

The spring 2010 deployment of the Tempest UAS during the VORTEX2 field campaign verified that a small UAS, supported by a customized mobile communications, command, and control (C3) architecture, could simultaneously satisfy Federal Aviation Administration (FAA) airspace requirements, and make in-situ thermodynamic measurements in supercell thunderstorms. A multi-hole airdata probe was recently integrated into the Tempest UAS airframe and verification flights were made in spring 2013 to collect in-situ wind measurements behind gust fronts produced by supercell thunderstorms in northeast Colorado. Using instantaneous aircraft attitude estimates from the autopilot, the in-situ measurements were converted to inertial wind estimates, and estimates of uncertainty in the wind measurements was examined. To date, the limited deployments of the Tempest UAS have primarily focused on addressing the engineering and regulatory requirements to conduct supercell research, and the Tempest UAS team of engineers and meteorologists is preparing for deployments with the focus on collecting targeted data for meteorological exploration and hypothesis testing. We describe the recent expansion of the operations area and altitude ceiling of the Tempest UAS, engineering issues for accurate inertial wind estimates, new concepts of operation that include the simultaneous deployment of multiple aircraft with mobile ground stations, and a brief description of our current effort to develop a capability for the Tempest UAS to perform autonomous path planning to maximize energy harvesting from the local wind field for increased endurance.
Treatment of delocalized electron transfer in periodic and embedded cluster DFT calculations: The case of Cu on ZnO (10(1)0).

PubMed

Hellström, Matti; Spångberg, Daniel; Hermansson, Kersti

2015-12-15

We assess the consequences of the interface model-embedded-cluster or periodic-slab model-on the ability of DFT calculations to describe charge transfer (CT) in a particularly challenging case where periodic-slab calculations indicate a delocalized charge-transfer state. Our example is Cu atom adsorption on ZnO(10(1)0), and in fact the periodic slab calculations indicate three types of CT depending on the adsorption site: full CT, partial CT, and no CT. Interestingly, when full CT occurs in the periodic calculations, the calculated Cu atom adsorption energy depends on the underlying ZnO substrate supercell size, since when the electron enters the ZnO it delocalizes over as many atoms as possible. In the embedded-cluster calculations, the electron transferred to the ZnO delocalizes over the entire cluster region, and as a result the calculated Cu atom adsorption energy does not agree with the value obtained using a large periodic supercell, but instead to the adsorption energy obtained for a periodic supercell of roughly the same size as the embedded cluster. Different density functionals (of GGA and hybrid types) and basis sets (local atom-centered and plane-waves) were assessed, and we show that embedded clusters can be used to model Cu adsorption on ZnO(10(1)0), as long as care is taken to account for the effects of CT. © 2015 Wiley Periodicals, Inc.

Exploring links between biomass burning smoke and tornado likelihood: From regional to large-eddy scale simulations

NASA Astrophysics Data System (ADS)

Saide, P. E.; Thompson, G.; Eidhammer, T.; da Silva, A. M., Jr.; Pierce, R. B.; Carmichael, G. R.

2015-12-01

Biomass burning smoke from Central America can have the potential to enhance the likelihood of tornado occurrence and intensity in the SE US by changing the environment where tornadic storms form (Saide et al., GRL 2015). In this presentation we build over this study to further our understanding of these interactions on multiple dimensions: 1) Biomass burning smoke emissions are constrained using an inverse modeling technique to improve the representation of smoke loads and its impacts, 2) The representation of these smoke-tornado interactions are assessed when using a simplified aerosol scheme with the intent of introducing these feedbacks into numerical weather prediction in the future, 3) The occurrence of these interactions is investigated for other tornado outbreaks on the record to learn about their frequency and under what conditions they occur, and 4) Multi-scale simulations are performed from regional to tornado-resolving scales to assess the impact of smoke on the number of tornadoes formed and their EF intensity. Future steps will also be discussed. The image below shows MODIS-Aqua satellite products for 27 April 2011 over the southeast US, Central America and the Gulf of Mexico (GoM), along with tornado tracks (red solid lines, thickness indicates the magnitude of the tornado reports , thickest=5, thinnest=1) for the period from April 26-28. The background is a true color image of the surface, clouds, and smoke, with yellow markers indicating fire detections and an iridescent overlay showing aerosol optical depth (AOD). Red, green and purple colors show high (1.0), medium (0.6) and low (0.1) AOD values. The article by Saide et al. (2015) shows that the increase in aerosol loads in the GoM is produced by fires in Central America, and this smoke is further transported to the southeast US where it can interact with clouds and radiation producing environmental conditions more favorable to significant tornado occurrence for the historical outbreak on 27 April 2011. Satellite true color image, AOD, and fire detection retrievals obtained from the NASA Level 1 and Atmosphere Archive and Distribution System (LAADS); Tornado reports obtained from the NOAA Storm Prediction Center; imagery courtesy of Brad Pierce NOAA Satellite and Information Service (NESDIS) Center for Satellite Applications and Research (STAR).
Pre-Launch Algorithms and Risk Reduction in Support of the Geostationary Lightning Mapper for GOES-R and Beyond

NASA Technical Reports Server (NTRS)

Goodman, Steven J.; Blakeslee, R. J.; Koshak, W.; Petersen, W.; Buechler, D. E.; Krehbiel, P. R.; Gatlin, P.; Zubrick, S.

2008-01-01

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR imager/optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk as part of a 3-axis stabilized, geostationary weather satellite system. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series with a planned launch in 2014 will carry a GLM that will provide continuous day and night observations of lightning from the west coast of Africa (GOES-E) to New Zealand (GOES-W) when the constellation is fUlly operational. The mission objectives for the GLM are to 1) provide continuous, full-disk lightning measurements for storm warning and nowcasting, 2) provide early warning of tornadic activity, and 3) accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997-Present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. Instrument formulation studies were completed in March 2007 and the implementation phase to develop a prototype model and up to four flight models is expected to be underway in the latter part of 2007. In parallel with the instrument development, a GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2 ground processing algorithms and applications. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama and the Washington DC Metropolitan area)
A Presentation of Spectacular Visualizations

NASA Technical Reports Server (NTRS)

Hasler, Fritz; Einaudi, Franco (Technical Monitor)

2000-01-01

The NASA/NOAA/AMS Earth Science Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to Florida and the KSC Visitor's Center. Go back to the early weather satellite images from the 1960s see them contrasted with the latest International global satellite weather movies including killer hurricanes and tornadic thunderstorms. See the latest spectacular images from NASA and the National Oceanic and Atmospheric Administration (NOAA) remote sensing missions like the Geostationary Operational Environmental Satellites (GOES), NOAA, Tropical Rainfall Measuring Mission (TRMM), SeaWiFS, Landsat7, and new Terra which will be visualized with state-of-the art tools. Shown in High Definition TV resolution (2048 x 768 pixels) are visualizations of hurricanes Lenny, Floyd, Georges, Mitch, Fran, and Linda. See visualizations featured on covers of magazines like Newsweek, TIME, National Geographic, Popular Science, and on National and International Network TV. New Digital Earth visualization tools allow us to roam and zoom through massive global images including a Landsat tour of the US, with drill-downs into major cities using one meter resolution spy-satellite technology from the Space Imaging IKONOS satellite. Spectacular new visualizations of the global atmosphere and oceans are shown. See massive dust storms sweeping across Africa. See ocean vortexes and currents that bring up the nutrients to feed tiny plankton and draw the fish, giant whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with dual CPUs, 5 Gigabytes of RAM and Terabyte disk using two projectors across the super sized Universe Theater panoramic screen.
Numerical simulation of tornadoes' meteorological conditions over Greece: A case study of tornadic activity over NW Peloponnese on March 25, 2009

NASA Astrophysics Data System (ADS)

Matsangouras, Ioannis T.; Nastos, Panagiotis T.; Pytharoulis, Ioannis

2014-05-01

Recent research revealed that NW Peloponnese, Greece is an area that favours pre-frontal tornadic incidence. This study presents the results of the synoptic analysis of the meteorological conditions during a tornado event over NW Peloponnese on March 25, 2009. Further, the role of topography in tornado genesis is examined. The tornado was formed approximately at 10:30 UTC, south-west of Vardas village, crossed the Nea Manolada and faded away at Lappas village, causing several damage. The length of its track was approximately 9-10 km and this tornado was characterized as F2 (Fujita scale) or T4-T5 in TORRO intensity scale. Synoptic analysis was based on ECMWF datasets, as well as on daily composite mean and anomaly of the geopotential heights at the middle and lower troposphere from NCEP/NCAR reanalysis. In addition, numerous datasets derived from weather observations and remote sensing were used in order to interpret better the examined extreme event. Finally, a numerical simulation was performed using the non-hydrostatic Weather Research and Forecasting model (WRF), initialized with ECMWF gridded analyses, with telescoping nested grids that allow the representation of atmospheric circulations ranging from the synoptic scale down to the meso-scale. In the numerical simulations the topography of the inner grid was modified by: a) 0% (actual topography) and b) -100% (without topography).
Computational studies of physical properties of Nb-Si based alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Lizhi

2015-04-16

The overall goal is to provide physical properties data supplementing experiments for thermodynamic modeling and other simulations such as phase filed simulation for microstructure and continuum simulations for mechanical properties. These predictive computational modeling and simulations may yield insights that can be used to guide materials design, processing, and manufacture. Ultimately, they may lead to usable Nb-Si based alloy which could play an important role in current plight towards greener energy. The main objectives of the proposed projects are: (1) developing a first principles method based supercell approach for calculating thermodynamic and mechanic properties of ordered crystals and disordered latticesmore » including solid solution; (2) application of the supercell approach to Nb-Si base alloy to compute physical properties data that can be used for thermodynamic modeling and other simulations to guide the optimal design of Nb-Si based alloy.« less
Mercury Wet Scavenging and Deposition Differences by Precipitation Type.

PubMed

Kaulfus, Aaron S; Nair, Udaysankar; Holmes, Christopher D; Landing, William M

2017-03-07

We analyze the effect of precipitation type on mercury wet deposition using a new database of individual rain events spanning the contiguous United States. Measurements from the Mercury Deposition Network (MDN) containing single rainfall events were identified and classified into six precipitation types. Mercury concentrations in surface precipitation follow a power law of precipitation depth that is modulated by precipitation system morphology. After controlling for precipitation depth, the highest mercury deposition occurs in supercell thunderstorms, with decreasing deposition in disorganized thunderstorms, quasi-linear convective systems (QLCS), extratropical cyclones, light rain, and land-falling tropical cyclones. Convective morphologies (supercells, disorganized, and QLCS) enhance wet deposition by a factor of at least 1.6 relative to nonconvective morphologies. Mercury wet deposition also varies by geographic region and season. After controlling for other factors, we find that mercury wet deposition is greater over high-elevation sites, seasonally during summer, and in convective precipitation.
Broadband high-efficiency half-wave plate: a supercell-based plasmonic metasurface approach.

PubMed

Ding, Fei; Wang, Zhuoxian; He, Sailing; Shalaev, Vladimir M; Kildishev, Alexander V

2015-04-28

We design, fabricate, and experimentally demonstrate an ultrathin, broadband half-wave plate in the near-infrared range using a plasmonic metasurface. The simulated results show that the linear polarization conversion efficiency is over 97% with over 90% reflectance across an 800 nm bandwidth. Moreover, simulated and experimental results indicate that such broadband and high-efficiency performance is also sustained over a wide range of incident angles. To further obtain a background-free half-wave plate, we arrange such a plate as a periodic array of integrated supercells made of several plasmonic antennas with high linear polarization conversion efficiency, consequently achieving a reflection-phase gradient for the cross-polarized beam. In this design, the anomalous (cross-polarized) and the normal (copolarized) reflected beams become spatially separated, hence enabling highly efficient and robust, background-free polarization conversion along with broadband operation. Our results provide strategies for creating compact, integrated, and high-performance plasmonic circuits and devices.
Tornado risks and design windspeeds for the Oak Ridge Plant Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1975-08-01

The effects of tornadoes and other extreme winds should be considered in establishing design criteria for structures to resist wind loads. Design standards that are incorporated in building codes do not normally include the effects of tornadoes in their wind load criteria. Some tornado risk models ignore the presence of nontornadic extreme winds. The purpose of this study is to determine the probability of tornadic and straight winds exceeding a threshold value in the geographical region surrounding the Oak Ridge, Tennessee plant site.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Rouxelin, Pascal Nicolas; Strydom, Gerhard

Best-estimate plus uncertainty analysis of reactors is replacing the traditional conservative (stacked uncertainty) method for safety and licensing analysis. To facilitate uncertainty analysis applications, a comprehensive approach and methodology must be developed and applied. High temperature gas cooled reactors (HTGRs) have several features that require techniques not used in light-water reactor analysis (e.g., coated-particle design and large graphite quantities at high temperatures). The International Atomic Energy Agency has therefore launched the Coordinated Research Project on HTGR Uncertainty Analysis in Modeling to study uncertainty propagation in the HTGR analysis chain. The benchmark problem defined for the prismatic design is represented bymore » the General Atomics Modular HTGR 350. The main focus of this report is the compilation and discussion of the results obtained for various permutations of Exercise I 2c and the use of the cross section data in Exercise II 1a of the prismatic benchmark, which is defined as the last and first steps of the lattice and core simulation phases, respectively. The report summarizes the Idaho National Laboratory (INL) best estimate results obtained for Exercise I 2a (fresh single-fuel block), Exercise I 2b (depleted single-fuel block), and Exercise I 2c (super cell) in addition to the first results of an investigation into the cross section generation effects for the super-cell problem. The two dimensional deterministic code known as the New ESC based Weighting Transport (NEWT) included in the Standardized Computer Analyses for Licensing Evaluation (SCALE) 6.1.2 package was used for the cross section evaluation, and the results obtained were compared to the three dimensional stochastic SCALE module KENO VI. The NEWT cross section libraries were generated for several permutations of the current benchmark super-cell geometry and were then provided as input to the Phase II core calculation of the stand alone neutronics Exercise II 1a. The steady state core calculations were simulated with the INL coupled-code system known as the Parallel and Highly Innovative Simulation for INL Code System (PHISICS) and the system thermal-hydraulics code known as the Reactor Excursion and Leak Analysis Program (RELAP) 5 3D using the nuclear data libraries previously generated with NEWT. It was observed that significant differences in terms of multiplication factor and neutron flux exist between the various permutations of the Phase I super-cell lattice calculations. The use of these cross section libraries only leads to minor changes in the Phase II core simulation results for fresh fuel but shows significantly larger discrepancies for spent fuel cores. Furthermore, large incongruities were found between the SCALE NEWT and KENO VI results for the super cells, and while some trends could be identified, a final conclusion on this issue could not yet be reached. This report will be revised in mid 2016 with more detailed analyses of the super-cell problems and their effects on the core models, using the latest version of SCALE (6.2). The super-cell models seem to show substantial improvements in terms of neutron flux as compared to single-block models, particularly at thermal energies.« less
An observational analysis of a derecho in South China

NASA Astrophysics Data System (ADS)

Xia, Rudi; Wang, Donghai; Sun, Jianhua; Wang, Gaili; Xia, Guancong

2012-12-01

Derechos occur frequently in Europe and the United States, but reports of derechos in China are scarce. In this paper, radar, satellite, and surface observation data are used to analyze a derecho event in South China on 17 April 2011. A derecho-producing mesoscale convective system formed in an environment with medium convective available energy, strong vertical wind shear, and a dry layer in the middle troposphere, and progressed southward in tandem with a front and a surface wind convergence line. The windstorm can be divided into two stages according to differences in the characteristics of the radar echo and the causes of the gale. One stage was a supercell stage, in which the sinking rear inflow of a high-precipitation supercell with a bow-shaped radar echo induced a Fujita F0 class gale. The other stage was a non-supercell stage (the echo was sequentially kidney-shaped, foot-shaped, and an ordinary single cell), in which downbursts induced a gale in Fujita F1 class. This derecho event had many similarities with derechos observed in western countries. For example, the windstorm was perpendicular to the mean flow, the gale was located in the bulging portion of the bow echo, and the derecho moved southward along with the surface front. Some differences were observed as well. The synoptic-scale forcing was weak in the absence of an advancing high-amplitude midlevel trough and an accompanying strong surface cyclone; however, the vertical wind shear was very strong, a characteristic typical of derechos associated with strong synoptic-scale forcing. Extremely high values of convective available potential energy and downdraft convective available potential energy have previously been considered necessary to the formation of weak-forcing archetype and hybrid derechos; however, these values were much less than 2000 J during this derecho event.
Anomalous Lightning Behavior During the 26-27 August 2007 Northern Great Plains Severe Weather Event

NASA Astrophysics Data System (ADS)

Logan, Timothy

2018-02-01

Positive polarity lightning strokes can be useful indicators of thunderstorm behavior. A combination of National Lightning Detection Network and Next Generation Radar retrievals is used to analyze the anomalous positive cloud-to-ground (CG) lightning behavior of a rare, late summer severe weather event that occurred on 26-27 August 2007 in the Northern Great Plains region of the United States and southern Canada. Seven discrete supercells (SC1-SC7) exhibiting frequent and intense lightning were responsible for numerous reports of severe weather (e.g., severe hail and 16 tornadoes) including catastrophic damage to the town of Northwood, North Dakota, caused by SC2. Biomass burning smoke from wildfires in Idaho and Montana was present prior to convective initiation. A positive CG lightning stroke rate of nearly 30 strokes per minute was observed 10 min before the EF4 tornado struck Northwood. SC2 was also responsible for all the reports of tornadoes exceeding an EF2 rating. The strongest peak currents (>200 kA) were observed in SC1-SC4 with SC2 having a maximum value of 280 kA. SC2 dominated the statistics of the line of supercells accounting for 27% of all CG lightning strokes. Positive CG lightning accounted for over 40% of all CG lightning strokes in SC4-SC7 on average, and the maximum exceeded 90% in SC6 and SC7. Increasing positive CG lightning dominance was correlated with an increasing northward gradient of smoke aerosol loading in addition to severe weather being reported before the maximum in positive CG lighting stroke rate (SC5 and SC6). This suggests that a complex combination of synoptic forcing and aerosol perturbation likely led to the observed anomalous positive CG lightning behavior in the supercells.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Plessow, Philipp N.; Bajdich, Michal; Greene, Joshua

The formation of thin oxide films on metal supports is an important phenomenon, especially in the context of strong metal support interaction (SMSI). Computational predictions of the stability of these films are hampered by their structural complexity and a varying lattice mismatch with different supports. In this study, we report a large combination of supports and ultrathin oxide films studied with density functional theory (DFT). Trends in stability are investigated through a descriptor-based analysis. Since the studied films are bound to the support exclusively through metal–metal interaction, the adsorption energy of the oxide-constituting metal atom can be expected to bemore » a reasonable descriptor for the stability of the overlayers. If the same supercell is used for all supports, the overlayers experience different amounts of stress. Using supercells with small lattice mismatch for each system leads to significantly improved scaling relations for the stability of the overlayers. Finally, this approach works well for the studied systems and therefore allows the descriptor-based exploration of the thermodynamic stability of supported thin oxide layers.« less
Ab initio calculations of the concentration dependent band gap reduction in dilute nitrides

NASA Astrophysics Data System (ADS)

Rosenow, Phil; Bannow, Lars C.; Fischer, Eric W.; Stolz, Wolfgang; Volz, Kerstin; Koch, Stephan W.; Tonner, Ralf

2018-02-01

While being of persistent interest for the integration of lattice-matched laser devices with silicon circuits, the electronic structure of dilute nitride III/V-semiconductors has presented a challenge to ab initio computational approaches. The origin of the computational problems is the strong distortion exerted by the N atoms on most host materials. Here, these issues are resolved by combining density functional theory calculations based on the meta-GGA functional presented by Tran and Blaha (TB09) with a supercell approach for the dilute nitride Ga(NAs). Exploring the requirements posed to supercells, it is shown that the distortion field of a single N atom must be allowed to decrease so far that it does not overlap with its periodic images. This also prevents spurious electronic interactions between translational symmetric atoms, allowing us to compute band gaps in very good agreement with experimentally derived reference values. In addition to existing approaches, these results offer a promising ab initio avenue to the electronic structure of dilute nitride semiconductor compounds.
Possibility of transforming the electronic structure of one species of graphene adatoms into that of another by application of gate voltage: First-principles calculations

NASA Astrophysics Data System (ADS)

Chan, Kevin T.; Lee, Hoonkyung; Cohen, Marvin L.

2011-10-01

Graphene provides many advantages for controlling the electronic structure of adatoms and other adsorbates via gating. Using the projected density of states and charge density obtained from first-principles density-functional periodic supercell calculations, we investigate the possibility of performing “alchemy” of adatoms on graphene, i.e., transforming the electronic structure of one species of adatom into that of another species by application of a gate voltage. Gating is modeled as a change in the number of electrons in the unit cell, with the inclusion of a compensating uniform background charge. Within this model and the generalized gradient approximation to the exchange-correlation functional, we find that such transformations are possible for K, Ca, and several transition-metal adatoms. Gate control of the occupation of the p states of In on graphene is also investigated. The validity of the supercell approximation with uniform compensating charge and the model for exchange and correlation is also discussed.
Local lattice distortion in high-entropy alloys

NASA Astrophysics Data System (ADS)

Song, Hongquan; Tian, Fuyang; Hu, Qing-Miao; Vitos, Levente; Wang, Yandong; Shen, Jiang; Chen, Nanxian

2017-07-01

The severe local lattice distortion, induced mainly by the large atomic size mismatch of the alloy components, is one of the four core effects responsible for the unprecedented mechanical behaviors of high-entropy alloys (HEAs). In this work, we propose a supercell model, in which every lattice site has similar local atomic environment, to describe the random distributions of the atomic species in HEAs. Using these supercells in combination with ab initio calculations, we investigate the local lattice distortion of refractory HEAs with body-centered-cubic structure and 3 d HEAs with face-centered-cubic structure. Our results demonstrate that the local lattice distortion of the refractory HEAs is much more significant than that of the 3 d HEAs. We show that the atomic size mismatch evaluated with the empirical atomic radii is not accurate enough to describe the local lattice distortion. Both the lattice distortion energy and the mixing entropy contribute significantly to the thermodynamic stability of HEAs. However the local lattice distortion has negligible effect on the equilibrium lattice parameter and bulk modulus.
First-principles studies of Te line-ordered alloys in a MoS2 monolayer

NASA Astrophysics Data System (ADS)

Andriambelaza, N. F.; Mapasha, R. E.; Chetty, N.

2018-04-01

The thermodynamic stability, structural and electronic properties of Te line-ordered alloys are investigated using density functional theory (DFT) methods. Thirty four possible Te line-ordered alloy configurations are found in a 5×5 supercell of a MoS2 monolayer. The calculated formation energies show that the Te line-ordered alloy configurations are thermodynamically stable at 0 K and agree very well with the random alloys. The lowest energy configurations at each concentration correspond to the configuration where the Te atom rows are far apart from each other (avoiding clustering) within the supercell. The variation of the lattice constant at different concentrations obey Vegard's law. The Te line-ordered alloys fine tune the band gap of a MoS2 monolayer although deviating from linearity behavior. Our results suggest that the Te line-ordered alloys can be an effective way to modulate the band gap of a MoS2 monolayer for nanoelectronic, optoelectronic and nanophotonic applications.
Traffic sharing algorithms for hybrid mobile networks

NASA Technical Reports Server (NTRS)

Arcand, S.; Murthy, K. M. S.; Hafez, R.

1995-01-01

In a hybrid (terrestrial + satellite) mobile personal communications networks environment, a large size satellite footprint (supercell) overlays on a large number of smaller size, contiguous terrestrial cells. We assume that the users have either a terrestrial only single mode terminal (SMT) or a terrestrial/satellite dual mode terminal (DMT) and the ratio of DMT to the total terminals is defined gamma. It is assumed that the call assignments to and handovers between terrestrial cells and satellite supercells take place in a dynamic fashion when necessary. The objectives of this paper are twofold, (1) to propose and define a class of traffic sharing algorithms to manage terrestrial and satellite network resources efficiently by handling call handovers dynamically, and (2) to analyze and evaluate the algorithms by maximizing the traffic load handling capability (defined in erl/cell) over a wide range of terminal ratios (gamma) given an acceptable range of blocking probabilities. Two of the algorithms (G & S) in the proposed class perform extremely well for a wide range of gamma.
Models for some aspects of atmospheric vortices

NASA Technical Reports Server (NTRS)

Deissler, R. G.

1977-01-01

A frictionless adiabatic model is used to study the growth of random vortices in an atmosphere with buoyant instability and vertical wind shear, taking account of the effects of axial drag, heat transfer and precipitation-induced downdrafts. It is found that downdrafts of tornadic magnitude may occur in negatively buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. A tornado model which involves a rotating parent cloud as well as buoyancy and precipitation effects is also discussed.
Assessment of realistic nowcasting lead-times based on predictability analysis of Mediterranean Heavy Precipitation Events

NASA Astrophysics Data System (ADS)

Bech, Joan; Berenguer, Marc

2014-05-01

Operational quantitative precipitation forecasts (QPF) are provided routinely by weather services or hydrological authorities, particularly those responsible for densely populated regions of small catchments, such as those typically found in Mediterranean areas prone to flash-floods. Specific rainfall values are used as thresholds for issuing warning levels considering different time frameworks (mid-range, short-range, 24h, 1h, etc.), for example 100 mm in 24h or 60 mm in 1h. There is a clear need to determine how feasible is a specific rainfall value for a given lead-time, in particular for very short range forecasts or nowcasts typically obtained from weather radar observations (Pierce et al 2012). In this study we assess which specific nowcast lead-times can be provided for a number of heavy precipitation events (HPE) that affected Catalonia (NE Spain). The nowcasting system we employed generates QPFs through the extrapolation of rainfall fields observed with weather radar following a Lagrangian approach developed and tested successfully in previous studies (Berenguer et al. 2005, 2011).Then QPFs up to 3h are compared with two quality controlled observational data sets: weather radar quantitative precipitation estimates (QPE) and raingauge data. Several high-impact weather HPE were selected including the 7 September 2005 Llobregat Delta river tornado outbreak (Bech et al. 2007) or the 2 November 2008 supercell tornadic thunderstorms (Bech et al. 2011) both producing, among other effects, local flash floods. In these two events there were torrential rainfall rates (30' amounts exceeding 38.2 and 12.3 mm respectively) and 24h accumulation values above 100 mm. A number of verification scores are used to characterize the evolution of precipitation forecast quality with time, which typically presents a decreasing trend but showing an strong dependence on the selected rainfall threshold and integration period. For example considering correlation factors, 30' precipitation forecasts showed some skill (improvement over persistence) for lead times up to 60' for moderate intensities (up to 1 mm in 30') and up to 2.5h for lower rates (above 0.1 mm). However an important event-to-event variability has been found as illustrated by the fact that hit rates of rain-no-rain forecasts achieved the 60% value at 90' in the 7 September 2005 and only 40' in the 2 November 2008 case. The discussion of these results provides useful information on the potential application of nowcasting systems and realistic values to be contrasted with specific end-user requirements. This work has been done in the framework of the Hymex research programme and has been partly funded by the ProFEWS project (CGL2010-15892). References Bech J, N Pineda, T Rigo, M Aran, J Amaro, M Gayà, J Arús, J Montanyà, O van der Velde, 2011: A Mediterranean nocturnal heavy rainfall and tornadic event. Part I: Overview, damage survey and radar analysis. Atmospheric Research 100:621-637 http://dx.doi.org/10.1016/j.atmosres.2010.12.024 Bech J, R Pascual, T Rigo, N Pineda, JM López, J Arús, and M Gayà, 2007: An observational study of the 7 September 2005 Barcelona tornado outbreak. Natural Hazards and Earth System Science 7:129-139 http://dx.doi.org/10.5194/nhess-7-129-2007 Berenguer M, C Corral, R Sa'nchez-Diezma, D Sempere-Torres, 2005: Hydrological validation of a radarbased nowcasting technique. Journal of Hydrometeorology 6: 532-549 http://dx.doi.org/10.1175/JHM433.1 Berenguer M, D Sempere, G Pegram, 2011: SBMcast - An ensemble nowcasting technique to assess the uncertainty in rainfall forecasts by Lagrangian extrapolation. Journal of Hydrology 404: 226-240 http://dx.doi.org/10.1016/j.jhydrol.2011.04.033 Pierce C, A Seed, S Ballard, D Simonin, Z Li, 2012: Nowcasting. In Doppler Radar Observations (J Bech, JL Chau, ed.) Ch. 13, 98-142. InTech, Rijeka, Croatia http://dx.doi.org/10.5772/39054
Estimating dispersion from a tornado vortex and mesocyclone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weber, A.H.; Hunter, C.H.

Atmospheric dispersion modeling is required to ensure that a postulated breach in radionuclide storage containers at the Savannah River Site (SRS) from a tornado strike of Fujita-scale intensity F2 or higher will not result in an unacceptable dose to individuals. Fujita-scale tornado descriptions are included in Appendix A of this report. Dispersion models previously used at SRS for estimating dispersion following a tornado strike were developed by D.W. Pepper in 1975 (DP-1387, Dispersion of Small Particles) and H.R. Haynes and D.W. Taylor in 1983 (DPST-82-982, Estimating Doses from Tornado Winds). Research conducted in 1983 on the formation and evolution ofmore » tornadic thunderstorms has lead to a more complete understanding of the tornado vortex and associated persistent updraft and downdraft regions within the parent thunderstorm. To ensure that appropriate, contemporary methods are used for safety analysis, the Pepper model and the Haynes and Taylor model were evaluated with respect to current knowledge of circulations within tornadic thunderstorms. Pepper`s model is complex numerically but contains most of the desired physical parameterizations. Haynes and Taylor`s model is used with the Puff-Plume model (an emergency response model on the Weather INformation and Display System at SRS) and has provisions for radionuclide deposition and rainout. Haynes and Taylor assumed heavy rain following the tornado for a period of ten minutes, followed by a lighter rain for another ten minutes, then no rain for the period when the material is transported to 100 km downwind. However, neither model incorporates the effects of a nearby thunderstorm downdraft.« less

Self-Assembled Layered Supercell Structure of Bi2AlMnO6 with Strong Room-Temperature Multiferroic Properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Leigang; Boullay, Philippe; Lu, Ping

2017-02-01

Room-temperature (RT) multiferroics, possessing ferroelectricity and ferromagnetism simultaneously at RT, hold great promise in miniaturized devices including sensors, actuators, transducers, and multi-state memories. In this work, we report a novel 2D layered RT multiferroic system with self-assembled layered supercell structure consisting of two mismatch-layered sub-lattices of [Bi 3O 3+δ] and [MO 2] 1.84 (M=Al/Mn, simply named as BAMO), i.e., alternative layered stacking of two mutually incommensurate sublattices made of a three-layer-thick Bi-O slab and a one-layer-thick Al/Mn-O octahedra slab along the out-of-plane direction. Strong room-temperature multiferroic responses, e.g., ferromagnetic and ferroelectric properties, have been demonstrated and attributed to the highlymore » anisotropic 2D nature of the non-ferromagnetic and ferromagnetic sublattices which are highly mismatched. The work demonstrates an alternative design approach for new 2D layered oxide materials that hold promises as single-phase multiferroics, 2D oxides with tunable bandgaps, and beyond.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Leigang; Boullay, Philippe; Lu, Ping

Layered materials, e.g., graphene and transition metal (di)chalcogenides, holding great promises in nanoscale device applications have been extensively studied in fundamental chemistry, solid state physics and materials research areas. In parallel, layered oxides (e.g., Aurivillius and Ruddlesden–Popper phases) present an attractive class of materials both because of their rich physics behind and potential device applications. In this work, we report a novel layered oxide material with self-assembled layered supercell structure consisting of two mismatch-layered sublattices of [Bi 3O 3+δ] and [MO 2] 1.84 (M = Al/Mn, simply named BAMO), i.e., alternative layered stacking of two mutually incommensurate sublattices made ofmore » a three-layer-thick Bi–O slab and a one-layer-thick Al/Mn–O octahedra slab in the out-of-plane direction. Strong room-temperature ferromagnetic and piezoelectric responses as well as anisotropic optical property have been demonstrated with great potentials in various device applications. Furthermore, the realization of the novel BAMO layered supercell structure in this work has paved an avenue toward exploring and designing new materials with multifunctionalities.« less
Primal Eukaryogenesis: On the Communal Nature of Precellular States, Ancestral to Modern Life

PubMed Central

Egel, Richard

2012-01-01

This problem-oriented, exploratory and hypothesis-driven discourse toward the unknown combines several basic tenets: (i) a photo-active metal sulfide scenario of primal biogenesis in the porespace of shallow sedimentary flats, in contrast to hot deep-sea hydrothermal vent conditions; (ii) an inherently complex communal system at the common root of present life forms; (iii) a high degree of internal compartmentalization at this communal root, progressively resembling coenocytic (syncytial) super-cells; (iv) a direct connection from such communal super-cells to proto-eukaryotic macro-cell organization; and (v) multiple rounds of micro-cellular escape with streamlined reductive evolution-leading to the major prokaryotic cell lines, as well as to megaviruses and other viral lineages. Hopefully, such nontraditional concepts and approaches will contribute to coherent and plausible views about the origins and early life on Earth. In particular, the coevolutionary emergence from a communal system at the common root can most naturally explain the vast discrepancy in subcellular organization between modern eukaryotes on the one hand and both archaea and bacteria on the other. PMID:25382122
Phonon Calculations Using the Real-Space Multigrid Method (RMG)

NASA Astrophysics Data System (ADS)

Zhang, Jiayong; Lu, Wenchang; Briggs, Emil; Cheng, Yongqiang; Ramirez-Cuesta, A. J.; Bernholc, Jerry

RMG, a DFT-based open-source package using the real-space multigrid method, has proven to work effectively on large scale systems with thousands of atoms. Our recent work has shown its practicability for high accuracy phonon calculations employing the frozen phonon method. In this method, a primary unit cell with a small lattice constant is enlarged to a supercell that is sufficiently large to obtain the force constants matrix by finite displacements of atoms in the supercell. An open-source package PhonoPy is used to determine the necessary displacements by taking symmetry into account. A python script coupling RMG and PhonoPy enables us to perform high-throughput calculations of phonon properties. We have applied this method to many systems, such as silicon, silica glass, ZIF-8, etc. Results from RMG are compared to the experimental spectra measured using the VISION inelastic neutron scattering spectrometer at the Spallation Neutron Source at ORNL, as well as results from other DFT codes. The computing resources were made available through the VirtuES (Virtual Experiments in Spectroscopy) project, funded by Laboratory Directed Research and Development program (LDRD project No. 7739)
Trends in the thermodynamic stability of ultrathin supported oxide films

DOE PAGES

Plessow, Philipp N.; Bajdich, Michal; Greene, Joshua; ...

2016-05-05

The formation of thin oxide films on metal supports is an important phenomenon, especially in the context of strong metal support interaction (SMSI). Computational predictions of the stability of these films are hampered by their structural complexity and a varying lattice mismatch with different supports. In this study, we report a large combination of supports and ultrathin oxide films studied with density functional theory (DFT). Trends in stability are investigated through a descriptor-based analysis. Since the studied films are bound to the support exclusively through metal–metal interaction, the adsorption energy of the oxide-constituting metal atom can be expected to bemore » a reasonable descriptor for the stability of the overlayers. If the same supercell is used for all supports, the overlayers experience different amounts of stress. Using supercells with small lattice mismatch for each system leads to significantly improved scaling relations for the stability of the overlayers. Finally, this approach works well for the studied systems and therefore allows the descriptor-based exploration of the thermodynamic stability of supported thin oxide layers.« less
Self-consistent Green's function embedding for advanced electronic structure methods based on a dynamical mean-field concept

NASA Astrophysics Data System (ADS)

Chibani, Wael; Ren, Xinguo; Scheffler, Matthias; Rinke, Patrick

2016-04-01

We present an embedding scheme for periodic systems that facilitates the treatment of the physically important part (here a unit cell or a supercell) with advanced electronic structure methods, that are computationally too expensive for periodic systems. The rest of the periodic system is treated with computationally less demanding approaches, e.g., Kohn-Sham density-functional theory, in a self-consistent manner. Our scheme is based on the concept of dynamical mean-field theory formulated in terms of Green's functions. Our real-space dynamical mean-field embedding scheme features two nested Dyson equations, one for the embedded cluster and another for the periodic surrounding. The total energy is computed from the resulting Green's functions. The performance of our scheme is demonstrated by treating the embedded region with hybrid functionals and many-body perturbation theory in the GW approach for simple bulk systems. The total energy and the density of states converge rapidly with respect to the computational parameters and approach their bulk limit with increasing cluster (i.e., computational supercell) size.
Visions of our Planet's Atmosphere, Land and Oceans: NASA/NOAA Electronic-Theater 2002. Spectacular Visualizations of our Blue Marble

NASA Technical Reports Server (NTRS)

Hasler, A. F.; Starr, David (Technical Monitor)

2002-01-01

Spectacular Visualizations of our Blue Marble The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to the 2002 Winter Olympic Stadium Site of the Olympic Opening and Closing Ceremonies in Salt Lake City. Fly in and through Olympic Alpine Venues using 1 m IKONOS "Spy Satellite" data. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes & "tornadoes". See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including new 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained. See how High-Definition Television (HDTV) is revolutionizing the way we communicate science. (In cooperation with the American Museum of Natural History in NYC). See dust storms in Africa and smoke plumes from fires in Mexico. See visualizations featured on the covers of Newsweek, TIME, National Geographic, Popular Science & on National & International Network TV. New computer software tools allow us to roam & zoom through massive global images e.g. Landsat tours of the US, and Africa, showing desert and mountain geology as well as seasonal changes in vegetation. See animations of the polar ice packs and the motion of gigantic Antarctic Icebergs from SeaWinds data. Spectacular new visualizations of the global atmosphere & oceans are shown. See vertexes and currents in the global oceans that bring up the nutrients to feed tiny algae and draw the fish, whales and fisherman. See the how the ocean blooms in response to these currents and El Nicola Nina climate changes. See the city lights, fishing fleets, gas flares and biomass burning of the Earth at night observed by the "night-vision" DMSP military satellite.
The Interactive Virtual Earth Science Teaching (InVEST) project: preliminary results

NASA Astrophysics Data System (ADS)

Gallus, W.; Cervato, C.; Parham, T.; Larsen, M.; Cruz-Neira, C.; Boudreaux, H.

2009-04-01

The InVEST (Interactive Virtual Earth Science Teaching) project has as its goal the development of state-of-the-art virtual reality geoscience tools that can be used to correct student misunderstandings about some geoscience phenomena. One tool, originally developed several years ago, the virtual tornadic thunderstorm, was recently modified based on feedback from instructors given the opportunity to use the tool. The modified virtual storm will be demonstrated during the presentation. In addition, a virtual volcano application is currently under development. To steer the development of this application, a Volcanic Concept Survey was recently administered to over 600 students at six U.S. institutions with the goal of identifying areas of greatest misconception relating to volcanoes. Both mean and median scores on the instrument were exceptionally low, indicating that students generally possessed minimal understanding of volcanic systems. High scores were restricted to the simplest aspects of volcanism (terminology, basic volcano shape) while questions requiring higher thinking and deeper conceptual connections (analysis of patterns, eruptive controls, and hazards) saw much lower scores. Categorical analysis of response types revealed the extent of specific misconceptions, the most predominant of which demonstrated a failure to link tectonics to a global volcanic pattern. Eruptive catalysts and controls also appear poorly understood, as are volcanic impacts on the environment and human endeavors. The survey also included demographic information which has been analyzed. Analysis of student sources of knowledge found that over 41% of students said that they had acquired most of their understanding about volcanoes from non-traditional sources such as the popular media and Hollywood films. Application of a multiple linear regression model and an expanded model suggests that these students were much less likely to receive high scores on questions relating to understanding. In contrast, traditional sources of knowledge (in-class learning, learning from textbooks) were highly significant predictors of high score in both models.
A study of the 21 March 2012 tornadic quasi linear convective system in Catalonia

NASA Astrophysics Data System (ADS)

Bech, Joan; Arús, Joan; Castán, Salvador; Pineda, Nicolau; Rigo, Tomeu; Montanyà, Joan; van der Velde, Oscar

2015-05-01

This study presents a description of a quasi linear convective system that took place in Catalonia (NE Spain) on 21 March 2012 producing heavy rainfall, moderate lightning activity and a weak tornado in the village of Ivars d'Urgell around 19 UTC after local sunset. A post-event survey indicated EF0 and EF1 damage in houses of the village - roofs and ceilings, broken windows, fences and walls and trees knocked down - along a track approximately 4 km long and about 20 m wide. Doppler radar observations show that the parent thunderstorm that spawned the tornado was one of a series that developed along a convective line that moved from S to N, initiating convective activity in terms of precipitation and lightning in the Mediterranean Sea and moving inland in S Catalonia (Tarragona and Salou coastal areas, producing local flash floods). Convective activity remained several hours with series of thunderstorms developing along the same paths. The synoptic situation was dominated by a high pressure ridge extending from northern Africa to central Europe, with a closed maximum sea level pressure area around 1036 hPa over northern France, southern Germany and Austria. On the other hand a relative low pressure area seen on 850 hPa and upper levels was present over the Iberian Peninsula, favouring a southern maritime flow from the Mediterranean between the forward part of the low pressure area and the high pressure system which blocked the advance of the low to the east. In the study we examine both the synoptic environment and storm scale observations with Doppler radar and total lightning data (cloud to ground and intracloud flashes) that lead to this cool-season severe convective event which is remarkable given the fact that, unlike in this case, most reported tornadoes in the region occur during the warm season (with peaks in August and September) and during daylight hours (6 to 18 UTC).
Visions of our Planet's Atmosphere, Land and Oceans: NASA/NOAA Electronic Theater 2002

NASA Technical Reports Server (NTRS)

Haser, Fritz; Starr, David (Technical Monitor)

2002-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to the 2002 Winter Olympic Stadium Site of the Olympic Opening and Closing Ceremonies in Salt Lake City. Fly in and through Olympic Alpine Venues using 1 m IKONOS "Spy Satellite" data. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes and "tornadoes". See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including new 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained. See how High-Definition Television (HDTV) is revolutionizing the way we communicate science. (In cooperation with the American Museum of Natural History in NYC) See dust storms in Africa and smoke plumes from fires in Mexico. See visualizations featured on the covers of Newsweek, TIME, National Geographic, Popular Science and on National and International Network TV. New computer software tools allow us to roam and zoom through massive global images e.g. Landsat tours of the US, and Africa, showing desert and mountain geology as well as seasonal changes in vegetation. See animations of the polar ice packs and the motion of gigantic Antarctic Icebergs from SeaWinds. data. Spectacular new visualizations of the global atmosphere and oceans are shown. See vortexes and currents in the global oceans that bring up the nutrients to feed tiny algae and draw the fish, whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. See the city lights, fishing fleets, gas flares and bio-mass burning of the Earth at night observed by the "night-vision" DMSP military satellite.
Geostationary Lightning Mapper for GOES-R and Beyond

NASA Technical Reports Server (NTRS)

Goodman, Steven J.; Blakeslee, R. J.; Koshak, W.

2008-01-01

The Geostationary Lightning Mapper (GLM) is a single channel, near-IR imager/optical transient event detector, used to detect, locate and measure total lightning activity over the full-disk as part of a 3-axis stabilized, geostationary weather satellite system. The next generation NOAA Geostationary Operational Environmental Satellite (GOES-R) series with a planned launch readiness in December 2014 will carry a GLM that will provide continuous day and night observations of lightning from the west coast of Africa (GOES-E) to New Zealand (GOES-W) when the constellation is fUlly operational. The mission objectives for the GLM are to 1) provide continuous, full-disk lightning measurements for storm warning and nowcasting, 2) provide early warning of tornadic activity, and 3) accumulate a long-term database to track decadal changes of lightning. The GLM owes its heritage to the NASA Lightning Imaging Sensor (1997-Present) and the Optical Transient Detector (1995-2000), which were developed for the Earth Observing System and have produced a combined 13 year data record of global lightning activity. Instrument formulation studies were completed in March 2007 and the implementation phase to develop a prototype model and up to four flight models will be underway in the latter part of 2007. In parallel with the instrument development, a GOES-R Risk Reduction Team and Algorithm Working Group Lightning Applications Team have begun to develop the Level 2 algorithms and applications. Proxy total lightning data from the NASA Lightning Imaging Sensor on the Tropical Rainfall Measuring Mission (TRMM) satellite and regional test beds (e.g., Lightning Mapping Arrays in North Alabama and the Washington DC Metropolitan area) are being used to develop the pre-launch algorithms and applications, and also improve our knowledge of thunderstorm initiation and evolution. Real time lightning mapping data are being provided in an experimental mode to selected National Weather Service (NWS) forecast offices in Southern and Eastern Region. This effort is designed to help improve our understanding of the application of these data in operational settings.
New Cloud and Precipitation Research Avenues Enabled by low-cost Phased-array Radar Technology

NASA Astrophysics Data System (ADS)

Kollias, P.; Oue, M.; Fridlind, A. M.; Matsui, T.; McLaughlin, D. J.

2017-12-01

For over half a century, radars operating in a wide range of frequencies have been the primary source of observational insights of clouds and precipitation microphysics and dynamics and contributed to numerous significant advancements in the field of cloud and precipitation physics. The development of multi-wavelength and polarization diversity techniques has further strengthened the quality of microphysical and dynamical retrievals from radars and has assisted in overcoming some of the limitations imposed by the physics of scattering. Atmospheric radars have historically employed a mechanically-scanning dish antenna and their ability to point to, survey, and revisit specific points or regions in the atmosphere is limited by mechanical inertia. Electronically scanned, or phased-array, radars capable of high-speed, inertialess beam steering, have been available for several decades, but the cost of this technology has limited its use to military applications. During the last 10 years, lower power and lower-cost versions of electronically scanning radars have been developed, and this presents an attractive and affordable new tool for the atmospheric sciences. The operational and research communities are currently exploring phased array advantages in signal processing (i.e. beam multiplexing, improved clutter rejection, cross beam wind estimation, adaptive sensing) and science applications (i.e. tornadic storm morphology studies). Here, we will present some areas of atmospheric research where inertia-less radars with ability to provide rapid volume imaging offers the potential to advance cloud and precipitation research. We will discuss the added value of single phased-array radars as well as networks of these radars for several problems including: multi-Doppler wind retrieval techniques, cloud lifetime studies and aerosol-convection interactions. The performance of current (dish) and future (e-scan) radar systems for these atmospheric studies will be evaluated using numerical model output and a sophisticated radar simulator package.
Elastic and optical properties of Cu2ZnSn(SexS1 - x)4 alloys: density functional calculations

NASA Astrophysics Data System (ADS)

Camps, I.; Coutinho, J.; Mir, M.; da Cunha, A. F.; Rayson, M. J.; Briddon, P. R.

2012-11-01

Cu2ZnSn(S1 - xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 - xGaxSe2 (CIGS) as the absorber layer for thin film solar cells. The former compound has the important advantage of using abundant Zn and Sn instead of the expensive In and Ga. A better understanding of the properties of CZT(S, Se) is being sought through experimental and theoretical means. Thus far, however, very little is known about the fundamental properties of the CZT(S, Se) alloys. In this work, theoretical studies on the structural, elastic, electronic and optical properties of CZT(S, Se) alloys through first-principles calculations are reported. We use a density functional code (aimpro), along with the Padé parametrization for the local density approximation to the exchange correlation potential. For the alloying calculations we employed 64 atom supercells (approximately cubic) with a 2 × 2 × 2 k-point sampling set. These supercells possess a total of 32 chalcogen species and the CZTSexS1 - x alloys are described by using the ordered alloy approximation. Accordingly, to create a perfectly diluted alloying host, the species type of the 32 chalcogen sites is selected randomly with uniform probability x and 1 - x for Se and S, respectively. Properties of alloys (structural, elastic, electronic and optical) are obtained by averaging the results of ten supercell configurations generated for each composition. For each configuration, lattice vectors and atomic positions were allowed to relax (although enforcing the tetragonal lattice type) and the Murnaghan equation of state was fitted to the total energy data. The results presented here permit a better understanding of the properties of the CZT(S, Se) alloys which in turn result in the design of more efficient solar cells.
X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

NASA Astrophysics Data System (ADS)

Ching, Wai-Yim; Rulis, Paul

2009-03-01

Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B12) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.
Mass casualty following unprecedented tornadic events in the Southeast: natural disaster outcomes at a Level I trauma center.

PubMed

Hartmann, Elizabeth H; Creel, Nathan; Lepard, Jacob; Maxwell, Robert A

2012-07-01

On April 27, 2011, an EF4 (enhanced Fujita scale) tornado struck a 48-mile path across northwest Georgia and southeast Tennessee. Traumatic injuries sustained during this tornado and others in one of the largest tornado outbreaks in history presented to the regional Level I trauma center, Erlanger Health System, in Chattanooga, TN. Patients were triaged per mass casualty protocols through an incident command center and triage officer. Medical staffing was increased to anticipate a large patient load. Records of patients admitted as a result of tornado-related injury were retrospectively reviewed and characterized by the injury patterns, demographics, procedures performed, length of stay, and complications. One hundred four adult patients were treated in the emergency department; of these, 28 (27%) patients required admission to the trauma service. Of those admitted, 16 (57%) were male with an age range of 21 to 87 years old and an average length of stay of 10.9 ± 11.8 days. Eleven (39%) patients required intensive care unit admissions. The most common injuries seen were those of soft tissue, bony fractures, and the chest. Interventions included tube thoracostomies, exploratory laparotomies, orthopedic fixations, soft tissue reconstructions, and craniotomy. All 28 patients admitted survived to discharge. Nineteen (68%) patients were discharged home, six (21%) went to a rehabilitation hospital, and three (11%) were transferred to skilled nursing facilities. Emergency preparedness and organization are key elements in effectively treating victims of natural disasters. Those victims who survive the initial tornadic event and present to a Level I trauma center have low mortality. Like in our experience, triage protocols need to be implemented to quickly and effectively manage mass injuries.
Oxygen vacancy diffusion in bulk SrTiO3 from density functional theory calculations

DOE PAGES

Zhang, Lipeng; Liu, Bin; Zhuang, Houlong; ...

2016-04-01

Point defects and point defect diffusion contribute significantly to the properties of perovskite materials. However, even for the prototypical case of oxygen vacancies in SrTiO 3 (STO), predictions vary widely. Here we present a comprehensive and systematic study of the diffusion barriers for this material. We use density functional theory (DFT) and assess the role of different cell sizes, density functionals, and charge states. Our results show that vacancy-induced octahedral rotations, which are limited by the boundary conditions of the supercell, can significantly affect the computed oxygen vacancy diffusion energy barrier. The diffusion energy barrier of a charged oxygen vacancymore » is lower than that of a neutral one. Unexpectedly, we find that with increasing supercell size, the effects of the oxygen vacancy charge state, the type of DFT exchange and correlation functional on the energy barrier diminish, and the different DFT predictions asymptote to a value in the range of 0.39-0.49 eV. This work provides important insight and guidance that should be considered for investigations of point defect diffusion in other perovskite materials and in oxide superlattices.« less
Simple intrinsic defects in GaP and InP

NASA Astrophysics Data System (ADS)

Schultz, Peter A.

2012-02-01

To faithfully simulate evolution of defect chemistry and electrical response in irradiated semiconductor devices requires accurate defect reaction energies and energy levels. In III-Vs, good data is scarce, theory hampered by band gap and supercell problems. I apply density functional theory (DFT) to intrinsic defects in GaP and InP, predicting stable charge states, ground state configurations, defect energy levels, and identifying mobile species. The SeqQuest calculations incorporate rigorous charge boundary conditions removing supercell artifacts, demonstrated converged to the infinite limit. Computed defect levels are not limited by a band gap problem, despite Kohn-Sham gaps much smaller than the experimental gap. As in GaAs, [P.A. Schultz and O.A. von Lilienfeld, Modeling Simul. Mater. Sci. Eng. 17, 084007 (2009)], defects in GaP and InP exhibit great complexity---multitudes of charge states, bistabilities, and negative U systems---but show similarities to each other (and to GaAs). Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Effective band structure of random III-V alloys

NASA Astrophysics Data System (ADS)

Popescu, Voicu; Zunger, Alex

2010-03-01

Random substitutional alloys have no long range order (LRO) or translational symmetry so rigorously speaking they have no E(k) band structure or manifestations thereof. Yet, many experiments on alloys are interpreted using the language of band theory, e.g. inferring Van Hove singularities, band dispersion and effective masses. Many standard alloy theories (VCA- or CPA-based) have the LRO imposed on the alloy Hamiltonian, assuming only on-site disorder, so they can not be used to judge the extent of LRO that really exists. We adopt the opposite way, by using large (thousand atom) randomly generated supercells in which chemically identical alloy atoms are allowed to have different local environments (a polymorphous representation). This then drives site-dependent atomic relaxation as well as potential fluctuations. The eigenstates from such supercells are then mapped onto the Brillouin zone (BZ) of the primitive cell, producing effective band dispersion. Results for (In,Ga)X show band-like behaviour only near the centre and faces of the BZ but rapidly lose such characteristics away from γ or for higher bands. We further analyse the effects of stoichiometry variation, internal relaxation, and short-range order on the alloy band structure.
Simulation of a severe convective storm using a numerical model with explicitly incorporated aerosols

NASA Astrophysics Data System (ADS)

Lompar, Miloš; Ćurić, Mladjen; Romanic, Djordje

2017-09-01

Despite an important role the aerosols play in all stages of cloud lifecycle, their representation in numerical weather prediction models is often rather crude. This paper investigates the effects the explicit versus implicit inclusion of aerosols in a microphysics parameterization scheme in Weather Research and Forecasting (WRF) - Advanced Research WRF (WRF-ARW) model has on cloud dynamics and microphysics. The testbed selected for this study is a severe mesoscale convective system with supercells that struck west and central parts of Serbia in the afternoon of July 21, 2014. Numerical products of two model runs, i.e. one with aerosols explicitly (WRF-AE) included and another with aerosols implicitly (WRF-AI) assumed, are compared against precipitation measurements from surface network of rain gauges, as well as against radar and satellite observations. The WRF-AE model accurately captured the transportation of dust from the north Africa over the Mediterranean and to the Balkan region. On smaller scales, both models displaced the locations of clouds situated above west and central Serbia towards southeast and under-predicted the maximum values of composite radar reflectivity. Similar to satellite images, WRF-AE shows the mesoscale convective system as a merged cluster of cumulonimbus clouds. Both models over-predicted the precipitation amounts; WRF-AE over-predictions are particularly pronounced in the zones of light rain, while WRF-AI gave larger outliers. Unlike WRF-AI, the WRF-AE approach enables the modelling of time evolution and influx of aerosols into the cloud which could be of practical importance in weather forecasting and weather modification. Several likely causes for discrepancies between models and observations are discussed and prospects for further research in this field are outlined.
Characteristics of radar-derived hailstreaks across Central Europe

NASA Astrophysics Data System (ADS)

Kunz, Michael; Fluck, Elody; Schmidberger, Manuel; Jürgen Punge, Heinz; Baumstark, Sven

2017-04-01

Hailstorms are among the most damaging natural disasters in various parts of Europe. For example, two supercells in Germany, on 27 and 28 July 2013, bearing hailstones with a diameter of up to 10 cm, caused economic losses of around 4.0 billion EUR. Despite the large damage potential of severe hailstorms, knowledge about the probability and severity of hail events and hailstorm-favoring conditions in Europe still is limited. A large event set of past severe thunderstorms that occurred between 2004 and 2014 was identified for Germany, France, Belgium, and Luxembourg from radar data considering a lower threshold of 55 dBZ of the maximum Constant Altitude Plan Position Indicator (maxCAPPI). Additional filtering with lightning data and applying a cell tracking algorithm improves the reliability of the detected severe thunderstorm tracks. The obtained statistics show a gradual increase of the track density with increasing distance to the Atlantic and several local-scale maxima, mostly around the mountains. Both the seasonal and daily cycle of severe thunderstorms show large differences across the investigation area. For example, while in Southern France most events occur in June, the peak month in Northern Germany is August, which can be plausibly explained by differences in convective energy due to the large-scale circulation. Furthermore, ambient conditions in terms of convection-related quantities (e.g., CAPE, wind shear, lapse rate) and prevailing synoptic scale fronts were studied both for the entire event set and a subset, where radar-derived storm tracks were combined with hail observations provided by the European Severe Weather Database ESWD. Over Northern Germany, for example, up to 40% of all radar-derived thunderstorm tracks were associated with cold fronts, while in Southern Germany the ratio is only around 20%. Overall, around 25% of all hail streaks were associated with cold fronts.

A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review

PubMed Central

Romero, Cristina; Noyola, Juan C.; Santiago, Ulises; Valladares, Renela M.; Valladares, Alexander; Valladares, Ariel A.

2010-01-01

We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists first of constructing crystalline supercells with a large number of atoms and a density close to the real value and then lowering the density by increasing the volume. The resulting supercells are subjected to either ab initio or parameterized—Tersoff-based—molecular dynamics processes at various temperatures, all below the corresponding bulk melting points, followed by geometry relaxations. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions without the need of incorporating ad hoc semiconducting atomic structural elements such as graphene-like sheets and/or chain-like patterns (reconstructive simulations) or of reproducing the experimental processes (mimetic simulations). We report radial (pair) distribution functions, nanoporous structures of C and Si, and some computational predictions for their vibrational density of states. We present numerical estimates and discuss possible applications of semiconducting materials for hydrogen storage in potential fuel tanks. Nanopore structures for metallic elements like Al and Au also obtained through the expanding lattice method are reported.
Towards a systematic assessment of errors in diffusion Monte Carlo calculations of semiconductors: Case study of zinc selenide and zinc oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jaehyung; Wagner, Lucas K.; Ertekin, Elif, E-mail: ertekin@illinois.edu

2015-12-14

The fixed node diffusion Monte Carlo (DMC) method has attracted interest in recent years as a way to calculate properties of solid materials with high accuracy. However, the framework for the calculation of properties such as total energies, atomization energies, and excited state energies is not yet fully established. Several outstanding questions remain as to the effect of pseudopotentials, the magnitude of the fixed node error, and the size of supercell finite size effects. Here, we consider in detail the semiconductors ZnSe and ZnO and carry out systematic studies to assess the magnitude of the energy differences arising from controlledmore » and uncontrolled approximations in DMC. The former include time step errors and supercell finite size effects for ground and optically excited states, and the latter include pseudopotentials, the pseudopotential localization approximation, and the fixed node approximation. We find that for these compounds, the errors can be controlled to good precision using modern computational resources and that quantum Monte Carlo calculations using Dirac-Fock pseudopotentials can offer good estimates of both cohesive energy and the gap of these systems. We do however observe differences in calculated optical gaps that arise when different pseudopotentials are used.« less
Optoelectronic properties of Fe impurities in delafossite oxide materials. A high-throughput investigation

NASA Astrophysics Data System (ADS)

Haycock, Barry; Lewis, James P.

2014-03-01

A group of materials that shows promise in optoelectronic applications is the family of oxide materials (delafossites), of the form ABO2, where the A site is a monovalent cation (e . g . , Cu, Ag, or Au) and the B site is a trivalent cation (e . g ., Ga, Y, Al, or In). The bandgap of some delafossites can be tailored for specific purposes, such as in photocatalysis applications, with B-site doping. We report on our recent investigations of the properties of CuGaO2, CuInO2, CuAlO2 and NaInO2 and predict the relative disorder of Fe impurities by comparing crystallographic metrics resulting from Fe doping. We performed approximately 10K calculations, in parallel on the Titan platform (Oak Ridge Leadership Computing Facility), of possible Fe-impurity permutations to determine the most-likely configurations of Fe impurities relative to each another. Our computational approach allows us to study large supercells, consisting of 432 atoms, which enable us to examine the properties of these materials in increments of 1% for the B-site doping of Fe. We will present results from our energetically-preferred supercells and discuss further applications of our techniques applied for characterization of new reconstructions via derived metrics.
Traceable Mueller polarimetry and scatterometry for shape reconstruction of grating structures

NASA Astrophysics Data System (ADS)

Hansen, Poul-Erik; Madsen, Morten H.; Lehtolahti, Joonas; Nielsen, Lars

2017-11-01

Dimensional measurements of multi-patterned transmission gratings with a mixture of long and small periods are great challenges for optical metrology today. It is a further challenge when the aspect ratio of the structures is high, that is, when the height of structures is larger than the pitch. Here we consider a double patterned transmission grating with pitches of 500 nm and 20 000 nm. For measuring the geometrical properties of double patterned transmission grating we use a combined spectroscopic Mueller polarimetry and scatterometry setup. For modelling the experimentally obtained data we rigorously compute the scattering signal by solving Maxwell's equations using the RCWA method on a supercell structure. We also present a new method for analyzing the Mueller polarimetry parameters that performs the analysis in the measured variables. This new inversion method for finding the best fit between measured and calculated values are tested on silicon gratings with periods from 300 to 600 nm. The method is shown to give results within the expanded uncertainty of reference AFM measurements. The application of the new inversion method and the supercell structure to the double patterned transmission grating gives best estimates of dimensional quantities that are in fair agreement with those derived from local AFM measurements
Constructing the GW self-energy of a point defect from the perfect crystal and the near neighborhood of the defect

NASA Astrophysics Data System (ADS)

Skachkov, Dmitry; van Schilfgaarde, Mark; Lambrecht, Walter

The full-potential linearized muffin-tin orbital method allows for a real space representation of the GW or quasi-particle self-consistent (QS)GW self-energy ΣR , L ; R' + T , L'. This can be used to construct the self-energy matrix for a point defect system in a large supercell from that of the perfect crystal in the primitive cell and the self-energy of the defect site and its near neighborhood, obtained self-consistently in a smaller supercell. At the interface between both regions we can average the two types of ΣR , L ; R' + T , L' matrix blocks. The result relies on the limited range of the self-energy matrix in real space. It means that we can calculate the quasiparticle energy levels of the defect system at essentially the cost of a DFT calculation and a few QSGW calculations for relatively small systems. The approach presently focuses on quasiparticle energy levels of band structures of the defect system rather than total energies. We will present test results for AsGa\\ in GaAs, ZnGe in ZnGeN2, NO, VO, VZn, and NO - VZn in ZnO. Supported by the US-DOE-BES under Grant No. DE-SC0008933.
Structure and cation ordering in La 2UO 6, Ce 2UO 6, LaUO 4, and CeUO 4 by first principles calculations

DOE PAGES

Casillas-Trujillo, Luis; Xu, H.; McMurray, Jake W.; ...

2016-07-06

In the present work, we have used density functional theory (DFT) and DFT+U to investigate the crystal structure and phase stability of four model compounds in the Ln 2O 3-UO 2-UO 3 ternary oxide system: La2UO 6, Ce 2UO 6, LaUO 4, CeUO 4, due to the highly-correlated nature of the f-electrons in uranium. We have considered both hypothetical ordered compounds and compounds in which the cations randomly occupy atomic sites in a fluorite-like lattice. We determined that ordered compounds are stable and are energetically favored compared to disordered configurations, though the ordering tendencies are weak. To model and analyzemore » the structures of these complex oxides, we have used supercells based on a layered atomic model. In the layer model, the supercell is composed of alternating planes of anions and cations. We have considered two different ordering motifs for the cations, namely single species (isoatomic) cation layers versus mixed species cation layers. Energy differences between various ordered cationic arrangements were found to be small. This may have implications regarding radiation stability, since cationic arrangements should be able to change under irradiation with little cost in energy.« less
Vacancies and Vacancy-Mediated Self Diffusion in Cr 2 O 3 : A First-Principles Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medasani, Bharat; Sushko, Maria L.; Rosso, Kevin M.

Charged and neutral vacancies and vacancy mediated self diffusion in alpha-Cr2O3 were investigated using first principles density functional theory (DFT) and periodic supercell formalism. The vacancy formation energies of charged defects were calculated using the electrostatic finite-size corrections to account for electrostatic interactions between supercells and the corrections for the bandgap underestimation in DFT. Calculations predict that neutral oxygen (O) vacancies are predominant in chromium (Cr)-rich conditions and Cr vacancies with -2 charge state are the dominant defects in O-rich conditions. The charge transition levels of both O and Cr vacancies are deep within the bandgap indicating the stability ofmore » these defects. Transport calculations indicate that vacancy mediated diffusion along the basal plane has lower energy barriers for both O and Cr ions. The most favorable vacancy mediated self diffusion processes correspond to the diffusion of Cr ion in 3+ charge state and O ion in 2- state, respectively. Our calculations reveal that Cr triple defects comprised of Cr in octahedral interstitial sites with two adjacent Cr vacancies along the c-axis have a lower formation energy compared to that of charged Cr vacancies. The formation of such triple defects facilitate Cr self diffusion along the c-axis.« less
Tornadoes within the Czech Republic: from early medieval chronicles to the "internet society"

NASA Astrophysics Data System (ADS)

Setvák, Martin; Šálek, Milan; Munzar, Jan

This paper addresses the historical documentation of tornadoes and the awareness of tornadic events in the area of the present Czech Republic throughout the last nine centuries. The oldest records of tornado occurrence in the region can be found in chronicles from the first half of the 12th century—the two most interesting of these are presented here in translation from the original Latin texts. Several other cases of possible tornadoes and waterspouts can be found in chronicles from the 12th and 13th centuries. However, from the descriptions of the events, it is not always clear if the phenomenon was a tornado, waterspout, dust swirl, or if it was of a non-tornadic nature. From the 14th to 19th centuries, tornado records are rather scarce for the region. However, this is likely to have a non-meteorological explanation. Gregor Mendel's (1871) essay " Die Windhose vom 13. October 1870" can be considered as a distinctive "breakpoint" in the documentation history of tornadoes in the territory of the present Czech Republic, followed later by the work of Edler von Wahlburg [Das Wetter 28 (1911) 135] and Wegener [Wind-und-Wasserhosen in Europa. F. Vieweg & Sohn, Braunschweig, 1917]. During the "socialist" period, the term " tornado" was seldom used and they were poorly understood, producing a view that "tornadoes do not occur in Central Europe". The situation began to change with the works of Munzar [Tromby (tonáda) na území Èeské republiky v letech 1119-1993. Zborník Dejin Fyziky, vol. XI. Voj. Akadémia SNP, Liptovský Mikuláš, pp. 69-72, 1993 (in Czech)] and Šálek [Meteorol. Zpr. 47 (1994) 172], and new records showed that about one tornado per year occurred between 1994 and 1999. Finally, between 2000 and 2002, the number of documented tornadoes in the Czech Republic was five to eight cases per year.
An Analysis of Operational Total Lightning Data During Long-Track Tornadoes

NASA Technical Reports Server (NTRS)

Carcione, Brian C.; Stano, Geoffrey T.

2012-01-01

The 27 April 2011 tornado outbreak brought three distinct waves of tornadic thunderstorms to portions of Mississippi, Alabama, Tennessee, and Georgia, striking the Tennessee Valley of north Alabama and southern Tennessee particularly hard. A total of 42 tornado paths were surveyed across the fourteen county area covered by the National Weather Service (NWS) forecast office in Huntsville, Alabama. Ten of these tornadoes were on the ground for at least 20 miles, two had total path lengths over 130 miles, and six tornadoes were classified as violent (EF-4 or EF-5 on the Enhanced Fujita Scale). Many of these tornadoes occurred within the domain of the North Alabama Lightning Mapping Array (NALMA), a ground-based total lightning detection network owned and operated by the NASA Marshall Space Flight Center. Since 2003, the NASA Short-term Prediction Research and Transition Center has supplied data from NALMA in real time to NWS forecast offices in Huntsville, Knoxville/Tri-Cities, Birmingham, and Nashville. Previous research has documented the utility of total lightning information in predicting tornadogenesis, particularly when combined with other remote sensing tools. Basic warning decision-making during events such as 27 April is not the most difficult part of the process; instead, the focus of warning meteorologists shifts to looking for changes in intensity or possible particularly dangerous situations, since doppler radar velocity data often cannot distinguish between weak and strong tornadoes. To that end, this research attempts to determine if any correlation exists between flash densities of the longest-tracked tornadoes over time, and the surveyed wind speeds of the tornadoes. The long-track EF-5 tornado which struck the Hackleburg, Phil Campbell, and Tanner communities in north Alabama was the primary focus of this research due to its intensity and extended life cycle. However, not all tornadoes were available for total lightning analysis due to widespread power outages which negatively affected the detection efficiency and operation of the NALMA. Therefore, additional storms from 2008-2010 with tracks of at least 20 miles were analyzed for comparison purposes.
Numerical modeling and analysis of the effect of Greek complex topography on tornado genesis

NASA Astrophysics Data System (ADS)

Matsangouras, I. T.; Pytharoulis, I.; Nastos, P. T.

2014-02-01

Tornadoes have been reported in Greece over the last decades in specific sub-geographical areas and have been associated with strong synoptic forcing. It is well known that meteorological conditions over Greece are affected at various scales by the significant variability of topography, the Ionian Sea at the west and the Aegean Sea at the east. However, there is still uncertainty regarding topography's importance on tornadic generation and development. The aim of this study is to investigate the role of topography in significant tornado genesis events that were triggered under strong synoptic scale forcing over Greece. Three tornado events that occurred over the last years in Thiva (Boeotia, 17 November 2007), Vrastema (Chalkidiki, 12 February 2010) and Vlychos (Lefkada, 20 September 2011) have been selected for numerical experiments. These events were associated with synoptic scale forcing, while their intensity was T4-T5 (Torro scale) and caused significant damage. The simulations were performed using the non-hydrostatic Weather Research and Forecasting model (WRF), initialized with ECMWF gridded analyses, with telescoping nested grids that allow the representation of atmospheric circulations ranging from the synoptic scale down to the meso scale. In the experiments the topography of the inner grid was modified by: (a) 0% (actual topography) and (b) -100% (without topography). The aim was to determine whether the occurrence of tornadoes - mainly identified by various severe weather instability indices - could be indicated by modifying topography. The main utilized instability variables concerned the Bulk Richardson number shear (BRN), the energy helicity index (EHI), the storm-relative environmental helicity (SRH) and the maximum convective available potential energy (MCAPE, for parcel with maximum theta-e). Additional a verification of model was conducted for every sensitivity experiment accompanied with analysis absolute vorticity budget. Numerical simulations revealed that the complex topography was denoted as an important factor during 17 November 2007 and 12 February 2010 events, based on EHI and BRN analyses. Topography around 20 September 2011 event was characterized as the least factor based on EHI, SRH, BRN analyses.
Numerical modeling and analysis of the effect of complex Greek topography on tornadogenesis

NASA Astrophysics Data System (ADS)

Matsangouras, I. T.; Pytharoulis, I.; Nastos, P. T.

2014-07-01

Tornadoes have been reported in Greece over recent decades in specific sub-geographical areas and have been associated with strong synoptic forcing. While it has been established that meteorological conditions over Greece are affected at various scales by the significant variability of topography, the Ionian Sea to the west and the Aegean Sea to the east, there is still uncertainty regarding topography's importance on tornadic generation and development. The aim of this study is to investigate the role of topography in significant tornadogenesis events that were triggered under strong synoptic scale forcing over Greece. Three tornado events that occurred over the last years in Thebes (Boeotia, 17 November 2007), Vrastema (Chalkidiki, 12 February 2010) and Vlychos (Lefkada, 20 September 2011) were selected for numerical experiments. These events were associated with synoptic scale forcing, while their intensities were T4-T5 (on the TORRO scale), causing significant damage. The simulations were performed using the non-hydrostatic weather research and forecasting model (WRF), initialized by European Centre for Medium-Range Weather Forecasts (ECMWF) gridded analyses, with telescoping nested grids that allow for the representation of atmospheric circulations ranging from the synoptic scale down to the mesoscale. In the experiments, the topography of the inner grid was modified by: (a) 0% (actual topography) and (b) -100% (without topography), making an effort to determine whether the occurrence of tornadoes - mainly identified by various severe weather instability indices - could be indicated by modifying topography. The principal instability variables employed consisted of the bulk Richardson number (BRN) shear, the energy helicity index (EHI), the storm-relative environmental helicity (SRH), and the maximum convective available potential energy (MCAPE, for parcels with maximum θe). Additionally, a model verification was conducted for every sensitivity experiment accompanied by analysis of the absolute vorticity budget. Numerical simulations revealed that the complex topography constituted an important factor during the 17 November 2007 and 12 February 2010 events, based on EHI, SRH, BRN, and MCAPE analyses. Conversely, topography around the 20 September 2011 event was characterized as the least significant factor based on EHI, SRH, BRN, and MCAPE analyses.
Visions of our Planet's Atmosphere, Land & Oceans

NASA Technical Reports Server (NTRS)

Hasler, Arthur F.

2002-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to South Africa, Cape Town and Johannesburg using NASA Terra MODIS data, Landsat data and 1m IKONOS "Spy Satellite" data. Zoom in to any place South Africa using Earth Viewer 3D from Keyhole Inc. and Landsat data at 30 m resolution. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes & "tornadoes". See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained. See how High-Definition Television (HDTV) is revolutionizing the way we present science to the public. See dust storms and flooding in Africa and smoke plumes from fires in Mexico. See visualizations featured on the covers of Newsweek, TIME, National Geographic, Popular Science & on National & International Network TV. New computer software tools allow us to roam & zoom through massive global images e.g. Landsat tours of the US, and Africa, showing desert and mountain geology as well as seasonal changes in vegetation. See animations of the north and south polar ice packs and with icebergs on the coasts of Greenland and off the coast of Antarctica. Spectacular new visualizations of the global land, atmosphere & oceans are shown. Listen to the pulse of our planet. See how land vegetation, ocean plankton, clouds and temperatures respond to the sun & seasons. See vortexes and currents in the global oceans that bring up the nutrients to feed tiny algae and draw the fish, whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. See the city lights, fishing fleets, gas flares and biomass burning of the Earth at night observed by the "night-vision" DMSP military satellite. The presentation will be made using the latest HDTV and video projection technology that is now done from a laptop computer through an entirely digital path.
Charge-density-shear-moduli relationships in aluminum-lithium alloys.

PubMed

Eberhart, M

2001-11-12

Using the first principles full-potential linear-augmented-Slater-type orbital technique, the energies and charge densities of aluminum and aluminum-lithium supercells have been computed. The experimentally observed increase in aluminum's shear moduli upon alloying with lithium is argued to be the result of predictable changes to aluminum's total charge density, suggesting that simple rules may allow the alloy designer to predict the effects of dilute substitutional elements on alloy elastic response.
Numeric and fluid dynamic representation of tornadic double vortex thunderstorms

NASA Technical Reports Server (NTRS)

Connell, J. R.; Marquart, E. J.; Frost, W.; Boaz, W.

1980-01-01

Current understanding of a double vortex thunderstorm involves a pair of contra-rotating vortices that exists in the dynamic updraft. The pair is believed to be a result of a blocking effect which occurs when a cylindrical thermal updraft of a thunderstorm protrudes into the upper level air and there is a large amount of vertical wind shear between the low level and upper level air layers. A numerical tornado prediction scheme based on the double vortex thunderstorm was developed. The Energy-Shear Index (ESI) is part of the scheme and is calculated from radiosonde measurements. The ESI incorporates parameters representative of thermal instability and blocking effect, and indicates appropriate environments for which the development of double vortex thunderstorms is likely.
Spatial-temporal clustering of tornadoes

NASA Astrophysics Data System (ADS)

Malamud, Bruce D.; Turcotte, Donald L.; Brooks, Harold E.

2016-12-01

The standard measure of the intensity of a tornado is the Enhanced Fujita scale, which is based qualitatively on the damage caused by a tornado. An alternative measure of tornado intensity is the tornado path length, L. Here we examine the spatial-temporal clustering of severe tornadoes, which we define as having path lengths L ≥ 10 km. Of particular concern are tornado outbreaks, when a large number of severe tornadoes occur in a day in a restricted region. We apply a spatial-temporal clustering analysis developed for earthquakes. We take all pairs of severe tornadoes in observed and modelled outbreaks, and for each pair plot the spatial lag (distance between touchdown points) against the temporal lag (time between touchdown points). We apply our spatial-temporal lag methodology to the intense tornado outbreaks in the central United States on 26 and 27 April 2011, which resulted in over 300 fatalities and produced 109 severe (L ≥ 10 km) tornadoes. The patterns of spatial-temporal lag correlations that we obtain for the 2 days are strikingly different. On 26 April 2011, there were 45 severe tornadoes and our clustering analysis is dominated by a complex sequence of linear features. We associate the linear patterns with the tornadoes generated in either a single cell thunderstorm or a closely spaced cluster of single cell thunderstorms moving at a near-constant velocity. Our study of a derecho tornado outbreak of six severe tornadoes on 4 April 2011 along with modelled outbreak scenarios confirms this association. On 27 April 2011, there were 64 severe tornadoes and our clustering analysis is predominantly random with virtually no embedded linear patterns. We associate this pattern with a large number of interacting supercell thunderstorms generating tornadoes randomly in space and time. In order to better understand these associations, we also applied our approach to the Great Plains tornado outbreak of 3 May 1999. Careful studies by others have associated individual tornadoes with specified supercell thunderstorms. Our analysis of the 3 May 1999 tornado outbreak directly associated linear features in the largely random spatial-temporal analysis with several supercell thunderstorms, which we then confirmed using model scenarios of synthetic tornado outbreaks. We suggest that it may be possible to develop a semi-automated modelling of tornado touchdowns to match the type of observations made on the 3 May 1999 outbreak.
Spatial-Temporal Clustering of Tornadoes

NASA Astrophysics Data System (ADS)

Malamud, Bruce D.; Turcotte, Donald L.; Brooks, Harold E.

2017-04-01

The standard measure of the intensity of a tornado is the Enhanced Fujita scale, which is based qualitatively on the damage caused by a tornado. An alternative measure of tornado intensity is the tornado path length, L. Here we examine the spatial-temporal clustering of severe tornadoes, which we define as having path lengths L ≥ 10 km. Of particular concern are tornado outbreaks, when a large number of severe tornadoes occur in a day in a restricted region. We apply a spatial-temporal clustering analysis developed for earthquakes. We take all pairs of severe tornadoes in observed and modelled outbreaks, and for each pair plot the spatial lag (distance between touchdown points) against the temporal lag (time between touchdown points). We apply our spatial-temporal lag methodology to the intense tornado outbreaks in the central United States on 26 and 27 April 2011, which resulted in over 300 fatalities and produced 109 severe (L ≥ 10 km) tornadoes. The patterns of spatial-temporal lag correlations that we obtain for the 2 days are strikingly different. On 26 April 2011, there were 45 severe tornadoes and our clustering analysis is dominated by a complex sequence of linear features. We associate the linear patterns with the tornadoes generated in either a single cell thunderstorm or a closely spaced cluster of single cell thunderstorms moving at a near-constant velocity. Our study of a derecho tornado outbreak of six severe tornadoes on 4 April 2011 along with modelled outbreak scenarios confirms this association. On 27 April 2011, there were 64 severe tornadoes and our clustering analysis is predominantly random with virtually no embedded linear patterns. We associate this pattern with a large number of interacting supercell thunderstorms generating tornadoes randomly in space and time. In order to better understand these associations, we also applied our approach to the Great Plains tornado outbreak of 3 May 1999. Careful studies by others have associated individual tornadoes with specified supercell thunderstorms. Our analysis of the 3 May 1999 tornado outbreak directly associated linear features in the largely random spatial-temporal analysis with several supercell thunderstorms, which we then confirmed using model scenarios of synthetic tornado outbreaks. We suggest that it may be possible to develop a semi-automated modelling of tornado touchdowns to match the type of observations made on the 3 May 1999 outbreak.
Modeling CANDU-6 liquid zone controllers for effects of thorium-based fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

St-Aubin, E.; Marleau, G.

2012-07-01

We use the DRAGON code to model the CANDU-6 liquid zone controllers and evaluate the effects of thorium-based fuels on their incremental cross sections and reactivity worth. We optimize both the numerical quadrature and spatial discretization for 2D cell models in order to provide accurate fuel properties for 3D liquid zone controller supercell models. We propose a low computer cost parameterized pseudo-exact 3D cluster geometries modeling approach that avoids tracking issues on small external surfaces. This methodology provides consistent incremental cross sections and reactivity worths when the thickness of the buffer region is reduced. When compared with an approximate annularmore » geometry representation of the fuel and coolant region, we observe that the cluster description of fuel bundles in the supercell models does not increase considerably the precision of the results while increasing substantially the CPU time. In addition, this comparison shows that it is imperative to finely describe the liquid zone controller geometry since it has a strong impact of the incremental cross sections. This paper also shows that liquid zone controller reactivity worth is greatly decreased in presence of thorium-based fuels compared to the reference natural uranium fuel, since the fission and the fast to thermal scattering incremental cross sections are higher for the new fuels. (authors)« less
Phonon structures of GaN-based random semiconductor alloys

NASA Astrophysics Data System (ADS)

Zhou, Mei; Chen, Xiaobin; Li, Gang; Zheng, Fawei; Zhang, Ping

2017-12-01

Accurate modeling of thermal properties is strikingly important for developing next-generation electronics with high performance. Many thermal properties are closely related to phonon dispersions, such as sound velocity. However, random substituted semiconductor alloys AxB1-x usually lack translational symmetry, and simulation with periodic boundary conditions often requires large supercells, which makes phonon dispersion highly folded and hardly comparable with experimental results. Here, we adopt a large supercell with randomly distributed A and B atoms to investigate substitution effect on the phonon dispersions of semiconductor alloys systematically by using phonon unfolding method [F. Zheng, P. Zhang, Comput. Mater. Sci. 125, 218 (2016)]. The results reveal the extent to which phonon band characteristics in (In,Ga)N and Ga(N,P) are preserved or lost at different compositions and q points. Generally, most characteristics of phonon dispersions can be preserved with indium substitution of gallium in GaN, while substitution of nitrogen with phosphorus strongly perturbs the phonon dispersion of GaN, showing a rapid disintegration of the Bloch characteristics of optical modes and introducing localized impurity modes. In addition, the sound velocities of both (In,Ga)N and Ga(N,P) display a nearly linear behavior as a function of substitution compositions. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-80481-0.
Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering.

PubMed

Wall, Michael E

2018-03-01

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structure to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.
DFT with larger supercells explains the band gap formation in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Zunger, Alex; Trimarchi, Giancarlo

The existence of large band gaps both in the antiferromagnetic (AFM) and the paramagnetic (PM) phases of the classic Mott insulators MnO, FeO, CoO, and NiO has traditionally been discussed in terms of theoretical methods requiring both (i) simple (often primitive) unit cells and (ii) correlated-electron methodologies. We show that if condition (i) is avoided (by using supercells, such as PM special quasi-random structures, in which chemically identical atoms can have different local environments), then even without condition (ii) one can describe the gaps and moments within a single-determinant DFT band structure approach. In this approach gapping is caused by basic structure, magnetism, and bonding effects underlying DFT, not via dynamic correlation (absent from DFT). As long as correlation is simplistically considered as ``anything that DFT does not get right'', gap formation in the AFM and PM phases is not due to correlation. This result defines the minimal theoretical methods needed to explain gapping and points to the possibility that some transition-metal oxides generally considered to have localized electrons detrimental to transport, could, in fact, rejoin the family of electronic semiconductors, to the benefit of a carrier transport technologies. A. Z. supported by DOE-OS-BES-MSE, Grant DE-FG02-13ER46959.

Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wall, Michael E.

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structuremore » to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.« less
Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering

DOE PAGES

Wall, Michael E.

2018-01-25

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structuremore » to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.« less
The behavior of the radar parameters of cumulonimbus clouds during cloud seeding with AgI

NASA Astrophysics Data System (ADS)

Vujović, D.; Protić, M.

2017-06-01

Deep convection yielding severe weather phenomena (hail, flash floods, thunder) is frequent in Serbia during the warmer part of the year, i.e. April to September. As an effort to mitigate any potential damage to material goods, agricultural crops and vegetation from larger hailstones, cloud seeding is performed. In this paper, we analyzed 29 severe hailstorms seeded by silver iodide. From these, we chose five intense summer thunderstorm cells to analyze in detail the influence of silver-iodide cloud seeding on the radar parameters. Four of them were seeded and one was not. We also used data from firing stations (hail fall occurrence, the size of the hailstones). The most sensitive radar parameter in seeding was the height where maximum reflectivity in the cloud was observed. Its cascade appeared in every case of seeding, but was absent from the non-seeded case. In the case of the supercell, increase and decrease of the height where maximum reflectivity in the cloud was observed occurred in almost regular intervals, 12 to 15 min. The most inert parameter in seeding was maximum radar reflectivity. It changed one to two dBz during one cycle. The height of the top of the cloud and the height of the zone exhibiting enhanced radar echo both had similar behavior. It seems that both increased after seeding due to a dynamic effect: upward currents increasing due to the release of latent heat during the freezing of supercooled droplets. Mean values of the height where maximum reflectivity in the cloud was observed, the height of the top of the cloud and the height of the zone exhibiting enhanced radar echo during seeded period were greater than during unseeded period in 75.9%, 72.4% and 79.3% cases, respectively. This is because the values of the chosen storm parameters were higher when the seeding started, and then those values decreased after the seeded was conducted.
Finding the Stable Structures of N1-xWx with an Ab Initio High-Throughput Approach

DTIC Science & Technology

2015-05-26

W. These include borides , carbides, oxides, and other nitrides. We also invented many structures to mimic the random pattern of vacancies on both the...structures. These include nitrides, oxides, borides , and carbides, as well as supercells of standard structures with atoms removed to mimic the random patter...1930). [15] R. Kiessling and Y. H. Liu, Thermal stability of the chromium, iron, and tungsten borides in streaming ammonia and the existence of a new
Visions of our Planet's Atmosphere, Land and Oceans

NASA Technical Reports Server (NTRS)

Hasler, A. F.

2002-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to South Africa, Cape Town and Johannesburg using NASA Terra/MODIS data, Landsat data and 1 m IKONOS 'Spy Satellite' data. Zoom in to any place South Africa using Earth Viewer 3D from Keyhole Inc. and Landsat data at 30 m resolution Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes & 'tornadoes'. See the latest visualizations of spectacular images from NASANOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained.
Discrimination of tornadic and non-tornadic severe weather outbreaks

NASA Astrophysics Data System (ADS)

Mercer, Andrew Edward

Outbreaks of severe weather affect the majority of the conterminous United States. An outbreak is characterized by multiple severe weather occurrences within a single synoptic system. Outbreaks can be categorized by whether or not they produce tornadoes. It is hypothesized that the antecedent synoptic signal contains important information about outbreak type. Accordingly, the scope of this research is to determine the extent that the synoptic signal can be utilized to classify outbreak type at various lead times. Outbreak types are classified using the NCEP/NCAR reanalysis data, which are arranged on a global 2.5° latitude-longitude grid, include 17 vertical pressure levels, and span from 1948 to the present (2008). Fifty major tornado outbreak (TO) cases and fifty major non-tornadic severe weather outbreak (NTO) cases are selected for this work. Two types of analyses are performed on these cases to assess discrimination ability. One analysis involves outbreak classification using the Weather Research and Forecasting (WRF) model initialized with the NCEP/NCAR reanalysis dataset. Meteorological covariates are computed from the WRF output and used in training and testing of statistical classification models. The covariate fields are depicted on a 21 X 21 gridpoint field with an 18 km grid spacing centered on the outbreak. Covariates with large discrimination potential are determined using permutation testing. A P-mode principal component analysis (PCA) is used on the subset of covariates determined by permutation testing to reduce data dimensionality, since numerous redundancies exist in the initial covariate set. Three statistical classification models are trained and tested with the resulting PC scores: a support vector machine (SVM), a logistic regression model (LogR), and a multiple linear regression model (LR). Promising results emerge from these methods, as a probability of detection (POD) of 0.89 and a false alarm ratio (FAR) of 0.13 are obtained from the best discriminating statistical technique (SVM) at 24-hours lead time. Results degrade only slightly by 72-hours lead time (maximum POD of 0.833 and minimum FAR of 0.276). Synoptic composites of the outbreak types are the second analysis considered. Composites are used to reveal synoptic features of outbreak types, which can be utilized to diagnose the differences between classes (in this case, TOs and NTOs). The composites are created using PCA. Five raw variables, height, temperature, relative humidity, and u and v wind components, are extracted from the NCEP/NCAR reanalysis data for North America. Converging longitude lines with increasing latitude on the reanalysis grid introduce bias into correlation calculations in higher latitudes; hence, the data are mapped onto both a latitudinal density grid and a Fibonacci grid. The resulting PCA produces two significant principal components (PCs), and a cluster analysis on these PCs for each outbreak type results in two types of TOs and NTOs. TO composites are characterized by a trough of low pressure over the central United States and major quasigeostrophic forcing features such as an upper level jet streak, cyclonic vorticity advection increasing with height, and warm air advection. These dynamics result in a strong surface cyclone in most tornado outbreaks. These features are considerably less pronounced in NTOs. The statistical analyses presented herein were successful in classifying outbreak types at various lead times, using synoptic scale data as input.
First-principles research on the optical and electrical properties and mechanisms of In-doped ZnO

NASA Astrophysics Data System (ADS)

Hou, Qingyu; Xi, Dongmin; Li, Wenling; Jia, Xiaofang; Xu, Zhenchao

2018-05-01

The absorption spectra and conductivity of In-doped ZnO still exhibit differences. To resolve this contradiction, the ZnO supercell models with different In doping amounts and the Zn0.9375In0.0625(Zni)0.0625O supercell model were both constructed. When the geometrical structure of all the models was optimized, the GGA + U and GGA used to calculate the energy. In the range of In doping used in this study, the formation energy of In-doped ZnO under Zn-rich conditions is lower than that under O-rich conditions, thereby implying a more stability of In-doped ZnO under Zn-rich than that under O-rich. With the increased In doping content, the volume and the formation energy of the doped system increase, the doped systems become unstable, and doping becomes difficult. Furthermore, the band gaps are narrowed, and the red shift of absorption spectrum is enhanced. In the In doping amount ranging within 0.01389-0.05556, the electron effective mass decreases first and subsequently increases, and the electron concentration increases. The mobility and conductivity also increase first and subsequently decrease. These results are in accordance with the experimental results. The volume of Zn0.9375In0.0625(Zni)0.0625O with the coexistence of In replacing Zn and interstitial Zn is large. The band gap is widened and the absorption spectrum is blue-shifted in the UV region.
Surface calculations with asymptotically long-ranged potentials in the full-potential linearized augmented plane-wave method

NASA Astrophysics Data System (ADS)

Ye, Lin-Hui

2015-09-01

Although the supercell method has been widely used for surface calculations, it only works well with short-ranged potentials, but meets difficulty when the potential decays very slowly into the vacuum. Unfortunately, the exact exchange-correlation potential of the density functional theory is asymptotically long ranged, and therefore is not easily handled by use of supercells. This paper illustrates that the authentic slab geometry, another technique for surface calculations, is not affected by this issue: It works equally well with both short- and long-ranged potentials, with the computational cost and the convergence speed being essentially the same. Using the asymptotically long-ranged Becke-Roussel'89 exchange potential as an example, we have calculated six surfaces of various types. We found that accurate potential values can be obtained even in extremely low density regions of more than 100 Å away from the surface. This high performance allows us to explore the asymptotic region, and prove with clean numerical evidence that the Becke-Roussel'89 potential satisfies the correct asymptotic behavior for slab surfaces, as it does for finite systems. Our finding further implies that the Slater component of the exact exchange optimized effective potential is responsible for the asymptotic behavior, not only for jellium slabs, but for slabs of any type. The Becke-Roussel'89 potential may therefore be used to build asymptotically correct model exchange potentials applicable to both finite systems and slab surfaces.
Superlattice Structures, Electronic Properties, and Spin Dynamics of the Partially Cu-Extracted Phase for the Composite Crystal System CuxV4O11

NASA Astrophysics Data System (ADS)

Onoda, Masashige; Tamura, Asato

2017-02-01

The crystal structures, electronic properties, and spin dynamics of CuxV4O11 with 1.2 ≤ x < 2, classified as the partially Cu-extracted phase for the composite crystal system, are explored through measurements of x-ray four-circle diffraction, electrochemistry, electrical resistivity, thermoelectric power, magnetization, and electron paramagnetic resonance. This system has superlattice structures mainly ascribed to the partial ordering of Cu ions. Cu1.78V4O11 is triclinic with space group Pbar{1} and the double supercell of the V4O11 substructure of the composite crystal. The significantly Cu-extracted crystal Cu1.40V4O11 has a quadruple supercell with space group P1. The electron transport for V ions is nonmetallic owing to the polaronic nature and/or phonon softening and to the random potential of Cu ions. The Curie-Weiss-type paramagnetism basically originates from the Cu2+ chain coordinated octahedrally, and the EPR relaxation at low temperatures is understood through the exchange mechanism for the dipole-dipole and anisotropic exchange interactions. The near absence of paramagnetic behaviors of V4+ ions might be due to the spin-singlet ladder model or alternating-exchange chain model depending on the superlattice structure and valence distribution. The electrochemical performance of Li rechargeable batteries using this superlattice system is about 300 A h kg-1 at voltages above 2 V.
Role of defects in ferromagnetism in Zn1-xCoxO : A hybrid density-functional study

NASA Astrophysics Data System (ADS)

Patterson, C. H.

2006-10-01

Experimental studies of Zn1-xCoxO as thin films or nanocrystals have found ferromagnetism and Curie temperatures above room temperature and that p - or n -type doping of Zn1-xCoxO can change its magnetic state. Bulk Zn1-xCoxO with a low defect density and x in the range used in experimental thin-film studies exhibits ferromagnetism only at very low temperatures. Therefore defects in thin-film samples or nanocrystals may play an important role in promoting magnetic interactions between Co ions in Zn1-xCoxO . The mechanism of exchange coupling induced by defect states is considered and compared to a model for ferromagnetism in dilute magnetic semiconductors [T. Dietl , Science 287, 1019 (2000)]. The electronic structures of Co substituted for Zn in ZnO, Zn, and O vacancies, substituted N, and interstitial Zn in ZnO were calculated using the B3LYP hybrid density functional in a supercell. The B3LYP functional predicts a band gap of 3.34eV for bulk ZnO, close to the experimental value of 3.47eV . Occupied minority-spin Co 3d levels are at the top of the valence band and unoccupied levels lie above the conduction-band minimum. Majority-spin Co 3d levels hybridize strongly with bulk ZnO states. The neutral O vacancy defect level is predicted to lie deep in the band gap, and interstitial Zn is predicted to be a deep donor. The Zn vacancy is a deep acceptor, and the acceptor level for substituted N is at midgap. The possibility that p - or n -type dopants promote exchange coupling of Co ions was investigated by computing the total energies of magnetic states of ZnO supercells containing two Co ions and an oxygen vacancy, substituted N, or interstitial Zn in various charge states. The neutral N defect and the singly positively charged O vacancy are the only defects which strongly promote ferromagnetic exchange coupling of Co ions at intermediate range. Total energy calculations on supercells containing two O vacancies and one Zn vacancy clearly show that pairs of singly positively charged O vacancies are unstable with respect to dissociation into neutral and doubly positively charged vacancies; the oxygen vacancy is a “negative U ” defect. This apparently precludes simple charged O vacancies as a mediator of ferromagnetism in Zn1-xCoxO .
Modeling of Coastal Inundation, Storm Surge, and Relative Sea-Level Rise at Naval Station Norfolk, Norfolk, Virginia, U.S.A.

DTIC Science & Technology

2012-01-01

of 2 m. ADDITIONAL INDEX WORDS: Nearshore hydrodynamic modeling, waves, synthetic tropical storms , extratropical storms , Hurricane Isabel, land...an increase in SLR and coastal storms , including hurricanes (tropical storms ) and winter storms ( extratropical storms ), will increase the risk of... storms ) corresponding to 50-year and 100-year return periods and a most probable winter storm ( extratropical ) that occurred in October 1982 (Burks-Copes
Band engineering in transition metal dichalcogenides: Stacked versus lateral heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Yuzheng; Robertson, John

2016-06-06

We calculate a large difference in the band alignments for transition metal dichalcogenide (TMD) heterojunctions when arranged in the stacked layer or lateral (in-plane) geometries, using direct supercell calculations. The stacked case follows the unpinned limit of the electron affinity rule, whereas the lateral geometry follows the strongly pinned limit of alignment of charge neutrality levels. TMDs therefore provide one of the few clear tests of band alignment models, whereas three-dimensional semiconductors give less stringent tests because of accidental chemical trends in their properties.
The 1886 tornado of Madrid

NASA Astrophysics Data System (ADS)

Gayà, Miquel

2007-02-01

Considering the number of dead people, the worst tornado in the last two centuries in Spain is presented. The words used to describe the phenomenon have hidden it to the general public and the specialist The coetaneous press and other printed sources have been revised, and this has let us know the true sense of those words as well as the sequence of the tornadic event. The synoptic situation that was presented by some European Meteorological Offices in 1886 has been revised when all available data and some indirect information have been included. Tornado track and force have been plotted on the actual map of the city following the available information in the newspapers and other documents. Other subjective comments made by the paper writers have allowed us to find out some psychological and sociological aspects used to enhance the tragic perception of their readers.
Visions of our Planet's Atmosphere, Land and Oceans: Spectacular Visualizations of our Blue Marble

NASA Technical Reports Server (NTRS)

Hasler, A. F.; Starr, David (Technical Monitor)

2002-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to South Africa, Cape Town and Johannesburg using NASA Terra/MODIS data, Landsat data and 1 m IKONOS 'Spy Satellite' data. Zoom in to any place South Africa using Earth Viewer 3D from Keyhole Inc. and Landsat data at 30 m resolution. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes and 'tornadoes'. See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained.
Wind shear and wet and dry thermodynamic indices as predictors of thunderstorm motion and severity and application to the AVE 4 experimental data

NASA Technical Reports Server (NTRS)

Connell, J. R.; Ey, L.

1977-01-01

Two types of parameters are computed and mapped for use in assessing their individual merits as predictors of occurrence and severity of thunderstorms. The first group is comprised of equivalent potential temperature, potential temperature, water vapor mixing ratio, and wind speed. Equivalent potential temperature maxima and strong gradients of equivalent potential temperature at the surface correlate well with regions of thunderstorm activity. The second type, comprised of the energy index, shear index, and energy shear index, incorporates some model dynamics of thunderstorms, including nonthermodynamic forcing. The energy shear index is found to improve prediction of tornadic and high-wind situations slightly better than other indices. It is concluded that further development and refinement of nonthermodynamic aspects of predictive indices are definitely warranted.
NASA/NOAA: Earth Science Electronic Theater 1999. Earth Science Observations, Analysis and Visualization: Roots in the 60s - Vision for the Next Millennium

NASA Technical Reports Server (NTRS)

Hasler, A. Fritz

1999-01-01

The Etheater presents visualizations which span the period from the original Suomi/Hasler animations of the first ATS-1 GEO weather satellite images in 1966, to the latest 1999 NASA Earth Science Vision for the next 25 years. Hot off the SGI-Onyx Graphics-Supercomputer are NASA''s visualizations of Hurricanes Mitch, Georges, Fran and Linda. These storms have been recently featured on the covers of National Geographic, Time, Newsweek and Popular Science. Highlights will be shown from the NASA hurricane visualization resource video tape that has been used repeatedly this season on National and International network TV. Results will be presented from a new paper on automatic wind measurements in Hurricane Luis from 1-min GOES images that appeared in the November BAMS. The visualizations are produced by the NASA Goddard Visualization & Analysis Laboratory, and Scientific Visualization Studio, as well as other Goddard and NASA groups using NASA, NOAA, ESA, and NASDA Earth science datasets. Visualizations will be shown from the Earth Science ETheater 1999 recently presented in Tokyo, Paris, Munich, Sydney, Melbourne, Honolulu, Washington, New York, and Dallas. The presentation Jan 11-14 at the AMS meeting in Dallas used a 4-CPU SGI/CRAY Onyx Infinite Reality Super Graphics Workstation with 8 GB RAM and a Terabyte Disk at 3840 X 1024 resolution with triple synchronized BarcoReality 9200 projectors on a 60ft wide screen. Visualizations will also be featured from the new Earth Today Exhibit which was opened by Vice President Gore on July 2, 1998 at the Smithsonian Air & Space Museum in Washington, as well as those presented for possible use at the American Museum of Natural History (NYC), Disney EPCOT, and other venues. New methods are demonstrated for visualizing, interpreting, comparing, organizing and analyzing immense HyperImage remote sensing datasets and three dimensional numerical model results. We call the data from many new Earth sensing satellites, HyperImage datasets, because they have such high resolution in the spectral, temporal, spatial, and dynamic range domains. The traditional numerical spreadsheet paradigm has been extended to develop a scientific visualization approach for processing HyperImage datasets and 3D model results interactively. The advantages of extending the powerful spreadsheet style of computation to multiple sets of images and organizing image processing were demonstrated using the Distributed Image SpreadSheet (DISS). The DISS is being used as a high performance testbed Next Generation Internet (NGI) VisAnalysis of: 1) El Nino SSTs and NDVI response 2) Latest GOES 10 5-min rapid Scans of 26 day 5000 frame movie of March & April 198 weather and tornadic storms 3) TRMM rainfall and lightning 4)GOES 9 satellite images/winds and NOAA aircraft radar of hurricane Luis, 5) lightning detector data merged with GOES image sequences, 6) Japanese GMS, TRMM, & ADEOS data 7) Chinese FY2 data 8) Meteosat & ERS/ATSR data 9) synchronized manipulation of multiple 3D numerical model views; etc. will be illustrated. The Image SpreadSheet has been highly successful in producing Earth science visualizations for public outreach.
Variation of Magnetic Field (By , Bz) Polarity and Statistical Analysis of Solar Wind Parameters during the Magnetic Storm Period

NASA Astrophysics Data System (ADS)

Moon, Ga-Hee

2011-06-01

It is generally believed that the occurrence of a magnetic storm depends upon the solar wind conditions, particularly the southward interplanetary magnetic field (IMF) component. To understand the relationship between solar wind parameters and magnetic storms, variations in magnetic field polarity and solar wind parameters during magnetic storms are examined. A total of 156 storms during the period of 1997~2003 are used. According to the interplanetary driver, magnetic storms are divided into three types, which are coronal mass ejection (CME)-driven storms, co-rotating interaction region (CIR)-driven storms, and complicated type storms. Complicated types were not included in this study. For this purpose, the manner in which the direction change of IMF By and Bz components (in geocentric solar magnetospheric coordinate system coordinate) during the main phase is related with the development of the storm is examined. The time-integrated solar wind parameters are compared with the time-integrated disturbance storm time (Dst) index during the main phase of each magnetic storm. The time lag with the storm size is also investigated. Some results are worth noting: CME-driven storms, under steady conditions of Bz < 0, represent more than half of the storms in number. That is, it is found that the average number of storms for negative sign of IMF Bz (T1~T4) is high, at 56.4%, 53.0%, and 63.7% in each storm category, respectively. However, for the CIR-driven storms, the percentage of moderate storms is only 29.2%, while the number of intense storms is more than half (60.0%) under the Bz < 0 condition. It is found that the correlation is highest between the time-integrated IMF Bz and the time-integrated Dst index for the CME-driven storms. On the other hand, for the CIR-driven storms, a high correlation is found, with the correlation coefficient being 0.93, between time-integrated Dst index and time-integrated solar wind speed, while a low correlation, 0.51, is found between timeintegrated Bz and time-integrated Dst index. The relationship between storm size and time lag in terms of hours from Bz minimum to Dst minimum values is investigated. For the CME-driven storms, time lag of 26% of moderate storms is one hour, whereas time lag of 33% of moderate storms is two hours for the CIR-driven storms. The average values of solar wind parameters for the CME and CIR-driven storms are also examined. The average values of |Dstmin| and |Bzmin| for the CME-driven storms are higher than those of CIR-driven storms, while the average value of temperature is lower.
Numerical modeling studies of wake vortex transport and evolution within the planetary boundary layer

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.

1994-01-01

The proposed research involves four tasks. The first of these is to simulate accurately the turbulent processes in the atmospheric boundary layer. TASS was originally developed to study meso-gamma scale phenomena, such as tornadic storms, microbursts and windshear effects in terminal areas. Simulation of wake vortex evolution, however, will rely on appropriate representation of the physical processes in the surface layer and mixed layer. This involves two parts. First, a specified heat flux boundary condition must be implemented at the surface. Using this boundary condition, simulation results will be compared to experimental data and to other model results for validation. At this point, any necessary changes to the model will be implemented. Next, a surface energy budget parameterization will be added to the model. This will enable calculation of the surface fluxes by accounting for the radiative heat transfer to and from the ground and heat loss to the soil rather than simple specification of the fluxes. The second task involves running TASS with prescribed wake vortices in the initial condition. The vortex models will be supplied by NASA Langley Research Center. Sensitivity tests will be performed on different meteorological environments in the atmospheric boundary layer, which include stable, neutral, and unstable stratifications, calm and severe wind conditions, and dry and wet conditions. Vortex strength may be varied as well. Relevant non-dimensional parameters will include the following: Richardson number or Froude number, Bowen ratio, and height to length scale ratios. The model output will be analyzed and visualized to better understand the transport, decay, and growth rates of the wake vortices. The third task involves running simulations using observed data. MIT Lincoln Labs is currently planning field experiments at the Memphis airport to measure both meteorological conditions and wake vortex characteristics. Once this data becomes available, it can be used to validate the model for vortex behavior under different atmospheric conditions. The fourth task will be to simulate the wake in a more realistic environment covering a wider area. This will involve grid nesting, since high resolution will be required in the wake region but a larger total domain will be used. During the first allocation year, most of the first task will be accomplished.
76 FR 38618 - Proposed Information Collection; Comment Request; StormReadyTM

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-01

... Collection; Comment Request; StormReady\\TM\\, TsunamiReady\\TM\\ and StormReady/TsunamiReady\\TM\\ Application... information collection. The StormReady Program, like the TsunamiReady and StormReady/TsunamiReady programs... certain guidelines that qualify them for StormReady recognition. The full StormReady recognition is not...
Defining Coastal Storm and Quantifying Storms Applying Coastal Storm Impulse Parameter

NASA Astrophysics Data System (ADS)

Mahmoudpour, Nader

2014-05-01

What defines a storm condition and what would initiate a "storm" has not been uniquely defined among scientists and engineers. Parameters that have been used to define a storm condition can be mentioned as wind speed, beach erosion and storm hydrodynamics parameters such as wave height and water levels. Some of the parameters are storm consequential such as beach erosion and some are not directly related to the storm hydrodynamics such as wind speed. For the purpose of the presentation, the different storm conditions based on wave height, water levels, wind speed and beach erosion will be discussed and assessed. However, it sounds more scientifically to have the storm definition based on the hydrodynamic parameters such as wave height, water level and storm duration. Once the storm condition is defined and storm has initiated, the severity of the storm would be a question to forecast and evaluate the hazard and analyze the risk in order to determine the appropriate responses. The correlation of storm damages to the meteorological and hydrodynamics parameters can be defined as a storm scale, storm index or storm parameter and it is needed to simplify the complexity of variation involved developing the scale for risk analysis and response management. A newly introduced Coastal Storm Impulse (COSI) parameter quantifies storms into one number for a specific location and storm event. The COSI parameter is based on the conservation of linear, horizontal momentum to combine storm surge, wave dynamics, and currents over the storm duration. The COSI parameter applies the principle of conservation of momentum to physically combine the hydrodynamic variables per unit width of shoreline. This total momentum is then integrated over the duration of the storm to determine the storm's impulse to the coast. The COSI parameter employs the mean, time-averaged nonlinear (Fourier) wave momentum flux, over the wave period added to the horizontal storm surge momentum above the Mean High Water (MHW) integrated over the storm duration. The COSI parameter methodology has been applied to a 10-year data set from 1994 to 2003 at US Army Corps of Engineers, Field Research Facility (FRF) located on the Atlantic Ocean in Duck, North Carolina. The storm duration was taken as the length of time (hours) that the spectral significant wave heights were equal or greater than 1.6 meters for at least a 12 hour, continuous period. Wave heights were measured in 8 meters water depth and water levels measured at the NOAA/NOS tide gauge at the end of the FRF pier. The 10-year data set were analyzed applying the aforementioned storm criteria and produced 148 coastal events including Hurricanes and Northeasters. The results of this analysis and application of the COSI parameter to determine "Extra Ordinary" storms in Federal Projects for the Gulf of Mexico, 2012 hurricane season will be discussed at the time of presentation.

On the mid-latitude ionospheric storm association with intense geomagnetic storms

NASA Astrophysics Data System (ADS)

Okpala, Kingsley Chukwudi; Ogbonna, Chinasa Edith

2018-04-01

The bulk association between ionospheric storms and geomagnetic storms has been studied. Hemispheric features of seasonal variation of ionospheric storms in the mid-latitude were also investigated. 188 intense geomagnetic storms (Dst ≤ 100 nT) that occurred during solar cycles 22 and 23 were considered, of which 143 were observed to be identified with an ionospheric storm. Individual ionospheric storms were identified as maximum deviations of the F2 layer peak electron density from quiet time values. Only ionospheric storms that could clearly be associated with the peak of a geomagnetic storm were considered. Data from two mid-latitude ionosonde stations; one in the northern hemisphere (i.e. Moscow) and the other in the southern hemisphere (Grahamstown) were used to study ionospheric conditions at the time of the individual geomagnetic storms. Results show hemispheric and latitudinal differences in the intensity and nature of ionospheric storms association with different types of geomagnetic storms. These results are significant for our present understanding of the mechanisms which drive the changes in electron density during different types of ionospheric storms.
A Study of Ionospheric Storm Association with Intense Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Okpala, K. C.

2017-12-01

The bulk association between ionospheric storms and geomagnetic storms have been studied. Hemispheric features of seasonal variation of ionospheric storms in the mid-latitude were also investigated. 188 intense geomagnetic storms (Dst ≤100nT) that occurred during solar cycle 22 and 23 were considered, of which 143 were observed to be identified with an ionospheric storm. Individual ionospheric storms were identified as maximum deviations of the F2 layer peak electron density from quiet time values. Only ionospheric storms that could clearly be associated with the peak of a geomagnetic storms were considered. Data from two mid-latitude ionosonde stations; one in the northern hemisphere (i.e Moscow) and the other in the southern hemisphere (Grahamstown) were used to study ionospheric condition at the time of the individual geomagnetic storms. Results show hemispheric and latitudinal differences in the intensity and nature of ionospheric storms association with different types of geomagnetic storms. These results are significant for our present understanding of the mechanisms which drive the changes in electron density during different types of ionospheric storms.
Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

NASA Astrophysics Data System (ADS)

Dissanayake, P.; Brown, J.; Karunarathna, H.

2015-07-01

Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.
Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

NASA Astrophysics Data System (ADS)

Dissanayake, P.; Brown, J.; Karunarathna, H.

2015-04-01

Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/14 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross-section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.
7 CFR 760.702 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-01-01

..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms, ice storms, snow, blizzard, hurricane, typhoons, tropical storms, and cold wet weather. A disaster..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms...
7 CFR 760.702 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-01-01

..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms, ice storms, snow, blizzard, hurricane, typhoons, tropical storms, and cold wet weather. A disaster..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms...
7 CFR 760.702 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-01-01

..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms, ice storms, snow, blizzard, hurricane, typhoons, tropical storms, and cold wet weather. A disaster..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms...
7 CFR 760.702 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-01-01

..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms, ice storms, snow, blizzard, hurricane, typhoons, tropical storms, and cold wet weather. A disaster..., moisture, humidity, severe storms, thunderstorms, ground saturation or standing water, hail, winter storms...
Development of a Geomagnetic Storm Correction to the International Reference Ionosphere E-Region Electron Densities Using TIMED/SABER Observations

NASA Technical Reports Server (NTRS)

Mertens, C. J.; Xu, X.; Fernandez, J. R.; Bilitza, D.; Russell, J. M., III; Mlynczak, M. G.

2009-01-01

Auroral infrared emission observed from the TIMED/SABER broadband 4.3 micron channel is used to develop an empirical geomagnetic storm correction to the International Reference Ionosphere (IRI) E-region electron densities. The observation-based proxy used to develop the storm model is SABER-derived NO+(v) 4.3 micron volume emission rates (VER). A correction factor is defined as the ratio of storm-time NO+(v) 4.3 micron VER to a quiet-time climatological averaged NO+(v) 4.3 micron VER, which is linearly fit to available geomagnetic activity indices. The initial version of the E-region storm model, called STORM-E, is most applicable within the auroral oval region. The STORM-E predictions of E-region electron densities are compared to incoherent scatter radar electron density measurements during the Halloween 2003 storm events. Future STORM-E updates will extend the model outside the auroral oval.
Empirical, dimensionless, cumulative-rainfall hyetographs developed from 1959-86 storm data for selected small watersheds in Texas

USGS Publications Warehouse

Williams-Sether, Tara; Asquith, William H.; Thompson, David B.; Cleveland, Theodore G.; Fang, Xing

2004-01-01

A database of incremental cumulative-rainfall values for storms that occurred in small urban and rural watersheds in north and south central Texas during the period from 1959 to 1986 was used to develop empirical, dimensionless, cumulative-rainfall hyetographs. Storm-quartile classifications were determined from the cumulative-rainfall values, which were divided into data groups on the basis of storm-quartile classification (first, second, third, fourth, and first through fourth combined), storm duration (0 to 6, 6 to 12, 12 to 24, 24 to 72, and 0 to 72 hours), and rainfall amount (1 inch or more). Removal of long leading tails, in effect, shortened the storm duration and, in some cases, affected the storm-quartile classification. Therefore, two storm groups, untrimmed and trimmed, were used for analysis. The trimmed storms generally are preferred for interpretation. For a 12-hour or less trimmed storm duration, approximately 49 percent of the storms are first quartile. For trimmed storm durations of 12 to 24 and 24 to 72 hours, 47 and 38 percent, respectively, of the storms are first quartile. For a trimmed storm duration of 0 to 72 hours, the first-, second-, third-, and fourth-quartile storms accounted for 46, 21, 20, and 13 percent of all storms, respectively. The 90th-percentile curve for first-quartile storms indicated about 90 percent of the cumulative rainfall occurs during the first 20 percent of the storm duration. The 10th-percentile curve for first-quartile storms indicated about 30 percent of the cumulative rainfall occurs during the first 20 percent of the storm duration. The 90th-percentile curve for fourth-quartile storms indicated about 33 percent of the cumulative rainfall occurs during the first 20 percent of the storm duration. The 10th-percentile curve for fourth-quartile storms indicated less than 5 percent of the cumulative rainfall occurs during the first 20 percent of the storm duration. Statistics for the empirical, dimensionless, cumulative-rainfall hyetographs are presented in the report along with hyetograph curves and tables. The curves and tables presented do not present exact mathematical relations but can be used to estimate distributions of rainfall with time for small drainage areas of less than about 160 square miles in urban and small rural watersheds in north and south central Texas.
Stabilizing stored PuO2 with addition of metal impurities

NASA Astrophysics Data System (ADS)

Moten, Shafaq; Huda, Muhammad

Plutonium oxides is of widespread significance due its application in nuclear fuels, space missions, as well as the long-termed storage of plutonium from spent fuel and nuclear weapons. The processes to refine and store plutonium bring many other elements in contact with the plutonium metal and thereby affect the chemistry of the plutonium. Pure plutonium metal corrodes to an oxide in air with the most stable form of this oxide is stoichiometric plutonium dioxide, PuO2. Defects such as impurities and vacancies can form in the plutonium dioxide before, during and after the refining processes as well as during storage. An impurity defect manifests itself at the bottom of the conduction band and affects the band gap of the unit cell. Studying the interaction between transition metals and plutonium dioxide is critical for better, more efficient storage plans as well as gaining insights to provide a better response to potential threats of exposure to the environment. Our study explores the interaction of a few metals within the plutonium dioxide structure which have a likelihood of being exposed to the plutonium dioxide powder. Using Density Functional Theory, we calculated a substituted metal impurity in PuO2 supercell. We repeated the calculations with an additional oxygen vacancy. Our results reveal interesting volume contraction of PuO2 supercell when one plutonium atom is substituted with a metal atom. The authors acknowledge the Texas Computing Center (TACC) at The University of Texas at Austin and High Performance Computing (HPC) at The University of Texas at Arlington.
Electronic structure of stoichiometric and reduced ZnO from periodic relativistic all electron hybrid density functional calculations using numeric atom-centered orbitals.

PubMed

Viñes, Francesc; Illas, Francesc

2017-03-30

The atomic and electronic structure of stoichiometric and reduced ZnO wurtzite has been studied using a periodic relativistic all electron hybrid density functional (PBE0) approach and numeric atom-centered orbital basis set with quality equivalent to aug-cc-pVDZ. To assess the importance of relativistic effects, calculations were carried out without and with explicit inclusion of relativistic effects through the zero order regular approximation. The calculated band gap is ∼0.2 eV smaller than experiment, close to previous PBE0 results including relativistic calculation through the pseudopotential and ∼0.25 eV smaller than equivalent nonrelativistic all electron PBE0 calculations indicating possible sources of error in nonrelativistic all electron density functional calculations for systems containing elements with relatively high atomic number. The oxygen vacancy formation energy converges rather fast with the supercell size, the predicted value agrees with previously hybrid density functional calculations and analysis of the electronic structure evidences the presence of localized electrons at the vacancy site with a concomitant well localized peak in the density of states ∼0.5 eV above the top of the valence band and a significant relaxation of the Zn atoms near to the oxygen vacancy. Finally, present work shows that accurate results can be obtained in systems involving large supercells containing up to ∼450 atoms using a numeric atomic-centered orbital basis set within a full all electron description including scalar relativistic effects at an affordable cost. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Ab initio elastic tensor of cubic Ti0.5Al0.5N alloys: Dependence of elastic constants on size and shape of the supercell model and their convergence

NASA Astrophysics Data System (ADS)

Tasnádi, Ferenc; Odén, M.; Abrikosov, Igor A.

2012-04-01

In this study we discuss the performance of the special quasirandom structure (SQS) method in predicting the elastic properties of B1 (rocksalt) Ti0.5Al0.5N alloy. We use a symmetry-based projection technique, which gives the closest cubic approximate of the elastic tensor and allows us to align the SQSs of different shapes and sizes for a comparison in modeling elastic tensors. We show that the derived closest cubic approximate of the elastic tensor converges faster with respect to SQS size than the elastic tensor itself. That establishes a less demanding computational strategy to achieve convergence for the elastic constants. We determine the cubic elastic constants (Cij) and Zener's type elastic anisotropy (A) of Ti0.5Al0.5N. Optimal supercells, which capture accurately both the configurational disorder and cubic symmetry of elastic tensor, result in C11=447 GPa, C12=158 GPa, and C44=203 GPa with 3% of error and A=1.40 with 6% of error. In addition, we establish the general importance of selecting proper SQS with symmetry arguments to reliably model elasticity of alloys. We suggest the calculation of nine elastic tensor elements: C11, C22, C33, C12, C13, C23, C44, C55, and C66, to analyze the performance of SQSs and predict elastic constants of cubic alloys. The described methodology is general enough to be extended for alloys with other symmetry at arbitrary composition.
Synthesis, structure, and magnetic characterization of Cr{sub 4}US{sub 8}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.

The compound Cr{sub 4}US{sub 8} has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2{sub 1}/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS{sub 6} octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magneticmore » behavior of Cr{sub 4}US{sub 8} is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie–Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength. - Graphical abstract: Structure of Cr{sub 4}US{sub 8} viewed down the a axis. - Highlights: • At 1073 K Cr{sub 4}US{sub 8} was synthesized and at 100 K its crystal structure was determined. • The 3D structure comprises CrS{sub 6} octahedra with channels partially occupied by U. • The magnetic behavior of Cr{sub 4}US{sub 8} is complex.« less
Macroscopic elastic properties of textured ZrN-AlN polycrystalline aggregates: From ab initio calculations to grain-scale interactions

NASA Astrophysics Data System (ADS)

Holec, D.; Tasnádi, F.; Wagner, P.; Friák, M.; Neugebauer, J.; Mayrhofer, P. H.; Keckes, J.

2014-11-01

Despite the fast development of computational material modeling, the theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this study we use a supercell-based approach to obtain the elastic properties of a random solid solution cubic Zr1 -xAlxN system as a function of the metallic sublattice composition and texture descriptors. The employed special quasirandom structures are optimized not only with respect to short-range-order parameters, but also to make the three cubic directions [1 0 0 ] , [0 1 0 ] , and [0 0 1 ] as similar as possible. In this way, only a small spread of elastic constant tensor components is achieved and an optimum trade-off between modeling of chemical disorder and computational limits regarding the supercell size and calculational time is proposed. The single-crystal elastic constants are shown to vary smoothly with composition, yielding x ≈0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Young's modulus independent of the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit and with fiber textures with various orientations and sharpness. It turns out that for low AlN mole fractions, the spread of the possible Young's modulus data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Young's modulus data of cubic Zr1 -xAlxN contains also the evaluation of the texture typical for thin films.
Assessing a Tornado Climatology from Global Tornado Intensity Distributions.

NASA Astrophysics Data System (ADS)

Feuerstein, Bernold; Dotzek, Nikolai; Grieser, Jürgen

2005-02-01

Recent work demonstrated that the shape of tornado intensity distributions from various regions worldwide is well described by Weibull functions. This statistical modeling revealed a strong correlation between the fit parameters c for shape and b for scale regardless of the data source. In the present work it is shown that the quality of the Weibull fits is optimized if only tornado reports of F1 and higher intensity are used and that the c-b correlation does indeed reflect a universal feature of the observed tornado intensity distributions. For regions with likely supercell tornado dominance, this feature is the number ratio of F4 to F3 tornado reports R(F4/F3) = 0.238. The c-b diagram for the Weibull shape and scale parameters is used as a climatological chart, which allows different types of tornado climatology to be distinguished, presumably arising from supercell versus nonsupercell tornadogenesis. Assuming temporal invariance of the climatology and using a detection efficiency function for tornado observations, a stationary climatological probability distribution from large tornado records (U.S. decadal data 1950-99) is extracted. This can be used for risk assessment, comparative studies on tornado intensity distributions worldwide, and estimates of the degree of underreporting for areas with poor databases. For the 1990s U.S. data, a likely tornado underreporting of the weak events (F0, F1) by a factor of 2 can be diagnosed, as well as asymptotic climatological c,b values of c = 1.79 and b = 2.13, to which a convergence in the 1950-99 U.S. decadal data is verified.
Optimization of process parameters for a quasi-continuous tablet coating system using design of experiments.

PubMed

Cahyadi, Christine; Heng, Paul Wan Sia; Chan, Lai Wah

2011-03-01

The aim of this study was to identify and optimize the critical process parameters of the newly developed Supercell quasi-continuous coater for optimal tablet coat quality. Design of experiments, aided by multivariate analysis techniques, was used to quantify the effects of various coating process conditions and their interactions on the quality of film-coated tablets. The process parameters varied included batch size, inlet temperature, atomizing pressure, plenum pressure, spray rate and coating level. An initial screening stage was carried out using a 2(6-1(IV)) fractional factorial design. Following these preliminary experiments, optimization study was carried out using the Box-Behnken design. Main response variables measured included drug-loading efficiency, coat thickness variation, and the extent of tablet damage. Apparent optimum conditions were determined by using response surface plots. The process parameters exerted various effects on the different response variables. Hence, trade-offs between individual optima were necessary to obtain the best compromised set of conditions. The adequacy of the optimized process conditions in meeting the combined goals for all responses was indicated by the composite desirability value. By using response surface methodology and optimization, coating conditions which produced coated tablets of high drug-loading efficiency, low incidences of tablet damage and low coat thickness variation were defined. Optimal conditions were found to vary over a large spectrum when different responses were considered. Changes in processing parameters across the design space did not result in drastic changes to coat quality, thereby demonstrating robustness in the Supercell coating process. © 2010 American Association of Pharmaceutical Scientists
Statistical characteristics of storm interevent time, depth, and duration for eastern New Mexico, Oklahoma, and Texas

USGS Publications Warehouse

Asquith, William H.; Roussel, Meghan C.; Cleveland, Theodore G.; Fang, Xing; Thompson, David B.

2006-01-01

The design of small runoff-control structures, from simple floodwater-detention basins to sophisticated best-management practices, requires the statistical characterization of rainfall as a basis for cost-effective, risk-mitigated, hydrologic engineering design. The U.S. Geological Survey, in cooperation with the Texas Department of Transportation, has developed a framework to estimate storm statistics including storm interevent times, distributions of storm depths, and distributions of storm durations for eastern New Mexico, Oklahoma, and Texas. The analysis is based on hourly rainfall recorded by the National Weather Service. The database contains more than 155 million hourly values from 774 stations in the study area. Seven sets of maps depicting ranges of mean storm interevent time, mean storm depth, and mean storm duration, by county, as well as tables listing each of those statistics, by county, were developed. The mean storm interevent time is used in probabilistic models to assess the frequency distribution of storms. The Poisson distribution is suggested to model the distribution of storm occurrence, and the exponential distribution is suggested to model the distribution of storm interevent times. The four-parameter kappa distribution is judged as an appropriate distribution for modeling the distribution of both storm depth and storm duration. Preference for the kappa distribution is based on interpretation of L-moment diagrams. Parameter estimates for the kappa distributions are provided. Separate dimensionless frequency curves for storm depth and duration are defined for eastern New Mexico, Oklahoma, and Texas. Dimension is restored by multiplying curve ordinates by the mean storm depth or mean storm duration to produce quantile functions of storm depth and duration. Minimum interevent time and location have slight influence on the scale and shape of the dimensionless frequency curves. Ten example problems and solutions to possible applications are provided.
An empirical probability density distribution of planetary ionosphere storms with geomagnetic precursors

NASA Astrophysics Data System (ADS)

Gulyaeva, Tamara; Stanislawska, Iwona; Arikan, Feza; Arikan, Orhan

The probability of occurrence of the positive and negative planetary ionosphere storms is evaluated using the W index maps produced from Global Ionospheric Maps of Total Electron Content, GIM-TEC, provided by Jet Propulsion Laboratory, and transformed from geographic coordinates to magnetic coordinates frame. The auroral electrojet AE index and the equatorial disturbance storm time Dst index are investigated as precursors of the global ionosphere storm. The superposed epoch analysis is performed for 77 intense storms (Dst≤-100 nT) and 227 moderate storms (-100
Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation

USGS Publications Warehouse

Lamjiri, Maryam A.; Dettinger, Michael; Ralph, F. Martin; Guan, B.

2017-01-01

Gridded hourly precipitation observations over the conterminous U.S., from 1948 to 2002, are analyzed to determine climatological characteristics of storm precipitation totals. Despite generally lower hourly intensities, precipitation totals along the U.S. West Coast (USWC) are comparable to those in southeast U.S. (SEUS). Storm durations, more so than hourly intensities, strongly modulate precipitation-total variability over the USWC, where the correlation coefficients between storm durations and storm totals range from 0.7 to 0.9. Atmospheric rivers (ARs) contribute 30–50% of annual precipitation on the USWC and make such large contributions to extreme storms that 60–100% of the most extreme storms, i.e., storms with precipitation-total return intervals longer than 2 years, are associated with ARs. These extreme storm totals are more strongly tied to storm durations than to storm hourly or average intensities, emphasizing the importance of AR persistence to extreme storms on the USWC.

Classification and Feature Selection Algorithms for Modeling Ice Storm Climatology

NASA Astrophysics Data System (ADS)

Swaminathan, R.; Sridharan, M.; Hayhoe, K.; Dobbie, G.

2015-12-01

Ice storms account for billions of dollars of winter storm loss across the continental US and Canada. In the future, increasing concentration of human populations in areas vulnerable to ice storms such as the northeastern US will only exacerbate the impacts of these extreme events on infrastructure and society. Quantifying the potential impacts of global climate change on ice storm prevalence and frequency is challenging, as ice storm climatology is driven by complex and incompletely defined atmospheric processes, processes that are in turn influenced by a changing climate. This makes the underlying atmospheric and computational modeling of ice storm climatology a formidable task. We propose a novel computational framework that uses sophisticated stochastic classification and feature selection algorithms to model ice storm climatology and quantify storm occurrences from both reanalysis and global climate model outputs. The framework is based on an objective identification of ice storm events by key variables derived from vertical profiles of temperature, humidity and geopotential height. Historical ice storm records are used to identify days with synoptic-scale upper air and surface conditions associated with ice storms. Evaluation using NARR reanalysis and historical ice storm records corresponding to the northeastern US demonstrates that an objective computational model with standard performance measures, with a relatively high degree of accuracy, identify ice storm events based on upper-air circulation patterns and provide insights into the relationships between key climate variables associated with ice storms.
Fallout of Debris from Tornadic Thunderstorms: A Historical Perspective and Two Examples from VORTEX.

NASA Astrophysics Data System (ADS)

Snow, John T.; Wyatt, Amy Lee; McCarthy, Ann K.; Bishop, Eric K.

1995-10-01

Preliminary results of an investigation of debris lofted by tornadoes, its long-distance transport by thunderstorms, and its subsequent fallout are reported. The authors begin with a review of historical accounts, including the unique study of the 1984 Barneveld, Wisconsin, tornado by Anderson, which shows that long-distance transport and fallout of debris have occurred and that distances involved have been significant. The authors then report first-hand evidence of these phenomena in two events with F2 tornadoes: the Tuskahoma, Oklahorna, tornado of 25 April 1994 and the Gainesville, Texas, tornadoes of 26 April 1994. In both cases, traceable material in the form of canceled checks, bills-of-sale, invoices, and legal documents were reported to the authors, who were able to locate the source locations for several of these items. The authors close with some conjectures on the implications of these first findings.
Research instrumentation for tornado electromagnetics emissions detection

NASA Technical Reports Server (NTRS)

Jenkins, H. H.; Wilson, C. S.

1977-01-01

Instrumentation for receiving, processing, and recording HF/VHF electromagnetic emissions from severe weather activity is described. Both airborne and ground-based instrumentation units are described on system and subsystem levels. Design considerations, design decisions, and the rationale behind the decisions are given. Performance characteristics are summarized and recommendations for improvements are given. The objectives, procedures, and test results of the following are presented: (1) airborne flight test in the Midwest U.S.A. (Spring 1975) and at the Kennedy Space Center, Florida (Summer 1975); (2) ground-based data collected in North Georgia (Summer/Fall 1975); and (3) airborne flight test in the Midwest (late Spring 1976) and at the Kennedy Space Center, Florida (Summer 1976). The Midwest tests concentrated on severe weather with tornadic activity; the Florida and Georgia tests monitored air mass convective thunderstorm characteristics. Supporting ground truth data from weather radars and sferics DF nets are described.
The cascade from local to global dust storms on Mars: Temporal and spatial thresholds on thermal and dynamical feedback

NASA Astrophysics Data System (ADS)

Toigo, Anthony D.; Richardson, Mark I.; Wang, Huiqun; Guzewich, Scott D.; Newman, Claire E.

2018-03-01

We use the MarsWRF general circulation model to examine the temporal and spatial response of the atmosphere to idealized local and regional dust storm radiative heating. The ability of storms to modify the atmosphere away from the location of dust heating is a likely prerequisite for dynamical feedbacks that aid the growth of storms beyond the local scale, while the ability of storms to modify the atmosphere after the cessation of dust radiative heating is potentially important in preconditioning the atmosphere prior to large scale storms. Experiments were conducted over a range of static, prescribed storm sizes, durations, optical depth strengths, locations, and vertical extents of dust heating. Our results show that for typical sizes (order 105 km2) and durations (1-10 sols) of local dust storms, modification of the atmosphere is less than the typical variability of the unperturbed (storm-free) state. Even if imposed on regional storm length scales (order 106 km2), a 1-sol duration storm similarly does not significantly modify the background atmosphere. Only when imposed for 10 sols does a regional dust storm create a significant impact on the background atmosphere, allowing for the possibility of self-induced dynamical storm growth. These results suggest a prototype for how the subjective observational categorization of storms may be related to objective dynamical growth feedbacks that only become available to storms after they achieve a threshold size and duration, or if they grow into an atmosphere preconditioned by a prior large and sustained storm.
Lamb waves in phononic crystal slabs with square or rectangular symmetries

NASA Astrophysics Data System (ADS)

Brunet, Thomas; Vasseur, Jérôme; Bonello, Bernard; Djafari-Rouhani, Bahram; Hladky-Hennion, Anne-Christine

2008-08-01

We report on both numerical and experimental results showing the occurrence of band gaps for Lamb waves propagating in phononic crystal plates. The structures are made of centered rectangular and square arrays of holes drilled in a silicon plate. A supercell plane wave expansion method is used to calculate the band structures and to predict the position and the magnitude of the gaps. The band structures of phononic crystal slabs are then measured using a laser ultrasonic technique. Lamb waves in the megahertz range and with wave vectors ranging over more than the first two reduced Brillouin zones are investigated.
Vacancy effects on the electronic and structural properties pentacene

NASA Astrophysics Data System (ADS)

Laraib, Iflah; Janotti, Anderson

Defects in organic crystals are likely to affect charge transport in organic electronic devices. Vacancies can create lattice distortions and modify electronic states associated with the molecules in its surrounding. Spectroscopy experiments indicate that molecular vacancies trap charge carriers. Experimental characterization of individual defects is challenging and unambiguous. Here we use density functional calculations including van der Waals interactions in a supercell approach to study the single vacancy in pentacene, a prototype organic semiconductor. We determine formation energies, local lattice relaxations, and discuss how vacancies locally distort the lattice and affect the electronic properties of the host organic semiconductor.
Ultrafast electron diffraction pattern simulations using GPU technology. Applications to lattice vibrations.

PubMed

Eggeman, A S; London, A; Midgley, P A

2013-11-01

Graphical processing units (GPUs) offer a cost-effective and powerful means to enhance the processing power of computers. Here we show how GPUs can greatly increase the speed of electron diffraction pattern simulations by the implementation of a novel method to generate the phase grating used in multislice calculations. The increase in speed is especially apparent when using large supercell arrays and we illustrate the benefits of fast encoding the transmission function representing the atomic potentials through the simulation of thermal diffuse scattering in silicon brought about by specific vibrational modes. © 2013 Elsevier B.V. All rights reserved.
Evanescent waves and deaf bands in sonic crystals

NASA Astrophysics Data System (ADS)

Romero-García, V.; Garcia-Raffi, L. M.; Sánchez-Pérez, J. V.

2011-12-01

The properties of sonic crystals (SC) are theoretically investigated in this work by solving the inverse problem k(ω) using the extended plane wave expansion (EPWE). The solution of the resulting eigenvalue problem gives the complex band structure which takes into account both the propagating and the evanescent modes. In this work we show the complete mathematical formulation of the EPWE for SC and the supercell approximation for its use in both a complete SC and a SC with defects. As an example we show a novel interpretation of the deaf bands in a complete SC in good agreement with multiple scattering simulations.
Tight-Binding study of Boron structures

NASA Astrophysics Data System (ADS)

McGrady, Joseph W.; Papaconstantopoulos, Dimitrios A.; Mehl, Michael J.

2014-10-01

We have performed Linearized Augmented Plane Wave (LAPW) calculations for five crystal structures (alpha, dhcp, sc, fcc, bcc) of Boron which we then fitted to a non-orthogonal tight-binding model following the Naval Research Laboratory Tight-Binding (NRL-TB) method. The predictions of the NRL-TB approach for complicated Boron structures such as R105 (or β-rhombohedral) and T190 are in agreement with recent first-principles calculations. Fully utilizing the computational speed of the NRL-TB method we calculated the energy differences of various structures, including those containing vacancies using supercells with up to 5000 atoms.
Rain fall data for the design of sewer pipe systems

NASA Astrophysics Data System (ADS)

Arnell, V.

1982-03-01

A comparison of designs of sewer pipes for different types of rainfall data is presented. Local coefficients were evaluated from an 18-year historical rainfall record for the following design storms: The Average-Intensity-Duration Design Storm, The Chicago Design Storm, The Sifalda Design Storm, The Illinois State Water Survey Design Storm, and The Flood Studies Report Design Storm. Historical rainfalls as well as the above design storms were used for the calculations of peak-flow values.
Proxy records of Holocene storm events in coastal barrier systems: Storm-wave induced markers

NASA Astrophysics Data System (ADS)

Goslin, Jérôme; Clemmensen, Lars B.

2017-10-01

Extreme storm events in the coastal zone are one of the main forcing agents of short-term coastal system behavior. As such, storms represent a major threat to human activities concentrated along the coasts worldwide. In order to better understand the frequency of extreme events like storms, climate science must rely on longer-time records than the century-scale records of instrumental weather data. Proxy records of storm-wave or storm-wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia. This review provides a detailed state-of-the-art compilation of the proxies available from coastal barrier systems to reconstruct Holocene storm chronologies (paleotempestology). The present paper aims (I) to describe the erosional and depositional processes caused by storm-wave action in barrier and back-barrier systems (i.e. beach ridges, storm scarps and washover deposits), (ii) to understand how storm records can be extracted from barrier and back-barrier sedimentary bodies using stratigraphical, sedimentological, micro-paleontological and geochemical proxies and (iii) to show how to obtain chronological control on past storm events recorded in the sedimentary successions. The challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm-chronologies using these various proxies are discussed, and future research prospects are outlined.
A global scale picture of ionospheric peak electron density changes during geomagnetic storms

NASA Astrophysics Data System (ADS)

Kumar, Vickal V.; Parkinson, Murray L.

2017-04-01

Changes in ionospheric plasma densities can affect society more than ever because of our increasing reliance on communication, surveillance, navigation, and timing technology. Models struggle to predict changes in ionospheric densities at nearly all temporal and spatial scales, especially during geomagnetic storms. Here we combine a 50 year (1965-2015) geomagnetic disturbance storm time (Dst) index with plasma density measurements from a worldwide network of 132 vertical incidence ionosondes to develop a picture of global scale changes in peak plasma density due to geomagnetic storms. Vertical incidence ionosondes provide measurements of the critical frequency of the ionospheric F2 layer (foF2), a direct measure of the peak electron density (NmF2) of the ionosphere. By dissecting the NmF2 perturbations with respect to the local time at storm onset, season, and storm intensity, it is found that (i) the storm-associated depletions (negative storm effects) and enhancements (positive storm effects) are driven by different but related physical mechanisms, and (ii) the depletion mechanism tends to dominate over the enhancement mechanism. The negative storm effects, which are detrimental to HF radio links, are found to start immediately after geomagnetic storm onset in the nightside high-latitude ionosphere. The depletions in the dayside high-latitude ionosphere are delayed by a few hours. The equatorward expansion of negative storm effects is found to be regulated by storm intensity (farthest equatorward and deepest during intense storms), season (largest in summer), and time of day (generally deeper on the nightside). In contrast, positive storm effects typically occur on the dayside midlatitude and low-latitude ionospheric regions when the storms are in the main phase, regardless of the season. Closer to the magnetic equator, moderate density enhancements last up to 40 h during the recovery phase of equinox storms, regardless of the local time. Strikingly, high-latitude plasma densities are moderately enhanced for up to 60 h prior to the actual onset of storms during the equinoxes and summer; a potential precursor of a geomagnetic storm.
The observed clustering of damaging extra-tropical cyclones in Europe

NASA Astrophysics Data System (ADS)

Cusack, S.

2015-12-01

The clustering of severe European windstorms on annual timescales has substantial impacts on the re/insurance industry. Management of the risk is impaired by large uncertainties in estimates of clustering from historical storm datasets typically covering the past few decades. The uncertainties are unusually large because clustering depends on the variance of storm counts. Eight storm datasets are gathered for analysis in this study in order to reduce these uncertainties. Six of the datasets contain more than 100~years of severe storm information to reduce sampling errors, and the diversity of information sources and analysis methods between datasets sample observational errors. All storm severity measures used in this study reflect damage, to suit re/insurance applications. It is found that the shortest storm dataset of 42 years in length provides estimates of clustering with very large sampling and observational errors. The dataset does provide some useful information: indications of stronger clustering for more severe storms, particularly for southern countries off the main storm track. However, substantially different results are produced by removal of one stormy season, 1989/1990, which illustrates the large uncertainties from a 42-year dataset. The extended storm records place 1989/1990 into a much longer historical context to produce more robust estimates of clustering. All the extended storm datasets show a greater degree of clustering with increasing storm severity and suggest clustering of severe storms is much more material than weaker storms. Further, they contain signs of stronger clustering in areas off the main storm track, and weaker clustering for smaller-sized areas, though these signals are smaller than uncertainties in actual values. Both the improvement of existing storm records and development of new historical storm datasets would help to improve management of this risk.
Beyond the Storm: Comparison of Clinical Factors, Arrhythmogenic Substrate, and Catheter Ablation Outcomes in Structural Heart Disease Patients With versus Those Without a History of Ventricular Tachycardia Storm.

PubMed

Kumar, Saurabh; Fujii, Akira; Kapur, Sunil; Romero, Jorge; Mehta, Nishaki K; Tanigawa, Shinichi; Epstein, Laurence M; Koplan, Bruce A; Michaud, Gregory F; John, Roy M; Stevenson, William G; Tedrow, Usha B

2017-01-01

Catheter ablation can be lifesaving in ventricular tachycardia (VT) storm, but the underlying substrate in patients with storm is not well characterized. We sought to compare the clinical factors, substrate, and outcomes differences in patients with sustained monomorphic VT who present for catheter ablation with VT storm versus those with a nonstorm presentation. Consecutive ischemic (ICM; n = 554) or nonischemic cardiomyopathy patients (NICM; n = 369) with a storm versus nonstorm presentation were studied (ICM storm 186; NICM storm 101). In ICM, storm compared with nonstorm patients had significantly lower left ventricular (LV) ejection fraction (EF), greater number of antiarrhythmic drug (AAD) failures, slower VTs, greater number of scarred LV segments, higher incidence of anterior, septal, and apical endocardial LV scar (all P < 0.05). However, outcomes in follow-up were similar (12-month ventricular arrhythmia [VA]-free survival: 51% vs. 52%, P = 0.6; survival free of death/transplant 75% vs. 87%, P = 0.7). In addition to the above differences, NICM storm patients were also older; however, the extent and distribution of scar was similar except for a higher incidence of lateral endocardial scar in storm patients (P = 0.05). VA-free survival (36% vs. 47%, P = 0.004) and survival free of death/transplant, however, were worse in NICM storm than nonstorm patients (72% vs. 88%, P = 0.001). NICM storm patients had worse VA-free survival than ICM storm patients. There are differences in clinical factors and scar patterns in patients undergoing VT ablation who present with VT storm versus those with a nonstorm presentation. Clinical outcomes are worse in NICM storm patients. © 2016 Wiley Periodicals, Inc.
Interannual Similarity in the Martian Atmosphere During the Dust Storm Season

NASA Technical Reports Server (NTRS)

Kass, D. M.; Kleinboehl, A.; McCleese, D. J.; Schofield, J. T.; Smith, M. D.

2016-01-01

We find that during the dusty season on Mars (southern spring and summer) of years without a global dust storm there are three large regional-scale dust storms. The storms are labeled A, B, and C in seasonal order. This classification is based on examining the zonal mean 50 Pa (approximately 25 km) daytime temperature retrievals from TES/MGS and MCS/MRO over 6 Mars Years. Regional-scale storms are defined as events where the temperature exceeds 200 K. Examining the MCS dust field at 50 Pa indicates that warming in the Southern Hemisphere is dominated by direct heating, while northern high latitude warming is a dynamical response. A storms are springtime planet encircling Southern Hemisphere events. B storms are southern polar events that begin near perihelion and last through the solstice. C storms are southern summertime events starting well after the end of the B storm. C storms show the most interannual variability.
Acceleration and loss of relativistic electrons during small geomagnetic storms.

PubMed

Anderson, B R; Millan, R M; Reeves, G D; Friedel, R H W

2015-12-16

Past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms ( D s t > -50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result in flux depletion than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. Small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.
Interannual similarity in the Martian atmosphere during the dust storm season

NASA Astrophysics Data System (ADS)

Kass, D. M.; Kleinböhl, A.; McCleese, D. J.; Schofield, J. T.; Smith, M. D.

2016-06-01

We find that during the dusty season on Mars (southern spring and summer) of years without a global dust storm there are three large regional-scale dust storms. The storms are labeled A, B, and C in seasonal order. This classification is based on examining the zonal mean 50 Pa (˜25 km) daytime temperature retrievals from TES/MGS and MCS/MRO over 6 Mars Years. Regional-scale storms are defined as events where the temperature exceeds 200 K. Examining the MCS dust field at 50 Pa indicates that warming in the Southern Hemisphere is dominated by direct heating, while northern high latitude warming is a dynamical response. A storms are springtime planet encircling Southern Hemisphere events. B storms are southern polar events that begin near perihelion and last through the solstice. C storms are southern summertime events starting well after the end of the B storm. C storms show the most interannual variability.
[Diagnosis and treatment of thyroid storm].

PubMed

Akamizu, Takashi

2012-11-01

Thyrotoxic storm is a life-threatening condition requiring emergency treatment. Neither its epidemiological data nor diagnostic criteria have been fully established. We clarified the clinical and epidemiological characteristics of thyroid storm using nationwide surveys and then formulate diagnostic criteria for thyroid storm. To perform the nationwide survey on thyroid storm, we first developed tentative diagnostic criteria for thyroid storm, mainly based upon the literature (the first edition). We analyzed the relationship of the major features of thyroid storm to mortality and to certain other features. Finally, based upon the findings of these surveys, we revised the diagnostic criteria. Thyrotoxic storm is still a life-threatening disorder with over 10% mortality in Japan.
Modeling the refraction of microbaroms by the winds of a large maritime storm.

PubMed

Blom, Philip; Waxler, Roger

2017-12-01

Continuous infrasonic signals produced by the ocean surface interacting with the atmosphere, termed microbaroms, are known to be generated by a number of phenomena including large maritime storms. Storm generated microbaroms exhibit axial asymmetry when observed at locations far from the storm due to the source location being offset from the storm center. Because of this offset, a portion of the microbarom energy will radiate towards the storm center and interact with the winds in the region. Detailed here are predictions for the propagation of microbaroms through an axisymmetric, three-dimensional model storm. Geometric propagation methods have been utilized and the predicted horizontal refraction is found to produce signals that appear to emanate from a virtual source near the storm center when observed far from the storm. This virtual source near the storm center is expected to be observed only from a limited arc around the storm system with increased extent associated with more intense wind fields. This result implies that identifying the extent of the arc observing signal from the virtual source could provide a means to estimate the wind structure using infrasonic observations far from the storm system.
A Peek into a Cul-De-Sac and a Mews of Martian Dust Storm Activity: Western Hellas and Syria-Claritas Fossae During Mars Year 29

NASA Astrophysics Data System (ADS)

Heavens, N. G.

2016-12-01

Western Hellas Planitia (WHP) and the region encompassed by Syria Planum and Claritas Fossae are the main centers of textured dust storm activity in Mars's southern low to mid-latitudes. (Texture in this context refers to distinct fine structure at the cloud tops indicative of active lifting.) WHP is a well-known initiation zone for regional and global dust storm activity and often the end point of the Utopia "flushing storm" track. Syria-Claritas Fossae (SCF), too, can be a lifting center in global dust storm activity. Indeed, SCF and the area to its west was the region most denuded of dust by the Mars Year (MY) 25 global dust storm, perhaps suggesting that SCF contained the principal lifting center of the storm. Thus, if the Acidalia and Utopia storm tracks are Mars's dust storm alleys, through which dust storms pass quickly again and again; WHP might be a cul-de-sac and SCF something like a mews, where dust storm activity can enter more or less easily but may not as easily leave. In this presentation, I will focus on dust storm activity in these areas in a typical non-global dust storm year, MY 29. Synthesizing visible imagery by the Mars Color Imager (MARCI) on board Mars Reconnaissance Orbiter (MRO) and Mars Climate Sounder (MCS) also on board MRO, I will consider the climatology, morphology, texture, and vertical structure of dust storm activity in these areas in order to infer their governing dynamics. This investigation has two aims: (1) to understand why these areas are centers of textured dust storm activity; and (2) to connect the characteristics of smaller-scale dust storm activity in these regions to the underlying dynamics in order to understand the role of WHP and SCF in the dynamics of global dust storms. This work is supported by NASA's Mars Data Analysis Program (NNX14AM32G).

Winter storm intensity, hazards, and property losses in the New York tristate area.

PubMed

Shimkus, Cari E; Ting, Mingfang; Booth, James F; Adamo, Susana B; Madajewicz, Malgosia; Kushnir, Yochanan; Rieder, Harald E

2017-07-01

Winter storms pose numerous hazards to the Northeast United States, including rain, snow, strong wind, and flooding. These hazards can cause millions of dollars in damages from one storm alone. This study investigates meteorological intensity and impacts of winter storms from 2001 to 2014 on coastal counties in Connecticut, New Jersey, and New York and underscores the consequences of winter storms. The study selected 70 winter storms on the basis of station observations of surface wind strength, heavy precipitation, high storm tide, and snow extremes. Storm rankings differed between measures, suggesting that intensity is not easily defined with a single metric. Several storms fell into two or more categories (multiple-category storms). Following storm selection, property damages were examined to determine which types lead to high losses. The analysis of hazards (or events) and associated damages using the Storm Events Database of the National Centers for Environmental Information indicates that multiple-category storms were responsible for a greater portion of the damage. Flooding was responsible for the highest losses, but no discernible connection exists between the number of storms that afflict a county and the damage it faces. These results imply that losses may rely more on the incidence of specific hazards, infrastructure types, and property values, which vary throughout the region. © 2017 The Authors. Annals of the New York Academy of Sciences published by Wiley Periodicals Inc. on behalf of The New York Academy of Sciences.
Subtropical Storm Andrea

NASA Technical Reports Server (NTRS)

2007-01-01

The circling clouds of an intense low-pressure system sat off the southeast coast of the United States on May 8, 2007, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this image. By the following morning, the storm developed enough to be classified as a subtropical storm, a storm that forms outside of the tropics, but has many of the characteristics--hurricane-force winds, driving rains, low pressure, and sometimes an eye--of a tropical storm. Although it arrived several weeks shy of the official start of the hurricane season (June 1), Subtropical Storm Andrea became the first named storm of the 2007 Atlantic hurricane season. The storm has the circular shape of a tropical cyclone in this image, but lacks the tight organization seen in more powerful storms. By May 9, the storm's winds reached 75 kilometers per hour (45 miles per hour), and the storm was not predicted to get any stronger, said the National Hurricane Center. Though Subtropical Storm Andrea was expected to remain offshore, its strong winds and high waves pummeled coastal states, prompting a tropical storm watch. The winds fueled wild fires (marked with red boxes) in Georgia and Florida. The wind-driven flames generated thick plumes of smoke that concentrated in a gray-brown mass over Tampa Bay, Florida. Unfortunately for Georgia and Florida, which are experiencing moderate to severe drought, Subtropical Storm Andrea was not predicted to bring significant rain to the region right away, according to reports on the Washington Post Website.
Risk assessment of storm surge disaster based on numerical models and remote sensing

NASA Astrophysics Data System (ADS)

Liu, Qingrong; Ruan, Chengqing; Zhong, Shan; Li, Jian; Yin, Zhonghui; Lian, Xihu

2018-06-01

Storm surge is one of the most serious ocean disasters in the world. Risk assessment of storm surge disaster for coastal areas has important implications for planning economic development and reducing disaster losses. Based on risk assessment theory, this paper uses coastal hydrological observations, a numerical storm surge model and multi-source remote sensing data, proposes methods for valuing hazard and vulnerability for storm surge and builds a storm surge risk assessment model. Storm surges in different recurrence periods are simulated in numerical models and the flooding areas and depth are calculated, which are used for assessing the hazard of storm surge; remote sensing data and GIS technology are used for extraction of coastal key objects and classification of coastal land use are identified, which is used for vulnerability assessment of storm surge disaster. The storm surge risk assessment model is applied for a typical coastal city, and the result shows the reliability and validity of the risk assessment model. The building and application of storm surge risk assessment model provides some basis reference for the city development plan and strengthens disaster prevention and mitigation.
Coastal Storm Hazards from Virginia to Maine

DTIC Science & Technology

2015-11-01

study, storm surge, tide, waves, wind, atmospheric pressure, and currents were the dominant storm responses computed. The effect of sea level change on...coastal storm hazards and vulnerability nationally (USACE 2015). NACCS goals also included evaluating the effect of future sea level change (SLC) on...the computed high-fidelity responses included storm surge, astronomical tide, waves, wave effects on water levels, storm duration, wind, currents
The effects of storms and storm-generated currents on sand beaches in Southern Maine, USA

USGS Publications Warehouse

Hill, H.W.; Kelley, J.T.; Belknap, D.F.; Dickson, S.M.

2004-01-01

Storms are one of the most important controls on the cycle of erosion and accretion on beaches. Current meters placed in shoreface locations of Saco Bay and Wells Embayment, ME, recorded bottom currents during the winter months of 2000 and 2001, while teams of volunteers profiled the topography of nearby beaches. Coupling offshore meteorological and beach profile data made it possible to determine the response of nine beaches in southern Maine to various oceanographic and meteorological conditions. The beaches selected for profiling ranged from pristine to completely developed and permitted further examination of the role of seawalls on the response of beaches to storms. Current meters documented three unique types of storms: frontal passages, southwest storms, and northeast storms. In general, the current meter results indicate that frontal passages and southwest storms were responsible for bringing sediment towards the shore, while northeast storms resulted in a net movement of sediment away from the beach. During the 1999-2000 winter, there were a greater percentage of frontal passages and southwest storms, while during the 2000-2001 winter, there were more northeast storms. The sediment that was transported landward during the 1999-2000 winter was reworked into the berm along moderately and highly developed beaches during the next summer. A northeast storm on March 5-6, 2001, resulted in currents in excess of 1 m s-1 and wave heights that reached six meters. The storm persisted over 10 high tides and caused coastal flooding and property damage. Topographic profiles made before and after the storm demonstrate that developed beaches experienced a loss of sediment volume during the storm, while sediment was redistributed along the profile on moderately developed and undeveloped beaches. Two months after the storm, the profiles along the developed beaches had not reached their pre-storm elevation. In comparison, the moderately developed and undeveloped beaches reached and exceeded their pre-storm elevation and began to show berm buildup characteristic of the summer months. ?? 2004 Elsevier B.V. All rights reserved.
The threshold between storm overwash and inundation and the implication to paleo-storm records and climate signatures.

NASA Astrophysics Data System (ADS)

Smith, C. G.; Long, J.; Osterman, L. E.; Plant, N. G.; Marot, M. E.; Bernier, J.; Flocks, J. G.; Adams, C. S.

2014-12-01

In modern coastal systems, the sensitivity of a coastal site to erosion or deposition during storm conditions depends largely on the geomorphic configuration (e.g. dune or beach height and width) and the storm-induced oceanographic processes (surge and waves). Depending on the magnitude of these variables, coastal systems may be eroded, overwashed, breached, and/or inundated during the storm. To date, there has been no attempt to evaluate how these observable modern differences in storm-impact regimes might be utilized to interpret paleo-storm intensities and frequencies. Time-series of sediment texture, radioisotopic, and foraminiferal data from back-barrier environments along the Chandeleur Islands (Louisiana, USA) document the emplacement of a storm event deposit from Hurricane Isaac and we use this event to test paleo-storm intensity reconstruction methods. Water level reconstructed for the event layer using an advection (grain-size) settling model are 2 - 3 times greater than measured during the storm. The over-estimation is linked to the reconstruction model's assumptions concerning sediment transport during storms (i.e., overwash only), while actual processes included inundation as well. These contrasts may result in misidentification (i.e., presence/absence) and/or misclassification (i.e., intensity) of storms in the geologic record (e.g., low geomorphic conditions and high water levels) that would in turn affect the ability to link storm frequency or intensity to climatic drivers.
An Investigation of Dust Storms Observed with the Mars Color Imager

NASA Technical Reports Server (NTRS)

Guzewich, Scott D.; Toigo, Anthony D.; Wang, Huiqun

2017-01-01

Daily global imaging by the Mars Color Imager (MARCI) continues the record of the Mars Orbiter Camera (MOC) and has allowed creation of a long-duration record of Martian dust storms. We observe dust storms over the first two Mars years of the MARCI record, including tracking individual storms over multiple sols, as well as tracking the growth and recession of the seasonal polar caps. Using the combined 6 Mars year record of textured dust storms (storms with visible textures on the observed dust cloud tops), we study the relationship between textured dust storm activity and meteorology (as simulated by the MarsWRF general circulation model) and surface properties. We find that textured dust storms preferentially occur in places and seasons with above average surface wind stress. Textured dust storm occurrence also has a modest linear anti-correlation with surface albedo (0.43) and topography (0.40). Lastly, we perform an empirical orthogonal function (EOF) analysis on the distribution of occurrence of textured dust storms and find that over 50 of the variance in textured dust storm activity can be explained by two EOF modes. We associate the first EOF mode with cap-edge storms just before Ls = 180deg and the second EOF mode with flushing dust storms that occur from Ls = 180-210deg and again near Ls = 320deg.
Stalling Tropical Cyclones over the Atlantic Basin

NASA Astrophysics Data System (ADS)

Nielsen-Gammon, J. W.; Emanuel, K.

2017-12-01

Hurricane Harvey produced massive amounts of rain over southeast Texas and southwest Louisiana. Average storm total rainfall amounts over a 10,000 square mile (26,000 square km) area exceeded 30 inches (750 mm). An important aspect of the storm that contributed to the large rainfall totals was its unusual motion. The storm stalled shortly after making landfall, then moved back offshore before once again making landfall five days later. This storm motion permitted heavy rainfall to occur in the same general area for an extended period of time. The unusual nature of this event motivates an investigation into the characteristics and potential climate change influences on stalled tropical cyclones in the Atlantic basin using the HURDAT 2 storm track database for 1866-2016 and downscaled tropical cyclones driven by simulations of present and future climate. The motion of cyclones is quantified as the size of a circle circumscribing all storm locations during a given length of time. For a three-day period, Harvey remained inside a circle with a radius of 123 km. This ranks within the top 0.6% of slowest-moving historical storm instances. Among the 2% of slowest-moving storm instances prior to Harvey, only 13 involved storms that stalled near the continental United States coast, where they may have produced substantial rainfall onshore while tapping into marine moisture. Only two such storms stalled in the month of September, in contrast to 20 September stalls out of the 36 storms that stalled over the nearby open Atlantic. Just four of the stalled coastal storms were hurricanes, implying a return frequency for such storms of much less than once per decade. The synoptic setting of these storms is examined for common features, and historical and projected trends in occurrences of stalled storms near the coast and farther offshore are investigated.
A statistical model of extreme storm rainfall

NASA Astrophysics Data System (ADS)

Smith, James A.; Karr, Alan F.

1990-02-01

A model of storm rainfall is developed for the central Appalachian region of the United States. The model represents the temporal occurrence of major storms and, for a given storm, the spatial distribution of storm rainfall. Spatial inhomogeneities of storm rainfall and temporal inhomogeneities of the storm occurrence process are explicitly represented. The model is used for estimating recurrence intervals of extreme storms. The parameter estimation procedure developed for the model is based on the substitution principle (method of moments) and requires data from a network of rain gages. The model is applied to a 5000 mi2 (12,950 km2) region in the Valley and Ridge Province of Virginia and West Virginia.
Examples of storm impacts on barrier islands: Chapter 4

USGS Publications Warehouse

Plant, Nathaniel G.; Doran, Kara; Stockdon, Hilary F.

2017-01-01

This chapter focuses on the morphologic variability of barrier islands and on the differences in storm response. It describes different types of barrier island response to individual storms, as well as the integrated response of barrier islands to many storms. The chapter considers case study on the Chandeleur Island chain, where a decadal time series of island elevation measurements have documented a wide range of barrier island responses to storms and long-term processes that are representative of barrier island behaviour at many other locations. These islands are low elevation, extremely vulnerable to storms and exhibit a diversity of storm responses. Additionally, this location experiences a moderately high rate of relative sea-level rise, increasing its vulnerability to the combined impacts of storms and long-term erosional processes. Understanding how natural processes, including storm impacts and intervening recovery periods interact with man-made restoration processes is also broadly relevant to understand the natural and human response to future storms.
Acceleration and loss of relativistic electrons during small geomagnetic storms

DOE PAGES

Anderson, B. R.; Millan, R. M.; Reeves, G. D.; ...

2015-12-02

We report that past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms (Dst >₋50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result inmore » flux depletion than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. Small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.« less
Observing storm surges from space: Hurricane Igor off Newfoundland

PubMed Central

Han, Guoqi; Ma, Zhimin; Chen, Dake; deYoung, Brad; Chen, Nancy

2012-01-01

Coastal communities are becoming increasingly more vulnerable to storm surges under a changing climate. Tide gauges can be used to monitor alongshore variations of a storm surge, but not cross-shelf features. In this study we combine Jason-2 satellite measurements with tide-gauge data to study the storm surge caused by Hurricane Igor off Newfoundland. Satellite observations reveal a storm surge of 1 m in the early morning of September 22, 2010 (UTC) after the passage of the storm, consistent with the tide-gauge measurements. The post-storm sea level variations at St. John's and Argentia are associated with free equatorward-propagating continental shelf waves (with a phase speed of ~10 m/s and a cross-shelf decaying scale of ~100 km). The study clearly shows the utility of satellite altimetry in observing and understanding storm surges, complementing tide-gauge observations for the analysis of storm surge characteristics and for the validation and improvement of storm surge models. PMID:23259048
Implementation of a gust front head collapse scheme in the WRF numerical model

NASA Astrophysics Data System (ADS)

Lompar, Miloš; Ćurić, Mladjen; Romanic, Djordje

2018-05-01

Gust fronts are thunderstorm-related phenomena usually associated with severe winds which are of great importance in theoretical meteorology, weather forecasting, cloud dynamics and precipitation, and wind engineering. An important feature of gust fronts demonstrated through both theoretical and observational studies is the periodic collapse and rebuild of the gust front head. This cyclic behavior of gust fronts results in periodic forcing of vertical velocity ahead of the parent thunderstorm, which consequently influences the storm dynamics and microphysics. This paper introduces the first gust front pulsation parameterization scheme in the WRF-ARW model (Weather Research and Forecasting-Advanced Research WRF). The influence of this new scheme on model performances is tested through investigation of the characteristics of an idealized supercell cumulonimbus cloud, as well as studying a real case of thunderstorms above the United Arab Emirates. In the ideal case, WRF with the gust front scheme produced more precipitation and showed different time evolution of mixing ratios of cloud water and rain, whereas the mixing ratios of ice and graupel are almost unchanged when compared to the default WRF run without the parameterization of gust front pulsation. The included parameterization did not disturb the general characteristics of thunderstorm cloud, such as the location of updraft and downdrafts, and the overall shape of the cloud. New cloud cells in front of the parent thunderstorm are also evident in both ideal and real cases due to the included forcing of vertical velocity caused by the periodic collapse of the gust front head. Despite some differences between the two WRF simulations and satellite observations, the inclusion of the gust front parameterization scheme produced more cumuliform clouds and seem to match better with real observations. Both WRF simulations gave poor results when it comes to matching the maximum composite radar reflectivity from radar measurement. Similar to the ideal case, WRF model with the gust front scheme gave more precipitation than the default WRF run. In particular, the gust front scheme increased the area characterized with light precipitation and diminished the development of very localized and intense precipitation.
Earlier vegetation green-up has reduced spring dust storms.

PubMed

Fan, Bihang; Guo, Li; Li, Ning; Chen, Jin; Lin, Henry; Zhang, Xiaoyang; Shen, Miaogen; Rao, Yuhan; Wang, Cong; Ma, Lei

2014-10-24

The observed decline of spring dust storms in Northeast Asia since the 1950s has been attributed to surface wind stilling. However, spring vegetation growth could also restrain dust storms through accumulating aboveground biomass and increasing surface roughness. To investigate the impacts of vegetation spring growth on dust storms, we examine the relationships between recorded spring dust storm outbreaks and satellite-derived vegetation green-up date in Inner Mongolia, Northern China from 1982 to 2008. We find a significant dampening effect of advanced vegetation growth on spring dust storms (r = 0.49, p = 0.01), with a one-day earlier green-up date corresponding to a decrease in annual spring dust storm outbreaks by 3%. Moreover, the higher correlation (r = 0.55, p < 0.01) between green-up date and dust storm outbreak ratio (the ratio of dust storm outbreaks to times of strong wind events) indicates that such effect is independent of changes in surface wind. Spatially, a negative correlation is detected between areas with advanced green-up dates and regional annual spring dust storms (r = -0.49, p = 0.01). This new insight is valuable for understanding dust storms dynamics under the changing climate. Our findings suggest that dust storms in Inner Mongolia will be further mitigated by the projected earlier vegetation green-up in the warming world.
Computational simulation of the effects of oxygen on the electronic states of hydrogenated 3C-porous SiC

PubMed Central

2012-01-01

A computational study of the dependence of the electronic band structure and density of states on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using ab initio density functional theory and the supercell method. The effects of the porosity and the surface chemistry composition on the energetic stability of pSiC were also investigated. The porous structures were modeled by removing atoms in the [001] direction to produce two different surface chemistries: one fully composed of silicon atoms and one composed of only carbon atoms. The changes in the electronic states of the porous structures as a function of the oxygen (O) content at the surface were studied. Specifically, the oxygen content was increased by replacing pairs of hydrogen (H) atoms on the pore surface with O atoms attached to the surface via either a double bond (X = O) or a bridge bond (X-O-X, X = Si or C). The calculations show that for the fully H-passivated surfaces, the forbidden energy band is larger for the C-rich phase than for the Si-rich phase. For the partially oxygenated Si-rich surfaces, the band gap behavior depends on the O bond type. The energy gap increases as the number of O atoms increases in the supercell if the O atoms are bridge-bonded, whereas the band gap energy does not exhibit a clear trend if O is double-bonded to the surface. In all cases, the gradual oxygenation decreases the band gap of the C-rich surface due to the presence of trap-like states. PMID:22913486
High Ice Water Concentrations in the 19 August 2015 Coastal Mesoconvective System

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Harrah, Steven; Switzer, George F.; Strickland, Justin K.; Hunt, Patricia J.

2017-01-01

During August 2015, NASA's DC-8 research aircraft was flown into High Ice Water Content (HIWC) events as part of a three-week campaign to collect airborne radar data and to obtain measurements from microphysical probes. Goals for this flight campaign included improved characterization of HIWC events, especially from an airborne radar perspective. This paper focuses on one of the flight days, in which a coastal mesoscale convective system (MCS) was investigated for HIWC conditions. The system appears to have been maintained by bands of convection flowing in from the Gulf of Mexico. These convective bands were capped by a large cloud canopy, which masks the underlying structure if viewed from an infrared sensing satellite. The DC-8 was equipped with an IsoKinetic Probe that measured ice concentrations of up to 2.3 g m(exp -3) within the cloud canopy of this system. Sustained measurements of ice crystals with concentrations exceeding 1 g m(exp -3) were encountered for up to ten minutes of flight time. Airborne Radar reflectivity factors were found to be weak within these regions of high ice water concentrations, suggesting that Radar detection of HIWC would be a challenging endeavor. This case is then investigated using a three-dimensional numerical cloud model. Profiles of ice water concentrations and radar reflectivity factor demonstrate similar magnitudes and scales between the flight measurements and model simulation. Also discussed are recent modifications to the numerical model's ice-microphysics that are based on measurements during the flight campaign. The numerical model and its updated ice-microphysics are further validated with a simulation of a well-known case of a supercell hailstorm measured during the Cooperative Convective Precipitation Experiment. Differences in HIWC between the continental supercell and the coastal MCS are discussed.
Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Liang; Wang, Jin; Dongare, Avinash M., E-mail: dongare@uconn.edu

2015-06-28

The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer andmore » a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.« less
Vertically integrated visible and near-infrared metasurfaces enabling an ultra-broadband and highly angle-resolved anomalous reflection.

PubMed

Gao, Song; Lee, Sang-Shin; Kim, Eun-Soo; Choi, Duk-Yong

2018-06-21

An optical device with minimized dimensions, which is capable of efficiently resolving an ultra-broad spectrum into a wide splitting angle but incurring no spectrum overlap, is of importance in advancing the development of spectroscopy. Unfortunately, this challenging task cannot be easily addressed through conventional geometrical or diffractive optical elements. Herein, we propose and demonstrate vertically integrated visible and near-infrared metasurfaces which render an ultra-broadband and highly angle-resolved anomalous reflection. The proposed metasurface capitalizes on a supercell that comprises two vertically concatenated trapezoid-shaped aluminum antennae, which are paired with a metallic ground plane via a dielectric layer. Under normal incidence, reflected light within a spectral bandwidth of 1000 nm ranging from λ = 456 nm to 1456 nm is efficiently angle-resolved to a single diffraction order with no spectrum overlap via the anomalous reflection, exhibiting an average reflection efficiency over 70% and a substantial angular splitting of 58°. In light of a supercell pitch of 1500 nm, to the best of our knowledge, the micron-scale bandwidth is the largest ever reported. It is noted that the substantially wide bandwidth has been accomplished by taking advantage of spectral selective vertical coupling effects between antennae and ground plane. In the visible regime, the upper antenna primarily renders an anomalous reflection by cooperating with the lower antenna, which in turn cooperates with the ground plane and produces phase variations leading to an anomalous reflection in the near-infrared regime. Misalignments between the two antennae have been particularly inspected to not adversely affect the anomalous reflection, thus guaranteeing enhanced structural tolerance of the proposed metasurface.
Resonant scattering due to adatoms in graphene: Top, bridge, and hollow positions

NASA Astrophysics Data System (ADS)

Irmer, Susanne; Kochan, Denis; Lee, Jeongsu; Fabian, Jaroslav

2018-02-01

We present a theoretical study of resonance characteristics in graphene from adatoms with s or pz character binding in top, bridge, and hollow positions. The adatoms are described by two tight-binding parameters: on-site energy and hybridization strength. We explore a wide range of different magnitudes of these parameters by employing T -matrix calculations in the single adatom limit and by tight-binding supercell calculations for dilute adatom coverage. We calculate the density of states and the momentum relaxation rate and extract the resonance level and resonance width. The top position with a large hybridization strength or, equivalently, small on-site energy, induces resonances close to zero energy. The bridge position, compared to top, is more sensitive to variation in the orbital tight-binding parameters. Resonances within the experimentally relevant energy window are found mainly for bridge adatoms with negative on-site energies. The effect of resonances from the top and bridge positions on the density of states and momentum relaxation rate is comparable and both positions give rise to a power-law decay of the resonant state in graphene. The hollow position with s orbital character is affected from destructive interference, which is seen from the very narrow resonance peaks in the density of states and momentum relaxation rate. The resonant state shows no clear tendency to a power-law decay around the impurity and its magnitude decreases strongly with lowering the adatom content in the supercell calculations. This is in contrast to the top and bridge positions. We conclude our study with a comparison to models of pointlike vacancies and strong midgap scatterers. The latter model gives rise to significantly higher momentum relaxation rates than caused by single adatoms.
Single and multi-band electromagnetic induced transparency-like metamaterials with coupled split ring resonators

NASA Astrophysics Data System (ADS)

Bagci, Fulya; Akaoglu, Baris

2017-08-01

We present a metamaterial configuration exhibiting single and multi-band electromagnetic induced transparency (EIT)-like properties. The unit cell of the single band EIT-like metamaterial consists of a multi-split ring resonator surrounded by a split ring resonator. The multi-split ring resonator acts as a quasi-dark or dark resonator, depending on the polarization of the incident wave, and the split ring resonator serves as the bright resonator. Combination of these two resonators results in a single band EIT-like transmission inside the stop band. EIT-like transmission phenomenon is also clearly observed in the measured transmission spectrum at almost the same frequencies for vertical and horizontal polarized waves, and the numerical results are verified for normal incidence. Moreover, multi-band transmission windows are created within a wide band by combining the two slightly different single band EIT-like metamaterial unit cells that exhibit two different coupling strengths inside a supercell configuration. Group indices as high as 123 for single band and 488 for tri-band transmission, accompanying with high transmission rates (over 80%), are achieved, rendering the metamaterial very suitable for multi-band slow light applications. It is shown that the group delay of the propagating wave can be increased and dynamically controlled by changing the polarization angle. Multi-band EIT-like transmission is also verified experimentally, and a good agreement with simulations is obtained. The proposed novel methodology for obtaining multi-band EIT, which takes advantage of a supercell configuration by hosting slightly different configured unit cells, can be utilized for easily formation and manipulation of multi-band transmission windows inside a stop band.

Supercell Depletion Studies for Prismatic High Temperature Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

J. Ortensi

2012-10-01

The traditional two-step method of analysis is not accurate enough to represent the neutronic effects present in the prismatic high temperature reactor concept. The long range coupling of the various regions in high temperature reactors poses a set of challenges that are not seen in either LWRs or fast reactors. Unlike LWRs, which exhibit large, localized effects, the dominant effects in PMRs are, for the most part, distributed over larger regions, but with lower magnitude. The 1-D in-line treatment currently used in pebble bed reactor analysis is not sufficient because of the 2-D nature of the prismatic blocks. Considerable challengesmore » exist in the modeling of blocks in the vicinity of reflectors, which, for current small modular reactor designs with thin annular cores, include the majority of the blocks. Additional challenges involve the treatment of burnable poisons, operational and shutdown control rods. The use of a large domain for cross section preparation provides a better representation of the neutron spectrum, enables the proper modeling of BPs and CRs, allows the calculation of generalized equivalence theory parameters, and generates a relative power distribution that can be used in compact power reconstruction. The purpose of this paper is to quantify the effects of the reflector, burnable poison, and operational control rods on an LEU design and to delineate an analysis approach for the Idaho National Laboratory. This work concludes that the use of supercells should capture these long-range effects in the preparation of cross sections and along with a set of triangular meshes to treat BPs, and CRs a high fidelity neutronics computation is attainable.« less
Structural and electronic properties of GaN nanowires with embedded In{sub x}Ga{sub 1−x}N nanodisks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kioseoglou, J., E-mail: sifisl@auth.gr; Pavloudis, Th.; Kehagias, Th.

2015-07-21

In the present study, the effects of various types of strain and indium concentration on the total energy and optoelectronic properties of GaN nanowires (NWs) with embedded In{sub x}Ga{sub 1−x}N nanodisks (NDs) are examined. In particular, the bi-axial, hydrostatic, and uniaxial strain states of the embedded In{sub x}Ga{sub 1−x}N NDs are investigated for multiple In concentrations. Density functional theory is employed to calculate the band structure of the NWs. The theoretical analysis finds that the supercell-size-dependent characteristics calculated for our 972-atom NW models are very close to the infinite supercell-size limit. It is established that the embedded In{sub x}Ga{sub 1−x}Nmore » NDs do not induce deep states in the band gap of the NWs. A bowing parameter of 1.82 eV is derived from our analysis in the quadratic Vegard's formula for the band gaps at the various In concentrations of the investigated In{sub x}Ga{sub 1−x}N NDs in GaN NW structures. It is concluded that up to ∼10% of In, the hydrostatic strain state is competitive with the bi-axial due to the radial absorption of the strain on the surfaces. Above this value, the dominant strain state is the bi-axial one. Thus, hydrostatic and bi-axial strain components coexist in the embedded NDs, and they are of different physical origin. The bi-axial strain comes from growth on lattice mismatched substrates, while the hydrostatic strain originates from the lateral relaxation of the surfaces.« less
Models for Amorphous Calcium Carbonate

NASA Astrophysics Data System (ADS)

Sinha, Sourabh

Many species e.g. sea urchin form amorphous calcium carbonate (ACC) precursor phases that subsequently transform into crystalline CaCO3. It is certainly possible that the biogenic ACC might have more than 10 wt% Mg and ˜3 wt% of water. The structure of ACC and the mechanisms by which it transforms to crystalline phase are still poorly understood. In this dissertation our goal is to determine an atomic structure model that is consistent with diffraction and IR measurements of ACC. For this purpose a calcite supercell with 24 formula units, containing 120 atoms, was constructed. Various configurations with substitution of Ca by 6 Mg ions (6 wt.%) and insertion of 3-5 H 2O molecules (2.25-3.75 wt.%) in the interstitial positions of the supercell, were relaxed using a robust density function code VASP. The most noticeable effects were the tilts of CO3 groups and the distortion of Ca sub-lattice, especially in the hydrated case. The distributions of Ca-Ca nearest neighbor distance and CO3 tilts were extracted from various configurations. The same methods were also applied to aragonite. Sampling from the calculated distortion distributions, we built models for amorphous calcite/aragonite of size ˜ 1700 nm3 based on a multi-scale modeling scheme. We used these models to generate diffraction patterns and profiles with our diffraction code. We found that the induced distortions were not enough to generate a diffraction profile typical of an amorphous material. We then studied the diffraction profiles from several nano-crystallites as recent studies suggest that ACC might be a random array of nano-cryatallites. It was found that the generated diffraction profile from a nano-crystallite of size ˜ 2 nm3 is similar to that from the ACC.
Clustering/anticlustering effects on the GeSi Raman spectra at moderate (Ge,Si) contents: Percolation scheme vs. ab initio calculations

NASA Astrophysics Data System (ADS)

Torres, V. J. B.; Hajj Hussein, R.; Pagès, O.; Rayson, M. J.

2017-02-01

We test a presumed ability behind the phenomenological percolation scheme used for the basic description of the multi-mode Raman spectra of mixed crystals at one dimension along the linear chain approximation, to determine, via the Raman intensities, the nature of the atom substitution, as to whether this is random or due to local clustering/anticlustering. For doing so, we focus on the model percolation-type GeySi1-y system characterized by six oscillators { 1 × ( G e - G e ) , 3 × ( G e - S i ) , 2 × ( S i - S i ) } and place the study around the critical compositions y ˜ (0.16, 0.71, and 0.84) corresponding to nearly matching of intensities between the like Raman modes from a given multiplet ( G e - S i triplet or S i - S i doublet). The interplay between the GeySi1-y Raman intensities predicted by the percolation scheme depending on a suitable order parameter κ of local clustering/anticlustering is found to be consistent with ab initio calculations of the GeySi1-y Raman spectra done with the Ab Initio Modeling PROgram code using large (64-, 216-, and 512-atoms) disordered cubic supercells matching the required ( y , κ ) values. The actual "percolation vs. ab initio" comparative insight at moderate/dilute-(Ge,Si) limits, with an emphasis on the κ -induced intra-bond transfer of oscillator strength, extends a pioneering one earlier achieved at an intermediate composition ( y ˜ 0.50) by using small (32-atom) supercells [O. Pagès et al., J. Appl. Phys. 114, 033513 (2013)], mainly concerned with the inter-bond transfer of oscillator strength, providing altogether a complete picture.
Watershed and land use-based sources of trace metals in urban storm water.

PubMed

Tiefenthaler, Liesl L; Stein, Eric D; Schiff, Kenneth C

2008-02-01

Trace metal contributions in urban storm water are of concern to environmental managers because of their potential impacts on ambient receiving waters. The mechanisms and processes that influence temporal and spatial patterns of trace metal loading in urban storm water, however, are not well understood. The goals of the present study were to quantify trace metal event mean concentration (EMC), flux, and mass loading associated with storm water runoff from representative land uses; to compare EMC, flux, and mass loading associated with storm water runoff from urban (developed) and nonurban (undeveloped) watersheds; and to investigate within-storm and within-season factors that affect trace metal concentration and flux. To achieve these goals, trace metal concentrations were measured in 315 samples over 11 storm events in five southern California, USA, watersheds representing eight different land use types during the 2000 through 2005 storm seasons. In addition, 377 runoff samples were collected from 12 mass emission sites (end of watershed) during 15 different storm events. Mean flux at land use sites ranged from 24 to 1,238, 0.1 to 1,272, and 6 to 33,189 g/km(2) for total copper, total lead, and total zinc, respectively. Storm water runoff from industrial land use sites contained higher EMCs and generated greater flux of trace metals than other land use types. For all storms sampled, the highest metal concentrations occurred during the early phases of storm water runoff, with peak concentrations usually preceding peak flow. Early season storms produced significantly higher metal flux compared with late season storms at both mass emission and land use sites.
Lightning Evolution In Two North Central Florida Summer Multicell Storms and Three Winter/Spring Frontal Storms

NASA Astrophysics Data System (ADS)

Caicedo, J. A.; Uman, M. A.; Pilkey, J. T.

2018-01-01

We present the first lightning evolution studies, via the Lightning Mapping Array (LMA) and radar, performed in North Central Florida. Parts of three winter/spring frontal storms (cold season) and two complete summer (warm season) multicell storms are studied. Storm parameters measured are as follows: total number of flashes, flash-type classification, first flashes, flash initiation altitude, flash initiation power, flash rate (flashes per minute), charge structure, altitude and temperature ranges of the inferred charge regions, atmospheric isotherm altitude, radar base reflectivity (dBZ), and radar echo tops (EET). Several differences were found between summer multicell and winter/spring frontal storms in North Central Florida: (1) in winter/spring storms, the range of altitudes that all charge regions occupy is up to 1 km lower in altitude than in summer storms, as are the 0°C, -10°C, and -20°C isotherms; (2) lightning activity in summer storms is highly correlated with changes in radar signatures, in particular, echo tops; and (3) the LMA average initiation power of all flash types in winter/frontal storms is about an order of magnitude larger than that for summer storms. In relation to storms in other geographical locations, North Central Florida seasonal storms were found to have similarities in most parameters studied with a few differences, examples in Florida being (1) colder initiation altitudes for intracloud flashes, (2) charge regions occupying larger ranges of atmospheric temperatures, and (3) winter/spring frontal storms not having much lightning activity in the stratiform region.
Episodic acidification of a coastal plain stream in Virginia

USGS Publications Warehouse

O'Brien, A. K.; Eshleman, K.N.

1996-01-01

This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid- base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO4/2- concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg2+, Ca2+, K+ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na+ and Cl- concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO4/2- concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na+ and Cl- concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO4/2- concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO4/2- concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.
Monitoring Hurricane Rita Inland Storm Surge: Chapter 7J in Science and the storms-the USGS response to the hurricanes of 2005

USGS Publications Warehouse

McGee, Benton D.; Tollett, Roland W.; Goree, Burl B.

2007-01-01

Pressure transducers (sensors) are accurate, reliable, and cost-effective tools to measure and record the magnitude, extent, and timing of hurricane storm surge. Sensors record storm-surge peaks more accurately and reliably than do high-water marks. Data collected by sensors may be used in storm-surge models to estimate when, where, and to what degree stormsurge flooding will occur during future storm-surge events and to calibrate and verify stormsurge models, resulting in a better understanding of the dynamics of storm surge.
Advances in using satellite altimetry to observe storm surge

NASA Astrophysics Data System (ADS)

Han, Guoqi

2017-04-01

Storm surges are the major cause for coastal flooding, resulting in catastrophic damage to properties and loss of life in coastal communities. Thus it is important to utilize new technology to enhance our capabilities of observing storm surges and ultimately to improve our capacity for forecasting storm surges and mitigating damage and loss. In this talk we first review traditional methods of monitoring storm surges. We then provide examples of storm surges observed by nadir satellite altimetry, during Hurricane Sandy and Igor, as well as typhoon and cyclone events. We further evaluate satellite results against tide-gauge data and explain storm surge features. Finally, we discuss the potential of a wide-swath altimetry mission, the Surface Water and Ocean Topography (SWOT), for observing storm surges.
Modeling storms improves estimates of long-term shoreline change

NASA Astrophysics Data System (ADS)

Frazer, L. Neil; Anderson, Tiffany R.; Fletcher, Charles H.

2009-10-01

Large storms make it difficult to extract the long-term trend of erosion or accretion from shoreline position data. Here we make storms part of the shoreline change model by means of a storm function. The data determine storm amplitudes and the rate at which the shoreline recovers from storms. Historical shoreline data are temporally sparse, and inclusion of all storms in one model over-fits the data, but a probability-weighted average model shows effects from all storms, illustrating how model averaging incorporates information from good models that might otherwise have been discarded as un-parsimonious. Data from Cotton Patch Hill, DE, yield a long-term shoreline loss rate of 0.49 ± 0.01 m/yr, about 16% less than published estimates. A minimum loss rate of 0.34 ± 0.01 m/yr is given by a model containing the 1929, 1962 and 1992 storms.
Major coastal impact induced by a 1000-year storm event

PubMed Central

Fruergaard, Mikkel; Andersen, Thorbjørn J.; Johannessen, Peter N.; Nielsen, Lars H.; Pejrup, Morten

2013-01-01

Extreme storms and storm surges may induce major changes along sandy barrier coastlines, potentially causing substantial environmental and economic damage. We show that the most destructive storm (the 1634 AD storm) documented for the northern Wadden Sea within the last thousand years both caused permanent barrier breaching and initiated accumulation of up to several metres of marine sand. An aggradational storm shoal and a prograding shoreface sand unit having thicknesses of up to 8 m and 5 m respectively were deposited as a result of the storm and during the subsequent 30 to 40 years long healing phase, on the eroded shoreface. Our results demonstrate that millennial-scale storms can induce large-scale and long-term changes on barrier coastlines and shorefaces, and that coastal changes assumed to take place over centuries or even millennia may occur in association with and be triggered by a single extreme storm event.
Adolescent storm and stress, reconsidered.

PubMed

Arnett, J J

1999-05-01

G. S. Hall's (1904) view that adolescence is a period of heightened "storm and stress" is reconsidered in light of contemporary research. The author provides a brief history of the storm-and-stress view and examines 3 key aspects of this view: conflict with parents, mood disruptions, and risk behavior. In all 3 areas, evidence supports a modified storm-and-stress view that takes into account individual differences and cultural variations. Not all adolescents experience storm and stress, but storm and stress is more likely during adolescence than at other ages. Adolescent storm and stress tends to be lower in traditional cultures than in the West but may increase as globalization increases individualism. Similar issues apply to minority cultures in American society. Finally, although the general public is sometimes portrayed by scholars as having a stereotypical view of adolescent storm and stress, both scholars and the general public appear to support a modified storm-and-stress view.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, B. R.; Millan, R. M.; Reeves, G. D.

We report that past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms (Dst >₋50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result inmore » flux depletion than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. Small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.« less
Progress in the Study of Coastal Storm Deposits

NASA Astrophysics Data System (ADS)

Xiong, Haixian; Huang, Guangqing; Fu, Shuqing; Qian, Peng

2018-05-01

Numerous studies have been carried out to identify storm deposits and decipher storm-induced sedimentary processes in coastal and shallow-marine areas. This study aims to provide an in-depth review on the study of coastal storm deposits from the following five aspects. 1) The formation of storm deposits is a function of hydrodynamic and sedimentary processes under the constraints of local geological and ecological factors. Many questions remain to demonstrate the genetic links between storm-related processes and a variety of resulting deposits such as overwash deposits, underwater deposits and hummocky cross-stratification (HCS). Future research into the formation of storm deposits should combine flume experiments, field observations and numerical simulations, and make full use of sediment source tracing methods. 2) Recently there has been rapid growth in the number of studies utilizing sediment provenance analysis to investigate the source of storm deposits. The development of source tracing techniques, such as mineral composition, magnetic susceptibility, microfossil and geochemical property, has allowed for better understanding of the depositional processes and environmental changes associated with coastal storms. 3) The role of extreme storms in the sedimentation of low-lying coastal wetlands with diverse ecosystem services has also drawn a great deal of attention. Many investigations have attempted to quantify widespread land loss, vertical marsh sediment accumulation and wetland elevation change induced by major hurricanes. 4) Paleostorm reconstructions based on storm sedimentary proxies have shown many advantages over the instrumental records and historic documents as they allow for the reconstruction of storm activities on millennial or longer time scales. Storm deposits having been used to establish proxies mainly include beach ridges and shelly cheniers, coral reefs, estuary-deltaic storm sequences and overwash deposits. Particularly over the past few decades, the proxies developed from overwash deposits have successfully retrieved many records of storm activities during the mid to late Holocene worldwide. 5) Distinguishing sediments deposited by storms and tsunamis is one of the most difficult issues among the many aspects of storm deposit studies. Comparative studies have investigated numerous diagnostic evidences including hydrodynamic condition, landward extent, grain property, texture and grading, thickness, microfossil assemblage and landscape conformity. Perhaps integrating physical, biological and geochemical evidences will, in the future, allow unambiguous identification of tsunami deposits and storm deposits.
NASA/NOAA: Earth Science Electronic Theater 1999

NASA Technical Reports Server (NTRS)

Hasler, A. Fritz

1999-01-01

The Electronic Theater (E-theater) presents visualizations which span the period from the original Suomi/Hasler animations of the first ATS-1 GEO weather satellite images in 1966 to the latest 1999 NASA Earth Science Vision for the next 25 years. Hot off the SGI-Onyx Graphics-Supercomputer are NASA's visualizations of Hurricanes Mitch, Georges, Fran and Linda. These storms have been recently featured on the covers of National Geographic, Time, Newsweek and Popular Science. Highlights will be shown from the NASA hurricane visualization resource video tape that has been used repeatedly this season on National and International network TV. Results will be presented from a new paper on automatic wind measurements in Hurricane Luis from 1-min GOES images that appeared in the November BAMS. The visualizations are produced by the NASA Goddard Visualization and Analysis Laboratory (VAL/912), and Scientific Visualization Studio (SVS/930), as well as other Goddard and NASA groups using NASA, NOAA, ESA, and NASDA Earth science datasets. Visualizations will be shown from the Earth Science E-Theater 1999 recently presented in Tokyo, Paris, Munich, Sydney, Melbourne, Honolulu, Washington, New York, and Dallas. The presentation Jan 11-14 at the AMS meeting in Dallas used a 4-CPU SGI/CRAY Onyx Infinite Reality Super Graphics Workstation with 8 GB RAM and a Terabyte Disk at 3840 X 1024 resolution with triple synchronized BarcoReality 9200 projectors on a 60ft wide screen. Visualizations will also be featured from the new Earth Today Exhibit which was opened by Vice President Gore on July 2, 1998 at the Smithsonian Air & Space museum in Washington, as well as those presented for possible use at the American Museum of Natural History (NYC), Disney EPCOT, and other venues. New methods are demonstrated for visualizing, interpreting, comparing, organizing and analyzing immense HyperImage remote sensing datasets and three dimensional numerical model results. We call the data from many new Earth sensing satellites, HyperImage datasets, because they have such high resolution in the spectral, temporal, spatial, and dynamic range domains. The traditional numerical spreadsheet paradigm has been extended to develop a scientific visualization approach for processing HyperImage datasets and 3D model results interactively. The advantages of extending the powerful spreadsheet style of computation to multiple sets of images and organizing image processing were demonstrated using the Distributed image SpreadSheet (DISS). The DISS is being used as a high performance testbed Next Generation Internet (NGI) VisAnalysis of: 1) El Nino SSTs and NDVI response 2) Latest GOES 10 5-min rapid Scans of 26 day 5000 frame movie of March & April '98 weather and tornadic storms 3) TRMM rainfall and lightning 4)GOES 9 satellite images/winds and NOAA aircraft radar of hurricane Luis, 5) lightning detector data merged with GOES image sequences, 6) Japanese GMS, TRMM, & ADEOS data 7) Chinese FY2 data 8) Meteosat & ERS/ATSR data 9) synchronized manipulation of multiple 3D numerical model views; and others will be illustrated. The Image SpreadSheet has been highly successful in producing Earth science visualizations for public outreach. Many of these visualizations have been widely disseminated through the world wide web pages of the HPCC/LTP/RSD program which can be found at http://rsd.gsfc.nasa.gov/rsd The one min interval animations of Hurricane Luis on ABC Nightline and the color perspective rendering of Hurricane Fran published by TIME, LIFE, Newsweek, Popular Science, National Geographic, Scientific American, and the "Weekly Reader" are some of the examples which will be shown.
Are inundation limit and maximum extent of sand useful for differentiating tsunamis and storms? An example from sediment transport simulations on the Sendai Plain, Japan

NASA Astrophysics Data System (ADS)

Watanabe, Masashi; Goto, Kazuhisa; Bricker, Jeremy D.; Imamura, Fumihiko

2018-02-01

We examined the quantitative difference in the distribution of tsunami and storm deposits based on numerical simulations of inundation and sediment transport due to tsunami and storm events on the Sendai Plain, Japan. The calculated distance from the shoreline inundated by the 2011 Tohoku-oki tsunami was smaller than that inundated by storm surges from hypothetical typhoon events. Previous studies have assumed that deposits observed farther inland than the possible inundation limit of storm waves and storm surge were tsunami deposits. However, confirming only the extent of inundation is insufficient to distinguish tsunami and storm deposits, because the inundation limit of storm surges may be farther inland than that of tsunamis in the case of gently sloping coastal topography such as on the Sendai Plain. In other locations, where coastal topography is steep, the maximum inland inundation extent of storm surges may be only several hundred meters, so marine-sourced deposits that are distributed several km inland can be identified as tsunami deposits by default. Over both gentle and steep slopes, another difference between tsunami and storm deposits is the total volume deposited, as flow speed over land during a tsunami is faster than during a storm surge. Therefore, the total deposit volume could also be a useful proxy to differentiate tsunami and storm deposits.
Earlier vegetation green-up has reduced spring dust storms

PubMed Central

Fan, Bihang; Guo, Li; Li, Ning; Chen, Jin; Lin, Henry; Zhang, Xiaoyang; Shen, Miaogen; Rao, Yuhan; Wang, Cong; Ma, Lei

2014-01-01

The observed decline of spring dust storms in Northeast Asia since the 1950s has been attributed to surface wind stilling. However, spring vegetation growth could also restrain dust storms through accumulating aboveground biomass and increasing surface roughness. To investigate the impacts of vegetation spring growth on dust storms, we examine the relationships between recorded spring dust storm outbreaks and satellite-derived vegetation green-up date in Inner Mongolia, Northern China from 1982 to 2008. We find a significant dampening effect of advanced vegetation growth on spring dust storms (r = 0.49, p = 0.01), with a one-day earlier green-up date corresponding to a decrease in annual spring dust storm outbreaks by 3%. Moreover, the higher correlation (r = 0.55, p < 0.01) between green-up date and dust storm outbreak ratio (the ratio of dust storm outbreaks to times of strong wind events) indicates that such effect is independent of changes in surface wind. Spatially, a negative correlation is detected between areas with advanced green-up dates and regional annual spring dust storms (r = −0.49, p = 0.01). This new insight is valuable for understanding dust storms dynamics under the changing climate. Our findings suggest that dust storms in Inner Mongolia will be further mitigated by the projected earlier vegetation green-up in the warming world. PMID:25343265
Probability of occurrence of planetary ionosphere storms associated with the magnetosphere disturbance storm time events

NASA Astrophysics Data System (ADS)

Gulyaeva, T. L.; Arikan, F.; Stanislawska, I.

2014-11-01

The ionospheric W index allows to distinguish state of the ionosphere and plasmasphere from quiet conditions (W = 0 or ±1) to intense storm (W = ±4) ranging the plasma density enhancements (positive phase) or plasma density depletions (negative phase) regarding the quiet ionosphere. The global W index maps are produced for a period 1999-2014 from Global Ionospheric Maps of Total Electron Content, GIM-TEC, designed by Jet Propulson Laboratory, converted from geographic frame (-87.5:2.5:87.5° in latitude, -180:5:180° in longitude) to geomagnetic frame (-85:5:85° in magnetic latitude, -180:5:180° in magnetic longitude). The probability of occurrence of planetary ionosphere storm during the magnetic disturbance storm time, Dst, event is evaluated with the superposed epoch analysis for 77 intense storms (Dst ≤ -100 nT) and 230 moderate storms (-100 < Dst ≤ -50 nT) with start time, t0, defined at Dst storm main phase onset. It is found that the intensity of negative storm, iW-, exceeds the intensity of positive storm, iW+, by 1.5-2 times. An empirical formula of iW+ and iW- in terms of peak Dst is deduced exhibiting an opposite trends of relation of intensity of ionosphere-plasmasphere storm with regard to intensity of Dst storm.
Modeling urban storm rainfall runoff from diverse underlying surfaces and application for control design in Beijing.

PubMed

Ouyang, Wei; Guo, Bobo; Hao, Fanghua; Huang, Haobo; Li, Junqi; Gong, Yongwei

2012-12-30

Managing storm rainfall runoff is paramount in semi-arid regions with urban development. In Beijing, pollution prevention in urban storm runoff and storm water utilization has been identified as the primary strategy for urban water management. In this paper, we sampled runoff during storm rainfall events and analyzed the concentration of chemical oxygen demand (COD), total suspended solids (TSS) and total phosphorus (TP) in the runoff. Furthermore, the first flush effect of storm rainfall from diverse underlying surfaces was also analyzed. With the Storm Water Management Model (SWMM), the different impervious rates of underlying surfaces during the storm runoff process were expressed. The removal rates of three typical pollutants and their interactions with precipitation and underlying surfaces were identified. From these rates, the scenarios regarding the urban storm runoff pollution loading from different designs of underlying previous rates were assessed with the SWMM. First flush effect analysis showed that the first 20% of the storm runoff should be discarded, which can help in utilizing the storm water resource. The results of this study suggest that the SWMM can express in detail the storm water pollution patterns from diverse underlying surfaces in Beijing, which significantly affected water quality. The scenario analysis demonstrated that impervious rate adjustment has the potential to reduce runoff peak and decrease pollution loading. Copyright © 2012 Elsevier Ltd. All rights reserved.
46 CFR 72.40-10 - Storm rails.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 3 2010-10-01 2010-10-01 false Storm rails. 72.40-10 Section 72.40-10 Shipping COAST... and Guards § 72.40-10 Storm rails. (a) Suitable storm rails shall be installed in all passageways and at the deckhouse sides where passengers or crew might have normal access. Storm rails shall be...

46 CFR 72.40-10 - Storm rails.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 3 2013-10-01 2013-10-01 false Storm rails. 72.40-10 Section 72.40-10 Shipping COAST... and Guards § 72.40-10 Storm rails. (a) Suitable storm rails shall be installed in all passageways and at the deckhouse sides where passengers or crew might have normal access. Storm rails shall be...
46 CFR 72.40-10 - Storm rails.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 3 2011-10-01 2011-10-01 false Storm rails. 72.40-10 Section 72.40-10 Shipping COAST... and Guards § 72.40-10 Storm rails. (a) Suitable storm rails shall be installed in all passageways and at the deckhouse sides where passengers or crew might have normal access. Storm rails shall be...
46 CFR 72.40-10 - Storm rails.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 3 2012-10-01 2012-10-01 false Storm rails. 72.40-10 Section 72.40-10 Shipping COAST... and Guards § 72.40-10 Storm rails. (a) Suitable storm rails shall be installed in all passageways and at the deckhouse sides where passengers or crew might have normal access. Storm rails shall be...
46 CFR 72.40-10 - Storm rails.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 3 2014-10-01 2014-10-01 false Storm rails. 72.40-10 Section 72.40-10 Shipping COAST... and Guards § 72.40-10 Storm rails. (a) Suitable storm rails shall be installed in all passageways and at the deckhouse sides where passengers or crew might have normal access. Storm rails shall be...
Rainfall Data Simulation

Treesearch

T.L. Rogerson

1980-01-01

A simple simulation model to predict rainfall for individual storms in central Arkansas is described. Output includes frequency distribution tables for days between storms and for storm size classes; a storm summary by day number (January 1 = 1 and December 31 = 365) and rainfall amount; and an annual storm summary that includes monthly values for rainfall and number...
The Association between Dust Storms and Daily Non-Accidental Mortality in the United States, 1993-2005.

EPA Science Inventory

Background:The impact of dust storms on human health has been studied in the context of Asian,Saharan, Arabian, and Australian storms,but there has been no recent population-level epidemiological research on the dust storms in North America . The relevance of dust storms to publi...
Interplanetary radio storms. 2: Emission levels and solar wind speed in the range 0.05-0.8 AU

NASA Technical Reports Server (NTRS)

Bougeret, J. L.; Fainberg, J.; Stone, R. G.

1982-01-01

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetry medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the Sun. Usng a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the central meridian passage of the storm. The comparison with average in situ density measurements compiled from the HELIOS 1-2 observations favors type III storm burst radio emission at the harmonic of the local plasma frequency.
Global distribution of ULF waves during magnetic storms on March 27, 2017 and April 4, 2017

NASA Astrophysics Data System (ADS)

Takahashi, N.; Seki, K.; Teramoto, M.; Matsuoka, A.; Higashio, N.; Fok, M. C. H.

2017-12-01

The relativistic electron population in the Earth's outer radiation belt is drastically variable, especially during the active condition of the magnetosphere such as magnetic storms. One of the candidate mechanisms to cause the increase or decrease of relativistic electrons is the radial diffusion of the electrons driven by ultra-low-frequency (ULF) waves in Pc5 frequency ranges. However, how much ULF Pc5 waves contribute to the evolution of the radiation belt is still an open issue. In particular, previous papers have investigated the radial distribution of ULF Pc5 waves in the inner magnetosphere, but the spatial distribution is not well understood because of the limited number of satellite. In December 2016, the Arase satellite was launched into the inner magnetosphere, and the campaign observations between Arase and ground-based observations are now operated. During the first campaign observation from the end of March to April 2017, two distinct magnetic storms were occurred. The first storm was occurred on March 27, 2017 (Storm 1), which lasted for about six days. On the other hand, the second storm on April 4, 2017 (Storm 2) lasted for about two days. The temporal variation of the dynamic pressure and density of solar wind during each storm is almost similar. However, the solar wind flow speed data shows that Storm 1 is caused by the CIR, while Storm 2 might be caused by the CME. Therefore, background field variations that excite ULF Pc5 waves in the inner magnetosphere can be different between Storm 1 and 2. In addition, the Extremely High-Energy Electron Experiment (XEP) data onboard Arase clearly show the increase of high-energy electrons (400 keV-20 MeV) during the recovery phase of Storm 1, while they did not recover to the pre-storm level during Storm 2. Remarkable difference between two storms is the substorm activities in the recovery phase. The AE index continuously increased in Storm 1, while in Storm 2, it stayed in low level. The global simulation by BATS-R-US with the CRCM show that ULF Pc5 wave power during Storm 1 is larger than that during Storm 2. In this study, based on the multiple satellite observations including Arase and the global simulation, we investigate the temporal and spatial distribution of ULF Pc5 waves and their relation to solar wind conditions and substorm injections.
[Dust storms trend in the Capital Circle of China over the past 50 years and its correlation with temperature, precipitation and wind].

PubMed

Chen, Yu-fu; Tang, Hai-ping

2005-01-01

The trends of number of dust storm days of the selected 11 meteorological stations from their established year to 2000 as well as their correlations with temperature, precipitation and wind are revealed. The number of dust storm days of the Capital Circle of China is distinctly variable in space and time. The numbers of dust storm days of the western area are far more than those of the eastern area. The interannual variability of number of dust storm days is remarkable. The number of dust storm days of the following 7 stations, Erlianhaote, Abaga, Xilinhaote, Fengning, Zhangjiakou, Huailai and Beijing, declined along the past decades, but those of the other four stations had no significant upward or downward trends. There is a marked seasonality of the number of dust storm days, and the maximum was in April. The correlation between number of dust storm days and number of days of mean wind velocity > 5 m/s, which is critical wind velocity to entrain sand into the air, was strongest among the three climatic factor. There were significant positive correlations between the number of dust storm days and number of days of mean wind velocity > 5 m/s in 6 stations. The second strongest climatic factor correlated with the number of dust storm days is temperature. There are significant negative correlations between the number of dust storm days and mean annual temperature, mean winter temperature, mean spring temperature in 3 or 4 stations. The correlation between the number of dust storm days and precipitation is weakest. Only one station, Zhurihe, showes significant negative correlation between the number of dust storm days and spring rainfall. There are 4 stations whose number of dust storm days don't significantly correlate with the climate. In the end, the spatial-temporal variability of dust storms and its relation with climate in the Capital Circle of China were discussed thoroughly.
Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California

USGS Publications Warehouse

Dettinger, M.D.; Martin, Ralph F.; Hughes, M.; Das, T.; Neiman, P.; Cox, D.; Estes, G.; Reynolds, D.; Hartman, R.; Cayan, D.; Jones, L.

2012-01-01

The USGS Multihazards Project is working with numerous agencies to evaluate and plan for hazards and damages that could be caused by extreme winter storms impacting California. Atmospheric and hydrological aspects of a hypothetical storm scenario have been quantified as a basis for estimation of human, infrastructure, economic, and environmental impacts for emergency-preparedness and flood-planning exercises. In order to ensure scientific defensibility and necessary levels of detail in the scenario description, selected historical storm episodes were concatentated to describe a rapid arrival of several major storms over the state, yielding precipitation totals and runoff rates beyond those occurring during the individual historical storms. This concatenation allowed the scenario designers to avoid arbitrary scalings and is based on historical occasions from the 19th and 20th Centuries when storms have stalled over the state and when extreme storms have arrived in rapid succession. Dynamically consistent, hourly precipitation, temperatures, barometric pressures (for consideration of storm surges and coastal erosion), and winds over California were developed for the so-called ARkStorm scenario by downscaling the concatenated global records of the historical storm sequences onto 6- and 2-km grids using a regional weather model of January 1969 and February 1986 storm conditions. The weather model outputs were then used to force a hydrologic model to simulate ARkStorm runoff, to better understand resulting flooding risks. Methods used to build this scenario can be applied to other emergency, nonemergency and non-California applications. ?? 2011 The Author(s).
Winter in the Ouachitas--a severe winter storm signature in Pinus echinata in the Ouachita Mountains of Oklahoma and Arkansas, USA

Treesearch

Douglas J. Stevenson; Thomas B. Lynch; Pradip Saud; Robert Heineman; Randal Holeman; Dennis Wilson; Keith Anderson; Chris Cerny; James M. Guldin

2016-01-01

Each year severe winter storms (âice storms) damage trees throughout the southern USA. Arkansas andÂ Oklahoma have a history of severe winter storms. To extend that history back beyond the reach of writtenÂ records, a distinctive tree ring pattern or signature is needed. Storm-caused breakage, branch loss andÂ bending stress provide that signature. We found a severe storm...
Observations and global numerical modelling of the St. Patrick's Day 2015 geomagnetic storm event

NASA Astrophysics Data System (ADS)

Foerster, M.; Prokhorov, B. E.; Doornbos, E.; Astafieva, E.; Zakharenkova, I.

2017-12-01

With a sudden storm commencement (SSC) at 04:45 UT on St. Patrick's day 2015 started the most severe geomagnetic storm in solar cycle 24. It appeared as a two-stage geomagnetic storm with a minimum SYM-H value of -233 nT. In the response to the storm commencement in the first activation, a short-term positive effect in the ionospheric vertical electron content (VTEC) occurred at low- and mid-latitudes on the dayside. The second phase commencing around 12:30 UT lasted longer and caused significant and complex storm-time changes around the globe with hemispherical different ionospheric storm reactions in different longitudinal ranges. Swarm-C observations of the neutral mass density variation along the orbital path as well as Langmuir probe plasma and magnetometer measurements of all three Swarm satellites and global TEC records are used for physical interpretations and modelling of the positive/negative storm scenario. These observations pose a challenge for the global numerical modelling of thermosphere-ionosphere storm processes as the storm, which occurred around spring equinox, obviously signify the existence of other impact factors than seasonal dependence for hemispheric asymmetries to occur. Numerical simulation trials using the Potsdam version of the Upper Atmosphere Model (UAM-P) are presented to explain these peculiar M-I-T storm processes.
Trace fossils, sedimentary facies and parasequence architecture from the Lower Cretaceous Mulichinco Formation of Argentina: The role of fair-weather waves in shoreface deposits

NASA Astrophysics Data System (ADS)

Wesolowski, Lindsey J. N.; Buatois, Luis A.; Mángano, M. Gabriela; Ponce, Juan José; Carmona, Noelia B.

2018-05-01

Shorefaces can display strong facies variability and integration of sedimentology and ichnology provides a high-resolution model to identify variations among strongly storm-dominated (high energy), moderately storm-affected (intermediate energy), and weakly storm-affected (low energy) shoreface deposits. In addition, ichnology has proved to be of help to delineate parasequences as trace-fossil associations are excellent indicators of environmental conditions which typically change along the depositional profile. Shallow-marine deposits and associated ichnofaunas from the Mulichinco Formation (Valanginian, Lower Cretaceous) in Puerta Curaco, Neuquén Basin, western Argentina, were analyzed to evaluate stress factors on shoreface benthos and parasequence architecture. During storm-dominated conditions, the Skolithos Ichnofacies prevails within the offshore transition and lower shoreface represented by assemblages dominated by Thalassinoides isp. and Ophiomorpha irregulaire. Under weakly storm-affected conditions, the Cruziana Ichnofacies is recognized, characterized by assemblages dominated by Thalassinoides isp. and Gyrochorte comosa in the offshore transition, and by Gyrochorte comosa within the lower shoreface. Storm-influenced conditions yield wider ichnologic variability, showing elements of both ichnofacies. Storm influence on sedimentation is affected by both allogenic (e.g. tectonic subsidence, sea-level, and sediment influx) and autogenic (e.g. hydrodynamic) controls at both parasequence and intra-parasequence scales. Four distinct types of parasequences were recognized, strongly storm-dominated, moderately storm-affected, moderately storm-affected - strongly fair-weather reworked, and weakly storm-affected, categorized based on parasequence architectural variability derived from varying degrees of storm and fair-weather wave influence. The new type of shoreface described here, the moderately storm-affected - strongly fair-weather reworked shoreface, features storm deposits reworked thoroughly by fair-weather waves. During fair-weather wave reworking, elements of the Cruziana Ichnofacies are overprinted upon relict elements of the Skolithos Ichnofacies from previous storm induced deposition. This type of shoreface, commonly overlooked in past literature, expands our understanding of the sedimentary dynamics and stratigraphic architecture in a shoreface susceptible to various parasequence and intra-parasequence scale degrees of storm and fair-weather wave influence.
Recent Responses of Western North American Forests and Hydroclimate to Pacific Storm Track Position and Intensity

NASA Astrophysics Data System (ADS)

Dannenberg, M. P.; Wise, E.

2017-12-01

Much of the precipitation delivered to western North America arrives during the October to March cool season via midlatitude Pacific storm tracks, which may shift in the future due to climate change. Using historical climate, tree-ring, and remote sensing data, we assessed the sensitivity of western North American hydroclimate and ecosystems to the position and intensity of cool-season Pacific storm tracks. From 1980-2014, mean annual cool-season storm tracks entered western North America between approximately 41°N to 53°N, with substantial interannual variability in both the position and intensity of the storm tracks. We examined relationships between storm tracks and two hydroclimatic variables: the cool-season standardized precipitation-evapotranspiration index and April snow water equivalent. We also assessed how historical storm track variability affected ecosystems using forest growth estimates from a large tree-ring network as well as land surface phenology and wildfire estimates from AVHRR and Landsat, respectively. Cool-season moisture supply and snowpack responded strongly to storm track position, with positive correlations to storm track latitude in eastern Alaska and northwestern Canada but negative correlations in the northwestern U.S. These hydroclimatic impacts were largely driven by the latitudinal position of storm tracks during the "shoulder" seasons (i.e., autumn and early spring). Ecosystems of the western U.S. tended to be greener and more productive following winters with south-shifted storm tracks, while Canadian ecosystems were greener in years when the cool-season storm track was shifted to the north. On average, larger areas of the northwestern U.S. were burned by moderate to high severity wildfires when storm tracks were displaced north, and the average burn area per fire also tended to be higher in years with north-shifted storm tracks. Assuming that these historical relationships continue to hold under future climate scenarios, our results suggest that projected long-term shifts of Pacific storm tracks over the 21st century would likely alter hydroclimatic and ecological regimes in western North America, particularly in the northwestern U.S., where moisture supply and ecosystem processes are highly sensitive to the position of cool-season storm tracks.
The 1973 dust storm on Mars: Maps from hourly photographs

NASA Technical Reports Server (NTRS)

Martin, L. J.

1975-01-01

The hourly progress of the 1973 major Martian storm was mapped using photographic images from the International Planetary Patrol. Two series of 20 daily maps show the semi-hourly positions of the storm brightenings in red light and blue light. The maps indicate that the 1973 storm had many similarities to the 1971 storm.
In the Eye of the Storm: A Participatory Course on Coastal Storms

ERIC Educational Resources Information Center

Curtis, Scott

2013-01-01

Storm disasters are amplified in the coastal environment due to population pressures and the power of the sea. The upper-division/graduate university course "Coastal Storms" was designed to equip future practitioners with the skills necessary to understand, respond to, and mitigate for these natural disasters. To accomplish this, "Coastal Storms"…
Observed and Simulated Radiative and Microphysical Properties of Tropical Convective Storms

NASA Technical Reports Server (NTRS)

DelGenio, Anthony D.; Hansen, James E. (Technical Monitor)

2001-01-01

Increases in the ice content, albedo and cloud cover of tropical convective storms in a warmer climate produce a large negative contribution to cloud feedback in the GISS GCM. Unfortunately, the physics of convective upward water transport, detrainment, and ice sedimentation, and the relationship of microphysical to radiative properties, are all quite uncertain. We apply a clustering algorithm to TRMM satellite microwave rainfall retrievals to identify contiguous deep precipitating storms throughout the tropics. Each storm is characterized according to its size, albedo, OLR, rain rate, microphysical structure, and presence/absence of lightning. A similar analysis is applied to ISCCP data during the TOGA/COARE experiment to identify optically thick deep cloud systems and relate them to large-scale environmental conditions just before storm onset. We examine the statistics of these storms to understand the relative climatic roles of small and large storms and the factors that regulate convective storm size and albedo. The results are compared to GISS GCM simulated statistics of tropical convective storms to identify areas of agreement and disagreement.
Mathematical modeling of the moderate storm on 28 February 2008

NASA Astrophysics Data System (ADS)

Eroglu, Emre

2018-04-01

The sun is an active star with plasma-filled prominences. The sudden ejection of the solar plasma creates storms in the form of bursting or spraying. A magnetospheric storm is a typical phenomenon that lasts 1-3 days and involves all magnetosphere from the earth's ionosphere to the magnetotail. The storms are known by different categorical names such as weak, moderate, strong, intense. One of these is the moderate geomagnetic storm on February 28, 2008, which occurred in the 24th solar cycle. The reason for discussing this storm is that it is the first moderate storm in the 24th solar cycle. In this study, we investigate the storm and entered the 24th solar cycle. The correlation among the parametres has been investigated via statistics. The solar wind parameters and the zonal geomagnetic indices have been analyzed separately and then the interaction with each other has been exhibited. The author has concluded the work with two new nonlinear mathematical models. These explain the storm with 79.1% and 87.5% accuracy.
Interplanetary radio storms. II - Emission levels and solar wind speed in the range 0.05-0.8 AU

NASA Technical Reports Server (NTRS)

Bougeret, J.-L.; Fainberg, J.; Stone, R. G.

1984-01-01

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetary medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the sun. Using a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the III storm burst radio emission at the harmonic of the local plasma frequency.
Geomagnetic storm forecasting service StormFocus: 5 years online

NASA Astrophysics Data System (ADS)

Podladchikova, Tatiana; Petrukovich, Anatoly; Yermolaev, Yuri

2018-04-01

Forecasting geomagnetic storms is highly important for many space weather applications. In this study, we review performance of the geomagnetic storm forecasting service StormFocus during 2011-2016. The service was implemented in 2011 at SpaceWeather.Ru and predicts the expected strength of geomagnetic storms as measured by Dst index several hours ahead. The forecast is based on L1 solar wind and IMF measurements and is updated every hour. The solar maximum of cycle 24 is weak, so most of the statistics are on rather moderate storms. We verify quality of selection criteria, as well as reliability of real-time input data in comparison with the final values, available in archives. In real-time operation 87% of storms were correctly predicted while the reanalysis running on final OMNI data predicts successfully 97% of storms. Thus the main reasons for prediction errors are discrepancies between real-time and final data (Dst, solar wind and IMF) due to processing errors, specifics of datasets.

First principles investigation of structural, vibrational and thermal properties of black and blue phosphorene

NASA Astrophysics Data System (ADS)

Arif Khalil, R. M.; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, Syed Hamad; Tufiq Jamil, M.; Tehreem, Tuba; Nissar, Umair

2018-05-01

In this investigation, structural, dynamical and thermal properties of black and blue phosphorene (P) are presented through the first principles calculations based on the density functional theory (DFT). These DFT calculations depict that due to the approximately same values of ground state energy at zero Kelvin and Helmholtz free energy at room-temperature, it is expected that both structures can coexist at transition temperature. Lattice dynamics of both phases were investigated by using the finite displacement supercell approach. It is noticed on the basis of harmonic approximation thermodynamic calculations that the blue phase is thermodynamically more stable than the black phase above 155 K.
Comment on "Eliminating the major tornado threat in Tornado Alley"

NASA Astrophysics Data System (ADS)

Dahl, Johannes M. L.; Markowski, Paul M.

2014-11-01

The authors draw from half a century of meteorological research to expose flaws in a recent proposal to build 300-m-tall tornado-prevention walls across the U.S. Great Plains. The idea behind the walls is that they would prevent cold and warm air masses from clashing and would therefore suppress tornadoes. The problem with this proposal, however, is that atmospheric fronts ("airmass clashes") are neither a necessary nor a sufficient condition for tornadoes and that the proposed walls would not prevent the formation of fronts in the first place. Additional misconceptions about supercells thunderstorms and tornado formation also are identified.
Experimental study on slow flexural waves around the defect modes in a phononic crystal beam using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Chuang, Kuo-Chih; Zhang, Zhi-Qiang; Wang, Hua-Xin

2016-12-01

This work experimentally studies influences of the point defect modes on the group velocity of flexural waves in a phononic crystal Timoshenko beam. Using the transfer matrix method with a supercell technique, the band structures and the group velocities around the defect modes are theoretically obtained. Particularly, to demonstrate the existence of the localized defect modes inside the band gaps, a high-sensitivity fiber Bragg grating sensing system is set up and the displacement transmittance is measured. Slow propagation of flexural waves via defect coupling in the phononic crystal beam is then experimentally demonstrated with Hanning windowed tone burst excitations.
Theory of spin-conserving excitation of the N-V(-) center in diamond.

PubMed

Gali, Adam; Janzén, Erik; Deák, Péter; Kresse, Georg; Kaxiras, Efthimios

2009-10-30

The negatively charged nitrogen-vacancy defect in diamond is an important atomic-scale structure that can be used as a qubit in quantum computing and as a marker in biomedical applications. Its usefulness relies on the ability to optically excite electrons between well-defined gap states, which requires a clear and detailed understanding of the relevant states and excitation processes. Here we show that by using hybrid density-functional-theory calculations in a large supercell we can reproduce the zero-phonon line and the Stokes and anti-Stokes shifts, yielding a complete picture of the spin-conserving excitation of this defect.
The narrow pass band filter of tunable 1D phononic crystals with a dielectric elastomer layer

NASA Astrophysics Data System (ADS)

Wu, Liang-Yu; Wu, Mei-Ling; Chen, Lien-Wen

2009-01-01

In this paper, we study the defect bands of a 1D phononic crystal consisting of aluminum (Al) and polymethyl methacrylate (PMMA) layers with a dielectric elastomer (DE) defect layer. The plane wave expansion (PWE) method and supercell calculation are used to calculate the band structure and the defect bands. The transmission spectra are obtained using the finite element method (FEM). Since the thickness of the dielectric elastomer defect layer is controlled by applying an electric voltage, the frequencies of the defect bands can be tuned. A narrow pass band filter can be developed and designed by using the dielectric elastomer.
Dynamic interactions between coastal storms and salt marshes: A review

NASA Astrophysics Data System (ADS)

Leonardi, Nicoletta; Carnacina, Iacopo; Donatelli, Carmine; Ganju, Neil Kamal; Plater, Andrew James; Schuerch, Mark; Temmerman, Stijn

2018-01-01

This manuscript reviews the progresses made in the understanding of the dynamic interactions between coastal storms and salt marshes, including the dissipation of extreme water levels and wind waves across marsh surfaces, the geomorphic impact of storms on salt marshes, the preservation of hurricanes signals and deposits into the sedimentary records, and the importance of storms for the long term survival of salt marshes to sea level rise. A review of weaknesses, and strengths of coastal defences incorporating the use of salt marshes including natural, and hybrid infrastructures in comparison to standard built solutions is then presented. Salt marshes are effective in dissipating wave energy, and storm surges, especially when the marsh is highly elevated, and continuous. This buffering action reduces for storms lasting more than one day. Storm surge attenuation rates range from 1.7 to 25 cm/km depending on marsh and storms characteristics. In terms of vegetation properties, the more flexible stems tend to flatten during powerful storms, and to dissipate less energy but they are also more resilient to structural damage, and their flattening helps to protect the marsh surface from erosion, while stiff plants tend to break, and could increase the turbulence level and the scour. From a morphological point of view, salt marshes are generally able to withstand violent storms without collapsing, and violent storms are responsible for only a small portion of the long term marsh erosion. Our considerations highlight the necessity to focus on the indirect long term impact that large storms exerts on the whole marsh complex rather than on sole after-storm periods. The morphological consequences of storms, even if not dramatic, might in fact influence the response of the system to normal weather conditions during following inter-storm periods. For instance, storms can cause tidal flats deepening which in turn promotes wave energy propagation, and exerts a long term detrimental effect for marsh boundaries even during calm weather. On the other hand, when a violent storm causes substantial erosion but sediments are redistributed across nearby areas, the long term impact might not be as severe as if sediments were permanently lost from the system, and the salt marsh could easily recover to the initial state.
Ionospheric storms—A challenge for empirical forecast of the total electron content

NASA Astrophysics Data System (ADS)

Borries, C.; Berdermann, J.; Jakowski, N.; Wilken, V.

2015-04-01

Since the last decades, the functioning of society depends more and more on well-functioning communication and navigation systems. As the availability and reliability of most of these satellite-based systems can be severely impacted by ionospheric storms, the accurate forecast of these events becomes a required task for mitigating social and economic risks. Here we aim to make initial steps toward an empirical model for ionospheric perturbations related to space weather events that are observable in the total electron content (TEC). The perturbation TEC forecast model will be a fast and robust approach, improving TEC forecasts based on climatological models during storm conditions. The derivation of such a model is a challenging task, because although a general dependence of the storm features (enhancement or depletion of electron density) on the storm onset time, local time, season and geomagnetic latitude is well known, there is a large deviation from the mean behavior. For a better understanding of storm conditions, this paper presents analyses of ionospheric storms observed in the TEC, broken down into diverse classes of storms. It provides a detailed characterization of the typical ionospheric storm behavior over Europe from high to midlatitudes, beyond case studies. Generally, the typical clear strong TEC enhancement starting in high latitudes and propagating equatorward is found to be strongest for storms starting in the morning hours independent of the season. In midlatitudes, it is strongest during noon. In addition, a clear difference between summer and winter storms is reported. While only winter storms develop high-latitude TEC enhancements, only summer storms typically exhibit TEC depletions during the storm recovery phase. During winter storms TEC enhancements can also occur the day following the storm onset, in contrast to summer storms. Strong correlation of TEC perturbation amplitudes to the Bz component of the interplanetary magnetic field and to a proxy of the polar cap potential are shown especially for summer midlatitude TEC enhancements during storms with and onset in the morning hours (6 to 12 UT over Europe) and for winter high-latitude TEC enhancements (around 60∘N). The results indicate the potential to derive improved predictions of maximum TEC deviations during space weather events, based on solar wind measurements.
Dynamic interactions between coastal storms and salt marshes: A review

USGS Publications Warehouse

Leonardi, Nicoletta; Carnacina, Iacopo; Donatelli, Carmine; Ganju, Neil K.; Plater, Andrew James; Schuerch, Mark; Temmerman, Stijn

2018-01-01

This manuscript reviews the progresses made in the understanding of the dynamic interactions between coastal storms and salt marshes, including the dissipation of extreme water levels and wind waves across marsh surfaces, the geomorphic impact of storms on salt marshes, the preservation of hurricanes signals and deposits into the sedimentary records, and the importance of storms for the long term survival of salt marshes to sea level rise. A review of weaknesses, and strengths of coastal defences incorporating the use of salt marshes including natural, and hybrid infrastructures in comparison to standard built solutions is then presented.Salt marshes are effective in dissipating wave energy, and storm surges, especially when the marsh is highly elevated, and continuous. This buffering action reduces for storms lasting more than one day. Storm surge attenuation rates range from 1.7 to 25 cm/km depending on marsh and storms characteristics. In terms of vegetation properties, the more flexible stems tend to flatten during powerful storms, and to dissipate less energy but they are also more resilient to structural damage, and their flattening helps to protect the marsh surface from erosion, while stiff plants tend to break, and could increase the turbulence level and the scour. From a morphological point of view, salt marshes are generally able to withstand violent storms without collapsing, and violent storms are responsible for only a small portion of the long term marsh erosion.Our considerations highlight the necessity to focus on the indirect long term impact that large storms exerts on the whole marsh complex rather than on sole after-storm periods. The morphological consequences of storms, even if not dramatic, might in fact influence the response of the system to normal weather conditions during following inter-storm periods. For instance, storms can cause tidal flats deepening which in turn promotes wave energy propagation, and exerts a long term detrimental effect for marsh boundaries even during calm weather. On the other hand, when a violent storm causes substantial erosion but sediments are redistributed across nearby areas, the long term impact might not be as severe as if sediments were permanently lost from the system, and the salt marsh could easily recover to the initial state.
Storm-centric view of Tropical Cyclone oceanic wakes

NASA Astrophysics Data System (ADS)

Gentemann, C. L.; Scott, J. P.; Smith, D.

2012-12-01

Tropical cyclones (TCs) have a dramatic impact on the upper ocean. Storm-generated oceanic mixing, high amplitude near-inertial currents, upwelling, and heat fluxes often warm or cool the surface ocean temperatures over large regions near tropical cyclones. These SST anomalies occur to the right (Northern Hemisphere) or left (Southern Hemisphere) of the storm track, varying along and across the storm track. These wide swaths of temperature change have been previously documented by in situ field programs as well as IR and visible satellite data. The amplitude, temporal and spatial variability of these surface temperature anomalies depend primarily upon the storm size, storm intensity, translational velocity, and the underlying ocean conditions. Tropical cyclone 'cold wakes' are usually 2 - 5 °C cooler than pre-storm SSTs, and persist for days to weeks. Since storms that occur in rapid succession typically follow similar paths, the cold wake from one storm can affect development of subsequent storms. Recent studies, on both warm and cold wakes, have mostly focused on small subsets of global storms because of the amount of work it takes to co-locate different data sources to a storm's location. While a number of hurricane/typhoon websites exist that co-locate various datasets to TC locations, none provide 3-dimensional temporal and spatial structure of the ocean-atmosphere necessary to study cold/warm wake development and impact. We are developing a global 3-dimensional storm centric database for TC research. The database we propose will include in situ data, satellite data, and model analyses. Remote Sensing Systems (RSS) has a widely-used storm watch archive which provides the user an interface for visually analyzing collocated NASA Quick Scatterometer (QuikSCAT) winds with GHRSST microwave SSTs and SSM/I, TMI or AMSR-E rain rates for all global tropical cyclones 1999-2009. We will build on this concept of bringing together different data near storm locations when developing the storm-centric database. This database will be made available to researchers via the web display tools previously developed for RSS web pages. The database will provide scientists with a single data format collection of various atmospheric and oceanographic data, and will include all tropical storms since 1998, when the passive MW SSTs from the TMI instrument first became available. Initial results showing an analysis of Typhoon Man-Yi will be presented.
Thyroid storm precipitated by duodenal ulcer perforation.

PubMed

Natsuda, Shoko; Nakashima, Yomi; Horie, Ichiro; Ando, Takao; Kawakami, Atsushi

2015-01-01

Thyroid storm is a rare and life-threatening complication of thyrotoxicosis that requires prompt treatment. Thyroid storm is also known to be associated with precipitating events. The simultaneous treatment of thyroid storm and its precipitant, when they are recognized, in a patient is recommended; otherwise such disorders, including thyroid storm, can exacerbate each other. Here we report the case of a thyroid storm patient (a 55-year-old Japanese male) complicated with a perforated duodenal ulcer. The patient was successfully treated with intensive treatment for thyroid storm and a prompt operation. Although it is believed that peptic ulcer rarely coexists with hyperthyroidism, among patients with thyroid storm, perforation of a peptic ulcer has been reported as one of the causes of fatal outcome. We determined that surgical intervention was required in this patient, reported despite ongoing severe thyrotoxicosis, and reported herein a successful outcome.
Aircraft measurements and analysis of severe storms: 1976 field experiment

NASA Technical Reports Server (NTRS)

Sinclair, P. C.

1982-01-01

Severe storm aircraft measurements are documented, as well as the instrumentation and operational features of aircraft mobility capabilities. The measurements and data analyses indicate that the concept of a highly mobile research aircraft capability for obtaining detailed measurements of wind, temperature, moisture, spherics, etc., near and within severe storm systems, forecast 48 hours in advance in a 1000 nm operating radius, is feasible, and was successfully demonstrated. The measurements and analyses reveal several severe storm features and insights with respect to storm air flow circulations and inflow-outflow orientation. Precipitation downdraft air is recirculated back into the updraft core below the scud cloud in both back and front feeder type storms. In a back feeder type storm, the downdraft outflow air ahead of the storm is also recirculated back into the updraft region near cloud base.
Mapping and Visualization of Storm-Surge Dynamics for Hurricane Katrina and Hurricane Rita

USGS Publications Warehouse

Gesch, Dean B.

2009-01-01

The damages caused by the storm surges from Hurricane Katrina and Hurricane Rita were significant and occurred over broad areas. Storm-surge maps are among the most useful geospatial datasets for hurricane recovery, impact assessments, and mitigation planning for future storms. Surveyed high-water marks were used to generate a maximum storm-surge surface for Hurricane Katrina extending from eastern Louisiana to Mobile Bay, Alabama. The interpolated surface was intersected with high-resolution lidar elevation data covering the study area to produce a highly detailed digital storm-surge inundation map. The storm-surge dataset and related data are available for display and query in a Web-based viewer application. A unique water-level dataset from a network of portable pressure sensors deployed in the days just prior to Hurricane Rita's landfall captured the hurricane's storm surge. The recorded sensor data provided water-level measurements with a very high temporal resolution at surveyed point locations. The resulting dataset was used to generate a time series of storm-surge surfaces that documents the surge dynamics in a new, spatially explicit way. The temporal information contained in the multiple storm-surge surfaces can be visualized in a number of ways to portray how the surge interacted with and was affected by land surface features. Spatially explicit storm-surge products can be useful for a variety of hurricane impact assessments, especially studies of wetland and land changes where knowledge of the extent and magnitude of storm-surge flooding is critical.
Phosphorus loss from an agricultural watershed as a function of storm size.

PubMed

Sharpley, Andrew N; Kleinman, Peter J A; Heathwaite, A Louise; Gburek, William J; Folmar, Gordon J; Schmidt, John P

2008-01-01

Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1-3, 3-5, 5-10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha(-1) yr(-1)) and 80% of total P (TP) exported (515 g ha(-1) yr(-1)). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m(3) ha(-1); 63%) and export of DP (574 g ha(-1); 54%) and TP (2423 g ha(-1); 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09-0.16 mg L(-1)) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.
Automatic Detection of Storm Damages Using High-Altitude Photogrammetric Imaging

NASA Astrophysics Data System (ADS)

Litkey, P.; Nurminen, K.; Honkavaara, E.

2013-05-01

The risks of storms that cause damage in forests are increasing due to climate change. Quickly detecting fallen trees, assessing the amount of fallen trees and efficiently collecting them are of great importance for economic and environmental reasons. Visually detecting and delineating storm damage is a laborious and error-prone process; thus, it is important to develop cost-efficient and highly automated methods. Objective of our research project is to investigate and develop a reliable and efficient method for automatic storm damage detection, which is based on airborne imagery that is collected after a storm. The requirements for the method are the before-storm and after-storm surface models. A difference surface is calculated using two DSMs and the locations where significant changes have appeared are automatically detected. In our previous research we used four-year old airborne laser scanning surface model as the before-storm surface. The after-storm DSM was provided from the photogrammetric images using the Next Generation Automatic Terrain Extraction (NGATE) algorithm of Socet Set software. We obtained 100% accuracy in detection of major storm damages. In this investigation we will further evaluate the sensitivity of the storm-damage detection process. We will investigate the potential of national airborne photography, that is collected at no-leaf season, to automatically produce a before-storm DSM using image matching. We will also compare impact of the terrain extraction algorithm to the results. Our results will also promote the potential of national open source data sets in the management of natural disasters.
Contrasting patterns of nutrient dynamics during different storm events in a semi-arid catchment of northern China.

PubMed

Du, Xinzhong; Li, Xuyong; Hao, Shaonan; Wang, Huiliang; Shen, Xiao

2014-01-01

Nutrient discharge during storm events is a critical pathway for nutrient export in semi-arid catchments. We investigated nutrient dynamics during three summer storms characterized by different rainfall magnitude in 2012 in a semi-arid catchment of northern China. The results showed that, in response to storm events, nutrient dynamics displayed big variation in temporal trends of nutrient concentration and in nutrient concentration-flow discharge relationships. Nutrient concentrations had broader fluctuations during an extreme storm than during lesser storms, whereas the concentration ranges of the a moderate storm were no broader than those of a smaller one. The different concentration fluctuations were caused by storm magnitude and intensity coupled with the antecedent rainfall amount and cumulative nutrients. Correlation coefficients between nutrient concentrations and flow discharge varied from positive to negative for the three different events. There were no consistent hysteresis effects for the three different events, and no hysteresis effects were observed for any of the variables during the moderate storm (E2). Our findings provide useful information for better understanding nutrient loss mechanisms during storm events in semi-arid areas of a monsoon climate region.
Synthetic calibration of a Rainfall-Runoff Model

USGS Publications Warehouse

Thompson, David B.; Westphal, Jerome A.; ,

1990-01-01

A method for synthetically calibrating storm-mode parameters for the U.S. Geological Survey's Precipitation-Runoff Modeling System is described. Synthetic calibration is accomplished by adjusting storm-mode parameters to minimize deviations between the pseudo-probability disributions represented by regional regression equations and actual frequency distributions fitted to model-generated peak discharge and runoff volume. Results of modeling storm hydrographs using synthetic and analytic storm-mode parameters are presented. Comparisons are made between model results from both parameter sets and between model results and observed hydrographs. Although mean storm runoff is reproducible to within about 26 percent of the observed mean storm runoff for five or six parameter sets, runoff from individual storms is subject to large disparities. Predicted storm runoff volume ranged from 2 percent to 217 percent of commensurate observed values. Furthermore, simulation of peak discharges was poor. Predicted peak discharges from individual storm events ranged from 2 percent to 229 percent of commensurate observed values. The model was incapable of satisfactorily executing storm-mode simulations for the study watersheds. This result is not considered a particular fault of the model, but instead is indicative of deficiencies in similar conceptual models.
Tropical Storm Sam, Eastern Indian Ocean

NASA Image and Video Library

1990-01-20

STS032-80-036 (9-20 Jan. 1990) --- This oblique view of Tropical Storm Sam in the eastern Indian Ocean off the western coast of Australia was photographed with a 70mm camera by the astronauts. Tropical Storm Sam (known as Willy-Willy in Australia) was born in the eastern Indian Ocean near the islands of Timor and Sumba in Indonesia. The storm tracked southwestward attaining sustained winds in excess of 60 knots (70 miles per hour). Other than on Christmas Island and the Cocos (Keeling) Islands south of Java, and for strong swells along the western Australia coast, the storm had little impact on land areas. At the time this photograph was taken, the storm was beginning to dissipate in the south Indian Ocean. The eye of the storm is still visible near center, with the swirling bands of the storm propagating in a clockwise direction toward the center. Winds aloft have begun to shear the tops of thunderstorms associated with the storm, forming a high cirrus cloud cover over the center portions of the storm. This picture was used by the crew at their January 30, 1990 Post-Flight Press Conference (PFPC).
Quantification of non-stormwater flow entries into storm drains using a water balance approach.

PubMed

Xu, Zuxin; Yin, Hailong; Li, Huaizheng

2014-07-15

To make decisions about correcting illicit or inappropriate connections to storm drains, quantification of non-stormwater entries into storm drains was performed using a water flow balance approach, based on data analysis from 2008 to 2011 in a separate storm drainage system in a Shanghai downtown area of 374 ha. The study revealed severe sewage connections to storm drains; meanwhile, misconnections between surface water and storm drains were found to drive frequent non-stormwater pumping discharges at the outfall, producing a much larger volume of outfall flows in a short period. This paper presented a methodology to estimate quantities of inappropriate sewage flow, groundwater infiltration and river water backflow into the storm drains. It was concluded that inappropriate sewage discharge and groundwater seepage into storm drains were approximately 17,860 m(3)/d (i.e., up to 51% of the total sewage flow in the catchment) and 3,624 m(3)/d, respectively, and surface water backflow was up to an average 28,593 m(3)/d. On the basis of this work, end-of-storm pipe interceptor sewers of 0.25 m(3)/s (i.e., 21,600 m(3)/d) would be effective to tackle the problem of sewage connections and groundwater seepage to storm drains. Under this circumstance, the follow-up non-stormwater outfall pumping events indicate misconnections between surface water and storm drains, featuring pumping discharge equivalent to surface water backflow; hence the misconnections should be repaired. The information provided here is helpful in estimating the magnitude of non-stormwater flow entries into storm drains and designing the necessary pollution control activities, as well as combating city floods in storm events. Copyright © 2014. Published by Elsevier B.V.
Arctic storms simulated in atmospheric general circulation models under uniform high, uniform low, and variable resolutions

NASA Astrophysics Data System (ADS)

Roesler, E. L.; Bosler, P. A.; Taylor, M.

2016-12-01

The impact of strong extratropical storms on coastal communities is large, and the extent to which storms will change with a warming Arctic is unknown. Understanding storms in reanalysis and in climate models is important for future predictions. We know that the number of detected Arctic storms in reanalysis is sensitive to grid resolution. To understand Arctic storm sensitivity to resolution in climate models, we describe simulations designed to identify and compare Arctic storms at uniform low resolution (1 degree), at uniform high resolution (1/8 degree), and at variable resolution (1 degree to 1/8 degree). High-resolution simulations resolve more fine-scale structure and extremes, such as storms, in the atmosphere than a uniform low-resolution simulation. However, the computational cost of running a globally uniform high-resolution simulation is often prohibitive. The variable resolution tool in atmospheric general circulation models permits regional high-resolution solutions at a fraction of the computational cost. The storms are identified using the open-source search algorithm, Stride Search. The uniform high-resolution simulation has over 50% more storms than the uniform low-resolution and over 25% more storms than the variable resolution simulations. Storm statistics from each of the simulations is presented and compared with reanalysis. We propose variable resolution as a cost-effective means of investigating physics/dynamics coupling in the Arctic environment. Future work will include comparisons with observed storms to investigate tuning parameters for high resolution models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2016-7402 A
Empirical STORM-E Model. [I. Theoretical and Observational Basis

NASA Technical Reports Server (NTRS)

Mertens, Christopher J.; Xu, Xiaojing; Bilitza, Dieter; Mlynczak, Martin G.; Russell, James M., III

2013-01-01

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region peak electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) volume emission rates (VER) derived from the TIMED/SABER 4.3 lm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3 lm VER is sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3 lm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part II of this series describes the explicit development of the empirical storm-time correction factor for E-region peak electron densities, and shows comparisons of E-region electron densities between STORM-E predictions and incoherent scatter radar measurements. In this paper, Part I of the series, the efficacy of using SABER-derived NO+(v) VER as a proxy for the E-region response to solar-geomagnetic disturbances is presented. Furthermore, a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3 lm limb emission measurements is given. Finally, an assessment of key uncertainties in retrieving NO+(v) VER is presented

Phosphorus export during storm events from a human perturbed watershed, southeast China: Implications for coastal ecology

NASA Astrophysics Data System (ADS)

Chen, Nengwang; Wu, Yinqi; Chen, Zhuhong; Hong, Huasheng

2015-12-01

Understanding how major storms impact riverine nutrient export to estuaries and the coastal region is crucial in the context of increasing anthropogenic climate and environmental perturbation. In this study, the effects of major storms on river phosphorus (P) were investigated in an agricultural river (SE China), through continuous sampling of dissolved and particulate P during the three largest storm events (A-C) in 2013. There was a major increase in the total P load (3.4-16 fold compared with baseflow). The event mean concentration of storm A was the highest likely due to the first flush effect mobilizing accumulated waste. The flux of DOP and DRP was controlled by discharge as DOP in storm B and DRP in storm C with a relatively simple hysteresis effect with higher fluxes on the rising limb being diluted by rainfall on the falling limb. DOP in storm B remained relatively constant due to delay in DOP flushed from upstream areas balancing dilution by rainfall down stream. DRP in storm C also remained relatively constant caused by successive release of soil DRP to the river from previous unsaturated surface layers. TPP export was greatest towards the early to high stages of the storm events suggesting that most of the eroded sediment and resuspended sediment-bound P are exported during the early stages of the storm. The total flux of P is elevated in watersheds with high levels of human perturbation while climate change is predicted to increase the frequency of major storms. The results of this study are important in predicting the ecosystem response of estuarine and coastal regions to major storms in the riverine catchment area.
Comparison of estimated and observed stormwater runoff for fifteen watersheds in west-central Florida, using five common design techniques

USGS Publications Warehouse

Trommer, J.T.; Loper, J.E.; Hammett, K.M.; Bowman, Georgia

1996-01-01

Hydrologists use several traditional techniques for estimating peak discharges and runoff volumes from ungaged watersheds. However, applying these techniques to watersheds in west-central Florida requires that empirical relationships be extrapolated beyond tested ranges. As a result there is some uncertainty as to their accuracy. Sixty-six storms in 15 west-central Florida watersheds were modeled using (1) the rational method, (2) the U.S. Geological Survey regional regression equations, (3) the Natural Resources Conservation Service (formerly the Soil Conservation Service) TR-20 model, (4) the Army Corps of Engineers HEC-1 model, and (5) the Environmental Protection Agency SWMM model. The watersheds ranged between fully developed urban and undeveloped natural watersheds. Peak discharges and runoff volumes were estimated using standard or recommended methods for determining input parameters. All model runs were uncalibrated and the selection of input parameters was not influenced by observed data. The rational method, only used to calculate peak discharges, overestimated 45 storms, underestimated 20 storms and estimated the same discharge for 1 storm. The mean estimation error for all storms indicates the method overestimates the peak discharges. Estimation errors were generally smaller in the urban watersheds and larger in the natural watersheds. The U.S. Geological Survey regression equations provide peak discharges for storms of specific recurrence intervals. Therefore, direct comparison with observed data was limited to sixteen observed storms that had precipitation equivalent to specific recurrence intervals. The mean estimation error for all storms indicates the method overestimates both peak discharges and runoff volumes. Estimation errors were smallest for the larger natural watersheds in Sarasota County, and largest for the small watersheds located in the eastern part of the study area. The Natural Resources Conservation Service TR-20 model, overestimated peak discharges for 45 storms and underestimated 21 storms, and overestimated runoff volumes for 44 storms and underestimated 22 storms. The mean estimation error for all storms modeled indicates that the model overestimates peak discharges and runoff volumes. The smaller estimation errors in both peak discharges and runoff volumes were for storms occurring in the urban watersheds, and the larger errors were for storms occurring in the natural watersheds. The HEC-1 model overestimated peak discharge rates for 55 storms and underestimated 11 storms. Runoff volumes were overestimated for 44 storms and underestimated for 22 storms using the Army Corps of Engineers HEC-1 model. The mean estimation error for all the storms modeled indicates that the model overestimates peak discharge rates and runoff volumes. Generally, the smaller estimation errors in peak discharges were for storms occurring in the urban watersheds, and the larger errors were for storms occurring in the natural watersheds. Estimation errors in runoff volumes; however, were smallest for the 3 natural watersheds located in the southernmost part of Sarasota County. The Environmental Protection Agency Storm Water Management model produced similar peak discharges and runoff volumes when using both the Green-Ampt and Horton infiltration methods. Estimated peak discharge and runoff volume data calculated with the Horton method was only slightly higher than those calculated with the Green-Ampt method. The mean estimation error for all the storms modeled indicates the model using the Green-Ampt infiltration method overestimates peak discharges and slightly underestimates runoff volumes. Using the Horton infiltration method, the model overestimates both peak discharges and runoff volumes. The smaller estimation errors in both peak discharges and runoff volumes were for storms occurring in the five natural watersheds in Sarasota County with the least amount of impervious cover and the lowest slopes. The largest er
Storms in Space

NASA Astrophysics Data System (ADS)

Freeman, John W.

2012-11-01

Introduction; The cast of characters; Vignettes of the storm; 1. Two kinds of weather; 2. The saga of the storm; 3. Weather stations in space; 4. Lights in the night: the signature of the storm; 5. A walking tour of the magnetosphere; 6. The sun: where it all begins; 7. Nowcasting and forecasting storms in space; 8. Technology and the risks from storms in space; 9. A conversation with Joe Allen; 10. Manned exploration and space weather hazards; 11. The present and future of space weather forecasting; Mathematical appendix. A closer look; Glossary; Figure captions.
A storm-based CSLE incorporating the modified SCS-CN method for soil loss prediction on the Chinese Loess Plateau

NASA Astrophysics Data System (ADS)

Shi, Wenhai; Huang, Mingbin

2017-04-01

The Chinese Loess Plateau is one of the most erodible areas in the world. In order to reduce soil and water losses, suitable conservation practices need to be designed. For this purpose, there is an increasing demand for an appropriate model that can accurately predict storm-based surface runoff and soil losses on the Loess Plateau. The Chinese Soil Loss Equation (CSLE) has been widely used in this region to assess soil losses from different land use types. However, the CSLE was intended only to predict the mean annual gross soil loss. In this study, a CSLE was proposed that would be storm-based and that introduced a new rainfall-runoff erosivity factor. A dataset was compiled that comprised measurements of soil losses during individual storms from three runoff-erosion plots in each of three different watersheds in the gully region of the Plateau for 3-7 years in three different time periods (1956-1959; 1973-1980; 2010-13). The accuracy of the soil loss predictions made by the new storm-based CSLE was determined using the data for the six plots in two of the watersheds measured during 165 storm-runoff events. The performance of the storm-based CSLE was further compared with the performance of the storm-based Revised Universal Soil Loss Equation (RUSLE) for the same six plots. During the calibration (83 storms) and validation (82 storms) of the storm-based CSLE, the model efficiency, E, was 87.7% and 88.9%, respectively, while the root mean square error (RMSE) was 2.7 and 2.3 t ha-1 indicating a high degree of accuracy. Furthermore, the storm-based CSLE performed better than the storm-based RULSE (E: 75.8% and 70.3%; RMSE: 3.8 and 3.7 t ha-1, for the calibration and validation storms, respectively). The storm-based CSLE was then used to predict the soil losses from the three experimental plots in the third watershed. For these predictions, the model parameter values, previously determined by the calibration based on the data from the initial six plots, were used in the storm-based CSLE. In addition, the surface runoff used by the storm-based CSLE was either obtained from measurements or from the values predicted by the modified Soil Conservation Service Curve Number (SCS-CN) method. When using the measured runoff, the storm-based CSLE had an E of 76.6%, whereas the use of the predicted runoff gave an E of 76.4%. The high E values indicated that the storm-based CSLE incorporating the modified SCS-CN method could accurately predict storm-event-based soil losses resulting from both sheet and rill erosion at the field scale on the Chinese Loess Plateau. This approach could be applicable to other areas of the world once the model parameters have been suitably calibrated.
Developing an early warning system for storm surge inundation in the Philippines

NASA Astrophysics Data System (ADS)

Tablazon, Judd; Mahar Francisco Lagmay, Alfredo; Francia Mungcal, Ma. Theresa; Gonzalo, Lia Anne; Dasallas, Lea; Briones, Jo Brianne Louise; Santiago, Joy; Suarez, John Kenneth; Lapidez, John Phillip; Caro, Carl Vincent; Ladiero, Christine; Malano, Vicente

2014-05-01

A storm surge is the sudden rise of sea water generated by an approaching storm, over and above the astronomical tides. This event imposes a major threat in the Philippine coastal areas, as manifested by Typhoon Haiyan on 08 November 2013 where more than 6,000 people lost their lives. It has become evident that the need to develop an early warning system for storm surges is of utmost importance. To provide forecasts of the possible storm surge heights of an approaching typhoon, the Nationwide Operational Assessment of Hazards under the Department of Science and Technology (DOST-Project NOAH) simulated historical tropical cyclones that entered the Philippine Area of Responsibility. Bathymetric data, storm track, central atmospheric pressure, and maximum wind speed were used as parameters for the Japan Meteorological Agency (JMA) Storm Surge Model. The researchers calculated the frequency distribution of maximum storm surge heights of all typhoons under a specific Public Storm Warning Signal (PSWS) that passed through a particular coastal area. This determines the storm surge height corresponding to a given probability of occurrence. The storm surge heights from the model were added to the maximum astronomical tide data from WXTide software. The team then created maps of probable area inundation and flood levels of storm surges along coastal areas for a specific PSWS using the results of the frequency distribution. These maps were developed from the time series data of the storm tide at 10-minute intervals of all observation points in the Philippines. This information will be beneficial in developing early warnings systems, static maps, disaster mitigation and preparedness plans, vulnerability assessments, risk-sensitive land use plans, shoreline defense efforts, and coastal protection measures. Moreover, these will support the local government units' mandate to raise public awareness, disseminate information about storm surge hazards, and implement appropriate counter-measures for a given PSWS.
Developing an early warning system for storm surge inundation in the Philippines

NASA Astrophysics Data System (ADS)

Tablazon, J.; Caro, C. V.; Lagmay, A. M. F.; Briones, J. B. L.; Dasallas, L.; Lapidez, J. P.; Santiago, J.; Suarez, J. K.; Ladiero, C.; Gonzalo, L. A.; Mungcal, M. T. F.; Malano, V.

2014-10-01

A storm surge is the sudden rise of sea water generated by an approaching storm, over and above the astronomical tides. This event imposes a major threat in the Philippine coastal areas, as manifested by Typhoon Haiyan on 8 November 2013 where more than 6000 people lost their lives. It has become evident that the need to develop an early warning system for storm surges is of utmost importance. To provide forecasts of the possible storm surge heights of an approaching typhoon, the Nationwide Operational Assessment of Hazards under the Department of Science and Technology (DOST-Project NOAH) simulated historical tropical cyclones that entered the Philippine Area of Responsibility. Bathymetric data, storm track, central atmospheric pressure, and maximum wind speed were used as parameters for the Japan Meteorological Agency Storm Surge Model. The researchers calculated the frequency distribution of maximum storm surge heights of all typhoons under a specific Public Storm Warning Signal (PSWS) that passed through a particular coastal area. This determines the storm surge height corresponding to a given probability of occurrence. The storm surge heights from the model were added to the maximum astronomical tide data from WXTide software. The team then created maps of probable area inundation and flood levels of storm surges along coastal areas for a specific PSWS using the results of the frequency distribution. These maps were developed from the time series data of the storm tide at 10 min intervals of all observation points in the Philippines. This information will be beneficial in developing early warnings systems, static maps, disaster mitigation and preparedness plans, vulnerability assessments, risk-sensitive land use plans, shoreline defense efforts, and coastal protection measures. Moreover, these will support the local government units' mandate to raise public awareness, disseminate information about storm surge hazards, and implement appropriate counter-measures for a given PSWS.
Shifting Pacific storm tracks as stressors to ecosystems of western North America.

PubMed

Dannenberg, Matthew P; Wise, Erika K

2017-11-01

Much of the precipitation delivered to western North America arrives during the cool season via midlatitude Pacific storm tracks, which may experience future shifts in response to climate change. Here, we assess the sensitivity of the hydroclimate and ecosystems of western North America to the latitudinal position of cool-season Pacific storm tracks. We calculated correlations between storm track variability and three hydroclimatic variables: gridded cool-season standardized precipitation-evapotranspiration index, April snow water equivalent, and water year streamflow from a network of USGS stream gauges. To assess how historical storm track variability affected ecosystem processes, we derived forest growth estimates from a large network of tree-ring widths and land surface phenology and wildfire estimates from remote sensing. From 1980 to 2014, cool-season storm tracks entered western North America between approximately 41°N and 53°N. Cool-season moisture supply and snowpack responded strongly to storm track position, with positive correlations to storm track latitude in eastern Alaska and northwestern Canada but negative correlations in the northwestern U.S. Ecosystems of the western United States were greener and more productive following winters with south-shifted storm tracks, while Canadian ecosystems were greener in years when the cool-season storm track was shifted to the north. On average, larger areas of the northwestern United States were burned by moderate to high severity wildfires when storm tracks were displaced north, and the average burn area per fire also tended to be higher in years with north-shifted storm tracks. These results suggest that projected shifts of Pacific storm tracks over the 21st century would likely alter hydroclimatic and ecological regimes in western North America, particularly in the northwestern United States, where moisture supply and ecosystem processes are highly sensitive to the position of cool-season storm tracks. © 2017 John Wiley & Sons Ltd.
Ionospheric and Thermospheric Response to the 2015 St. Patrick's Day Storm: a Global Multi-Instrumental Overview

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Zakharenkova, I.; Foerster, M.; Doornbos, E.; Encarnacao, J.; Siemes, C.

2015-12-01

We study the ionospheric response to the geomagnetic storm of 17-18 March 2015 (the St. Patrick's Day 2015 storm) that was up to now the strongest in the 24th solar cycle (minimum SYM-H value of -233 nT). For this purpose, we use data of ground-based GPS-receivers and ionosondes, along space-borne instruments onboard the following satellites: Jason-2, GRACE, Terra-SAR-X, the three Swarm satellites (A, B, and C), and GUVI/TIMED. The storm consisted of two successive moderate storms. In the response to the first short storm, a short-term positive effect in the ionospheric vertical electron content (VTEC) occurred at low- and mid-latitudes on the dayside. The second event lasted longer and caused significant and complex storm-time changes around the globe. At high-latitudes, negative storm signatures were recorded in all longitudinal regions. The negative storm phase was found to be strongest in the Asian sector, in particular in the northern hemisphere (NH), but developed globally on March 18 at the beginning of the recovery phase. At mid-latitudes, inverse hemispheric asymmetries occurred in different longitudinal regions: in the European-African sector, positive storm signatures were observed in the NH, whereas in the American sector, a large positive storm occurred in the southern hemisphere (SH), and the NH experienced a negative storm. These observations performed around the spring equinox signify the existence of other impact factors than seasonal dependence for hemispheric asymmetries to occur. At low-latitudes, data from multiple satellites revealed the strongest storm-time effects in the morning (~100-150% enhancement) and post-sunset (~80-100% enhancement) sectors in the topside ionosphere. These dramatic VTEC enhancements were observed at different UT, but around the same area of Eastern Pacific region. To further understand the storm development, we are planning to use thermospheric data from Swarm-C satellite, as well as the data from the electric field instrument onboard the three Swarm satellites.
Pesticides in storm runoff from agricultural and urban areas in the Tuolumne River basin in the vicinity of Modesto, California

USGS Publications Warehouse

Kratzer, Charles R.

1998-01-01

The occurrence, concentrations, and loads of dissolved pesticides in storm runoff were compared for two contrasting land uses in the Tuolumne River Basin, California, during two different winter storms: agricultural areas (February 1994) and the Modesto urban area (February 1995). Both storms followed the main application period of pesticides on dormant almond orchards. Eight samples of runoff from agricultural areas were collected from a Tuolumne River site, and 10 samples of runoff from urban areas were collected from five storm drains. All samples were analyzed for 46 pesticides. Six pesticides were detected in runoff from agricultural areas, and 15 pesticides were detected in runoff from urban areas. Chlorpyrifos, diazinon, dacthal (DCPA), metolachlor, and simazine were detected in almost every sample. Median concentrations were higher in the runoff from urban areas for all pesticides except napropamide and simazine. The greater occurrence and concentrations in storm drains is partly attributed to dilution of agricultural runoff by nonstorm base-flow in the Tuolumne River and by storm runoff from nonagricultural and nonurban land. In most cases, the occurrence and relative concentrations of pesticides found in storm runoff from agricultural and urban areas were related to reported pesticide application. Pesticide concentrations in runoff from agricultural areas were more variable during the storm hydrograph than were concentrations in runoff from urban areas. All peak pesticide concentrations in runoff from agricultural areas occurred during the rising limb of the storm hydrograph, whereas peak concentrations in the storm drains occurred at varying times during the storm hydrograph. Transport of pesticides from agricultural areas during the February 1994 storm exceeded transport from urban areas during the February 1995 storm for chlorpyrifos, diazinon, metolachlor, napropamide, and simazine. Transport of DCPA was about the same from agricultural and urban sources, and the main source of transport for the other pesticides could not be determined because of concentrations less than the method detection limit.
Study of the mid-latitude ionospheric response to geomagnetic storms in the European region

NASA Astrophysics Data System (ADS)

Berényi, Kitti Alexandra; Barta, Veronika; Kis, Arpad

2016-07-01

Geomagnetic storms affect the ionospheric regions of the terrestrial upper atmosphere through different physical and atmospheric processes. The phenomena that can be regarded as a result of these processes, generally is named as "ionospheric storm". The processes depend on altitude, segment of the day, the geomagnetic latitude and longitude, strength of solar activity and the type of the geomagnetic storm. We examine the data of ground-based radio wave ionosphere sounding measurements of European ionospheric stations (mainly the data of Nagycenk Geophysical Observatory) in order to determine how and to what extent a geomagnetic disturbance of a certain strength affects the mid-latitude ionospheric regions in winter and in summer. For our analysis we used disturbed time periods between November 2012 and June 2015. Our results show significant changing of the ionospheric F2 layer parameters on strongly disturbed days compared to quiet ones. We show that the critical frequencies (foF2) increase compared to their quiet day value when the ionospheric storm was positive. On the other hand, the critical frequencies become lower, when the storm was negative. In our analysis we determined the magnitude of these changes on the chosen days. For a more complete analysis we compare also the evolution of the F2 layer parameters of the European ionosonde stations on a North-South geographic longitude during a full storm duration. The results present the evolution of an ionospheric storm over a geographic meridian. Furthermore, we compared the two type of geomagnetic storms, namely the CME caused geomagnetic storm - the so-called Sudden impulse (Si) storms- and the HSS (High Speed Solar Wind Streams) caused geomagnetic storms -the so-called Gradual storms (Gs)- impact on the ionospheric F2-layer (foF2 parameter). The results show a significant difference between the effect of Si and of the Gs storms on the ionospheric F2-layer.
The Identification of Hail Storms in the Early Stage Using Time Series Analysis

NASA Astrophysics Data System (ADS)

Wang, Ping; Shi, Jinyu; Hou, Jinyi; Hu, Yan

2018-01-01

This study investigates the characteristics of hail storms and cumulonimbus storms in China from 2005 to 2016. Ten features are proposed to identify storm cells that can produce hail, especially in the early stage of hail formation. These features describe hail storms based on three factors: the height and thickness of the cell core, the radar echo intensity, and the overhang structure and the horizontal reflectivity gradient. The 10 features are transformed into two-dimensional comprehensive features by principal component analysis (PCA). The two comprehensive features are named the volume measurement comprehensive feature (VMCF) and the height-gradient comprehensive feature (HGCF). Through an analysis of 49 hail cases and 35 heavy rainfall cases with S-band radar data, the time series exhibit a distinct increase in VMCF or HGCF values in the early stage of a hail storm. However, the VMCF and HGCF values of heavy rainfall events remain relatively stable throughout the storm life cycle. An experiment involving real-storm events, including 31 hail cases and 33 heavy rainfall cases, indicated that the probability of detection of hail storms was 93.33% and the false alarm ratio was 15.66%. In the cases that could be successfully identified as hail storms, 80.00% were detected within 18 min of reaching a hail storm reflectivity of 40 dBZ.
Evaluation of Loss Due to Storm Surge Disasters in China Based on Econometric Model Groups.

PubMed

Jin, Xue; Shi, Xiaoxia; Gao, Jintian; Xu, Tongbin; Yin, Kedong

2018-03-27

Storm surge has become an important factor restricting the economic and social development of China's coastal regions. In order to improve the scientific judgment of future storm surge damage, a method of model groups is proposed to refine the evaluation of the loss due to storm surges. Due to the relative dispersion and poor regularity of the natural property data (login center air pressure, maximum wind speed, maximum storm water, super warning water level, etc.), storm surge disaster is divided based on eight kinds of storm surge disaster grade division methods combined with storm surge water, hypervigilance tide level, and disaster loss. The storm surge disaster loss measurement model groups consist of eight equations, and six major modules are constructed: storm surge disaster in agricultural loss, fishery loss, human resource loss, engineering facility loss, living facility loss, and direct economic loss. Finally, the support vector machine (SVM) model is used to evaluate the loss and the intra-sample prediction. It is indicated that the equations of the model groups can reflect in detail the relationship between the damage of storm surges and other related variables. Based on a comparison of the original value and the predicted value error, the model groups pass the test, providing scientific support and a decision basis for the early layout of disaster prevention and mitigation.
Flow of Energy through the Inner Magnetosphere during the March 17, 2015 solar storm as observed by the Van Allen Probes Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE)

NASA Astrophysics Data System (ADS)

Manweiler, J. W.; Madanian, H.; Gerrard, A. J.; Patterson, J. D.; Mitchell, D. G.; Lanzerotti, L. J.

2017-12-01

On March 17, 2015, a large solar storm impacted the Earth's magnetosphere with a maximum negative Dst of -232 nT. We report on the temporal and spatial evolution of the proton energetic particle distributions in phase space during this storm, as measured by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on board each of the Van Allen Probes. We characterize the distribution prior to onset of the storm to provide a definition of quiet time conditions. We then show how the distribution evolves during the storm noting key changes of the distribution as a function of L and MLT and showing how the pitch angle distributions change throughout the storm. These observations displayed a number of interesting features of the storm including high beta plasma conditions and multiple injections of protons into the inner magnetosphere. We present the radial changes of the distribution at storm onset and following the evolution of the distribution during storm recovery. We compare observations of the East/West asymmetry in the proton distribution before versus after onset using both Van Allen Probes A and B spacecraft observations. Finally, we note interesting changes in the distribution showing an anomalous dropout in mid-energies of the distribution and observe an outward radial propagation of this dropout during recovery.
Arctic Storms and Their Influence on Surface Climate in the Chukchi-Beaufort Seas

NASA Astrophysics Data System (ADS)

Yang, Y.; Zhang, X.; Rinke, A.; Zhang, J.

2017-12-01

Increases in the frequency and intensity of Arctic storms and resulting weather hazards may endanger the offshore environment, coastal community, and energy infrastructure in the Arctic as sea ice retreats. Advancing ability to identify fine-scale variations in surface climate produced by progressively stronger storm would be extremely helpful to resources management and sustainable development for coastal community. In this study, we analyzed the storms and their impacts on surface climate over the Beaufort-Chukchi seas by employing the date sets from both the hindcast simulations of the coupled Arctic regional climate model HIRHAM-NAOSIM and the recently developed Chukchi-Beaufort High-resolution Atmospheric Reanalysis (CBHAR). Based on the characteristics of spatial pattern and temporal variability of the Arctic storm activity, we categorized storms to three groups with their different origins: the East Siberia Sea, Alaska and the central Arctic Ocean. The storms originating from the central Arctic Ocean have the strongest intensity in winter with relatively less storm number. Storms traveling from Alaska to the Beaufort Sea most frequently occurred in autumn with weaker intensity. A large portion of storms originated from the East Siberia Sea region in summer. Further statistical analysis suggests that increase in surface air temperature and wind speed could be attributed to the increased frequency of storm occurrence in autumn (September to November) along the continental shelf in the Beaufort Sea.
Evaluation of Loss Due to Storm Surge Disasters in China Based on Econometric Model Groups

PubMed Central

Shi, Xiaoxia; Xu, Tongbin; Yin, Kedong

2018-01-01

Storm surge has become an important factor restricting the economic and social development of China’s coastal regions. In order to improve the scientific judgment of future storm surge damage, a method of model groups is proposed to refine the evaluation of the loss due to storm surges. Due to the relative dispersion and poor regularity of the natural property data (login center air pressure, maximum wind speed, maximum storm water, super warning water level, etc.), storm surge disaster is divided based on eight kinds of storm surge disaster grade division methods combined with storm surge water, hypervigilance tide level, and disaster loss. The storm surge disaster loss measurement model groups consist of eight equations, and six major modules are constructed: storm surge disaster in agricultural loss, fishery loss, human resource loss, engineering facility loss, living facility loss, and direct economic loss. Finally, the support vector machine (SVM) model is used to evaluate the loss and the intra-sample prediction. It is indicated that the equations of the model groups can reflect in detail the relationship between the damage of storm surges and other related variables. Based on a comparison of the original value and the predicted value error, the model groups pass the test, providing scientific support and a decision basis for the early layout of disaster prevention and mitigation. PMID:29584628
The Dragon Storm

NASA Image and Video Library

2005-02-24

A large, bright and complex convective storm that appeared in Saturn's southern hemisphere in mid-September 2004 was the key in solving a long-standing mystery about the ringed planet. Saturn's atmosphere and its rings are shown here in a false color composite made from Cassini images taken in near infrared light through filters that sense different amounts of methane gas. Portions of the atmosphere with a large abundance of methane above the clouds are red, indicating clouds that are deep in the atmosphere. Grey indicates high clouds, and brown indicates clouds at intermediate altitudes. The rings are bright blue because there is no methane gas between the ring particles and the camera. The complex feature with arms and secondary extensions just above and to the right of center is called the Dragon Storm. It lies in a region of the southern hemisphere referred to as "storm alley" by imaging scientists because of the high level of storm activity observed there by Cassini in the last year. The Dragon Storm was a powerful source of radio emissions during July and September of 2004. The radio waves from the storm resemble the short bursts of static generated by lightning on Earth. Cassini detected the bursts only when the storm was rising over the horizon on the night side of the planet as seen from the spacecraft; the bursts stopped when the storm moved into sunlight. This on/off pattern repeated for many Saturn rotations over a period of several weeks, and it was the clock-like repeatability that indicated the storm and the radio bursts are related. Scientists have concluded that the Dragon Storm is a giant thunderstorm whose precipitation generates electricity as it does on Earth. The storm may be deriving its energy from Saturn's deep atmosphere. One mystery is why the radio bursts start while the Dragon Storm is below the horizon on the night side and end when the storm is on the day side, still in full view of the Cassini spacecraft. A possible explanation is that the lightning source lies to the east of the visible cloud, perhaps because it is deeper where the currents are eastward relative to those at cloud top levels. If this were the case, the lightning source would come up over the night side horizon and would sink down below the day side horizon before the visible cloud. This would explain the timing of the visible storm relative to the radio bursts. The Dragon Storm is of great interest for another reason. In examining images taken of Saturn's atmosphere over many months, imaging scientists found that the Dragon Storm arose in the same part of Saturn's atmosphere that had earlier produced large bright convective storms. In other words, the Dragon Storm appears to be a long-lived storm deep in the atmosphere that periodically flares up to produce dramatic bright white plumes which subside over time. One earlier sighting, in July 2004, was also associated with strong radio bursts. And another, observed in March 2004 and captured in a movie created from images of the atmosphere (PIA06082 and PIA06083) spawned three little dark oval storms that broke off from the arms of the main storm. Two of these subsequently merged with each other; the current to the north carried the third one off to the west, and Cassini lost track of it. Small dark storms like these generally get stretched out until they merge with the opposing currents to the north and south. These little storms are the food that sustains the larger atmospheric features, including the larger ovals and the eastward and westward currents. If the little storms come from the giant thunderstorms, then together they form a food chain that harvests the energy of the deep atmosphere and helps maintain the powerful currents. Cassini has many more chances to observe future flare-ups of the Dragon Storm, and others like it over the course of the mission. It is likely that scientists will come to solve the mystery of the radio bursts and observe storm creation and merging in the next 2 or 3 years. http://photojournal.jpl.nasa.gov/catalog/PIA06197
At the eye of the storm

NASA Astrophysics Data System (ADS)

Flasar, F. M.

1991-01-01

The great storm now going on in the atmosphere of Saturn is discussed. Observational results are summarized, and possible explanations for the storm's origin are addressed. The potential for ongoing observations to clarify the storm's causes is considered.
Solar radio continuum storms and a breathing magnetic field model

NASA Technical Reports Server (NTRS)

1975-01-01

Radio noise continuum emissions observed in metric and decametric wave frequencies are, in general, associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. These continuum emission sources, often called type I storm sources, are often associated with type III burst storm activity from metric to hectometric wave frequencies. This storm activity is, therefore, closely connected with the development of these continuum emission sources. It is shown that the S-component emission in microwave frequencies generally precedes, by several days, the emission of these noise continuum storms of lower frequencies. In order for these storms to develop, the growth of sunspot groups into complex types is very important in addition to the increase of the average magnetic field intensity and area of these groups. After giving a review on the theory of these noise continuum storm emissions, a model is briefly considered to explain the relation of the emissions to the storms.
Equatorial ionospheric disturbances over the East African sector during the 2015 St. Patrick's day storm

NASA Astrophysics Data System (ADS)

Olwendo, O. J.; Cesaroni, C.; Yamazaki, Y.; Cilliers, P.

2017-10-01

During solar cycle 24, the St. Patrick's Day storm on 17 March, 2015 was one of the most severe geomagnetic storms. Several research investigations have been done and are still ongoing about this storm since the dynamics of this storm differs on a global scale from one sector to another. This study examines the response of the equatorial ionosphere to the storm in the East African sector. Total electron content (TEC) data from ground stations are used to investigate the evolution of the Equatorial Ionization Anomaly (EIA) during the storm. The TEC observations show a reduced EIA during 18-20 March 2015, consistent with previous studies at other longitudes. Analyses of ground magnetometer data and the thermospheric composition data from the NASA/TIMED satellite reveal that the reduced EIA during the storm can arise from the combined effect of the disturbance dynamo and composition change.
Storm flow export of metolachlor from a coastal plain watershed.

PubMed

Watts, D W; Novak, J M; Johnson, M H; Stone, K C

2000-03-01

During an 18-month (1994-1995) survey of the surface water in an Atlantic Coastal Plain watershed, metolachlor was most frequently detected during storm flow events. Therefore, a sampling procedure, focused on storm flow, was implemented in June of 1996. During 1996, three tropical cyclones made landfall within 150 km of the watershed. These storms, as well as several summer thunderstorms, produced six distinct storm flow events within the watershed. Metolachlor was detected leaving the watershed during each event. In early September, Hurricane Fran produced the largest storm flow event and accounted for the majority of the metolachlor exports. During the storm event triggered by Hurricane Fran, the highest daily average flow (7.5 m2 s-1) and highest concentration (5.1 micrograms L-1) ever measured at the watershed outlet were recorded. Storm flow exports leaving the watershed represented 0.1 g ha-1 or about 0.04% of active ingredient applied.

Study of the Western Black Sea Storms with a Focus on the Storms Caused by Cyclones of North African Origin

NASA Astrophysics Data System (ADS)

Galabov, Vasko; Chervenkov, Hristo

2018-04-01

We present a study of the Black Sea storms, using a long hindcast of the western Black Sea wind waves. The goal of the work is to study the trends in the storminess indicators. We identify 238 storms with significant wave height above 4 m for the period 1900-2015. We study the cyclogenetic regions of the cyclones causing these storms and focus specifically on the Black Sea storms associated with cyclones originating over the Gulf of Sidra and the adjacent areas. We also identify which of these storms are associated with the so-called explosive cyclogenesis (with deepening rate above 1 Bergeron) and find that 3 out of 5 cases of severe Black Sea storms associated with explosive cyclones are caused by cyclones originating in the Gulf of Sidra. We find no evidence of steady trends in the western Black Sea storminess.
Convective rain rates and their evolution during storms in a semiarid climate

NASA Technical Reports Server (NTRS)

Doneaud, A. A.; Miller, J. R., Jr.; Ionescu-Niscov, S.

1984-01-01

The semiarid climate of the U.S. northern High Plains region has been studied with respect to rain rates and their evolution during summertime convective storms, using radar data from a total of 750 radar echo clusters. Analysis of this data suggests that the average rain rate R among storms is in a first approximation independent of the total rain volume, if the entire storm duration is considered in the averaging process. R primarily depends on the reflectivity threshold considered in calculating the area coverage integrated over the lifetime of the storm. R evolution during storms is analyzed by dividing each storm lifetime into 10 min, 1, 2, and 4 hours, as well as growing and decaying periods. The value of R remained independent of the total rain volume when the growing or decaying periods of storms were considered separately.
Interannual Modulation of Northern Hemisphere Winter Storm Tracks by the QBO

NASA Astrophysics Data System (ADS)

Wang, Jiabao; Kim, Hye-Mi; Chang, Edmund K. M.

2018-03-01

Storm tracks, defined as the preferred regions of extratropical synoptic-scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi-biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity. The North Atlantic storm track varies vertically with a downward shrinking (upward expansion) in easterly (westerly) QBO winters associated with the change of the tropopause height. These results not only fill the knowledge gap of QBO-storm track relationship but also suggest a potential route to improve the seasonal prediction of extratropical storm activities owing to the high predictability of the QBO.
Storm track response to climate change: Insights from simulations using an idealized dry GCM.

NASA Astrophysics Data System (ADS)

Mbengue, Cheikh; Schneider, Tapio

2013-04-01

The midlatitude storm tracks, where the most intense extratropical cyclones are found, are an important fixture in the general circulation. They are instrumental in balancing the Earth's heat, momentum, and moisture budgets and are responsible for the weather and climatic patterns over large regions of the Earth's surface. As a result, the midlatitude storm tracks are the subject of a considerable amount of scientific research to understand their response to global warming. This has produced the robust result showing that the storm tracks migrate poleward with global warming. However, the dynamical mechanisms responsible for this migration remain unclear. Our work seeks to broaden understanding of the dynamical mechanisms responsible for storm track migration. Competing mechanisms present in the comprehensive climate models often used to study storm track dynamics make it difficult to determine the primary mechanisms responsible for storm track migration. We are thus prompted to study storm track dynamics from a simplified and idealized framework, which enables the decoupling of mean temperature effects from the effects of static stability and of tropical from extratropical effects. Using a statistically zonally symmetric, dry general circulation model (GCM), we conduct a series of numerical simulations to help understand the storm track response to global mean temperatures and to the tropical convective static stability, which we can vary independently. We define storm tracks as regions of zonally and temporally averaged maxima of barotropic eddy kinetic energy (EKE). This storm track definition also allows us to use previously found scalings between the magnitude of bulk measures of mean available potential energy (MAPE) and EKE, to decompose MAPE, and to obtain some mechanistic understanding of the storm track response in our simulations. These simulations provide several insights, which enable us to extend upon existing theories on the mechanisms driving the poleward migration of the storm tracks. We demonstrate a poleward migration of the midlatitude storm tracks in dry atmospheres with fixed pole-equator temperature contrast and increasing radiative equilibrium mean temperature, without changes in convective static stability. We also show scalings between the location of maxima of surface MAPE and of barotropic EKE. In the simulations where we independently vary tropical convective static stability, we find a marked poleward migration of the storm tracks. However, our decomposition shows that meridional temperature gradients, and not static stability, determine the location and the intensity of the storm tracks. This suggests that although the storm tracks are sensitive to tropical convective static stability, it influences them indirectly. Furthermore, our simulations show that the storm tracks generally migrate in tandem with the terminus of the Hadley cell. Therefore, we hypothesize that it is possible that the Hadley cell provides the tropical-extratropical communication necessary to generate the storm track response to tropical convective static stability we observe in the simulations. The results contained herein could be used to supplement ongoing storm track research in moist atmospheres using comparatively more comprehensive GCMs to understand storm track dynamics in earth-like environments.
78 FR 73456 - List of Approved Spent Fuel Storage Casks: HI-STORM 100 Cask System; Amendment No. 9

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-06

...-2012-0052] RIN 3150-AJ12 List of Approved Spent Fuel Storage Casks: HI-STORM 100 Cask System; Amendment... International HI-STORM 100 Cask System listing within the ``List of Approved Spent Fuel Storage Casks'' to... requirements for the HI-STORM 100U part of the HI-STORM 100 Cask System and updates the thermal model and...
Storm Identification and Tracking for Hydrologic Modeling Using Hourly Accumulated NEXRAD Precipitation Data

NASA Astrophysics Data System (ADS)

Olivera, F.; Choi, J.; Socolofsky, S.

2006-12-01

Watershed responses to storm events are strongly affected by the spatial and temporal patterns of rainfall; that is, the spatial distribution of the precipitation intensity and its evolution over time. Although real storms are moving entities with non-uniform intensities in both space and time, hydrological applications often synthesize these attributes by assuming storms that are uniformly distributed and have variable intensity according to a pre-defined hyetograph shape. As one considers watersheds of greater size, the non-uniformity of rainfall becomes more important, because a storm may not cover the watershed's entire area and may not stay in the watershed for its full duration. In order to incorporate parameters such as storm area, propagation velocity and direction, and intensity distribution in the definition of synthetic storms, it is necessary to determine these storm characteristics from spatially distributed precipitation data. To date, most algorithms for identifying and tracking storms have been applied to short time-step radar reflectivity data (i.e., 15 minutes or less), where storm features are captured in an effectively synoptic manner. For the entire United States, however, the most reliable distributed precipitation data are the one-hour accumulated 4 km × 4 km gridded NEXRAD data of the U.S. National Weather Service (NWS) (NWS 2005. The one-hour aggregation level of the data, though, makes it more difficult to identify and track storms than when using sequences of synoptic radar reflectivity data, because storms can traverse over a number of NEXRAD cells and change size and shape appreciably between consecutive data maps. In this paper, we present a methodology to overcome the identification and tracking difficulties and to extract the characteristics of moving storms (e.g. size, propagation velocity and direction, and intensity distribution) from one-hour accumulated distributed rainfall data. The algorithm uses Gaussian Mixture Models (GMM) for storm identification and image processing for storm tracking. The method has been successfully applied to Brazos County in Texas using the 2003 Multi-sensor Precipitation Estimator (MPE) NEXRAD rainfall data.
Characterisation of atmospheric deposited particles during a dust storm in urban areas of Eastern Australia.

PubMed

Gunawardena, Janaka; Ziyath, Abdul M; Bostrom, Thor E; Bekessy, Lambert K; Ayoko, Godwin A; Egodawatta, Prasanna; Goonetilleke, Ashantha

2013-09-01

The characteristics of dust particles deposited during the 2009 dust storm in the Gold Coast and Brisbane regions of Australia are discussed in this paper. The study outcomes provide important knowledge in relation to the potential impacts of dust storm related pollution on ecosystem health in the context that the frequency of dust storms is predicted to increase due to anthropogenic desert surface modifications and climate change impacts. The investigated dust storm contributed a large fraction of fine particles to the environment with an increased amount of total suspended solids, compared to dry deposition under ambient conditions. Although the dust storm passed over forested areas, the organic carbon content in the dust was relatively low. The primary metals present in the dust storm deposition were aluminium, iron and manganese, which are common soil minerals in Australia. The dust storm deposition did not contain significant loads of nickel, cadmium, copper and lead, which are commonly present in the urban environment. Furthermore, the comparison between the ambient and dust storm chromium and zinc loads suggested that these metals were contributed to the dust storm by local anthropogenic sources. The potential ecosystem health impacts of the 2009 dust storm include, increased fine solids deposition on ground surfaces resulting in an enhanced capacity to adsorb toxic pollutants as well as increased aluminium, iron and manganese loads. In contrast, the ecosystem health impacts related to organic carbon and other metals from dust storm atmospheric deposition are not considered to be significant. Copyright © 2013 Elsevier B.V. All rights reserved.
The observed clustering of damaging extratropical cyclones in Europe

NASA Astrophysics Data System (ADS)

Cusack, Stephen

2016-04-01

The clustering of severe European windstorms on annual timescales has substantial impacts on the (re-)insurance industry. Our knowledge of the risk is limited by large uncertainties in estimates of clustering from typical historical storm data sets covering the past few decades. Eight storm data sets are gathered for analysis in this study in order to reduce these uncertainties. Six of the data sets contain more than 100 years of severe storm information to reduce sampling errors, and observational errors are reduced by the diversity of information sources and analysis methods between storm data sets. All storm severity measures used in this study reflect damage, to suit (re-)insurance applications. The shortest storm data set of 42 years provides indications of stronger clustering with severity, particularly for regions off the main storm track in central Europe and France. However, clustering estimates have very large sampling and observational errors, exemplified by large changes in estimates in central Europe upon removal of one stormy season, 1989/1990. The extended storm records place 1989/1990 into a much longer historical context to produce more robust estimates of clustering. All the extended storm data sets show increased clustering between more severe storms from return periods (RPs) of 0.5 years to the longest measured RPs of about 20 years. Further, they contain signs of stronger clustering off the main storm track, and weaker clustering for smaller-sized areas, though these signals are more uncertain as they are drawn from smaller data samples. These new ultra-long storm data sets provide new information on clustering to improve our management of this risk.
Extreme EEJ and Topside Ionospheric Response to the 22-23 June 2015 Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Zakharenkova, I.; Alken, P.; Coisson, P.

2016-12-01

In this work, we study the ionospheric and thermospheric response to the intense geomagnetic storm of 22-23 June 2015. With the minimum SYM-H excursion of -207 nT, this storm is so far the 2nd strongest geomagnetic storm in the current 24th solar cycle. The storm started with the arrival of a coronal mass ejection at 18:37UT on 22 June 2015. The interplanetary magnetic field (IMF) Bz component changed polarity several times during this storm. Consequently, the interplanetary electric field Ey component repeated this oscillatory behavior, and varied from -15 to +20 mV/m, which is comparable with storm-time levels. Data from multiple ground-based and space-borne instruments showed that both positive and negative ionospheric storms occurred during this storm at middle and low latitudes on both day and night sides. To study the drivers of the observed ionospheric effects, we further analyze variations of thermospheric parameters (neutral mass density and thermospheric O/N2 ratio), as well as the equatorial electrojet (EEJ) data as retrieved from magnetic measurements onboard Swarm satellites. One of the most interesting features of the June 2015 storm is observation of extremely high EEJ values (both eastward and westward), that correlate with variations of the IEF Ey. We find that the storm-time penetration electric fields were, most likely, the main driver of the observed ionospheric effects at the initial phase of the storm, and at the beginning of the main phase. At the end of the main phase, the thermospheric composition changes seemed to contribute as well.
Climate Change Implications and Use of Early Warning Systems for Global Dust Storms

NASA Astrophysics Data System (ADS)

Harriman, L.

2014-12-01

Increased changes in land cover and global climate have led to increased frequency and/or intensity of dust storms in some regions of the world. Early detection and warning of dust storms, in conjunction with effective and widespread information broadcasts, will be essential to the prevention and mitigation of future risks and impacts to people and the environment. Since frequency and intensity of dust storms can vary from region to region, there is a demonstrated need for more research to be conducted over longer periods of time to analyze trends of dust storm events [1]. Dust storms impact their origin area, but also land, water and people a great distance away from where dust finally settles [2, 3]. These transboundary movements and accompanying impacts further warrant the need for global collaboration to help predict the onset, duration and path of a dust storm. Early warning systems can help communicate when a dust storm is occurring, the projected intensity of the dust storm and its anticipated physical impact over a particular geographic area. Development of regional dust storm models, such as CUACE/Dust for East Asia, and monitoring networks, like the Sand and Dust Storm Warning Network operated by the World Meteorological Organization, and the use of remote sensing and satellite imagery derived products [4], including MODIS, are currently being incorporated into early warning and monitoring initiatives. However, to increase future certainty of impacts of dust storms on vulnerable populations and ecosystems, more research is needed to analyze the influences of human activities, seasonal variations and long-term climatic patterns on dust storm generation, movement and impact. Sources: [1] Goudie, A.S. (2009), Dust storms: recent developments, J Environ. Manage., 90. [2] Lee, H., and Liu, C. (2004), Coping with dust storm events: information, impacts, and policymaking in Taiwan, TAO, 15(5). [3] Marx, S.K., McGowan, H.A., and Balz, K.S. (2009), Long-range dust transport from eastern Australia: a proxy for Holocene aridity and ENSO-type climate variability, Earth Planet Sci. Lett., 282. [4] Kimura, R. (2012), Factors contributing to dust storms in source regions producing the yellow-sand phenomena observed in Japan from 1993 to 2002, J. Arid Environ. 80
Interannual variability of planet-encircling dust storms on Mars

NASA Technical Reports Server (NTRS)

Zurek, Richard W.; Martin, Leonard J.

1993-01-01

A recent review of earth-based telescopic observations of Mars together with Viking orbiter and lander data are employed to estimate the frequency of occurrence of planet-encircling dust storms over the past century and to test whether the period spanned by the Mariner 9 and Viking missions to Mars is representative of the decades prior to 1950. Both spacecraft and earth-based observations suggest that planet-encircling dust storms on Mars occur during a 'dust storm season' in southern spring and summer. Viking data show that planet-encircling dust storms could have occurred in the past on Mars without being detected from earth during years in which Mars was far from earth during the dust storm season. Planet-encircling storms were absent during the dust storm seasons monitored during several favorable oppositions prior to 1956 and after 1986. The change of a planet-encircling dust storm occurring in any arbitrary Mars year is estimated to be approximately one in three, if this occurrence is random from year to year and yet restricted seasonally to southern spring and summer.
Searching for storm water inflows in foul sewers using fibre-optic distributed temperature sensing.

PubMed

Schilperoort, Rémy; Hoppe, Holger; de Haan, Cornelis; Langeveld, Jeroen

2013-01-01

A major drawback of separate sewer systems is the occurrence of illicit connections: unintended sewer cross-connections that connect foul water outlets from residential or industrial premises to the storm water system and/or storm water outlets to the foul sewer system. The amount of unwanted storm water in foul sewer systems can be significant, resulting in a number of detrimental effects on the performance of the wastewater system. Efficient removal of storm water inflows into foul sewers requires knowledge of the exact locations of the inflows. This paper presents the use of distributed temperature sensing (DTS) monitoring data to localize illicit storm water inflows into foul sewer systems. Data results from two monitoring campaigns in foul sewer systems in the Netherlands and Germany are presented. For both areas a number of storm water inflow locations can be derived from the data. Storm water inflow can only be detected as long as the temperature of this inflow differs from the in-sewer temperatures prior to the event. Also, the in-sewer propagation of storm and wastewater can be monitored, enabling a detailed view on advection.
Water quality of storm runoff and comparison of procedures for estimating storm-runoff loads, volume, event-mean concentrations, and the mean load for a storm for selected properties and constituents for Colorado Springs, southeastern Colorado, 1992

USGS Publications Warehouse

Von Guerard, Paul; Weiss, W.B.

1995-01-01

The U.S. Environmental Protection Agency requires that municipalities that have a population of 100,000 or greater obtain National Pollutant Discharge Elimination System permits to characterize the quality of their storm runoff. In 1992, the U.S. Geological Survey, in cooperation with the Colorado Springs City Engineering Division, began a study to characterize the water quality of storm runoff and to evaluate procedures for the estimation of storm-runoff loads, volume and event-mean concentrations for selected properties and constituents. Precipitation, streamflow, and water-quality data were collected during 1992 at five sites in Colorado Springs. Thirty-five samples were collected, seven at each of the five sites. At each site, three samples were collected for permitting purposes; two of the samples were collected during rainfall runoff, and one sample was collected during snowmelt runoff. Four additional samples were collected at each site to obtain a large enough sample size to estimate storm-runoff loads, volume, and event-mean concentrations for selected properties and constituents using linear-regression procedures developed using data from the Nationwide Urban Runoff Program (NURP). Storm-water samples were analyzed for as many as 186 properties and constituents. The constituents measured include total-recoverable metals, vola-tile-organic compounds, acid-base/neutral organic compounds, and pesticides. Storm runoff sampled had large concentrations of chemical oxygen demand and 5-day biochemical oxygen demand. Chemical oxygen demand ranged from 100 to 830 milligrams per liter, and 5.-day biochemical oxygen demand ranged from 14 to 260 milligrams per liter. Total-organic carbon concentrations ranged from 18 to 240 milligrams per liter. The total-recoverable metals lead and zinc had the largest concentrations of the total-recoverable metals analyzed. Concentrations of lead ranged from 23 to 350 micrograms per liter, and concentrations of zinc ranged from 110 to 1,400 micrograms per liter. The data for 30 storms representing rainfall runoff from 5 drainage basins were used to develop single-storm local-regression models. The response variables, storm-runoff loads, volume, and event-mean concentrations were modeled using explanatory variables for climatic, physical, and land-use characteristics. The r2 for models that use ordinary least-squares regression ranged from 0.57 to 0.86 for storm-runoff loads and volume and from 0.25 to 0.63 for storm-runoff event-mean concentrations. Except for cadmium, standard errors of estimate ranged from 43 to 115 percent for storm- runoff loads and volume and from 35 to 66 percent for storm-runoff event-mean concentrations. Eleven of the 30 concentrations collected during rainfall runoff for total-recoverable cadmium were censored (less than) concentrations. Ordinary least-squares regression should not be used with censored data; however, censored data can be included with uncensored data using tobit regression. Standard errors of estimate for storm-runoff load and event-mean concentration for total-recoverable cadmium, computed using tobit regression, are 247 and 171 percent. Estimates from single-storm regional-regression models, developed from the Nationwide Urban Runoff Program data base, were compared with observed storm-runoff loads, volume, and event-mean concentrations determined from samples collected in the study area. Single-storm regional-regression models tended to overestimate storm-runoff loads, volume, and event-mean con-centrations. Therefore, single-storm local- and regional-regression models were combined using model-adjustment procedures to take advantage of the strengths of both models while minimizing the deficiencies of each model. Procedures were used to develop single-stormregression equations that were adjusted using local data and estimates from single-storm regional-regression equations. Single-storm regression models developed using model- adjustment proce
7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...
7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...
7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...
Two Pairs of Storms

NASA Image and Video Library

2004-06-04

Two pairs of dark spots, or storms, in Saturn atmosphere squeeze past each other as they dance around the planet. In this group of four storms, the top left and lower right storms are fringed with white clouds as seen by NASA Cassini spacecraft.
Analysis of Best Management Practices for Storm Water Compliance at Air Force Airfields

DTIC Science & Technology

1993-09-01

before selecting an infiltration system. These factors include the local vegetation, soil type and condition, groundwater condition, and storm water quality . The...reduce the peak flow rate of storm water discharges and remove sediments in order to improve storm water quality . Detention facilities should be...discharge rate of runoff and/or provide significant detention time to improve storm water quality through natural physical, chemical, and biological
Large Geomagnetic Storms: Introduction to Special Section

NASA Technical Reports Server (NTRS)

Gopalswamy, N.

2010-01-01

Solar cycle 23 witnessed the accumulation of rich data sets that reveal various aspects of geomagnetic storms in unprecedented detail both at the Sun where the storm causing disturbances originate and in geospace where the effects of the storms are directly felt. During two recent coordinated data analysis workshops (CDAWs) the large geomagnetic storms (Dst < or = -100 nT) of solar cycle 23 were studied in order to understand their solar, interplanetary, and geospace connections. This special section grew out of these CDAWs with additional contributions relevant to these storms. Here I provide a brief summary of the results presented in the special section.
Forecasts of geomagnetic activities and HF radio propagation conditions made at Hiraiso/Japan

NASA Technical Reports Server (NTRS)

Marubashi, K.; Miyamoto, Y.; Kidokoro, T.; Ishii, T.

1979-01-01

The Hiraiso Branch of RRL prediction techniques are summarized separately for the 27 day recurrent storm and the flare-associated storm. The storm predictions are compared with the actual geomagnetic activities in two ways. The first one is the comparison on a day to day basis. In the second comparison, the accuracy of the storm predictions during 1965-1976 are evaluated. In addition to the storm prediction, short-term predictions of HF radio propagation conditions are conducted at Hiraiso. The HF propagation predictions are briefly described as an example of the applications of the magnetic storm prediction.

Survey of minor-to-moderate magnetic storm effects on ionosphere: American sector

NASA Astrophysics Data System (ADS)

Buresova, Dalia; Lastovicka, Jan; Chum, Jaroslav; Pezzopane, Michael; Staciarini Batista, Inez; Gularte, Erika; Novotna, Dagmar

2014-05-01

The paper is focused on ionospheric reaction to occasional minor-to-moderate magnetic storms above selected ionospheric stations located across the Northern and Southern America. Most of the storms analysed occurred under extremely low solar activity conditions of 2007-2009. We analysed variability of the F2 layer critical frequency foF2 and the F2 layer peak height hmF2 obtained for different latitudinal and longitudinal sectors of both hemispheres for the entire period of selected magnetic storms. Observations were compared with the effects of strong magnetic storms and with the IRI2000 outputs when STORM model option is activated. We analysed ionospheric reaction during each storm phase with main emphasis paid on the recovery phase. In general, storm recovery phase is characterized by an abatement of perturbations and a gradual return to the "ground state" of ionosphere. Magnetospheric substorms, typical for the main phase, as a rule cease during the storm recovery phase. However, observations of stormy ionosphere show significant departures from the climatology also within this phase, which are comparable with those usually observed during the storm main phase. Both positive and negative deviations of foF2 and hmF2 have been observed independent on season and location.
Observed Changes at Viking Lander 1

NASA Technical Reports Server (NTRS)

Moore, H. J.

1985-01-01

A local dust storm raged in Chryse Planitia, Mars, in June 1981. The changes wrought in the vicinity of the lander (Mutch Memorial Station) by this storm sometime near Sol 1742 were partly described previously. Here, changes related to the storm are itemized, evidence for wind directions during the peak of the storm are cited, and two observations unrelated to the storm are noted. The observations suggest that the eroding winds of the Sol 1742 storm were more easterly (N. 35 deg to 90 deg E.) than those (N. 5 deg to 11 deg E.) that formed the large wind tails; and fragments in erosional residues are 0.7 cm and larger, but smaller ones may be present. Some fragments 0.4 to 0.5 cm and smaller were somehow removed, at least locally; wind speeds of the 1742 local storm were probably greater than those of a previous local dust storm (25 to 30 m/s) that occurred during the same season on Sol 423 because the earlier storm did not alter the surface; the major, if not entire, amount of erosion by the storm occurred between Sols 1728 and 1757; and erosion chiefly occurred where the surface configuration and material properties were altered by the lander and its sampler.
Great geomagnetic storm of 9 November 1991: Association with a disappearing solar filament

NASA Astrophysics Data System (ADS)

Cliver, E. W.; Balasubramaniam, K. S.; Nitta, N. V.; Li, X.

2009-02-01

We attribute the great geomagnetic storm on 8-10 November 1991 to a large-scale eruption that encompassed the disappearance of a ~25° solar filament in the southern solar hemisphere. The resultant soft X-ray arcade spanned ~90° of solar longitude. The rapid growth of an active region lying at one end of the X-ray arcade appears to have triggered the eruption. This is the largest geomagnetic storm yet associated with the eruption of a quiescent filament. The minimum hourly Dst value of -354 nT on 9 November 1991 compares with a minimum Dst value of -161 nT for the largest 27-day recurrent (coronal hole) storm observed from 1972 to 2005 and the minimum -559 nT value observed during the flare-associated storm of 14 March 1989, the greatest magnetic storm recorded during the space age. Overall, the November 1991 storm ranks 15th on a list of Dst storms from 1905 to 2004, surpassing in intensity such well-known storms as 14 July 1982 (-310 nT) and 15 July 2000 (-317 nT). We used the Cliver et al. and Gopalswamy et al. empirical models of coronal mass ejection propagation in the solar wind to provide consistency checks on the eruption/storm association.
Communicating Storm Surge Forecast Uncertainty

NASA Astrophysics Data System (ADS)

Troutman, J. A.; Rhome, J.

2015-12-01

When it comes to tropical cyclones, storm surge is often the greatest threat to life and property along the coastal United States. The coastal population density has dramatically increased over the past 20 years, putting more people at risk. Informing emergency managers, decision-makers and the public about the potential for wind driven storm surge, however, has been extremely difficult. Recently, the Storm Surge Unit at the National Hurricane Center in Miami, Florida has developed a prototype experimental storm surge watch/warning graphic to help communicate this threat more effectively by identifying areas most at risk for life-threatening storm surge. This prototype is the initial step in the transition toward a NWS storm surge watch/warning system and highlights the inundation levels that have a 10% chance of being exceeded. The guidance for this product is the Probabilistic Hurricane Storm Surge (P-Surge) model, which predicts the probability of various storm surge heights by statistically evaluating numerous SLOSH model simulations. Questions remain, however, if exceedance values in addition to the 10% may be of equal importance to forecasters. P-Surge data from 2014 Hurricane Arthur is used to ascertain the practicality of incorporating other exceedance data into storm surge forecasts. Extracting forecast uncertainty information through analyzing P-surge exceedances overlaid with track and wind intensity forecasts proves to be beneficial for forecasters and decision support.
Rainfall, discharge, and water-quality data during stormwater monitoring, H-1 storm drain, Oahu, Hawaii, July 1, 2009, to June 30, 2010

USGS Publications Warehouse

Presley, Todd K.; Jamison, Marcael T.J.

2010-01-01

Storm runoff water-quality samples were collected as part of the State of Hawaii Department of Transportation Stormwater Monitoring Program. The program is designed to assess the effects of highway runoff and urban runoff collected by the H-1 storm drain on the Manoa-Palolo Drainage Canal. This report summarizes rainfall, discharge, and water-quality data collected between July 1, 2009, and June 30, 2010. As part of this program, rainfall and continuous discharge data were collected at the H-1 storm drain. During the year, sampling strategy and sample processing methods were modified to improve the characterization of the effects of discharge from the storm drain on the Manoa-Palolo Drainage Canal. During July 1, 2009, to February 1, 2010, samples were collected from only the H-1 storm drain. Beginning February 2, 2010, samples were collected simultaneously from the H-1 storm drain and the Manoa-Palolo Drainage Canal at a location about 50 feet upstream of the discharge point of the H-1 storm drain. Three storms were sampled during July 1, 2009, to June 30, 2010. All samples were collected using automatic samplers. For the storm of August 12, 2009, grab samples (for oil and grease, and total petroleum hydrocarbons) and a composite sample were collected. The composite sample was analyzed for total suspended solids, nutrients, and selected dissolved and total (filtered and unfiltered) trace metals (cadmium, chromium, nickel, copper, lead, and zinc). Two storms were sampled in March 2010 at the H-1 storm drain and from the Manoa-Palolo Drainage Canal. Two samples were collected during the storm of March 4, 2010, and six samples were collected during the storm of March 8, 2010. These two storms were sampled using the modified strategy, in which discrete samples from the automatic sampler were processed and analyzed individually, rather than as a composite sample, using the simultaneously collected samples from the H-1 storm drain and from the Manoa-Palolo Drainage Canal. The discrete samples were analyzed for some or all of the following constituents: total suspended solids, nutrients, oil and grease, and selected dissolved (filtered) trace metals (cadmium, chromium, nickel, copper, lead, and zinc). Five quality-assurance/quality-control samples were analyzed during the year. These samples included one laboratory-duplicate, one field-duplicate, and one matrix-spike sample prepared and analyzed with the storm samples. In addition, two inorganic blank-water samples, one sample at the H-1 storm drain and one sample at the Manoa-Palolo Drainage Canal, were collected by running the blank water (water purified of all inorganic constituents) through the sampling and processing systems after cleaning automatic sampler lines to verify that the sampling lines were not contaminated.
Assimilation of attenuated data from X-band network radars using ensemble Kalman filter

NASA Astrophysics Data System (ADS)

Cheng, Jing

To use reflectivity data from X-band radars for quantitative precipitation estimation and storm-scale data assimilation, the effect of attenuation must be properly accounted for. Traditional approaches try to make correction to the attenuated reflectivity first before using the data. An alternative, theoretically more attractive approach builds the attenuation effect into the reflectivity observation operator of a data assimilation system, such as an ensemble Kalman filter (EnKF), allowing direct assimilation of the attenuated reflectivity and taking advantage of microphysical state estimation using EnKF methods for a potentially more accurate solution. This study first tests the approach for the CASA (Center for Collaborative Adaptive Sensing of the Atmosphere) X-band radar network configuration through observing system simulation experiments (OSSE) for a quasi-linear convective system (QLCS) that has more significant attenuation than isolated storms. To avoid the problem of potentially giving too much weight to fully attenuated reflectivity, an analytical, echo-intensity-dependent model for the observation error (AEM) is developed and is found to improve the performance of the filter. By building the attenuation into the forward observation operator and combining it with the application of AEM, the assimilation of attenuated CASA observations is able to produce a reasonably accurate analysis of the QLCS inside CASA radar network coverage. Compared with foregoing assimilation of radar data with weak radar reflectivity or assimilating only radial velocity data, our method can suppress the growth of spurious echoes while obtaining a more accurate analysis in the terms of root-mean-square (RMS) error. Sensitivity experiments are designed to examine the effectiveness of AEM by introducing multiple sources of observation errors into the simulated observations. The performance of such an approach in the presence of resolution-induced model error is also evaluated and good results are obtained. The same EnKF framework with attenuation correction is used to test different possible configurations of 2 hypothetical radars added to the existing network of 4 CASA radars through OSSEs. Though plans to expand the CASA radar network did not materialize, such experiments can provide guidance in the site selection of future X-band or other short-wavelength radar networks, as well as examining the benefit of X-band radar networks that consist of a much larger number of radars. Two QLCSs with different propagation speeds are generated and serve as the truth for our OSSEs. Assimilation and forecast results are compared among the OSSEs, assimilating only X-band or short-wavelength radar data. Overall, radar networks with larger downstream spatial coverage tend to provide overall the best analyses and 1-hour forecasts. The best analyses and forecasts of convective scale structure, however, are obtained when Dual- or Multi-Doppler coverage is preferred, even at the expense of minor loss in spatial coverage. Built-in attenuation correction is then applied, for the first time, to a real case (the 24 May 2011 tornadic storm near Chickasha, Oklahoma), using data from the X-band CASA radars. The attenuation correction procedure is found to be very effective---the analyses obtained using attenuated data are better than those obtained using pre-corrected data when all the values of reflectivity observations are assimilated. The effectiveness of the procedure is further examined by comparing the deterministic and ensemble forecasts started from the analysis of each experiment. The deterministic forecast experiment results indicate that assimilating un-corrected observations directly actually retains some information that might be lost in the pre-corrected CASA observations by forecasting a longer-lasting trailing line, similar to that observed in WSR-88D data. In the ensemble forecasts, assimilating un-corrected observations directly, using our attenuation-correcting EnKF, results in a forecast with a more intense tornado track than the experiment that assimilates all values of pre-corrected CASA data. This work is the first to assimilate attenuated observations from a radar network in OSSEs, as well as the first attempt to directly assimilate real, uncorrected CASA data into a numerical weather prediction (NWP) model using EnKF.
Combined Aircraft and Satellite-Derived Storm Electric Current and Lightning Rates Measurements and Implications for the Global Electric Circuit

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Blakeslee, Richard J.; Bateman, Monte G.

2010-01-01

Using rotating vane electric field mills and Gerdien capacitors, we measured the electric field profile and conductivity during 850 overflights of electrified shower clouds and thunderstorms spanning regions including the Southeastern United States, the Western Atlantic Ocean, the Gulf of Mexico, Central America and adjacent oceans, Central Brazil, and the South Pacific. The overflights include storms over land and ocean, with and without lightning, and with positive and negative fields above the storms. The measurements were made with the NASA ER-2 and the Altus-II high altitude aircrafts. Peak electric fields, with lightning transients removed, ranged from -1.0 kV/m to 16 kV/m, with a mean value of 0.9 kV/m. The median peak field was 0.29 kV/m. Integrating our electric field and conductivity data, we determined total conduction currents and flash rates for each overpass. With knowledge of the storm location (land or ocean) and type (with or without lightning), we determine the mean currents by location and type. The mean current for ocean storms with lightning is 1.6 A while the mean current for land storms with lightning is 1.0 A. The mean current for oceanic storms without lightning (i.e., electrified shower clouds) is 0.39 A and the mean current for land storms without lightning is 0.13 A. Thus, on average, land storms with or without lightning have about half the mean current as their corresponding oceanic storm counterparts. Over three-quarters (78%) of the land storms had detectable lightning, while less than half (43%) of the oceanic storms had lightning. We did not find any significant regional or latitudinal based patterns in our total conduction currents. By combining the aircraft derived storm currents and flash rates with diurnal lightning statistics derived from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) low Earth orbiting satellites, we reproduce the diurnal variation in the global electric circuit (i.e., the Carnegie curve) to within 4% for all but two short periods of time. This excellent agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. Given our data and assumptions, mean contributions to the global electric circuit are 0.7 kA (ocean) and 1.1 kA (land) from lightning-producing storms, and 0.22 kA (ocean) and 0.04 (land) from electrified shower clouds, resulting in a mean total conduction current estimate for the global electric circuit of 2.0 kA. Breaking the results down into mean storm counts reveals 1100 for land storms with lightning, 530 for ocean storms without lightning, 390 for ocean storms with lightning, and 330 for land storms without lightning.
Watershed-based sources of polycyclic aromatic hydrocarbons in urban storm water.

PubMed

Stein, Eric D; Tiefenthaler, Liesl L; Schiff, Kenneth

2006-02-01

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic and mutagenic compounds, ubiquitous in the air and water of urban environments, and have been shown to accumulate in coastal estuarine and marine sediments. Although previous studies have documented concentrations and loads of PAHs in urban runoff, little is known about the sources and temporal patterns of PAH loading from storm water. This study characterized the sources and temporal patterns of PAHs in urban storm water by analyzing PAH concentrations and loads from a range of homogeneous land use sites and in-river mass emission sites throughout the greater Los Angeles, California, USA, region. Samples were collected at 30- to 60-min intervals over the course of a storm during multiple storm events over a four-year period in order to investigate PAH sources and inter- and intrastorm patterns in loading. Polycyclic aromatic hydrocarbon storm fluxes ranged from 1.3 g/km2 for the largely undeveloped Arroyo Sequit watershed to 223.7 g/km2 for the highly urbanized Verdugo Wash watershed, with average storm fluxes being 46 times higher in developed versus undeveloped watersheds. Early-season storms repeatedly produced substantially higher loads than comparably sized late-season storms. Within individual storms, PAHs exhibited a moderate first flush with between 30 and 60% of the total PAH load being discharged in the first 20% of the storm volume. The relative distribution of individual PAHs demonstrated a consistent predominance of high-molecular-weight compounds indicative of pyrogenic sources.
Enhanced object-based tracking algorithm for convective rain storms and cells

NASA Astrophysics Data System (ADS)

Muñoz, Carlos; Wang, Li-Pen; Willems, Patrick

2018-03-01

This paper proposes a new object-based storm tracking algorithm, based upon TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting). TITAN is a widely-used convective storm tracking algorithm but has limitations in handling small-scale yet high-intensity storm entities due to its single-threshold identification approach. It also has difficulties to effectively track fast-moving storms because of the employed matching approach that largely relies on the overlapping areas between successive storm entities. To address these deficiencies, a number of modifications are proposed and tested in this paper. These include a two-stage multi-threshold storm identification, a new formulation for characterizing storm's physical features, and an enhanced matching technique in synergy with an optical-flow storm field tracker, as well as, according to these modifications, a more complex merging and splitting scheme. High-resolution (5-min and 529-m) radar reflectivity data for 18 storm events over Belgium are used to calibrate and evaluate the algorithm. The performance of the proposed algorithm is compared with that of the original TITAN. The results suggest that the proposed algorithm can better isolate and match convective rainfall entities, as well as to provide more reliable and detailed motion estimates. Furthermore, the improvement is found to be more significant for higher rainfall intensities. The new algorithm has the potential to serve as a basis for further applications, such as storm nowcasting and long-term stochastic spatial and temporal rainfall generation.
Hurricane Isaac: A Longitudinal Analysis of Storm Characteristics and Power Outage Risk.

PubMed

Tonn, Gina L; Guikema, Seth D; Ferreira, Celso M; Quiring, Steven M

2016-10-01

In August 2012, Hurricane Isaac, a Category 1 hurricane at landfall, caused extensive power outages in Louisiana. The storm brought high winds, storm surge, and flooding to Louisiana, and power outages were widespread and prolonged. Hourly power outage data for the state of Louisiana were collected during the storm and analyzed. This analysis included correlation of hourly power outage figures by zip code with storm conditions including wind, rainfall, and storm surge using a nonparametric ensemble data mining approach. Results were analyzed to understand how correlation of power outages with storm conditions differed geographically within the state. This analysis provided insight on how rainfall and storm surge, along with wind, contribute to power outages in hurricanes. By conducting a longitudinal study of outages at the zip code level, we were able to gain insight into the causal drivers of power outages during hurricanes. Our analysis showed that the statistical importance of storm characteristic covariates to power outages varies geographically. For Hurricane Isaac, wind speed, precipitation, and previous outages generally had high importance, whereas storm surge had lower importance, even in zip codes that experienced significant surge. The results of this analysis can inform the development of power outage forecasting models, which often focus strictly on wind-related covariates. Our study of Hurricane Isaac indicates that inclusion of other covariates, particularly precipitation, may improve model accuracy and robustness across a range of storm conditions and geography. © 2016 Society for Risk Analysis.
NASA Sees Heavy Rainfall in Tropical Storm Andrea

NASA Image and Video Library

2013-06-06

NASA’s Terra satellite passed over Tropical Storm Andrea on June 5 at 16:25 UTC (12:25 p.m. EDT) and the MODIS instrument captured this visible image of the storm. Andrea’s clouds had already extended over more than half of Florida. Credit: NASA Goddard MODIS Rapid Response Team --- NASA Sees Heavy Rainfall in Tropical Storm Andrea NASA’s TRMM satellite passed over Tropical Storm Andrea right after it was named, while NASA’s Terra satellite captured a visible image of the storm’s reach hours beforehand. TRMM measures rainfall from space and saw that rainfall rates in the southern part of the storm was falling at almost 5 inches per hour. NASA’s Terra satellite passed over Tropical Storm Andrea on June 5 at 16:25 UTC (12:25 p.m. EDT) and the Moderate Resolution Imaging Spectroradiometer or MODIS instrument, captured a visible image of the storm. At that time, Andrea’s clouds had already extended over more than half of Florida. At 8 p.m. EDT on Wednesday, June 5, System 91L became the first tropical storm of the Atlantic Ocean hurricane season. Tropical Storm Andrea was centered near 25.5 North and 86.5 West, about 300 miles (485 km) southwest of Tampa, Fla. At the time Andrea intensified into a tropical storm, its maximum sustained winds were near 40 mph (65 kph). Full updates can be found at NASA's Hurricane page: www.nasa.gov/hurricane Rob Gutro NASA’s Goddard Space Flight Center
NASA Sees Heavy Rainfall in Tropical Storm Andrea

NASA Image and Video Library

2017-12-08

This NOAA GOES-East satellite animation shows the development of System 91L into Tropical Storm Andrea over the course of 3 days from June 4 to June 6, just after Andrea was officially designated a tropical storm. Credit: NASA's GOES Project --- NASA Sees Heavy Rainfall in Tropical Storm Andrea NASA’s TRMM satellite passed over Tropical Storm Andrea right after it was named, while NASA’s Terra satellite captured a visible image of the storm’s reach hours beforehand. TRMM measures rainfall from space and saw that rainfall rates in the southern part of the storm was falling at almost 5 inches per hour. NASA’s Terra satellite passed over Tropical Storm Andrea on June 5 at 16:25 UTC (12:25 p.m. EDT) and the Moderate Resolution Imaging Spectroradiometer or MODIS instrument, captured a visible image of the storm. At that time, Andrea’s clouds had already extended over more than half of Florida. At 8 p.m. EDT on Wednesday, June 5, System 91L became the first tropical storm of the Atlantic Ocean hurricane season. Tropical Storm Andrea was centered near 25.5 North and 86.5 West, about 300 miles (485 km) southwest of Tampa, Fla. At the time Andrea intensified into a tropical storm, its maximum sustained winds were near 40 mph (65 kph). Full updates can be found at NASA's Hurricane page: www.nasa.gov/hurricane Rob Gutro NASA’s Goddard Space Flight Center
Effect of hurricane paths on storm surge response at Tianjin, China

NASA Astrophysics Data System (ADS)

Feng, Xingru; Yin, Baoshu; Yang, Dezhou

2012-06-01

A hurricane induced storm surge simulation system was developed for Tianjin coast, which consists of a hurricane model and a storm surge model. The peak storm surge result of the simulation agreed well with that of the observation. Three observed paths (Rita, Mimie and WINNIE) and a hypothetical path (Rita2) were chosen as the selective hurricane paths according to their positions relative to Tianjin. The sensitivity of Tianjin storm surge to the four paths was investigated using the validated storm surge simulation system. Three groups of experiments were done. In group one, the models were forced by the wind field and air pressure; in group two and three the models were forced by the wind only and the air pressure only respectively. In the experiments, the hurricane moved with a fixed speed and an intensity of 50 year return period. The simulation results show that path of the type Rita2 is the easiest to cause storm surge disaster in Tianjin, and the effect of air pressure forcing is most evident for path of the type Rita in Tianjin storm surge process. The above conclusions were analyzed through the evolution of the wind fields and the air pressure distributions. Comparing the experiment results of Group one, two and three, it can be seen that the storm surge is mainly induced by the wind forcing and the nonlinear interaction between the effect of wind forcing and air pressure forcing on the storm surge tends to weaken the storm surge.
Study of the tornado event in Greece on March 25, 2009: Synoptic analysis and numerical modeling using modified topography

NASA Astrophysics Data System (ADS)

Matsangouras, I. T.; Nastos, P. T.; Pytharoulis, I.

2016-03-01

Recent research revealed that western Greece and NW Peloponnese are regions that favor prefrontal tornadic incidence. On March 25, 2009 a tornado developed approximately at 10:30 UTC near Varda village (NW Peloponnese). Tornado intensity was T4-T5 (TORRO scale) and consequently caused an economic impact of 350,000 € over the local society. The goals of this study are: (i) to analyze synoptic and remote sensing features regarding the tornado event over NW Peloponnese and (ii) to investigate the role of topography in tornadogenesis triggered under strong synoptic scale forcing over that area. Synoptic analysis was based on the European Centre for Medium-Range Weather Forecasts (ECMWF) data sets. The analysis of daily anomaly of synoptic conditions with respect to 30 years' climatology (1981-2010), was based on the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data sets. In addition, numerous remote sensing data sets were derived by the Hellenic National Meteorological Service (HNMS) weather station network in order to better interpret the examined tornado event. Finally, numerical modeling was performed using the non-hydrostatic Weather Research and Forecasting model (WRF), initialized by ECMWF gridded analyses, with telescoping nested grids that allow the representation of atmospheric circulations ranging from the synoptic scale down to the meso-scale. The two numerical experiments were performed on the basis of: (a) the presence and (b) the absence of topography (landscape), so as to determine whether the occurrence of a tornado - identified by diagnostic instability indices - could be indicated by modifying topography. The energy helicity index (EHI), the bulk Richardson number (BRN) shear, the storm-relative environmental helicity (SRH), and the maximum convective available potential energy (MCAPE, for parcels with maximum θe) were considered as principal diagnostic instability variables and employed in both numerical experiments. Furthermore, model verification was conducted, accompanied by analysis of the absolute vorticity budget. Synoptic analysis revealed that the synoptic weather conditions on March 25, 2009 are in agreement with the composite synoptic climatology for tornado days over western Greece. In addition, maximum daily anomalies at the barometric levels of 500, 700, 850 and 925 hPa were found, compared to the climatology of composite mean anomalies for tornado days over western Greece. Numerical simulations revealed that the topography of NW Peloponnese did not constitute an important factor during the tornado event on March 25, 2009, based on EHI, SRH, BRN, and MCAPE analyses.
Visions of our Planet's Atmosphere, Land and Oceans: NASA/NOAA Electronic Theater 2002

NASA Technical Reports Server (NTRS)

Hasler, A. F.; Starr, David (Technical Monitor)

2001-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to the Olympic Medals Plaza, the new Gateway Center, and the University of Utah Stadium Site of the Olympic Opening and Closing Ceremonies in Salt Lake City. Fly in and through the Park City, and Snow Basin sites of the 2002 Winter Olympic Alpine Venues using 1 m IKONOS "Spy Satellite" data. See the four seasons of the Wasatch Front as observed by Landsat 7 at 15m resolution and watch the trees turn color in the Fall, snow come and go in the mountains and the reservoirs freeze and melt. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies including hurricanes & "tornadoes". See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including new 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained. See how High-Definition Television (HDTV) is revolutionizing the way we communicate science. (In cooperation with the American Museum of Natural History in NYC) See dust storms in Africa and smoke plumes from fires in Mexico. See visualizations featured on the covers of Newsweek, TIME, National Geographic, Popular Science & on National & International Network TV. New computer software tools allow us to roam & zoom through massive global images e.g. Landsat tours of the US, and Africa, showing desert and mountain geology as well as seasonal changes in vegetation. See animations of the polar ice packs and the motion of gigantic Antarctic Icebergs from SeaWinds data. Spectacular new visualizations of the global atmosphere & oceans are shown. See vortexes and currents in the global oceans that bring up the nutrients to feed tiny algae and draw the fish, whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. See the city lights, fishing fleets, gas flares and bio-mass burning of the Earth at night observed by the "night-vision" DMSP military satellite. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with two CPUs, 4 Gigabytes of RAM and 0.5 Terabyte of disk using two projectors across a super sized panoramic 48 foot screen. In addition new HDTV technology will be demonstrated from a portable computer server.
Visions of our Planet's Atmosphere, Land and Oceans: NASA/NOAA Electronic Theater 2002

NASA Technical Reports Server (NTRS)

Hasler, A. F.; Starr, David (Technical Monitor)

2002-01-01

The NASA/NOAA Electronic Theater presents Earth science observations and visualizations in a historical perspective. Fly in from outer space to the Olympic Medals Plaza, the new Gateway Center, and the University of Utah Stadium Site of the Olympic Opening and Closing Ceremonies in Salt Lake City. Fly in and through the Park City, and Snow Basin sites of the 2002 Winter Olympic Alpine Venues using 1 m IKONOS "Spy Satellite" data. See the four seasons of the Wasatch Front as observed by Landsat 7 at 15m resolution and watch the trees turn color in the Fall, snow come and go in the mountains and the reservoirs freeze and melt. Go back to the early weather satellite images from the 1960s and see them contrasted with the latest US and international global satellite weather movies Including hurricanes & "tornadoes". See the latest visualizations of spectacular images from NASA/NOAA remote sensing missions like Terra, GOES, TRMM, SeaWiFS, Landsat 7 including new 1 - min GOES rapid scan image sequences of Nov 9th 2001 Midwest tornadic thunderstorms and have them explained. See how High-Definition Television (HDTV) is revolutionizing the way we communicate science. (In cooperation with the American Museum of Natural History in NYC) See dust storms in Africa and smoke plumes from fires in Mexico. See visualizations featured on the covers Of Newsweek, TIME, National Geographic, Popular Science & on National & International Network TV. New computer software. tools allow us to roam & zoom through massive global images e.g. Landsat tours of the US, and Africa, showing desert and mountain geology as well as seasonal changes in vegetation. See animations of the polar ice packs and the motion of gigantic Antarctic Icebergs from SeaWinds data. Spectacular new visualizations of the global atmosphere & oceans are shown. See vertexes and currents in the global oceans that bring up the nutrients to feed tin) algae and draw the fish, whales and fisherman. See the how the ocean blooms in response to these currents and El Nino/La Nina climate changes. See the city lights, fishing fleets, gas flares and biomass burning of the Earth at night observed by the "night-vision" DMSP military satellite. The demonstration is interactively driven by a SGI Octane Graphics Supercomputer with two CPUs, 4 Gigabytes of RAM and 0.5 Terabyte of disk using two projectors across a super sized panoramic 48 foot screen. In addition new HDTV technology will be demonstrated from a portable computer server.
The Electric Storm of November 1882

NASA Astrophysics Data System (ADS)

Love, Jeffrey J.

2018-01-01

In November 1882, an intense magnetic storm related to a large sunspot group caused widespread interference to telegraph and telephone systems and provided spectacular and unusual auroral displays. The (ring current) storm time disturbance index for this storm reached maximum -Dst ≈ 386 nT, comparable to Halloween storm of 29-31 October 2003, but from 17 to 20 November the aa midlatitude geomagnetic disturbance index averaged 214.25 nT, the highest 4 day level of disturbance since the beginning of aa index in 1868. This storm contributed to scientists' understanding of the reality of solar-terrestrial interaction. Past occurrences of magnetic storms, like that of November 1882, can inform modern evaluations of the deleterious effects that a magnetic superstorm might have on technological systems of importance to society.
Hurricane Harvey rapid response: observations of infragravity wave dynamics and morphological change during inundation of a barrier island cut

NASA Astrophysics Data System (ADS)

Anarde, K.; Figlus, J.; Dellapenna, T. M.; Bedient, P. B.

2017-12-01

Prior to landfall of Hurricane Harvey on August 25, 2017, instrumentation was deployed on the seaward and landward sides of a barrier island on the central Texas Gulf Coast to collect in-situ hydrodynamic measurements during storm impact. High-resolution devices capable of withstanding extreme conditions included inexpensive pressure transducers and tilt current meters mounted within and atop (respectively) shallow monitoring wells. In order to link measurements of storm hydrodynamics with the morphological evolution of the barrier, pre- and post-storm digital elevation models were generated using a combination of unmanned aerial imagery, LiDAR, and real-time kinematic GPS. Push-cores were collected and analyzed for grain size and sedimentary structure to relate hydrodynamic observations with the local character of storm-generated deposits. Observations show that at Hog Island, located approximately 160 miles northeast of Harvey's landfall location, storm surge inundated an inactive storm channel. Infragravity waves (0.003 - 0.05 Hz) dominated the water motion onshore of the berm crest over a 24-hour period proximate to storm landfall. Over this time, approximately 50 cm of sediment accreted vertically atop the instrument located in the backshore. Storm deposits at this location contained sub-parallel alternating laminae of quartz and heavy mineral-enriched sand. While onshore progression of infragravity waves into the back-barrier was observed over several hours prior to storm landfall, storm deposits in the back-barrier lack the characteristic laminae preserved in the backshore. These field measurements will ultimately be used to constrain and validate numerical modeling schemes that explore morphodynamic conditions of barriers in response to extreme storms (e.g., XBeach, CSHORE). This study provides a unique data set linking extreme storm hydrodynamics with geomorphic changes during a relatively low surge, but highly dissipative wave event.
Analysis of dust storms observed in Mongolia during 1937-1999

NASA Astrophysics Data System (ADS)

Natsagdorj, L.; Jugder, D.; Chung, Y. S.

Climatology of dust storms in Mongolia is compiled based on observational data of 49 meteorological stations from 1960 to 1999 and compared them with data between 1937 and 1989. Three different maps of the distribution of dust storms, drifting dust and the number of dusty days are presented. The results of the analysis show that the number of days with dust storms is <5 days over the Altai, the Khangai and the Khentei mountainous regions and more than 20-37 days in the Gobi Desert and semi-desert area. The greatest occurrence of drifting dust arises around the Mongol Els area of west Mongolia. The number of dusty days, which is derived from the sum of the number of days with dust storms and drifting dust, is <10 days in the mountainous area and 61-127 days in the Gobi Desert and the Great Lakes hollow of west Mongolia. It is found that 61% of dust storms occur in the spring in Mongolia and a dust storm lasts on average from 3.1 to 6.0 h. About 65.5-91.0% of dust storms occur in daytime and 9.0-34.5% at night. Dust storms occur more frequently in the city region and are accompanied by surface wind speeds usually from 6 to 20 ms -1. Dust storms usually occur when soil and air are dry, and 70% of dust storms occur in dry soil conditions. When dust storms occur, relative humidity averages 20-40% in Mongolia. An important outcome of this study is the trend of dusty days between 1960 and 1999. It shows that the number of dusty days has tripled from the 1960s to 1990s and has decreased since 1990.
Study of storm surge trends in typhoon-prone coastal areas based on observations and surge-wave coupled simulations

NASA Astrophysics Data System (ADS)

Feng, Xingru; Li, Mingjie; Yin, Baoshu; Yang, Dezhou; Yang, Hongwei

2018-06-01

This is a study of the storm surge trends in some of the typhoon-prone coastal areas of China. An unstructured-grid, storm surge-wave-tide coupled model was established for the coastal areas of Zhejiang, Fujian and Guangdong provinces. The coupled model has a high resolution in coastal areas, and the simulated results compared well with the in situ observations and satellite altimeter data. The typhoon-induced storm surges along the coast of the study areas were simulated based on the established coupled model for the past 20 years (1997-2016). The simulated results were used to analyze the trends of the storm surges in the study area. The extreme storm surge trends along the central coast of Fujian Province reached up to 0.06 m/y, significant at the 90% confidence level. The duration of the storm surges greater than 1.0 and 0.7 m had an increasing trend along the coastal area of northern Fujian Province, significant at confidence levels of 70%-91%. The simulated trends of the extreme storm surges were also validated by observations from two tide gauge stations. Further studies show that the correlation coefficient (RTE) between the duration of the storm surge greater than 1 m and the annual ENSO index can reach as high as 0.62, significant at the 99% confidence level. This occurred in a location where the storm surge trend was not significant. For the areas with significant increasing storm surge trends, RTE was small and not significant. This study identified the storm surge trends for the full complex coastline of the study area. These results are useful both for coastal management by the government and for coastal engineering design.

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