Observation of a high-quality quasi-periodic rapidly propagating wave train using SDO/AIA

NASA Astrophysics Data System (ADS)

Nisticò, G.; Pascoe, D. J.; Nakariakov, V. M.

2014-09-01

Context. We present a new event of quasi-periodic wave trains observed in EUV wavebands that rapidly propagate away from an active region after a flare. Aims: We measured the parameters of a wave train observed on 7 December 2013 after an M1.2 flare, such as the phase speeds, periods and wavelengths, in relationship to the local coronal environment and the energy sources. Methods: We compared our observations with a numerical simulation of fast magnetoacoustic waves that undergo dispersive evolution and leakage in a coronal loop embedded in a potential magnetic field. Results: The wave train is observed to propagate as several arc-shaped intensity disturbances for almost half an hour, with a speed greater than 1000 km s-1 and a period of about 1 min. The wave train followed two different patterns of propagation, in accordance with the magnetic structure of the active region. The oscillatory signal is found to be of high-quality, i.e. there is a large number (10 or more) of subsequent wave fronts observed. The observations are found to be consistent with the numerical simulation of a fast wave train generated by a localised impulsive energy release. Conclusions: Transverse structuring in the corona can efficiently create and guide high-quality quasi-periodic propagating fast wave trains. The movies are available in electronic form at http://www.aanda.org

Direct evidence for EMIC wave scattering of relativistic electrons in space

NASA Astrophysics Data System (ADS)

Zhang, X.-J.; Li, W.; Ma, Q.; Thorne, R. M.; Angelopoulos, V.; Bortnik, J.; Chen, L.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Baker, D. N.; Reeves, G. D.; Spence, H. E.; Blake, J. B.; Fennell, J. F.

2016-07-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave-driven relativistic electron losses in the Earth's outer radiation belt.

MMS Observations of Harmonic Electromagnetic Cyclotron Waves

NASA Astrophysics Data System (ADS)

Usanova, M.; Ahmadi, N.; Ergun, R.; Trattner, K. J.; Fuselier, S. A.; Torbert, R. B.; Mauk, B.; Le Contel, O.; Giles, B. L.; Russell, C. T.; Burch, J.; Strangeway, R. J.

2017-12-01

Harmonically related electromagnetic ion cyclotron waves with the fundamental frequency near the O+ cyclotron frequency were observed by the four MMS spacecraft on May 20, 2016. The wave activity was detected by the spacecraft on their inbound passage through the Earth's morning magnetosphere during generally quiet geomagnetic conditions but enhanced solar wind dynamic pressure. It was also associated with an enhancement of energetic H+ and O+ ions. The waves are seen in both magnetic and electric fields, formed by over ten higher order harmonics, most pronounced in the electric field. The wave activity lasted for about an hour with some wave packets giving rise to short-lived structures extending from Hz to kHz range. These observations are particularly interesting since they suggest cross-frequency coupling between the lower and higher frequency modes. Further work will focus on examining the nature and role of these waves in the energetic particle dynamics from a theoretical perspective.

Hi-C and AIA observations of transverse magnetohydrodynamic waves in active regions

NASA Astrophysics Data System (ADS)

Morton, R. J.; McLaughlin, J. A.

2013-05-01

The recent launch of the High resolution Coronal imager (Hi-C) provided a unique opportunity of studying the EUV corona with unprecedented spatial resolution. We utilize these observations to investigate the properties of low-frequency (50-200 s) active region transverse waves, whose omnipresence had been suggested previously. The five-fold improvement in spatial resolution over SDO/AIA reveals coronal loops with widths 150-310 km and that these loops support transverse waves with displacement amplitudes <50 km. However, the results suggest that wave activity in the coronal loops is of low energy, with typical velocity amplitudes <3 km s-1. An extended time-series of SDO data suggests that low-energy wave behaviour is typical of the coronal structures both before and after the Hi-C observations. Appendix A and five movies associated to Figs. A.2-A.6 are available in electronic form at http://www.aanda.org

Study of stratospheric-ionospheric coupling during thunderstorms and tornadoes

NASA Technical Reports Server (NTRS)

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

1977-01-01

A continuous-wave-spectrum high-frequency Doppler sounder array with three transmitters at each of three sites was used to observe the dynamics of the coupling of energy between the stratosphere and the ionosphere. During times of severe weather activity wavelike disturbances have been detected on ground-based ionospheric sounding records as perturbations in electron densities. Infrasonic waves with wave periods of 3-7 min and with horizontal phase velocities of 600-800 m/s were observed when there was thunderstorm activity; gravity waves with wave periods of 10-15 min and horizontal phase velocities of 100-200 m/s were detected when there was tornado activity. Both triangulations from the cross correlation functions of the Doppler records based on an assumption of no background wind shear and ray-tracing computations including an assumed background wind shear indicate that the waves originated in the vicinity of the thunderstorms and tornadoes. A comparison of the wavelengths of the infrasonic and gravity waves observed at ionospheric heights and those in cloud-top pictures from satellites show that they are all of the order of 100-300 km.

Path planning on cellular nonlinear network using active wave computing technique

NASA Astrophysics Data System (ADS)

Yeniçeri, Ramazan; Yalçın, Müstak E.

2009-05-01

This paper introduces a simple algorithm to solve robot path finding problem using active wave computing techniques. A two-dimensional Cellular Neural/Nonlinear Network (CNN), consist of relaxation oscillators, has been used to generate active waves and to process the visual information. The network, which has been implemented on a Field Programmable Gate Array (FPGA) chip, has the feature of being programmed, controlled and observed by a host computer. The arena of the robot is modelled as the medium of the active waves on the network. Active waves are employed to cover the whole medium with their own dynamics, by starting from an initial point. The proposed algorithm is achieved by observing the motion of the wave-front of the active waves. Host program first loads the arena model onto the active wave generator network and command to start the generation. Then periodically pulls the network image from the generator hardware to analyze evolution of the active waves. When the algorithm is completed, vectorial data image is generated. The path from any of the pixel on this image to the active wave generating pixel is drawn by the vectors on this image. The robot arena may be a complicated labyrinth or may have a simple geometry. But, the arena surface always must be flat. Our Autowave Generator CNN implementation which is settled on the Xilinx University Program Virtex-II Pro Development System is operated by a MATLAB program running on the host computer. As the active wave generator hardware has 16, 384 neurons, an arena with 128 × 128 pixels can be modeled and solved by the algorithm. The system also has a monitor and network image is depicted on the monitor simultaneously.

Antarctic NAT PSC Belt of June 2003: Observational Validation of the Mountain Wave Seeding Hypothesis

NASA Technical Reports Server (NTRS)

Eckermann, S. D.; Hoffmann, L.; Hoepfner, M.; Wu, D. L.; Alexander, M. J.

2009-01-01

Satellite observations of polar stratospheric clouds (PSCs) over Antarctica in June 2003 revealed small nitric acid trihydrate (NAT) particles forming suddenly along the vortex edge. Models suggest the trigger was mountain waves over the Antarctic Peninsula (AP) forming ice for NAT nucleation. We test this hypothesis by analyzing perturbations in stratospheric radiances from the Atmospheric Infrared Sounder (AIRS). AIRS data show mountain waves over the AP on 10-14 June, with no resolved wave activity before or after. Peak wave temperature amplitudes derived from independent 40 hPa channels all return values of 10-12 K, in agreement with values used to model this NAT event. These observations support a NAT wake from a small region of mountain wave activity over the AP as the source of this circumpolar NAT outbreak.

Rayleigh lidar observations of gravity wave activity in the upper stratosphere at Urbana, Ill.

NASA Technical Reports Server (NTRS)

Gardner, C. S.; Miller, M. S.; Liu, C. H.

1988-01-01

During 13 nights of Rayleigh lidar measurements at Urbana, Ill. in 1984 to 1986, thirty-six quasi-monochromatic gravity waves were observed in the 35 to 50 km altitude region of the stratosphere. The characteristics of the waves are compared with other lidar and radar measurements of gravity waves and the theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths ranged from 2 to 11.5 km and the measured vertical phase velocities ranged from 10 to 85 cm/s. The vertical wavelengths and vertical phase velocities were used to infer observed wave periods which ranged from 100 to 1000 min and horizontal wavelengths which ranged from 70 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No significant seasonal variations were evident in the observed parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with wave periods, which is consistent with recent sodium lidar studies of quasi-monochromatic waves near the mesopause. An average amplitude growth length of 20.9 km for the rms wind perturbations was estimated from the data. Kinetic energy density associated with the waves decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

Synoptic-scale variability of arctic gravity wave activity during summer and potential impacts on the high latitude middle atmosphere

NASA Astrophysics Data System (ADS)

Gerrard, Andrew John

Although the role of gravity waves in the global atmospheric circulation is generally understood, discussion of synoptic gravity wave activity, especially pertaining to high latitude summer environments, is lacking in the literature. Tropospherically generated gravity waves greatly contribute to the zonal drag necessary to induce meridional outflow and subsequent upwelling observed in the adiabatically cooled summer mesosphere, ultimately resulting in an environment conducive to mesospheric cloud formation. However, the very gravity wave activity responsible for this induced cooling is also believed to be a major source of variability on mesospheric clouds over shorter time scales, and this topic should be of considerable interest if such clouds are to be used as tracers of the global climate. It is therefore the purpose of this thesis to explore high latitude synoptic gravity wave activity and ultimately seek an understanding of the associated influence on overlaying summer mesospheric clouds. Another goal is to better understand and account for potential variability in high latitude middle and upper atmospheric measurements that can be directly associated with "weather conditions" at lower altitudes. These endeavors are addressed through Rayleigh/aerosol lidar data obtained from the ARCtic LIdar TEchnology (ARCLITE) facility located at Sondrestrom, Greenland (67°N, 310°E), global tropospheric and stratospheric analyses and forecasts, and the Gravity-wave Regional Or Global RAy Tracer (GROGRAT) model. In this study we are able to show that (a) the upper stratospheric gravity wave strength and the brightness of overlaying mesospheric clouds, as measured by representative field proxies, are negatively correlated over time scales of less than a day, (b) such upper stratospheric gravity wave variability is inversely related to mesospheric cloud variability on time scales of ˜1 to 4 hours, (c) gravity wave hindcasts faithfully reproduce experimental lidar observations taken over the month of August 1996, (d) the observed upper stratospheric gravity wave activity is shown to originate from regionalized, non-orographic sources in the troposphere, (e) such gravity wave activity can propagate through the middle atmosphere, potentially impacting overlaying mesospheric clouds, and (f) the forecasting of such upper stratospheric gravity wave activity, and therefore the corresponding mesospheric cloud activity, is feasible. In conclusion, the results herein provide additional evidence of gravity wave influence on mesospheric clouds, a step towards the forecasting of regional gravity wave activity, and ultimately a better understanding of synoptic gravity wave activity at high latitudes.

Observations of thunderstorm-related 630 nm airglow depletions

NASA Astrophysics Data System (ADS)

Kendall, E. A.; Bhatt, A.

2015-12-01

The Midlatitude All-sky imaging Network for Geophysical Observations (MANGO) is an NSF-funded network of 630 nm all-sky imagers in the continental United States. MANGO will be used to observe the generation, propagation, and dissipation of medium and large-scale wave activity in the subauroral, mid and low-latitude thermosphere. This network is actively being deployed and will ultimately consist of nine all-sky imagers. These imagers form a network providing continuous coverage over the western United States, including California, Oregon, Washington, Utah, Arizona and Texas extending south into Mexico. This network sees high levels of both medium and large scale wave activity. Apart from the widely reported northeast to southwest propagating wave fronts resulting from the so called Perkins mechanism, this network observes wave fronts propagating to the west, north and northeast. At least three of these anomalous events have been associated with thunderstorm activity. Imager data has been correlated with both GPS data and data from the AIRS (Atmospheric Infrared Sounder) instrument on board NASA's Earth Observing System Aqua satellite. We will present a comprehensive analysis of these events and discuss the potential thunderstorm source mechanism.

Mesoscale Variability in SUCCESS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.

1998-01-01

Analysis of meteorological, chemical, and microphysical data from the airborne SUCCESS mission is reported. Careful analysis of the complex DC-8 flight pattern of May 2, 1996 reveals 19 linear or nearly linear flight segments within six main geographical areas, which we have analyzed. Significant mountain wave activity is revealed in the data from the MMS and MTP instruments on the DC-8, which resembles previous observations of mountain wave structures near Boulder, CO. Strong mountain-wave-induced upwelling downwind of the Rockies is noted. Turbulence is also noted in regions of the mountain wave consistent with overturning near the tropopause. Zonal winds recorded on the ER-2 are shown to consistent with mountain wave breaking at or near critical levels in the stratosphere, consistent with the strong turbulence reported by the pilot during the ER-2 flight. Those observations have been supported with spectral analyses and modeling studies. "Postcasts" of mountain wave activity on May 2, 1996, using the Naval Research Laboratory Mountain Wave Forecast Model (NRL/MWFM) predicts both strong mountain wave activity near the tropopause (as measured by the DC-8) and strong mountain-wave-induced turbulence in the stratosphere (as encountered by the ER-2). Two-dimensional simulations of fluid flow over topography reveal similar isentropic structures to observations.

Facilitating Heliophysics Research by the Virtual Wave Observatory (VWO) Context Data Search Capability

NASA Technical Reports Server (NTRS)

Fung, Shing F.; Shao, Xi; Garcia, Leonard N.; Galkin, Ivan A.; Benson, Robert F.

2009-01-01

Wave phenomena, ranging from freely propagating electromagnetic radiation (e.g., solar radio bursts, AKR) to plasma wave modes trapped in various plasma regimes (e.g., whistlers, Langmuir and ULF waves) and atmospheric gravity waves, are ubiquitous in the heliosphere. Because waves can propagate, wave data obtained at a given observing location may pertain to wave oscillations generated locally or from afar. While wave data analysis requires knowledge of wave characteristics specific to different wave modes, the search for appropriate data for heliophysics wave studies also requires knowledge of wave phenomena. In addition to deciding whether the interested wave activity is electrostatic (i.e., locally trapped) or electromagnetic (with propagation over distances), considerations must be given to the dependence of the wave activity on observer's location or viewing geometry, propagating frequency range and whether the wave data were acquired by passive or active observations. Occurances of natural wave emissions i the magnetosphere (e.g, auroral kilometric radiation) are often dependent also on the state (e.e., context) of the magnetosphere that varies with the changing solar wind, IMF and geomagnetic conditions. Fung and Shao [2008] showed recently that magnetospheric state can be specified by a set of suitably time-shifted solar wind, IMF and the multi-scale geomagnetic response parameters. These parameters form a magnetospheric state vector that provides the basis for searching magnetospheric wave data by their context conditions. Using the IMAGE Radio Plasma Imager (RPI) data and the NASA Magnetospheric State Query System (MSOS) [Fung, 2004], this presentation demonstrates the VWO context data search capability under development and solicits feedback from the Heliophysics research community for improvements.

Seasonal variation of wave activities near the mesopause region observed at King Sejong Station (62.22°S, 58.78°W), Antarctica

NASA Astrophysics Data System (ADS)

Lee, Changsup; Kim, Yong Ha; Kim, Jeong-Han; Jee, Geonhwa; Won, Young-In; Wu, Dong L.

2013-12-01

We analyzed the neutral wind data at altitudes of 80-100 km obtained from a VHF meteor radar at King Sejong Station (KSS, 62.22°S, 58.78°W), a key location to study wave activities above the stratospheric vortex near the Antarctic Peninsula. The seasonal behavior of the semidiurnal tides is generally consistent with the prediction of Global Scale Wave Model (GSWM02) except in the altitude region above ~96 km. Gravity wave (GW) activities inferred from the neutral wind variances show a seasonal variation very similar to the semidiurnal tide amplitudes, suggesting a strong interaction between gravity waves and the tide. Despite the consistent seasonal variations of the GW wind variances observed at the adjacent Rothera station, the magnitudes of the wind variance obtained at KSS are much larger than those at Rothera, especially during May-September. The enhanced GW activity at KSS is also observed by Aura Microwave Limb Sounder (MLS) from space in its temperature variance. The observed large wind variances at KSS imply that the Antarctic vortex in the stratosphere may act as an effective filter and source for the GWs in the upper atmosphere.

Observational Evidence Against Mountain-Wave Generation of Ice Nuclei as a Prerequisite for the Formation of Three Solid Nitric Acid Polar Stratospheric Clouds Observed in the Arctic in Early December 1999

NASA Technical Reports Server (NTRS)

Pagan, Kathy L.; Tabazadeh, Azadeh; Drdla, Katja; Hervig, Mark E.; Eckermann, Stephen D.; Browell, Edward V.; Legg, Marion J.; Foschi, Patricia G.

2004-01-01

A number of recently published papers suggest that mountain-wave activity in the stratosphere, producing ice particles when temperatures drop below the ice frost point, may be the primary source of large NAT particles. In this paper we use measurements from the Advanced Very High Resolution Radiometer (AVHRR) instruments on board the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites to map out regions of ice clouds produced by stratospheric mountain-wave activity inside the Arctic vortex. Lidar observations from three DC-8 flights in early December 1999 show the presence of solid nitric acid (Type Ia or NAT) polar stratospheric clouds (PSCs). By using back trajectories and superimposing the position maps on the AVHRR cloud imagery products, we show that these observed NAT clouds could not have originated at locations of high-amplitude mountain-wave activity. We also show that mountain-wave PSC climatology data and Mountain Wave Forecast Model 2.0 (MWFM-2) raw hemispheric ray and grid box averaged hemispheric wave temperature amplitude hindcast data from the same time period are in agreement with the AVHRR data. Our results show that ice cloud formation in mountain waves cannot explain how at least three large scale NAT clouds were formed in the stratosphere in early December 1999.

MMS Observations of Ion-Scale Magnetic Island in the Magnetosheath Turbulent Plasma

NASA Technical Reports Server (NTRS)

Huang, S. Y.; Sahraoui, F.; Retino, A.; Contel, O. Le; Yuan, Z. G.; Chasapis, A.; Aunai, N.; Breuillard, H.; Deng, X. H.; Zhou, M.;

Propagating wave in active region-loops, located over the solar disk observed by the Interface Region Imaging Spectrograph

NASA Astrophysics Data System (ADS)

Zhang, B.; Hou, Y. J.; Zhang, J.

2018-03-01

Aims: We aim to ascertain the physical parameters of a propagating wave over the solar disk detected by the Interface Region Imaging Spectrograph (IRIS). Methods: Using imaging data from the IRIS and the Solar Dynamic Observatory (SDO), we tracked bright spots to determine the parameters of a propagating transverse wave in active region (AR) loops triggered by activation of a filament. Deriving the Doppler velocity of Si IV line from spectral observations of IRIS, we have determined the rotating directions of active region loops which are relevant to the wave. Results: On 2015 December 19, a filament was located on the polarity inversion line of the NOAA AR 12470. The filament was activated and then caused a C1.1 two-ribbon flare. Between the flare ribbons, two rotation motions of a set of bright loops were observed to appear in turn with opposite directions. Following the end of the second rotation, a propagating wave and an associated transverse oscillation were detected in these bright loops. In 1400 Å channel, there was bright material flowing along the loops in a wave-like manner, with a period of 128 s and a mean amplitude of 880 km. For the transverse oscillation, we tracked a given loop and determine the transverse positions of the tracking loop in a limited longitudinal range. In both of 1400 Å and 171 Å channels, approximately four periods are distinguished during the transverse oscillation. The mean period of the oscillation is estimated as 143 s and the displacement amplitude as between 1370 km and 690 km. We interpret these oscillations as a propagating kink wave and obtain its speed of 1400 km s-1. Conclusions: Our observations reveal that a flare associated with filament activation could trigger a kink propagating wave in active region loops over the solar disk. Movies associated to Figs. 1-4 are available at http://https://www.aanda.org

Observation of severe weather activities by Doppler sounder array

NASA Technical Reports Server (NTRS)

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

1975-01-01

A three-dimensional, nine-element, high-frequency CW Doppler sounder array has been used to detect ionospheric disturbances during periods of severe weather, particularly during periods with severe thunderstorms and tornadoes. One typical disturbance recorded during a period of severe thunderstorm activity and one during a period of tornado activity have been chosen for analysis in this note. The observations indicate that wave-like disturbances possibly generated by the severe weather have wave periods in the range 2-8 min which place them in the infrasonic wave category.

A Model Simulation of Mountain Waves in the Middle Atmosphere and Its Comparison with Microwave Limb Sounder Observations

NASA Astrophysics Data System (ADS)

Jiang, J. H.; Eckermann, S. D.; Wu, D. L.; Ma, J.; Wang, D. Y.

2003-04-01

Topography-related wintertime stratospheric gravity waves in both Northern and Southern Hemisphere are simulated using the Naval Research Laboratory Mountain Wave Forecast Model (MWFM). The results agree well with the observations from Upper Atmospheric Research Satellite Microwave Limb Sounder (MLS). Both the MWFM simulation and MLS observations found strong wave activities over the high-latitude mountain ridges of Scandinavia, Central Eurasia, Alaska, southern Greenland in Northern Hemisphere, and Andes, New Zealand, Antarctic rim in Southern Hemisphere. These mountain waves are dominated by wave modes with downward phase progression and horizontal phase velocities opposite to the stratospheric jet-stream. Agreements of minor wave activities are also found at low- to mid-latitudes over Zagros Mountains of Middle East, Colorado Rocky Mountains, Appalachians, and Sierra Madres of Central America. Some differences between the MWFM results and MLS data are explained by different horizontal resolution between the model and observation, and the fact that MLS may also see the non-orographic wave sources, such as mesoscale storms and jet-stream instabilities. The findings from this model-measurement comparison study demonstrate that satellite instruments such as MLS can provide global data needed to characterize mountain wave sources, their inter-annual variations, and to improve gravity wave parameterizations in global climate and forecast models.

Direct evidence for EMIC wave scattering of relativistic electrons in space: EMIC-Driven Electron Losses in Space

DOE PAGES

Zhang, X. -J.; Li, W.; Ma, Q.; ...

2016-07-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes.more » EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. In conclusion, by comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave-driven relativistic electron losses in the Earth’s outer radiation belt.« less

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

NASA Astrophysics Data System (ADS)

Zaqarashvili, Teimuraz

2018-03-01

The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20°–40°, coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90–100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1–2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magneto-inertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

Nonlinear Electron Acoustic Waves in the Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Dillard, C. S.; Vasko, I.; Mozer, F.; Agapitov, O. V.

2017-12-01

The Van Allen Probes observe intense broad-band electrostatic wave activity in the inner magnetosphere. The high-resolution electric field measurements show that these broad-band wave activity is made of large-amplitude electrostatic solitary waves propagating generally along the background magnetic field with velocities of a few thousands km/s. There are generally two types of the observed solitary waves. The solitary waves with the bipolar parallel electric field are interpreted as electron phase space holes, while the nature of solitary waves with asymmetric parallel electric field has remained puzzling. In the present work we show that asymmetric solitary waves propagate with velocities (1000-5000 km/s) and have spatial scales (100 m-1 km) similar to those for electron-acoustic waves existing due to two temperature electron population. Through the numerical fluid simulation we show that the spikes are produced from the initially harmonic electron-acoustic perturbation due to the nonlinear steepening. Through the analysis of the modified KdV equation we show that the steepening is arrested at some moment by the collisionless Landau dissipation and results in formation of the observed asymmetric spikes (shocklets).

Kelvin Wave Influence on the Shallow-to-Deep Transition Over the Amazon

NASA Astrophysics Data System (ADS)

Rowe, A.; Serra, Y. L.

2017-12-01

The suite of observations from GOAmazon and CHUVA offers a unique opportunity to examine land-based convective processes in the tropics, including the poorly represented shallow-to-deep transition. This study uses these data to investigate impacts of Kelvin waves on the the shallow-to-deep transition over the Central Amazon. The Kelvin waves that propagate over the region often originate over the tropical central and east Pacific, with local generation over the Andes also observed. The observed 15 m s-1 phase speed and 4500 km wave length during the two-year campaign are in agreement with previously published studies of these waves across the tropics. Also in agreement with previous studies, we find the waves are most active during the wet season (November-May) for this region. Using four separate convective event classes (clear-sky, nonprecipitating cumulus congestus, afternoon deep convection, and mesoscale convective systems), we examine how the convection preferentially develops for different phases of the Kelvin waves seen during GOAmazon. We additionally examine surface meteorological variables, the vertical thermodynamic and dynamic structure of the troposphere, vertical moist static stability, integrated column water vapor and liquid water, and surface energy fluxes within the context of these convective classes to identify the important environmental factors contributing to observed periods of enhanced deep convection related to the waves. Results suggest that the waves significantly modify the local environment, such as creating a deep layer of moisture throughout the troposphere, favoring more organized convection in the active than in the suppressed phase of the wave. The significance of wave-related environmental modifications are assessed by comparing local rainfall accumulations during Kelvin wave activity to that when the waves are not present. Future work will further explore the shallow-to-deep transition and its modulation by Kelvin wave activity over the Central Amazon in both global and regional model simulations with differing resolution and choice of convective parameterization. This work will test the hypothesis that when the environment is strongly modified by a Kelvin wave, model shallow-to-deep transition will be better simulated than when this forcing is not present.

A morphological study of waves in the thermosphere using DE-2 observations

NASA Technical Reports Server (NTRS)

Gross, S. H.; Kuo, S. P.; Shmoys, J.

1986-01-01

Theoretical model and data analysis of DE-2 observations for determining the correlation between the neutral wave activity and plasma irregularities have been presented. The relationships between the observed structure of the sources, precipitation and joule heating, and the fluctuations in neutral and plasma parameters are obtained by analyzing two measurements of neutral atmospheric wave activity and plasma irregularities by DE-2 during perigee passes at an altitude on the order of 300 to 350 km over the polar cap. A theoretical model based on thermal nonlinearity (joule heating) to give mode-mode coupling is developed to explore the role of neutral disturbance (winds and gravity waves) on the generation of plasma irregularities.

Seasonal variability of convectively coupled equatorial waves (CCEWs) in recent high-top CMIP5 models

NASA Astrophysics Data System (ADS)

Zakaria, Dzaki; Lubis, Sandro W.; Setiawan, Sonni

2018-05-01

Tropical weather system is controlled by periodic atmospheric disturbances ranging from daily to subseasonal time scales. One of the most prominent atmospheric disturbances in the tropics is convectively coupled equatorial waves (CCEWs). CCEWs are excited by latent heating due to a large-scale convective system and have a significant influence on weather system. They include atmospheric equatorial Kelvin wave, Mixed Rossby Gravity (MRG) wave, Equatorial Rossby (ER) wave and Tropical Depression (TD-type) wave. In this study, we will evaluate the seasonal variability of CCEWs activity in nine high-top CMIP5 models, including their spatial distribution in the troposphere. Our results indicate that seasonal variability of Kelvin waves is well represented in MPI-ESM-LR and MPI-ESM-MR, with maximum activity occurring during boreal spring. The seasonal variability of MRG waves is well represented in CanESM2, HadGEM2-CC, IPSL-CM5A-LR and IPSL-CM5A-MR, with maximum activity observed during boreal summer. On the other hand, ER waves are well captured by IPSL-CM5A-LR and IPSL-CM5A-MR and maximize during boreal fall; while TD-type waves, with maximum activity observed during boreal summer, are well observed in CanESM2, HadGEM2-CC, IPSL-CM5A-LR and IPSL-CM5A-MR. Our results indicate that the skill of CMIP5 models in representing seasonal variability of CCEWs highly depends on the convective parameterization and the spatial or vertical resolution used by each model.

Electron flat-top distributions and cross-scale wave modulations observed in the current sheet of geomagnetic tail

NASA Astrophysics Data System (ADS)

Zhao, Duo; Fu, Suiyan; Parks, George K.; Sun, Weijie; Zong, Qiugang; Pan, Dongxiao; Wu, Tong

2017-08-01

We present new observations of electron distributions and the accompanying waves during the current sheet activities at ˜60 RE in the geomagnetic tail detected by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) spacecraft. We find that electron flat-top distribution is a common feature near the neutral sheet of the tailward flowing plasmas, consistent with the electron distributions that are shaped in the reconnection region. Whistler mode waves are generated by the anisotropic electron temperature associated with the electron flat-top distributions. These whistler mode waves are modulated by low frequency ion scale waves that are possibly excited by the high-energy ions injected during the current sheet instability. The magnetic and electric fields of the ion scale waves are in phase with electron density variations, indicating that they are compressional ion cyclotron waves. Our observations present examples of the dynamical processes occurring during the current sheet activities far downstream of the geomagnetic tail.

Stratospheric gravity waves at southern hemisphere orographic hotspots: 2003-2014 AIRS/Aqua observations

NASA Astrophysics Data System (ADS)

Hoffmann, Lars; Grimsdell, Alison W.; Alexander, M. Joan

2017-04-01

Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behaviour of the southern hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003 - 2014) of stratospheric gravity wave activity at southern hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA's) Aqua satellite. We introduce a simple and effective approach, referred to as the 'two-box method', to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid fall to mid spring (April - October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90%), followed by the Antarctic Peninsula (76%), Kerguelen Islands (73%), Tasmania (70%), New Zealand (67%), Heard Island (60%), and other hotspots (24 - 54%). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 hPa and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60% with mean absolute errors of 4 - 5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation. Reference: Hoffmann, L., Grimsdell, A. W., and Alexander, M. J.: Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003-2014 AIRS/Aqua observations, Atmos. Chem. Phys., 16, 9381-9397, doi:10.5194/acp-16-9381-2016, 2016.

Cluster Observations of Non-Time Continuous Magnetosonic Waves

NASA Technical Reports Server (NTRS)

Walker, Simon N.; Demekhov, Andrei G.; Boardsen, Scott A.; Ganushkina, Natalia Y.; Sibeck, David G.; Balikhin, Michael A.

2016-01-01

Equatorial magnetosonic waves are normally observed as temporally continuous sets of emissions lasting from minutes to hours. Recent observations, however, have shown that this is not always the case. Using Cluster data, this study identifies two distinct forms of these non temporally continuous use missions. The first, referred to as rising tone emissions, are characterized by the systematic onset of wave activity at increasing proton gyroharmonic frequencies. Sets of harmonic emissions (emission elements)are observed to occur periodically in the region +/- 10 off the geomagnetic equator. The sweep rate of these emissions maximizes at the geomagnetic equator. In addition, the ellipticity and propagation direction also change systematically as Cluster crosses the geomagnetic equator. It is shown that the observed frequency sweep rate is unlikely to result from the sideband instability related to nonlinear trapping of suprathermal protons in the wave field. The second form of emissions is characterized by the simultaneous onset of activity across a range of harmonic frequencies. These waves are observed at irregular intervals. Their occurrence correlates with changes in the spacecraft potential, a measurement that is used as a proxy for electron density. Thus, these waves appear to be trapped within regions of localized enhancement of the electron density.

The Role of Gravity Waves in the Formation and Organization of Clouds during TWPICE

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

Reeder, Michael J.; Lane, Todd P.; Hankinson, Mai Chi Nguyen

2013-09-27

All convective clouds emit gravity waves. While it is certain that convectively-generated waves play important parts in determining the climate, their precise roles remain uncertain and their effects are not (generally) represented in climate models. The work described here focuses mostly on observations and modeling of convectively-generated gravity waves, using the intensive observations from the DoE-sponsored Tropical Warm Pool International Cloud Experiment (TWP-ICE), which took place in Darwin, from 17 January to 13 February 2006. Among other things, the research has implications the part played by convectively-generated gravity waves in the formation of cirrus, in the initiation and organization ofmore » further convection, and in the subgrid-scale momentum transport and associated large-scale stresses imposed on the troposphere and stratosphere. The analysis shows two groups of inertia-gravity waves are detected: group L in the middle stratosphere during the suppressed monsoon period, and group S in the lower stratosphere during the monsoon break period. Waves belonging to group L propagate to the south-east with a mean intrinsic period of 35 h, and have vertical and horizontal wavelengths of about 5-6 km and 3000-6000 km, respectively. Ray tracing calculations indicate that these waves originate from a deep convective region near Indonesia. Waves belonging to group S propagate to the south-south-east with an intrinsic period, vertical wavelength and horizontal wavelength of about 45 h, 2 km and 2000-4000 km, respectively. These waves are shown to be associated with shallow convection in the oceanic area within about 1000 km of Darwin. The intrinsic periods of high-frequency waves are estimated to be between 20-40 minutes. The high-frequency wave activity in the stratosphere, defined by mass-weighted variance of the vertical motion of the sonde, has a maximum following the afternoon local convection indicating that these waves are generated by local convection. The wave activity is strongest in the lower stratosphere below 22 km and, during the suppressed monsoon period, is modulated with a 3-4-day period. The concentration of the wave activity in the lower stratosphere is consistent with the properties of the environment in which these waves propagate, whereas its 3-4-day modulation is explained by the variation of the convection activity in the TWP-ICE domain. At low rainfall intensity the wave activity increases as rainfall intensity increases. At high values of rainfall intensity, however, the wave activity associated with deep convective clouds is independent of the rainfall intensity. The convection and gravity waves observed during TWP-ICE are simulated with the Weather Research and Forecasting (WRF) Model. These simulations are compared with radiosonde observations described above and are used to determine some of the properties of convectively generated gravity waves. The gravity waves appear to be well simulated by the model. The model is used to explore the relationships between the convection, the gravity waves and cirrus.« less

EMIC Wave Scale Size in the Inner Magnetosphere: Observations From the Dual Van Allen Probes

NASA Technical Reports Server (NTRS)

Blum, L. W.; Bonnell, J. W.; Agapitov, O.; Paulson, K.; Kletzing, C.

2017-01-01

Estimating the spatial scales of electromagnetic ion cyclotron (EMIC) waves is critical for quantifying their overall scattering efficiency and effects on thermal plasma, ring current, and radiation belt particles. Using measurements from the dual Van Allen Probes in 2013-2014, we characterize the spatial and temporal extents of regions of EMIC wave activity and how these depend on local time and radial distance within the inner magnetosphere. Observations are categorized into three types: waves observed by only one spacecraft, waves measured by both spacecraft simultaneously, and waves observed by both spacecraft with some time lag. Analysis reveals that dayside (and H+ band) EMIC waves more frequently span larger spatial areas, while nightside (and He+ band) waves are more often localized but can persist many hours. These investigations give insight into the nature of EMIC wave generation and support more accurate quantification of their effects on the ring current and outer radiation belt.

EMIC wave scale size in the inner magnetosphere: Observations from the dual Van Allen Probes

NASA Astrophysics Data System (ADS)

Blum, L. W.; Bonnell, J. W.; Agapitov, O.; Paulson, K.; Kletzing, C.

2017-02-01

Estimating the spatial scales of electromagnetic ion cyclotron (EMIC) waves is critical for quantifying their overall scattering efficiency and effects on thermal plasma, ring current, and radiation belt particles. Using measurements from the dual Van Allen Probes in 2013-2014, we characterize the spatial and temporal extents of regions of EMIC wave activity and how these depend on local time and radial distance within the inner magnetosphere. Observations are categorized into three types—waves observed by only one spacecraft, waves measured by both spacecraft simultaneously, and waves observed by both spacecraft with some time lag. Analysis reveals that dayside (and H+ band) EMIC waves more frequently span larger spatial areas, while nightside (and He+ band) waves are more often localized but can persist many hours. These investigations give insight into the nature of EMIC wave generation and support more accurate quantification of their effects on the ring current and outer radiation belt.

Using Forecast and Observed Weather Data to Assess Performance of Forecast Products in Identifying Heat Waves and Estimating Heat Wave Effects on Mortality

PubMed Central

Chen, Yeh-Hsin; Schwartz, Joel D.; Rood, Richard B.; O’Neill, Marie S.

2014-01-01

Background: Heat wave and health warning systems are activated based on forecasts of health-threatening hot weather. Objective: We estimated heat–mortality associations based on forecast and observed weather data in Detroit, Michigan, and compared the accuracy of forecast products for predicting heat waves. Methods: We derived and compared apparent temperature (AT) and heat wave days (with heat waves defined as ≥ 2 days of daily mean AT ≥ 95th percentile of warm-season average) from weather observations and six different forecast products. We used Poisson regression with and without adjustment for ozone and/or PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) to estimate and compare associations of daily all-cause mortality with observed and predicted AT and heat wave days. Results: The 1-day-ahead forecast of a local operational product, Revised Digital Forecast, had about half the number of false positives compared with all other forecasts. On average, controlling for heat waves, days with observed AT = 25.3°C were associated with 3.5% higher mortality (95% CI: –1.6, 8.8%) than days with AT = 8.5°C. Observed heat wave days were associated with 6.2% higher mortality (95% CI: –0.4, 13.2%) than non–heat wave days. The accuracy of predictions varied, but associations between mortality and forecast heat generally tended to overestimate heat effects, whereas associations with forecast heat waves tended to underestimate heat wave effects, relative to associations based on observed weather metrics. Conclusions: Our findings suggest that incorporating knowledge of local conditions may improve the accuracy of predictions used to activate heat wave and health warning systems. Citation: Zhang K, Chen YH, Schwartz JD, Rood RB, O’Neill MS. 2014. Using forecast and observed weather data to assess performance of forecast products in identifying heat waves and estimating heat wave effects on mortality. Environ Health Perspect 122:912–918; http://dx.doi.org/10.1289/ehp.1306858 PMID:24833618

Spatio-Temporal Evolutions of Non-Orthogonal Equatorial Wave Modes Derived from Observations

NASA Astrophysics Data System (ADS)

Barton, C.; Cai, M.

2015-12-01

Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCF), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. In this study, we propose a methodology that seeks to identify individual wave modes in instantaneous fields of observations by determining their projections on PCF modes according to the equatorial wave theory. The new method has the benefit of yielding a closed system with a unique solution for all waves' spatial structures, including IG waves, for a given instantaneous observed field. We have applied our method to the ERA-Interim reanalysis dataset in the tropical stratosphere where the wave-mean flow interaction mechanism for the quasi-biennial oscillation (QBO) is well-understood. We have confirmed the continuous evolution of the selection mechanism for equatorial waves in the stratosphere from observations as predicted by the theory for the QBO. This also validates the proposed method for decomposition of observed tropical wave fields into non-orthogonal equatorial wave modes.

The Properties of Large Amplitude Whistler Mode Waves in the Magnetosphere: Propagation and Relationship with Geomagnetic Activity

NASA Technical Reports Server (NTRS)

Wilson, L. B., III; Cattell, C. A.; Kellogg, P. J.; Wygant, J. R.; Goetz, K.; Breneman, A.; Kersten, K.

2011-01-01

Wepresent resultsof a studyof the characteristicsof very large amplitude whistler mode waves inside the terrestrial magnetosphere at radial distances of less than 15 RE using waveform capture data from the Wind spacecraft. We observed 247 whistler mode waves with at least one electric field component (105/247 had !80 mV/m peak!to!peak amplitudes) and 66 whistler mode waves with at least one search coil magnetic field component (38/66 had !0.8 nT peak!to!peak amplitudes). Wave vectors determined from events with three magnetic field components indicate that 30/46 propagate within 20 of the ambient magnetic field, though some are more oblique (up to "50 ). No relationship was observed between wave normal angle and GSM latitude. 162/247 of the large amplitude whistler mode waves were observed during magnetically active periods (AE > 200 nT). 217 out of 247 total whistler mode waves examined were observed inside the radiation belts. We present a waveform capture with the largest whistler wave magnetic field amplitude (^8 nT peak!to!peak) ever reported in the radiation belts. The estimated Poynting flux magnitude associated with this wave is ^300 mW/m2, roughly four orders of magnitude above estimates from previous satellite measurements. Such large Poynting flux values are consistent with rapid energization of electrons.

Direct Evidence of EMIC-Driven Electron Loss in Space: Evaluation of an Electron Dropout Event

NASA Astrophysics Data System (ADS)

Zhang, X.; Li, W.; Ma, Q.; Thorne, R. M.; Angelopoulos, V.

2015-12-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed as a mechanism to cause efficient losses of highly relativistic (>MeV) electrons via gyroresonant interactions. However, simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited. In the present study, we evaluate the effect of EMIC waves on the pitch angle scattering of relativistic and ultrarelativistic (0.5-5 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both the Van Allen Probes and one of the THEMIS probes. EMIC waves captured on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) and enhanced precipitation of >~0.7 MeV electrons captured by POES are used to infer the MLT coverage of EMIC waves. Based on the observed EMIC wave spectra, local fpe and fce, we estimate the wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing the modeled results with local observations of pitch angle distributions, for the first time, we are able to show direct, quantitative evidence of EMIC wave-driven relativistic electron loss in the Earth's outer radiation belt.

Van Allen Probe Observations of Chorus Wave Activity, Source and Seed electrons, and the Radiation Belt Response During ICME and CIR Storms

NASA Astrophysics Data System (ADS)

Bingham, S.; Mouikis, C.; Kistler, L. M.; Farrugia, C. J.; Paulson, K. W.; Huang, C. L.; Boyd, A. J.; Spence, H. E.; Kletzing, C.

2017-12-01

Whistler mode chorus waves are electromagnetic waves that have been shown to be a major contributor to enhancements in the outer radiation belt during geomagnetic storms. The temperature anisotropy of source electrons (10s of keV) provides the free energy for chorus waves, which can accelerate sub-relativistic seed electrons (100s of keV) to relativistic energies. This study uses Van Allen Probe observations to examine the excitation and plasma conditions associated with chorus wave observations, the development of the seed population, and the outer radiation belt response in the inner magnetosphere, for 25 ICME and 35 CIR storms. Plasma data from the Helium Oxygen Proton Electron (HOPE) instrument and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) are used to identify chorus wave activity and to model a linear theory based proxy for chorus wave growth. A superposed epoch analysis shows a peak of chorus wave power on the dawnside during the storm main phase that spreads towards noon during the storm recovery phase. According to the linear theory results, this wave activity is driven by the enhanced convection driving plasma sheet electrons across the dayside. Both ICME and CIR storms show comparable levels of wave growth. Plasma data from the Magnetic Electron Ion Spectrometer (MagEIS) and the Relativistic Electron Proton Telescope (REPT) are used to observe the seed and relativistic electrons. A superposed epoch analysis of seed and relativistic electrons vs. L shows radiation belt enhancements with much greater frequency in the ICME storms, coinciding with a much stronger and earlier seed electron enhancement in the ICME storms.

Evolution of Photon and Particle Spectra in Compact, Luminous Objects

NASA Technical Reports Server (NTRS)

Eilek, Jean A.; Caroff, Lawrence J.

1995-01-01

Physical conditions in the radiating plasma in the cores of radio-strong quasars and active galactic nuclei cannot be derived from observations until the effects of relativistic aberration are understood. This requires determining both the bulk flow speeds and any wave or signal speed in the parsec-scale nuclear jets. In this project we studied several aspects of such waves. We considered constraints on jet deceleration by mass pickup, and found that bolometric luminosities of the active nuclei cannot constrain core jet speeds usefully. We also simulated observations of ballistic, helical trajectories and helical waves moving directly outwards along the jet. We found that ballistic trajectories are not allowed by the data; the helical features seen are very likely to be helical waves. We believe these are waves propagating in the jet plasma. To this end, we studied waves propagating in relativistic pair plasma jets. In particular, we undertook a program whose goal was to determine the nature of waves which can propagate in relativistic pair plasmas, and how such waves propagating in streaming jet plasma would be observed by an external observer. We developed the possibility of using pulsars as test cases for our models; this takes advantage of new technology in pulsar observations, and the similarity of the physical conditions in the pulsar magnetosphere to the dense, relativistic pair plasmas which exist in radio-strong quasars.

Mesoscale Variability in SUCCESS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Stewart, Richard W. (Technical Monitor)

1998-01-01

Analysis of meteorological, chemical and microphysical data from the airborne SUCCESS (SUbsonic aircraft Contrail and Cloud Effects Special Study) mission is reported. Careful analysis of the complex DC-8 flight pattern of May 2, 1996 reveals 19 linear flight segments within six main geographical areas, which we have analyzed. Significant mountain wave activity is revealed in the data from the MMS (Meteorology Measurement System) and MTP (Microwave Temperature Profiler) instruments on the DC-8, which resembles previous observations of mountain wave structures near Boulder, Colorado. Strong mountain-wave-induced upwelling downwind of the Rockies is noted. Turbulence is also noted in regions of the mountain wave consistent with overturning near the tropopause. Zonal winds recorded on the ER-2 are shown to be consistent with mountain wave breaking at or near critical levels in the stratosphere, consistent with the strong turbulence reported by the pilot during the ER-2 flight. These observations have been supported with spectral analyses and modeling studies. 'Postcasts' of mountain wave activity on May 2, 1996 using the Naval Research Laboratory Mountain Wave Forecast Model predicts both strong mountain wave activity near the tropopause and strong mountain-wave-induced turbulence in the stratosphere.

Observation of frequency cutoff for self-excited dust acoustic waves

NASA Astrophysics Data System (ADS)

Nosenko, V.; Zhdanov, S. K.; Morfill, G. E.; Kim, S.-H.; Heinrich, J.; Merlino, R. L.

2009-11-01

Complex (dusty) plasmas consist of fine solid particles suspended in a weakly ionized gas. Complex plasmas are excellent model systems to study wave phenomena down to the level of individual ``atoms''. Spontaneously excited dust acoustic waves were observed with high temporal resolution in a suspension of micron-size kaolin particles in a dc discharge in argon. Wave activity was found at frequencies as high as 400 Hz. At high wave numbers, the wave dispersion relation was acoustic-like (frequency proportional to wave number). At low wave numbers, the wave frequency did not tend to zero, but reached a cutoff frequency fc instead. The value of fc declined with distance from the anode. We propose a simple model that explains the observed cutoff by particle confinement in plasma. The existence of a cutoff frequency is very important for the propagation of waves: the waves excited above fc are propagating, and those below fc are evanescent.

Planetary wave-like oscillations in the ionosphere retrieved with a longitudinal chain of ionosondes at high northern latitudes

NASA Astrophysics Data System (ADS)

Stray, Nora H.; Espy, Patrick J.

2018-06-01

This paper examines the influence of neutral dynamics on the high latitude ionosphere. Using a longitudinal chain of ionosondes at high northern latitudes (52°-65° N), planetary wave-like structures were observed in the spatial structure of the peak electron density in the ionosphere. Longitudinal wavenumbers S0, S1 and S2 have been extracted from these variations of the F layer. The observed wave activity in wavenumber one and two does not show any significant correlation with indices of magnetic activity, suggesting that this is not the primary driver. In addition, the motion of the S1 ionospheric wave structures parallels that of the S1 planetary waves observed in the winds of the mesosphere-lower-thermosphere derived from a longitudinal array of SuperDARN meteor-radar wind measurements. The time delay between the motions of the wave structures would indicate a indirect coupling, commensurate with the diffusion to the ionosphere of mesospheric atomic oxygen perturbations.

Characteristics of offshore extreme wind-waves detected by surface drifters with a low-cost GPS wave sensor

NASA Astrophysics Data System (ADS)

Komatsu, Kosei

Wind-generated waves have been recognized as one of the most important factors of the sea surface roughness which plays crucial roles in various air-sea interactions such as energy, mo-mentum, heat and gas exchanges. At the same time, wind waves with extreme wave heights representatively called as freak or rogue waves have been a matter of great concern for many people involved in shipping, fishing, constracting, surfing and other marine activities, because such extreme waves frequently affect on the marine activities and sometimes cause serious dis-asters. Nevertheless, investigations of actual conditions for the evolution of wind waves in the offshore region are less and sparse in contrast to dense monitoring networks in the coastal re-gions because of difficulty of offshore observation with high accuracy. Recently accurate in situ observation of offshore wind waves is getting possible at low cost owing to a wave height and di-rection sensor developed by Harigae et al. (2004) by installing a point-positioning GPS receiver on a surface drifting buoy. The point-positioning GPS sensor can extract three dimensional movements of the buoy excited by ocean waves with minimizing effects of GPS point-positioning errors through the use of a high-pass filter. Two drifting buoys equipped with the GPS-based wave sensor charged by solar cells were drifted in the western North Pacific and one of them continued to observe wind waves during 16 months from Sep. 2007. The RMSE of the GPS-based wave sensor was less than 10cm in significant wave height and about 1s in significant wave period in comparison with other sensors, i.e. accelerometers installed on drifting buoys of Japan Meteorological Agency, ultrasonic sensors placed at the Hiratsuka observation station of the University of Tokyo and altimeter of the JASON-1. The GPS-based wave buoys enabled us to detect freak waves defined as waves whose height is more than twice the significant wave height. The observation conducted by the wave buoys in 2007-2008 indicated a little more frequent occurrence of freak waves comparing with Forristall's (1978) empirical formula and Naess's (1985) distribution for a narrow-band Gaussian sea.

Evolution of offshore wind waves tracked by surface drifters with a point-positioning GPS sensor

NASA Astrophysics Data System (ADS)

Komatsu, K.

2009-12-01

Wind-generated waves have been recognized as one of the most important factors of the sea surface roughness which plays crucial roles in various air-sea interactions such as energy, momentum, heat and gas exchanges. At the same time, wind waves with extreme wave heights representatively called as freak or rogue waves have been a matter of great concern for many people involved in shipping, fishing, constracting, surfing and other marine activities, because such extreme waves frequently affect on the marine activities and sometimes cause serious disasters. Nevertheless, investigations of actual conditions for the evolution of wind waves in the offshore region are less and sparse in contrast to dense monitoring networks in the coastal regions because of difficulty of offshore observation with high accuracy. Recently accurate in situ observation of offshore wind waves is getting possible at low cost owing to a wave height and direction sensor developed by Harigae et al. (2004) by installing a point-positioning GPS receiver on a surface drifting buoy. The point-positioning GPS sensor can extract three dimensional movements of the buoy excited by ocean waves with minimizing effects of GPS point-positioning errors through the use of a high-pass filter. Two drifting buoys equipped with the GPS-based wave sensor charged by solar cells were drifted in the western North Pacific and one of them continued to observe wind waves during 16 months from Sep. 2007. The RMSE of the GPS-based wave sensor was less than 10cm in significant wave height and about 1s in significant wave period in comparison with other sensors, i.e. accelerometers installed on drifting buoys of Japan Meteorological Agency, ultrasonic sensors placed at the Hiratsuka observation station of the University of Tokyo and altimeter of the JASON-1. The GPS-based wave buoys enabled us to detect freak waves defined as waves whose height is more than twice the significant wave height. The observation conducted by the wave buoys in 2007-2008 indicated a little more frequent occurrence of freak waves comparing with Forristall’s (1978) empirical formula and Naess’s (1985) distribution for a narrow-band Gaussian sea. Fig.1. Time series of the ratio of the significant wave height to the maximum wave height in 20 minutes sampling period observed by a drifting buoy with a GPS sensor

Effects of subsurface ocean dynamics on instability waves in the tropical Pacific

NASA Astrophysics Data System (ADS)

Lawrence, Sean P.; Allen, Myles R.; Anderson, David L. T.; Llewellyn-Jones, David T.

1998-08-01

Tropical instability waves in a primitive equation model of the tropical Pacific Ocean, forced with analyzed wind stresses updated daily, show unexpectedly close phase correspondence with observation through the latter half of 1992. This suggests that these waves are not pure instabilities developing from infinitesimal disturbances, but that their phases and phase speeds are at least partially determined by the wind stress forcing. To quantify and explain this observation, we perfomed several numerical experiments, which indicate that remotely forced Rossby waves can influence both the phase and phase speed of tropical instability waves. We suggest that a remote wind forcing determines the high model/observation phase correspondence of tropical instability waves through a relatively realistic simulation of equatorial Kelvin and Rossby wave activity.

Studies of electromagnetic ion cyclotron waves using AMPTE/CCE and Dynamics Explorer

NASA Technical Reports Server (NTRS)

Erlandson, Robert E.

1993-01-01

The principal activity during the past six months has involved the analysis of ion cyclotron waves recorded from DE-2 using the magnetic field experiment and electric field experiment. The results of this study have been published in the Geophysical Research Letters (GRL). The primary finding of this paper is that ion cyclotron waves were found to heat electrons, as observed in the DE-2 Langmuir probe data, through a Landau damping process. A second activity, which was started during the last six months, involves the study of large amplitude approximately one Hz electric and magnetic field oscillations recorded in the nightside auroral zone at substorm onset. Work is under way to determine the properties of these waves and investigate any association these waves may have with the substorm initiation process. A third activity under way involves a comprehensive study of ion cyclotron waves recorded at ionospheric altitudes by DE-2. This study will be an extension of the work reported in the GRL paper and will involve a larger sampling of wave events. This paper will focus on wave properties at ionospheric altitudes. A fourth activity involves a more in-depth analysis of the acceleration mechanisms and the resulting electron distributions based on the observations presented in the GRL paper.

A novel role for WAVE1 in controlling actin network growth rate and architecture.

PubMed

Sweeney, Meredith O; Collins, Agnieszka; Padrick, Shae B; Goode, Bruce L

2015-02-01

Branched actin filament networks in cells are assembled through the combined activities of Arp2/3 complex and different WASP/WAVE proteins. Here we used TIRF and electron microscopy to directly compare for the first time the assembly kinetics and architectures of actin filament networks produced by Arp2/3 complex and dimerized VCA regions of WAVE1, WAVE2, or N-WASP. WAVE1 produced strikingly different networks from WAVE2 or N-WASP, which comprised unexpectedly short filaments. Further analysis showed that the WAVE1-specific activity stemmed from an inhibitory effect on filament elongation both in the presence and absence of Arp2/3 complex, which was observed even at low stoichiometries of WAVE1 to actin monomers, precluding an effect from monomer sequestration. Using a series of VCA chimeras, we mapped the elongation inhibitory effects of WAVE1 to its WH2 ("V") domain. Further, mutating a single conserved lysine residue potently disrupted WAVE1's inhibitory effects. Taken together, our results show that WAVE1 has unique activities independent of Arp2/3 complex that can govern both the growth rates and architectures of actin filament networks. Such activities may underlie previously observed differences between the cellular functions of WAVE1 and WAVE2. © 2015 Sweeney et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Gravity Waves and Mesospheric Clouds in the Summer Middle Atmosphere: A Comparison of Lidar Measurements and Ray Modeling of Gravity Waves Over Sondrestrom, Greenland

NASA Technical Reports Server (NTRS)

Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.

2004-01-01

We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

A Comparison Between Internal Waves Observed in the Southern Ocean and Lee Wave Generation Theory

NASA Astrophysics Data System (ADS)

Nikurashin, M.; Benthuysen, J.; Naveira Garabato, A.; Polzin, K. L.

2016-02-01

Direct observations in the Southern Ocean report enhanced internal wave activity and turbulence in a few kilometers above rough bottom topography. The enhancement is co-located with the deep-reaching fronts of the Antarctic Circumpolar Current, suggesting that the internal waves and turbulence are sustained by near-bottom flows interacting with rough topography. Recent numerical simulations confirm that oceanic flows impinging on rough small-scale topography are very effective generators of internal gravity waves and predict vigorous wave radiation, breaking, and turbulence within a kilometer above bottom. However, a linear lee wave generation theory applied to the observed bottom topography and mean flow characteristics has been shown to overestimate the observed rates of the turbulent energy dissipation. In this study, we compare the linear lee wave theory with the internal wave kinetic energy estimated from finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). We show that the observed internal wave kinetic energy levels are generally in agreement with the theory. Consistent with the lee wave theory, the observed internal wave kinetic energy scales quadratically with the mean flow speed, stratification, and topographic roughness. The correlation coefficient between the observed internal wave kinetic energy and mean flow and topography parameters reaches 0.6-0.8 for the 100-800 m vertical wavelengths, consistent with the dominant lee wave wavelengths, and drops to 0.2-0.5 for wavelengths outside this range. A better agreement between the lee wave theory and the observed internal wave kinetic energy than the observed turbulent energy dissipation suggests remote breaking of internal waves.

Trends in the Northern-hemisphere Climatologies of Local Wave Activity and Fluxes in a Warming Climate

NASA Astrophysics Data System (ADS)

Huang, S. Y.; Nakamura, N.

2016-12-01

The finite-amplitude local wave activity (LWA) identifies both the locations and magnitudes of anomalous wave events (Huang and Nakamura 2016, JAS), which are often associated with extreme weather conditions such as heat waves and storms at the rim. Variance in LWA in synoptic timescale is well-explained by the wave activity flux variance (i.e. conservative dynamics), while beyond seasonal time scale, the convergence/divergence of wave activity flux is balanced by non-conservative processes (e.g. vertical fluxes of heat and momentum at the surface, mixing, radiative forcing etc.). Analysis of ERA-Interim data during 1979-2015 shows that there is generally an increasing trend in the vertically-integrated interior LWA in Northern Winter, except over Central Pacific and Southern Europe. There is, in contrast, a decreasing trend in LWA in Northern summer, except over the high-latitude oceanic regions and low-latitude continental regions. The trends in the wave activity flux convergence in both seasons are consistent with such observations in LWA except over the Atlantic sector. In this presentation, I will illustrate how the change in circulation in a warming climate is associated with change in spatial distribution and frequency of extreme weather events by comparing the change in wave activity flux vectors with the observed change in LWA climatology. I will also quantify the permanent effect of non-conservative processes in terms of decadal change in eddy-free reference states of zonal wind and temperature (Nakamura and Solomon 2011).

STEREO OBSERVATIONS OF FAST MAGNETOSONIC WAVES IN THE EXTENDED SOLAR CORONA ASSOCIATED WITH EIT/EUV WAVES

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

Kwon, Ryun-Young; Ofman, Leon; Kramar, Maxim

2013-03-20

We report white-light observations of a fast magnetosonic wave associated with a coronal mass ejection observed by STEREO/SECCHI/COR1 inner coronagraphs on 2011 August 4. The wave front is observed in the form of density compression passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. Together with measured electron densities determined with STEREO COR1 and Extreme UltraViolet Imager (EUVI) data, we use our kinematic measurements of the wave front to calculate coronal magnetic fields and find that the measured speeds are consistent with characteristic fast magnetosonic speeds in the corona. In addition, the wave front turns outmore » to be the upper coronal counterpart of the EIT wave observed by STEREO EUVI traveling against the solar coronal disk; moreover, stationary fronts of the EIT wave are found to be located at the footpoints of deflected streamers and boundaries of coronal holes, after the wave front in the upper solar corona passes through open magnetic field lines in the streamers. Our findings suggest that the observed EIT wave should be in fact a fast magnetosonic shock/wave traveling in the inhomogeneous solar corona, as part of the fast magnetosonic wave propagating in the extended solar corona.« less

Statistical Analysis of Acoustic Wave Power and Flows around Solar Active Regions

NASA Astrophysics Data System (ADS)

Rabello-Soares, M. Cristina; Bogart, Richard S.; Scherrer, Philip H.

2018-05-01

We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of 6°–7° from the sunspot center. The amplification of higher frequency waves is highest 6° away from the active region and is largely independent of the wave’s direction. We observe a mean clockwise flow around active regions, the angular speed of which decreases exponentially with distance and has a coefficient close to ‑0.7 degree‑1. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7° from the sunspot center, where we observe an inflow close to the surface down to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm.

Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

NASA Astrophysics Data System (ADS)

Meyer, Catrin I.; Ern, Manfred; Hoffmann, Lars; Trinh, Quang Thai; Alexander, M. Joan

2018-01-01

We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's Aura satellite. AIRS operational temperature retrievals are typically not used for studies of gravity waves, because their vertical and horizontal resolution is rather limited. This study uses data of a high-resolution retrieval which provides stratospheric temperature profiles for each individual satellite footprint. Therefore the horizontal sampling of the high-resolution retrieval is 9 times better than that of the operational retrieval. HIRDLS provides 2-D spectral information of observed gravity waves in terms of along-track and vertical wavelengths. AIRS as a nadir sounder is more sensitive to short-horizontal-wavelength gravity waves, and HIRDLS as a limb sounder is more sensitive to short-vertical-wavelength gravity waves. Therefore HIRDLS is ideally suited to complement AIRS observations. A calculated momentum flux factor indicates that the waves seen by AIRS contribute significantly to momentum flux, even if the AIRS temperature variance may be small compared to HIRDLS. The stratospheric wave structures observed by AIRS and HIRDLS often agree very well. Case studies of a mountain wave event and a non-orographic wave event demonstrate that the observed phase structures of AIRS and HIRDLS are also similar. AIRS has a coarser vertical resolution, which results in an attenuation of the amplitude and coarser vertical wavelengths than for HIRDLS. However, AIRS has a much higher horizontal resolution, and the propagation direction of the waves can be clearly identified in geographical maps. The horizontal orientation of the phase fronts can be deduced from AIRS 3-D temperature fields. This is a restricting factor for gravity wave analyses of limb measurements. Additionally, temperature variances with respect to stratospheric gravity wave activity are compared on a statistical basis. The complete HIRDLS measurement period from January 2005 to March 2008 is covered. The seasonal and latitudinal distributions of gravity wave activity as observed by AIRS and HIRDLS agree well. A strong annual cycle at mid- and high latitudes is found in time series of gravity wave variances at 42 km, which has its maxima during wintertime and its minima during summertime. The variability is largest during austral wintertime at 60° S. Variations in the zonal winds at 2.5 hPa are associated with large variability in gravity wave variances. Altogether, gravity wave variances of AIRS and HIRDLS are complementary to each other. Large parts of the gravity wave spectrum are covered by joint observations. This opens up fascinating vistas for future gravity wave research.

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

DOE PAGES

Li, Zan; Millan, Robyn M.; Hudson, Mary K.; ...

2014-12-23

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution,more » and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.« less

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

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

Li, Zan; Millan, Robyn M.; Hudson, Mary K.

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution,more » and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.« less

DEMETER observations of manmade waves that propagate in the ionosphere

NASA Astrophysics Data System (ADS)

Parrot, Michel

2018-01-01

This paper is a review of manmade waves observed by the ionospheric satellite DEMETER. It concerns waves emitted by the ground-based VLF and ELF transmitters, by broadcasting stations, by the power line harmonic radiation, by industrial noise, and by active experiments. Examples are shown including, for the first time, the record of a wave coming from an ELF transmitter. These waves propagate upwards in the magnetosphere and they can be observed in the magnetically conjugated region of emission. Depending on their frequencies, they perturb the ionosphere and the particles in the radiation belts, and additional emissions are triggered. xml:lang="fr"

Large Amplitude Whistler Waves and Electron Acceleration in the Earth's Radiation Belts: A Review of STEREO and Wind Observations

NASA Technical Reports Server (NTRS)

Cattell, Cynthia; Breneman, A.; Goetz, K.; Kellogg, P.; Kersten, K.; Wygant, J.; Wilson, L. B., III; Looper, Mark D.; Blake, J. Bernard; Roth, I.

2012-01-01

One of the critical problems for understanding the dynamics of Earth's radiation belts is determining the physical processes that energize and scatter relativistic electrons. We review measurements from the Wind/Waves and STEREO S/Waves waveform capture instruments of large amplitude whistler-mode waves. These observations have provided strong evidence that large amplitude (100s mV/m) whistler-mode waves are common during magnetically active periods. The large amplitude whistlers have characteristics that are different from typical chorus. They are usually nondispersive and obliquely propagating, with a large longitudinal electric field and significant parallel electric field. We will also review comparisons of STEREO and Wind wave observations with SAMPEX observations of electron microbursts. Simulations show that the waves can result in energization by many MeV and/or scattering by large angles during a single wave packet encounter due to coherent, nonlinear processes including trapping. The experimental observations combined with simulations suggest that quasilinear theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, may be inadequate for understanding radiation belt dynamics.

Observation of gravity waves during the extreme tornado outbreak of 3 April 1974

NASA Technical Reports Server (NTRS)

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

1978-01-01

A continuous wave-spectrum high-frequency radiowave Doppler sounder array was used to observe upper-atmospheric disturbances during an extreme tornado outbreak. The observations indicated that gravity waves with two harmonic wave periods were detected at the F-region ionospheric height. Using a group ray path computational technique, the observed gravity waves were traced in order to locate potential sources. The signals were apparently excited 1-3 hours before tornado touchdown. Reverse ray tracing indicated that the wave source was located at the aurora zone with a Kp index of 6 at the time of wave excitation. The summation of the 24-hour Kp index for the day was 36. The results agree with existing theories (Testud, 1970; Titheridge, 1971; Kato, 1976) for the excitation of large-scale traveling ionospheric disturbances associated with geomagnetic activity in the aurora zone.

Acoustic waves in the atmosphere and ground generated by volcanic activity

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

Ichihara, Mie; Lyons, John; Oikawa, Jun

2012-09-04

This paper reports an interesting sequence of harmonic tremor observed in the 2011 eruption of Shinmoe-dake volcano, southern Japan. The main eruptive activity started with ashcloud forming explosive eruptions, followed by lava effusion. Harmonic tremor was transmitted into the ground and observed as seismic waves at the last stage of the effusive eruption. The tremor observed at this stage had unclear and fluctuating harmonic modes. In the atmosphere, on the other hand, many impulsive acoustic waves indicating small surface explosions were observed. When the effusion stopped and the erupted lava began explosive degassing, harmonic tremor started to be transmitted alsomore » to the atmosphere and observed as acoustic waves. Then the harmonic modes became clearer and more stable. This sequence of harmonic tremor is interpreted as a process in which volcanic degassing generates an open connection between the volcanic conduit and the atmosphere. In order to test this hypothesis, a laboratory experiment was performed and the essential features were successfully reproduced.« less

Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause

NASA Astrophysics Data System (ADS)

Ergun, R. E.; Holmes, J. C.; Goodrich, K. A.; Wilder, F. D.; Stawarz, J. E.; Eriksson, S.; Newman, D. L.; Schwartz, S. J.; Goldman, M. V.; Sturner, A. P.; Malaspina, D. M.; Usanova, M. E.; Torbert, R. B.; Argall, M.; Lindqvist, P.-A.; Khotyaintsev, Y.; Burch, J. L.; Strangeway, R. J.; Russell, C. T.; Pollock, C. J.; Giles, B. L.; Dorelli, J. J. C.; Avanov, L.; Hesse, M.; Chen, L. J.; Lavraud, B.; Le Contel, O.; Retino, A.; Phan, T. D.; Eastwood, J. P.; Oieroset, M.; Drake, J.; Shay, M. A.; Cassak, P. A.; Nakamura, R.; Zhou, M.; Ashour-Abdalla, M.; André, M.

2016-06-01

We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10 eV) plasma in the magnetosphere with warm (~100 eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause.

Multi-wavelength and High-resolution Observations of Solar Eruptive Activities

NASA Astrophysics Data System (ADS)

Shen, Y. D.

2014-09-01

In recent years, various solar eruptive activities have been observed in the solar atmosphere, such as solar flares, filament eruptions, jets, coronal mass ejections (CMEs), and magnetohydrodynamics (MHD) waves. Previous observations have indicated that solar magnetic field plays a dominant role in the processes of all kinds of solar activities. Since many large-scale solar eruptive activities can cause significant effects on the space environment of the Earth as well as the human life, studying and forecasting the solar activities are urgent tasks for us. In addition, the Sun is the nearest star to the Earth, so that people can directly observe and study it in detail. Hence, studying the Sun can also provide a reference to study other stars in the universe. This thesis focuses on the multi-wavelength and high-resolution observations of three types of solar eruptive activities: filament eruptions, coronal jets, and coronal MHD waves. By analyzing various observations taken by ground-based and space-borne instruments, we try to understand the inherent physical mechanisms, and construct models to interpret different kinds of solar eruptive activities. The triggering mechanism and the cause of a failed filament eruption are studied in Chapter 3, which indicates that the energy released in the flare is a key factor to the fate of the filament. Two successive filament eruptions are studied in Chapter 4, which indicates that the magnetic implosion could be the physical linkage between them, and the structures of coronal magnetic fields are important for producing sympathetic eruptions. A magnetic unwinding jet and a blowout jet are studied in Chapters 5 and 6, respectively. The former exhibits obvious radial expansion, which undergoes three distinct phases: the slow expansion phase, the fast expansion phase, and the steady phase. In addition, calculation indicates that the non-potential magnetic field in the jet can supply sufficient energy for producing the unwinding jet. The latter is associated with a simultaneous bubble-like and a jet-like CME. It is found that the jet-like CME is driven by the reconnection between the closed field and the ambient open field, while the bubble-like CME is associated with the mini-filament confined by the closed field. In Chapter 7, a quasi-periodic fast propagating (QFP) magnetosonic wave and the associated flare are studied. It is found that the wave and the flare have the same periods, suggesting their common origin. In addition, the leakage of photospheric p-mode oscillation to the corona is also an important source of QFP waves. Large-scale coronal waves are studied in Chapters 8 and 9. It is found that coronal waves can be observed in the low solar atmosphere like the top of the photosphere. Based on the analysis, we propose that large-scale coronal waves are fast magnetosonic or shock waves, which are driven by the expanding flanks of the associated CMEs. A short summary and unsolved problems are given in Chapter 10. Along with the fast development of many new solar telescopes, high quality observations will certainly help us to reveal the true physics behind various solar eruptive activities.

Seasonal and height variation of gravity wave activities observed by a meteor radar at King Sejong Station (62°S, 57°W), Antarctica

NASA Astrophysics Data System (ADS)

Kim, Y.; Lee, C.; Kim, J.; Choi, J.; Jee, G.

2010-12-01

We have analyzed wind data from individual meteor echoes detected by a meteor radar at King Sejong Station, Antarctica to measure gravity wave activity in the mesopause region. Wind data in the meteor altitudes has been obtained routinely by the meteor radar since its installation in March 2007. The mean variances in the wind data that were filtered for large scale motions (mean winds and tides) can be regarded as the gravity wave activity. Monthly mean gravity wave activities show strong seasonal and height dependences in the altitude range of 80 to 100 km. The gravity wave activities except summer monotonically increase with altitude, which is expected since decreasing atmospheric densities cause wave amplitudes to increase. During summer (Dec. - Feb.) the height profiles of gravity wave activities show a minimum near 90 - 95 km, which may be due to different zonal wind and strong wind shear near 80 - 95 km. Our gravity wave activities are generally stronger than those of the Rothera station, implying sensitive dependency on location. The difference may be related to gravity wave sources in the lower atmosphere near Antarctic vortex.

Rocket Observations of Kelvin Waves in the Upper Stratosphere over India.

NASA Astrophysics Data System (ADS)

Devarajan, M.; Reddy, C. A.; Ragrava Reddi, C.

1985-09-01

The upper atmospheric winds (20-40 km) at two Indian stations, Sriharikota Range (SHAR 13.7°N, 80.2°E) and Balasore (2 1.5°N, 86.93°E) during the years 1979-80 were analyzed for short scale vertical variations (6-16 km) of the zonal wind. The analysis involves high-pass filtering of the wind profiles to extract the short-scale wavelike perturbations and Fourier analysis of the wave disturbances.The results of the analysis are presented. The dominant vertical wavelengths are in the 6-12 km range in 67% of the observed cases, and the amplitudes are significantly larger during the easterly background wind. The amplitudes are systematically larger by about a factor of 2 at Sriharikota (13.7°N) than at 1Wasore (21.5°N). Corresponding wave perturbations are absent in the meridional wind in as much as 70% of the observations. These characteristics lead to the conclusion that the observed wavelike disturbances are the manifestation of Kelvin waves in the upper stratosphere. In some cases, the periods of the waves are inferred to be in the range of 4-8 days. The short vertical wavelengths, together with the shorter periods, indicate the possible dominance of zonal wavenumber 2 during many disturbance events.The observations of the wave activity in relation to the semiannual oscillation (SAO) and the annual oscillation (AO) show that 1) the more active periods correspond to the easterly phase of the SAO in the middle stratosphere and that 2) the wave activity persists for a longer duration when both the AO and SAO are in easterly phase.

Measurements of the power spectrum and dispersion relation of self-excited dust acoustic waves

NASA Astrophysics Data System (ADS)

Nosenko, V.; Zhdanov, S. K.; Kim, S.-H.; Heinrich, J.; Merlino, R. L.; Morfill, G. E.

2009-12-01

The spectrum of spontaneously excited dust acoustic waves was measured. The waves were observed with high temporal resolution using a fast video camera operating at 1000 frames per second. The experimental system was a suspension of micron-size kaolin particles in the anode region of a dc discharge in argon. Wave activity was found at frequencies as high as 450 Hz. At high wave numbers, the wave dispersion relation was acoustic-like (frequency proportional to wave number). At low wave numbers, the wave frequency did not tend to zero, but reached a cutoff frequency instead. The cutoff value declined with distance from the anode. We ascribe the observed cutoff to the particle confinement in this region.

Interaction between spiral and paced waves in cardiac tissue

PubMed Central

Agladze, Konstantin; Kay, Matthew W.; Krinsky, Valentin; Sarvazyan, Narine

2010-01-01

For prevention of lethal arrhythmias, patients at risk receive implantable cardioverter-defibrillators, which use high-frequency antitachycardia pacing (ATP) to convert tachycardias to a normal rhythm. One of the suggested ATP mechanisms involves paced-induced drift of rotating waves followed by their collision with the boundary of excitable tissue. This study provides direct experimental evidence of this mechanism. In monolayers of neonatal rat cardiomyocytes in which rotating waves of activity were initiated by premature stimuli, we used the Ca2+-sensitive indicator fluo 4 to observe propagating wave patterns. The interaction of the spiral tip with a paced wave was then monitored at a high spatial resolution. In the course of the experiments, we observed spiral wave pinning to local heterogeneities within the myocyte layer. High-frequency pacing led, in a majority of cases, to successful termination of spiral activity. Our data show that 1) stable spiral waves in cardiac monolayers tend to be pinned to local heterogeneities or areas of altered conduction, 2) overdrive pacing can shift a rotating wave from its original site, and 3) the wave break, formed as a result of interaction between the spiral tip and a paced wave front, moves by a paced-induced drift mechanism to an area where it may become unstable or collide with a boundary. The data were complemented by numerical simulations, which was used to further analyze experimentally observed behavior. PMID:17384124

Excitation of flare-induced waves in coronal loops and the effects of radiative cooling

NASA Astrophysics Data System (ADS)

Provornikova, Elena; Ofman, Leon; Wang, Tongjiang

2018-01-01

EUV imaging observations from several space missions (SOHO/EIT, TRACE, and SDO/AIA) have revealed a presence of propagating intensity disturbances in solar coronal loops. These disturbances are typically interpreted as slow magnetoacoustic waves. However, recent spectroscopic observations with Hinode/EIS of active region loops revealed that the propagating intensity disturbances are associated with intermittent plasma upflows (or jets) at the footpoints which are presumably generated by magnetic reconnection. For this reason, whether these disturbances are waves or periodic flows is still being studied. This study is aimed at understanding the physical properties of observed disturbances by investigating the excitation of waves by hot plasma injections from below and the evolution of flows and wave propagation along the loop. We expand our previous studies based on isothermal 3D MHD models of an active region to a more realistic model that includes full energy equation accounting for the effects of radiative losses. Computations are initialized with an equilibrium state of a model active region using potential (dipole) magnetic field, gravitationally stratified density and temperature obtained from the polytropic equation of state. We model an impulsive injection of hot plasma into the steady plasma outflow along the loops of different temperatures, warm (∼1 MK) and hot (∼6 MK). The simulations show that hot jets launched at the coronal base excite slow magnetoacoustic waves that propagate to high altitudes along the loops, while the injected hot flows decelerate rapidly with heights. Our results support that propagating disturbances observed in EUV are mainly the wave features. We also find that the effect of radiative cooling on the damping of slow-mode waves in 1-6 MK coronal loops is small, in agreement with the previous conclusion based on 1D MHD models.

Gravitational-wave localization alone can probe origin of stellar-mass black hole mergers.

PubMed

Bartos, I; Haiman, Z; Marka, Z; Metzger, B D; Stone, N C; Marka, S

2017-10-10

The recent discovery of gravitational waves from stellar-mass binary black hole mergers by the Laser Interferometer Gravitational-wave Observatory opened the door to alternative probes of stellar and galactic evolution, cosmology and fundamental physics. Probing the origin of binary black hole mergers will be difficult due to the expected lack of electromagnetic emission and limited localization accuracy. Associations with rare host galaxy types-such as active galactic nuclei-can nevertheless be identified statistically through spatial correlation. Here we establish the feasibility of statistically proving the connection between binary black hole mergers and active galactic nuclei as hosts, even if only a sub-population of mergers originate from active galactic nuclei. Our results are the demonstration that the limited localization of gravitational waves, previously written off as not useful to distinguish progenitor channels, can in fact contribute key information, broadening the range of astrophysical questions probed by binary black hole observations.Binary black hole mergers have recently been observed through the detection of gravitational wave signatures. The authors demonstrate that their association with active galactic nuclei can be made through a statistical spatial correlation.

Initial results from SKiYMET meteor radar at Thumba (8.5°N, 77°E): 2. Gravity wave observations in the MLT region

NASA Astrophysics Data System (ADS)

Kumar, Karanam Kishore; Antonita, T. Maria; Shelbi, S. T.

2007-12-01

In the present communication, allSKy interferometric METeor (SKiYMET) radar observations of gravity wave activity in the mesosphere lower thermosphere (MLT) region over Thumba (8.5°N, 77°E) are presented. The present meteor radar system provides hourly zonal and meridional winds in the MLT region, which can be readily used for studying the tides, planetary waves, gravity waves of periods 2-6 hours, and other long period oscillations in this region. However, these hourly winds are not sufficient for studying short period gravity waves having periods less than an hour, which demand high temporal resolution measurements. Even though the winds are estimated on an hourly basis, information such as zenith angle, azimuth angle, and radial velocity of each detected meteor are archived. Using these details of the meteor, an algorithm is developed to obtain the 15-min temporal resolution wind data. The output of the algorithm is compared with hourly wind data, and it showed a good agreement during the high meteor shower periods. Most of the times high meteor counts are observed during late night and early morning hours (local) over this latitude. Continuous wind measurements during the high meteor shower periods are used for studying the gravity wave activity in the MLT region. As the wave activity is intermittent and nonstationary, wavelet analysis has been used for delineating the wave features. The results showed the upward propagating intermittent gravity waves with periods 1-2 and 4-5 hours. The new aspect of the present communication is the usage of meteor radar for gravity wave studies for the first time over this latitude and studying their seasonal variability.

Simultaneous Observations of a Large-scale Wave Event in the Solar Atmosphere: From Photosphere to Corona

NASA Astrophysics Data System (ADS)

Shen, Yuandeng; Liu, Yu

2012-06-01

For the first time, we report a large-scale wave that was observed simultaneously in the photosphere, chromosphere, transition region, and low corona layers of the solar atmosphere. Using the high temporal and high spatial resolution observations taken by the Solar Magnetic Activity Research Telescope at Hida Observatory and the Atmospheric Imaging Assembly (AIA) on board Solar Dynamic Observatory, we find that the wave evolved synchronously at different heights of the solar atmosphere, and it propagated at a speed of 605 km s-1 and showed a significant deceleration (-424 m s-2) in the extreme-ultraviolet (EUV) observations. During the initial stage, the wave speed in the EUV observations was 1000 km s-1, similar to those measured from the AIA 1700 Å (967 km s-1) and 1600 Å (893 km s-1) observations. The wave was reflected by a remote region with open fields, and a slower wave-like feature at a speed of 220 km s-1 was also identified following the primary fast wave. In addition, a type-II radio burst was observed to be associated with the wave. We conclude that this wave should be a fast magnetosonic shock wave, which was first driven by the associated coronal mass ejection and then propagated freely in the corona. As the shock wave propagated, its legs swept the solar surface and thereby resulted in the wave signatures observed in the lower layers of the solar atmosphere. The slower wave-like structure following the primary wave was probably caused by the reconfiguration of the low coronal magnetic fields, as predicted in the field-line stretching model.

Generation and Micro-scale Effects of Electrostatic Waves in an Oblique Shock

NASA Astrophysics Data System (ADS)

Goodrich, K.; Ergun, R.; Schwartz, S. J.; Newman, D.; Johlander, A.; Argall, M. R.; Wilder, F. D.; Torbert, R. B.; Khotyaintsev, Y. V.; Lindqvist, P. A.; Strangeway, R. J.; Russell, C. T.; Giles, B. L.; Gershman, D. J.; Burch, J. L.

2017-12-01

We present an analysis of large amplitude (>100 mV/m), high frequency (≤1 kHz), electrostatic waves observed by MMS during an oblique bow shock crossing event. The observed waves primarily consist of electrostatic solitary waves (ESWs) and oblique ion plasma waves (IPWs). ESWs typically include nonlinear structures such as double layers, ion phase-space holes, and electron phase-space holes. Oblique IPWs are observed to be similar to ion acoustic waves, but can propagate up to 70° from the ambient magnetic field direction. Both wave-modes, particularly IPWs, are observed to have very short wavelengths ( 100 m) and are highly localized. While such wave-modes have been previously observed in the terrestrial bow shock, instrumental constraints have limited detailed insight into their generation and their effect on their plasma shock environment. Analysis of this oblique shock event shows evidence that ESWs and oblique IPWs can be generated through field-aligned currents associated with magnetic turbulence and through a counterstreaming ion instability respectively. We also present evidence that this wave activity can facilitate momentum exchange between ion populations, resulting in deceleration of incoming solar wind, and localized electron heating.

The Heating of Solar Coronal Loops by Alfvén Wave Turbulence

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

Van Ballegooijen, A. A.; Asgari-Targhi, M.; Voss, A.

2017-11-01

In this paper we further develop a model for the heating of coronal loops by Alfvén wave turbulence (AWT). The Alfvén waves are assumed to be launched from a collection of kilogauss flux tubes in the photosphere at the two ends of the loop. Using a three-dimensional magnetohydrodynamic model for an active-region loop, we investigate how the waves from neighboring flux tubes interact in the chromosphere and corona. For a particular combination of model parameters we find that AWT can produce enough heat to maintain a peak temperature of about 2.5 MK, somewhat lower than the temperatures of 3–4 MKmore » observed in the cores of active regions. The heating rates vary strongly in space and time, but the simulated heating events have durations less than 1 minute and are unlikely to reproduce the observed broad differential emission measure distributions of active regions. The simulated spectral line nonthermal widths are predicted to be about 27 km s{sup −1}, which is high compared to the observed values. Therefore, the present AWT model does not satisfy the observational constraints. An alternative “magnetic braiding” model is considered in which the coronal field lines are subject to slow random footpoint motions, but we find that such long-period motions produce much less heating than the shorter-period waves launched within the flux tubes. We discuss several possibilities for resolving the problem of producing sufficiently hot loops in active regions.« less

First direct observation of runaway electron-driven whistler waves in tokamaks

NASA Astrophysics Data System (ADS)

Spong, Donald A.

2017-10-01

Whistlers are electromagnetic waves that can be driven unstable by energetic electrons and are observed in natural plasmas, such as the ionosphere and Van Allen belts. Recent DIII-D experiments at low density demonstrate the first direct observation of whistlers in tokamaks, with 100-200 MHz waves excited by runaway electrons (REs) in the multi-MeV range. Whistler activity is correlated with RE intensity and the frequencies scale with magnetic field strength and electron density consistent with a whistler dispersion relation. Fluctuations occur in discrete frequency bands, and not a continuum as would be expected from plane wave analysis, suggesting the important role of toroidicity. An MHD model including the bounded/periodic nature of the plasma identifies multiple eigenmode branches. For a toroidal mode number n = 10, the predicted frequencies and spacing are similar to observations. The instabilities are stabilized with increasing magnetic field, as expected from the anomalous Doppler resonance. The whistler amplitudes show intermittent time variations. Predator-prey cycles with electron cyclotron emission (ECE) signals are observed, which can be interpreted as wave-induced pitch angle scattering of moderate energy REs. Such nonlinear dynamics are supported by quasi-linear simulations indicating that REs are scattered both by whistlers and high frequency magnetized plasma waves. The whistler wave predominantly scatters the high energy REs, while the magnetized plasma wave scatters the low energy REs, abruptly enhancing the ECE signal. Amplitude variations are also associated with sawtooth activity, indicating that the REs sample the q = 1 surface. These features of the RE-driven whistler have connections to ionospheric plasmas and open up new directions for the modeling and active control of tokamak REs. Work supported by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA27344, DE-FG02-07ER54917, DE-SC00-16268, and DE-AC05-00OR22725.

Applying the cold plasma dispersion relation to whistler mode chorus waves: EMFISIS wave measurements from the Van Allen Probes

DOE PAGES

Hartley, D. P.; Chen, Y.; Kletzing, C. A.; ...

2015-01-26

Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1–0.9 f ce). Results from this study indicate that the calculatedmore » wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10⁻³ nT², using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.« less

Dispersion analysis of passive surface-wave noise generated during hydraulic-fracturing operations

USGS Publications Warehouse

Forghani-Arani, Farnoush; Willis, Mark; Snieder, Roel; Haines, Seth S.; Behura, Jyoti; Batzle, Mike; Davidson, Michael

2014-01-01

Surface-wave dispersion analysis is useful for estimating near-surface shear-wave velocity models, designing receiver arrays, and suppressing surface waves. Here, we analyze whether passive seismic noise generated during hydraulic-fracturing operations can be used to extract surface-wave dispersion characteristics. Applying seismic interferometry to noise measurements, we extract surface waves by cross-correlating several minutes of passive records; this approach is distinct from previous studies that used hours or days of passive records for cross-correlation. For comparison, we also perform dispersion analysis for an active-source array that has some receivers in common with the passive array. The active and passive data show good agreement in the dispersive character of the fundamental-mode surface-waves. For the higher mode surface waves, however, active and passive data resolve the dispersive properties at different frequency ranges. To demonstrate an application of dispersion analysis, we invert the observed surface-wave dispersion characteristics to determine the near-surface, one-dimensional shear-wave velocity.

TRACING p -MODE WAVES FROM THE PHOTOSPHERE TO THE CORONA IN ACTIVE REGIONS

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

Zhao, Junwei; Chen, Ruizhu; Felipe, Tobías

Atmosphere above sunspots is abundant with different types of waves. Among these waves are running penumbral waves in the chromosphere, quasi-periodic oscillations in the lower coronal loops, and recently reported running waves in sunspots’ photosphere, all of which were interpreted as magnetoacoustic waves by some authors. Are these waves in different atmospheric layers related to each other, what is the nature of these waves, and where are the ultimate sources of these waves? Applying a time–distance helioseismic analysis over a suite of multi-wavelength observations above a sunspot, we demonstrate that the helioseismic p -mode waves are able to channel upmore » from the photosphere through the chromosphere and transition region into the corona, and that the magnetoacoustic waves observed in different atmospheric layers are a same wave originating from the photosphere but exhibiting differently under different physical conditions. We also show waves of different frequencies travel along different paths, which can be used to derive the physical properties of the atmosphere above sunspots. Our numerical simulation of traveling of waves from a subphotospheric source qualitatively resembles the observed properties of the waves and offers an interpretation of the shapes of the wavefronts above the photosphere.« less

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

Yukhimuk, V.; Roussel-Dupre, R.

In this paper the evolution of nonlinear scattering of whistler mode waves by kinetic Alfven waves (KAW) in time and two spatial dimensions is studied analytically. The authors suggest this nonlinear process as a mechanism of kinetic Alfven wave generation in space plasmas. This mechanism can explain the dependence of Alfven wave generation on whistler waves observed in magnetospheric and ionospheric plasmas. The observational data show a dependence for the generation of long periodic pulsations Pc5 on whistler wave excitation in the auroral and subauroral zone of the magnetosphere. This dependence was first observed by Ondoh T.I. For 79 casesmore » of VLF wave excitation registered by Ondoh at College Observatory (L=64.6 N), 52 of them were followed by Pc5 geomagnetic pulsation generation. Similar results were obtained at the Loparskaia Observatory (L=64 N) for auroral and subauroral zone of the magnetosphere. Thus, in 95% of the cases when VLF wave excitation occurred the generation of long periodic geomagnetic pulsations Pc5 were observed. The observations also show that geomagnetic pulsations Pc5 are excited simultaneously or insignificantly later than VLF waves. In fact these two phenomena are associated genetically: the excitation of VLF waves leads to the generation of geomagnetic pulsations Pc5. The observations show intensive generation of geomagnetic pulsations during thunderstorms. Using an electromagnetic noise monitoring system covering the ULF range (0.01-10 Hz) A.S. Fraser-Smith observed intensive ULF electromagnetic wave during a large thunderstorm near the San-Francisco Bay area on September 23, 1990. According to this data the most significant amplification in ULF wave activity was observed for waves with a frequency of 0.01 Hz and it is entirely possible that stronger enhancements would have been measured at lower frequencies.« less

Magnetospheric Multiscale Observations of Large-Amplitude Parallel, Electrostatic Waves Associated with Magnetic Reconnection at the Magnetopause

NASA Technical Reports Server (NTRS)

Ergun, R. E.; Holmes, J. C.; Goodrich, K. A.; Wilder, F. D.; Stawarz, J. E.; Eriksson, S.; Newman, D. L.; Schwartz, S. J.; Goldman, M. V.; Sturner, A. P.;

An eastward propagating compressional Pc 5 wave observed by AMPTE/CCE in the postmidnight sector. [Active Magnetospheric Particle Tracer Explorers

NASA Technical Reports Server (NTRS)

Takahashi, K.; Mcentire, R. W.; Zanetti, L. J.; Lopez, R. E.; Kistler, L. M.

1987-01-01

This paper presents a detailed analysis of a compressional Pc 5 wave observed in the postmidnight sector on July 21, 1986, using data from the magnetometer, the charge-energy-mass spectrometer, and the medium-energy particle analyzer aboard the AMPTE/Charge Composition Explorer (CCE) spacecraft. The Pc 5 wave exhibited harmonically related transverse and compressional magnetic oscillations, modulation of the flux of medium energy protons, and a large azimuthal wave number, i.e., properties that are similar to those of compressional Pc5 waves observed previously at geostationary orbit. The unique observations recorded by the AMPTE/CCE included the occurrence of the wave in the postmidnight sector, its sunward propagation with respect to the spacecraft, and the left-handed polarization of the perturbed magnetic field. In spite of the morphological uniqueness observed, the excitation of the July 21 event is considered to be due to the same type of instability as operates at geostationary orbit.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation.

PubMed

Tsuda, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10-100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50-90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10-50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation

PubMed Central

TSUDA, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet. PMID:24492645

Activity of convective coupled equatorial wave in tropical Tropopause layer in reanalysis and high-top CMIP5 models

NASA Astrophysics Data System (ADS)

Harza, Alia; Lubis, Sandro W.; Setiawan, Sonni

2018-05-01

The activity of convectively coupled equatorial waves (CCEWs), including Kelvin waves, Mixed Rossby-Gravity (MRG), and Equatorial Rossby (ER), in the tropical tropopause layer (TTL) is investigated in the Reanalysis and nine high-top CMIP5 models using the zonal wave number-frequency spectral analysis with equatorially symmetric-antisymmetric decomposition. We found that the TTL activities in the high-top CMIP5 models show significant difference among the high-top CMIP5 models with respect to the observation. The MIROC and HadGEM2-CC models work best in simulating Kelvin wave in the TTL, while the HadGEM2-CC and MPI-ESM-LR models work best in simulating MRG waves. The ER waves in TTL are best simulated in the MRI-CGCM model. None of the models are good in simulating all waves at once. It is concluded that the broad range of wave activity found in the different CMIP5 models depend on the convective parameterization used by each model and the representation of the tropical stratosphere variability, including the QBO.

Equatorial Kelvin waves: A UARS MLS view

NASA Technical Reports Server (NTRS)

Canziani, Pablo O.; Holton, James R.; Fishbein, Evan; Froidevaux, Lucien; Waters, Joe W.

1994-01-01

Data from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS) are used to compare two periods of Kelvin wave activity during different stages of the equatorial quasi-biennial oscillation. The analysis is carried out using an asynoptic mapping technique. A wide bandpass filter is used to isolate the frequency bands where Kelvin waves have been identified in previous studies. Time-height and time-latitude plots of the bandpassed data are used to identify Kelvin wave activity in the temperature and ozone fields. Frequency spectra of temperature and ozone amplitudes are constructed to further analyze the latitudinal and meridional distribution of Kelvin wave activity in zonal wavenumbers 1 and 2. The characteristics identified in these plots agree well with theoretical predictions and previous observations of middle atmosphere Kelvin waves. The time-height and time-latitude plots support the existence of Kelvin waves in discrete frequency bands; the slow, fast, and ultrafast Kelvin modes are all identified in the data. The characteristics of these modes do not vary much despite different mean flow conditions in the two periods examined. For the Kelvin wave-induced perturbations in ozone, the change from a transport-dominated regime below 10 hPa to a photochemically controlled regime above 10 hPa is clearly apparent in the height dependence of the phase difference between temperature and ozone. The ratios of the ozone perturbation amplitude to the temperature perturbation amplitude for the various observed Kelvin wave modes are in agreement with model estimates and LIMS (Limb Infrared Monitor of the Stratosphere) observations in the lower half of the region sampled but appear to be too large in the upper stratosphere and lower mesosphere.

3D radiation belt diffusion model results using new empirical models of whistler chorus and hiss

NASA Astrophysics Data System (ADS)

Cunningham, G.; Chen, Y.; Henderson, M. G.; Reeves, G. D.; Tu, W.

2012-12-01

3D diffusion codes model the energization, radial transport, and pitch angle scattering due to wave-particle interactions. Diffusion codes are powerful but are limited by the lack of knowledge of the spatial & temporal distribution of waves that drive the interactions for a specific event. We present results from the 3D DREAM model using diffusion coefficients driven by new, activity-dependent, statistical models of chorus and hiss waves. Most 3D codes parameterize the diffusion coefficients or wave amplitudes as functions of magnetic activity indices like Kp, AE, or Dst. These functional representations produce the average value of the wave intensities for a given level of magnetic activity; however, the variability of the wave population at a given activity level is lost with such a representation. Our 3D code makes use of the full sample distributions contained in a set of empirical wave databases (one database for each wave type, including plasmaspheric hiss, lower and upper hand chorus) that were recently produced by our team using CRRES and THEMIS observations. The wave databases store the full probability distribution of observed wave intensity binned by AE, MLT, MLAT and L*. In this presentation, we show results that make use of the wave intensity sample probability distributions for lower-band and upper-band chorus by sampling the distributions stochastically during a representative CRRES-era storm. The sampling of the wave intensity probability distributions produces a collection of possible evolutions of the phase space density, which quantifies the uncertainty in the model predictions caused by the uncertainty of the chorus wave amplitudes for a specific event. A significant issue is the determination of an appropriate model for the spatio-temporal correlations of the wave intensities, since the diffusion coefficients are computed as spatio-temporal averages of the waves over MLT, MLAT and L*. The spatiotemporal correlations cannot be inferred from the wave databases. In this study we use a temporal correlation of ~1 hour for the sampled wave intensities that is informed by the observed autocorrelation in the AE index, a spatial correlation length of ~100 km in the two directions perpendicular to the magnetic field, and a spatial correlation length of 5000 km in the direction parallel to the magnetic field, according to the work of Santolik et al (2003), who used multi-spacecraft measurements from Cluster to quantify the correlation length scales for equatorial chorus . We find that, despite the small correlation length scale for chorus, there remains significant variability in the model outcomes driven by variability in the chorus wave intensities.

A statistical study of EMIC waves observed by Cluster: 1. Wave properties

NASA Astrophysics Data System (ADS)

Allen, R. C.; Zhang, J.-C.; Kistler, L. M.; Spence, H. E.; Lin, R.-L.; Klecker, B.; Dunlop, M. W.; André, M.; Jordanova, V. K.

2015-07-01

Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001-2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.

Observations of a free-energy source for intense electrostatic waves. [in upper atmosphere near upper hybrid resonance frequency

NASA Technical Reports Server (NTRS)

Kurth, W. S.; Frank, L. A.; Gurnett, D. A.; Burek, B. G.; Ashour-Abdalla, M.

1980-01-01

Significant progress has been made in understanding intense electrostatic waves near the upper hybrid resonance frequency in terms of the theory of multiharmonic cyclotron emission using a classical loss-cone distribution function as a model. Recent observations by Hawkeye 1 and GEOS 1 have verified the existence of loss-cone distributions in association with the intense electrostatic wave events, however, other observations by Hawkeye and ISEE have indicated that loss cones are not always observable during the wave events, and in fact other forms of free energy may also be responsible for the instability. Now, for the first time, a positively sloped feature in the perpendicular distribution function has been uniquely identified with intense electrostatic wave activity. Correspondingly, we suggest that the theory is flexible under substantial modifications of the model distribution function.

Moreton wave, "EIT wave", and type II radio burst as manifestations of a single wave front

NASA Astrophysics Data System (ADS)

Kuzmenko, I. V.; Grechnev, V. V.; Uralov, A. M.

2011-12-01

We show that a Moreton wave, an "EIT wave," and a type II radio burst observed during a solar flare of July 13, 2004, might have been a manifestation of a single front of a decelerating shock wave, which appeared in an active region (AR) during a filament eruption. We propose describing a quasi-spheroidal wave propagating upward and along the solar surface by using relations known from a theory of a point-like explosion in a gas whose density changes along the radius according to a power law. By applying this law to fit the drop in density of the coronal plasma enveloping the solar active region, we first managed to bring the measured positions and velocities of surface Moreton wave and "EIT wave" into correspondence with the observed frequency drift rate of the meter type II radio burst. The exponent of the vertical coronal density falloff is selected by fitting the power law to the Newkirk and Saito empirical distributions in the height range of interest. Formal use of such a dependence in the horizontal direction with a different exponent appears to be reasonable up to distances of less than 200 Mm around the eruption center. It is possible to assume that the near-surface shock wave weakens when leaving this radius and finally the active region, entering the region of the quiet Sun where the coronal plasma density and the fast-mode speed are almost constant along the horizontal.

Towards a quantification of ocean wave heights off the west coast of Ireland using land based seismic data

NASA Astrophysics Data System (ADS)

Donne, S.; Bean, C. J.; Lokmer, I.; Lambkin, K.; Creamer, C.

2012-12-01

Ocean gravity waves are driven by atmospheric pressure systems. Their interactions with one another and reflection off coastlines generate pressure changes at the sea floor. These pressure fluctuations are the cause of continuous background seismic noise known as microseisms. The levels of microseism activity vary as a function of the sea state and increase during periods of intensive ocean wave activity. In 2011 a seismic network was deployed along the west coast of Ireland to continuously record microseisms generated in the Atlantic Ocean, as part of the Wave Observation (WaveObs) project based in University College Dublin. This project aims to determine the characteristics of the causative ocean gravity waves through calibration of the microseism data with ocean buoy data. In initial tests we are using a Backpropagation Feed-forward Artificial Neural Network (BP ANN) to establish the underlying relationships between microseisms and ocean waves. ANNs were originally inspired by studies of the mammalian brain and nervous system and are designed to learn by example. If successful these tools could then be used to estimate ocean wave heights and wave periods using a land-based seismic network and complement current wave observations being made offshore by marine buoys. Preliminary ANN results are promising with the network successfully able to reconstruct trends in ocean wave heights and periods. Microseisms can provide significant information about oceanic processes. With a deeper understanding of how these processes work there is potential for 1) locating and tracking the evolution of the largest waves in the Atlantic and 2) reconstructing the wave climate off the west coast of Ireland using legacy seismic data on a longer time scale than is currently available using marine based observations.

Wavenumber-4 structures observed in the low-latitude ionosphere during low and high solar activity periods using FORMOSAT/COSMIC observations

NASA Astrophysics Data System (ADS)

Onohara, Amelia Naomi; Staciarini Batista, Inez; Prado Batista, Paulo

2018-03-01

The main purpose of this study is to investigate the four-peak structure observed in the low-latitude equatorial ionosphere by the FORMOSAT/COSMIC satellites. Longitudinal distributions of NmF2 (the density of the F layer peak) and hmF2 (ionospheric F2-layer peak height) averages, obtained around September equinox periods from 2007 to 2015, were submitted to a bi-spectral Fourier analysis in order to obtain the amplitudes and phases of the main waves. The four-peak structure in the equatorial and low-latitude ionosphere was present in both low and high solar activity periods. This kind of structure possibly has tropospheric origins related to the tidal waves propagating from below that modulate the E-region dynamo, mainly the eastward non-migrating diurnal tide with wavenumber 3 (DE3, E for eastward). This wave when combined with the migrating diurnal tide (DW1, W for westward) presents a wavenumber-4 (wave-4) structure under a synoptic view. Electron densities observed during 2008 and 2013 September equinoxes revealed that the wave-4 structures became more prominent around or above the F-region altitude peak (˜ 300-350 km). The four-peak structure remains up to higher ionosphere altitudes (˜ 800 km). Spectral analysis showed DE3 and SPW4 (stationary planetary wave with wavenumber 4) signatures at these altitudes. We found that a combination of DE3 and SPW4 with migrating tides is able to reproduce the wave-4 pattern in most of the ionospheric parameters. For the first time a study using wave variations in ionospheric observations for different altitude intervals and solar cycle was done. The conclusion is that the wave-4 structure observed at high altitudes in ionosphere is related to effects of the E-region dynamo combined with transport effects in the F region.

Planetary and tidal wave-type oscillations in the ionospheric sporadic E layers over Tehran region

NASA Astrophysics Data System (ADS)

Karami, K.; Ghader, S.; Bidokhti, A. A.; Joghataei, M.; Neyestani, A.; Mohammadabadi, A.

2012-04-01

It is believed that in the lower ionosphere, particularly in the ionospheric sporadic E (Es) layers (90-130 km), the planetary and tidal wave-type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere. In the present work, the presence of wave-type oscillations, including planetary and tidal waves in the ionospheric sporadic E layers over Tehran region is examined. Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran, from July 2006 to June 2007 are used to investigate seasonal variations of planetary and tidal waves activities. For the purpose of accurate comparison between different seasons, wavelet transform is applied to time series of foEs and h‧Es, namely, the critical frequency and virtual height of Es layers, respectively. The results show that the sporadic E layers over Tehran region are strongly under the influence of upward propagation of waves from below. More specifically, among diverse range of periodicities in the sporadic E layers, we found that diurnal (24 hours) and semidiurnal (12 hours) oscillations in all seasons for both parameters. Moreover, terdiurnal (8 hours) tide-like variation is observed during spring and summer for foEs parameter and summer and winter for h‧Es. Furthermore, the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons, and their activities decrease during the late spring and summer. In addition, periods of about 2, 4, 6, 10, 14, and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere. Moreover, planetary waves have their maximum activities during equinox.

Estimation of the activation energy in the Belousov-Zhabotinsky reaction by temperature effect on excitable waves.

PubMed

Zhang, Jinzhong; Zhou, Luqun; Ouyang, Qi

2007-02-15

We report the temperature effect on the propagation of excitable traveling waves in a quasi-two-dimensional Belousov-Zhabotinsky reaction-diffusion system. The onset of excitable waves as a function of the sulfuric acid concentration and temperature is identified, on which the sulfuric acid concentration exhibits an Arrhenius dependence on temperature. On the basis of this experimental data, the activation energy of the self-catalyzed reaction in the Oregonator model is estimated to be 83-113 kJ/mol, which is further supported by our numerical simulations. The estimation proceeds without analyzing detailed reaction steps but rather through observing the global dynamic behaviors in the BZ reaction. For a supplement, the wave propagation velocities are calculated based on our results and compared with the experimental observations.

Planetary wave-gravity wave interactions during mesospheric inversion layer events

NASA Astrophysics Data System (ADS)

Ramesh, K.; Sridharan, S.; Raghunath, K.; Vijaya Bhaskara Rao, S.; Bhavani Kumar, Y.

2013-07-01

lidar temperature observations over Gadanki (13.5°N, 79.2°E) show a few mesospheric inversion layer (MIL) events during 20-25 January 2007. The zonal mean removed SABER temperature shows warm anomalies around 50°E and 275°E indicating the presence of planetary wave of zonal wave number 2. The MIL amplitudes in SABER temperature averaged for 10°N-15°N and 70°E-90°E show a clear 2 day wave modulation during 20-28 January 2007. Prior to 20 January 2007, a strong 2day wave (zonal wave number 2) is observed in the height region of 80-90 km and it gets largely suppressed during 20-26 January 2007 as the condition for vertical propagation is not favorable, though it prevails at lower heights. The 10 day mean zonal wind over Tirunelveli (8.7°N, 77.8°E) shows deceleration of eastward winds indicating the westward drag due to wave dissipation. The nightly mean MF radar observed zonal winds show the presence of alternating eastward and westward winds during the period of 20-26 January 2007. The two dimensional spectrum of Rayleigh lidar temperature observations available for the nights of 20, 22, and 24 January 2007 shows the presence of gravity wave activity with periods 18 min, 38 min, 38 min, and vertical wavelengths 6.4 km, 4.0 km, 6.4 km respectively. From the dispersion relation of gravity waves, it is inferred that these waves are internal gravity waves rather than inertia gravity waves with the horizontal phase speeds of ~40 m/s, ~37 m/s, and ~50 m/s respectively. Assuming the gravity waves are eastward propagating waves, they get absorbed only in the eastward local wind fields of the planetary wave thereby causing turbulence and eddy diffusion which can be inferred from the estimation of large drag force due to the breaking of gravity wave leading to the formation of large amplitude inversion events in alternate nights. The present study shows that, the mesospheric temperature inversion is caused mainly due to the gravity wave breaking and the inversion amplitude may get modulated by the interaction between gravity waves and planetary waves. The eddy diffusion associated with gravity wave drag may also cause suppression in the planetary wave activity.

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, Kiwamu; Kobayashi, Naoki; Fukao, Yoshio

2014-01-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the probable excitation source is atmospheric turbulence in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity.

Internal waves in the Gulf of California - Observations from a spaceborne radar

NASA Technical Reports Server (NTRS)

Fu, L.-L.; Holt, B.

1984-01-01

Pronounced signatures of internal waves were detected repeatedly in the Gulf of California by the Seasat synthetic aperture radar (SAR). A series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area. It was found that the number of observed wave groups was highly correlated with the strength of the local tides: the maximum number occurred during spring tides and the minimum number occurred during neap tides, indicating that the internal waves were tidally forced. Most of the wave activity was found to the north of 28 deg N where the tides were the strongest in the Gulf. The application of a simple, nonlinear internal wave model to the observations indicated that the peak-to-peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2. The estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 x 10 to the 15th erg/s, representing only 10 percent of the rate of the dissipation of the dominant M2 tide in the Gulf.

Ionospheric modifications in high frequency heating experiments

NASA Astrophysics Data System (ADS)

Kuo, Spencer P.

2015-01-01

Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena.

Ion Acoustic Waves Observed at Comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Gunell, H.; Nilsson, H.; Hamrin, M.; Eriksson, A.; Maggiolo, R.; Pierre, H.; Altwegg, K.; Tzou, C. Y.; Rubin, M.; Glassmeier, K. H.; Stenberg Wieser, G.; Wedlund, C. S.; De Keyser, J.; Dhooghe, F.; Cessateur, G.; Gibbons, A.

2016-12-01

We present observations of ion acoustic waves at Comet 67P/Churyumov-Gerasimenko performed on 20 January 2015 when the Rosetta spacecraft was located near the terminator, 28 km from the nucleus of the comet. At the time of the observations the activity of the comet was still low. We use distribution functions obtained by the Ion Composition Analyser of the Rosetta Plasma Consortium (RPC-ICA) and electron temperature estimatesfrom the Langmuir Probes (RPC-LAP) to compute dispersion relations for waves on the ion timescale, and compare the results to spectra obtained by RPC-LAP. The peaks of the wave spectra appear at frequencies near 500 Hz. We perform cross-calibrations between RPC-ICA, RPC-LAP, and the Mutual Impedance Probe (RPC-MIP). Matching the dispersion relations to the wave observations helps us to form an estimate of the plasma density. At times when there is significant wave activity the water ion distribution is constituted by a cold (0.01 eV) population of locally produced ions and a thin tail of ions that have been accelerated by an electric field. The tail is approximately unidirectional, covering a wide velocity range, and centred at 20km/s in the spacecraft frame. At other times a warm (approximately 1 eV), mainly isotropic, ion population renders the ion acoustic mode heavily damped, and no waves are observed. Observations of the neutral density by the ROSINA COPS instrument indicate that frictional heating by the radial neutral flow contributes to this warm ion population. This work was supported by the Belgian Science Policy Office through the Solar-Terrestrial Centre of Excellence and by PRODEX/ROSETTA/ROSINA PEA 4000107705.

Gastric dysrhythmias and the current status of electrogastrography

NASA Technical Reports Server (NTRS)

Koch, K. L.

1989-01-01

Myoelectrical activity recorded simultaneously from mucosal, serosal, and cutaneous electrodes has confirmed that the 3-cpm signal from such electrodes reflects gastric slow-wave activity. Now, the observation that patients with unexplained nausea and vomiting may have very rapid slow-wave frequencies (tachygastrias) and very slow, slow-wave frequencies (bradygastrias) suggests that electrogastrography, a reliable and noninvasive technique, may be useful in the diagnosis and management of patients with upper abdominal symptoms and gastroparesis.

Observed stratospheric downward reflection, and its relation to upward pulses of wave activity

NASA Astrophysics Data System (ADS)

Harnik, N.

2009-04-01

We examine the differences between observed stratospheric vertical wave reflection and wave absorption events, which differ in that the wave induced deceleration remains confined to upper levels in the former. The two types of events signify two types of stratospheric winter dynamics, associated with different downward coupling to the troposphere (Perlwitz and Harnik, 2004). Using time lag composites, we find that the main factor influencing which event will occur is the duration, in time, of the upward pulse of wave activity entering the stratosphere from the troposphere. Short pulses accelerate the flow at their trailing edge in the lower stratosphere while they decelerate it at upper levels, resulting in a vertical shear reversal, and corresponding downward reflection, while long pulses continue decelerating the vortex at progressively lower levels. The confinement of deceleration to upper levels for short wave forcing pulses is also found in an idealized model of an interaction between a planetary wave and the stratospheric vortex, though some aspects of the wave geometry evolution, and thus vertical reflection, are not captured realistically in the model. The results suggest the stratospheric influence on the type of wave interaction, in reality, is indirect - through a possible effect on the duration of upward wave fluxes through the tropopause.

Altimeter Observations of Wave Climate in the Arctic Ocean

NASA Astrophysics Data System (ADS)

Babanin, A. V.; Liu, Q.; Zieger, S.

2016-02-01

Wind waves are a new physical phenomenon to the Arctic Seas, which in the past were covered with ice. Now, over summer months, ice coverage retreats up to high latitudes and waves are generated. The marginal open seas provide new opportunities and new problems. Navigation and other maritime activities become possible, but wave heights, storm surges and coastal erosion will likely increase. Air-sea interactions enter a completely new regime, with momentum, energy, heat, gas and moisture fluxes being moderated or produced by the waves, and impacting on upper-ocean mixing. All these issues require knowledge of the wave climate. We will report results of investigation of wave climate and its trends by means of satellite altimetry. This is a challenging, but important topic. On one hand, no statistical approach is possible since in the past for most of the Arctic Ocean there was limited wave activity. Extrapolations of the current observations into the future are not feasible, because ice cover and wind patterns in the Arctic are changing. On the other hand, information on the mean and extreme wave properties, such as wave height, period, direction, on the frequency of occurrence and duration of the storms is of great importance for oceanographic, meteorological, climate, naval and maritime applications in the Arctic Seas.

A statistical study of EMIC waves observed by Cluster. 1. Wave properties. EMIC Wave Properties

DOE PAGES

Allen, R. C.; Zhang, J. -C.; Kistler, L. M.; ...

2015-07-23

Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In our study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of datamore » from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. Thus, the statistical analysis is presented in two papers. OUr paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.« less

Acceleration of Magnetospheric Relativistic Electrons by Ultra-Low Frequency Waves: A Comparison between Two Cases Observed by Cluster and LANL Satellites

NASA Technical Reports Server (NTRS)

Shao, X.; Fung, S. F.; Tan, L. C.; Sharma, A. S.

2010-01-01

Understanding the origin and acceleration of magnetospheric relativistic electrons (MREs) in the Earth's radiation belt during geomagnetic storms is an important subject and yet one of outstanding questions in space physics. It has been statistically suggested that during geomagnetic storms, ultra-low-frequency (ULF) Pc-5 wave activities in the magnetosphere are correlated with order of magnitude increase of MRE fluxes in the outer radiation belt. Yet, physical and observational understandings of resonant interactions between ULF waves and MREs remain minimum. In this paper, we show two events during storms on September 25, 2001 and November 25, 2001, the solar wind speeds in both cases were > 500 km/s while Cluster observations indicate presence of strong ULF waves in the magnetosphere at noon and dusk, respectively, during a approx. 3-hour period. MRE observations by the Los Alamos (LANL) spacecraft show a quadrupling of 1.1-1.5 MeV electron fluxes in the September 25, 2001 event, but only a negligible increase in the November 2.5, 2001 event. We present a detailed comparison between these two events. Our results suggest that the effectiveness of MRE acceleration during the September 25, 2001 event can be attributed to the compressional wave mode with strong ULF wave activities and the physical origin of MRE acceleration depends more on the distribution of toroidal and poloidal ULF waves in the outer radiation belt.

Wave and Particle Interactions in the High and Low-Altitude Auroral Region During Rising Solar Activity

NASA Technical Reports Server (NTRS)

Gurnett, Donald A.; Menietti, J. D.

2003-01-01

The project has resulted in four separate investigations, which are each in various stages of publication in the refereed scientific journals. The first investigation was of the generation of electrostatic electron cyclotron waves observed by the Polar spacecraft throughout the auroral regions, dayside cusp, and polar magnetosphere. We have since discovered that these waves are also present within the magnetopause and magnetosheath, which is one of the topics of a second study, entitled: 'Polar observations of plasma waves in and near the dayside magnetopause/magnetosheath.' A third study of plasma waves focussed on kilometric continuum (KC) emission. This work is reported in a paper entitled 'Near-source and Remote Observations of Kilometric Continuum Radiation From Multi-spacecraft Observations'.The final investigation of this program concerns the possible transverse heating of auroral ions by impulsive wave structures. We summarize that substantial transverse ion heating has already occurred at lower altitudes. Abstracts of the above four studies are included in the Appendix to this final report.

Satellite Observations of Stratospheric Gravity Waves Associated With the Intensification of Tropical Cyclones

NASA Astrophysics Data System (ADS)

Hoffmann, Lars; Wu, Xue; Alexander, M. Joan

2018-02-01

Forecasting the intensity of tropical cyclones is a challenging problem. Rapid intensification is often preceded by the formation of "hot towers" near the eyewall. Driven by strong release of latent heat, hot towers are high-reaching tropical cumulonimbus clouds that penetrate the tropopause. Hot towers are a potentially important source of stratospheric gravity waves. Using 13.5 years (2002-2016) of Atmospheric Infrared Sounder observations of stratospheric gravity waves and tropical cyclone data from the International Best Track Archive for Climate Stewardship, we found empirical evidence that stratospheric gravity wave activity is associated with the intensification of tropical cyclones. The Atmospheric Infrared Sounder and International Best Track Archive for Climate Stewardship data showed that strong gravity wave events occurred about twice as often for tropical cyclone intensification compared to storm weakening. Observations of stratospheric gravity waves, which are not affected by obscuring tropospheric clouds, may become an important future indicator of storm intensification.

Observation of Relativistic Electron Microbursts in Conjunction with Intense Radiation Belt Whistler-Mode Waves

NASA Technical Reports Server (NTRS)

Kersten, K.; Cattell, C. A.; Breneman, A.; Goetz, K.; Kellogg, P. J.; Wygant, J. R.; Wilson, L. B., III; Blake, J. B.; Looper, M. D.; Roth, I.

2011-01-01

We present multi-satellite observations of large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. This evidence of microburst precipitation occurring at the same time and at nearly the same magnetic local time and L-shell with a bursty temporal structure similar to that of the observed large amplitude wave packets suggests a causal connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave.particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

A statistical survey of ultralow-frequency wave power and polarization in the Hermean magnetosphere.

PubMed

James, Matthew K; Bunce, Emma J; Yeoman, Timothy K; Imber, Suzanne M; Korth, Haje

2016-09-01

We present a statistical survey of ultralow-frequency wave activity within the Hermean magnetosphere using the entire MErcury Surface, Space ENvironment, GEochemistry, and Ranging magnetometer data set. This study is focused upon wave activity with frequencies <0.5 Hz, typically below local ion gyrofrequencies, in order to determine if field line resonances similar to those observed in the terrestrial magnetosphere may be present. Wave activity is mapped to the magnetic equatorial plane of the magnetosphere and to magnetic latitude and local times on Mercury using the KT14 magnetic field model. Wave power mapped to the planetary surface indicates the average location of the polar cap boundary. Compressional wave power is dominant throughout most of the magnetosphere, while azimuthal wave power close to the dayside magnetopause provides evidence that interactions between the magnetosheath and the magnetopause such as the Kelvin-Helmholtz instability may be driving wave activity. Further evidence of this is found in the average wave polarization: left-handed polarized waves dominate the dawnside magnetosphere, while right-handed polarized waves dominate the duskside. A possible field line resonance event is also presented, where a time-of-flight calculation is used to provide an estimated local plasma mass density of ∼240 amu cm -3 .

Generation of whistler waves by continuous HF heating of the upper ionosphere

NASA Astrophysics Data System (ADS)

Vartanyan, A.; Milikh, G. M.; Eliasson, B.; Najmi, A. C.; Parrot, M.; Papadopoulos, K.

2016-07-01

Broadband VLF waves in the frequency range 7-10 kkHz and 15-19 kHz, generated by F region CW HF ionospheric heating in the absence of electrojet currents, were detected by the DEMETER satellite overflying the High Frequency Active Auroral Research Program (HAARP) transmitter during HAARP/BRIOCHE campaigns. The VLF waves are in a frequency range corresponding to the F region lower lybrid (LH) frequency and its harmonic. This paper aims to show that the VLF observations are whistler waves generated by mode conversion of LH waves that were parametrically excited by HF-pump-plasma interaction at the upper hybrid layer. The paper discusses the basic physics and presents a model that conjectures (1) the VLF waves observed at the LH frequency are due to the interaction of the LH waves with meter-scale field-aligned striations—generating whistler waves near the LH frequency; and (2) the VLF waves at twice the LH frequency are due to the interaction of two counterpropagating LH waves—generating whistler waves near the LH frequency harmonic. The model is supported by numerical simulations that show good agreement with the observations. The (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions results and model discussions are complemented by the Kodiak radar, ionograms, and stimulated electromagnetic emission observations.

Periodic collapse and long-time evolution of strong Langmuir turbulence

NASA Astrophysics Data System (ADS)

Cheung, P. Y.; Wong, A. Y.

1985-10-01

Experimental measurements on the long-time evolution of strong Langmuir turbulence in a beam-plasma system reveal a picture of periodic, short bursts of Langmuir wave collapse instead of the existence of long-lived solitons. The remnants of density cavities from burnout cavitons are observed to curtail wave growth periodically, creating time intervals of low wave activity between successive cycles of wave collapse, and establishing three regimes of wave evolution.

A Catalog of Coronal "EIT Wave" Transients

NASA Technical Reports Server (NTRS)

Thompson, B. J.; Myers, D. C.

2009-01-01

Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT) data have been visually searched for coronal "EIT wave" transients over the period beginning from 1997 March 24 and extending through 1998 June 24. The dates covered start at the beginning of regular high-cadence (more than one image every 20 minutes) observations, ending at the four-month interruption of SOHO observations in mid-1998. One hundred and seventy six events are included in this catalog. The observations range from "candidate" events, which were either weak or had insufficient data coverage, to events which were well defined and were clearly distinguishable in the data. Included in the catalog are times of the EIT images in which the events are observed, diagrams indicating the observed locations of the wave fronts and associated active regions, and the speeds of the wave fronts. The measured speeds of the wave fronts varied from less than 50 to over 700 km s(exp -1) with "typical" speeds of 200-400 km s(exp -1).

Retinal Wave Behavior through Activity-Dependent Refractory Periods

PubMed Central

Godfrey, Keith B; Swindale, Nicholas V

2007-01-01

In the developing mammalian visual system, spontaneous retinal ganglion cell (RGC) activity contributes to and drives several aspects of visual system organization. This spontaneous activity takes the form of spreading patches of synchronized bursting that slowly advance across portions of the retina. These patches are non-repeating and tile the retina in minutes. Several transmitter systems are known to be involved, but the basic mechanism underlying wave production is still not well-understood. We present a model for retinal waves that focuses on acetylcholine mediated waves but whose principles are adaptable to other developmental stages. Its assumptions are that a) spontaneous depolarizations of amacrine cells drive wave activity; b) amacrine cells are locally connected, and c) cells receiving more input during their depolarization are subsequently less responsive and have longer periods between spontaneous depolarizations. The resulting model produces waves with non-repeating borders and randomly distributed initiation points. The wave generation mechanism appears to be chaotic and does not require neural noise to produce this wave behavior. Variations in parameter settings allow the model to produce waves that are similar in size, frequency, and velocity to those observed in several species. Our results suggest that retinal wave behavior results from activity-dependent refractory periods and that the average velocity of retinal waves depends on the duration a cell is excitatory: longer periods of excitation result in slower waves. In contrast to previous studies, we find that a single layer of cells is sufficient for wave generation. The principles described here are very general and may be adaptable to the description of spontaneous wave activity in other areas of the nervous system. PMID:18052546

THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

NASA Technical Reports Server (NTRS)

Tang, Xiangwei; Cattell, Cynthia; Dombeck, John; Dai, Lei; Wilson, Lynn B. III; Breneman, Aaron; Hupack, Adam

2013-01-01

We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

Measuring the Seismic and Acoustic Time of Flight - Lessons in Earthquakes and Thunder

NASA Astrophysics Data System (ADS)

Leeman, J.; Ammon, C. J.

2016-12-01

When teaching the fundamentals of waves and wave propagation, students must appreciate and understand that different waves travel through different materials at different speeds. We describe a simple experiment to explore acoustic wave propagation through the ground and the air and how to use those observations to locate the source of the waves. The experiment that can be performed with a geophone, a microphone, and an oscilloscope. For this activity, students will strike a metal plate, equipped with a vibration trigger, with a hammer. The blow triggers an oscilloscope to begin recording data in a "single-shot" mode. The two channels of the oscilloscope record the output of the microphone (measuring the energy of sound waves in the air) and the geophone (measuring the seismic wave energy in the ground). Seismic waves reach the geophone earlier than the sound waves since they travel at approximately ten times the speed. Students can measure the travel time on the oscilloscope, or using data downloaded to a computer. With measurements of the travel time and distance to the hammer, students can calculate the velocity of each wave. Then, the hammer can be used at other distances from the sensors and by measuring the difference in arrival time of the two waves, students can estimate the distance to the source which they check by direct measurement. This exercise can be directly connected to common observations such as seeing lighting before hearing thunder. The activity also connects directly to concepts related to earthquake location. We describe pedagogical materials, including experiment instructions, videos and data for those who do not have access to the equipment, and simple exercise suggestions for classroom activities.

Anomalous tropical planetary wave activity during 2015/2016 quasi biennial oscillation disruption

NASA Astrophysics Data System (ADS)

Kumar, Karanam Kishore; Mathew, Sneha Susan; Subrahmanyam, K. V.

2018-01-01

In the present communication, a record breaking duration (23 months) of the eastward phase of the QBO at 20 hPa is reported and details of the tropical wave activity during the recent anomalous QBO event are discussed. Two-dimensional Fourier analysis revealed the presence of 30-40 and 10-15 day westward propagating wave number 1 structures at 40 hPa pressure level over the equator. A combination of the mid-latitude Rossby waves and the 30-40 day oscillations seems to be the most probable mechanism for the observed disruption of the QBO.

The effect of inhibition on the existence of traveling wave solutions for a neural field model of human seizure termination.

PubMed

González-Ramírez, L R; Kramer, M A

2018-06-01

In this paper we study the influence of inhibition on an activity-based neural field model consisting of an excitatory population with a linear adaptation term that directly regulates the activity of the excitatory population. Such a model has been used to replicate traveling wave data as observed in high density local field potential recordings (González-Ramírez et al. PLoS Computational Biology, 11(2), e1004065, 2015). In this work, we show that by adding an inhibitory population to this model we can still replicate wave properties as observed in human clinical data preceding seizure termination, but the parameter range over which such waves exist becomes more restricted. This restriction depends on the strength of the inhibition and the timescale at which the inhibition acts. In particular, if inhibition acts on a slower timescale relative to excitation then it is possible to still replicate traveling wave patterns as observed in the clinical data even with a relatively strong effect of inhibition. However, if inhibition acts on the same timescale as the excitation, or faster, then traveling wave patterns with the desired characteristics cease to exist when the inhibition becomes sufficiently strong.

Comparing simulated and observed EMIC wave amplitudes using in situ Van Allen Probes’ measurements

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

Saikin, A. A.; Jordanova, Vania Koleva; Zhang, J. C.

In this study, we perform a statistical study calculating electromagnetic ion cyclotron (EMIC) wave amplitudes based off in situ plasma measurements taken by the Van Allen Probes’ (1.1–5.8 R e) Helium, Oxygen, Proton, Electron (HOPE) instrument. Calculated wave amplitudes are compared to EMIC waves observed by the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes during the same period. The survey covers a 22-month period (1 November 2012 to 31 August 2014), a full Van Allen Probe magnetic local time (MLT) precession. The linear theory proxy was used to identify EMIC wave eventsmore » with plasma conditions favorable for EMIC wave excitation. Two hundred and thirty-two EMIC wave events (103 H +-band and 129 He +-band) were selected for this comparison. Nearly all events selected are observed beyond L = 4. Results show that calculated wave amplitudes exclusively using the in situ HOPE measurements produce amplitudes too low compared to the observed EMIC wave amplitudes. Hot proton anisotropy (Ahp) distributions are asymmetric in MLT within the inner (L < 7) magnetosphere with peak (minimum) A hp, ~0.81 to 1.00 (~0.62), observed in the dawn (dusk), 0000 < MLT ≤ 1200 (1200 < MLT ≤ 2400), sectors. Measurements of A hp are found to decrease in the presence of EMIC wave activity. A hp amplification factors are determined and vary with respect to EMIC wave-band and MLT. Lastly, He +-band events generally require double (quadruple) the measured A hp for the dawn (dusk) sector to reproduce the observed EMIC wave amplitudes.« less

Comparing simulated and observed EMIC wave amplitudes using in situ Van Allen Probes’ measurements

DOE PAGES

Saikin, A. A.; Jordanova, Vania Koleva; Zhang, J. C.; ...

2018-02-02

In this study, we perform a statistical study calculating electromagnetic ion cyclotron (EMIC) wave amplitudes based off in situ plasma measurements taken by the Van Allen Probes’ (1.1–5.8 R e) Helium, Oxygen, Proton, Electron (HOPE) instrument. Calculated wave amplitudes are compared to EMIC waves observed by the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes during the same period. The survey covers a 22-month period (1 November 2012 to 31 August 2014), a full Van Allen Probe magnetic local time (MLT) precession. The linear theory proxy was used to identify EMIC wave eventsmore » with plasma conditions favorable for EMIC wave excitation. Two hundred and thirty-two EMIC wave events (103 H +-band and 129 He +-band) were selected for this comparison. Nearly all events selected are observed beyond L = 4. Results show that calculated wave amplitudes exclusively using the in situ HOPE measurements produce amplitudes too low compared to the observed EMIC wave amplitudes. Hot proton anisotropy (Ahp) distributions are asymmetric in MLT within the inner (L < 7) magnetosphere with peak (minimum) A hp, ~0.81 to 1.00 (~0.62), observed in the dawn (dusk), 0000 < MLT ≤ 1200 (1200 < MLT ≤ 2400), sectors. Measurements of A hp are found to decrease in the presence of EMIC wave activity. A hp amplification factors are determined and vary with respect to EMIC wave-band and MLT. Lastly, He +-band events generally require double (quadruple) the measured A hp for the dawn (dusk) sector to reproduce the observed EMIC wave amplitudes.« less

Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)

NASA Astrophysics Data System (ADS)

Turner, D. L.; Lee, J. H.; Claudepierre, S. G.; Fennell, J. F.; Blake, J. B.; Jaynes, A. N.; Leonard, T.; Wilder, F. D.; Ergun, R. E.; Baker, D. N.; Cohen, I. J.; Mauk, B. H.; Strangeway, R. J.; Hartley, D. P.; Kletzing, C. A.; Breuillard, H.; Le Contel, O.; Khotyaintsev, Yu. V.; Torbert, R. B.; Allen, R. C.; Burch, J. L.; Santolik, O.

2017-11-01

Whistler mode chorus waves are a naturally occurring electromagnetic emission observed in Earth's magnetosphere. Here, for the first time, data from NASA's Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, fi>k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA's Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32° < MLAT < -15°), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLAT -31°). Most of the elements had "hook"-like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well-organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent, allowing for the direct calculation of fi>k. Error estimates on calculated fi>k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30° from the direction antiparallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of fi>k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory.

Interhemispheric Asymmetry in the Mesosphere and Lower Thermosphere Observed by SABER/TIMED

NASA Astrophysics Data System (ADS)

Yee, J. H.

2017-12-01

In this paper we analyze nearly 15 years of satellite observations of temperature, airglow, and composition in the Mesosphere and Lower Thermosphere (MLT) to quantify their interhemispheric asymmetries ao one can provide quantitative links between observed asymmetries and the spatial and temporal variations of the gravity wave activity. Two processes are believed to be responsible for observed interhemispheric differences in the MLT. The first is the direct radiation effect from the eccentricity of the Earth orbit amd the other is the difference in gravity wave source distribution and filtering due to asymmetries in mean winds of the lower atmosphere. Both processes have been theoretically investigated to explain the observed asymmetry in some of the atmospheric parameters, but not self-consistently in all observed parameters together. In this paper we will show the asymmetry in the time-varying zonal-mean latitudinal structures of temperature, airglow emission rate, and composition observed by TIMED/SABER. We will quantify their interhemispheric asymmetries for different seasons under different solar activity conditions. In addition, temperature measurements will also be used to obtain temporal and spatial morphology of gravity wave potential energies. We will interpret the asymmetry in the observed fields and examine qualitatively their consistency with the two responsible processes, especially the one due to gravity wave filtering process. Our goal is to introduce and to share the spatial and temporal morphologies of all the observed fields to the modeling community so, together self-consistently, they be can be used to gain physical insights into the relative importance of various drivers responsible for the observed asymmetry, especially the role of gravity wave induced eddy drag and mixing, a critical, but least quantitatively understood process.

Functional significance of the pattern of renal sympathetic nerve activation.

PubMed

Dibona, G F; Sawin, L L

1999-08-01

To assess the renal functional significance of the pattern of renal sympathetic nerve activation, computer-generated stimulus patterns (delivered at constant integrated voltage) were applied to the decentralized renal sympathetic nerve bundle and renal hemodynamic and excretory responses determined in anesthetized rats. When delivered at the same integrated voltage, stimulus patterns resembling those observed in in vivo multifiber recordings of renal sympathetic nerve activity (diamond-wave patterns) produced greater renal vasoconstrictor responses than conventional square-wave patterns. Within diamond-wave patterns, increasing integrated voltage by increasing amplitude produced twofold greater renal vasoconstrictor responses than by increasing duration. With similar integrated voltages that were subthreshold for renal vasoconstriction, neither diamond- nor square-wave pattern altered glomerular filtration rate, whereas diamond- but not square-wave pattern reversibly decreased urinary sodium excretion by 25 +/- 3%. At the same number of pulses per second, intermittent stimulation produced faster and greater renal vasoconstriction than continuous stimulation. At the same number of pulses per second, increases in rest period during intermittent stimulation proportionally augmented the renal vasoconstrictor response compared with that observed with continuous stimulation; the maximum augmentation of 55% occurred at a rest period of 500 ms. These results indicate that the pattern of renal sympathetic nerve stimulation (activity) significantly influences the rapidity, magnitude, and selectivity of the renal vascular and tubular responses.

Electron plasma oscillations in the Venus foreshock

NASA Technical Reports Server (NTRS)

Crawford, G. K.; Strangeway, R. J.; Russell, C. T.

1990-01-01

Plasma waves are observed in the solar wind upstream of the Venus bow shock by the Pioneer Venus Orbiter. These wave signatures occur during periods when the interplanetary magnetic field through the spacecraft position intersects the bow shock, thereby placing the spacecraft in the foreshock region. The electron foreshock boundary is clearly evident in the data as a sharp onset in wave activity and a peak in intensity. Wave intensity is seen to drop rapidly with increasing penetration into the foreshock. The peak wave electric field strength at the electron foreshock boundary is found to be similar to terrestrial observations. A normalized wave spectrum was constructed using measurements of the electron plasma frequency and the spectrum was found to be centered about this value. These results, along with polarization studies showing the wave electric field to be field aligned, are consistent with the interpretation of the waves as electron plasma oscillations.

Wave Dynamics and Transport in the Stratosphere

NASA Technical Reports Server (NTRS)

Holton, James R.; Alexander, M. Joan

1999-01-01

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model.

First results of warm mesospheric temperature over Gadanki (13.5°N, 79.2°E) during the sudden stratospheric warming of 2009

NASA Astrophysics Data System (ADS)

Sridharan, S.; Raghunath, K.; Sathishkumar, S.; Nath, D.

2010-09-01

Rayleigh lidar observations at Gadanki (13.5°N, 79.2°E) show an enhancement of the nightly mean temperature by 10-15 K at altitudes 70-80 km and of gravity wave potential energy at 60-70 km during the 2009 major stratospheric warming event. An enhanced quasi-16-day wave activity is observed at 50-70 km in the wavelet spectrum of TIMED-SABER temperatures, possibly due to the absence of a critical level in the low-latitude stratosphere because of less westward winds caused by this warming event. The observed low-latitude mesospheric warming could be due to wave breaking, as waves are damped at 80 km.

Characteristics of electron distributions observed during large amplitude whistler wave events in the magnetosphere

NASA Astrophysics Data System (ADS)

Wilson, L. B., III; Cattell, C. A.; Kellogg, P. J.; Goetz, K.; Wygant, J.; Breneman, A. W.; Kersten, K.

2010-12-01

We present a statistical study of the characteristics of electron distributions associated with large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data as an addition of the study by Kellogg et al., [2010b]. We identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics dependent upon the observed electron distributions. The majority of the waveforms observed in our study have f/fce ≤ 0.5 and are observed primarily in the radiation belts outside the plasmapause simultaneously with anisotropic electron distributions. We also present an example waveform capture of the largest magnetic field amplitude (≥ 8 nT pk-pk) whistler wave measured in the radiation belts. The majority of the largest amplitude whistlers occur during magnetically active periods (AE > 200 nT).

Characteristics of Electron Distributions Observed During Large Amplitude Whistler Wave Events in the Magnetosphere

NASA Technical Reports Server (NTRS)

Wilson, Lynn B., III

2010-01-01

We present a statistical study of the characteristics of electron distributions associated with large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data as an addition of the study by Kellogg et al., [2010b]. We identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics dependent upon the observed electron distributions. The majority of the waveforms observed in our study have f/fce < or = 0.5 and are observed primarily in the radiation belts outside the plasmapause simultaneously with anisotropic electron distributions. We also present an example waveform capture of the largest magnetic field amplitude (> or = 8 nT pk-pk) whistler wave measured in the radiation belts. The majority of the largest amplitude whistlers occur during magnetically active periods (AE > 200 nT).

New observations of Yanai waves and equatorial inertia-gravity waves in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Farrar, J. T.; Durland, T.

2011-12-01

In the 1970's and 1980's, there was a great deal of research activity on near-equatorial variability at periods of days to weeks associated with oceanic equatorial inertia-gravity waves and Yanai waves. At that time, the measurements available for studying these waves were much more limited than today: most of the available observations were from island tide gauges and a handful of short mooring records. We use more than a decade of the extensive modern data record from the TAO/TRITON mooring array in the Pacific Ocean to re-examine the internal-wave climate in the equatorial Pacific, with a focus on interpretation of the zonal-wavenumber/frequency spectrum of surface dynamic height relative to 500-m depth. Many equatorial-wave meridional modes can be identified, for both the first and second baroclinic mode. We also estimated zonal-wavenumber/frequency spectra for the zonal and meridional wind stress components. The location and extent of spectral peaks in dynamic height is readily rationalized using basic, linear theory of forced equatorial waves and the observed wind stress spectrum.

VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au

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

Aggarwal, Poornima; Taylor, David K.; Smith, Charles W.

We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H{sup +} and He{sup +} during 1978–1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source ions, are left-hand polarized in the spacecraft frame, and have minimum variance directions that are quasi-parallel to the local mean magnetic field. There is one exception to this in that one wave event that is excited by pickup H{sup +} is right-hand polarized in the spacecraft frame, butmore » similar exceptions have been reported by Cannon et al. and remain unexplained. We apply the theory of Lee and Ip that predicts the energy spectrum of the waves and then compare growth rates with turbulent cascade rates under the assumption that turbulence acts to destroy the enhanced wave activity and transport the associated energy to smaller scales where dissipation heats the background plasma. As with Cannon et al., we find that the ability to observe the waves depends on the ambient turbulence being weak when compared with growth rates, thereby allowing sustained wave growth. This analysis implies that the coupled processes of pitch-angle scattering and wave generation are continuously associated with newly ionized pickup ions, despite the fact that the waves themselves may not be directly observable. When waves are not observed, but wave excitation can be argued to be present, the wave energy is simply absorbed by the turbulence at a rate that prevents significant accumulation. In this way, the kinetic process of wave excitation by scattering of newborn ions continues to heat the plasma without producing observable wave energy. These findings support theoretical models that invoke efficient scattering of new pickup ions, leading to turbulent driving in the outer solar wind and in the IBEX ribbon beyond the heliopause.« less

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

NASA Astrophysics Data System (ADS)

Spong, D. A.; Heidbrink, W. W.; Paz-Soldan, C.; Du, X. D.; Thome, K. E.; Van Zeeland, M. A.; Collins, C.; Lvovskiy, A.; Moyer, R. A.; Austin, M. E.; Brennan, D. P.; Liu, C.; Jaeger, E. F.; Lau, C.

2018-04-01

DIII-D experiments at low density (ne˜1019 m-3 ) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.

Rac-WAVE2 signaling is involved in the invasive and metastatic phenotypes of murine melanoma cells.

PubMed

Kurisu, Shusaku; Suetsugu, Shiro; Yamazaki, Daisuke; Yamaguchi, Hideki; Takenawa, Tadaomi

2005-02-17

WAVEs (WASP-family verprolin-homologous proteins) regulate the actin cytoskeleton through activation of Arp2/3 complex. As cell motility is regulated by actin cytoskeleton rearrangement and is required for tumor invasion and metastasis, blocking actin polymerization may be an effective strategy to prevent tumor dissemination. We show that WAVEs, especially WAVE2, are essential for invasion and metastasis of melanoma cells. Malignant B16F10 mouse melanoma cells expressed more WAVE1 and WAVE2 proteins and showed higher Rac activity than B16 parental cells, which are neither invasive nor metastatic. The effect of WAVE2 silencing by RNA interference (RNAi) on the highly invasive nature of B16F10 cells was more dramatic than that of WAVE1 RNAi. Membrane ruffling, cell motility, invasion into the extracellular matrix, and pulmonary metastasis of B16F10 cells were suppressed by WAVE2 RNAi. WAVE2 RNAi also had a profound effect on invasion induced by a constitutively active form of Rac (RacCA). In addition, ectopic expression of both RacCA and WAVE2 in B16 cells resulted in further increase in the invasiveness than that observed in B16 cells expressing only RacCA. Thus, WAVE2 acts as the primary effector downstream of Rac to achieve invasion and metastasis, suggesting that suppression of WAVE2 activity holds a promise for preventing cancer invasion and metastasis.

Spatial coherence resonance and spatial pattern transition induced by the decrease of inhibitory effect in a neuronal network

NASA Astrophysics Data System (ADS)

Tao, Ye; Gu, Huaguang; Ding, Xueli

2017-10-01

Spiral waves were observed in the biological experiment on rat brain cortex with the application of carbachol and bicuculline which can block inhibitory coupling from interneurons to pyramidal neurons. To simulate the experimental spiral waves, a two-dimensional neuronal network composed of pyramidal neurons and inhibitory interneurons was built. By decreasing the percentage of active inhibitory interneurons, the random-like spatial patterns change to spiral waves and to random-like spatial patterns or nearly synchronous behaviors. The spiral waves appear at a low percentage of inhibitory interneurons, which matches the experimental condition that inhibitory couplings of the interneurons were blocked. The spiral waves exhibit a higher order or signal-to-noise ratio (SNR) characterized by spatial structure function than both random-like spatial patterns and nearly synchronous behaviors, which shows that changes of the percentage of active inhibitory interneurons can induce spatial coherence resonance-like behaviors. In addition, the relationship between the coherence degree and the spatial structures of the spiral waves is identified. The results not only present a possible and reasonable interpretation to the spiral waves observed in the biological experiment on the brain cortex with disinhibition, but also reveal that the spiral waves exhibit more ordered degree in spatial patterns.

Japanese contributions to MAP

NASA Technical Reports Server (NTRS)

Kato, S.

1989-01-01

Japan contributed much to MAP in many branches. The MU (middle and upper atmosphere) radar, in operation during the MAP period, produced various novel possibilities in observations of middle atmosphere dynamics; possibilities which were fairly well realized. Gravity wave saturation and its spectrum in the mesosphere were observed successfully. Campaign observations by radars between Kyoto and Adelaide were especially significant in tidal and planetary wave observations. In Antarctica, middle atmosphere observation of the dramatic behavior of aerosols in winter is well elucidated together with the ozone hole. Theoretical and numerical studies have been progressing actively since a time much earlier than MAP. Now it is pointed out that gravity waves play an important role in producing the weak wind region in the stratosphere as well as the mesosphere.

Periodic waves in the lower thermosphere observed by OI630 nm airglow images

NASA Astrophysics Data System (ADS)

Paulino, I.; Medeiros, A. F.; Vadas, S. L.; Wrasse, C. M.; Takahashi, H.; Buriti, R. A.; Leite, D.; Filgueira, S.; Bageston, J. V.; Sobral, J. H. A.; Gobbi, D.

2016-02-01

Periodic wave structures in the thermosphere have been observed at São João do Cariri (geographic coordinates: 36.5° W, 7.4° S; geomagnetic coordinates based on IGRF model to 2015: 35.8° E, 0.48° N) from September 2000 to November 2010 using OI630.0 nm airglow images. During this period, which corresponds to almost one solar cycle, characteristics of 98 waves were studied. Similarities between the characteristics of these events and observations at other places around the world were noted, primarily the spectral parameters. The observed periods were mostly found between 10 and 35 min; horizontal wavelengths ranged from 100 to 200 km, and phase speed from 30 to 180 m s-1. These parameters indicated that some of the waves, presented here, are slightly faster than those observed previously at low and middle latitudes (Indonesia, Carib and Japan), indicating that the characteristics of these waves may change at different places. Most of observed waves have appeared during magnetically quiet nights, and the occurrence of those waves followed the solar activity. Another important characteristic is the quasi-monochromatic periodicity that distinguish them from the single-front medium-scale traveling ionospheric disturbances (MSTIDs) that have been observed previously over the Brazilian region. Moreover, most of the observed waves did not present a phase front parallel to the northeast-southwest direction, which is predicted by the Perkins instability process. It strongly suggests that most of these waves must have had different generation mechanisms from the Perkins instability, which have been pointed out as being a very important mechanism for the generation of MSTIDs in the lower thermosphere.

DEMETER Observations of ELF Waves Injected With the HAARP HF Transmitter

DTIC Science & Technology

2006-08-17

DEMETER observations of ELF waves injected with the HAARP HF transmitter M. Platino,1 U. S. Inan,1 T. F. Bell,1 M. Parrot,2 and E. J. Kennedy3...Frequency Active Auroral Research Program ( HAARP ) facility in Gakona, Alaska, (located at L 4.9). Simultaneous observations of all six components of the ELF...signals generated by the HAARP heater are also simultaneously observed at a nearby ground-based site, allowing a comparison of the ELF power in the

Investigation of mesoscale meteorological phenomena as observed by geostationary satellite

NASA Technical Reports Server (NTRS)

Brundidge, K. C.

1982-01-01

Satellite imagery plus conventional synoptic observations were used to examine three mesoscale systems recently observed by the GOES-EAST satellite. The three systems are an arc cloud complex (ACC), mountain lee wave clouds and cloud streets parallel to the wind shear. Possible gravity-wave activity is apparent in all three cases. Of particular interest is the ACC because of its ability to interact with other mesoscale phenomena to produce or enhance convection.

Observations of wave-particle interactions in the flux pile-up region of asymmetric reconnection

NASA Astrophysics Data System (ADS)

Argall, M. R.; Paulson, K. W.; Ahmadi, N.; Matsui, H.; Torbert, R. B.; Alm, L.; Le Contel, O.; Khotyaintsev, Y. V.; Wilder, F. D.; Turner, D. L.; Strangeway, R. J.; Schwartz, S. J.; Magnes, W.; Giles, B. L.; Lindqvist, P. A.; Ergun, R.; Mauk, B.; Leonard, T. W.

2017-12-01

Recent observations have shown electron energization to >100keV with simultaneous whistler wave activity in the vicinity of the dayside reconnection site. We investigate one possible mechanism for producing these energetic particles. Counter-streaming electrons from the magnetosphere enter the diffusion region and are scattered to all pitch angles (PAs) by strong field-line curvature. As the electrons flow outward into the exhaust, they remagnetize and are focused toward 90° at mirror points within the flux pile-up region. This effect, combined with heating mechanisms in the EDR, produces a temperature anisotropy, while the weak magnetic field lowers the resonant energy into the bulk energy of the plasma. In the end, whistler waves are produced near 100Hz with a wave normal angle of 20°. Simultaneous with the waves, the Electron Drift Instrument observes particle flux modulations of 0° and 180° PA, 500 eV electrons. Multi-spacecraft analysis and Liouville mapping techniques allow us to determine the parallel wave current, potential, and associated energy dissipation. Bursts of 100keV electrons are observed and may interact with the whistler waves.

Statistical investigation of the efficiency of EMIC waves in precipitating relativistic electrons

NASA Astrophysics Data System (ADS)

Hudson, M. K.; Qin, M.; Millan, R. M.; Woodger, L. A.; Shekhar, S.

2017-12-01

Electromagnetic ion cyclotron (EMIC) waves have been proposed as an effective way to scatter relativistic electrons into the atmospheric loss cone. In our study, however, among the total 399 coincidence events when NOAA satellites goes through the region of EMIC wave activity, only 103 are associated with Relativistic Electron Precipitation (REP) events, which indicates that the link between EMIC waves and relativistic electrons is much weaker than expected. Most of the studies so far have been focused on the He+ band EMIC waves, and H+ band EMIC waves have been regarded as less important to the precipitation of electrons. In our study, we demonstrate that among the 103 EMIC wave events detected by Van Allen Probes that are in close conjunction with relativistic electron precipitation observed by POES satellites, the occurrence rate of H+ and He+ band EMIC waves coincident with REP is comparable, suggesting closer examination of the range of ΔL and ΔMLT used to determine coincidence between Van Allen Probes EMIC waves and POES precipitation observation.

A high-resolution OGCM simulation of the Tropical Pacific Ocean during the 1985-1994 TOGA period. Part I: Long equatorial waves

NASA Technical Reports Server (NTRS)

Boulanger, J. P.; Delecluse, F.; Maes, C.; Levy, C.

1995-01-01

A high resolution oceanic general circulation model of the three topical oceans is used to investigate long equatorial wave activity in the Pacific Ocean during the 1985-1994 TOGA period. Zonal wind stress forcing and simulated dynamic height are interpreted using techniques previously applied to data. Kelvin and first Rossby waves are observed propagating during all the period. A seasonal cycle and interannual anomalies are computed for each long equatorial wave. The east Pacific basin is mainly dominated by seasonal cycle variations while strong interannual anomalies are observed west of the dateline. Long wave interannual anomalies are then compared to wave coefficients simulated by a simple wind-forced model. Our results outline the major role played by wind forcing on interannual time scales in generating long equatorial waves. However, near both eastern and western boundaries, some differences can be attributed to long wave reflections. A comparison to wave coefficients calculated from GEOSAT sea-level data gives some insight of the model behavior.

Antarctic Polar Descent and Planetary Wave Activity Observed in ISAMS CO from April to July 1992

NASA Technical Reports Server (NTRS)

Allen, D. R.; Stanford, J. L.; Nakamura, N.; Lopez-Valverde, M. A.; Lopez-Puertas, M.; Taylor, F. W.; Remedios, J. J.

2000-01-01

Antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesosphere are observed in ISAMS CO data from April to July 1992. CO-derived mean April-to-May upper stratosphere descent rates of 15 K/day (0.25 km/day) at 60 S and 20 K/day (0.33 km/day) at 80 S are compared with descent rates from diabatic trajectory analyses. At 60 S there is excellent agreement, while at 80 S the trajectory-derived descent is significantly larger in early April. Zonal wavenumber 1 enhancement of CO is observed on 9 and 28 May, coincident with enhanced wave 1 in UKMO geopotential height. The 9 May event extends from 40 to 70 km and shows westward phase tilt with height, while the 28 May event extends from 40 to 50 km and shows virtually no phase tilt with height.

Relativistic Electron Precipitation Events Observed at Low Altitude During Electromagnetic Ion Cyclotron Wave Activities Identified Near The Equator.

NASA Astrophysics Data System (ADS)

Shin, D. K.; Lee, D. Y.; Noh, S. J.; Cho, J.; Choi, C.; Hwang, J.; Lee, J.

2017-12-01

Statistical significance of the efficiency of electron loss into the atmosphere by EMIC waves has yet not been quantified through observations. To better understand the dynamics of the radiation belt particle, its quantification through observations is indispensable. In this study, we used a large number of the EMIC wave events identified near the equator for which we determined relativistic electron precipitation (REP) events using the observations at low earth orbit satellites (POES satellite series).We focused on the difference between the wave properties, geomagnetic conditions and background states during the EMIC waves between the event group (EMIC wave with REP) and non-event group (EMIC wave without REP). First, for 11.5 % of the EMIC wave events we were able to identify the REP events within an hour of MLT separation from the EMIC wave location. The majority ( 80 %) of the precipitation-inducing EMIC waves were found in 11 - 17 MLT. Second, geomagnetic conditions (most notably AE) are more often stronger for the event group than non-event group. Third, the EMIC waves of a stronger power and/or a longer duration are on average preferred for event group. Lastly, the majority of the EMIC waves with REP lie outside the plasmapause, most often at L being higher by 2 than the plasmapause locations. In conclusion, this is the first time report on a statistical assessment about the extent to which the EMIC waves directly measured in the equator can be responsible for REP and about their distinguishing features.

Wave Activity and Its Changes in the Troposphere and Stratosphere of the Northern Hemisphere in Winters of 1979-2016

NASA Astrophysics Data System (ADS)

Guryanov, V. V.; Eliseev, A. V.; Mokhov, I. I.; Perevedentsev, Yu. P.

2018-03-01

An analysis of spectra of wave disturbances with zonal wave numbers 1 ≤ k ≤ 10 is carried out using winter (November to March) ERA-Interim reanalysis geopotential data in the troposphere and stratosphere for 1979-2016. Contributions of eastward-traveling ( E), westward-traveling ( W), and stationary ( S) waves are estimated. The intensification of wave activity is observed in the tropical troposphere and stratosphere and in the upper stratosphere of the entire Northern Hemisphere. The intensification of wave activity in the tropics and subtropics is noted for waves of all types ( E, W, and S), while in the middle and higher latitudes it is related mainly to stationary and eastward waves. Near the subtropical tropopause, the energy of stationary waves has increased in recent decades. In addition, in the tropical and subtropical troposphere and in the subtropical lower stratosphere, the energy of the eastward-traveling waves in El Niño years may be one and a half times or twice the energy in La Niña years. The spectrally weighted zonal wave numbers for waves of all types ( E, W, and S) are the largest in the upper subtropical troposphere. The spectrally weighted zonal wave number for W and S waves is correlated with the Atlantic Multidecadal Oscillation index and varies by 15% in 1979-2016 (on an interdecadal time scale). The spectrally weighted wave period is larger in the stratosphere than in the troposphere. It is maximal in the middle extratropical stratosphere. The spectrally weighted wave periods correlate with the activity of sudden stratospheric warmings. The sign of this correlation depends on the latitude, atmospheric layer, and zonal wave number.

Some observations on the role of planetary waves in determining the spring time ozone distribution in the Antarctic

NASA Technical Reports Server (NTRS)

Chandra, S.; Mcpeters, R. D.

1986-01-01

Ozone measurements from 1970 to 1984 from the Nimbus 4 backscattered ultraviolet and the Nimbus 7 solar backscattered ultraviolet spectrometers show significant decrease in total ozone only after 1979. The downward trend is most apparent in October south of 70 deg S in the longitude zone 0 to 30 deg W where planetary wave activity is weak. Outside this longitude region, the trend in total ozone is much smaller due to strong interannual variability of wave activity. This paper gives a phenomenological description of ozone depletion in the Antarctic region based on vertical advection and transient planetary waves.

FUSE Cycle 3 Program CO22: Chromospheric Activity in Population II Giants

NASA Technical Reports Server (NTRS)

Harper, Graham M.

2004-01-01

One of the mysteries of Population II giants is that they still show chromospheric emission despite their great age. The global dynamo which was active during their main-sequence lifetimes is expected to become extremely weak through magnetic rotational braking. The nature of the observed emission is not understood; although acoustic shock waves might provide the heating, acoustic waves are not predicted to drive the observed mass loss - which in turn requires the dissipation of magneto-hydrodynamic waves. This program was designed to search for the faint stellar H Ly(beta) emission wings and the fluorescent Fe II and H2 emission from one of the brightest, metal poor, Population II stars. These FUSE diagnostics, when combined with existing UV and optical spectra, help determine the major radiative cooling channels for the chromosphere. This observation was to complement that previously planned for the mildly metal deficient giant alpha Boo (K2 III). However, a Boo has yet to be observed with FUSE.

Chromospheric Activity in Population II Giants

NASA Technical Reports Server (NTRS)

Harper, Graham M.

2004-01-01

One of the mysteries of Population II giants is that they still show chromospheric emission despite their great age. The global dynamo which was active during their main-sequence lifetimes is expected to become extremely weak through magnetic rotational braking. The nature of the observed emission is not understood; although acoustic shock waves might provide the heating, acoustic waves are not predicted to drive the observed mass loss - which in turn requires the dissipation of magneto-hydrodynamic waves. This program was designed to search for the faint stellar H Ly beta emission wings and the fluorescent Fe II and H2 emission from one of the brightest, metal poor, Population II stars. These FUSE diagnostics, when combined with existing UV and optical spectra, help determine the major radiative cooling channels for the chromosphere. This observation was to complement that previously planned for the mildly metal deficient giant alpha Boo (K2 III). However, alpha Boo has yet to be observed with FUSE.

Modeling and observations of ULF waves trapped in a plasmaspheric density plume

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Zhang, S.; Foster, J. C.; Shi, Q.; Zong, Q. G.; Rankin, R.

2017-12-01

In order for ULF waves to effectively energise radiation belt electrons by drift-resonance, wave power must be significant in regions within the magnetosphere where the ULF wave phase propagation and electron drift directions are roughly aligned. For waves launched along the dayside magnetopause, such a region would be located in the afternoon - dusk sector of the inner magnetosphere. During periods of storm activity and enhanced convection, the plasma density in this region is highly dynamic due to the development of plasmaspheric drainage plume (PDP) structure. This significantly affects the local Alfvén speed, and alters the propagation of ULF waves launched from the magnetopause. It can therefore be expected that the accessibility of ULF wave power for radiation belt energisation is sensitively dependent on the recent history of magnetospheric convection, and the stage of development of the PDP. This is investigated using a 3D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (Volland - Stern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic-field day/night asymmetry, and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. We find that the plume structure significantly alters the field line resonance (FLR) location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than outside. This may explain satellite observations of the appearance of ULF wave activity within localized density enhancements associated with a PDP. Such an example, made by THEMIS following a geomagnetic storm on October 9, 2013, is described, and compared against the ULF wave model results, for which inputs are constrained by available observations.

Auroral Infrasound Observed at I53US at Fairbanks, Alaska

NASA Astrophysics Data System (ADS)

Wilson, C. R.; Olson, J. V.

2003-12-01

In this presentation we will describe two different types of auroral infrasound recently observed at Fairbanks, Alaska in the pass band from 0.015 to 0.10 Hz. Infrasound signals associated with auroral activity (AIW) have been observed in Fairbanks over the past 30 years with infrasonic microphone arrays. The installation of the new CTBT/IMS infrasonic array, I53US, at Fairbanks has resulted in a greatly increased quality of the infrasonic data with which to study natural sources of infrasound. In the historical data at Fairbanks all the auroral infrasonic waves (AIW) detected were found to be the result of bow waves that are generated by supersonic motion of auroral arcs that contain strong electrojet currents. This infrasound is highly anisotropic, moving in the same direction as that of the auroral arc. AIW bow waves observed in 2003 at I53US will be described. Recently at I53US we have observed many events of very high trace velocity that are comprised of continuous, highly coherent wave trains. These waves occur in the morning hours at times of strong auroral activity. This new type of very high trace velocity AIW appears to be associated with pulsating auroral displays. Pulsating auroras occur predominantly after magnetic midnight (10:00 UT at Fairbanks). They are a usual part of the recovery phase of auroral substorms and are produced by energetic electrons precipitating into the atmosphere. Given proper dark, cloudless sky conditions during the AIW events, bright pulsating auroral forms were sometimes visible overhead.

Trapped mountain wave excitations over the Kathmandu valley, Nepal

NASA Astrophysics Data System (ADS)

Regmi, Ram P.; Maharjan, Sangeeta

2015-11-01

Mid-wintertime spatial and temporal distributions of mountain wave excitation over the Kathmandu valley has been numerically simulated using Weather Research and Forecasting (WRF) modeling system. The study shows that low-level trapped mountain waves may remain very active during the night and early morning in the sky over the southern rim of the surrounding mountains, particularly, over the lee of Mt. Fulchoki. Calculations suggest that mountain wave activities are at minimum level during afternoon. The low-level trapped mountain waves in the sky over southern gateway of Tribhuvan International Airport (TIA) may pose risk for landings and takeoffs of light aircrafts. Detailed numerical and observational studies would be very important to reduce risk of air accidents and discomfort in and around the Kathmandu valley.

Disciplinary Knots and Learning Problems in Waves Physics

NASA Astrophysics Data System (ADS)

Di Renzone, Simone; Frati, Serena; Montalbano, Vera

An investigation on student understanding of waves is performed during an optional laboratory realized in informal extracurricular way with few, interested and talented pupils. The background and smart intuitions of students rendered the learning path very dynamic and ambitious. The activities started by investigating the basic properties of waves by means of a Shive wave machine. In order to make quantitative observed phenomena, the students used a camcorder and series of measures were obtained from the captured images. By checking the resulting data, it arose some learning difficulties especially in activities related to the laboratory. This experience was the starting point for a further analysis on disciplinary knots and learning problems in the physics of waves in order to elaborate a teaching-learning proposal on this topic.

Slow-Mode MHD Wave Penetration into a Coronal Null Point due to the Mode Transmission

NASA Astrophysics Data System (ADS)

Afanasyev, Andrey N.; Uralov, Arkadiy M.

2016-11-01

Recent observations of magnetohydrodynamic oscillations and waves in solar active regions revealed their close link to quasi-periodic pulsations in flaring light curves. The nature of that link has not yet been understood in detail. In our analytical modelling we investigate propagation of slow magnetoacoustic waves in a solar active region, taking into account wave refraction and transmission of the slow magnetoacoustic mode into the fast one. The wave propagation is analysed in the geometrical acoustics approximation. Special attention is paid to the penetration of waves in the vicinity of a magnetic null point. The modelling has shown that the interaction of slow magnetoacoustic waves with the magnetic reconnection site is possible due to the mode transmission at the equipartition level where the sound speed is equal to the Alfvén speed. The efficiency of the transmission is also calculated.

Survey of upper band chorus and ECH waves: Implications for the diffuse aurora

NASA Astrophysics Data System (ADS)

Meredith, Nigel; Horne, Richard; Thorne, Richard; Anderson, Roger

2010-05-01

The origin of the diffuse aurora has been a source of controversy for many years. More recently the question has taken a new significance in view of the associated changes in atmospheric chemistry which may affect the middle atmosphere. Here we use CRRES data to assess the importance of upper band chorus and electron cyclotron harmonic (ECH) waves in the production of the diffuse aurora. Both wave modes increase with increasing geomagnetic activity, suggesting they are related to periods of enhanced convection and/or substorm activity. They are confined to the near-equatorial region which excludes the pre-noon sector from the wave survey. During active conditions intense ECH waves and upper band chorus, with amplitudes exceeding 1 mVm-1, are observed in the region 4 < L < 7 from 2100 to 0600 MLT approximately 20% and 6% of the time respectively. This suggests that both wave modes can put electrons on strong diffusion, but only during active conditions and not at all local times. Scattering rates fall below the strong diffusion limit at other times when the wave amplitudes are weaker. Fluxes of low energy electrons (100 eV < E < 30 keV) also increase with increasing geomagnetic activity in approximately the same region of geospace as the waves, suggesting that these electrons are responsible for the generation of the waves. The patterns of the upper band chorus, ECH waves and low energy electrons are similar to the global morphology of the diffuse aurora, suggesting that both wave modes play significant roles in the production of the diffuse aurora.

The Nonlinear Coupling of Alfven and Lower Hybrid Waves in Space Plasma

NASA Technical Reports Server (NTRS)

Khazanov, George V.

2004-01-01

Space plasmas support a wide variety of waves, and wave-particle interactions as well as wave-wave interactions which are of crucial importance to magnetospheric and ionospheric plasma behavior. The excitation of lower hybrid waves (LHWs) in particular is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves may generate LHWs in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We present several examples of observational data which illustrate that the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in the ionosphere and magnetosphere and demonstrate electron and ion energization involving these processes. We discuss the morphology dynamics and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al. 2002) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

Predictions of lithium interactions with earth's bow shock in the presence of wave activity

NASA Technical Reports Server (NTRS)

Decker, R. B.; Lui, A. T. Y.; Vlahos, L.

1984-01-01

The results of a test-particle simulation studying the movement of a lithium tracer ion injected upstream of the bow shock are reported. Wave activity consists of parallel and antiparallel propagating Alfven waves characterized by a frequency power spectrum within a frequency or range of amplitudes defined separately in the upstream and downstream regions. The results show that even a moderate level of wave activity can substantially change the results obtained in the absence of waves. Among the effects observed are: (1) increased ion transmission; (2) both the average energy gain and spread about the average are increased for transmitted and reflected particles; (3) the average final pitch angle for transmitted particles tends to 90 deg, and the spread of reflected particles is reduced; and (4) the spatial dispersion of the ions on the bow shock after a single encounter is increased.

Response of thermal ions to electromagnetic ion cyclotron waves

NASA Technical Reports Server (NTRS)

Anderson, B. J.; Fuselier, S. A.

1994-01-01

Electromagnetic ion cyclotron waves generated by 10 - 50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H(+) and He(+) distribution functions from approx. equals 1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicular heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90 deg pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He(+) temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He(+) ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He(+) distributions are consistent with a gyroresonant interaction off the equator. The concentration of He(+) relative to H(+) is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He(+) accounts for the apparent increase in relative He(+) concentration by increasing the proportion of He(+) detected by the ion instrument.

Investigation of the High Latitude Magnetosphere and its Response to the Solar Wind

NASA Technical Reports Server (NTRS)

Taylor, William W. L.

1996-01-01

INSPIRE is a non-profit scientific, educational corporation whose objective is to bring the excitement of observing natural and manmade radio waves in the audio region to high school students. Stimulating students to learn and understand science and technology is the key to them fulfilling their potential in the best interests of our society. INSPIRE also is an innovative, unique opportunity for students to actively gather data that might be used in a basic research project. INSPIRE began with a test bed project, ACTIVE/HSGS, which involved 100 high schools, with a centerpiece of making observations of 10.5 kHz transmissions from the Soviet ACTIVE satellite. A large number of ground receiving sites was needed, both to enhance the probability of receiving the radio waves from ACTIVE, and to determine the propagation paths to the ground. The second major project was support to SEPAC (Space Experiments using Particle ACcelerators), a payload on the ATLAS I Spacelab mission, flown in March/April 1992. With its electron accelerator SEPAC performed many experiments in the ionosphere, including producing an artificial aurora and the electromagnetic waves produced by pulsing the electron beam. INSPIRE/SEPAC provided more than 1000 ground stations to receive the radio waves, and, at the same time, allowed high school students the opportunity to take data that would be used in a published basic research project. The third major project is to make observations of the effects of a pulsed electron beam and plasma generator on the MIR Space Station. On request, these instruments are operated over INSPIRE observers.

Van Allen Probes observation and modeling of chorus excitation and propagation during weak geomagnetic activities

DOE PAGES

He, Yihua; Xiao, Fuliang; Zhou, Qinghua; ...

2015-08-20

We report correlated data on nightside chorus waves and energetic electrons during two small storm periods: 1 November 2012 (Dst ≈ –45) and 14 January 2013 (Dst ≈ –18). The Van Allen Probes simultaneously observed strong chorus waves at locations L = 5.8 – 6.3, with a lower frequency band 0.1–0.5fce and a peak spectral density ~10 –4 nT 2/Hz. In the same period, the fluxes and anisotropy of energetic (~10–300 keV) electrons were greatly enhanced in the interval of large negative interplanetary magnetic field Bz. Using a bi-Maxwellian distribution to model the observed electron distribution, we perform ray tracingmore » simulations to show that nightside chorus waves are indeed produced by the observed electron distribution with a peak growth for a field-aligned propagation approximately between 0.3f ce and 0.4f ce, at latitude <7°. Moreover, chorus waves launched with initial normal angles either θ < 90° or > 90° propagate along the field either northward or southward and then bounce back either away from Earth for a lower frequency or toward Earth for higher frequencies. The current results indicate that nightside chorus waves can be excited even during weak geomagnetic activities in cases of continuous injection associated with negative Bz. Furthermore, we examine a dayside event during a small storm C on 8 May 2014 (Dst ≈ –45) and find that the observed anisotropic energetic electron distributions potentially contribute to the generation of dayside chorus waves, but this requires more thorough studies in the future.« less

Three-wave and four-wave interactions in gravity wave turbulence

NASA Astrophysics Data System (ADS)

Aubourg, Quentin; Campagne, Antoine; Peureux, Charles; Ardhuin, Fabrice; Sommeria, Joel; Viboud, Samuel; Mordant, Nicolas

2017-11-01

Weak-turbulence theory is a statistical framework to describe a large ensemble of nonlinearly interacting waves. The archetypal example of such system is the ocean surface that is made of interacting surface gravity waves. Here we describe a laboratory experiment dedicated to probe the statistical properties of turbulent gravity waves. We set up an isotropic state of interacting gravity waves in the Coriolis facility (13-m-diam circular wave tank) by exciting waves at 1 Hz by wedge wave makers. We implement a stereoscopic technique to obtain a measurement of the surface elevation that is resolved in both space and time. Fourier analysis shows that the laboratory spectra are systematically steeper than the theoretical predictions and the field observations in the Black Sea by Leckler et al. [F. Leckler et al., J. Phys. Oceanogr. 45, 2484 (2015), 10.1175/JPO-D-14-0237.1]. We identify a strong impact of surface dissipation on the scaling of the Fourier spectrum at the scales that are accessible in the experiments. We use bicoherence and tricoherence statistical tools in frequency and/or wave-vector space to identify the active nonlinear coupling. These analyses are also performed on the field data by Leckler et al. for comparison with the laboratory data. Three-wave coupling is characterized by and shown to involve mostly quasiresonances of waves with second- or higher-order harmonics. Four-wave coupling is not observed in the laboratory but is evidenced in the field data. We discuss temporal scale separation to explain our observations.

Electron-acoustic solitons and double layers in the inner magnetosphere: ELECTRON-ACOUSTIC SOLITONS

DOE PAGES

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; ...

2017-05-28

The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV)more » is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron-acoustic waves (existing due to the presence of cold and hot electrons) and follow the Korteweg-de Vries (KdV) dispersion relation derived for the observed plasma conditions (electron energy spectrum is a power law between about 100 eV and 10 keV and Maxwellian above 10 keV). The ESW spatial scales are in general agreement with the KdV theory. We interpret the asymmetric ESW in terms of electron-acoustic solitons and double layers (shocks waves).« less

Electron-acoustic solitons and double layers in the inner magnetosphere: ELECTRON-ACOUSTIC SOLITONS

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

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.

The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV)more » is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron-acoustic waves (existing due to the presence of cold and hot electrons) and follow the Korteweg-de Vries (KdV) dispersion relation derived for the observed plasma conditions (electron energy spectrum is a power law between about 100 eV and 10 keV and Maxwellian above 10 keV). The ESW spatial scales are in general agreement with the KdV theory. We interpret the asymmetric ESW in terms of electron-acoustic solitons and double layers (shocks waves).« less

Alfvén Wave Heating Model of an Active Region and Comparisons with the EIS Observations

NASA Astrophysics Data System (ADS)

Lawless, A. P.; Asgari-Targhi, M.

2013-12-01

We study the generation and dissipation of Alfvén waves in open and closed field lines using the images from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) (van Ballegouijen et al. 2011; Asgari-Targhi & van Ballegouijen 2012; Asgari et al. 2013). The goal is to search for observational evidence of Alfvén waves in the solar corona and to understand their role in coronal heating. We focus on one particular active region on the 10th of December 2007. Using the MDI magnetogram and the potential field modeling of this region, we create three-dimensional MHD models for several open and closed field lines in different locations in the active region. For each model, we compute the temperature, pressure, magnetic field strength, average heating rate, and other parameters along the loop. We then compare these results with the EIS observations. This research is supported by the NSF grant for the Solar physics REU Program at the Smithsonian Astrophysical Observatory (AGS-1263241) and contract SP02H1701R from Lockheed-Martin to SAO.

A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves

NASA Astrophysics Data System (ADS)

Long, D. M.; Murphy, P.; Graham, G.; Carley, E. P.; Pérez-Suárez, D.

2017-12-01

Solar eruptions are the most spectacular events in our solar system and are associated with many different signatures of energy release including solar flares, coronal mass ejections, global waves, radio emission and accelerated particles. Here, we apply the Coronal Pulse Identification and Tracking Algorithm (CorPITA) to the high-cadence synoptic data provided by the Solar Dynamics Observatory (SDO) to identify and track global waves observed by SDO. 164 of the 362 solar flare events studied (45%) were found to have associated global waves with no waves found for the remaining 198 (55%). A clear linear relationship was found between the median initial velocity and the acceleration of the waves, with faster waves exhibiting a stronger deceleration (consistent with previous results). No clear relationship was found between global waves and type II radio bursts, electrons or protons detected in situ near Earth. While no relationship was found between the wave properties and the associated flare size (with waves produced by flares from B to X-class), more than a quarter of the active regions studied were found to produce more than one wave event. These results suggest that the presence of a global wave in a solar eruption is most likely determined by the structure and connectivity of the erupting active region and the surrounding quiet solar corona rather than by the amount of free energy available within the active region.

Flow-Driven Waves and Phase-Locked Self-Organization in Quasi-One-Dimensional Colonies of Dictyostelium discoideum

NASA Astrophysics Data System (ADS)

Gholami, A.; Steinbock, O.; Zykov, V.; Bodenschatz, E.

2015-01-01

We report experiments on flow-driven waves in a microfluidic channel containing the signaling slime mold Dictyostelium discoideum. The observed cyclic adenosine monophosphate (cAMP) wave trains developed spontaneously in the presence of flow and propagated with the velocity proportional to the imposed flow velocity. The period of the wave trains was independent of the flow velocity. Perturbations of flow-driven waves via external periodic pulses of the signaling agent cAMP induced 1 ∶1 , 2 ∶1 , 3 ∶1 , and 1 ∶2 frequency responses, reminiscent of Arnold tongues in forced oscillatory systems. We expect our observations to be generic to active media governed by reaction-diffusion-advection dynamics, where spatially bound autocatalytic processes occur under flow conditions.

Global Neuromagnetic Cortical Fields Have Non-Zero Velocity

PubMed Central

Alexander, David M.; Nikolaev, Andrey R.; Jurica, Peter; Zvyagintsev, Mikhail; Mathiak, Klaus; van Leeuwen, Cees

2016-01-01

Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent activity occurred in the delta, theta, alpha and beta bands of the signal in the form of large-scale waves, which propagated with a variety of velocities. Their mean speed at each frequency band was proportional to temporal frequency, giving a range of 0.06 to 4.0 m/s, from delta to beta. The wave peaks moved over the entire measurement array, during both ongoing activity and task-relevant intervals; direction of motion was more predictable during the latter. A large proportion of the cortical signal, measurable at the scalp, exists as large-scale coherent motion. We argue that the distribution of observable phase velocities in MEG is dominated by spatial filtering considerations in combination with group velocity of cortical activity. Traveling waves may index processes involved in global coordination of cortical activity. PMID:26953886

A Statistical Analysis of Langmuir Wave-Electron Correlations Observed by the CHARM II Auroral Sounding Rocket

NASA Astrophysics Data System (ADS)

Dombrowski, M. P.; Labelle, J. W.; Kletzing, C.; Bounds, S. R.; Kaeppler, S. R.

2014-12-01

Langmuir-mode electron plasma waves are frequently observed by spacecraft in active plasma environments such as the ionosphere. Ionospheric Langmuir waves may be excited by the bump-on-tail instability generated by impinging beams of electrons traveling parallel to the background magnetic field (B). The Correlation of High-frequencies and Auroral Roar Measurement (CHARM II) sounding rocket was launched into a substorm at 9:49 UT on 17 February 2010, from the Poker Flat Research Range in Alaska. The primary instruments included the University of Iowa Wave-Particle Correlator (WPC), the Dartmouth High-Frequency Experiment (HFE), several charged particle detectors, low-frequency wave instruments, and a magnetometer. The HFE is a receiver system which effectively yields continuous (100% duty cycle) electric-field waveform measurements from 100 kHz to 5 MHz, and which had its detection axis aligned nominally parallel to B. The HFE output was fed on-payload to the WPC, which uses a phase-locked loop to track the incoming wave frequency with the most power, then sorting incoming electrons at eight energy levels into sixteen wave-phase bins. CHARM II encountered several regions of strong Langmuir wave activity throughout its 15-minute flight, and the WPC showed wave-lock and statistically significant particle correlation distributions during several time periods. We show results of an in-depth analysis of the CHARM II WPC data for the entire flight, including statistical analysis of correlations which show evidence of direct interaction with the Langmuir waves, indicating (at various times) trapping of particles and both driving and damping of Langmuir waves by particles. In particular, the sign of the gradient in particle flux appears to correlate with the phase relation between the electrons and the wave field, with possible implications for the wave physics.

Propagating Cell-Membrane Waves Driven by Curved Activators of Actin Polymerization

PubMed Central

Peleg, Barak; Disanza, Andrea; Scita, Giorgio; Gov, Nir

2011-01-01

Cells exhibit propagating membrane waves which involve the actin cytoskeleton. One type of such membranal waves are Circular Dorsal Ruffles (CDR) which are related to endocytosis and receptor internalization. Experimentally, CDRs have been associated with membrane bound activators of actin polymerization of concave shape. We present experimental evidence for the localization of convex membrane proteins in these structures, and their insensitivity to inhibition of myosin II contractility in immortalized mouse embryo fibroblasts cell cultures. These observations lead us to propose a theoretical model which explains the formation of these waves due to the interplay between complexes that contain activators of actin polymerization and membrane-bound curved proteins of both types of curvature (concave and convex). Our model predicts that the activity of both types of curved proteins is essential for sustaining propagating waves, which are abolished when one type of curved activator is removed. Within this model waves are initiated when the level of actin polymerization induced by the curved activators is higher than some threshold value, which allows the cell to control CDR formation. We demonstrate that the model can explain many features of CDRs, and give several testable predictions. This work demonstrates the importance of curved membrane proteins in organizing the actin cytoskeleton and cell shape. PMID:21533032

Generation of Highly Oblique Lower Band Chorus Via Nonlinear Three-Wave Resonance

DOE PAGES

Fu, Xiangrong; Gary, Stephen Peter; Reeves, Geoffrey D.; ...

2017-09-05

Chorus in the inner magnetosphere has been observed frequently at geomagnetically active times, typically exhibiting a two-band structure with a quasi-parallel lower band and an upper band with a broad range of wave normal angles. But recent observations by Van Allen Probes confirm another type of lower band chorus, which has a large wave normal angle close to the resonance cone angle. It has been proposed that these waves could be generated by a low-energy beam-like electron component or by temperature anisotropy of keV electrons in the presence of a low-energy plateau-like electron component. This paper, however, presents an alternativemore » mechanism for generation of this highly oblique lower band chorus. Through a nonlinear three-wave resonance, a quasi-parallel lower band chorus wave can interact with a mildly oblique upper band chorus wave, producing a highly oblique quasi-electrostatic lower band chorus wave. This theoretical analysis is confirmed by 2-D electromagnetic particle-in-cell simulations. Furthermore, as the newly generated waves propagate away from the equator, their wave normal angle can further increase and they are able to scatter low-energy electrons to form a plateau-like structure in the parallel velocity distribution. As a result, the three-wave resonance mechanism may also explain the generation of quasi-parallel upper band chorus which has also been observed in the magnetosphere.« less

Plasma waves at comet 67P/Churyumov-Gerasimenko: in the diamagnetic cavity and outside it

NASA Astrophysics Data System (ADS)

Gunell, Herbert; Altwegg, Kathrin; Cessateur, Gaël; De Keyser, Johan; Dhooghe, Frederik; Eriksson, Anders; Gibbons, Andrew; Glassmeier, Karl-Heinz; Goetz, Charlotte; Karlsson, Tomas; Hamrin, Maria; Henri, Pierre; Maggiolo, Romain; Nilsson, Hans; Odelstad, Elias; Rubin, Martin; Wedlund, Cyril Simon; Stenberg Wieser, Gabriella; Tzou, Chia-Yu; Vallieres, Xavier

2017-04-01

We present observations of waves at Comet 67P/Churyumov-Gerasimenko performed on 20 January 2015, when the activity of the comet was low, and in July and August 2015 when the activity had increased and the Rosetta spacecraft passed through the diamagnetic cavity several times. We use distribution functions obtained by the Ion Composition Analyser of the Rosetta Plasma Consortium (RPC-ICA) and electron temperature estimates from the Langmuir Probes (RPC-LAP) to compute dispersion relations for waves on the ion timescale, and we compare the results to spectra obtained by RPC-LAP. On 20 January 2015, at low activity, peaks of the wave spectra appeared at frequencies near 500 Hz, and we identify these waves as ion acoustic. We performed cross-calibrations between RPC-ICA, RPC-LAP, and the Mutual Impedance Probe (RPC-MIP) in order to determine the plasma density. Matching the dispersion relations to the wave observations also helps us estimating the density. We explore the relationship between the waves, the ion distribution functions, and the neutral density, which was measured by the ROSINA-COPS instrument. It is found that when the waves are seen, the ion temperature is low (approximately 0.01 eV). At times the ion temperature is higher (approximately 1 eV), approaching the electron temperature, which leads to strong damping of the ion acoustic waves. This happens when the neutral density is high, suggesting that the ions are heated by being accelerated by the solar wind electric field and scattered in collisions with the neutrals. These results are compared to measurements of wave spectra when Rosetta was inside the diamagnetic cavity in July and August 2015. In the cavity, the plasma is effectively unmagnetised. We identify cavity passages using the magnetometer RPC-MAG. The waves are analysed in the same way as in the earlier measurements outside the cavity, and the two cases are compared.

Van Allen Probes observations of structured whistler mode activity and coincident electron Landau acceleration inside a remnant plasmaspheric plume

NASA Astrophysics Data System (ADS)

Woodroffe, J. R.; Jordanova, V. K.; Funsten, H. O.; Streltsov, A. V.; Bengtson, M. T.; Kletzing, C. A.; Wygant, J. R.; Thaller, S. A.; Breneman, A. W.

2017-03-01

We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement.

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitations, Plasma Waves, and Convection Observed by POLAR

NASA Technical Reports Server (NTRS)

Hirahara, M.; Horwitz, J. L.; Moore, T. E.; Germany, G. A.; Spann, J. F.; Peterson, W. K.; Shelley, E. G.; Chandler, M. O.; Giles, B. L.; Craven, P. D.;

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitation, Plasma Waves, and Convection Observed by Polar

NASA Technical Reports Server (NTRS)

Hirahara, M.; Horwitz, J. L.; Moore, T. E.; Germany, G. A.; Spann, J. F.; Peterson, W. K.; Shelley, E. G.; Chandler, M. O.; Giles, B. L.; Craven, P. D.;

PFISR nightside observations of naturally enhanced ion acoustic lines, and their relation to boundary auroral features

NASA Astrophysics Data System (ADS)

Michell, R. G.; Lynch, K. A.; Heinselman, C. J.; Stenbaek-Nielsen, H. C.

2008-11-01

We present results from a coordinated camera and radar study of the auroral ionosphere conducted during March of 2006 from Poker Flat, Alaska. The campaign was conducted to coincide with engineering tests of the first quarter installation of the Poker Flat Incoherent Scatter Radar (PFISR). On 31 March 2006, a moderately intense auroral arc, (~10 kR at 557.7 nm), was located in the local magnetic zenith at Poker Flat. During this event the radar observed 7 distinct periods of abnormally large backscattered power from the F-region. These were only observed in the field-aligned radar beam, and radar spectra from these seven times show naturally enhanced ion-acoustic lines (NEIALs), the first observed with PFISR. These times corresponded to (a) when the polar cap boundary of the auroral oval passed through the magnetic zenith, and (b) when small-scale filamentary dark structures were visible in the magnetic zenith. The presence of both (a) and (b) was necessary for their occurrence. Soft electron precipitation occurs near the magnetic zenith during these same times. The electron density in the vicinity where NEIALs have been observed by previous studies is roughly between 5 and 30×1010 m-3. Broad-band extremely low frequency (BBELF) wave activity is observed in situ by satellites and sounding rockets to occur with similar morphology, during active auroral conditions, associated with the poleward edge of the aurora and soft electron precipitation. The observations presented here suggest further investigation of the idea that NEIALs and BBELF wave activity are differently-observed aspects of the same wave phenomenon. If a connection between NEIALs and BBELF can be established with more data, this could provide a link between in situ measurements of downward current regions (DCRs) and dynamic aurora, and ground-based observations of dark auroral structures and NEIALs. Identification of in situ processes, namely wave activity, in ground-based signatures could have many implications. One specific example of interest is identifying and following the temporal and spatial evolution of regions of potential ion outflow over large spatial and temporal scales using ground-based optical observations.

Spectral properties of Langmuir and beam-mode waves observed inside terrestrial foreshock by Cluster spacecraf

NASA Astrophysics Data System (ADS)

Pisa, D.; Soucek, J.; Santolik, O.

2016-12-01

Electrostatic plasma waves are commonly observed in the upstream regions of planetary shocks. Solar wind electrons accelerated at the shock front are reflected back into the solar wind and form electron beams. The electron distribution becomes unstable and electrostatic waves are generated inside the foreshock region. The processes of generation and evolution of electrostatic waves significantly depend on the solar wind plasma conditions and generally exhibit complex behavior. Langmuir waves can be identified as intense narrowband emission at the local plasma frequency and weaker broadband beam-mode waves below and above the plasma frequency deeper in the downstream region. We present a long-term survey of Langmuir and beam-mode waves in the vicinity of the plasma frequency observed upstream of the terrestrial bow shock by the Cluster spacecraft. Using solar wind data and bow shock positions from OMNI, as well as in-situ measurements of interplanetary magnetic field, we have mapped all available spacecraft positions into foreshock coordinates. For a study of plasma waves, we have used spectra and local plasma frequencies obtained from a passive and active mode of the WHISPER instrument. We show a spatial distribution of wave frequencies and spectral widths as a function of foreshock positions and solar wind conditions.

Ion cyclotron waves near comet C/2013 A1 (Siding Spring) and Mars

NASA Astrophysics Data System (ADS)

Crary, F. J.; Dols, V. J.; Connerney, J. E. P.; Espley, J. R.

2014-12-01

On October 19, 2014, comet C/2013 A1 (Siding Spring) passed approximately 135,000 km from Mars. Previously,we predicted the amplitude of ion cyclotron waves which might be observed during the Siding Spring encounter. Ioncyclotron waves have been observed both in the vicinity of comets and of Mars. These waves are generated by theionization of neutrals in the flowing solar wind, which produces an unstable ring-beam velocity distribution. We estimated that, for a production rate of 2x1028 s-1, ion cyclotron wave with amplitudes over 0.1 nT would be present within ‡5 hours (1.2 million km) of closest approach. We will compare the actual observations made by the MAVEN spacecraft with these predictions. The spacecraft was close to or downstream of the martian bow shock, which complicates the interpretation of the data. Taking thisinto account, we will describe the observations and their implications for wave activity and cometary neutral production. We also present updated hybrid simulations of ion cyclotron wave generation. The simulations use our best estimate of solar wind conditions at the time of the encounter and a variable injection of 18 AMU pickup ions, at a rates consistent a model of the cometary neutrals.

Radio physics of the sun; Proceedings of the Symposium, University of Maryland, College Park, Md., August 7-10, 1979

NASA Technical Reports Server (NTRS)

Kundu, M. R. (Editor); Gergely, T. E.

1980-01-01

Papers are presented in the areas of the radio characteristics of the quiet sun and active regions, the centimeter, meter and decameter wavelength characteristics of solar bursts, space observations of low-frequency bursts, theoretical interpretations of solar active regions and bursts, joint radio, visual and X-ray observations of active regions and bursts, and the similarities of stellar radio characteristics to solar radio phenomena. Specific topics include the centimeter and millimeter wave characteristics of the quiet sun, radio fluctuations arising upon the transit of shock waves through the transition region, microwave, EUV and X-ray observations of active region loops and filaments, interferometric observations of 35-GHz radio bursts, emission mechanisms for radio bursts, the spatial structure of microwave bursts, observations of type III bursts, the statistics of type I bursts, and the numerical simulation of type III bursts. Attention is also given to the theory of type IV decimeter bursts, Voyager observations of type II and III bursts at kilometric wavelengths, radio and whitelight observations of coronal transients, and the possibility of obtaining radio observations of current sheets on the sun.

Global Measurements of Stratospheric Mountain Waves from Space

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Preusse, Peter; Jackman, Charles H. (Technical Monitor)

1999-01-01

Temperatures acquired by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) during shuttle mission STS-66 have provided measurements of stratospheric mountain waves from space. Large-amplitude, long-wavelength mountain waves at heights of 15 to 30 kilometers above the southern Andes Mountains were observed and characterized, with vigorous wave breaking inferred above 30 kilometers. Mountain waves also occurred throughout the stratosphere (15 to 45 kilometers) over a broad mountainous region of central Eurasia. The global distribution of mountain wave activity accords well with predictions from a mountain wave model. The findings demonstrate that satellites can provide the global data needed to improve mountain wave parameterizations and hence global climate and forecast models.

Solar Jets as Sources of Outflows, Heating and Waves

NASA Astrophysics Data System (ADS)

Nishizuka, N.

2013-05-01

Recent space solar observations of the Sun, such as Hinode and SDO, have revealed that magnetic reconnection is ubiquitous in the solar atmosphere, ranging from small scale reconnection (observed as nanoflares) to large scale one (observed as long duration flares or giant arcades). Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets, penumbral microjets and light bridge jets from sunspot umbra. It was also found that the corona is full of tiny X-ray jets. Often they are seen as helical spinning jets with Alfvenic waves in the corona. Sometimes they are seen as chromospheric jets with slow-mode magnetoacoustic waves and sometimes as unresolved jet-like events at the footpoint of recurrent outflows and waves at the edge of the active region. There is increasing evidence of magnetic reconnection in these tiny jets and its association with waves. The origin of outflows and waves is one of the issues concerning coronal heating and solar wind acceleration. To answer this question, we had a challenge to reproduce solar jets with laboratory plasma experiment and directly measured outflows and waves. As a result, we could find a propagating wave excited by magnetic reconnection, whose energy flux is 10% of the released magnetic energy. That is enough for solar wind acceleration and locally enough for coronal heating, consistent with numerical MHD simulations of solar jets. Here we would discuss recent observations with Hinode, theories and experimental results related to jets and waves by magnetic reconnection, and discuss possible implication to reconnection physics, coronal heating and solar wind acceleration.

Characterization of Activity at Loki from Galileo and Ground-based Observations

NASA Technical Reports Server (NTRS)

Howell, R. R.; Lopes, R. M.

2004-01-01

While Loki is the most active volcanic center on Io, major questions remain concerning the nature of that activity. Rathbun et al. showed that the activity was semi-periodic, and suggested it was due to a resurfacing wave which swept across a lava lake as the crust cooled and become unstable. However in 2001 new observations showed that an intermediate level, less periodic mode of activity had apparently begun. Galileo-NIMS observations of Loki clearly show that the highest temperatures are found near the edge of the patera, consistent with disruption of a lava lake at the margins. NIMS observations also show gradients in temperature across the patera which, when modeled in terms of lava cooling models, are generally consistent with ages expected for the resurfacing wave but may also be consistent with spreading flows. We present a further analysis of NIMS data from I24 and I32 which help define the nature of the temperature variations present in Loki patera, along with Galileo-SSI images from the G1-I32 flybys which show albedo changes apparently correlated with the "periodic" activity measured from ground-based observations.

Relating Alfvén Wave Heating Model to Observations of a Solar Active Region

NASA Astrophysics Data System (ADS)

Yoritomo, J. Y.; Van Ballegooijen, A. A.

2012-12-01

We compared images from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) with simulations of propagating and dissipating Alfvén waves from a three-dimensional magnetohydrodynamic (MHD) model (van Ballegooijen et. al 2011; Asgari-Targhi & van Ballegooijen 2012). The goal was to search for observational evidence of Alfvén waves in the solar corona and understand their role in coronal heating. We looked at one particular active region on the 5th of May 2012. Certain distinct loops in the SDO/AIA observations were selected and expanded. Movies were created from these selections in an attempt to discover transverse motions that may be Alfvén waves. Using a magnetogram of that day and the corresponding synoptic map, a potential field model was created for the active region. Three-dimensional MHD models for several loops in different locations in the active region were created. Each model specifies the temperature, pressure, magnetic field strength, average heating rate, and other parameters along the loop. We find that the heating is intermittent in the loops and reflection occurs at the transition region. For loops at larger and larger height, a point is reached where thermal non-equilibrium occurs. In the center this critical height is much higher than in the periphery of the active region. Lastly, we find that the average heating rate and coronal pressure decrease with increasing height in the corona. This research was supported by an NSF grant for the Smithsonian Astrophysical Observatory (SAO) Solar REU program and a SDO/AIA grant for the Smithsonian Astrophysical Observatory.

Complex Non-volcanic Tremor in Guerrero Mexico Triggered by the 2010 Mw 8.8 Chilean Earthquake

NASA Astrophysics Data System (ADS)

Zigone, D.; Campillo, M.; Husker, A. L.; Kostoglodov, V.; Payero, J. S.; Frank, W.; Shapiro, N. M.; Voisin, C.; Cougoulat, G.; Cotte, N.

2010-12-01

In this study we analyze the tremors triggered in Guerrero region (Mexico) by the 2010 magnitude 8.8 Chilean Earthquake using mini-seismic array data from the French-Mexican G-GAP project and broadband data from the Servicio Sismologico Nacional of Mexico. The strong dynamic shaking by the earthquake produced the first observed triggered non-volcanic tremors (NVT) in Mexico so far with at least 3 different types of tremors at different time scales. There was a slow slip event (SSE) occurring at the time of the earthquake, which may have increased the probability of tremor triggering in the region. The first type of observed triggered tremors occurred during the S waves, Love waves and Rayleigh waves as already reported in other subductions zones and continental faults (Miyazawa and Mori, 2005, 2006; Rubinstein et al., 2007; Gomberg et al., 2008; Peng et al, 2009…). The greatest amount of energy and duration accompanies the long-period Rayleigh waves, with smaller bursts during the S and Love waves. For this particular tremor we observed the dispersion of Rayleigh waves in the envelopes of triggered tremors, which indicates a very strong modulation of the source by the passing surface wave. An unexpected short-term tremor occurred approximately one hour later of the arrival of the surface waves on the coastal stations. The NVT has only been previously observed at distances > 100 km inland. It also has a shorter frequency range (3-6 Hz) than other NVT (1-10 Hz) observed in the region. Finally, we observed a significant increase of so-called ambient tremor activity with higher intensity than all triggered NVT during the days after the earthquake. This study adds new types of tremors to the lexicon of triggered NVT observed in the world.

ULF Narrowband Emissions Analysis in the Terrestrial Polar Cusps

NASA Astrophysics Data System (ADS)

Grison, B.; Pisa, D.

2013-05-01

Polar cusps are known to be a key region for transfer of mass and momentum between the adjacent magnetosheath and the magnetosphere. The 4 spacecraft of the Cluster ESA mission crossed the polar cusps in their most distant part to the Earth in the early years of the mission (2000-2004) because of their highly eccentric orbit. The ULF wave activity in the cusp region has been linked with the magnetosheath plasma penetration since HEOS observations (D'Angelo et al., 1974). Wave and particle interaction play an important role in this colisionless plasma. The observed wave activity certainly results from both distant and local generation mechanisms. From Cluster case studies we propose to focus on one aspect for each of this place of generation. Concerning the distant generation, the possibility of a wave generation at the magnetopause itself is investigated. For this purpose we compare the propagation of the emissions on each side of the magnetopasue, i.e. in the cusp and in the magnetosheath. Concerning the local generation, the presence of locally generated waves above the local proton gyrofrequency that display a left hand polarization has been reported in Polar and Cluster studies (Le et al., 2001; Nykyri et al., 2003 ). The Doppler shift was not large enough to explain the observed frequency. We propose here to combine various techniques (k-filtering analysis, WHAMP simulations) to achieve a precise wave vector estimation and to explain these observations. References: D'Angelo, N., A. Bahnsen, and H. Rosenbauer (1974), Wave and particle measurements at the polar cusp, J. Geophys. Res., 79( 22), 3129-3134, doi:10.1029/JA079i022p03129. Le, G., X. Blanco-Cano, C. T. Russell, X.-W. Zhou, F. Mozer, K. J. Trattner, S. A. Fuselier, and B. J. Anderson (2001), Electromagnetic ion cyclotron waves in the high-altitude cusp: Polar observations, J. Geophys. Res., 106(A9), 19067-19079, doi:10.1029/2000JA900163. Nykyri, K., P. J. Cargill, E. A. Lucek, T. S. Horbury, A. Balogh, B. Lavraud, I. Dandouras, and H. Rème, Ion cyclotron waves in the high altitude cusp: CLUSTER observations at varying spacecraft separations, Geophys. Res. Lett., 30(24), 2263, doi:10.1029/2003GL018594, 2003.

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

DOE PAGES

Spong, D. A.; Heidbrink, W. W.; Paz-Soldan, C.; ...

2018-04-11

DIII-D experiments at low density (n e ~10 19 m -3) have directly measured whistler waves in the 100– 200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limitcycle- like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission thatmore » follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.« less

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks.

PubMed

Spong, D A; Heidbrink, W W; Paz-Soldan, C; Du, X D; Thome, K E; Van Zeeland, M A; Collins, C; Lvovskiy, A; Moyer, R A; Austin, M E; Brennan, D P; Liu, C; Jaeger, E F; Lau, C

2018-04-13

DIII-D experiments at low density (n_{e}∼10^{19}  m^{-3}) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks

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

Spong, D. A.; Heidbrink, W. W.; Paz-Soldan, C.

DIII-D experiments at low density (n e ~10 19 m -3) have directly measured whistler waves in the 100– 200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limitcycle- like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission thatmore » follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.« less

Advances in Inner Magnetosphere Passive and Active Wave Research

NASA Technical Reports Server (NTRS)

Green, James L.; Fung, Shing F.

2004-01-01

This review identifies a number of the principal research advancements that have occurred over the last five years in the study of electromagnetic (EM) waves in the Earth's inner magnetosphere. The observations used in this study are from the plasma wave instruments and radio sounders on Cluster, IMAGE, Geotail, Wind, Polar, Interball, and others. The data from passive plasma wave instruments have led to a number of advances such as: determining the origin and importance of whistler mode waves in the plasmasphere, discovery of the source of kilometric continuum radiation, mapping AKR source regions with "pinpoint" accuracy, and correlating the AKR source location with dipole tilt angle. Active magnetospheric wave experiments have shown that long range ducted and direct echoes can be used to obtain the density distribution of electrons in the polar cap and along plasmaspheric field lines, providing key information on plasmaspheric filling rates and polar cap outflows.

Lower Hybrid Frequency Range Waves Generated by Ion Polarization Drift Due to Electromagnetic Ion Cyclotron Waves: Analysis of an Event Observed by the Van Allen Probe B

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Boardsen, S.; Krivorutsky, E. N.; Engebretson, M. J.; Sibeck, D.; Chen, S.; Breneman, A.

2017-01-01

We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of approximately 0.86. We assume that the correlation is the result of LHFR wave generation by the ions polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD)parallel and perpendicular to the ambient magnetic eld to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions polarization drift in the electric field of an EMIC wave.

Diffusion, capture and recycling of SCAR/WAVE and Arp2/3 complexes observed in cells by single-molecule imaging.

PubMed

Millius, Arthur; Watanabe, Naoki; Weiner, Orion D

2012-03-01

The SCAR/WAVE complex drives lamellipodium formation by enhancing actin nucleation by the Arp2/3 complex. Phosphoinositides and Rac activate the SCAR/WAVE complex, but how SCAR/WAVE and Arp2/3 complexes converge at sites of nucleation is unknown. We analyzed the single-molecule dynamics of WAVE2 and p40 (subunits of the SCAR/WAVE and Arp2/3 complexes, respectively) in XTC cells. We observed lateral diffusion of both proteins and captured the transition of p40 from diffusion to network incorporation. These results suggest that a diffusive 2D search facilitates binding of the Arp2/3 complex to actin filaments necessary for nucleation. After nucleation, the Arp2/3 complex integrates into the actin network and undergoes retrograde flow, which results in its broad distribution throughout the lamellipodium. By contrast, the SCAR/WAVE complex is more restricted to the cell periphery. However, with single-molecule imaging, we also observed WAVE2 molecules undergoing retrograde motion. WAVE2 and p40 have nearly identical speeds, lifetimes and sites of network incorporation. Inhibition of actin retrograde flow does not prevent WAVE2 association and disassociation with the membrane but does inhibit WAVE2 removal from the actin cortex. Our results suggest that membrane binding and diffusion expedites the recruitment of nucleation factors to a nucleation site independent of actin assembly, but after network incorporation, ongoing actin polymerization facilitates recycling of SCAR/WAVE and Arp2/3 complexes.

Diffusion, capture and recycling of SCAR/WAVE and Arp2/3 complexes observed in cells by single-molecule imaging

PubMed Central

Millius, Arthur; Watanabe, Naoki; Weiner, Orion D.

2012-01-01

The SCAR/WAVE complex drives lamellipodium formation by enhancing actin nucleation by the Arp2/3 complex. Phosphoinositides and Rac activate the SCAR/WAVE complex, but how SCAR/WAVE and Arp2/3 complexes converge at sites of nucleation is unknown. We analyzed the single-molecule dynamics of WAVE2 and p40 (subunits of the SCAR/WAVE and Arp2/3 complexes, respectively) in XTC cells. We observed lateral diffusion of both proteins and captured the transition of p40 from diffusion to network incorporation. These results suggest that a diffusive 2D search facilitates binding of the Arp2/3 complex to actin filaments necessary for nucleation. After nucleation, the Arp2/3 complex integrates into the actin network and undergoes retrograde flow, which results in its broad distribution throughout the lamellipodium. By contrast, the SCAR/WAVE complex is more restricted to the cell periphery. However, with single-molecule imaging, we also observed WAVE2 molecules undergoing retrograde motion. WAVE2 and p40 have nearly identical speeds, lifetimes and sites of network incorporation. Inhibition of actin retrograde flow does not prevent WAVE2 association and disassociation with the membrane but does inhibit WAVE2 removal from the actin cortex. Our results suggest that membrane binding and diffusion expedites the recruitment of nucleation factors to a nucleation site independent of actin assembly, but after network incorporation, ongoing actin polymerization facilitates recycling of SCAR/WAVE and Arp2/3 complexes. PMID:22349699

Differential Immune Profiles in Two Pandemic Influenza A(H1N1)pdm09 Virus Waves at Pandemic Epicenter.

PubMed

Arriaga-Pizano, Lourdes; Ferat-Osorio, Eduardo; Rodríguez-Abrego, Gabriela; Mancilla-Herrera, Ismael; Domínguez-Cerezo, Esteban; Valero-Pacheco, Nuriban; Pérez-Toledo, Marisol; Lozano-Patiño, Fernando; Laredo-Sánchez, Fernando; Malagón-Rangel, José; Nellen-Hummel, Haiko; González-Bonilla, César; Arteaga-Troncoso, Gabriel; Cérbulo-Vázquez, Arturo; Pastelin-Palacios, Rodolfo; Klenerman, Paul; Isibasi, Armando; López-Macías, Constantino

2015-11-01

Severe influenza A(H1N1)pdm2009 virus infection cases are characterized by sustained immune activation during influenza pandemics. Seasonal flu data suggest that immune mediators could be modified by wave-related changes. Our aim was to determine the behavior of soluble and cell-related mediators in two waves at the epicenter of the 2009 influenza pandemic. Leukocyte surface activation markers were studied in serum from peripheral blood samples, collected from the 1(st) (April-May, 2009) and 2(nd) (October 2009-February 2010) pandemic waves. Patients with confirmed influenza A(H1N1)pdm2009 virus infection (H1N1), influenza-like illness (ILI) or healthy donors (H) were analyzed. Serum IL-6, IL-4 and IL-10 levels were elevated in H1N1 patients from the 2(nd) pandemic wave. Additionally, the frequency of helper and cytotoxic T cells was reduced during the 1(st) wave, whereas CD69 expression in helper T cells was increased in the 2(nd) wave for both H1N1 and ILI patients. In contrast, CD62L expression in granulocytes from the ILI group was increased in both waves but in monocytes only in the 2(nd) wave. Triggering Receptor Expressed on Myeloid cells (TREM)-1 expression was elevated only in H1N1 patients at the 1(st) wave. Our results show that during the 2009 influenza pandemic a T cell activation phenotype is observed in a wave-dependent fashion, with an expanded activation in the 2(nd) wave, compared to the 1(st) wave. Conversely, granulocyte and monocyte activation is infection-dependent. This evidence collected at the pandemic epicenter in 2009 could help us understand the differences in the underlying cellular mechanisms that drive the wave-related immune profile behaviors that occur against influenza viruses during pandemics. Copyright © 2015 IMSS. Published by Elsevier Inc. All rights reserved.

Radial anisotropy of the North American upper mantle based on adjoint tomography with USArray

NASA Astrophysics Data System (ADS)

Zhu, Hejun; Komatitsch, Dimitri; Tromp, Jeroen

2017-10-01

We use seismic data from USArray to image the upper mantle underneath the United States based on a so-called `adjoint tomography', an iterative full waveform inversion technique. The inversion uses data from 180 regional earthquakes recorded by 4516 seismographic stations, resulting in 586 185 frequency-dependent measurements. Three-component short-period body waves and long-period surface waves are combined to simultaneously constrain deep and shallow structures. The transversely isotropic model US22 is the result of 22 pre-conditioned conjugate-gradient iterations. Approximate Hessian maps and point-spread function tests demonstrate good illumination of the study region and limited trade-offs among different model parameters. We observe a distinct wave-speed contrast between the stable eastern US and the tectonically active western US. This boundary is well correlated with the Rocky Mountain Front. Stable cratonic regions are characterized by fast anomalies down to 250-300 km, reflecting the thickness of the North American lithosphere. Several fast anomalies are observed beneath the North American lithosphere, suggesting the possibility of lithospheric delamination. Slow wave-speed channels are imaged beneath the lithosphere, which might indicate weak asthenosphere. Beneath the mantle transition zone of the central US, an elongated north-south fast anomaly is observed, which might be the ancient subducted Farallon slab. The tectonically active western US is dominated by prominent slow anomalies with magnitudes greater than -6 per cent down to approximately 250 km. No continuous lower to upper mantle upwellings are observed beneath Yellowstone. In addition, our results confirm previously observed differences between oceans and continents in the anisotropic parameter ξ = (βh/βv)2. A slow wave-speed channel with ξ > 1 is imaged beneath the eastern Pacific at depths from 100 to 200 km, reflecting horizontal shear within the asthenosphere. Underneath continental areas, regions with ξ > 1 are imaged at shallower depths around 100 km. They are characterized by fast shear wave speeds, suggesting different origins of anisotropy underneath oceans and continents. The wave speed and anisotropic signatures of the western Atlantic are similar to continental areas in comparison with the eastern Pacific. Furthermore, we observe regions with ξ < 1 beneath the tectonically active western US at depths between 300 and 400 km, which might reflect vertical flows induced by subduction of the Farallon and Juan de Fuca Plates. Comparing US22 with several previous tomographic models, we observe relatively good correlations for long-wavelength features. However, there are still large discrepancies for small-scale features.

Scex 3 and Electron Echo 7, a Comparison of Data from Two Rocket Experiments.

NASA Astrophysics Data System (ADS)

Bale, Stuart Douglas

Results from two separate active sounding rocket experiments are presented and discussed. The SCEX III sounding rocket (NASA 39.002 UE) and Electron Echo 7 (NASA 36.015) were both launched from the Poker Flat Research Range (65.1^circ N, 147.5^circ W) near Fairbanks, Alaska, on 1 February, 1990 and 9 February, 1988, respectively. Each payload was equipped with an electron accelerator to study both natural and beam-related plasma phenomena. Data from the SCEX III retarding potential analyzer (RPA) and 3805 A and 3914 A photometers show evidence of a plasma discharge process occurring concomitant with operation of the electron gun. This appears as an enhanced electron current, nonlinear with gun injection current, in the RPA. The photometers register a sharp increase in luminosity during full current electron injection. This luminosity is an indicator of the ionizing electron-neutral collisions which liberate electrons and lead to the cascade-type discharge process. These observations are used to attempt to infer the mechanism of electron acceleration which leads to the discharge process. Before the electron gun was activated, the SCEX III payload flew through a region of auroral activity as evidenced by ground-based all-sky TV and energetic particle flux in the forward payload RPA. During this time, low frequency (10 Hz) electrostatic waves were observed in the DC receivers and Langmuir probe instrument. This data is analyzed, with a cross-spectral technique, and an approximate wave number is inferred. Comparison with theory suggests that the observed wave is the electrostatic ion cyclotron mode (EIC) operating on a heavy ion species (NO or O _2). The Echo 7 nose payload, carrying a plasma wave receiver, was ejected upfield of the main electron gun -equipped payload. Data from the swept frequency analyzer experiment provide wave amplitudes, at frequencies up to 15 MHz, as a function of separation of the main and nose payloads. These observations, and the wave modes inferred, shed light on the wave generation region upfield from a beam-emitting ionospheric payload.

Ion Upwelling and Height-Resolved Electrodynamic Response of the Ionosphere to ULF Waves and Precipitation: Comparison Between Simulation and EISCAT Observations

NASA Astrophysics Data System (ADS)

Sydorenko, D.; Rankin, R.

2013-12-01

We have developed a comprehensive two-dimensional (meridional) model of coupling between the magnetosphere and ionosphere that covers an altitude range from ~100 km to few thousand km at high latitudes [Sydorenko and Rankin, 2013]. The model describes propagation of inertial scale Alfven waves, including ponderomotive forces, and has a parametric model of energetic electron precipitation; it includes vertical ion flows and chemical reactions between ions and neutrals. Model results are presented that reproduce EISCAT radar observations of electron and ion temperatures, height integrated conductivity, ion densities, and ion flows during a period of ULF activity described in [Lester, Davies, and Yeoman, 2000]. We performed simulations where the precipitation and the Alfven wave perturb the ionosphere simultaneously. By adjusting parameters of the wave and the precipitation we have achieved qualitative, and sometimes even reasonable quantitative agreement between the observations and the simulation. The model results are discussed in the context of new results anticipated from the Canadian small satellite mission ePOP "Enhanced Polar Outflow Probe", scheduled for launch on September 9, 2013. Sydorenko D. and R. Rankin, 'Simulation of O+ upflows created by electron precipitation and Alfvén waves in the ionosphere' submitted to Journal of Geophysical Research, 2013. Lester M., J. A. Davies, and T. K. Yeoman, 'The ionospheric response during an interval of PC5 ULF wave activity', Ann. Geophysicae, v.18, p.257-261 (2000).

The aurora as a source of planetary-scale waves in the middle atmosphere. [atmospheric turbulence caused by auroral energy absorption

NASA Technical Reports Server (NTRS)

Chiu, Y. T.; Straus, J. M.

1974-01-01

Photographs of global scale auroral forms taken by scanning radiometers onboard weather satellites in 1972 show that auroral bands exhibit well organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well organized neutral wind fields in the 150- to 200-km region during the geomagnetic storm of May 27, 1967. Further, the horizontal scale size revealed by these observations are in agreement with that of high altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. Although there is, at present, no observation of substorm related waves of this scale size at mesospheric and stratospheric altitudes, the possible existence of a new source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.

Penetration of magnetosonic waves into the plasmasphere observed by the Van Allen Probes

DOE PAGES

Xiao, Fuliang; Zhou, Qinghua; He, Yihua; ...

2015-09-11

During the small storm on 14–15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate toward lower L shells outside the plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then graduallymore » cross the plasmapause into the deep plasmasphere, with almost unchanged path gains due to the falling proton ring distribution and higher ambient density. These results present the first report on how MS waves penetrate into the plasmasphere with the aid of the continuous proton ring distributions during weak geomagnetic activities.« less

The Effects of High Frequency ULF Wave Activity on the Spectral Characteristics of Coherent HF Radar Returns

NASA Astrophysics Data System (ADS)

Wright, D. M.; Yeoman, T. K.; Woodfield, E. E.

2003-12-01

It is now a common practice to employ ground-based radars in order to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromso, Norway (66° N geomagnetic). On this occasion, a series of transient regions of radar backscatter exhibiting large spectral widths are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band. These observations would then, seem to support the possibility that high frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the cusp and polar cap ionospheres.

QUASI-BIENNIAL OSCILLATIONS IN THE SOLAR TACHOCLINE CAUSED BY MAGNETIC ROSSBY WAVE INSTABILITIES

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

Zaqarashvili, Teimuraz V.; Carbonell, Marc; Oliver, Ramon

2010-11-20

Quasi-biennial oscillations (QBOs) are frequently observed in solar activity indices. However, no clear physical mechanism for the observed variations has been suggested so far. Here, we study the stability of magnetic Rossby waves in the solar tachocline using the shallow water magnetohydrodynamic approximation. Our analysis shows that the combination of typical differential rotation and a toroidal magnetic field with a strength of {>=}10{sup 5} G triggers the instability of the m = 1 magnetic Rossby wave harmonic with a period of {approx}2 years. This harmonic is antisymmetric with respect to the equator and its period (and growth rate) depends onmore » the differential rotation parameters and magnetic field strength. The oscillations may cause a periodic magnetic flux emergence at the solar surface and consequently may lead to the observed QBO in solar activity features. The period of QBOs may change throughout a cycle, and from cycle to cycle, due to variations of the mean magnetic field and differential rotation in the tachocline.« less

Photometry of symbiotic stars. X. EG And, Z And, BF Cyg, CH Cyg, V1329 Cyg, AG Dra, RW Hya, AX Per and IV Vir

NASA Astrophysics Data System (ADS)

Skopal, A.; Vanko, M.; Pribulla, T.; Wolf, M.; Semkov, E.; Jones, A.

2002-04-01

We present new photometric observations of EG And, Z And, BF Cyg, CH Cyg, V1329 Cyg, AG Dra, RW Hya, AX Per and IV Vir made in the standard Johnson UBVR system. The current issue summarizes observations of these objects to 2001 December. The main results can be summarized as follows: EG And: A periodic double-wave variation in all bands as a function of the orbital phase was confirmed. A maximum of the light changes was observed in U (Delta U ~ 0.5 mag). Z And: Our observations cover an active phase, which peaked around 8.4 in U at the beginning of 2000 December. Consequently, a gradual decrease in the star's brightness has been observed. BF Cyg: A periodic wave-like variation in the optical continuum reflects a quiescent phase of this star. A complex light curve (LC) profile was observed. CH Cyg: The recent episode of activity ended in Spring 2000. We determined the position of an eclipse in the outer binary at JD 2451426 +/- 3. Recent observations indicate a slow increase in the star's brightness. V1329 Cyg: Observations were made around a maximum at 2001.2. AG Dra: Our measurements from the Autumn of 2001 revealed a new eruption, which peaked at ~JD 2452217. RW Hya: The light minimum in our mean visual LC precedes the time of the spectroscopic conjunction of the giant in the binary. AX Per: A periodic wave-like variation was observed. Our recent observations revealed a secondary minimum at the orbital phase 0.5, seen best in the V and B bands. IV Vir: The LC displays a double-wave throughout the orbital cycle.

Electron wind in strong wave guide fields

NASA Astrophysics Data System (ADS)

Krienen, F.

1985-03-01

The X-ray activity observed near highly powered waveguide structures is usually caused by local electric discharges originating from discontinuities such as couplers, tuners or bends. In traveling waves electrons move in the direction of the power flow. Seed electrons can multipactor in a traveling wave, the moving charge pattern is different from the multipactor in a resonant structure and is self-extinguishing. The charge density in the wave guide will modify impedance and propagation constant of the wave guide. The radiation level inside the output wave guide of the SLAC, 50 MW, S-band, klystron is estimated. Possible contributions of radiation to window failure are discussed.

“Dandelion” Filament Eruption and Coronal Waves Associated with a Solar Flare on 2011 February 16

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

Cabezas, Denis P.; Ishitsuka, Mutsumi; Ishitsuka, José K.

Coronal disturbances associated with solar flares, such as H α Moreton waves, X-ray waves, and extreme ultraviolet (EUV) coronal waves, are discussed herein in relation to magnetohydrodynamic fast-mode waves or shocks in the corona. To understand the mechanism of coronal disturbances, full-disk solar observations with high spatial and temporal resolution over multiple wavelengths are of crucial importance. We observed a filament eruption, whose shape is like a “dandelion,” associated with the M1.6 flare that occurred on 2011 February 16 in H α images taken by the Flare Monitoring Telescope at Ica University, Peru. We derive the three-dimensional velocity field ofmore » the erupting filament. We also identify winking filaments that are located far from the flare site in the H α images, whereas no Moreton wave is observed. By comparing the temporal evolution of the winking filaments with those of the coronal wave seen in the EUV images data taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and by the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory-Ahead , we confirm that the winking filaments were activated by the EUV coronal wave.« less

An initial ULF wave index derived from 2 years of Swarm observations

NASA Astrophysics Data System (ADS)

Papadimitriou, Constantinos; Balasis, Georgios; Daglis, Ioannis A.; Giannakis, Omiros

2018-03-01

The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra low-frequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents - FACs - and the Ionospheric Bubble Index - IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20-100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications.

Effect of cyclone Nilofar on mesospheric wave dynamics as inferred from optical nightglow observations from Mount Abu, India

NASA Astrophysics Data System (ADS)

Singh, Ravindra P.; Pallamraju, Duggirala

2016-06-01

Mesospheric nightglow intensities at three emissions (O2(0-1), OH(6-2) bands, and Na(589.3 nm)) from a low-latitude location, Gurushikhar, Mount Abu (24.6°N, 72.8°E), in India, showed similar wave features on 26 October 2014 with a common periodicity of around 4 h. A convective activity due to the cyclone Nilofar, which had developed in the Arabian Sea during 25-31 October 2014, was found to be the source as this too showed a gravity wave period coherent with that of the mesospheric emissions on the 26th. The periodicities at the source region were obtained using outgoing longwave radiation fluxes (derived from Kalpana-1 satellite) which were used as a tracer of tropospheric activity. Cyclone Nilofar had two centers located at a distance of 1103 and 1665 km from the observational station. From the phase offset in time between residuals of O2 and OH emission intensities and the observed common periodicity the vertical phase speed and wavelength have been found to be 1.13 ms-1 and 16.47 km. From the wavelet analyses it is seen that the travel time of the wave from the convection region to O2 emission height was around 8.1 h. From these observations the horizontal phase speed and wavelength of the wave in the mesosphere were calculated to be 37.8 ms-1 and 553 km. These results thus provide not only unambiguous evidence on the vertical coupling of atmospheres engendered by the tropical cyclone Nilofar but also the characteristics of waves that exist during such cyclonic events.

QBO of temperature in mesopause and lower thermosphere caused by solar activity variations

NASA Astrophysics Data System (ADS)

Shefov, N. N.; Semenov, A. I.

2003-04-01

On the basis of the data of the emission (hydroxyl, sodium and atomic oxygen 557.7 nm) and radiophysical (87-107 km) measurements some regularities of quasi-biennial oscillation (QBO) of the atmospheric temperature at heights of the mesopause and lower thermosphere are investigated. It is shown, that they are closely connected with quasi-biennial variations of solar activity and form within the limits of a cycle of solar activity the fading wave train of oscillations. Such behaviour of the wave train can be adequately described by the Airy function. As a result of the analysis of characteristics of QBO of solar activity during 17-23rd cycles it is shown, that to each 11-years cycle correspond its wave train of QBO. Amplitudes and periods of this wave train decrease during a cycle, i.e. it represents Not harmonious oscillation but it is a cyclic aperiodic oscillation (CAO). Therefore usual methods of Fourier analysis used earlier did not result in the same values of the period. The wave train of the current cycle begins at the end of previous and some time together with the subsequent cycle proceeds. Thus, the time sequence of activity during solar cycle represents superposition of three wave trains. Period of CAO in the beginning of a cycle has ~ 38 months and decreases to the end of a cycle up to ~ 21 months. The first wide negative minimum of Airy function describing of the wave train of CAO corresponds to solar activity minimum in the 11-year cycle. The time scale of the wave train varies from one cycle to another. Full duration of individual wave train is ~ 22 years. Owing to a mutual interference of the consecutive wave trains in the 11-year cycles the observable variations of solar activity are not identical. Structure of CAO obviously displays magnetohydrodynamic processes inside the Sun. This work was supported by the Grant No. 2274 of ISTC.

Slow Magnetosonic Waves and Fast Flows in Active Region Loops

NASA Technical Reports Server (NTRS)

Ofman, L.; Wang, T. J.; Davila, J. M.

2012-01-01

Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (approx 100-300 km/s) quasiperiodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow.We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.

Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling

NASA Astrophysics Data System (ADS)

Ofman, Leon; Liu, Wei

2018-06-01

Since their discovery by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) in the extreme ultraviolet, rapid (phase speeds of ∼1000 km s‑1), quasi-periodic, fast-mode propagating (QFP) wave trains have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology (CS). The reported waves usually originate from a single localized source associated with the flare. Here we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of a 3D MHD model of counter-propagating QFPs in an idealized bipolar AR. We investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key model parameters, such as the properties of the sources and the background magnetic structure. In addition to QFPs, we also find evidence of trapped fast- (kink) and slow-mode waves associated with the event. We apply CS to determine the magnetic field strength in an oscillating loop during the event. Our model results are in qualitative agreement with the AIA-observed counter-propagating waves and used to identify the various MHD wave modes associated with the observed event, providing insights into their linear and nonlinear interactions. Our observations provide the first direct evidence of counter-propagating fast magnetosonic waves that can potentially lead to turbulent cascade and carry significant energy flux for coronal heating in low-corona magnetic structures.

A chain of winking (oscillating) filaments triggered by an invisible extreme-ultraviolet wave

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

Shen, Yuandeng; Tian, Zhanjun; Zhao, Ruijuan

2014-05-10

Winking (oscillating) filaments have been observed for many years. However, observations of successive winking filaments in one event have not yet been reported. In this paper, we present the observations of a chain of winking filaments and a subsequent jet that are observed right after the X2.1 flare in AR11283. The event also produced an extreme-ultraviolet (EUV) wave that has two components: an upward dome-like wave (850 km s{sup –1}) and a lateral surface wave (554 km s{sup –1}) that was very weak (or invisible) in imaging observations. By analyzing the temporal and spatial relationships between the oscillating filaments andmore » the EUV waves, we propose that all the winking filaments and the jet were triggered by the weak (or invisible) lateral surface EUV wave. The oscillation of the filaments last for two or three cycles, and their periods, Doppler velocity amplitudes, and damping times are 11-22 minutes, 6-14 km s{sup –1}, and 25-60 minutes, respectively. We further estimate the radial component magnetic field and the maximum kinetic energy of the filaments, and they are 5-10 G and ∼10{sup 19} J, respectively. The estimated maximum kinetic energy is comparable to the minimum energy of ordinary EUV waves, suggesting that EUV waves can efficiently launch filament oscillations on their path. Based on our analysis results, we conclude that the EUV wave is a good agent for triggering and connecting successive but separated solar activities in the solar atmosphere, and it is also important for producing solar sympathetic eruptions.« less

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, K.; Kobayashi, N.; Fukao, Y.

2013-12-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events [e.g. the major volcanic eruption of Krakatoa in 1833, the impact of Siberian meteorite in 1908, the testing of large nuclear tests and the huge earthquakes, Garrett1969]. In a case of the solid Earth, observation of background free oscillations in the millihertz band-now known as Earth's background free oscillations or seismic hum, has been firmly established. Above 5 mHz, their dominant excitation sources are oceanic infragravity waves. At 3.7 and 4.4 mHz an elasto-acoustic resonance between the solid Earth and the atmosphere was observed [Nishida et al., 2000]. These seismic observations show that the contribution of atmospheric disturbances to the seismic hum is dominant below 5 mHz. Such contribution implies background excitations of acoustic-gravity waves in this frequency range. For direct detection of the background acoustic-gravity waves, our group conducted observations using an array of barometers [Nishida et al. 2005]. However, the spatial scale of the array of about 10 km was too small to detect acoustic modes below 10 mHz. Since then, no direct observations of these waves have been reported. In 2011, 337 high-resolution microbarometers were installed on a continental scale at USArray Transportable Array. The large and dense array enables us to detect the background atmospheric waves. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the excitation sources are atmospheric disturbances in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity. Tropospheric disturbances exciting background Lamb waves may also be responsible for seismic hum at frequencies below 5 mHz.

Memory improvement via slow-oscillatory stimulation during sleep in older adults.

PubMed

Westerberg, Carmen E; Florczak, Susan M; Weintraub, Sandra; Mesulam, M-Marsel; Marshall, Lisa; Zee, Phyllis C; Paller, Ken A

2015-09-01

We examined the intriguing but controversial idea that disrupted sleep-dependent consolidation contributes to age-related memory decline. Slow-wave activity during sleep may help strengthen neural connections and provide memories with long-term stability, in which case decreased slow-wave activity in older adults could contribute to their weaker memories. One prediction from this account is that age-related memory deficits should be reduced by artificially enhancing slow-wave activity. In young adults, applying transcranial current oscillating at a slow frequency (0.75 Hz) during sleep improves memory. Here, we tested whether this procedure can improve memory in older adults. In 2 sessions separated by 1 week, we applied either slow-oscillatory stimulation or sham stimulation during an afternoon nap in a double-blind, crossover design. Memory tests were administered before and after sleep. A larger improvement in word-pair recall and higher slow-wave activity was observed with slow-oscillatory stimulation than with sham stimulation. This is the first demonstration that this procedure can improve memory in older adults, suggesting that declarative memory performance in older adults is partly dependent on slow-wave activity during sleep. Copyright © 2015 Elsevier Inc. All rights reserved.

Equatorial Wave Activity during NOAA's 2016 El Niño Rapid Response Field Campaign

NASA Astrophysics Data System (ADS)

Kiladis, G. N.; Dias, J.; Gehne, M.; Mayer, K.

2016-12-01

The El Niño Rapid Response (ENRR) field campaign targeted equatorial Pacific atmospheric convective activity during January-March 2016 through enhanced observations using dropsondes from the NOAA G-IV aircraft and radiosonde observations from Kiritimati (Christmas) Island and the NOAA research ship the Ronald H. Brown. This presentation examines the equatorial wave activity observed during ENRR and its relationship to tropical convection, and compares this activity to observations of past large El Niño events. The 2015-16 El Niño had much in common with the events during 1982-83 and 1997-98, with similar amplitude sea surface temperature (SST) anomalies, but also differed in several key aspects. All of these episodes featured enhanced convectively coupled Kelvin wave activity crossing the entire Pacific basin, which is generally absent during the northern winter seasons of near normal or La Niña SSTs. Prior to the ENRR period during December 2015 a large amplitude Madden-Julian Oscillation (MJO) was observed, with a convective signal that propagated unusually far to the east ( 150W). This was associated with an eastward displacement of the North Pacific storm track and heavy precipitation along the west coast of North America, broadly matching the large scale behavior of MJO evolution in statistical composites during El Niño. A second MJO-like event occurred during the latter part of February, 2016, but despite a similar convective heating field, the basic state flow was much different than during December, with a well-developed "westerly duct" which favored the intrusion of extratropical Rossby wave energy into the equatorial eastern Pacific region, as can be seen in E Vector fields. This latter event was accompanied by a distinct lack of an extended storm track and associated precipitation along the west coast of North America. Based on the preliminary results of AMIP simulations using observed SSTs, these differences are difficult to reproduce, and are hypothesized to be due to a certain level of "internal variability" within the storm track itself that may have been overriding the large scale forcing by the tropical diabatic heating field.

Wave reflections in the pulmonary arteries analysed with the reservoir–wave model

PubMed Central

Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

2014-01-01

Conventional haemodynamic analysis of pressure and flow in the pulmonary circulation yields incident and reflected waves throughout the cardiac cycle, even during diastole. The reservoir–wave model provides an alternative haemodynamic analysis consistent with minimal wave activity during diastole. Pressure and flow in the main pulmonary artery were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading and positive end-expiratory pressure were observed. The reservoir–wave model was used to determine the reservoir contribution to pressure and flow and once subtracted, resulted in ‘excess’ quantities, which were treated as wave-related. Wave intensity analysis quantified the contributions of waves originating upstream (forward-going waves) and downstream (backward-going waves). In the pulmonary artery, negative reflections of incident waves created by the right ventricle were observed. Overall, the distance from the pulmonary artery valve to this reflection site was calculated to be 5.7 ± 0.2 cm. During 100% O2 ventilation, the strength of these reflections increased 10% with volume loading and decreased 4% with 10 cmH2O positive end-expiratory pressure. In the pulmonary arterial circulation, negative reflections arise from the junction of lobar arteries from the left and right pulmonary arteries. This mechanism serves to reduce peak systolic pressure, while increasing blood flow. PMID:24756638

Arctic Stratospheric Temperature In The Winters 1999/2000 and 2000/2001: A Quantitative Assessment and Microphysical Implications

NASA Astrophysics Data System (ADS)

Buss, S.; Wernli, H.; Peter, T.; Kivi, R.; Bui, T. P.; Kleinböhl, A.; Schiller, C.

Stratospheric winter temperatures play a key role in the chain of microphysical and chemical processes that lead to the formation of polar stratospheric clouds (PSCs), chlorine activation and eventually to stratospheric ozone depletion. Here the tempera- ture conditions during the Arctic winters 1999/2000 and 2000/2001 are quantitatively investigated using observed profiles of water vapour and nitric acid, and tempera- tures from high-resolution radiosondes and aircraft observations, global ECMWF and UKMO analyses and mesoscale model simulations over Scandinavia and Greenland. The ECMWF model resolves parts of the gravity wave activity and generally agrees well with the observations. However, for the very cold temperatures near the ice frost point the ECMWF analyses have a warm bias of 1-6 K compared to radiosondes. For the mesoscale model HRM, this bias is generally reduced due to a more accurate rep- resentation of gravity waves. Quantitative estimates of the impact of the mesoscale temperature perturbations indicates that over Scandinavia and Greenland the wave- induced stratospheric cooling (as simulated by the HRM) affects only moderately the estimated chlorine activation and homogeneous NAT particle formation, but strongly enhances the potential for ice formation.

Direct Observations of ULF and Whistler-Mode Chorus Modulation of 500eV EDI Electrons by MMS

NASA Astrophysics Data System (ADS)

Paulson, K. W.; Argall, M. R.; Ahmadi, N.; Torbert, R. B.; Le Contel, O.; Ergun, R.; Khotyaintsev, Y. V.; Strangeway, R. J.; Magnes, W.; Russell, C. T.

2016-12-01

We present here direct observations of chorus-wave modulated field-aligned 500 eV electrons using the Electron Drift Instrument (EDI) on board the Magnetospheric Multiscale mission. These periods of wave activity were additionally observed to be modulated by Pc5-frequency magnetic perturbations, some of which have been identified as drifting mirror-mode structures. The spacecraft encountered these mirror-mode structures just inside of the duskside magnetopause. Using the high sampling rate provided by EDI in burst sampling mode, we are able to observe the individual count fluctuations of field-aligned electrons in this region up to 512 Hz. We use the multiple look directions of EDI to generate both pitch angle and gyrophase plots of the fluctuating counts. Our observations often show unidirectional flow of these modulated electrons along the background field, and in some cases demonstrate gyrophase bunching in the wave region.

First observations of stimulated electromagnetic emission in the ionosphere modified by the spear heating facility on Spitsbergen

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Yurik, R. Yu.; Yeoman, T. K.; Robinson, T. R.

2008-11-01

We present the first results of observations of the stimulated electromagnetic emission (SEE) in the ionosphere modified by the Space Plasma Exploration by Active Radar (SPEAR) heating facility. Observation of the SEE is the key method of ground-based diagnostics of the ionospheric plasma disturbances due to high-power HF radiation. The presented results were obtained during the heating campaign performed at the SPEAR facility in February-March 2007. Prominent SEE special features were observed in periods in which the critical frequency of the F 2 layer was higher than the pump-wave frequency (4.45 MHz). As an example, such special features as the downshifted maximum and the broad continuum in the region of negative detunings from the pump-wave frequency are presented. Observations clearly demonstrate that the ionosphere was efficiently excited by the SPEAR heating facility despite the comparatively low pump-wave power.

Local finite-amplitude wave activity as an objective diagnostic of midlatitude extreme weather

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

Chen, Gang; Lu, Jian; Burrows, Alex D.

Midlatitude extreme weather events are responsible for a large part of climate related damage, yet our understanding of these extreme events is limited, partly due to the lack of a theoretical basis for midlatitude extreme weather. In this letter, the local finite-amplitude wave activity (LWA) of Huang and Nakamura [2015] is introduced as a diagnostic of the 500-hPa geopotential height (Z500) to characterizing midlatitude weather events. It is found that the LWA climatology and its variability associated with the Arctic Oscillation (AO) agree broadly with the previously reported blocking frequency in literature. There is a strong seasonal and spatial dependencemore » in the trend13 s of LWA in recent decades. While there is no observational evidence for a hemispheric-scale increase in wave amplitude, robust trends in wave activity can be identified at the regional scales, with important implications for regional climate change.« less

Electron beam injection during active experiments. I - Electromagnetic wave emissions

NASA Technical Reports Server (NTRS)

Winglee, R. M.; Kellogg, P. J.

1990-01-01

The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

Nano-antenna in a photoconductive photomixer for highly efficient continuous wave terahertz emission

PubMed Central

Tanoto, H.; Teng, J. H.; Wu, Q. Y.; Sun, M.; Chen, Z. N.; Maier, S. A.; Wang, B.; Chum, C. C.; Si, G. Y.; Danner, A. J.; Chua, S. J.

2013-01-01

We report highly efficient continuous-wave terahertz (THz) photoconductive antenna based photomixer employing nano-gap electrodes in the active region. The tip-to-tip nano-gap electrode structure provides strong THz field enhancement and acts as a nano-antenna to radiate the THz wave generated in the active region of the photomixer. In addition, it provides good impedance matching to the THz planar antenna and exhibits a lower RC time constant, allowing more efficient radiation especially at the higher part of the THz spectrum. As a result, the output intensity of the photomixer with the new nano-gap electrode structure in the active region is two orders of magnitude higher than that of a photomixer with typical interdigitated electrodes. Significant improvement in the THz emission bandwidth was also observed. An efficient continuous wave THz source will greatly benefit compact THz system development for high resolution THz spectroscopy and imaging applications. PMID:24100840

ELF/VLF Wave Generation and Scattering from Modulated Heating of the Ionosphere at Arecibo Observatory

NASA Astrophysics Data System (ADS)

Maxworth, A. S.; Golkowski, M.; McCormick, J.; Cohen, M.; Hosseini, P.; Bittle, J.

2017-12-01

The recently completed ionospheric heater at Arecibo Observatory is used for modulated HF (5 or 8 MHz) heating of the ionosphere, to generate ELF/VLF (3 Hz - 30 kHz) waves. Observation of ramp and tone signals at frequencies from hundreds of Hz to several kHz at multiple receivers confirms the ability of the heater to modulate D region currents and create an ELF/VLF antenna in the ionosphere. Observed ELF/VLF signal amplitudes are lower than for similar experiments performed at high latitudes at the HAARP and Tromso facilities, for a variety of reasons including the reduced natural currents at mid latitudes, and the lower HF power of the Arecibo heater. The heating of the overhead ionosphere is also observed to change the Earth-ionosphere waveguide propagation characteristics as is evident from simultaneous observations of lightning induced sferics and VLF transmitter signals that propagate under the heated region. The active heating of the ionosphere modifies the reflection of incident VLF (3-30 kHz) waves. We present initial observations of HF heating of the D-region and resulting ELF/VLF wave generation.

Plasma waves associated with the first AMPTE magnetotail barium release

NASA Technical Reports Server (NTRS)

Gurnett, D. A.; Anderson, R. R.; Bernhardt, P. A.; Luehr, H.; Haerendel, G.

1986-01-01

Plasma waves observed during the March 21, 1985, AMPTE magnetotail barium release are described. Electron plasma oscillations provided local measurements of the plasma density during both the expansion and decay phases. Immediately after the explosion, the electron density reached a peak of about 400,000/cu cm, and then started decreasing approximately as t to the -2.4 as the cloud expanded. About 6 minutes after the explosion, the electron density suddenly began to increase, reached a secondary peak of about 240/cu cm, and then slowly decayed down to the preevent level over a period of about 15 minutes. The density increase is believed to be caused by the collapse of the ion cloud into the diamagnetic cavity created by the initial expansion. The plasma wave intensities observed during the entire event were quite low. In the diamagnetic cavity, electrostatic emissions were observed near the barium ion plasma frequency, and in another band at lower frequencies. A broadband burst of electrostatic noise was also observed at the boundary of the diamagnetic cavity. Except for electron plasma oscillations, no significant wave activity was observed outside of the diamagnetic cavity.

High-frequency Plasma Waves Associated with Magnetic Reconnection in the Solar Wind

NASA Astrophysics Data System (ADS)

Wang, Y.

2015-12-01

Activities of high-frequency plasma waves associated with magnetic reconnection in the solar wind observed by Time Domain Sampler (TDS) experiments on STEREO/WAVES are preliminarily analyzed. The TDS instrument can provide burst mode electric fields data with as long as 16384 sample points at 250 kHz sampling rate. In all 1120 suspected reconnection events, it is found that the most commonly occurred waves are neither ion acoustic waves, electrostatic solitary waves, nor Langmuir/upper hybrid waves, but Bernstein-like waves with harmonics of the electron cyclotron frequency. In addition, to each type of waves, Langmuir/upper hybrid waves reveal the largest occurrence rate in the reconnection region than in the ambient solar wind. These results indicate that Bernstein-like waves and Langmuir/upper hybrid waves might play important roles in the reconnection associated particle heating processes and they might also influence the dissipation of magnetic reconnection.

Simultaneous Observations of p-mode Light Walls and Magnetic Reconnection Ejections above Sunspot Light Bridges

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

Hou, Yijun; Zhang, Jun; Li, Ting

Recent high-resolution observations from the Interface Region Imaging Spectrograph reveal bright wall-shaped structures in active regions (ARs), especially above sunspot light bridges. Their most prominent feature is the bright oscillating front in the 1400/1330 Å channel. These structures are named light walls and are often interpreted to be driven by p-mode waves. Above the light bridge of AR 12222 on 2014 December 06, we observed intermittent ejections superimposed on an oscillating light wall in the 1400 Å passband. At the base location of each ejection, the emission enhancement was detected in the Solar Dynamics Observatory 1600 Å channel. Thus, wemore » suggest that in wall bases (light bridges), in addition to the leaked p-mode waves consistently driving the oscillating light wall, magnetic reconnection could happen intermittently at some locations and eject the heated plasma upward. Similarly, in the second event occurring in AR 12371 on 2015 June 16, a jet was simultaneously detected in addition to the light wall with a wave-shaped bright front above the light bridge. At the footpoint of this jet, lasting brightening was observed, implying magnetic reconnection at the base. We propose that in these events, two mechanisms, p-mode waves and magnetic reconnection, simultaneously play roles in the light bridge, and lead to the distinct kinetic features of the light walls and the ejection-like activities, respectively. To illustrate the two mechanisms and their resulting activities above light bridges, in this study we present a cartoon model.« less

Interharmonic modulation products as a means to quantify nonlinear D-region interactions

NASA Astrophysics Data System (ADS)

Moore, Robert

Experimental observations performed during dual beam ionospheric HF heating experiments at the High frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska are used to quantify the relative importance of specific nonlinear interactions that occur within the D region ionosphere. During these experiments, HAARP broadcast two amplitude modulated HF beams whose center frequencies were separated by less than 20 kHz. One beam was sinusoidally modulated at 500 Hz while the second beam was sinusoidally modulated using a 1-7 kHz linear frequency-time chirp. ELF/VLF observations performed at two different locations (3 and 98 km from HAARP) provide clear evidence of strong interactions between all field components of the two HF beams in the form of low and high order interharmonic modulation products. From a theoretical standpoint, the observed interharmonic modulation products could be produced by several different nonlinearities. The two primary nonlinearities take the form of wave-medium interactions (i.e., cross modulation), wherein the ionospheric conductivity modulation produced by one signal crosses onto the other signal via collision frequency modification, and wave-wave interactions, wherein the conduction current associated with one wave mixes with the electric field of the other wave to produce electron temperature oscillations. We are able to separate and quantify these two different nonlinearities, and we conclude that the wave-wave interactions dominate the wave-medium interactions by a factor of two. These results are of great importance for the modeling of transioinospheric radio wave propagation, in that both the wave-wave and the wave-medium interactions could be responsible for a significant amount of anomalous absorption.

Study of atmospheric gravity waves and infrasonic sources using the USArray Transportable Array pressure data

NASA Astrophysics Data System (ADS)

Hedlin, Michael; de Groot-Hedlin, Catherine; Hoffmann, Lars; Alexander, M. Joan; Stephan, Claudia

2016-04-01

The upgrade of the USArray Transportable Array (TA) with microbarometers and infrasound microphones has created an opportunity for a broad range of new studies of atmospheric sources and the large- and small-scale atmospheric structure through which signals from these events propagate. These studies are akin to early studies of seismic events and the Earth's interior structure that were made possible by the first seismic networks. In one early study with the new dataset we use the method of de Groot-Hedlin and Hedlin (2015) to recast the TA as a massive collection of 3-element arrays to detect and locate large infrasonic events. Over 2,000 events have been detected in 2013. The events cluster in highly active regions on land and offshore. Stratospherically ducted signals from some of these events have been recorded more than 2,000 km from the source and clearly show dispersion due to propagation through atmospheric gravity waves. Modeling of these signals has been used to test statistical models of atmospheric gravity waves. The network is also useful for making direct observations of gravity waves. We are currently studying TA and satellite observations of gravity waves from singular events to better understand how the waves near ground level relate to those observed aloft. We are also studying the long-term statistics of these waves from the beginning of 2010 through 2014. Early work using data bandpass filtered from 1-6 hr shows that both the TA and satellite data reveal highly active source regions, such as near the Great Lakes. de Groot-Hedlin and Hedlin, 2015, A method for detecting and locating geophysical events using clusters of arrays, Geophysical Journal International, v203, p960-971, doi: 10.1093/gji/ggv345.

Nonlinear MHD Waves in a Prominence Foot

NASA Astrophysics Data System (ADS)

Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.

2015-11-01

We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ˜ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5-11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ˜20 km s-1, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.

Theory of Type 3 and Type 2 Solar Radio Emissions

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Cairns, I. H.

2000-01-01

The main features of some current theories of type III and type II bursts are outlined. Among the most common solar radio bursts, type III bursts are produced at frequencies of 10 kHz to a few GHz when electron beams are ejected from solar active regions, entering the corona and solar wind at typical speeds of 0.1c. These beams provide energy to generate Langmuir waves via a streaming instability. In the current stochastic-growth theory, Langmuir waves grow in clumps associated with random low-frequency density fluctuations, leading to the observed spiky waves. Nonlinear wave-wave interactions then lead to secondary emission of observable radio waves near the fundamental and harmonic of the plasma frequency. Subsequent scattering processes modify the dynamic radio spectra, while back-reaction of Langmuir waves on the beam causes it to fluctuate about a state of marginal stability. Theories based on these ideas can account for the observed properties of type III bursts, including the in situ waves and the dynamic spectra of the radiation. Type 11 bursts are associated with shock waves propagating through the corona and interplanetary space and radiating from roughly 30 kHz to 1 GHz. Their basic emission mechanisms are believed to be similar to those of type III events and radiation from Earth's foreshock. However, several sub-classes of type II bursts may exist with different source regions and detailed characteristics. Theoretical models for type II bursts are briefly reviewed, focusing on a model with emission from a foreshock region upstream of the shock for which observational evidence has just been reported.

Active experiments in space; Proceedings of the Topical Meeting of the Interdisciplinary Scientific Commission D (Meeting D3) of the COSPAR 28th Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990

NASA Astrophysics Data System (ADS)

Torbert, R.

1992-12-01

The present volume on active experiments in space discusses dynamic trapping of electrons in the Porcupine ionospheric ion beam experiment, plasma wave observations during electron gun experiments on ISEE-1, spatial coherence and electromagnetic wave generation during electron beam experiments in space, and recent experimental measurements of space platform charging at LEO altitudes. Attention is given to high voltage spheres in an unmagnetized plasma, energetic ion emission for active spacecraft control, the collective gyration of a heavy ion cloud in a magnetized plasma, and remote sensing of artificial luminous clouds by lidars. Topics addressed include modulation of the background flux of energetic particles by artificial injection, wave measurements in active experiments on plasma beam injection, field formation around negatively biased solar arrays in the LEO-plasma, and the registration of ELF waves in rocket-satellite experiments with plasma injection.

Stimulated electromagnetic emission polarization under different polarizations of pump waves

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Yurik, R. Y.; Baddeley, L.

2015-03-01

The results of investigations into the stimulated electromagnetic emission (SEE) polarization under different modes of the pump wave polarization are presented. The present results were obtained in November 2012 during a heating campaign utilizing the SPEAR (Space Plasma Exploration by Active Radar) heating facility, transmitting in both O- and X-mode polarization, and a PGI (Polar Geophysical Institute) radio interferometer capable of recording the polarization of the received radiation. The polarization ellipse parameters of the SEE DM (downshifted maximum) components were determined under both O-mode and X-mode polarization of the pump waves. The polarization direction of the SEE DM component was preserved under different polarizations of the pump waves. Different polarizations of the pump waves have a different SEE generation efficiency. The intensity of the DM component is observed to be greater during O-mode pumping. In addition, the numbers of observed SEE features are also greater during O-mode pumping.

The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake over Taiwan

NASA Astrophysics Data System (ADS)

Liu, J. Y.; Chen, C. H.; Sun, Y. Y.; Chen, C. H.; Tsai, H. F.; Yen, H. Y.; Chum, J.; Lastovicka, J.; Yang, Q. S.; Chen, W. S.; Wen, S.

2016-02-01

In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan.

Preseismic Velocity Changes Observed from Active Source Monitoringat the Parkfield SAFOD Drill Site

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

Daley, Thomas; Niu, Fenglin; Silver, Paul G.

2008-06-10

Measuring stress changes within seismically active fault zones has been a long-sought goal of seismology. Here we show that such stress changes are measurable by exploiting the stress dependence of seismic wave speed from an active source cross-well experiment conducted at the SAFOD drill site. Over a two-month period we observed an excellent anti-correlation between changes in the time required for an S wave to travel through the rock along a fixed pathway--a few microseconds--and variations in barometric pressure. We also observed two large excursions in the traveltime data that are coincident with two earthquakes that are among those predictedmore » to produce the largest coseismic stress changes at SAFOD. Interestingly, the two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies.« less

HOT PLASMA FROM SOLAR ACTIVE-REGION CORES: CONSTRAINTS FROM THE HINODE X-RAY TELESCOPE

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

Schmelz, J. T.; Christian, G. M.; Matheny, P. O., E-mail: jschmelz@usra.edu

2016-12-20

Mechanisms invoked to heat the solar corona to millions of degrees kelvin involve either magnetic waves or magnetic reconnections. Turbulence in the convection zone produces MHD waves, which travel upward and dissipate. Photospheric motions continuously build up magnetic energy, which is released through magnetic reconnection. In this paper, we concentrate on hot non-flaring plasma with temperatures of 5 MK <  T  < 10 MK because it is one of the few observables for which wave and reconnection models make different predictions. Wave models predict no (or little) hot plasma, whereas reconnection models predict it, although in amounts that are challenging to detectmore » with current instrumentation. We used data from the X-ray Telescope (XRT) and the Atmospheric Imaging Assembly (AIA). We requested a special XRT observing sequence, which cycled through the thickest XRT filter several times per hour so we could average these images and improve the signal-to-noise. We did differential emission measure (DEM) analysis using the time-averaged thick-filter data as well as all available channels from both the XRT and AIA for regions observed on 2014 December 11. Whereas our earlier work was only able to determine that plasma with a temperature greater than 5 MK was present , we are now able to find a well-constrained DEM distribution. We have therefore added a strong observational constraint that must be explained by any viable coronal heating model. Comparing state-of-the-art wave and reconnection model predictions, we can conclude that reconnection is heating the hot plasma in these active regions.« less

Mitotic waves in the early embryogenesis of Drosophila: Bistability traded for speed.

PubMed

Vergassola, Massimo; Deneke, Victoria E; Di Talia, Stefano

2018-03-06

Early embryogenesis of most metazoans is characterized by rapid and synchronous cleavage divisions. Chemical waves of Cdk1 activity were previously shown to spread across Drosophila embryos, and the underlying molecular processes were dissected. Here, we present the theory of the physical mechanisms that control Cdk1 waves in Drosophila The in vivo dynamics of Cdk1 are captured by a transiently bistable reaction-diffusion model, where time-dependent reaction terms account for the growing level of cyclins and Cdk1 activation across the cell cycle. We identify two distinct regimes. The first one is observed in mutants of the mitotic switch. There, waves are triggered by the classical mechanism of a stable state invading a metastable one. Conversely, waves in wild type reflect a transient phase that preserves the Cdk1 spatial gradients while the overall level of Cdk1 activity is swept upward by the time-dependent reaction terms. This unique mechanism generates a wave-like spreading that differs from bistable waves for its dependence on dynamic parameters and its faster speed. Namely, the speed of "sweep" waves strikingly decreases as the strength of the reaction terms increases and scales as the powers 3/4, -1/2, and 7/12 of Cdk1 molecular diffusivity, noise amplitude, and rate of increase of Cdk1 activity in the cell-cycle S phase, respectively. Theoretical predictions are supported by numerical simulations and experiments that couple quantitative measurements of Cdk1 activity and genetic perturbations of the accumulation rate of cyclins. Finally, our analysis bears upon the inhibition required to suppress Cdk1 waves at the cell-cycle pause for the maternal-to-zygotic transition.

Cluster observations of band-limited Pc 1 waves associated with streaming H+ and O+ ions in the high-altitude plasma mantle

NASA Astrophysics Data System (ADS)

Engebretson, M. J.; Kahlstorf, C. R. G.; Murr, D. L.; Posch, J. L.; Keiling, A.; Lavraud, B.; Rème, H.; Lessard, M. R.; Kim, E.-H.; Johnson, J. R.; Dombeck, J.; Grison, B.; Robert, P.; Glassmeier, K.-H.; Décréau, P. M. E.

2012-10-01

Bursts of band-limited Pc 1 waves (0.2 to ˜1.0 Hz) with normalized frequency f/fH+ ˜ 0.5 have been observed by the Cluster spacecraft during many passes through the high-latitude plasma mantle. These transverse, left-hand polarized waves are associated with regions of H+ and O+ ions streaming away from Earth along magnetic field lines at the same velocity (˜140 km/s). Waves were observed only when H+ fluxes increased by factors of 10-1000 and energies of both ion species increased by factors of up to 10. We present two satellite-ground conjunctions to demonstrate the high latitude localization of these waves and their ability to reach the polar ionosphere and two extended examples of waves and associated ion distribution functions near the southern dusk flank magnetopause. We also present the results of a search for all such events during Cluster's 2002 and 2003 passages through the magnetotail, with orbital precession covering dawn to dusk on Earth's night side (June through December). A total of 46 events (band-limited Pc 1-2 waves accompanied by a sustained population of streaming H+ and O+ ions, separated by at least 12 min) were observed on 29 days. The waves were generally associated with intervals of southward IMF Bz and/or large IMF By (times of active cusp reconnection), and often but not always occurred during the main phase or early recovery phase of magnetic storms. Analysis of selected events shows that the waves are associated with large H+ temperature anisotropy, and that the waves propagate opposite to the direction of the streaming ions. A wave instability analysis using the WHAMP code confirms that the generation of these waves, via the ion cyclotron instability, is basically consistent with known physics. Their extended region of wave growth is likely, however, to reach tailward significantly beyond the Cluster orbit.

Wii mote as hydrological sensor: observation of water level fluctuations

NASA Astrophysics Data System (ADS)

Luxemburg, W.; Hut, R.; Weijs, S.; Hegnauer, M.

2009-12-01

The input device of the Nintendo Wii, the Wii-mote offers scientist a multitude of cheap, high quality sensors; ideal for proof of concept testing. For a specific application, i.e. the water level fluctuation in a floating evaporation pan the Wii-mote was tested as the observing device. It is shown that the controller can observe movements with high enough temporal and spatial resolution of up to 4 infrared LED’s to describe water level movements. Floating pans positioned in lakes and reservoirs better represent open water evaporation than evaporation pans installed on land. On the other hand performing water level measurements in a floating pan is more complicated due to movement of the pan and wave activities in the pan. The Wii-mote was mounted on the side of a standard class A-pan and a float was placed in the middle of the pan, with 4 LED’s on top moving along a fixed bar. The information that the Wii-mote wirelessly sends by blue tooth was captured on a laptop. With a MATLAB routine this data was converted into movement of the LED’s relatively to the controller. The observations show that wave activities are nicely captured with a typical spatial resolution smaller than 0.1 mm in our set-up and a temporal resolution of maximum 100 Hz. A frequency domain filter was applied to the observed datasets to obtain average water levels. In our laboratory setting the pan was placed in a large basin with a wave generator. A constant, but small, rate of water was added to the evaporation pan. The average pan levels from the filtered datasets showed systematically lower levels compared to the level without any wave activities. This is a typical effect of waves that occur in shallow basins. However, the added water with rates up to 5 mm/hour were clearly recognized in the filtered datasets which indicates that the Wii-mote is very well capable as a sensor for water level observations.

Nonlinear electric field structures in the inner magnetosphere

DOE PAGES

Malaspina, D. M.; Andersson, L.; Ergun, R. E.; ...

2014-08-28

Recent observations by the Van Allen Probes spacecraft have demonstrated that a variety of electric field structures and nonlinear waves frequently occur in the inner terrestrial magnetosphere, including phase space holes, kinetic field-line resonances, nonlinear whistler-mode waves, and several types of double layer. However, it is nuclear whether such structures and waves have a significant impact on the dynamics of the inner magnetosphere, including the radiation belts and ring current. To make progress toward quantifying their importance, this study statistically evaluates the correlation of such structures and waves with plasma boundaries. A strong correlation is found. These statistical results, combinedmore » with observations of electric field activity at propagating plasma boundaries, are consistent with the identification of these boundaries as the source of free energy responsible for generating the electric field structures and nonlinear waves of interest. Therefore, the ability of these structures and waves to influence plasma in the inner magnetosphere is governed by the spatial extent and dynamics of macroscopic plasma boundaries in that region.« less

Observation of Bernstein Waves Excited by Newborn Interstellar Pickup Ions in the Solar Wind

NASA Technical Reports Server (NTRS)

Joyce, Colin J.; Smith, Charles W.; Isenberg, Philip A.; Gary, S. Peter; Murphy, Neil; Gray, Perry C.; Burlaga, Leonard F.

2012-01-01

A recent examination of 1.9 s magnetic field data recorded by the Voyager 2 spacecraft in transit to Jupiter revealed several instances of strongly aliased spectra suggestive of unresolved high-frequency magnetic fluctuations at 4.4 AU. A closer examination of these intervals using the highest resolution data available revealed one clear instance of wave activity at spacecraft frame frequencies from 0.2 to 1 Hz. Using various analysis techniques, we have characterized these fluctuations as Bernstein mode waves excited by newborn interstellar pickup ions. We can find no other interpretation or source consistent with the observations, but this interpretation is not without questions. In this paper, we report a detailed analysis of the waves, including their frequency and polarization, that supports our interpretation.

Rogue-wave bullets in a composite (2+1)D nonlinear medium.

PubMed

Chen, Shihua; Soto-Crespo, Jose M; Baronio, Fabio; Grelu, Philippe; Mihalache, Dumitru

2016-07-11

We show that nonlinear wave packets localized in two dimensions with characteristic rogue wave profiles can propagate in a third dimension with significant stability. This unique behavior makes these waves analogous to light bullets, with the additional feature that they propagate on a finite background. Bulletlike rogue-wave singlet and triplet are derived analytically from a composite (2+1)D nonlinear wave equation. The latter can be interpreted as the combination of two integrable (1+1)D models expressed in different dimensions, namely, the Hirota equation and the complex modified Korteweg-de Vries equation. Numerical simulations confirm that the generation of rogue-wave bullets can be observed in the presence of spontaneous modulation instability activated by quantum noise.

Transdimensional inversion of scattered body waves for 1D S-wave velocity structure - Application to the Tengchong volcanic area, Southwestern China

NASA Astrophysics Data System (ADS)

Li, Mengkui; Zhang, Shuangxi; Bodin, Thomas; Lin, Xu; Wu, Tengfei

2018-06-01

Inversion of receiver functions is commonly used to recover the S-wave velocity structure beneath seismic stations. Traditional approaches are based on deconvolved waveforms, where the horizontal component of P-wave seismograms is deconvolved by the vertical component. Deconvolution of noisy seismograms is a numerically unstable process that needs to be stabilized by regularization parameters. This biases noise statistics, making it difficult to estimate uncertainties in observed receiver functions for Bayesian inference. This study proposes a method to directly invert observed radial waveforms and to better account for data noise in a Bayesian formulation. We illustrate its feasibility with two synthetic tests having different types of noises added to seismograms. Then, a real site application is performed to obtain the 1-D S-wave velocity structure beneath a seismic station located in the Tengchong volcanic area, Southwestern China. Surface wave dispersion measurements spanning periods from 8 to 65 s are jointly inverted with P waveforms. The results show a complex S-wave velocity structure, as two low velocity zones are observed in the crust and uppermost mantle, suggesting the existence of magma chambers, or zones of partial melt. The upper magma chambers may be the heart source that cause the thermal activity on the surface.

Technical support for geopressured-geothermal well activities in Louisiana

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

Not Available

1991-07-01

Continuous recording microearthquake monitoring networks have been established around US Department of Energy (DOE) geopressured-geothermal design wells in southwestern Louisiana and southeastern Texas since summer 1980 to assess the effects well development may have had on subsidence and growth-fault activation. This monitoring has shown several unusual characteristics of Gulf Coast seismic activity. The observed activity is classified into two dominant types, one with identifiable body phases (type 1) and the other with only surface-wave signatures (type 2). During this reporting period no type 1 or body-wave events were reported. A total of 230 type 2 or surface-wave events were recorded.more » Origins of the type 2 events are still not positively understood; however, little or no evidence is available to connect them with geopressured-geothermal well activity. We continue to suspect sonic booms from military aircraft or some other human-induced source. 37 refs., 16 figs., 6 tabs.« less

Observations and analyses of an intense waves-in-ice event in the Sea of Okhotsk

NASA Astrophysics Data System (ADS)

Marko, John R.

2003-09-01

Ice draft, ice velocity, ice concentration, and current profile data gathered at an array of eight continental shelf monitoring sites east of Sakhalin Island were analyzed in conjunction with regional meteorological data to document and explain intense wave occurrences several hundred kilometers inside the Sea of Okhotsk ice pack. The studied event was associated with the 19-21 March 1998 passage of an intense cyclone, which produced waves with amplitudes in excess of 1 m at the most offshore monitoring location. The relatively monochromatic character of the waves allowed extraction of wave intensity time series from ice draft time series data. Spatial and temporal variations in these data were used to establish directions and speeds of wave energy propagation for comparisons with an earlier interpretation [, 1988] of an Antarctic intense waves-in-ice event. It was concluded that although both events are compatible with a two-stage process in which initially slowly advancing wave activity increases subsequent ice cover wave transmissivity, the first stage of the Sea of Okhotsk event was not explicable in terms of the static stress-induced changes in the waves-in-ice dispersion relationship proposed by Liu and Mollo-Christensen. An alternative explanation is offered that eschews the linkage between wave group velocities and the observed slow rates of wave energy propagation and attributes the subsequent transition to more normal wave propagation behavior to ice pack divergence.

An extreme ultraviolet wave associated with a failed eruption observed by the Solar Dynamics Observatory

NASA Astrophysics Data System (ADS)

Zheng, R.; Jiang, Y.; Yang, J.; Bi, Y.; Hong, J.; Yang, B.; Yang, D.

2012-05-01

Aims: Taking advantage of the high temporal and spatial resolution of the Solar Dynamics Observatory (SDO) observations, we present an extreme ultraviolet (EUV) wave associated with a failed filament eruption that generated no coronal mass ejection (CME) on 2011 March 1. We aim at understanding the nature and origin of this EUV wave. Methods: Combining the high-quality observations in the photosphere, the chromosphere, and the corona, we studied the characteristics of the wave and its relations to the associated eruption. Results: The event occurred at an ephemeral region near a small active region. The continuous magnetic flux cancelation in the ephemeral region produced pre-eruption brightenings and two EUV jets, and excited the filament eruption, accompanying it with a microflare. After the eruption, the filament material appeared far from the eruption center, and the ambient loops seemed to be intact. It was evident that the filament eruption had failed and was not associated with a CME. The wave happened just after the north jet arrived, and apparently emanated ahead of the north jet, far from the eruption center. The wave propagated at nearly constant velocities in the range of 260-350 km s-1, with a slight negative acceleration in the last phase. Remarkably, the wave continued to propagate, and a loop in its passage was intact when wave and loop met. Conclusions: Our analysis confirms that the EUV wave is a true wave, which we interpret as a fast-mode wave. In addition, the close temporal and spatial relationship between the wave and the jet provides evidence that the wave was likely triggered by the jet when the CME failed to happen. Three movies are available in electronic form at http://www.aanda.org

Sound-Induced Intracellular Ca2+ Dynamics in the Adult Hearing Cochlea

PubMed Central

Chan, Dylan K.; Rouse, Stephanie L.

2016-01-01

Ca2+ signaling has been implicated in the initial pathophysiologic mechanisms underlying the cochlea's response to acoustic overstimulation. Intracellular Ca2+ signaling (ICS) waves, which occur in glia and retinal cells in response to injury to activate cell regulatory pathways, have been proposed as an early event in cochlear injury. Disruption of ICS activity is thought to underlie Connexin 26-associated hearing loss, the most common genetic form of deafness, and downstream sequelae of ICS wave activity, such as MAP kinase pathway activation, have been implicated in noise-induced hearing loss. However, ICS waves have only been observed in neonatal cochlear cultures and are thought to be quiescent after the onset of hearing. In this study, we employ an acute explant model of an adult, hearing cochlea that retains many in vivo physiologic features to investigate Ca2+ changes in response to sound. We find that both slow monotonic changes in intracellular Ca2+ concentration as well as discrete ICS waves occur with acoustic overstimulation. The ICS waves share many intrinsic features with their better-described neonatal counterparts, including ATP and gap-junction dependence, and propagation velocity and distance. This identification of ICS wave activity in the adult, hearing cochlea thus confirms and characterizes an important early detection mechanism for cochlear trauma and provides a target for interventions for noise-induced and Connexin 26-associated hearing loss. PMID:27959894

First electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Karlsson, Tomas; Eriksson, Anders; Odelstad, Elias; André, Mats; Dickeli, Guillaume; Kullen, Anita; Lindqvist, Per-Arne

2017-04-01

We present the first electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko, performed by the Rosetta dual Langmuir probe instrument LAP. For two time intervals, measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of the spacecraft potential, which can be used as an indicator of plasma density changes. Persistent wave activity around the local water ion lower hybrid frequency (determined from the magnetic field measurements from the fluxgate magnetometer MAG) is observed. The largest amplitudes are observed at sharp plasma gradients. We discuss the probability that these waves are excited by the lower hybrid drift instability (LHDI), and conclude that the necessary requirements for the LHDI to be operating are fulfilled. We also present first statistical results of the electric field measurements, showing that the wave activity is concentrated to certain regions of the comet, and varies with heliocentric distance. We also discuss the possible effects the waves have on the ambient plasma, and suggest that they may explain hot plasma populations.

Thirty-minutes' exposure to smartphone call triggers neutrophil activation in vitro.

PubMed

Lippi, Giuseppe; Danese, Elisa; Brocco, Giorgio; Benati, Marco; Salvagno, Gian Luca; Montagnana, Martina; Franchini, Massimo

2016-09-01

Despite accumulating evidence about the negative health effects of exposure to electromagnetic fields emitted by mobile phones, no information is available on the potential impact of radiofrequency (RF) waves on polymorphonuclear leukocytes biology. Two sequential whole blood tubes were collected from 16 ostensibly healthy volunteers. After placing the former tube of each subject in a plastic rack, 1 cm from a commercial smartphone (carrier frequency, 900 MHz), a call was placed on the smartphone and a communication lasting 30 min was manually activated. The latter blood tube of each volunteer was placed in another plastic rack, for an identical period of time, avoiding close contact with sources of RF waves. A complete blood count was then assessed in all whole blood samples, using Advia 2120. The 30-min exposure of blood to RF waves did not induce significant variations of total and differential leukocyte counts. A significant decrease was however observed for many neutrophils parameters, with median percentage variation of -3.9% for the lobularity index (LI), -29.8% for the myeloperoxidase index (MPXI), -0.6% for the neutrophil cluster mean x (NEUTx) and -0.7% for the neutrophil cluster mean y (NEUTy), respectively. The percentage of blood samples with reduced values after exposure to RF waves was 81% for LI, 88% for NEUTx and 100% for both MPXI and NEUTy. The results of this study show that exposure to smartphone RF waves triggers activation of neutrophils in vitro, as mirrored by the significant variations observed in many activation parameters in Advia 2120.

Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity

PubMed Central

Bennett, James E. M.; Bair, Wyeth

2015-01-01

Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli. PMID:26308406

Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity.

PubMed

Bennett, James E M; Bair, Wyeth

2015-08-01

Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli.

The Nonlinear Coupling of Electromagnetic Ion Cyclotron and Lower Hybrid Waves in the Ring Current Region: The Magnetic Storm May 1-7 1998

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Krivorutsky, E.; Gamayunov, K.; Avanov, L.

2003-01-01

The excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7, 1998 storm period on the global scale. The LHWs were calculated based on our newly developed self-consistent model that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

The Nonlinear Coupling of Electromagnetic Ion Cyclotron and Lower Hybrid Waves in the Ring Current Region

NASA Technical Reports Server (NTRS)

Khazanov, G. V.

2004-01-01

The excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7, 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al., 2002, 2003) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

Changes in Leisure Activities and Dimensions of Depressive Symptoms in Later Life: A 12-Year Follow-Up.

PubMed

Chao, Shiau-Fang

2016-06-01

Although leisure activities benefit the mental health of the elderly population, the effect of changes in leisure activities on dimensions of depressive symptoms remains unclear. This investigation examined the influences of changes in intellectual, social, and physical activities between waves on four dimensions of depressive symptoms at follow-up. Random effects modeling was utilized with data from a nationwide longitudinal study conducted in Taiwan. The study data comprised 6,942 observations from 2,660 older adults over a 12-year period. The results suggested that changes in physical activities contributed to depressive symptoms which reflected positive affect in the later wave. Increased social activities between waves predicted higher positive affect and lower interpersonal difficulties scores at follow-up. Increased intellectual activities between waves did not substantially affect any domain of depressive symptoms. In contrast, declines in intellectual activities between waves predicted higher scores in three depressive symptoms domains, including depressed mood, somatic symptoms, and interpersonal difficulties. Engagement in a varied range of activities benefits mental health among elders more than participation in any single type of activity among elders. Reducing physical activities can lower positive affect, while the adverse effect may be balanced by increasing social activities. Also, the impact of decreasing intellectual activities on the interpersonal difficulties domain of depressive symptoms may be offset by increasing social activities. © The Author 2014. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Whistler-triggered chorus emissions observed during daytime at low latitude ground station Jammu

NASA Astrophysics Data System (ADS)

Pratap Patel, Ravindra; Singh, K. K.; Singh, A. K.; Singh, R. P.

In this paper, we present whistler-triggered chorus emission recorded during daytime at low latitude ground station Jammu (geomag. Lat. = 22 degree 26 minute N; L = 1.17) during the period from 1996 to 2003. After analysis of the eight years collected data, we found out 29 events, which are definitely identified as chorus emission triggered by whistlers. During the observation period the magnetic activity is high. Analysis shows that the whistlers have propagated along the geomagnetic field line having L-values lying between L = 1.9 and 4.4. These waves could have propagated along the geomagnetic field lines either in ducted mode or pro-longitudinal mode. The measured relative intensity of the triggered emission and whistler wave is approximately the same and also varies from one event to another. It is proposed that these waves are generated through a process of wave-particle interaction and wave-wave interactions. Related parameters of this interaction are computed for different L-value and wave amplitude. With the help of dynamic spectra of these emissions, the proposed mechanisms are explained.

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

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

Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.

We present observations of transverse oscillations in slender Ca ii H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in a 1.1 Å wide passband covering the line core of Ca ii H 3969 Å from the second flight of the Sunrise balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes andmore » periods on the order of 2.4 ± 0.8 km s{sup −1} and 83 ± 29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9 ± 14 km s{sup −1}. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvénic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere with an estimated energy flux of ≈15 kW m{sup −2}. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.« less

Ground-based Observations for the Upper Atmosphere at King Sejong Station, Antarctica

NASA Astrophysics Data System (ADS)

Jee, Geonhwa; Kim, Jeong-Han; Lee, Changsup; Kim, Yong Ha

2014-06-01

Since the operation of the King Sejong Station (KSS) started in Antarctic Peninsula in 1989, there have been continuous efforts to perform the observation for the upper atmosphere. The observations during the initial period of the station include Fabry-Perot Interferometer (FPI) and Michelson Interferometer for the mesosphere and thermosphere, which are no longer in operation. In 2002, in collaboration with York University, Canada, the Spectral Airglow Temperature Imager (SATI) was installed to observe the temperature in the mesosphere and lower thermosphere (MLT) region and it has still been producing the mesopause temperature data until present. The observation was extended by installing the meteor radar in 2007 to observe the neutral winds and temperature in the MLT region during the day and night in collaboration with Chungnam National University. We also installed the all sky camera in 2008 to observe the wave structures in the MLT region. All these observations are utilized to study on the physical characteristics of the MLT region and also on the wave phenomena such as the tide and gravity wave in the upper atmosphere over KSS that is well known for the strong gravity wave activity. In this article, brief introductions for the currently operating instruments at KSS will be presented with their applications for the study of the upper atmosphere

Specular Reflection from Rough Surfaces Revisited

NASA Astrophysics Data System (ADS)

Yasuda, Kensei; Kim, Alvin; Cho, Hayley; Timofejev, Timofej; Walecki, Wojciech J.; Klep, James; Edelson, Amy S.; Walecki, Abigail S.; Walecki, Eve S.; Walecki, Peter S.

2016-10-01

In his beautiful paper, Hasan Fakhruddin reported observations of mirror-like reflections in the rough surface of a ground glass plate. Similar effects have been recently employed for metrology of the roughness of optical diffusers used in modern light emitting device illumination systems. We report the observations of specular reflection in nontransparent rough surfaces at oblique angles, where roughness was treated as a variable. We present a simple trigonometry-based model explaining the observed phenomenon, which we experimentally validated using aluminum surfaces that have controlled roughness. The reported demonstration requires no special equipment, other than cellphone cameras, dielectric or metal plate, and sandpaper, and serves as an introduction to wave optics. This activity can be used to get further insight into everyday applications of wave optics for students already familiar with wave optics fundamentals.

DE 1 and Viking observations associated with electron conical distributions

NASA Technical Reports Server (NTRS)

Menietti, J. D.; Weimer, D. R.; Andre, M.; Eliasson, L.

1994-01-01

Data from the electron detectors on board the Swedish Viking satellite launched during a period of low solar activity and from the Dynamic Explorer (DE) 1 satellite launched during active solar coditions have been examined for the occurrence and location of electron conical distributions and several conclusions can be drawn. First, we note that most of the best examples of electron conics observed by the V-3 experiment onboard Viking occurred in the afternoon sector in the range of magneitc local time 14 hours less than Magnetic Local Time (MLT) less than 18 hours, at midaltitudes in the range 10,000 km less than h less than 13,500 km, with few occurring in the nightside auroral region, a region poorly sampled at altitudes greater than 5000 km. For the Viking data there is an association of electron conics with upper hybrid waves. DE 1 observations made by the high-altitude plasma instrument (HAPI) indicate that electron conics were observed in the midmorning sector and the late evening sector, and as has been reported earlier, the correlation with upper hybird waves was good. The HAPI did not sample the afternoon sector. The electon conics observed on both satellites occurred in the presence of at least a modest (several kilovolts) potential difference beneath the satellite with a maximum energy that was usually, but not always, equal to or greater than the maximum energy of the electron conics. Two independent sets of observations by DE 1 suggest two distinct production mechanisms for electron conics. Examiniation of DE 1 electric field measurements from the plasma wave instrument during the observation of electron conics show simultaneous parallel oscillations in the frequency range of 0.2 Hz less than f less than 0.5 Hz during one and perhaps two of four events examined, and upper hybrid waves were observed on all four events. In addition, recent observations of '90-deg' electron conics associated with auroral kilometric radiation source regions suggest a perpendicular heating mechanism produced by wave-particle interaction. Such distributions may be observed as electron conics at higher altitudes. These results suggest more than one possible source mechanism may be responsible for electron conics.

Links between atmosphere, ocean, and cryosphere from two decades of microseism observations on the Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Anthony, Robert E.; Aster, Richard C.; McGrath, Daniel

2017-01-01

The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between the latitudes of 50°S to 65°S produce exceptional storm-driven wave conditions in the Southern Ocean. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high-amplitude wave activity and thus, ocean-swell-driven microseism noise in both the primary (direct wave-coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined across 23 years (1993-2015) from Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from East Falkland Island (EFI). These records provide a spatially integrative measure of both Southern Ocean wave amplitudes and the interactions between ocean waves and the solid Earth in the presence of sea ice, which can reduce wave coupling with the continental shelf. We utilize a spatiotemporal correlation-based approach to illuminate how the distribution of sea ice influences seasonal microseism power. We characterize primary and secondary microseism power due to variations in sea ice and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the Southern Annular Mode, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, thus strongly increasing microseism power levels.

The Role of African Easterly Wave on Dust Transport and the Interaction Between Saharan Dust Layer and Atlantic ITCZ During Boreal Summer

NASA Technical Reports Server (NTRS)

Kim, Kyu-Myong; Lau, William K-M

2011-01-01

Saharan dust outbreaks not only transport large amount of dust to the northern Atlantic Ocean, but also alter African easterly jet and wave activities along the jet by changing north-south temperature gradient. Recent modeling and observational studies show that during periods of enhance outbreaks, rainfall on the northern part of ITCZ increases in conjunction with a northward shift of ITCZ toward the dust layer. In this paper, we study the radiative forcing of Saharan dust and its interactions with the Atlantic Inter-tropical Convergence Zone (ITCZ), through African easterly waves (AEW), African easterly jet (AEJ), using the Terra/Aqua observations as well as MERRA data. Using band pass filtered EOF analysis, we find that African easterly waves propagating westward along two principal tracks, centered at 15-25N and 5-10N respectively. The easterly waves in the northern track are slower, with propagation speed of 9 ms-1, and highly correlated with major dust outbreak over North Africa. On the other hand, easterly waves along the southern track are faster with propagating speed of 10 ms-1, and are closely tied to rainfall/cloud variations along the Atlantic ITCZ. Dust transport along the southern track leads rainfall/cloud anomalies in the same region by one or two days, suggesting the southern tracks of dust outbreak are regions of strong interaction between Saharan dust layer and Atlantic ITCZ. Possible linkage between two tracks of easterly waves, as well as the long-term change of easterly wave activities and dust outbreaks, are also discussed.

Correlation between terrestrial myriametric and kilometric radio bursts observed with Galileo

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

Louarn, P.; Hilgers, A.; Roux, A.

The authors present results from wave measurements made by Galileo on transects of the magnetotail between R{sub e} of 30 and 80. They observe radiation in the myriametric and kilometric range. The myriametric radition has a continuous components, and a burstly component which correlated with the bursty nature of the kilometric radiation, originating on auroral field lines much closer to the earth. They present a mechanism to account for this wave activity, and its frequency dependence.

Temperature effects on the pickup process of water group and hydrogen ions - Extensions of 'A theory for low-frequency waves observed at Comet Giacobini-Zinner' by M. L. Goldstein and H. K. Wong

NASA Technical Reports Server (NTRS)

Brinca, Armando L.; Tsurutani, Bruce T.

1988-01-01

Cometary heavy ions can resonantly excite hydromagnetic wave activity with spacecraft frequency spectra strongly deviating from the ion cyclotron frequency. The influence of the newborn particle temperature on this effect is assessed, its relevance to the interpretation of the observations is discussed, and an alternative, more efficient mechanism to generate spacecraft frequencies of the order of the proton cyclotron frequency is suggested.

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

Ofman, L.; Knizhnik, K.; Kucera, T.

We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ∼ δn/n). The waves are evidentmore » as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5–11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5–14 G. For the typical prominence density the corresponding fast magnetosonic speed is ∼20 km s{sup −1}, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.« less

H.F. emission related to the Li+ ion beam injected into ionosphere - ``PLAZMA'' rocket experiment

NASA Astrophysics Data System (ADS)

Klos, Z.; Zbyszynski, Z.; Agafonov, U. F.; Managadze, G. G.; Mayorov, A. D.

1993-10-01

The H.F. emission generated by artificial ion beam injected into ionosphere was observed either with a wave detector and ion gun attached to the rocket through out the flight, or when the gun was deployed on subpayload. Generally the observations show unstructured shape of the H.F. spectrum. In the PLAZMA active rocket experiment - when ionospheric plasma was perturbed by the operation of impulse ion gun, which injected 300 A, 8.3 eV Li+ions - the waves in the 0.1 - 10 MHz frequency range were observed. The results have shown, that when the wave detector and the ion gun are attached to the rocket the emission enhances in the lower as well as in the upper parts of the spectrum. On the other hand only the lower increase is maintained when ion gun is removing away on the subpayload. The observed sequence of H.F. spectra is presented.

GCM simulations of intraseasonal variability in the Pacific/North American region

NASA Technical Reports Server (NTRS)

Schubert, Siegfried; Suarez, Max; Park, Chung-Kyu; Moorthi, Shrinivas

1993-01-01

General circulation model (GCM) simulations of low-frequency variability with time scales of 20 to 70 days are analyzed for the Pacific sector during boreal winter. The GCM's leading mode in the upper-tropospheric zonal wind is associated with fluctuations of the East Asian jet; this mode resembles, in both structure and amplitude, the Pacific/North American (PNA) pattern found in the observations on these time scales. In both the model and observations, the PNA anomaly is characterized by: (1) a linear balance in the upper-tropospheric vorticity budget with no significant Rossby wave source in the tropics, (2) a barotropic conversion of kinetic energy from the time mean Pacific jet, and (3) a north/south displacement of the Pacific storm track. In the GCM, the latter is associated with synoptic eddy heat flux and latent heat anomalies that appear to contribute to a strong lower-tropospheric source of wave activity over the North Pacific. This is in contrast to the observations, which show only a weak source of wave activity in this region.

New Observation of Wave Excitation and Inverse Cascade in the Foreshock Region

NASA Astrophysics Data System (ADS)

He, Jiansen; Duan, Die; Yan, Limei; Huang, Shiyong; Tu, Chuanyi; Marsch, Eckart; Wang, Linghua; Tian, Hui

2016-04-01

Foreshock with nascent plasma turbulence is regarded as a fascinating region to understand the basic plasma physical processes, e.g., wave-particle interactions as well as wave-wave couplings. Although there have been a bunch of intensive studies on this topic, some key clues about the chain of the physical processes still lacks from observations, e.g., the co-existence of upstream energetic particles as the free energy source, excited pump waves as the wave seed, inverse cascaded daughter waves, and scattered energetic particles as the end of nonlinear processes. A relatively comprehensive case study with some new observations is presented in this work. In our case, upstream energetic protons drifting at tens of Alfvén speed with respect to the background plasma protons is observed from 3DP/PESA-High onboard the WIND spacecraft. When looking at the wave magnetic activities, we are surprised to find the co-existence of high-frequency (0.1-0.5 Hz) large-amplitude right-hand polarized (RHP) waves and low-frequency (0.02-0.1 Hz) small-amplitude left-hand polarized (LHP) waves in the spacecraft (SC) frame. The anti-correlation between magnetic and velocity fluctuations along with the sunward magnetic field direction indicates the low-frequency LHP waves in the SC frame is in fact the sunward upstream RHP waves in the solar wind frame. This new observation lays solid foundation for the applicability of plasma non-resonance instability theory and inverse cascade theory to the foreshock region, in which the downstream high-frequency RHP pump waves are excited by the upstream reflected energetic protons through non-resonance instability and low-frequency RHP daughter waves are generated by the pump waves due to nonlinear parametric decay. The weak signal of alpha particle flux in the foreshock region concerned is also favorable to the occurrence of nonlinear decay process. Furthermore, enhanced downstream energetic proton fluxes are found and inferred to be scattered by the nascent turbulent fluctuations. Therefore, some key clues about the newborn turbulence in the foreshock are supplemented in this work. Nevertheless, the more complete scenario about the fundamental plasma physical processes in the foreshock is left for the newly launched MMS project and the proposed THOR mission.

Excito-oscillatory dynamics as a mechanism of ventricular fibrillation.

PubMed

Gray, Richard A; Huelsing, Delilah J

2008-04-01

The instabilities associated with reentrant spiral waves are of paramount importance to the initiation and maintenance of tachyarrhythmias, especially ventricular fibrillation (VF). In addition to tissue heterogeneities, there are only a few basic purported mechanisms of spiral wave breakup, most notably restitution. We test the hypothesis that oscillatory membrane properties act to destabilize spiral waves. We recorded transmembrane potential (V(m)) from isolated rabbit myocytes using a constant current stimulation protocol. We developed a mathematical model that included both the stable excitable equilibrium point at resting V(m) (-80 mV) and the unstable oscillatory equilibrium point at elevated V(m) (-10 mV). Spiral wave dynamics were studied in 2-dimensional grids using variants of the model. All models showed restitution and reproduced the experimental values of transmembrane resistance at rest and during the action potential plateau. Stable spiral waves were observed when the model showed only 1 equilibrium point. However, spatio-temporal complexity was observed if the model showed both excitable and oscillatory equilibrium points (i.e., excito-oscillatory models). The initial wave breaks resulted from oscillatory waves expanding in all directions; after a few beats, the patterns were characterized by a combination of unstable spiral waves and target patterns consistent with the patterns observed on the heart surface during VF. In our model, this VF-like activity only occurred when the single cell period of V(m) oscillations was within a specific range. The VF-like patterns observed in our excito-oscillatory models could not be explained by the existing proposed instability mechanisms. Our results introduce the important suggestion that membrane dynamics responsible for V(m) oscillations at elevated V(m) levels can destabilize spiral waves and thus may be a novel therapeutic target for preventing VF.

Electroencephalograph (EEG) study on self-contemplating image formation

NASA Astrophysics Data System (ADS)

Meng, Qinglei; Hong, Elliot; Choa, Fow-Sen

2016-05-01

Electroencephalography (EEG) is one of the most widely used electrophysiological monitoring methods and plays a significant role in studies of human brain electrical activities. Default mode network (DMN), is a functional connection of brain regions that are activated while subjects are not in task positive state or not focused on the outside world. In this study, EEG was used for human brain signals recording while all subjects were asked to sit down quietly on a chair with eyes closed and thinking about some parts of their own body, such as left and right hands, left and right ears, lips, nose, and the images of faces that they were familiar with as well as doing some simple mathematical calculation. The time is marker when the image is formed in the subject's mind. By analyzing brain activity maps 300ms right before the time marked instant for each of the 4 wave bands, Delta, Theta, Alpha and Beta waves. We found that for most EEG datasets during this 300ms, Delta wave activity would mostly locate at the frontal lobe or the visual cortex, and the change and movement of activities are slow. Theta wave activity tended to rotate along the edge of cortex either clockwise or counterclockwise. Beta wave behaved like inquiry types of oscillations between any two regions spread over the cortex. Alpha wave activity looks like a mix of the Theta and Beta activities but more close to Theta activity. From the observation we feel that Beta and high Alpha are playing utility role for information inquiry. Theta and low Alpha are likely playing the role of binding and imagination formation in DMN operations.

Temporal coordination of olfactory cortex sharp-wave activity with up- and downstates in the orbitofrontal cortex during slow-wave sleep.

PubMed

Onisawa, Naomi; Manabe, Hiroyuki; Mori, Kensaku

2017-01-01

During slow-wave sleep, interareal communications via coordinated, slow oscillatory activities occur in the large-scale networks of the mammalian neocortex. Because olfactory cortex (OC) areas, which belong to paleocortex, show characteristic sharp-wave (SPW) activity during slow-wave sleep, we examined whether OC SPWs in freely behaving rats occur in temporal coordination with up- and downstates of the orbitofrontal cortex (OFC) slow oscillation. Simultaneous recordings of local field potentials and spike activities in the OC and OFC showed that during the downstate in the OFC, the OC also exhibited downstate with greatly reduced neuronal activity and suppression of SPW generation. OC SPWs occurred during two distinct phases of the upstate of the OFC: early-phase SPWs occurred at the start of upstate shortly after the down-to-up transition in the OFC, whereas late-phase SPWs were generated at the end of upstate shortly before the up-to-down transition. Such temporal coordination between neocortical up- and downstates and olfactory system SPWs was observed between the prefrontal cortex areas (OFC and medial prefrontal cortex) and the OC areas (anterior piriform cortex and posterior piriform cortex). These results suggest that during slow-wave sleep, OC and OFC areas communicate preferentially in specific time windows shortly after the down-to-up transition and shortly before the up-to-down transition. Simultaneous recordings of local field potentials and spike activities in the anterior piriform cortex (APC) and orbitofrontal cortex (OFC) during slow-wave sleep showed that APC sharp waves tended to occur during two distinct phases of OFC upstate: early phase, shortly after the down-to-up transition, and late phase, shortly before the up-to-down transition, suggesting that during slow-wave sleep, olfactory cortex and OFC areas communicate preferentially in the specific time windows. Copyright © 2017 the American Physiological Society.

Temporal coordination of olfactory cortex sharp-wave activity with up- and downstates in the orbitofrontal cortex during slow-wave sleep

PubMed Central

Onisawa, Naomi; Mori, Kensaku

2016-01-01

During slow-wave sleep, interareal communications via coordinated, slow oscillatory activities occur in the large-scale networks of the mammalian neocortex. Because olfactory cortex (OC) areas, which belong to paleocortex, show characteristic sharp-wave (SPW) activity during slow-wave sleep, we examined whether OC SPWs in freely behaving rats occur in temporal coordination with up- and downstates of the orbitofrontal cortex (OFC) slow oscillation. Simultaneous recordings of local field potentials and spike activities in the OC and OFC showed that during the downstate in the OFC, the OC also exhibited downstate with greatly reduced neuronal activity and suppression of SPW generation. OC SPWs occurred during two distinct phases of the upstate of the OFC: early-phase SPWs occurred at the start of upstate shortly after the down-to-up transition in the OFC, whereas late-phase SPWs were generated at the end of upstate shortly before the up-to-down transition. Such temporal coordination between neocortical up- and downstates and olfactory system SPWs was observed between the prefrontal cortex areas (OFC and medial prefrontal cortex) and the OC areas (anterior piriform cortex and posterior piriform cortex). These results suggest that during slow-wave sleep, OC and OFC areas communicate preferentially in specific time windows shortly after the down-to-up transition and shortly before the up-to-down transition. NEW & NOTEWORTHY Simultaneous recordings of local field potentials and spike activities in the anterior piriform cortex (APC) and orbitofrontal cortex (OFC) during slow-wave sleep showed that APC sharp waves tended to occur during two distinct phases of OFC upstate: early phase, shortly after the down-to-up transition, and late phase, shortly before the up-to-down transition, suggesting that during slow-wave sleep, olfactory cortex and OFC areas communicate preferentially in the specific time windows. PMID:27733591

Regular Wave Propagation Out of Noise in Chemical Active Media

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

Alonso, S.; Sendina-Nadal, I.; Perez-Munuzuri, V.

2001-08-13

A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

Coupling between the lower and middle atmosphere observed during a very severe cyclonic storm 'Madi'

NASA Astrophysics Data System (ADS)

Hima Bindu, H.; Venkat Ratnam, M.; Yesubabu, V.; Narayana Rao, T.; Eswariah, S.; Naidu, C. V.; Vijaya Bhaskara Rao, S.

2018-04-01

Synoptic-scale systems like cyclones can generate broad spectrum of waves, which propagate from its source to the middle atmosphere. Coupling between the lower and middle atmosphere over Tirupati (13.6°N, 79.4°E) is studied during a very severe cyclonic storm 'Madi' (06-13 December 2013) using Weather Research and Forecast (WRF) model assimilated fields and simultaneous meteor radar observations. Since high temporal and spatial measurements are difficult to obtain during these disturbances, WRF model simulations are obtained by assimilating conventional and satellite observations using 3DVAR technique. The obtained outputs are validated for their consistency in predicting cyclone track and vertical structure by comparing them with independent observations. The good agreement between the assimilated outputs and independent observations prompted us to use the model outputs to investigate the gravity waves (GWs) and tides over Tirupati. GWs with the periods 1-5 h are observed with clear downward phase propagation in the lower stratosphere. These upward propagating waves obtained from the model are also noticed in the meteor radar horizontal wind observations in the MLT region (70-110 km). Interestingly, enhancement in the tidal activity in both the zonal and meridional winds in the mesosphere and lower thermosphere (MLT) region is noticed during the peak cyclonic activity except the suppression of semi-diurnal tide in meridional wind. A very good agreement in the tidal activity is also observed in the horizontal winds in the troposphere and lower stratosphere from the WRF model outputs and ERA5. These results thus provide evidence on the vertical coupling of lower and middle atmosphere induced by the tropical cyclone.

Collaborative analysis of Planetary Waves in the Mesospheric Neutral Winds with SuperDARN and TIMED Observations

NASA Astrophysics Data System (ADS)

Ruohoniemi, J. M.

2004-12-01

The SuperDARN HF radars are best known for observing the ExB drift of ionospheric plasma in the high-latitude F region. At mesospheric altitudes the trails of ionization produced by meteors provide another kind of target for radar backscatter, and the motions imparted to these trails by winds in the neutral atmosphere can be measured. In the northern hemisphere the coverage of mesospheric winds currently extends over a 180 deg longitude sector but is confined by propagation conditions to latitudes near 55 deg geographic. We have analyzed several extended periods of simultaneous observations of the neutral wind involving SuperDARN and the TIMED suite of instruments. Often, the winds show clear evidence of large-scale wave events. The quasi 2-day planetary waves are prominent and their occurrence is seen to depend on season. By comparing the wave characteristics between the satellite and ground observations we obtain a complete breakdown of the wave activity in terms of wave periods and zonal wavenumbers. In addition, the semidiurnal tide is a ubiquitous feature of the mid-latitude mesosphere. A single radar station cannot resolve the sun-synchronous component from other contributions at the semidiurnal frequency. We show that with a chain of radars along a latitude band, the true sun-synchronous, or migrating, component can be inferred. Joint analysis can be performed chiefly with data from the SABRE and TIDI instruments.

Excitation of MHD waves upstream of Jupiter by energetic sulfur or oxygen ions

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Wong, H. K.; Eviatar, A.

1986-01-01

Large fluxes of heavy ions have been reported upstream of Jupiter's bow shock as Voyager 1 approached the planet (Zwickl et al., 1981; Krimigis et al., 1985). Enhanced low-frequency magnetic wave activity was also observed during the particle events. The fluctuations are left-handed, elliptically polarized in the plasma frame. The spectrum of these fluctuations contains a peak close to the Doppler-shifted resonance frequency of a sulfur or oxygen beam with streaming energy of approximately 30 keV. These fluctuations are also present in the spectrum of the magnitude of the field. It is concluded that the observations result from an instability driven by an energetic beam of either sulfur or oxygen. The wave observations can be described by a heavy ion distribution with both a streaming anisotropy and a temperature anisotropy. This class of heavy ion streaming instabilities may also play a role in wave-particle interactions in the vicinity of comets.

First Imaging Observation of Standing Slow Wave in Coronal Fan Loops

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

Pant, V.; Tiwari, A.; Banerjee, D.

2017-09-20

We observe intensity oscillations along coronal fan loops associated with the active region AR 11428. The intensity oscillations were triggered by blast waves that were generated due to X-class flares in the distant active region AR 11429. To characterize the nature of oscillations, we created time–distance maps along the fan loops and noted that the intensity oscillations at two ends of the loops were out of phase. As we move along the fan loop, the amplitude of the oscillations first decreased and then increased. The out-of-phase nature together with the amplitude variation along the loop implies that these oscillations aremore » very likely to be standing waves. The period of the oscillations is estimated to be ∼27 minutes, damping time to be ∼45 minutes, and phase velocity projected in the plane of sky to be ∼65–83 km s{sup −1}. The projected phase speeds were in the range of the acoustic speed of coronal plasma at about 0.6 MK, which further indicates that these are slow waves. To the best of our knowledge, this is the first report on the existence of the standing slow waves in non-flaring fan loops.« less

Treatment of Viscosity in the Shock Waves Observed After Two Consecutive Coronal Mass Ejection Activities CME08/03/2012 and CME15/03/2012

NASA Astrophysics Data System (ADS)

Cavus, Huseyin

2016-11-01

A coronal mass ejection (CME) is one of the most the powerful activities of the Sun. There is a possibility to produce shocks in the interplanetary medium after CMEs. Shock waves can be observed when the solar wind changes its velocity from being supersonic nature to being subsonic nature. The investigations of such activities have a central place in space weather purposes, since; the interaction of shocks with viscosity is one of the most important problems in the supersonic and compressible gas flow regime (Blazek in Computational fluid dynamics: principles and applications. Elsevier, Amsterdam 2001). The main aim of present work is to achieve a search for the viscosity effects in the shocks occurred after two consecutive coronal mass ejection activities in 2012 (i.e. CME08/03/2012 and CME15/03/2012).

Rapid-run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere

NASA Astrophysics Data System (ADS)

Kozlovsky, Alexander; Turunen, Tauno; Ulich, Thomas

2013-08-01

2007, the Sodankylä Geophysical Observatory routinely performs vertical ionosphere soundings once per minute, using a frequency-modulated continuous-wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. We used these data to study traveling ionospheric disturbances (TIDs) during 10-16 local time. The observations were made between April 2007 and June 2012, mostly during low solar activity. The TIDs were studied in five bands of periods corresponding to the following: infrasonic (acoustic) waves and the buoyancy cutoff (periods from 5 to 10 min); small-scale gravity waves (GWs; 10-15 min); medium-scale (MS; 15-30 min) GWs; medium-large scale (MS-LS; 30-60 min) GWs; and large-scale (LS; 60-120 min) GWs. Relative contribution (with respect to LS TIDs) of the short-period (5-15 min) and MS (15-30 min) TIDs shows minima in winter and maxima in summer. These annual variations anticorrelate with variations of true height, namely, the largest relative amplitudes occur in summer, when TIDs were observed at minimal heights. We suggest that the summer increase of shorter-period TIDs is due to lowering reflection to the height where the Brunt-Väisälä period is smaller and, hence, shorter-period gravity waves exist. The summer maxima were most prominent during the 3 years of minimal solar activity (2008-2010). In 2011, when solar activity increased, the annual variation seems less prominent. Annual variations of the longer-period (30-120 min) TIDs are essentially less significant. For all TIDs, no obvious dependences on the AE and Ap indices of magnetic activity were found.

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.; Luehr, H.; Acuna, M. H.

1987-01-01

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Traveling waves in actin dynamics and cell motility

PubMed Central

Allard, Jun; Mogilner, Alex

2012-01-01

Much of current understanding of cell motility arose from studying steady treadmilling of actin arrays. Recently, there have been a growing number of observations of a more complex, non-steady, actin behavior, including self-organized waves. It is becoming clear that these waves result from activation and inhibition feedbacks in actin dynamics acting on different scales, but the exact molecular nature of these feedbacks and respective roles of biomechanics and biochemistry are still unclear. Here, we review recent advances achieved in experimental and theoretical studies of actin waves and discuss mechanisms and physiological significance of wavy protrusions. PMID:22985541

SLOW MAGNETOACOUSTIC WAVES OBSERVED ABOVE A QUIET-SUN REGION IN A DARK CAVITY

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

Liu Jiajia; Zhou Zhenjun; Wang Yuming

Waves play a crucial role in diagnosing the plasma properties of various structures in the solar corona and coronal heating. Slow magnetoacoustic (MA) waves are one of the important types of magnetohydrodynamic waves. In past decades, numerous slow MA waves were detected above active regions and coronal holes, but were rarely found elsewhere. Here, we investigate a 'tornado'-like structure consisting of quasi-periodic streaks within a dark cavity at about 40-110 Mm above a quiet-Sun region on 2011 September 25. Our analysis reveals that these streaks are actually slow MA wave trains. The properties of these wave trains, including phase speed,more » compression ratio, and kinetic energy density, are similar to those of the reported slow MA waves, except that the period of these waves is about 50 s, much shorter than the typical reported values (3-5 minutes).« less

Observation of Kelvin-Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

NASA Astrophysics Data System (ADS)

Stober, Gunter; Sommer, Svenja; Schult, Carsten; Latteck, Ralph; Chau, Jorge L.

2018-05-01

We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin-Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s-1 with intrinsic periods of 5-10 min.

Compressional ULF waves in the outer magnetosphere. 2: A case study of Pc 5 type wave activity

NASA Technical Reports Server (NTRS)

Zhu, Xiaoming; Kivelson, Margaret G.

1994-01-01

In previously published work (Zhu and Kivelson, 1991) the spatial distribution of compressional magnetic pulsations of period 2 - 20 min in the outer magnetosphere was described. In this companion paper, we study some specific compressional events within our data set, seeking to determine the structure of the waves and identifying the wave generation mechanism. We use both the magnetic field and three-dimensional plasma data observed by the International Sun-Earth Explorer (ISEE) 1 and/or 2 spacecraft to characterize eight compressional ultra low frequency (ULF) wave events with frequencies below 8 mHz in the outer magnetosphere. High time resolution plasma data for the event of July 24, 1978, made possible a detailed analysis of the waves. Wave properties specific to the event of July 24, 1978, can be summarized as follows: (1) Partial plasma pressures in the different energy ranges responded to the magnetic field pressure differently. In the low-energy range they oscillated in phase with the magnetic pressure, while oscillations in higher-energy ranges were out-of-phase; (2) Perpendicular wavelengths for the event were determined to be 60,000 and 30,000 km in the radial and azimuthal directions, respectively. Wave properties common to all events can be summarized as follows: (1) Compressional Pc 5 wave activity is correlated with Beta, the ratio of the plasma pressure to the magnetic pressure; the absolute magnitude of the plasma pressure plays a minor role for the wave activity; (2) The magnetic equator is a node of the compressional perturbation of the magnetic field; (3) The criterion for the mirror mode instability is often satisfied near the equator in the outer magnetosphere when the compressional waves are present. We believe these waves are generated by internal magnetohydrodynamic (MHD) instabilities.

Shear-wave velocity structure of the Tongariro Volcanic Centre, New Zealand: Fast Rayleigh and slow Love waves indicate strong shallow anisotropy

NASA Astrophysics Data System (ADS)

Godfrey, Holly J.; Fry, Bill; Savage, Martha K.

2017-04-01

Models of the velocity structure of volcanoes can help define possible magma pathways and contribute to calculating more accurate earthquake locations, which can help with monitoring volcanic activity. However, shear-wave velocity of volcanoes is difficult to determine from traditional seismic techniques, such as local earthquake tomography (LET) or refraction/reflection surveys. Here we use the recently developed technique of noise cross correlation of continuous seismic data to investigate the subsurface shear-wave velocity structure of the Tongariro Volcanic Centre (TgVC) of New Zealand, focusing on the active Ruapehu and Tongariro Volcanoes. We observe both the fundamental and first higher-order modes of Rayleigh and Love waves within our noise dataset, made from stacks of 15 min cross-correlation functions. We manually pick group velocity dispersion curves from over 1900 correlation functions, of which we consider 1373 to be high quality. We subsequently invert a subset of the fundamental mode Rayleigh- and Love-wave dispersion curves both independently and jointly for one dimensional shear-wave velocity (Vs) profiles at Ruapehu and Tongariro Volcanoes. Vs increases very slowly at a rate of approximately 0.2 km/s per km depth beneath Ruapehu, suggesting that progressive hydrothermal alteration mitigates the effects of compaction driven velocity increases. At Tongariro, we observe larger Vs increases with depth, which we interpret as different layers within Tongariro's volcanic system above altered basement greywacke. Slow Vs, on the order of 1-2 km/s, are compatible with P-wave velocities (using a Vp/Vs ratio of 1.7) from existing velocity profiles of areas within the TgVC, and the observations of worldwide studies of shallow volcanic systems that used ambient noise cross-correlation methods. Most of the measured group velocities of fundamental mode Love-waves across the TgVC are 0.1-0.4 km/s slower than those of fundamental mode Rayleigh-waves in the frequency range of 0.25-1 Hz. First-higher mode Love-waves are similarly slower than first-higher mode Rayleigh waves. This is incompatible with synthetic dispersion curves we calculate using isotropic, layered velocity models appropriate for Ruapehu and Tongariro, in which Love waves travel more quickly than Rayleigh waves of the same period. The Love-Rayleigh discrepancy is likely due to structures such as dykes or cracks in the vertical plane having increased influence on surface-wave propagation. However, several measurements at Ruapehu have Love-wave group velocities that are faster than Rayleigh-wave group velocities. The differences between the Love- and Rayleigh-wave dispersion curves also vary with the azimuth of the interstation path across Ruapehu and Tongariro Volcanoes. Significant azimuthal dependence of both Love and Rayleigh-wave velocities are also observed. This suggests azimuthal anisotropy within the volcanic structures, which coupled with radial anisotropy, makes the Vs structures of Ruapehu and Tongariro Volcanoes anisotropic with orthorhombic or lower order symmetry. We suggest that further work to determine three-dimensional volcanic structures should include provisions for such anisotropy.

Magnetospheric Multiscale observations of Poynting flux associated with magnetic reconnection in the Earth's magnetotail from 10 to 25 RE

NASA Astrophysics Data System (ADS)

Stawarz, J. E.; Eastwood, J. P.; Ergun, R.; Shay, M. A.; Phan, T.; Nakamura, R.; Varsani, A.; Burch, J. L.; Fuselier, S. A.; Gershman, D. J.; Giles, B. L.; Goodrich, K.; Khotyaintsev, Y. V.; Lindqvist, P. A.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.

2017-12-01

Magnetic reconnection plays an important role in energy conversion and transport in space plasmas. In the Earth's magnetotail, fast Earthward, as well as tailward, flows known as bursty bulk flows (BBFs) are thought to be jets caused by reconnection. Alfvénic Poynting flux associated with these reconnection events is thought to transport energy that results in auroral activity. It has been proposed that the reconnection event itself can generate a kinetic Alfvén wave signature along the separatrix. Furthermore, the process of BBF braking as the reconnection jet impinges on the dipolar near-Earth magnetic field can excite turbulence and wave activity, which can propagate along the field to the auroral region. Recently, Poynting flux at 10 RE in the tail near the plasma sheet boundary has been examined using observations from the Magnetospheric Multiscale (MMS) mission. The 3D structure of the fluctuations was investigated and it was demonstrated that they are consistent with kinetic Alfvén waves with non-plane-wave structure. However, at this location in the tail, the observed Poynting flux may be linked to either the reconnection separatrix or waves excited by BBF braking. Some evidence for two classes of Poynting flux events that may be consistent with these two source mechanisms has been found at 10 RE distances. In this presentation, these results will be discussed and compared with new MMS observations nearer to the reconnection site at 25 RE. At this location, BBF braking is likely not contributing to the Poynting flux, which helps to further elucidate the importance of the various sources of reconnection related Alfvénic Poynting flux in the magnetotail.

Oscillations and uniaxial mechanochemical waves in a model of an active poroelastic medium: Application to deformation patterns in protoplasmic droplets of Physarum polycephalum

NASA Astrophysics Data System (ADS)

Alonso, Sergio; Strachauer, Ulrike; Radszuweit, Markus; Bär, Markus; Hauser, Marcus J. B.

2016-04-01

Self-organization in cells often manifests itself in oscillations and waves. Here, we address deformation waves in protoplasmic droplets of the plasmodial slime mould Physarum polycephalum by modelling and experiments. In particular, we extend a one-dimensional model that considered the cell as a poroelastic medium, where active tension caused mechanochemical waves that were regulated by an inhibitor (Radszuweit et al., 2013). Our extension consists of a simple, qualitative chemical reaction-diffusion model (Brusselator) that describes the regulation of the inhibitor by another biochemical species. The biochemical reaction enhances the formation of mechanochemical waves if the reaction rates and input concentrations are near or inside an oscillatory regime. The period of the waves is found to be controlled by the characteristic oscillation period, whereas their wavelength is set by mechanical parameters. The model also allows for a systematic study of the chemical activity at the onset of mechanochemical waves. We also present examples for pattern formation in protoplasmic droplets of Physarum polycephalum including global oscillations where the central region of the droplets is in antiphase to the boundary zone, as well as travelling and standing wave-like uniaxial patterns. Finally, we apply our model to reproduce these experimental results by identifying the active tension inhibitor with the intracellular calcium concentration in the Physarum droplets and by using parameter values from mechanical experiments, respectively knowledge about the properties of calcium oscillations in Physarum. The simulation results are then found to be in good agreement with the experimental observations.

Observing the Microseism Source Regions from Space

NASA Astrophysics Data System (ADS)

Simard, M.; Kedar, S.; Rodriguez, E.; Webb, F. H.

2005-12-01

Correlations of this ambient seismic signal between seismic stations has recently emerged as a powerful technique for tomography of the Earth's crust, allowing continuous global monitoring of the crust to seismogenic depths without relying on the occurrence of earthquakes. The technique has the potential for resolving changes in the crust during periods of little or no earthquake activity. Since ambient seismic noise is predominantly generated by ocean wave-wave interactions known to originate in narrowly defined geographical source areas that vary according to ocean swell state and season, it may be possible to derive physical constraints of the source characteristics by globallyly observing candidate source regions from space. At present, such observations have been confined to point measurements such as directional buoys and ocean-bottom seismometers. Using a technique formulated by Engen and Jonsen [1995], a 'field view' of the generating region can be obtained by deriving ocean directional spectra from Synthetic Aperature Radar (SAR) images by analysis of cross correlation of single-look SAR images. In November 2004, the Jet Propulsion Laboratory's (JPL) air-borne SAR instrument, has collected data off the Alaska coast, while a large storm with wave heights of ~8m was pounding the coast. This was contemporaneous with the recording of strong microseismic activity by the Canadian National Seismic (CNSN). The AirSAR collected over a 100km long, 10km wide swath offshore, the region most likely to involve wave-wave interaction between the incoming swell and coast-reflected waves. JPL has implemented the cross correlation spectral technique, and applied it to the 2004 data-set. We will present results of the analysis of the SAR data in conjunction with analysis of the CNSN broadband seismic data.

STEREO/Waves Education and Public Outreach

NASA Astrophysics Data System (ADS)

MacDowall, R. J.; Bougeret, J.; Bale, S. D.; Goetz, K.; Kaiser, M. L.

2005-05-01

We present the education and public outreach plan and activities of the STEREO Waves (aka SWAVES) investigation. SWAVES measures radio emissions from the solar corona, interplanetary medium, and terrestrial magnetosphere, as well as in situ waves in the solar wind. In addition to the web site components that display stereo/multi-spacecraft data in a graphical form and explain the science and instruments, we will focus on the following three areas of EPO: class-room demonstrations using models of the STEREO spacecraft with battery powered radio receivers (and speakers) to illustrate spacecraft radio direction finding, teacher developed and tested class-room activities using SWAVES solar radio observations to motivate geometry and trigonometry, and sound-based delivery of characteristic radio and plasma wave events from the SWAVES web site for accessibility and esthetic reasons. Examples of each element will be demonstrated.

Shock compression and release of a-axis magnesium single crystals: Anisotropy and time dependent inelastic response

DOE PAGES

Renganathan, P.; Winey, J. M.; Gupta, Y. M.

2017-01-19

Here, to gain insight into inelastic deformation mechanisms for shocked hexagonal close-packed (hcp) metals, particularly the role of crystal anisotropy, magnesium (Mg) single crystals were subjected to shock compression and release along the a-axis to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles measured at several thicknesses, using laser interferometry, show a sharply peaked elastic wave followed by the plastic wave. Additionally, a smooth and featureless release wave is observed following peak compression. When compared to wave profiles measured previously for c-axis Mg, the elastic wave amplitudes for a-axis Mg are lower for the same propagation distance, and less attenuation of elastic wave amplitude is observed for a given peak stress. The featureless release wave for a-axis Mg is in marked contrast to the structured features observed for c-axis unloading. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using prismatic slip or (10more » $$\\bar{1}$$2) twinning, individually, do not match the measured compression profiles for a-axis Mg. However, a combination of slip and twinning provides a good overall match to the measured compression profiles. In contrast to compression,prismatic slip alone provides a reasonable match to the measured release wave profiles; (10$$\\bar{1}$$2) twinning due to its uni-directionality is not activated during release. The experimental results and wave profile simulations for a-axis Mg presented here are quite different from the previously published c-axis results, demonstrating the important role of crystal anisotropy on the time-dependent inelastic deformation of Mg single crystals under shock compression and release.« less

Shock compression and release of a-axis magnesium single crystals: Anisotropy and time dependent inelastic response

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

Renganathan, P.; Winey, J. M.; Gupta, Y. M.

Here, to gain insight into inelastic deformation mechanisms for shocked hexagonal close-packed (hcp) metals, particularly the role of crystal anisotropy, magnesium (Mg) single crystals were subjected to shock compression and release along the a-axis to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles measured at several thicknesses, using laser interferometry, show a sharply peaked elastic wave followed by the plastic wave. Additionally, a smooth and featureless release wave is observed following peak compression. When compared to wave profiles measured previously for c-axis Mg, the elastic wave amplitudes for a-axis Mg are lower for the same propagation distance, and less attenuation of elastic wave amplitude is observed for a given peak stress. The featureless release wave for a-axis Mg is in marked contrast to the structured features observed for c-axis unloading. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using prismatic slip or (10more » $$\\bar{1}$$2) twinning, individually, do not match the measured compression profiles for a-axis Mg. However, a combination of slip and twinning provides a good overall match to the measured compression profiles. In contrast to compression,prismatic slip alone provides a reasonable match to the measured release wave profiles; (10$$\\bar{1}$$2) twinning due to its uni-directionality is not activated during release. The experimental results and wave profile simulations for a-axis Mg presented here are quite different from the previously published c-axis results, demonstrating the important role of crystal anisotropy on the time-dependent inelastic deformation of Mg single crystals under shock compression and release.« less

Spiral wave classification using normalized compression distance: Towards atrial tissue spatiotemporal electrophysiological behavior characterization.

PubMed

Alagoz, Celal; Guez, Allon; Cohen, Andrew; Bullinga, John R

2015-08-01

Analysis of electrical activation patterns such as re-entries during atrial fibrillation (Afib) is crucial in understanding arrhythmic mechanisms and assessment of diagnostic measures. Spiral waves are a phenomena that provide intuitive basis for re-entries occurring in cardiac tissue. Distinct spiral wave behaviors such as stable spiral waves, meandering spiral waves, and spiral wave break-up may have distinct electrogram manifestations on a mapping catheter. Hence, it is desirable to have an automated classification of spiral wave behavior based on catheter recordings for a qualitative characterization of spatiotemporal electrophysiological activity on atrial tissue. In this study, we propose a method for classification of spatiotemporal characteristics of simulated atrial activation patterns in terms of distinct spiral wave behaviors during Afib using two different techniques: normalized compressed distance (NCD) and normalized FFT (NFFTD). We use a phenomenological model for cardiac electrical propagation to produce various simulated spiral wave behaviors on a 2D grid and labeled them as stable, meandering, or breakup. By mimicking commonly used catheter types, a star shaped and a circular shaped both of which do the local readings from atrial wall, monopolar and bipolar intracardiac electrograms are simulated. Virtual catheters are positioned at different locations on the grid. The classification performance for different catheter locations, types and for monopolar or bipolar readings were also compared. We observed that the performance for each case differed slightly. However, we found that NCD performance is superior to NFFTD. Through the simulation study, we showed the theoretical validation of the proposed method. Our findings suggest that a qualitative wavefront activation pattern can be assessed during Afib without the need for highly invasive mapping techniques such as multisite simultaneous electrogram recordings.

The 4-5 day mode oscillation in zonal winds of Indian middle atmosphere during MONEX-79

NASA Astrophysics Data System (ADS)

Reddy, R. S.; Mukherjee, B. K.; Indira, K.; Murty, B. V. R.

1985-12-01

In the early studies based on time series of balloon observations, the existence of 4 to 5 day period waves and 10 to 20 day wind fluctuations were found in the tropical lower stratosphere, and they are identified theoretically as the mixed Rossby-gravity wave and the Kelvin wave, respectively. On the basis of these studies, it was established that the vertically propagating equatorial waves play an important role in producing the QBO (quasi-biennial oscillation) in the mean zonal wind through the mechanism of wave-zonal interaction. These studies are mainly concentrated over the equatorial Pacific and Atlantic Oceans. Similar prominent wave disturbances have been observed over the region east of the Indian Ocean during a quasi-biennial oscillation. Zonal winds in upper troposphere and lower stratosphere (10 to 20) km of the middle atmosphere over the Indian subcontinent may bear association with the activity of summer monsoon (June-September). Monsoon Experiment (MONEX-79) has provided upper air observations at Balasore (21 deg. 30 min.N; 85 deg. 56 min.E), during the peak of monsoon months July and August. A unique opportunity has, therefore, been provided to study the normal oscillations present in the zonal winds of lower middle atmosphere over India, which may have implication on large scale wave dynamics. This aspect is examined in the present study.

Observational evidence of competing source, loss, and transport processes for relativistic electrons in Earth's outer radiation belt

NASA Astrophysics Data System (ADS)

Turner, Drew; Mann, Ian; Usanova, Maria; Rodriguez, Juan; Henderson, Mike; Angelopoulos, Vassilis; Morley, Steven; Claudepierre, Seth; Li, Wen; Kellerman, Adam; Boyd, Alexander; Kim, Kyung-Chan

Earth’s outer electron radiation belt is a region of extreme variability, with relativistic electron intensities changing by orders of magnitude over time scales ranging from minutes to years. Extreme variations of outer belt electrons ultimately result from the relative impacts of various competing source (and acceleration), loss, and transport processes. Most of these processes involve wave-particle interactions between outer belt electrons and different types of plasma waves in the inner magnetosphere, and in turn, the activity of these waves depends on different solar wind and magnetospheric driving conditions and thus can vary drastically from event to event. Using multipoint analysis with data from NASA’s Van Allen Probes, THEMIS, and SAMPEX missions, NOAA’s GOES and POES constellations, and ground-based observatories, we present results from case studies revealing how different source/acceleration and loss mechanisms compete during active periods to result in drastically different distributions of outer belt electrons. By using a combination of low-Earth orbiting and high-altitude-equatorial orbiting satellites, we briefly review how it is possible to get a much more complete picture of certain wave activity and electron losses over the full range of MLTs and L-shells throughout the radiation belt. We then show example cases highlighting the importance of particular mechanisms, including: substorm injections and whistler-mode chorus waves for the source and acceleration of relativistic electrons; magnetopause shadowing and wave-particle interactions with EMIC waves for sudden losses; and ULF wave activity for driving radial transport, a process which is important for redistributing relativistic electrons, contributing both to acceleration and loss processes. We show how relativistic electron enhancement events involve local acceleration that is consistent with wave-particle interactions between a seed population of 10s to 100s of keV electrons, with a source in the plasma sheet, and chorus waves. We show how sudden losses during outer belt dropout events are dominated at higher L-shells (L>~4) by magnetopause shadowing and outward radial transport, which is effective over the full ranges of energy and equatorial pitch angle of outer belt electrons, but at lower L-shells near the plasmapause, energy and pitch angle dependent losses can also occur and are consistent with rapid scattering by interactions between relativistic electrons and EMIC waves. We show cases demonstrating how these different processes occur simultaneously during active periods, with relative effects that vary as a function of L-shell and electron energy and pitch angle. Ultimately, our results highlight the complexity of competing source/acceleration, loss, and transport processes in Earth’s outer radiation belt and the necessity of using multipoint observations to disambiguate between them for future studies.

DEMETER observations of bursty MF emissions and their relation to ground-level auroral MF burst

NASA Astrophysics Data System (ADS)

Broughton, M. C.; LaBelle, J.; Parrot, M.

2014-12-01

A survey of medium frequency (MF) electric field data from selected orbits of the Detection of Electro-Magnetic Emissions Transmitted from Earthquakes (DEMETER) spacecraft reveals 68 examples of a new type of bursty MF emissions occurring at high latitudes associated with auroral phenomena. These resemble auroral MF burst, a natural radio emission observed at ground level near local substorm onsets. Similar to MF burst, the bursty MF waves observed by DEMETER have broadband, impulsive frequency structure covering 1.5-3.0 MHz, amplitudes of 50-100 μV/m, an overall occurrence rate of ˜0.76% with higher occurrence during active times, and strong correlation with auroral hiss. The magnetic local time distribution of the MF waves observed by DEMETER shows peak occurrence rate near 18 MLT, somewhat earlier than the equivalent peak in the occurrence rate of ground level MF burst, though propagation effects and differences in the latitudes sampled by the two techniques may explain this discrepancy. Analysis of solar wind and SuperMAG data suggests that while the bursty MF waves observed by DEMETER are associated with enhanced auroral activity, their coincidence with substorm onset may not be as exact as that of ground level MF burst. One conjunction occurs in which MF burst is observed at Churchill, Manitoba, within 8 min of MF emissions detected by DEMETER on field lines approximately 1000 km southeast of Churchill. These observations may plausibly be associated with the same auroral event detected by ground level magnetometers at several Canadian observatories. Although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground level MF burst. Hence, theories of MF burst generation in the ionosphere, such as beam-generated Langmuir waves excited over a range of altitudes or strong Langmuir turbulence generating a range of frequencies within a narrow altitude range, need to be revisited to see whether they predict in situ detection of MF burst.

Large-Amplitude High-Frequency Waves at Earth's Magnetopause

NASA Astrophysics Data System (ADS)

Graham, D. B.; Vaivads, A.; Khotyaintsev, Yu. V.; André, M.; Le Contel, O.; Malaspina, D. M.; Lindqvist, P.-A.; Wilder, F. D.; Ergun, R. E.; Gershman, D. J.; Giles, B. L.; Magnes, W.; Russell, C. T.; Burch, J. L.; Torbert, R. B.

2018-04-01

Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1 V m-1, and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.

SDO/AIA Observations of Quasi-periodic Fast (~1000 km/s) Propagating (QFP) Waves as Evidence of Fast-mode Magnetosonic Waves in the Low Corona: Statistics and Implications

NASA Astrophysics Data System (ADS)

Liu, W.; Ofman, L.; Title, A. M.; Zhao, J.; Aschwanden, M. J.

2011-12-01

Recent EUV imaging observations from SDO/AIA led to the discovery of quasi-periodic fast (~2000 km/s) propagating (QFP) waves in active regions (Liu et al. 2011). They were interpreted as fast-mode magnetosonic waves and reproduced in 3D MHD simulations (Ofman et al. 2011). Since then, we have extended our study to a sample of more than a dozen such waves observed during the SDO mission (2010/04-now). We will present the statistical properties of these waves including: (1) Their projected speeds measured in the plane of the sky are about 400-2200 km/s, which, as the lower limits of their true speeds in 3D space, fall in the expected range of coronal Alfven or fast-mode speeds. (2) They usually originate near flare kernels, often in the wake of a coronal mass ejection, and propagate in narrow funnels of coronal loops that serve as waveguides. (3) These waves are launched repeatedly with quasi-periodicities in the 30-200 seconds range, often lasting for more than one hour; some frequencies coincide with those of the quasi-periodic pulsations (QPPs) in the accompanying flare, suggestive a common excitation mechanism. We obtained the k-omega diagrams and dispersion relations of these waves using Fourier analysis. We estimate their energy fluxes and discuss their contribution to coronal heating as well as their diagnostic potential for coronal seismology.

Measurement study on stratospheric turbulence generation by wave-wave interaction

NASA Astrophysics Data System (ADS)

Söder, Jens; Gerding, Michael; Schneider, Andreas; Wagner, Johannes; Lübken, Franz-Josef

2017-04-01

During a joint campaign of the research programmes METROSI and GW-LCYCLE 2 (Northern Scandinavia, January 2016), an extraordinary case of turbulence generation by wave-wave interaction has been observed. To describe this turbulence, we will focus on the energy dissipation rate. The most feasible way to measure dissipation is to resolve the inner scale of turbulence. This is done by our balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) that combines a precise turbulence measurement method with the capability of being launched from every radiosonde station. For the flight in discussion further information on the meteorological background is obtained by a radiosonde. Due to the fact that the balloon drifts horizontally during ascent, measurements of vertical and horizontal wave parameters are ambiguous. Hence further understanding of the wave field is aided by 3d-simulations using WRF and ECMWF. Concentrating on one out of six LITOS launches during that campaign, we see some turbulent activity across the whole flightpath as on most other LITOS measurements. Nevertheless, we find pronounced maxima in the middle stratosphere (24 - 32 km). They coincide with a distinct phase of a mountain wave. As seen from WRF and ECMWF wind fields, this mountain wave interacts with another larger scale gravity wave. That is, the second wave influences the propagation of the smaller scale mountain wave. With LITOS we see the strongest dissipation rates in areas where the phase direction of the smaller wave changes due to wave-wave interaction. Therefore, these measurements provide an opportunity for further investigation into breakdown processes of internal gravity waves.

Initial observations from seismometers frozen into a borehole through the McMurdo Ice Shelf.

NASA Astrophysics Data System (ADS)

Prior, David; Eccles, Jennifer; Cooper, Joanna; Craw, Lisa; van Haastrecht, Laurine; Hamish Bowman, M.; Stevens, Craig; Gamble Rosevear, Madi; Hulbe, Christina; Gorman, Andrew; Horgan, Huw; Pyne, Alex

2017-04-01

A seismometer cable with two, three-component seismometers was frozen into a hot water borehole through the McMurdo Ice Shelf at Windless Bight in late December 2016. The seismometers are at 39m and 189m depth. The upper seismometer lies just below the firn-ice transition ( 37m) and very close to sea level ( 38m). The lower seismometer is positioned 30m above the base of the ice shelf ( 222m). The seismometers froze in within 40 (upper) to 60 (lower) hours of the last reaming operation. The temperature evolution during freezing is complicated, particularly for the lower seismometer. The complications are interpreted as the result of brine expulsion and brine pocket migration. We conducted an active source experiment using the frozen-in seismometers together with a surface seismometer and four lines of geophones radiating from the borehole, at 45-degree angles, to a distance of 240m. Sources included a traditional hammer and surface plate, two types of hammer activated surface shear wave sources (for hard and soft surfaces) and a hammer activated borehole source. The frozen-in seismometers show excellent separation of P - wave and S - wave arrivals for all sources, particularly on the lower seismometer. The surface shear sources give clearer separation of arrivals on the vertical and horizontal components. For some source to receiver geometries the surface shear sources give no P - wave arrival on the horizontal seismometer components and a very strong S - wave arrival that is partitioned between the horizontal components in correspondence with the source orientation. The borehole source (at 3 to 10m in the firn) also gives clearer separation of P - wave and S - wave arrivals compared to a surface hammer and plate. The frozen-in seismometers were also used to listen for natural events in the ice. Comparing the same events recorded at the surface and at depth, the latter are much less noisy than the former, leading to more clear interpretation. As in the active source experiments, P-wave and S-wave arrivals are clear and the partitioning onto different components (vertical and horizontal) is very clear. Using seismology to interpret the physical properties of ice masses is dependent on quality data. The patterns of anisotropy related to ice crystallographic preferred orientations (CPOs) are particularly rich for S - waves and the ability to measure S - wave velocities and shear wave splitting is of particular importance in using seismology to constrain CPOs. Our initial observations suggest that seismometers frozen-in at depth, together with artificial sources with controlled shear wave kinematics have great potential to help us constrain ice CPOs and resultant plastic anisotropy through seismic data.

Do gravity waves significantly impact PSC occurrence in the Antarctic?

NASA Astrophysics Data System (ADS)

McDonald, A. J.; George, S. E.; Woollands, R. M.

2009-02-01

This study uses a combination of POAM III aerosol extinction measurements and CHAMP GPS/RO temperature measurements to examine the role of atmospheric gravity waves in Polar Stratospheric Cloud (PSC) formation in the Antarctic. POAM III aerosol extinction observations are used to identify Type I Polar Stratospheric Clouds using an unsupervised clustering algorithm. The seasonal and spatial distribution of PSCs observed by POAM III is examined to determine whether there is a bias towards regions of high wave activity early in the Antarctic winter which may enhance PSC formation. Examination of the probability of temperatures below the Type Ia formation temperature threshold based on UKMO analyses displays a good correspondence to the PSC occurrence derived from POAM III extinction data in general. However, in June the POAM III observations of PSC are more abundant than expected from temperature thresholds. In addition the PSC occurrence based on temperature thresholds in September and October is often significantly higher than the PSC occurrence observed by POAM III, this observation probably being due to dehydration and denitrification. Use of high resolution temperatures from CHAMP GPS/RO observations provide a slightly improved relationship to the POAM III derived values. Analysis of the CHAMP temperature observations indicates that temperature perturbations associated with gravity waves may explain the enhanced PSC incidence observed in June compared to the UKMO analyses. Comparison of the UKMO analyses temperatures relative to corresponding CHAMP observations also suggests a small warm bias in the UKMO analyses during June. Examination of the longitudinal structure PSC occurrence in June 2005 also shows that regions of enhancement are associated with data near the Antarctic peninsula a known Mountain wave "hotspot". The impact of temperature perturbations causing enhanced temperature threshold crossings is shown to be particularly important early in the Antarctic winter while later in the season temperature perturbations associated with gravity waves could contribute to about 15% of the PSC observed, a value which corresponds well to several previous studies.

Statistical Study in the mid-altitude cusp region: wave and particle data comparison using a normalized cusp crossing duration

NASA Astrophysics Data System (ADS)

Grison, B.; Escoubet, C. P.; Pitout, F.; Cornilleau-Wehrlin, N.; Dandouras, I.; Lucek, E.

2009-04-01

In the mid altitude cusp region the DC magnetic field presents a diamagnetic cavity due to intense ion earthward flux coming from the magnetosheath. A strong ultra low frequency (ULF) magnetic activity is also commonly observed in this region. Most of the mid altitude cusp statistical studies have focused on the location of the cusp and its dependence and response to solar wind, interplanetary magnetic field, dipole tilt angle parameters. In our study we use the database build by Pitout et al. (2006) in order to study the link of wave power in the ULF range (0.35-10Hz) measured by STAFF SC instrument with the ion plasma properties as measured by CIS (and CODIF) instrument as well as the diamagnetic cavity in the mid-altitude cusp region with FGM data. To compare the different crossings we don`t use the cusp position and dynamics but we use a normalized cusp crossing duration that permits to easily average the properties over a large number of crossings. As usual in the cusp, it is particularly relevant to sort the crossings by the corresponding interplanetary magnetic field (IMF) orientation in order to analyse the results. In particular we try to find out what is the most relevant parameter to link the strong wave activity with. The global statistic confirms previous single case observations that have noticed a simultaneity between ion injections and wave activity enhancements. We will also present results concerning other ion parameters and the diamagnetic cavity observed in the mid altitude cusp region.

Spatiotemporal Stochastic Resonance:Theory and Experiment

NASA Astrophysics Data System (ADS)

Peter, Jung

1996-03-01

The amplification of weak periodic signals in bistable or excitable systems via stochastic resonance has been studied intensively over the last years. We are going one step further and ask: Can noise enhance spatiotemporal patterns in excitable media and can this effect be observed in nature? To this end, we are looking at large, two dimensional arrays of coupled excitable elements. Due to the coupling, excitation can propagate through the array in form of nonlinear waves. We observe target waves, rotating spiral waves and other wave forms. If the coupling between the elements is below a critical threshold, any excitational pattern will die out in the absence of noise. Below this threshold, large scale rotating spiral waves - as they are observed above threshold - can be maintained by a proper level of the noise[1]. Furthermore, their geometric features, such as the curvature can be controlled by the homogeneous noise level[2]. If the noise level is too large, break up of spiral waves and collisions with spontaneously nucleated waves yields spiral turbulence. Driving our array with a spatiotemporal pattern, e.g. a rotating spiral wave, we show that for weak coupling the excitational response of the array shows stochastic resonance - an effect we have termed spatiotemporal stochastic resonance. In the last part of the talk I'll make contact with calcium waves, observed in astrocyte cultures and hippocampus slices[3]. A. Cornell-Bell and collaborators[3] have pointed out the role of calcium waves for long-range glial signaling. We demonstrate the similarity of calcium waves with nonlinear waves in noisy excitable media. The noise level in the tissue is characterized by spontaneous activity and can be controlled by applying neuro-transmitter substances[3]. Noise effects in our model are compared with the effect of neuro-transmitters on calcium waves. [1]P. Jung and G. Mayer-Kress, CHAOS 5, 458 (1995). [2]P. Jung and G. Mayer-Kress, Phys. Rev. Lett.62, 2682 (1995). [3] A. Cornell-Bell, Steven M. Finkbeiner, Mark.S. Cooper and Stephen J. Smith, SCIENCE, 247, 373 (1990).

Effects of observation of hand movements reflected in a mirror on cortical activation in patients with stroke

PubMed Central

Chang, Moon-Young; Kim, Hwan-Hee; Kim, Kyeong-Mi; Oh, Jae-Seop; Jang, Chel; Yoon, Tae-Hyung

2017-01-01

[Purpose] The purpose of this study was to examine what changes occur in brain waves when patients with stroke receive mirror therapy intervention. [Subjects and Methods] The subjects of this study were 14 patients with stroke (6 females and 8 males). The subjects were assessed by measuring the alpha and beta waves of the EEG (QEEG-32 system CANS 3000). The mirror therapy intervention was delivered over the course of four weeks (a total of 20 sessions). [Results] Relative alpha power showed statistically significant differences in the F3, F4, O1, and O2 channels in the situation comparison and higher for hand observation than for mirror observation. Relative beta power showed statistically significant differences in the F3, F4, C3, and C4 channels. [Conclusion] This study analyzed activity of the brain in each area when patients with stroke observed movements reflected in a mirror, and future research on diverse tasks and stimuli to heighten activity of the brain should be carried out. PMID:28210035

ON THE BRIGHTNESS AND WAITING-TIME DISTRIBUTIONS OF A TYPE III RADIO STORM OBSERVED BY STEREO/WAVES

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

Eastwood, J. P.; Hudson, H. S.; Krucker, S.

2010-01-10

Type III solar radio storms, observed at frequencies below {approx}16 MHz by space-borne radio experiments, correspond to the quasi-continuous, bursty emission of electron beams onto open field lines above active regions. The mechanisms by which a storm can persist in some cases for more than a solar rotation whilst exhibiting considerable radio activity are poorly understood. To address this issue, the statistical properties of a type III storm observed by the STEREO/WAVES radio experiment are presented, examining both the brightness distribution and (for the first time) the waiting-time distribution (WTD). Single power-law behavior is observed in the number distribution asmore » a function of brightness; the power-law index is {approx}2.1 and is largely independent of frequency. The WTD is found to be consistent with a piecewise-constant Poisson process. This indicates that during the storm individual type III bursts occur independently and suggests that the storm dynamics are consistent with avalanche-type behavior in the underlying active region.« less

Effects of observation of hand movements reflected in a mirror on cortical activation in patients with stroke.

PubMed

Chang, Moon-Young; Kim, Hwan-Hee; Kim, Kyeong-Mi; Oh, Jae-Seop; Jang, Chel; Yoon, Tae-Hyung

2017-01-01

[Purpose] The purpose of this study was to examine what changes occur in brain waves when patients with stroke receive mirror therapy intervention. [Subjects and Methods] The subjects of this study were 14 patients with stroke (6 females and 8 males). The subjects were assessed by measuring the alpha and beta waves of the EEG (QEEG-32 system CANS 3000). The mirror therapy intervention was delivered over the course of four weeks (a total of 20 sessions). [Results] Relative alpha power showed statistically significant differences in the F3, F4, O1, and O2 channels in the situation comparison and higher for hand observation than for mirror observation. Relative beta power showed statistically significant differences in the F3, F4, C3, and C4 channels. [Conclusion] This study analyzed activity of the brain in each area when patients with stroke observed movements reflected in a mirror, and future research on diverse tasks and stimuli to heighten activity of the brain should be carried out.

Jupiter cloud morphology and zonal winds from ground-based observations during Juno's first year around Jupiter

NASA Astrophysics Data System (ADS)

Hueso, R.; Sánchez-Lavega, A.; Gómez-Forrellad, J. M.; Rojas, J. F.; Pérez-Hoyos, S.; Sanz-Requena, J. F.; Peralta, J.; Ordonez-Etxeberria, I.; Chen-Chen, H.; Mendikoa, I.; Peach, D.; Go, C.; Wesley, A.; Miles, P.; Olivetti, T.

2017-09-01

We present an analysis of Jupiter's atmospheric activity over Juno's first year around the planet based on ground-based observations. We present variability of the zonal winds associated to large outbreaks of convective activity at different belts in the planet, a study of short-scale atmospheric waves at low latitudes and examine polar views of the planet that can be compared with JunoCam observations.

MANGO Imager Network Observations of Geomagnetic Storm Impact on Midlatitude 630 nm Airglow Emissions

NASA Astrophysics Data System (ADS)

Kendall, E. A.; Bhatt, A.

2017-12-01

The Midlatitude Allsky-imaging Network for GeoSpace Observations (MANGO) is a network of imagers filtered at 630 nm spread across the continental United States. MANGO is used to image large-scale airglow and aurora features and observes the generation, propagation, and dissipation of medium and large-scale wave activity in the subauroral, mid and low-latitude thermosphere. This network consists of seven all-sky imagers providing continuous coverage over the United States and extending south into Mexico. This network sees high levels of medium and large scale wave activity due to both neutral and geomagnetic storm forcing. The geomagnetic storm observations largely fall into two categories: Stable Auroral Red (SAR) arcs and Large-scale traveling ionospheric disturbances (LSTIDs). In addition, less-often observed effects include anomalous airglow brightening, bright swirls, and frozen-in traveling structures. We will present an analysis of multiple events observed over four years of MANGO network operation. We will provide both statistics on the cumulative observations and a case study of the "Memorial Day Storm" on May 27, 2017.

Wave-induced boundary-layer separation: A case study comparing airborne observations and results from a mesoscale model

NASA Astrophysics Data System (ADS)

Strauss, L.; Serafin, S.; Grubišić, V.

2012-04-01

Wave-induced boundary-layer separation (BLS) results from the adverse-pressure gradient forces that are exerted on the atmospheric boundary-layer by internal gravity waves in flow over orography. BLS has received significant attention in recent years, particularly so, because it is a key ingredient in the formation of atmospheric rotors. Traditionally depicted as horizontal eddies in the lee of mountain ranges, rotors originate from the interaction between internal gravity waves and the atmospheric boundary-layer. Our study focuses on the first observationally documented case of wave-induced BLS, which occurred on 26 Jan 2006 in the lee of the Medicine Bow Mountains in SE Wyoming (USA). Observations from the University of Wyoming King Air (UWKA) aircraft, in particular, the remote sensing measurements with the Wyoming Cloud Radar (WCR), reveal strong wave activity, downslope winds in excess of 30 m/s, and near-surface flow reversal in the lee of the mountain range. The fine resolution of WCR data (on the order of 40x40 m2 for two-dimensional velocity fields) exhibits fine-scale vortical structures ("subrotors") which are embedded within the main rotor zone. Our case study intends to complete the characterisation of the observed boundary-layer separation event. Modelling of the event with the mesoscale Weather Research and Forecast Model (WRF) provides insight into the mesoscale triggers of wave-induced BLS and turbulence generation. Indeed, the mesoscale model underpins the expected concurrence of the essential processes (gravity waves, wave breaking, downslope windstorms, etc.) leading to BLS. To exploit the recorded in situ and radar data to their full extent, a quantitative evaluation of the structure and intensity of turbulence is conducted by means of a power spectral analysis of the vertical wind component, measured along the flight track. An intercomparison of observational and modelling results serves the purpose of model verification and can shed some more light onto the limits of validity of airborne observations and mesoscale modelling. For example, the exact timing, magnitude, and evolution of the internal gravity waves present in the mesoscale model are carefully analysed. As for the observations, measures of turbulence gained from in situ and radar data, collected over complex topography within a limited period of time, must be interpreted with caution. Approaches to tackling these challenges are a matter of ongoing research and will be discussed in concluding.

Quasi 18 h wave activity in ground-based observed mesospheric H2O over Bern, Switzerland

NASA Astrophysics Data System (ADS)

Lainer, Martin; Hocke, Klemens; Rüfenacht, Rolf; Kämpfer, Niklaus

2017-12-01

Observations of oscillations in the abundance of middle-atmospheric trace gases can provide insight into the dynamics of the middle atmosphere. Long-term, high-temporal-resolution and continuous measurements of dynamical tracers within the strato- and mesosphere are rare but would facilitate better understanding of the impact of atmospheric waves on the middle atmosphere. Here we report on water vapor measurements from the ground-based microwave radiometer MIAWARA (MIddle Atmospheric WAter vapor RAdiometer) located close to Bern during two winter periods of 6 months from October to March. Oscillations with periods between 6 and 30 h are analyzed in the pressure range 0.02-2 hPa. Seven out of 12 months have the highest wave amplitudes between 15 and 21 h periods in the mesosphere above 0.1 hPa. The quasi 18 h wave signature in the water vapor tracer is studied in more detail by analyzing its temporal evolution in the mesosphere up to an altitude of 75 km. Eighteen-hour oscillations in midlatitude zonal wind observations from the microwave Doppler wind radiometer WIRA (WInd RAdiometer) could be identified within the pressure range 0.1-1 hPa during an ARISE (Atmospheric dynamics Research InfraStructure in Europe)-affiliated measurement campaign at the Observatoire de Haute-Provence (355 km from Bern) in France in 2013. The origin of the observed upper-mesospheric quasi 18 h oscillations is uncertain and could not be determined with our available data sets. Possible drivers could be low-frequency inertia-gravity waves or a nonlinear wave-wave interaction between the quasi 2-day wave and the diurnal tide.

Vertical structure and characteristics of 23-60 day (zonal) oscillations over the tropical latitudes during the winter months of 1986 - Results of equatorial wave campaign-II

NASA Technical Reports Server (NTRS)

Raghavarao, R.; Suhasini, R.; Sridharan, R.; Krishnamurthy, B. V.; Nagpal, O. P.

1990-01-01

Results are presented of the equatorial wave campaign-II, a meteorological rocket study which was part of the Indian Middle Atmosphere Program. The equatorial wave campaign-II was conducted from Shar, India (13.7 deg N, 80.2 deg E) from January 15-February 28, 1986. By means of high altitude balloon and the RH-200 meteorological rocket, winds were measured from ground level up to 60 km altitude once each day during the 45-day period. The oscillation frequencies of the deviations in the east-west component of the winds from their mean at each 1-km height interval are obtained by the maximum entropy method. The phases and amplitudes of these frequencies are determined by use of the least squares method on the wind variation time series. Enhanced wave activity is shown to take place in the troposphere and lower mesosphere. The tropospheric waves observed suggest themselves to be Rossby waves of extratropical origin penetrating to tropical latitudes. The observed stratospheric/mesospheric waves appear to emanate from a source around the stratopause.

VLF imaging of the Venus foreshock

NASA Technical Reports Server (NTRS)

Crawford, G. K.; Strangeway, R. J.; Russell, C. T.

1993-01-01

VLF plasma wave measurements obtained from the Pioneer Venus Orbiter Electric Field Detector (OEFD) have been used to construct statistical images of the Venus foreshock. Our data set contains all upstream measurements from an entire Venus year (approximately 200 orbits). Since the foreshock VLF characteristics vary with Interplanetary Magnetic Field (IMF) orientation we restrict the study to IMF orientations near the nominal Parker spiral angle (25 to 45). Our results show a strong decrease in 30 kHz wave intensity with both foreshock depth and distance. There is also an asymmetry in the 30 kHz emissions from the upstream and downstream foreshocks. The ion foreshock is characterized by strong emissions in the 5.4 kHz OEFD channel which are positioned much deeper in the foreshock than expected from terrestrial observations. No activity is observed in the region where field aligned ion distributions are expected. ULF wave activity, while weaker than at Earth, shows similar behavior and may indicate the presence of similar ion distributions.

FLARE-GENERATED SHOCK WAVE PROPAGATION THROUGH SOLAR CORONAL ARCADE LOOPS AND AN ASSOCIATED TYPE II RADIO BURST

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

Kumar, Pankaj; Cho, Kyung-Suk; Innes, D. E., E-mail: pankaj@kasi.re.kr

2016-09-01

This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ∼800 km s{sup −1} and it accelerated to ∼1490 km s{supmore » −1} after passing through the arcade loops. A fan–spine magnetic topology was revealed at the flare site. A small, confined filament eruption (∼340 km s{sup −1}) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan–spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.« less

NmF2 and hmF2 measurements at 95° E and 127° E around the EIA northern crest during 2010-2014

NASA Astrophysics Data System (ADS)

Kalita, Bitap Raj; Bhuyan, Pradip Kumar; Yoshikawa, Akimasa

2015-11-01

The characteristics of the F2 layer parameters NmF2 and hmF2 over Dibrugarh (27.5° N, 95° E, 17° N geomagnetic, 43° dip) measured by a Canadian Advanced Digital Ionosonde (CADI) for the period of August 2010 to July 2014 are reported for the first time from this low mid-latitude station lying within the daytime peak of the longitudinal wave number 4 structure of equatorial anomaly (EIA) around the northern edge of anomaly crest. Equinoctial asymmetry is clearly observed at all solar activity levels whereas the midday winter anomaly is observed only during high solar activity years and disappears during the temporary dip in solar activity in 2013 but forenoon winter anomaly can be observed even at moderate solar activity. The NmF2/hmF2 variations over Dibrugarh are compared with that of Okinawa (26.5° N, 127° E, 17° N geomagnetic), and the eastward propagation speed of the wave number 4 longitudinal structure from 95° E to 127° E is estimated. The speed is found to be close to the theoretical speed of the wave number 4 (WN4) structure. The correlation of daily NmF2 over Dibrugarh and Okinawa with solar activity exhibits diurnal and seasonal variations. The highest correlation in daytime is observed during the forenoon hours in equinox. The correlation of daily NmF2 (linear or non-linear) with solar activity exhibits diurnal variation. A tendency for amplification with solar activity is observed in the forenoon and late evening period of March equinox and the postsunset period of December solstice. NmF2 saturation effect is observed only in the midday period of equinox. Non-linear variation of neutral composition at higher altitudes and variation of recombination rates with solar activity via temperature dependence may be related to the non-linear trend. The noon time maximum NmF2 over Dibrugarh exhibits better correlation with equatorial electrojet (EEJ) than with solar activity and, therefore, new low-latitude NmF2 index is proposed taking both solar activity and EEJ strength into account.

Characterization of Electrocardiogram Changes Throughout a Marathon

PubMed Central

Callaway, Clifton; Salcido, David; McEntire, Serina; Roth, Ronald; Hostler, David

2014-01-01

Purpose There are few data examining cardiovascular physiology throughout a marathon. This study was devised to characterize electrocardiographic activity continuously throughout a marathon. Methods Cardiac activity was recorded from 19 subjects wearing a Holter monitor during a marathon. The 19 subjects (14 men and 5 women) were aged 39 ± 16 years (mean ± SD) and completed a marathon in 4:32:16 ± 1:23:35. Heart rate (HR), heart rate variability (HRV), T-wave amplitude, T-wave amplitude variability, and T-wave alternans (TWA) were evaluated continuously throughout the marathon. Results Averaged across all subjects, HRV, T-wave amplitude variability, and TWA increased throughout the marathon. Increased variability in T-wave amplitude occurred in 86% of subjects, characterized by complex oscillatory patterns and TWA. Three minutes after the marathon, HR was elevated and HRV was suppressed relative to the pre-marathon state. Conclusion HRV and T-wave amplitude variability, especially in the form of TWA, increase throughout a marathon. Increasing TWA as a marathon progresses likely represents a physiologic process as no arrhythmias or cardiac events were observed. PMID:24832192

ULF waves associated with enhanced subauroral proton precipitation

NASA Astrophysics Data System (ADS)

Immel, Thomas J.; Mende, S. B.; Frey, H. U.; Patel, J.; Bonnell, J. W.; Engebretson, M. J.; Fuselier, S. A.

Several types of sub-auroral proton precipitation events have been identified using the Spectrographic Imager (SI) onboard the NASA-IMAGE satellite, including dayside subauroral proton flashes and detached proton arcs in the dusk sector. These have been observed at various levels of geomagnetic activity and solar wind conditions and the mechanism driving the precipitation has often been assumed to be scattering of protons into the loss cone by enhancement of ion-cyclotron waves in the interaction of the thermal plasmaspheric populations and more energetic ring current particles. Indeed, recent investigation of the detached arcs using the MPA instruments aboard the LANL geosynchronous satellites has shown there are nearly always heightened densities of cold plasma on high-altitude field lines which map down directly to the sub-auroral precipitation. If the ion-cyclotron instability is a causative mechanism, the enhancement of wave activity at ion-cyclotron frequencies should be measurable. It is here reported that magnetic pulsations in the Pc1 range occur in the vicinity of each of 4 detached arcs observed in 2000-2002, though with widely varying signatures. Additionally, longer period pulsations in the Pc5 ranges are also observed in the vicinity of the arcs, leading to the conclusion that a bounce-resonance of ring-current protons with the azimuthal Pc5 wave structure may also contribute to the detached precipitation.

Upstream proton cyclotron waves at Venus near solar maximum

NASA Astrophysics Data System (ADS)

Delva, M.; Bertucci, C.; Volwerk, M.; Lundin, R.; Mazelle, C.; Romanelli, N.

2015-01-01

magnetometer data of Venus Express are analyzed for the occurrence of waves at the proton cyclotron frequency in the spacecraft frame in the upstream region of Venus, for conditions of rising solar activity. The data of two Venus years up to the time of highest sunspot number so far (1 Mar 2011 to 31 May 2012) are studied to reveal the properties of the waves and the interplanetary magnetic field (IMF) conditions under which they are observed. In general, waves generated by newborn protons from exospheric hydrogen are observed under quasi- (anti)parallel conditions of the IMF and the solar wind velocity, as is expected from theoretical models. The present study near solar maximum finds significantly more waves than a previous study for solar minimum, with an asymmetry in the wave occurrence, i.e., mainly under antiparallel conditions. The plasma data from the Analyzer of Space Plasmas and Energetic Atoms instrument aboard Venus Express enable analysis of the background solar wind conditions. The prevalence of waves for IMF in direction toward the Sun is related to the stronger southward tilt of the heliospheric current sheet for the rising phase of Solar Cycle 24, i.e., the "bashful ballerina" is responsible for asymmetric background solar wind conditions. The increase of the number of wave occurrences may be explained by a significant increase in the relative density of planetary protons with respect to the solar wind background. An exceptionally low solar wind proton density is observed during the rising phase of Solar Cycle 24. At the same time, higher EUV increases the ionization in the Venus exosphere, resulting in higher supply of energy from a higher number of newborn protons to the wave. We conclude that in addition to quasi- (anti)parallel conditions of the IMF and the solar wind velocity direction, the higher relative density of Venus exospheric protons with respect to the background solar wind proton density is the key parameter for the higher number of observable proton cyclotron waves near solar maximum.

Solar Terminator Waves in the Ionosphere Measured by the Wallops Island, VA Dynasonde

NASA Astrophysics Data System (ADS)

Zabotin, N. A.; Song, H.; Bullett, T. W.

2017-12-01

Solar terminator represents a unique source of atmospheric waves possessing of near-ideal coherent properties: its geometry and magnitude of the impact changes very little from day to day. This feature has been used in [Forbes et al., GRL, 2008] to obtain "snapshots" of terminator waves in the neutral atmosphere at the altitude 400 km by averaging CHAMP accelerometer data over relatively long sequences of the satellite passes. The results were represented in the geographic latitude vs local time coordinates. We apply a similar approach averaging time series of Wallops Island, VA Dynasonde Doppler data to obtain "snapshots" of terminator waves in the ionosphere in the true altitude vs local "terminator time" coordinates. The averaging is performed independently for every month of the yearlong observation period from May 2013 to April 2014. The altitude range covered is 90 km to 400 km with 2 km resolution, representing the entire bottom-side ionosphere. Individual local time segments used for the averaging were 12 hours long and all centered at the times of the sunrise or sunset terminator passing at every specific altitude. This procedure effectively suppresses all kinds of incoherent wave activity and allows one to reveal the perturbation phenomenon mainly caused by the solar terminator. This is an important advantage of this technique compared to multiple "terminator wave" studies based on simple time coincidence. Both sunrise and sunset terminator waves are easily visualized in all of the monthly images. Our results confirm observations of [Forbes et al., GRL, 2008] of the wave structures existing on both sides of the terminator. The phase fronts of the sunset terminator wave are propagating downward indicating upward movement of the terminator-related disturbance and of the wave energy generated by it. The phase fronts of the sunrise terminator waves are propagating upward indicating downward movement of the terminator-related disturbance and of the wave energy generated by it. Spectral analysis of the local time sequences reveals characteristic peaks in the terminator-related wave activity corresponding to the periods 40-60 min and 2 hours. We also analyze statistics of their horizontal wavelengths.

The role of spring precipitation deficits on European and North American summer heat wave activity

NASA Astrophysics Data System (ADS)

Cowan, Tim; Hegerl, Gabi

2017-04-01

Heat waves are relatively short-term climate phenomena with potentially severe societal impacts, particularly on health, agriculture and the natural environment. In water-limited regions, increased heat wave activity over intra-decadal periods is often associated with protracted droughts, as observed over North America's Central and Southern Great Plains in the 1930s and 1950s, highlighting the importance of land surface-atmosphere feedbacks. Here we present an analysis of the covariability of spring precipitation deficit and summer heat waves for North America and Europe, the latter having experienced an increase in summer heat wave frequency since the 1950s (Perkins et al. 2012). Over the Great Plains summer heat waves are significantly earlier, longer and hotter if following dry rather than wet springs, with the mega-heat waves of the 1930s Dust Bowl decade an extreme example (e.g. Cowan et al. 2017). Similar relationships can be found in some parts of Europe for heat wave frequency and duration, namely Southern and Eastern Europe, although the heat wave timing and amplitude (i.e. the hottest events) appear less sensitive to spring drying. Climate model results investigating the relationship between heat waves and precipitation deficit in regions in Europe and North America will also be presented. It is necessary to pinpoint the causes of large decadal variations in heat wave metrics, as seen in the 1930s over North America and more recently across Central Europe, for event attribution purposes and to improve near-decadal prediction. The tight link between spring drought and summer heat waves will also be important for understanding the impacts of these climatic events and supports the development of compound event analysis techniques. References: Cowan, T., G. Hegerl, I. Colfescu, A. Purich and G. Boshcat (2016), Factors contributing to record-breaking heat waves over the Great Plains during the 1930s Dust Bowl. Journal of Climate, doi: 10.1175/JCLI-D-16-0436.1 (in press). Perkins, S. E., L. V. Alexander, and J. R. Nairn (2012), Increasing frequency, intensity and duration of observed global heatwaves and warm spells, Geophys. Res. Lett., 39, L20714, doi:10.1029/2012GL053361.

The Waves to Weather Challenge: Do Large-Scale Equatorial Waves Modulate Regional Rainfall in Southern Vietnam?

NASA Astrophysics Data System (ADS)

Fink, A. H.; van der Linden, R.; Phan-Van, T.; Pinto, J. G.

2014-12-01

About 85% of the annual precipitation in southern Vietnam (ca. 8-12°N, 104-110°E) occurs during the southwest monsoon season (June to October). Large-scale equatorial waves like the Madden-Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEWs) are known to modulate the large-scale convective activity, often indicated by variations in (filtered) satellite-observed outgoing longwave radiation (OLR) anomalies. The present contribution analyses and quantifies the role of the MJO and CCEWs for rainfall not only in southern and central Vietnam as a whole, but also for smaller climatological sub-regions. Using circum-equatorial NOAA OLR (15°S-15°N), prominent spectral peaks are identified in wavenumber-frequency diagrams along the dispersion curves for the solutions of the shallow water equations. They are interpreted as CCEWs. Meridionally averaged wave-filtered OLR and its time derivatives are used to define phases and amplitudes of CCEWs. This will allow determining active and inactive phases of CCEWs in the vicinity of Vietnam. Eastward propagating deep convection is also related to the 30-90-day MJO. The OLR MJO Index (OMI) is used for the definition of convectively active and inactive phases of the MJO. TRMM 3B42 V7, APHRODITE MA V1101 data, and rain gauge measurements are used to investigate the relation between tropical wave phases and amplitudes and precipitation in southern and central Vietnam and adjacent regions. Results using the OMI are compared with those using the Real-time Multivariate MJO (RMM) Index. The major findings are: (a) Precipitation amounts in southern Vietnam are higher during convectively active phases of the MJO and CCEWs. The waves differ in terms of their relative importance for rainfall enhancement. (b) For increasing CCEW amplitudes, the difference between area-averaged precipitation during inactive and active phases increases. We provide evidence that precipitation amounts are higher when multiple wave types are in their convectively active phases over the Vietnam region.

Modulation of Gravity Waves by Tides as Seen in CRISTA Temperatures

NASA Technical Reports Server (NTRS)

Preusse, P.; Eckermann, S. D.; Oberheide, J.; Hagan, M. E.; Offermann, D.

2001-01-01

During shuttle missions STS-66 (November, 1994) and STS-85 (August, 1997) the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) acquired temperature data with very high spatial resolution. These are analyzed for gravity waves (GW). The altitude range spans the whole middle atmosphere from the tropopause up to the mesopause. In the upper mesosphere tidal amplitudes exceed values of 10 K. Modulation of GW activity by the tides is observed and analyzed using CRISTA temperatures and tidal predictions of the Global Scale Wave Model (GSWM). The modulation process is identified as a tidally-induced change of the background buoyancy frequency. The findings agree well with the expectations for saturated GW and are the first global scale observations of this process.

Biomechanics of stair walking and jumping.

PubMed

Loy, D J; Voloshin, A S

1991-01-01

Physical activities such as stair walking and jumping result in increased dynamic loading on the human musculoskeletal system. Use of light weight, externally attached accelerometers allows for in-vivo monitoring of the shock waves invading the human musculoskeletal system during those activities. Shock waves were measured in four subjects performing stair walking up and down, jumping in place and jumping off a fixed elevation. The results obtained show that walking down a staircase induced shock waves with amplitude of 130% of that observed in walking up stairs and 250% of the shock waves experienced in level gait. The jumping test revealed levels of the shock waves nearly eight times higher than that in level walking. It was also shown that the shock waves invading the human musculoskeletal system may be generated not only by the heel strike, but also by the metatarsal strike. To moderate the risk of degenerative joint disorders four types of viscoelastic insoles were utilized to reduce the impact generated shock waves. The insoles investigated were able to reduce the amplitude of the shock wave by between 9% and 41% depending on the insole type and particular physical activity. The insoles were more effective in the reduction of the heel strike impacts than in the reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping trials than in the stair walking studies. The insoles were ranked in three groups on the basis of their shock absorbing capacity.

EMIC waves and associated relativistic electron precipitation on 25-26 January 2013

DOE PAGES

Zhang, Jichun; Halford, Alexa J.; Saikin, Anthony A.; ...

2016-10-28

Using measurements from the Van Allen Probes and the Balloon Array for RBSP Relativistic Electron Losses (BARREL), we perform a case study of electromagnetic ion cyclotron (EMIC) waves and associated relativistic electron precipitation (REP) observed on 25–26 January 2013. Among all the EMIC wave and REP events from the two missions, the pair of the events is the closest both in space and time. The Van Allen Probe-B detected significant EMIC waves at L = 2.1–3.9 and magnetic local time (MLT) = 21.0–23.4 for 53.5 min from 2353:00 UT, 25 January 2013. Meanwhile, BARREL-1T observed clear precipitation of relativistic electronsmore » at L = 4.2–4.3 and MLT = 20.7–20.8 for 10.0 min from 2358 UT, 25 January 2013. Local plasma and field conditions for the excitation of the EMIC waves, wave properties, electron minimum resonant energy E min, and electron pitch angle diffusion coefficient D αα of a sample EMIC wave packet are examined along with solar wind plasma and interplanetary magnetic field parameters, geomagnetic activity, and results from the spectral analysis of the BARREL balloon observations to investigate the two types of events. The events occurred in the early main phase of a moderate storm (min. Dst* = -51.0 nT). The EMIC wave event consists of two parts. Finally, unlike the first part, the second part of the EMIC wave event was locally generated and still in its source region. It is found that the REP event is likely associated with the EMIC wave event.« less

A Finite-Difference Time-Domain Model of Artificial Ionospheric Modification

NASA Astrophysics Data System (ADS)

Cannon, Patrick; Honary, Farideh; Borisov, Nikolay

Experiments in the artificial modification of the ionosphere via a radio frequency pump wave have observed a wide range of non-linear phenomena near the reflection height of an O-mode wave. These effects exhibit a strong aspect-angle dependence thought to be associated with the process by which, for a narrow range of off-vertical launch angles, the O-mode pump wave can propagate beyond the standard reflection height at X=1 as a Z-mode wave and excite additional plasma activity. A numerical model based on Finite-Difference Time-Domain method has been developed to simulate the interaction of the pump wave with an ionospheric plasma and investigate different non-linear processes involved in modification experiments. The effects on wave propagation due to plasma inhomogeneity and anisotropy are introduced through coupling of the Lorentz equation of motion for electrons and ions to Maxwell’s wave equations in the FDTD formulation, leading to a model that is capable of exciting a variety of plasma waves including Langmuir and upper-hybrid waves. Additionally, discretized equations describing the time-dependent evolution of the plasma fluid temperature and density are included in the FDTD update scheme. This model is used to calculate the aspect angle dependence and angular size of the radio window for which Z-mode excitation occurs, and the results compared favourably with both theoretical predictions and experimental observations. The simulation results are found to reproduce the angular dependence on electron density and temperature enhancement observed experimentally. The model is used to investigate the effect of different initial plasma density conditions on the evolution of non-linear effects, and demonstrates that the inclusion of features such as small field-aligned density perturbations can have a significant influence on wave propagation and the magnitude of temperature and density enhancements.

EMIC waves and associated relativistic electron precipitation on 25-26 January 2013

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

Zhang, Jichun; Halford, Alexa J.; Saikin, Anthony A.

Using measurements from the Van Allen Probes and the Balloon Array for RBSP Relativistic Electron Losses (BARREL), we perform a case study of electromagnetic ion cyclotron (EMIC) waves and associated relativistic electron precipitation (REP) observed on 25–26 January 2013. Among all the EMIC wave and REP events from the two missions, the pair of the events is the closest both in space and time. The Van Allen Probe-B detected significant EMIC waves at L = 2.1–3.9 and magnetic local time (MLT) = 21.0–23.4 for 53.5 min from 2353:00 UT, 25 January 2013. Meanwhile, BARREL-1T observed clear precipitation of relativistic electronsmore » at L = 4.2–4.3 and MLT = 20.7–20.8 for 10.0 min from 2358 UT, 25 January 2013. Local plasma and field conditions for the excitation of the EMIC waves, wave properties, electron minimum resonant energy E min, and electron pitch angle diffusion coefficient D αα of a sample EMIC wave packet are examined along with solar wind plasma and interplanetary magnetic field parameters, geomagnetic activity, and results from the spectral analysis of the BARREL balloon observations to investigate the two types of events. The events occurred in the early main phase of a moderate storm (min. Dst* = -51.0 nT). The EMIC wave event consists of two parts. Finally, unlike the first part, the second part of the EMIC wave event was locally generated and still in its source region. It is found that the REP event is likely associated with the EMIC wave event.« less

Laboratory model of the cardiovascular system for experimental demonstration of pulse wave propagation

NASA Astrophysics Data System (ADS)

Stojadinović, Bojana; Nestorović, Zorica; Djurić, Biljana; Tenne, Tamar; Zikich, Dragoslav; Žikić, Dejan

2017-03-01

The velocity by which a disturbance moves through the medium is the wave velocity. Pulse wave velocity is among the key parameters in hemodynamics. Investigation of wave propagation through the fluid-filled elastic tube has a great importance for the proper biophysical understanding of the nature of blood flow through the cardiovascular system. Here, we present a laboratory model of the cardiovascular system. We have designed an experimental setup which can help medical and nursing students to properly learn and understand basic fluid hemodynamic principles, pulse wave and the phenomenon of wave propagation in blood vessels. Demonstration of wave propagation allowed a real time observation of the formation of compression and expansion waves by students, thus enabling them to better understand the difference between the two waves, and also to measure the pulse wave velocity for different fluid viscosities. The laboratory model of the cardiovascular system could be useful as an active learning methodology and a complementary tool for understanding basic principles of hemodynamics.

Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E) during major stratospheric warming in 2006

NASA Astrophysics Data System (ADS)

Sridharan, S.; Sathishkumar, S.; Raghunath, K.

2009-01-01

Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E) during January-February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office) zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending) motions at high (low) latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

Analysis of southwest propagating TIDs in the western United States

NASA Astrophysics Data System (ADS)

Kendall, E. A.; Bhatt, A.

2016-12-01

The MANGO network of 630 nm all-sky imagers in the continental United States has observed a number of westward propagating traveling ionospheric disturbances (TIDs). These TIDs include southwestward waves typically associated with Perkins electrodynamic instability, and also northwestward waves of unknown cause. A peak in the wave activity was observed during the summer of 2016 in the western US. Many of the observed structures evolve during their passage through the camera field of view. The southwestward propagating TIDs observed over California are often tilted westward or slightly northward, which may be a function of magnetic field declination. We will present analysis of MANGO network data along with GPS TEC data. This analysis will include shapes and sizes of the observed structures along with their velocities. We will present results from geomagnetic, seasonal and local time variations associated with observed TIDs. Wherever possible, we will include data from the broader MANGO network that is now taking data over the continental United States and compare with data from Boston University imagers in Massachusetts and Texas.

Radio Follow-Up of Gravitational-Wave Triggers during Advanced LIGO 01

DOE PAGES

Palliyaguru, N. T.; Corsi, Alessandra; Kasliwal, M. M.; ...

2016-09-28

We present radio follow-up observations carried out with the Karl G. Jansky Very Large Array during the first observing run (O1) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). A total of three gravitational-wave triggers were followed-up during the ≈4 months of O1, from 2015 September to 2016 January. Two of these triggers, GW150914 and GW151226, are binary black hole (BH) merger events of high significance. A third trigger, G194575, was subsequently declared as an event of no interest (i.e., a false alarm). Our observations targeted selected optical transients identified by the intermediate Palomar Transient Factory in the Advanced LIGOmore » error regions of the three triggers, and a limited region of the gravitational-wave localization area of G194575 not accessible to optical telescopes due to Sun constraints, where a possible high-energy transient was identified. No plausible radio counterparts to GW150914 and GW151226 were found, in agreement with expectations for binary BH mergers. We show that combining optical and radio observations is key to identifying contaminating radio sources that may be found in the follow-up of gravitational-wave triggers, such as emission associated with star formation and active galactic nuclei. We discuss our results in the context of the theoretical predictions for radio counterparts to gravitational-wave transients, and describe our future plans for the radio follow-up of Advanced LIGO (and Virgo) triggers.« less

Electric Current Activated Combustion Synthesis and Chemical Ovens Under Terrestrial and Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Fredrick, D.; Anselmi-Tamburini, U.; Manerbino, A.; Guigne, J. Y.; Munir, Z. A.; Shaw, B. D.

2004-01-01

Combustion synthesis (CS) generally involves mixing reactants together (e.g., metal powders) and igniting the mixture. Typically, a reaction wave will pass through the sample. In field activated combustion synthesis (FACS), the addition of an electric field has a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product as well as capillary flow, mass-transport in porous media, and Marangoni flows, which are influenced by gravity. The objective is to understand the role of an electric field in CS reactions under conditions where gravity-related effects are suppressed or altered. The systems being studied are Ti+Al and Ti+3Al. Two different ignition orientations have been used to observe effects of gravity when one of the reactants becomes molten. This consequentially influences the position and concentration of the electric current, which in turn influences the entire process. Experiments have also been performed in microgravity conditions. This process has been named Microgravity Field Activated Combustion Synthesis (MFACS). Effects of gravity have been demonstrated, where the reaction wave temperature and velocity demonstrate considerable differences besides the changes of combustion mechanisms with the different high currents applied. Also the threshold for the formation of a stable reaction wave is increased under zero gravity conditions. Electric current was also utilized with a chemical oven technique, where inserts of aluminum with minute amounts of tungsten and tantalum were used to allow observation of effects of settling of the higher density solid particles in liquid aluminum at the present temperature profile and wave velocity of the reaction.

Activity-induced instability of phonons in 1D microfluidic crystals.

PubMed

Tsang, Alan Cheng Hou; Shelley, Michael J; Kanso, Eva

2018-02-14

One-dimensional crystals of passively-driven particles in microfluidic channels exhibit collective vibrational modes reminiscent of acoustic 'phonons'. These phonons are induced by the long-range hydrodynamic interactions among the particles and are neutrally stable at the linear level. Here, we analyze the effect of particle activity - self-propulsion - on the emergence and stability of these phonons. We show that the direction of wave propagation in active crystals is sensitive to the intensity of the background flow. We also show that activity couples, at the linear level, transverse waves to the particles' rotational motion, inducing a new mode of instability that persists in the limit of large background flow, or, equivalently, vanishingly small activity. We then report a new phenomenon of phonons switching back and forth between two adjacent crystals in both passively-driven and active systems, similar in nature to the wave switching observed in quantum mechanics, optical communication, and density stratified fluids. These findings could have implications for the design of commercial microfluidic systems and the self-assembly of passive and active micro-particles into one-dimensional structures.

Multi-instrument gravity-wave measurements over Tierra del Fuego and the Drake Passage - Part 1: Potential energies and vertical wavelengths from AIRS, COSMIC, HIRDLS, MLS-Aura, SAAMER, SABER and radiosondes

NASA Astrophysics Data System (ADS)

Wright, Corwin J.; Hindley, Neil P.; Moss, Andrew C.; Mitchell, Nicholas J.

2016-03-01

Gravity waves in the terrestrial atmosphere are a vital geophysical process, acting to transport energy and momentum on a wide range of scales and to couple the various atmospheric layers. Despite the importance of these waves, the many studies to date have often exhibited very dissimilar results, and it remains unclear whether these differences are primarily instrumental or methodological. Here, we address this problem by comparing observations made by a diverse range of the most widely used gravity-wave-resolving instruments in a common geographic region around the southern Andes and Drake Passage, an area known to exhibit strong wave activity. Specifically, we use data from three limb-sounding radiometers (Microwave Limb Sounder, MLS-Aura; HIgh Resolution Dynamics Limb Sounder, HIRDLS; Sounding of the Atmosphere using Broadband Emission Radiometry, SABER), the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS-RO constellation, a ground-based meteor radar, the Advanced Infrared Sounder (AIRS) infrared nadir sounder and radiosondes to examine the gravity wave potential energy (GWPE) and vertical wavelengths (λz) of individual gravity-wave packets from the lower troposphere to the edge of the lower thermosphere ( ˜ 100 km). Our results show important similarities and differences. Limb sounder measurements show high intercorrelation, typically > 0.80 between any instrument pair. Meteor radar observations agree in form with the limb sounders, despite vast technical differences. AIRS and radiosonde observations tend to be uncorrelated or anticorrelated with the other data sets, suggesting very different behaviour of the wave field in the different spectral regimes accessed by each instrument. Evidence of wave dissipation is seen, and varies strongly with season. Observed GWPE for individual wave packets exhibits a log-normal distribution, with short-timescale intermittency dominating over a well-repeated monthly-median seasonal cycle. GWPE and λz exhibit strong correlations with the stratospheric winds, but not with local surface winds. Our results provide guidance for interpretation and intercomparison of such data sets in their full context.

Morphobathymetric analysis of the large fine-grained sediment waves over the Gulf of Valencia continental slope (NW Mediterranean)

NASA Astrophysics Data System (ADS)

Ribó, Marta; Puig, Pere; Muñoz, Araceli; Lo Iacono, Claudio; Masqué, Pere; Palanques, Albert; Acosta, Juan; Guillén, Jorge; Gómez Ballesteros, María

2016-01-01

Detailed analysis of recently acquired swath bathymetry, together with high-resolution seismic profiles and bottom sediment samples, revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. As many other deep-water sediment waves, these features were previously attributed to gravitational slope failure, related to creep-like deformation, and are here reinterpreted as sediment wave fields extending from 250 m depth to the continental rise, at 850 m depth. Geometric parameters were computed from the high-resolution multibeam dataset. Sediment wave lengths range between 500 and 1000 m, and maximum wave heights of up to 50 m are found on the upper slope, decreasing downslope to minimum values of 2 m high. Sediment waves on the lower part of the slope are quasi-stationary vertically accreting, whereas they show an upslope migrating pattern from the mid-slope to the upper part of the continental slope. High-resolution seismic profiles show continuous internal reflectors, with sediment waves merging down-section and sediment wave packages decreasing in thickness downslope. These sediment packages are thicker on the crest of each individual sediment wave and thinner on the downslope flank. 210Pb analyses conducted on sediment cores collected over the sediment wave fields also indicate slightly higher sediment accumulation rates on the wave crests. Sediment wave formation processes have been inferred from contemporary hydrodynamic observations, which reveal the presence of near-inertial internal waves interacting with the Gulf of Valencia continental slope. Internal wave activity is suggested to be the preferential mechanism for the transport and deposition of sediment, and the maintenance of the observed sediment wave fields.

The shallow elastic structure of the lunar crust: New insights from seismic wavefield gradient analysis

NASA Astrophysics Data System (ADS)

Sollberger, David; Schmelzbach, Cedric; Robertsson, Johan O. A.; Greenhalgh, Stewart A.; Nakamura, Yosio; Khan, Amir

2016-10-01

Enigmatic lunar seismograms recorded during the Apollo 17 mission in 1972 have so far precluded the identification of shear-wave arrivals and hence the construction of a comprehensive elastic model of the shallow lunar subsurface. Here, for the first time, we extract shear-wave information from the Apollo active seismic data using a novel waveform analysis technique based on spatial seismic wavefield gradients. The star-like recording geometry of the active seismic experiment lends itself surprisingly well to compute spatial wavefield gradients and rotational ground motion as a function of time. These observables, which are new to seismic exploration in general, allowed us to identify shear waves in the complex lunar seismograms, and to derive a new model of seismic compressional and shear-wave velocities in the shallow lunar crust, critical to understand its lithology and constitution, and its impact on other geophysical investigations of the Moon's deep interior.

Nonthermal ions and associated magnetic field behavior at a quasi-parallel earth's bow shock

NASA Technical Reports Server (NTRS)

Wilkinson, W. P.; Pardaens, A. K.; Schwartz, S. J.; Burgess, D.; Luehr, H.; Kessel, R. L.; Dunlop, M.; Farrugia, C. J.

1993-01-01

Attention is given to ion and magnetic field measurements at the earth's bow shock from the AMPTE-UKS and -IRM spacecraft, which were examined in high time resolution during a 45-min interval when the field remained closely aligned with the model bow shock normal. Dense ion beams were detected almost exclusively in the midst of short-duration periods of turbulent magnetic field wave activity. Many examples of propagation at large elevation angles relative to the ecliptic plane, which is inconsistent with reflection in the standard model shock configuration, were discovered. The associated waves are elliptically polarized and are preferentially left-handed in the observer's frame of reference, but are less confined to the maximum variance plane than other previously studied foreshock waves. The association of the wave activity with the ion beams suggests that the former may be triggered by an ion-driven instability, and possible candidates are discussed.

Long wavelength vertical cavity surface emitting laser

DOEpatents

Choquette, Kent D.; Klem, John F.

2005-08-16

Selectively oxidized vertical cavity lasers emitting near 1300 nm using InGaAsN quantum wells are reported for the first time which operate continuous wave below, at and above room temperature. The lasers employ two n-type Al.sub.0.94 Ga.sub.0.06 As/GaAs distributed Bragg reflectors each with a selectively oxidized current aperture adjacent to the active region, and the top output mirror contains a tunnel junction to inject holes into the active region. Continuous wave single mode lasing is observed up to 55.degree. C.

Quasi-biennial variation of equatorial waves as seen in satellite remote sensing data

NASA Astrophysics Data System (ADS)

Chen, Zeyu

The quasi-biennial oscillation (QBO) in zonal winds in the lower stratosphere at the Equator is the most prominent inter-annual variation signal in the middle atmosphere. Theoretically, it is driven by the drag from the damping of equatorial waves including the equatorially trapped planetary scale waves, such as Kelvin waves propagating eastward and Rossby-gravity waves propagating westward, inertio-gravity waves and gravity waves. In current research, the tem-perature data collected by the SABER/TIMED mission in 2002-2009 are used to investigate the equatorial waves activities. The Fast Fourier Synoptic Mapping (FFSM) method is applied to delineate planetary wave components with the zonal wavenumber spanning over -6 to +6, hereby, positive (negative) wavenumber is assigned to westward (eastward) propagating waves. Limited by the SABER/TIMED sampling scheme, only the waves with periods longer than one day can be resolved. Focusing on the height region 70-10 hPa where the QBO signal is most significant, it is clearly observed that the composite activity of all the eastward waves exhibit QBO like variation. Specifically, for each QBO cycle, the activity at 50 hPa level is characterized by the occurrence of a substantially clear minimum that coincides to the fast downward propagation of the westerly phase, the typical pattern of the QBO phenomenon. Phase speed spectra are derived by using the FFSM analysis results. And vertical shear of the zonal wind is derived by using the rawinsonde data at Singapore. Comparison of the phase speed spectra and the wind shear indicates that the minimum is due to the westerly shear below 30 hPa. Between the minimum, significant wave activities emerge, thus the property for the components are investigated. Results show that in height range 70-10 hPa, both wave 1 to wave 3 are prominent during the inter-minimum period for each QBO cycle. At 50 hPa level, wave 1 component exhibits amplitude spectral peak at three kinds of period, 8, 11 and 20 day. Meanwhile, shifting to shorter period is seen as wave number increases, for example, the 20-day period spectrum is attenuated substantially for wave 2 and wave 3 components. Moreover, results also show that although with small amplitude, wave 4 and wave 5 with shorter periods of 4-7 days are discernable in particular in the inter-minimum period. Further details will be presented in the talk.

Electroencephalographic slow waves prior to sleepwalking episodes.

PubMed

Perrault, Rosemarie; Carrier, Julie; Desautels, Alex; Montplaisir, Jacques; Zadra, Antonio

2014-12-01

Recent studies have suggested that the onset of sleepwalking episodes may be preceded by fluctuations in slow-wave sleep electroencephalographic characteristics. However, whether or not such fluctuations are specific to sleepwalking episodes or generalized to all sleep-wake transitions in sleepwalkers remains unknown. The goal of this study was to compare spectral power for delta (1-4 Hz) and slow delta (0.5-1 Hz) as well as slow oscillation density before the onset of somnambulistic episodes versus non-behavioral awakenings recorded from the same group of sleepwalkers. A secondary aim was to describe the time course of observed changes in slow-wave activity and slow oscillations during the 3 min immediately preceding the occurrence of somnambulistic episodes. Twelve adult sleepwalkers were investigated polysomnographically during the course of one night. Slow-wave activity and slow oscillation density were significantly greater prior to patients' somnambulistic episodes as compared with non-behavioral awakenings. However, there was no evidence for a gradual increase over the 3 min preceding the episodes. Increased slow-wave activity and slow oscillation density appear to be specific to sleepwalking episodes rather than generalized to all sleep-wake transitions in sleepwalkers. Copyright © 2014 Elsevier B.V. All rights reserved.

Respiratory modulation of sympathetic nerve activity is enhanced in male rat offspring following uteroplacental insufficiency.

PubMed

Menuet, C; Wlodek, M E; Fong, A Y; Allen, A M

2016-06-01

Sympathetic nerve activity to the cardiovascular system displays prominent respiratory-related modulation which leads to the generation of rhythmic oscillations in blood pressure called Traube-Hering waves. An amplification of this respiratory modulation of sympathetic activity is observed in hypertension of both genetic, the spontaneously hypertensive rat, and induced, chronic intermittent hypoxia or maternal protein restriction during gestation, origin. Male offspring of mothers with uteroplacental insufficiency, induced by bilateral uterine vessel ligation at 18 days of gestation, are also hypertensive in adulthood. In this study we examined whether these male offspring display altered respiratory modulation of sympathetic activity at pre-hypertensive ages compared to controls. Respiratory, cardiovascular and sympathetic parameters were examined using the working heart-brainstem preparation in 35 day old male rats that had reduced birth weight due to uteroplacental insufficiency. Whilst all respiratory parameters were not different between groups, we observed an enhanced respiratory-related burst of thoracic sympathetic nerve activity and amplified Traube-Hering waves in the growth-restricted group. This group also showed an increased sympathetic and bradycardic response to activation of peripheral chemoreceptors. The observations add support to the view that altered respiratory modulation of sympathetic activity represents a common mechanism involved in the development of several forms of hypertension. Copyright © 2015 Elsevier B.V. All rights reserved.

First Vlasiator results on foreshock ULF wave activity

NASA Astrophysics Data System (ADS)

Palmroth, M.; Eastwood, J. P.; Pokhotelov, D.; Hietala, H.; Kempf, Y.; Hoilijoki, S.; von Alfthan, S.; Vainio, R. O.

2013-12-01

For decades, a certain type of ultra low frequency waves with a period of about 30 seconds have been observed in the Earth's quasi-parallel foreshock. These waves, with a wavelength of about an Earth radius, are compressive and propagate obliquely with respect to the interplanetary magnetic field (IMF). The latter property has caused trouble to scientists as the growth rate for the instability causing the waves is maximized along the magnetic field. So far, these waves have been characterized by single or multi-spacecraft methods and 2-dimensional hybrid-PIC simulations, which have not fully reproduced the wave properties. Vlasiator is a newly developed, global hybrid-Vlasov simulation, which solves ions in the six-dimensional phase space using the Vlasov equation and electrons using magnetohydrodynamics (MHD). The outcome of the simulation is a global reproduction of ion-scale physics in a holistic manner where the generation of physical features can be followed in time and their consequences can be quantitatively characterized. Vlasiator produces the ion distribution functions and the related kinetic physics in unprecedented detail, in the global magnetospheric scale presently with a resolution of 0.13 RE in the ordinary space and 20 km/s in the velocity space. We run two simulations, where we use both a typical Parker-spiral and a radial IMF as an input to the code. The runs are carried out in the ecliptic 2-dimensional plane in the ordinary space, and with three dimensions in the velocity space. We observe the generation of the 30-second ULF waves, and characterize their evolution and physical properties in time, comparing to observations by Cluster spacecraft. We find that Vlasiator reproduces these waves in all reported observational aspects, i.e., they are of the observed size in wavelength and period, they are compressive and propagate obliquely to the IMF. In particular, we investigate the oblique propagation and discuss the issues related to the long-standing question of oblique propagation.

Eruption of a plasma blob, associated M-class flare, and large-scale extreme-ultraviolet wave observed by SDO

NASA Astrophysics Data System (ADS)

Kumar, P.; Manoharan, P. K.

2013-05-01

We present a multiwavelength study of the formation and ejection of a plasma blob and associated extreme ultraviolet (EUV) waves in active region (AR) NOAA 11176, observed by SDO/AIA and STEREO on 25 March 2011. The EUV images observed with the AIA instrument clearly show the formation and ejection of a plasma blob from the lower atmosphere of the Sun at ~9 min prior to the onset of the M1.0 flare. This onset of the M-class flare happened at the site of the blob formation, while the blob was rising in a parabolic path with an average speed of ~300 km s. The blob also showed twisting and de-twisting motion in the lower corona, and the blob speed varied from ~10-540 km s. The faster and slower EUV wavefronts were observed in front of the plasma blob during its impulsive acceleration phase. The faster EUV wave propagated with a speed of ~785 to 1020 km s, whereas the slower wavefront speed varied in between ~245 and 465 km s. The timing and speed of the faster wave match the shock speed estimated from the drift rate of the associated type II radio burst. The faster wave experiences a reflection by the nearby AR NOAA 11177. In addition, secondary waves were observed (only in the 171 Å channel), when the primary fast wave and plasma blob impacted the funnel-shaped coronal loops. The Helioseismic Magnetic Imager (HMI) magnetograms revealed the continuous emergence of new magnetic flux along with shear flows at the site of the blob formation. It is inferred that the emergence of twisted magnetic fields in the form of arch-filaments/"anemone-type" loops is the likely cause for the plasma blob formation and associated eruption along with the triggering of M-class flare. Furthermore, the faster EUV wave formed ahead of the blob shows the signature of fast-mode MHD wave, whereas the slower wave seems to be generated by the field line compression by the plasma blob. The secondary wave trains originated from the funnel-shaped loops are probably the fast magnetoacoustic waves. Three movies are available in electronic form at http://www.aanda.org

Investigation of mesoscale trace gas distributions across an Arctic tropopause fold affected by gravity wave activity

NASA Astrophysics Data System (ADS)

Woiwode, Wolfgang; Oelhaf, Hermann; Dörnbrack, Andreas; Bramberger, Martina; Diekmann, Christopher; Friedl-Vallon, Felix; Höpfner, Michael; Hoor, Peter; Johansson, Sören; Krause, Jens; Kunkel, Daniel; Orphal, Johannes; Preusse, Peter; Ruhnke, Roland; Schlage, Romy; Schröter, Jennifer; Sinnhuber, Björn-Martin; Ungermann, Jörn; Zahn, Andreas

2017-04-01

Tropopause folds are known of enabling efficient exchange of trace constituents between the stratosphere and troposphere. In particular, the modification of the vertical distributions of radiatively important H2O and other reactive trace gases associated with tropopause folds is relevant for accurate model simulations of the upper troposphere and lower stratosphere composition. During the POLSTRACC/GW-LCYCLE/SALSA flight on 12 January 2016, the HALO (High Altitude LOng range) aircraft crossed twice an extended tropopause fold in the vicinity of the Arctic polar vortex. At the same time, the ECMWF operational analysis shows that the meteorological scenario probed above Italy was accompanied by wide-spread gravity wave activity induced by north-westerly winds. Using high spectral resolution limb-observations by the GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) spectrometer aboard HALO and associated observations, we investigate the vertical distributions of H2O, O3, temperature, and associated parameters across the tropopause fold. In combination with a high-resolution simulation by the ICON-ART (ICOsahedral Nonhydrostatic- Aerosol and Reactive Trace gases) model, we search for indications for irreversible trace gas exchange between the stratosphere and troposphere and the potential influence of gravity waves.

A New Peak of Leonids observed by Radio Technics

NASA Astrophysics Data System (ADS)

Suzuki, K.; Maegawa, K.; Minagawa, Y.

Radio meteor observations with amateur ham radio wave have been carried out in Japan since August, 1996, by using forward-scattered meteor echoes of VHF radio waves (53.75MHz, 50W, CW) transmitted in Sabae, Fukui prefecture. A strong activity of Leonids was observed between 22h and 01h on November 16/17 (UT), 1996. The hourly rate of long duration echoes reached over 50 times larger than in non-shower period and 1.2 to 1.5 times larger than that at the normal maximum of Leonids, respectively. This enhanced activity occurred at a solar longitude (SL) of 234.95 plus or minus 0.05 degrees (2000.0 eq.), and is probably different from normal peak of Leonids at 235.45 plus or minus 0.05 degrees(2000.0 eq.) observed in 1990's. A corresponding peak in 1995 was also reported by visual meteor observation by many observers in Japan. The ascending node of Comet Tempel-Tuttle in 1966 was at 235.11 degrees in SL, and is closer to the new peak than the normal one (at 235.45 degrees in SL).

Interannual variability of the Submonthly Wave Patterns over the Western North Pacific

NASA Astrophysics Data System (ADS)

Ko, K. C.

2017-12-01

This study examines the interannual variability of the 5-16 day wave patterns by separating them into active (A4mV) and inactive (I4mV) years on the basis of the 4-month (July-October) variance of a Japan-South China Sea (JSCS) circulation index from 1979 to 2013. The sea surface temperature for the A4mV years exhibited an ENSO pattern but a reversed anomaly pattern was observed in the I4mV years. Composite results indicate that tropical cyclone (TC) tracks are closely linked to the activity of the wave patterns. When the wave patterns were strong with a solid wave structure in the A4mV years, TCs would follow the propagation routes of the cyclonic anomalies of the wave patterns and separated into two types of tracks: straight-moving and recurving. However, in the I4mV years when the wave patterns were weak and poorly organized, the shapes of the cyclonic anomalies became irregular and sporadic. The weakening structure of the wave patterns in the I4mV years would induce the TCs to undergo more scattered routes near Taiwan and east coast of China. Therefore, Taiwan experienced more rainfall in the I4mV years.

Evaluation of QT and P wave dispersion and mean platelet volume among inflammatory bowel disease patients.

PubMed

Dogan, Yuksel; Soylu, Aliye; Eren, Gulay A; Poturoglu, Sule; Dolapcioglu, Can; Sonmez, Kenan; Duman, Habibe; Sevindir, Isa

2011-01-01

In inflammatory bowel disease (IBD) number of thromboembolic events are increased due to hypercoagulupathy and platelet activation. Increases in mean platelet volume (MPV) can lead to platelet activation, this leads to thromboembolic events and can cause acute coronary syndromes. In IBD patients, QT-dispersion and P-wave dispersion are predictors of ventricular arrhythmias and atrial fibrilation; MPV is accepted as a risk factor for acute coronary syndromes, we aimed at evaluating the correlations of these with the duration of disease, its localization and activity. The study group consisted of 69 IBD (Ulcerative colitis n: 54, Crohn's Disease n: 15) patients and the control group included 38 healthy individuals. Disease activity was evaluated both endoscopically and clinically. Patients with existing cardiac conditions, those using QT prolonging medications and having systemic diseases, anemia and electrolyte imbalances were excluded from the study. QT-dispersion, P-wave dispersion and MPV values of both groups were compared with disease activity, its localization, duration of disease and the antibiotics used. The P-wave dispersion values of the study group were significantly higher than those of the control group. Duration of the disease was not associated with QT-dispersion, and MPV levels. QT-dispersion, P-wave dispersion, MPV and platelet count levels were similar between the active and in mild ulcerative colitis patients. QT-dispersion levels were similar between IBD patients and the control group. No difference was observed between P-wave dispersion, QT-dispersion and MPV values; with regards to disease duration, disease activity, and localization in the study group (p>0.05). P-wave dispersion which is accepted as a risk factor for the development of atrial fibirilation was found to be high in our IBD patients. This demonstrates us that the risk of developing atrial fibrillation may be high in patients with IBD. No significant difference was found in the QT-dispersion, and in the MPV values when compared to the control group.

Assimilation of Wave Imaging Radar Observations for Real-time Wave-by-Wave Forecasting

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

Simpson, Alexandra; Haller, Merrick; Walker, David

This project addressed Topic 3: “Wave Measurement Instrumentation for Feed Forward Controls” under the FOA number DE-FOA-0000971. The overall goal of the program was to develop a phase-resolving wave forecasting technique for application to the active control of Wave Energy Conversion (WEC) devices. We have developed an approach that couples a wave imaging marine radar with a phase-resolving linear wave model for real-time wave field reconstruction and forward propagation of the wave field in space and time. The scope of the project was to develop and assess the performance of this novel forecasting system. Specific project goals were as follows:more » Develop and verify a fast, GPU-based (Graphical Processing Unit) wave propagation model suitable for phase-resolved computation of nearshore wave transformation over variable bathymetry; Compare the accuracy and speed of performance of the wave model against a deep water model in their ability to predict wave field transformation in the intermediate water depths (50 to 70 m) typical of planned WEC sites; Develop and implement a variational assimilation algorithm that can ingest wave imaging radar observations and estimate the time-varying wave conditions offshore of the domain of interest such that the observed wave field is best reconstructed throughout the domain and then use this to produce model forecasts for a given WEC location; Collect wave-resolving marine radar data, along with relevant in situ wave data, at a suitable wave energy test site, apply the algorithm to the field data, assess performance, and identify any necessary improvements; and Develop a production cost estimate that addresses the affordability of the wave forecasting technology and include in the Final Report. The developed forecasting algorithm (“Wavecast”) was evaluated for both speed and accuracy against a substantial synthetic dataset. Early in the project, performance tests definitively demonstrated that the system was capable of forecasting in real-time, as the GPU-based wave model backbone was very computationally efficient. The data assimilation algorithm was developed on a polar grid domain in order to match the sampling characteristics of the observation system (wave imaging marine radar). For verification purposes, a substantial set of synthetic wave data (i.e. forward runs of the wave model) were generated to be used as ground truth for comparison to the reconstructions and forecasts produced by Wavecast. For these synthetic cases, Wavecast demonstrated very good accuracy, for example, typical forecast correlation coefficients were between 0.84-0.95 when compared to the input data. Dependencies on shadowing, observational noise, and forecast horizon were also identified. During the second year of the project, a short field deployment was conducted in order to assess forecast accuracy under field conditions. For this, a radar was installed on a fishing vessel and observations were collected at the South Energy Test Site (SETS) off the coast of Newport, OR. At the SETS site, simultaneous in situ wave observations were also available owing to an ongoing field project funded separately. Unfortunately, the position and heading information that was available for the fishing vessel were not of sufficient accuracy in order to validate the forecast in a phase-resolving sense. Instead, a spectral comparison was made between the Wavecast forecast and the data from the in situ wave buoy. Although the wave and wind conditions during the field test were complex, the comparison showed a promising reconstruction of the wave spectral shape, where both peaks in the bimodal spectrum were represented. However, the total reconstructed spectral energy (across all directions and frequencies) was limited to 44% of the observed spectrum. Overall, wave-by-wave forecasting using a data assimilation approach based on wave imaging radar observations and a physics-based wave model shows promise for short-term phase-resolved predictions. Two recommendations for future work are as follows: first, we would recommend additional focused field campaigns for algorithm validation. The field campaign should be long enough to capture a range of wave conditions relevant to the target application and WEC site. In addition, it will be crucial to make sure the vessel of choice has high accuracy position and heading instrumentation (this instrumentation is commercially available but not standard on commercial fishing vessels). The second recommendation is to expand the model physics in the wave model backbone to include some nonlinear effects. Specifically, the third-order correction to the wave speed due to amplitude dispersion would be the next step in order to more accurately represent the phase speeds of large amplitude waves.« less

Coherent structures in the Es layer and neutral middle atmosphere

NASA Astrophysics Data System (ADS)

Mošna, Zbyšek; Knížová, Petra Koucká; Potužníková, Kateřina

2015-12-01

The present paper shows results from the summer campaign performed during geomagnetically quiet period from June 1 to August 31, 2009. Within time-series of stratospheric and mesospheric temperatures at pressure levels 10-0.1 hPa, mesospheric winds measured in Collm, Germany, and the sporadic E-layer parameters foEs and hEs measured at the Pruhonice station we detected specific coherent wave-bursts in planetary wave domain. Permanent wave-like activity is observed in all analyzed data sets. However, the number of wave-like structures persistent in large range of height from the stratosphere to lower ionosphere is limited. The only coherent modes that are detected on consequent levels of the atmosphere are those corresponding to eigenmodes of planetary waves.

Facilitation of cytosolic calcium wave propagation by local calcium uptake into the sarcoplasmic reticulum in cardiac myocytes.

PubMed

Maxwell, Joshua T; Blatter, Lothar A

2012-12-01

The widely accepted paradigm for cytosolic Ca(2+) wave propagation postulates a 'fire-diffuse-fire' mechanism where local Ca(2+)-induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) via ryanodine receptor (RyR) Ca(2+) release channels diffuses towards and activates neighbouring release sites, resulting in a propagating Ca(2+) wave. A recent challenge to this paradigm proposed the requirement for an intra-SR 'sensitization' Ca(2+) wave that precedes the cytosolic Ca(2+) wave and primes RyRs from the luminal side to CICR. Here, we tested this hypothesis experimentally with direct simultaneous measurements of cytosolic ([Ca(2+)](i); rhod-2) and intra-SR ([Ca(2+)](SR); fluo-5N) calcium signals during wave propagation in rabbit ventricular myocytes, using high resolution fluorescence confocal imaging. The increase in [Ca(2+)](i) at the wave front preceded depletion of the SR at each point along the calcium wave front, while during this latency period a transient increase of [Ca(2+)](SR) was observed. This transient elevation of [Ca(2+)](SR) could be identified at individual release junctions and depended on the activity of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA). Increased SERCA activity (β-adrenergic stimulation with 1 μM isoproterenol (isoprenaline)) decreased the latency period and increased the amplitude of the transient elevation of [Ca(2+)](SR), whereas inhibition of SERCA (3 μM cyclopiazonic acid) had the opposite effect. In conclusion, the data provide experimental evidence that local Ca(2+) uptake by SERCA into the SR facilitates the propagation of cytosolic Ca(2+) waves via luminal sensitization of the RyR, and supports a novel paradigm of a 'fire-diffuse-uptake-fire' mechanism for Ca(2+) wave propagation in cardiac myocytes.

Facilitation of cytosolic calcium wave propagation by local calcium uptake into the sarcoplasmic reticulum in cardiac myocytes

PubMed Central

Maxwell, Joshua T; Blatter, Lothar A

2012-01-01

The widely accepted paradigm for cytosolic Ca2+ wave propagation postulates a ‘fire-diffuse-fire’ mechanism where local Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) via ryanodine receptor (RyR) Ca2+ release channels diffuses towards and activates neighbouring release sites, resulting in a propagating Ca2+ wave. A recent challenge to this paradigm proposed the requirement for an intra-SR ‘sensitization’ Ca2+ wave that precedes the cytosolic Ca2+ wave and primes RyRs from the luminal side to CICR. Here, we tested this hypothesis experimentally with direct simultaneous measurements of cytosolic ([Ca2+]i; rhod-2) and intra-SR ([Ca2+]SR; fluo-5N) calcium signals during wave propagation in rabbit ventricular myocytes, using high resolution fluorescence confocal imaging. The increase in [Ca2+]i at the wave front preceded depletion of the SR at each point along the calcium wave front, while during this latency period a transient increase of [Ca2+]SR was observed. This transient elevation of [Ca2+]SR could be identified at individual release junctions and depended on the activity of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA). Increased SERCA activity (β-adrenergic stimulation with 1 μm isoproterenol (isoprenaline)) decreased the latency period and increased the amplitude of the transient elevation of [Ca2+]SR, whereas inhibition of SERCA (3 μm cyclopiazonic acid) had the opposite effect. In conclusion, the data provide experimental evidence that local Ca2+ uptake by SERCA into the SR facilitates the propagation of cytosolic Ca2+ waves via luminal sensitization of the RyR, and supports a novel paradigm of a ‘fire-diffuse-uptake-fire’ mechanism for Ca2+ wave propagation in cardiac myocytes. PMID:22988145

Metabotropic glutamate receptors activate dendritic calcium waves and TRPM channels which drive rhythmic respiratory patterns in mice

PubMed Central

Mironov, S L

2008-01-01

Respiration in vertebrates is generated by a compact network which is located in the lower brainstem but cellular mechanisms which underlie persistent oscillatory activity of the respiratory network are yet unknown. Using two-photon imaging and patch-clamp recordings in functional brainstem preparations of mice containing pre-Bötzinger complex (preBötC), we examined the actions of metabotropic glutamate receptors (mGluR1/5) on the respiratory patterns. The agonist DHPG potentiated and antagonist LY367385 depressed respiration-related activities. In the inspiratory neurons, we observed rhythmic activation of non-selective channels which had a conductance of 24 pS. Their activity was enhanced with membrane depolarization and after elevation of calcium from the cytoplasmic side of the membrane. They were activated by a non-hydrolysable PIP2 analogue and blocked by flufenamate, ATP4− and Gd3+. All these properties correspond well to those of TRPM4 channels. Calcium imaging of functional slices revealed rhythmic transients in small clusters of neurons present in a network. Calcium transients in the soma were preceded by the waves in dendrites which were dependent on mGluR activation. Initiation and propagation of waves required calcium influx and calcium release from internal stores. Calcium waves activated TPRM4-like channels in the soma and promoted generation of inspiratory bursts. Simulations of activity of neurons communicated via dendritic calcium waves showed emerging activity within neuronal clusters and its synchronization between the clusters. The experimental and theoretical data provide a subcellular basis for a recently proposed group-pacemaker hypothesis and describe a novel mechanism of rhythm generation in neuronal networks. PMID:18308826

Activation of immobilized enzymes by acoustic wave resonance oscillation.

PubMed

Nishiyama, Hiroshi; Watanabe, Tomoya; Inoue, Yasunobu

2014-12-01

Acoustic wave resonance oscillation has been used successfully in the development of methods to activate immobilized enzyme catalysts. In this study, resonance oscillation effects were demonstrated for enzyme reactions on galactose oxidase (GAD), D-amino acid oxidase (DAAO), and L-amino acid oxidase (LAAO), all of which were immobilized covalently on a ferroelectric lead zirconate titanate (PZT) device that could generate thickness-extensional resonance oscillations (TERO) of acoustic waves. For galactose oxidation on immobilized GAD in a microreactor, TERO generation immediately increased enzyme activity 2- to 3-fold. Eliminating TERO caused a slight decrease in the activity, with ∼90% of the enhanced activity retained while the reaction proceeded. Contact of the enhanced enzyme with a galactose-free solution caused almost complete reversion of the activity to the original low level before TERO generation, indicating that, not only TERO-induced GAD activation, but also preservation of the increased activity, required a galactose substrate. Similar activity changes with TERO were observed for enzyme reactions on DAAO and LAAO. Kinetic analysis demonstrated that TERO helped strengthen the interactions of the immobilized enzyme with the reactant substrate and promoted formation of an activation complex. Copyright © 2014 Elsevier Inc. All rights reserved.

Equatorial Mesosphere and Lower Thermosphere/Ionosphere (MLTI) Response to Severe Cyclonic Storm `Aila' and `Ward' observed over North Indian Ocean

NASA Astrophysics Data System (ADS)

G J, B.

2016-12-01

The present work investigates the Equatorial Mesosphere Lower Thermosphere/Ionosphere (MLTI) response to severe cyclonic storm `Aila (23-26 May 2009)' and `Ward (10-16 December 2009)' which were observed over north Indian Ocean during the extended solar minimum of the year 2009. This report reveals the coupling between Tropical Cyclone and MLTI region. Tropical cyclone track and data can be obtained from Indian Meteorological Department (IMD), New Delhi. Mesospheric and Ionospheric variation can be examined with the help of ground based Mesosphere Lower Thermosphere (MLT) radar and Digisonde located at equatorial low latitude station, Tirunelveli (8.7oN, 77.8oE). The Outgoing Long wave Radiation (OLR) data is used as a proxy for identifying the convective activity, which are retrieved from NOAA Climate Data Centre. It is observed that the tropical cyclone induced convection as the driving agent for the increased gravity wave activity in the lower atmosphere. These upward propagating gravity waves deposit their energy and momentum into the upper region of atmosphere as `Travelling Ionospheric Disturbances (TIDs). During the cyclonic storm periods, we found increased gravity wave amplitude with upward propagation in the MLT region. Ionospheric response to severe cyclonic storm is examined with the dynamical parameters, foF2, hmF2, h'F2 and Total Election Content (TEC). Significant increase of foF2 frequency is observed during `Ward' cyclonic storm. Drastic variation in foF2 and h'F2 is observed during Aila cyclonic storm than ward event. More statistical analysis has been done for finding the correlation between cyclonic storm and Ionospheric parameters. Detailed results will be presented in the meeting.

Alternans and Spiral Breakup in an Excitable Reaction-Diffusion System: A Simulation Study

PubMed Central

Gani, M. Osman; Ogawa, Toshiyuki

2014-01-01

The determination of the mechanisms of spiral breakup in excitable media is still an open problem for researchers. In the context of cardiac electrophysiological activities, spiral breakup exhibits complex spatiotemporal pattern known as ventricular fibrillation. The latter is the major cause of sudden cardiac deaths all over the world. In this paper, we numerically study the instability of periodic planar traveling wave solution in two dimensions. The emergence of stable spiral pattern is observed in the considered model. This pattern occurs when the heart is malfunctioning (i.e., ventricular tachycardia). We show that the spiral wave breakup is a consequence of the transverse instability of the planar traveling wave solutions. The alternans, that is, the oscillation of pulse widths, is observed in our simulation results. Moreover, we calculate the widths of spiral pulses numerically and observe that the stable spiral pattern bifurcates to an oscillatory wave pattern in a one-parameter family of solutions. The spiral breakup occurs far below the bifurcation when the maximum and the minimum excited states become more distinct, and hence the alternans becomes more pronounced. PMID:27379274

Alternans and Spiral Breakup in an Excitable Reaction-Diffusion System: A Simulation Study.

PubMed

Gani, M Osman; Ogawa, Toshiyuki

2014-01-01

The determination of the mechanisms of spiral breakup in excitable media is still an open problem for researchers. In the context of cardiac electrophysiological activities, spiral breakup exhibits complex spatiotemporal pattern known as ventricular fibrillation. The latter is the major cause of sudden cardiac deaths all over the world. In this paper, we numerically study the instability of periodic planar traveling wave solution in two dimensions. The emergence of stable spiral pattern is observed in the considered model. This pattern occurs when the heart is malfunctioning (i.e., ventricular tachycardia). We show that the spiral wave breakup is a consequence of the transverse instability of the planar traveling wave solutions. The alternans, that is, the oscillation of pulse widths, is observed in our simulation results. Moreover, we calculate the widths of spiral pulses numerically and observe that the stable spiral pattern bifurcates to an oscillatory wave pattern in a one-parameter family of solutions. The spiral breakup occurs far below the bifurcation when the maximum and the minimum excited states become more distinct, and hence the alternans becomes more pronounced.

Using Near Surface P and S Wave Velocities and Seismic Reflection Images to Detect the Westerly Extension of the Active Meishan Fault in Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Putriani, E.; Huang, W. H.; Shih, R. C.

2017-12-01

The Southwestern Taiwan has higher potential seismic risks among the island. In 1906 the Meishan earthquake of magnitude 7.1 caused very severe damages. The associated Meishan fault was believed extended from Meishan westerly to Hsingang area for 23 km long; however, only the eastern part of the fault could be traces on the surface. The western part of the Meishan fault was simply proposed from the observed lineation of sand blow from the middle of the fault, the Minhsiung area westerly to the Hsingang area. The purpose of this paper is hope to prove the extension of this fault by using near surface P wave and S wave velocities and the seismic reflection images acquired across the suspicious fault location. Totally, we have conducted 20 seismic velocity survey lines, which were deployed in six areas with and without liquefaction observed, and 2 seismic reflection lines. The P and S wave velocities variations were used to analyze depth of the water table, the elastic modulus, soil porosity and the safety factor for soil liquefaction assessment. Preliminary result of the seismic velocity distribution was effective within 17 m deep from surface and showed no particular difference at the sites of liquefaction observed or no liquefaction. The results could indicate that the sand blow observed in 1906 were not site dependent, but more likely related to activity of the Meishan fault. In order to detect the detailed fault trace, the seismic reflection images will be combined for interpreting the buried Meishan fault in the final result.

A study of acoustic halos in active region NOAA 11330 using multi-height SDO observations

NASA Astrophysics Data System (ADS)

Tripathy, S. C.; Jain, K.; Kholikov, S.; Hill, F.; Rajaguru, S. P.; Cally, P. S.

2018-01-01

We analyze data from the Helioseismic Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) instruments on board the Solar Dynamics Observatory (SDO) to characterize the spatio-temporal acoustic power distribution in active regions as a function of the height in the solar atmosphere. For this, we use Doppler velocity and continuum intensity observed using the magnetically sensitive line at 6173 Å as well as intensity at 1600 Å and 1700 Å. We focus on the power enhancements seen around AR 11330 as a function of wave frequency, magnetic field strength, field inclination and observation height. We find that acoustic halos occur above the acoustic cutoff frequency and extends up to 10 mHz in HMI Doppler and AIA 1700 Å observations. Halos are also found to be strong functions of magnetic field and their inclination angle. We further calculate and examine the spatially averaged relative phases and cross-coherence spectra and find different wave characteristics at different heights.

Induced dynamic nonlinear ground response at Gamer Valley, California

USGS Publications Warehouse

Lawrence, Z.; Bodin, P.; Langston, C.A.; Pearce, F.; Gomberg, J.; Johnson, P.A.; Menq, F.-Y.; Brackman, T.

2008-01-01

We present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accelerometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitude-dependent sediment properties. Ground motion exceeding 1g acceleration was produced near the shaker truck. The wave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleigh-wave phase velocity decreased by as much as ???30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth dependence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.

LISA Pathfinder: First steps to observing gravitational waves from space

NASA Astrophysics Data System (ADS)

McNamara, Paul; LISA Pathfinder Collaboration

2017-01-01

With the first direct detection of gravitational waves a little over a year ago, the gravitational window to the Universe has been opened. The gravitational wave spectrum spans many orders of magnitude in frequency, with several of the most interesting astronomical sources emitting gravitational waves at frequencies only observable from space The European Space Agency (ESA) has been active in the field of space-borne gravitational wave detection for many years, and in 2013 selected the Gravitational Universe as the science theme for the third large class mission in the Cosmic Vision science programme. In addition, ESA took the step of developing the LISA Pathfinder mission to demonstrate the critical technologies required for a future mission. The goal of the LISA Pathfinder mission is to place a test body in free fall such that any external forces (acceleration) are reduced to levels lower than those expected from the passage of a gravitational wave LISA Pathfinder was launched on the 3rd December 2015 from the European Spaceport in Kourou, French Guiana. After a series of 6 apogee raising manoeuvres, the satellite left earth orbit, and travelled to its final science orbit around the first Sun-Earth Lagrange point (L1). Following a relatively short commissioning phase, science operations began on 1st March 2016. In the following 3 months over 100 experiments and over 1500hours of noise measurements have been performed, demonstrating that the observation of gravitational waves from space can be realised.

Jupiters North Equatorial Belt Expansion and Thermal Wave Activity Ahead of Junos Arrival.

NASA Technical Reports Server (NTRS)

Fletcher, L. N.; Orton, G. S.; Sinclair, J. A.; Donnelly, P.; Melin, H.; Rogers, J. H.; Greathouse, T. K.; Kasaba, Y.; Fujiyoshi, T.; Sato, T. M.;

Fire Hose Instability in the Multiple Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Alexandrova, A.; Retino, A.; Divin, A. V.; Le Contel, O.; Matteini, L.; Breuillard, H.; Deca, J.; Catapano, F.; Cozzani, G.; Nakamura, R.; Panov, E. V.; Voros, Z.

2017-12-01

We present observations of multiple reconnection in the Earth's magnetotail. In particular, we observe an ion temperature anisotropy characterized by large temperature along the magnetic field, between the two active X-lines. The anisotropy is associated with right-hand polarized waves at frequencies lower than the ion cyclotron frequency and propagating obliquely to the background magnetic field. We show that the observed anisotropy and the wave properties are consistent with linear kinetic theory of fire hose instability. The observations are in agreement with the particle-in-cell simulations of multiple reconnection. The results suggest that the fire hose instability can develop during multiple reconnection as a consequence of the ion parallel anisotropy that is produced by counter-streaming ions trapped between the X-lines.

Ion acceleration by Alfvén waves on auroral field lines

NASA Astrophysics Data System (ADS)

Bingham, Robert; Eliasson, Bengt; Tito Mendonça, José; Stenflo, Lennart

2013-05-01

Observations of ion acceleration along auroral field lines at the boundary of the plasma sheet and tail lobe of the Earth show that the energy of the ions increases with decreasing density. The observations can be explained by ion acceleration through Landau resonance with kinetic Alfvén waves (KAWs) such that kA·vi = ωA, where kA is the wave vector, vi is the ion resonance velocity and ωA is the Alfvén wave frequency. The ion resonance velocities are proportional to the Alfvén velocity which increases with decreasing density. This is in agreement with the data if the process is occurring at the plasma sheet tail lobe boundary. A quasi-linear theory of ion acceleration by KAWs is presented. These ions propagate both down towards and away from the Earth. The paths of the Freja and Polar satellites indicate that the acceleration takes place between the two satellites, between 1Re and 5Re. The downward propagating ions develop a horseshoe-type of distribution which has a positive slope in the perpendicular direction. This type of distribution can produce intense lower hybrid wave activity, which is also observed. Finally, the filamentation of shear Alfvén waves is considered. It may be responsible for large-scale density striations. In memory of Padma Kant Shukla, a great scientist and a good friend.

Shear wave splitting and crustal anisotropy at the Mid-Atlantic Ridge, 35°N

NASA Astrophysics Data System (ADS)

Barclay, Andrew H.; Toomey, Douglas R.

2003-08-01

Shear wave splitting observed in microearthquake data at the axis of the Mid-Atlantic Ridge near 35°N has a fast polarization direction that is parallel to the trend of the axial valley. The time delays between fast and slow S wave arrivals range from 35 to 180 ms, with an average of 90 ms, and show no relationship with ray path length, source-to-receiver azimuth, or receiver location. The anisotropy is attributed to a shallow distribution of vertical, fluid-filled cracks, aligned parallel to the trend of the axial valley. Joint modeling of the shear wave anisotropy and coincident P wave anisotropy results, using recent theoretical models for the elasticity of a porous medium with aligned cracks, suggests that the crack distribution that causes the observed P wave anisotropy can account for at most 10 ms of the shear wave delay. Most of the shear wave delay thus likely accrues within the shallowmost 500 m (seismic layer 2A), and the percent S wave anisotropy within this highly fissured layer is 8-30%. Isolated, fluid-filled cracks at 500 m to 3 km depth that are too thin or too shallow to be detected by the P wave experiment may also contribute to the shear wave delays. The joint analysis of P and S wave anisotropy is an important approach for constraining the crack distributions in the upper oceanic crust and is especially suited for seismically active hydrothermal systems at slow and intermediate spreading mid-ocean ridges.

WASP family members and formin proteins coordinate regulation of cell protrusions in carcinoma cells

PubMed Central

Sarmiento, Corina; Wang, Weigang; Dovas, Athanassios; Yamaguchi, Hideki; Sidani, Mazen; El-Sibai, Mirvat; DesMarais, Vera; Holman, Holly A.; Kitchen, Susan; Backer, Jonathan M.; Alberts, Art; Condeelis, John

2008-01-01

We examined the role of the actin nucleation promoters neural Wiskott-Aldrich syndrome protein (N-WASP) and WAVE2 in cell protrusion in response to epidermal growth factor (EGF), a key regulator in carcinoma cell invasion. We found that WAVE2 knockdown (KD) suppresses lamellipod formation and increases filopod formation, whereas N-WASP KD has no effect. However, simultaneous KD of both proteins results in the formation of large jagged protrusions with lamellar properties and increased filopod formation. This suggests that another actin nucleation activity is at work in carcinoma cells in response to EGF. A mammalian Diaphanous–related formin, mDia1, localizes at the jagged protrusions in double KD cells. Constitutively active mDia1 recapitulated the phenotype, whereas inhibition of mDia1 blocked the formation of these protrusions. Increased RhoA activity, which stimulates mDia1 nucleation, was observed in the N-WASP/WAVE2 KD cells and was shown to be required for the N-WASP/WAVE2 KD phenotype. These data show that coordinate regulation between the WASP family and mDia proteins controls the balance between lamellar and lamellipodial protrusion activity. PMID:18362183

WASP family members and formin proteins coordinate regulation of cell protrusions in carcinoma cells.

PubMed

Sarmiento, Corina; Wang, Weigang; Dovas, Athanassios; Yamaguchi, Hideki; Sidani, Mazen; El-Sibai, Mirvat; Desmarais, Vera; Holman, Holly A; Kitchen, Susan; Backer, Jonathan M; Alberts, Art; Condeelis, John

2008-03-24

We examined the role of the actin nucleation promoters neural Wiskott-Aldrich syndrome protein (N-WASP) and WAVE2 in cell protrusion in response to epidermal growth factor (EGF), a key regulator in carcinoma cell invasion. We found that WAVE2 knockdown (KD) suppresses lamellipod formation and increases filopod formation, whereas N-WASP KD has no effect. However, simultaneous KD of both proteins results in the formation of large jagged protrusions with lamellar properties and increased filopod formation. This suggests that another actin nucleation activity is at work in carcinoma cells in response to EGF. A mammalian Diaphanous-related formin, mDia1, localizes at the jagged protrusions in double KD cells. Constitutively active mDia1 recapitulated the phenotype, whereas inhibition of mDia1 blocked the formation of these protrusions. Increased RhoA activity, which stimulates mDia1 nucleation, was observed in the N-WASP/WAVE2 KD cells and was shown to be required for the N-WASP/WAVE2 KD phenotype. These data show that coordinate regulation between the WASP family and mDia proteins controls the balance between lamellar and lamellipodial protrusion activity.

Jupiter Data Analysis Program: Analysis of Voyager wideband plasma wave observations

NASA Technical Reports Server (NTRS)

Kurth, W. S.

1983-01-01

Voyager plasma wave wideband frames from the Jovian encounters are analyzed. The 511 frames which were analyzed were chosen on the basis of low-rate spectrum analyzer data from the plasma wave receiver. These frames were obtained in regions and during times of various types of plasma or radio wave activity as determined by the low-rate, low-resolution data and were processed in order to provide high resolution measurements of the plasma wave spectrum for use in the study of a number of outstanding problems. Chorus emissions at Jupiter were analyzed. The detailed temporal and spectral form of the very complex chorus emissions near L = 8 on the Voyager 1 inbound passage was compared to both terrestrial chorus emissions as well as to the theory which was developed to explain the terrestrial waves.

Activity induces traveling waves, vortices and spatiotemporal chaos in a model actomyosin layer

NASA Astrophysics Data System (ADS)

Ramaswamy, Rajesh; Jülicher, Frank

2016-02-01

Inspired by the actomyosin cortex in biological cells, we investigate the spatiotemporal dynamics of a model describing a contractile active polar fluid sandwiched between two external media. The external media impose frictional forces at the interface with the active fluid. The fluid is driven by a spatially-homogeneous activity measuring the strength of the active stress that is generated by processes consuming a chemical fuel. We observe that as the activity is increased over two orders of magnitude the active polar fluid first shows spontaneous flow transition followed by transition to oscillatory dynamics with traveling waves and traveling vortices in the flow field. In the flow-tumbling regime, the active polar fluid also shows transition to spatiotemporal chaos at sufficiently large activities. These results demonstrate that level of activity alone can be used to tune the operating point of actomyosin layers with qualitatively different spatiotemporal dynamics.

Report from the Gravitational Observatory Advisory Team

NASA Astrophysics Data System (ADS)

Mueller, Guido; Gravitational Observatory Advisory Team

2016-03-01

As a response to the selection of the Gravitational Universe as the science theme for ESA's L3 mission, ESA formed the Gravitational-Wave Observatory Advisory Team (GOAT) to advise ESA on the scientific and technological approach for a gravitational wave observatory. NASA is participating with three US scientists and one NASA observer; JAXA was also invited and participates with one observer. The GOAT looked at a range of mission technologies and designs, discussed their technical readiness with respect to the ESA schedule, recommended technology development activities for selected technologies, and worked with the wider gravitational-wave community to analyze the impact on the science of the various mission designs. The final report is expected to be submitted to ESA early March and I plan to summarize its content.

Can gravity waves significantly impact PSC occurrence in the Antarctic?

NASA Astrophysics Data System (ADS)

McDonald, A. J.; George, S. E.; Woollands, R. M.

2009-11-01

A combination of POAM III aerosol extinction and CHAMP RO temperature measurements are used to examine the role of atmospheric gravity waves in the formation of Antarctic Polar Stratospheric Clouds (PSCs). POAM III aerosol extinction observations and quality flag information are used to identify Polar Stratospheric Clouds using an unsupervised clustering algorithm. A PSC proxy, derived by thresholding Met Office temperature analyses with the PSC Type Ia formation temperature (TNAT), shows general agreement with the results of the POAM III analysis. However, in June the POAM III observations of PSC are more abundant than expected from temperature threshold crossings in five out of the eight years examined. In addition, September and October PSC identified using temperature thresholding is often significantly higher than that derived from POAM III; this observation probably being due to dehydration and denitrification. Comparison of the Met Office temperature analyses with corresponding CHAMP observations also suggests a small warm bias in the Met Office data in June. However, this bias cannot fully explain the differences observed. Analysis of CHAMP data indicates that temperature perturbations associated with gravity waves may partially explain the enhanced PSC incidence observed in June (relative to the Met Office analyses). For this month, approximately 40% of the temperature threshold crossings observed using CHAMP RO data are associated with small-scale perturbations. Examination of the distribution of temperatures relative to TNAT shows a large proportion of June data to be close to this threshold, potentially enhancing the importance of gravity wave induced temperature perturbations. Inspection of the longitudinal structure of PSC occurrence in June 2005 also shows that regions of enhancement are geographically associated with the Antarctic Peninsula; a known mountain wave "hotspot". The latitudinal variation of POAM III observations means that we only observe this region in June-July, and thus the true pattern of enhanced PSC production may continue operating into later months. The analysis has shown that early in the Antarctic winter stratospheric background temperatures are close to the TNAT threshold (and PSC formation), and are thus sensitive to temperature perturbations associated with mountain wave activity near the Antarctic peninsula (40% of PSC formation). Later in the season, and at latitudes away from the peninsula, temperature perturbations associated with gravity waves contribute to about 15% of the observed PSC (a value which corresponds well to several previous studies). This lower value is likely to be due to colder background temperatures already achieving the TNAT threshold unaided. Additionally, there is a reduction in the magnitude of gravity waves perturbations observed as POAM III samples poleward of the peninsula.

Study protocol: effects of school gardens on children's physical activity.

PubMed

Wells, Nancy M; Myers, Beth M; Henderson, Charles R

2014-01-01

Childhood obesity is an epidemic. Strategies are needed to promote children's healthy habits related to diet and physical activity. School gardens have the potential to bolster children's physical activity and reduce time spent in sedentary activity; however little research has examined the effect of gardens on children's physical activity. This randomized controlled trial (RCT) examines the effect of school gardens on children's overall physical activity and sedentary behavior; and on children's physical activity during the school day. In addition, physical activity levels and postures are compared using direct observation, outdoors, in the garden and indoors, in the classroom. Twelve New York State schools are randomly assigned to receive the school garden intervention or to serve in the wait-list control group that receives gardens and lessons at the end of the study. The intervention consists of a raised bed garden; access to a curriculum focused on nutrition, horticulture, and plant science and including activities and snack suggestions; resources for the school including information about food safety in the garden and related topics; a garden implementation guide provided guidance regarding planning, planting and maintaining the garden throughout the year; gardening during the summer; engaging volunteers; building community capacity, and sustaining the program. Data are collected at baseline and 3 post-intervention follow-up waves at 6, 12, and 18 months. Physical activity (PA) "usually" and "yesterday" is measured using surveys at each wave. In addition, at-school PA is measured using accelerometry for 3 days at each wave. Direct observation (PARAGON) is used to compare PA during an indoor classroom lesson versus outdoor, garden-based lesson. Results of this study will provide insight regarding the potential for school gardens to increase children's physical activity and decrease sedentary behaviors. Clinicaltrial.gov # NCT02148315.

Numerical study of alfvénic wave activity in the solar wind as a cause for pitch angle scattering with focus on kinetic processes

NASA Astrophysics Data System (ADS)

Keilbach, D.; Berger, L.; Drews, C.; Marsch, E.; Wimmer-Schweingruber, R. F.

2017-12-01

Recent studies, that determined the inflow longitude of the local interstellar medium from the anisotropy of interstellar pickup ion (PUI) radial velocity, have once again raised the question, how transport effects and especially wave activity in the solar wind modifies the velocity distribution function of PUIs.This study investigates the modification of an oxygen PUI torus distribution by alfvénic waves qualitatively with a numerical approach. The focus of this study is to understand this modification kinetically, which means, that instead of describing the PUI transport through diffusion approaches, we trace the trajectories of test particles in pitch angle space with a time resolution of at least 100 time steps per gyro orbit in order to find first principles of wave particle interactions on the most basic scale.Therefore we have implemented a Leapfrog solver of the Lorentz-Newton equations of motion for a charged test particle in a electro-magnetic field. The alfvénic waves were represented through a continuous circularly polarized wave superimposed to a constant 5 nT background magnetic field. In addition an electric field arising from induction has been added to the simulation's boundary conditions. The simulation code computes the particles' trajectories in the solar wind bulk system.Upon interaction with mono frequent single-frequency waves, the particles are found to perform stationary trajectories in pitch angle space, so that the pitch angle distribution of a conglomerate of test particles does not experience a systematic broadening over time. Also the particles do not react most strongly with waves at resonant frequencies, since the pitch angle modification by the waves sweeps their parallel velocity out of resonance quickly. However, within frequencies close to first order resonance, strong interactions between waves and particles are observed.Altogether the framework of our simulation is readily expandable to simulate additional effects, which may modify the test particles' pitch angle distribution strongly (e.g. collisions with solar wind particles or gradient drifts). So far we have expanded the simulation to support intermittent waves, where we have observed, that the pitch angle distribution of the test particles broadens systematically over time.

Empirical predictive models of daily relativistic electron flux at geostationary orbit: Multiple regression analysis

DOE PAGES

Simms, Laura E.; Engebretson, Mark J.; Pilipenko, Viacheslav; ...

2016-04-07

The daily maximum relativistic electron flux at geostationary orbit can be predicted well with a set of daily averaged predictor variables including previous day's flux, seed electron flux, solar wind velocity and number density, AE index, IMF Bz, Dst, and ULF and VLF wave power. As predictor variables are intercorrelated, we used multiple regression analyses to determine which are the most predictive of flux when other variables are controlled. Empirical models produced from regressions of flux on measured predictors from 1 day previous were reasonably effective at predicting novel observations. Adding previous flux to the parameter set improves the predictionmore » of the peak of the increases but delays its anticipation of an event. Previous day's solar wind number density and velocity, AE index, and ULF wave activity are the most significant explanatory variables; however, the AE index, measuring substorm processes, shows a negative correlation with flux when other parameters are controlled. This may be due to the triggering of electromagnetic ion cyclotron waves by substorms that cause electron precipitation. VLF waves show lower, but significant, influence. The combined effect of ULF and VLF waves shows a synergistic interaction, where each increases the influence of the other on flux enhancement. Correlations between observations and predictions for this 1 day lag model ranged from 0.71 to 0.89 (average: 0.78). Furthermore, a path analysis of correlations between predictors suggests that solar wind and IMF parameters affect flux through intermediate processes such as ring current ( Dst), AE, and wave activity.« less

Empirical predictive models of daily relativistic electron flux at geostationary orbit: Multiple regression analysis

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

Simms, Laura E.; Engebretson, Mark J.; Pilipenko, Viacheslav

The daily maximum relativistic electron flux at geostationary orbit can be predicted well with a set of daily averaged predictor variables including previous day's flux, seed electron flux, solar wind velocity and number density, AE index, IMF Bz, Dst, and ULF and VLF wave power. As predictor variables are intercorrelated, we used multiple regression analyses to determine which are the most predictive of flux when other variables are controlled. Empirical models produced from regressions of flux on measured predictors from 1 day previous were reasonably effective at predicting novel observations. Adding previous flux to the parameter set improves the predictionmore » of the peak of the increases but delays its anticipation of an event. Previous day's solar wind number density and velocity, AE index, and ULF wave activity are the most significant explanatory variables; however, the AE index, measuring substorm processes, shows a negative correlation with flux when other parameters are controlled. This may be due to the triggering of electromagnetic ion cyclotron waves by substorms that cause electron precipitation. VLF waves show lower, but significant, influence. The combined effect of ULF and VLF waves shows a synergistic interaction, where each increases the influence of the other on flux enhancement. Correlations between observations and predictions for this 1 day lag model ranged from 0.71 to 0.89 (average: 0.78). Furthermore, a path analysis of correlations between predictors suggests that solar wind and IMF parameters affect flux through intermediate processes such as ring current ( Dst), AE, and wave activity.« less

Standing wave contributions to the linear interference effect in stratosphere-troposphere coupling

NASA Astrophysics Data System (ADS)

Watt-Meyer, Oliver; Kushner, Paul

2014-05-01

A body of literature by Hayashi and others [Hayashi 1973, 1977, 1979; Pratt, 1976] developed a decomposition of the wavenumber-frequency spectrum into standing and travelling waves. These techniques directly decompose the power spectrum—that is, the amplitudes squared—into standing and travelling parts. This, incorrectly, does not allow for a term representing the covariance between these waves. We propose a simple decomposition based on the 2D Fourier transform which allows one to directly compute the variance of the standing and travelling waves, as well as the covariance between them. Applying this decomposition to geopotential height anomalies in the Northern Hemisphere winter, we show the dominance of standing waves for planetary wavenumbers 1 through 3, especially in the stratosphere, and that wave-1 anomalies have a significant westward travelling component in the high-latitude (60N to 80N) troposphere. Variations in the relative zonal phasing between a wave anomaly and the background climatological wave pattern—the "linear interference" effect—are known to explain a large part of the planetary wave driving of the polar stratosphere in both hemispheres. While the linear interference effect is robust across observations, models of varying degrees of complexity, and in response to various types of perturbations, it is not well understood dynamically. We use the above-described decomposition into standing and travelling waves to investigate the drivers of linear interference. We find that the linear part of the wave activity flux is primarily driven by the standing waves, at all vertical levels. This can be understood by noting that the longitudinal positions of the antinodes of the standing waves are typically close to being aligned with the maximum and minimum of the background climatology. We discuss implications for predictability of wave activity flux, and hence polar vortex strength variability.

Following the ontogeny of retinal waves: pan-retinal recordings of population dynamics in the neonatal mouse

PubMed Central

Maccione, Alessandro; Hennig, Matthias H; Gandolfo, Mauro; Muthmann, Oliver; van Coppenhagen, James; Eglen, Stephen J; Berdondini, Luca; Sernagor, Evelyne

2014-01-01

The immature retina generates spontaneous waves of spiking activity that sweep across the ganglion cell layer during a limited period of development before the onset of visual experience. The spatiotemporal patterns encoded in the waves are believed to be instructive for the wiring of functional connections throughout the visual system. However, the ontogeny of retinal waves is still poorly documented as a result of the relatively low resolution of conventional recording techniques. Here, we characterize the spatiotemporal features of mouse retinal waves from birth until eye opening in unprecedented detail using a large-scale, dense, 4096-channel multielectrode array that allowed us to record from the entire neonatal retina at near cellular resolution. We found that early cholinergic waves propagate with random trajectories over large areas with low ganglion cell recruitment. They become slower, smaller and denser when GABAA signalling matures, as occurs beyond postnatal day (P) 7. Glutamatergic influences dominate from P10, coinciding with profound changes in activity dynamics. At this time, waves cease to be random and begin to show repetitive trajectories confined to a few localized hotspots. These hotspots gradually tile the retina with time, and disappear after eye opening. Our observations demonstrate that retinal waves undergo major spatiotemporal changes during ontogeny. Our results support the hypotheses that cholinergic waves guide the refinement of retinal targets and that glutamatergic waves may also support the wiring of retinal receptive fields. PMID:24366261

Saharan Dust, Transport Processes, and Possible Impacts on Hurricane Activities

NASA Technical Reports Server (NTRS)

Lau, William K. M.; Kim, K. M.

2010-01-01

In this paper, we present observational evidence of significant relationships between Saharan dust outbreak, and African Easterly wave activities and hurricane activities. We found two dominant paths of transport of Saharan dust: a northern path, centered at 25degN associated with eastward propagating 6-19 days waves over northern Africa, and a southern path centered at 15degN, associated with the AEW, and the Atlantic ITCZ. Seasons with stronger dust outbreak from the southern path are associated with a drier atmosphere over the Maximum Development Region (MDR) and reduction in tropical cyclone and hurricane activities in the MDR. Seasons with stronger outbreak from the northern path are associated with a cooler N. Atlantic, and suppressed hurricane in the western Atlantic basin.

Volcanic Lightning, Pyroclastic Density Currents, Ballistic Fall, Vent Tremor, and One Very Loud Blast: Acoustic Analysis of the 14 July 2013 Vulcanian Eruption at Tungurahua, Ecuador.

NASA Astrophysics Data System (ADS)

Anderson, J.; Johnson, J. B.; Steele, A. L.; Anzieta, J. C.; Ortiz, H. D.; Hall, M. L.; Ruiz, M. C.

2014-12-01

Acoustic recordings reveal a variety of volcanic activities during an exceptionally loud vulcanian eruption at Tungurahua. A period of several months of mild surface activity came to an abrupt end with the emission of a powerful blast wave heard at least 180 km away. Sensors 2080 m from the vent recorded a stepped rise to its maximum overpressure of 1220 Pa (corresponding to a sound pressure level of 156 dB) and its unusually long dominant period of 5.6 s. We discuss source processes that produced the blast wave, considering that wave propagation could be nonlinear near the vent because of high overpressures. More than an hour of acoustic activity was recorded after the blast wave, including sound from falling ballistics, reflections of the blast wave from nearby mountains, pyroclastic density currents, and acoustic tremor at the vent. Glitches in the acoustic records related to plume lightning were also serendipitously observed, although thunder could not be unambiguously identified. We discuss acoustic signatures of falling ballistics and pyroclastic density currents and how array-style deployments and analytic methods can be used to reveal them. Placement of sensors high on the volcano's slopes facilitated resolving these distinct processes. This study demonstrates that near-vent, array-style acoustic installations can be used to monitor various types of volcanic activity.

A Self-Organizing Maps approach to assess the wave climate of the Adriatic Sea

NASA Astrophysics Data System (ADS)

Barbariol, Francesco; Marcello Falcieri, Francesco; Scotton, Carlotta; Benetazzo, Alvise; Bergamasco, Andrea; Bergamasco, Filippo; Bonaldo, Davide; Carniel, Sandro; Sclavo, Mauro

2015-04-01

The assessment of wave conditions at sea is fruitful for many research fields in marine and atmospheric sciences and for the human activities in the marine environment. To this end, in the last decades the observational network, that mostly relies on buoys, satellites and other probes from fixed platforms, has been integrated with numerical models outputs, which allow to compute the parameters of sea states (e.g. the significant wave height, the mean and peak wave periods, the mean and peak wave directions) over wider regions. Apart from the collection of wave parameters observed at specific sites or modeled on arbitrary domains, the data processing performed to infer the wave climate at those sites is a crucial step in order to provide high quality data and information to the community. In this context, several statistical techniques has been used to model the randomness of wave parameters. While univariate and bivariate probability distribution functions (pdf) are routinely used, multivariate pdfs that model the probability structure of more than two wave parameters are hardly managed. Recently, the Self-Organizing Maps (SOM) technique has been successfully applied to represent the multivariate random wave climate at sites around the Iberian peninsula and the South America continent. Indeed, the visualization properties offered by this technique allow to get the dependencies between the different parameters by visual inspection. In this study, carried out in the frame of the Italian National Flagship Project "RITMARE", we take advantage of the SOM technique to assess the multivariate wave climate over the Adriatic Sea, a semi-enclosed basin in the north-eastern Mediterranean Sea, where winds from North-East (called "Bora") and South-East (called "Sirocco") mainly blow causing sea storms. By means of the SOM techniques we can observe the multivariate character of the typical Bora and Sirocco wave features in the Adriatic Sea. To this end, we used both observed and modeled wave parameters. The "Acqua Alta" oceanographic tower in the northern Adriatic Sea (ISMAR-CNR) and the Italian Data Buoy Network (RON, managed by ISPRA) off the western Adriatic coasts furnished the wave parameters at specific sites of interest. Widespread wave parameters were obtained by means of a numerical SWAN wave model that was implemented on the whole Adriatic Sea with a 6x6 km2 resolution and forced by the high resolution COSMO-I7 atmospheric model for the period 2007-2013.

Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.

2007-01-01

Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives them out of the loss cone on the dayside. So convection and wave scattering reinforce each other in the nightside, but interfere in the dayside sector.

A theoretical analysis of anatomical and functional intestinal slow wave re-entry.

PubMed

Du, Peng; O'Grady, Gregory; Cheng, Leo K

2017-07-21

Intestinal bioelectrical slow waves are a key regulator of intestinal motility. Peripheral pacemakers, ectopic initiations and sustained periods of re-entrant activities have all been experimentally observed to be important factors in setting the frequency of intestinal slow waves, but the tissue-level mechanisms underpinning these activities are unclear. This theoretical analysis aimed to define the initiation, maintenance, and termination criteria of two classes of intestinal re-entrant activities: anatomical re-entry and functional re-entry. Anatomical re-entry was modeled in a three-dimensional (3D) cylindrical model, and functional rotor was modeled in a 2D rectangle model. A single-pulse stimulus was used to invoke an anatomical re-entry and a prolonged refractory block was used to invoke the rotor. In both cases, the simulated re-entrant activities operated at frequencies above the baseline entrainment frequency. The anatomical re-entry simulation results demonstrated that a temporary functional refractory block would be required to initiate the re-entrant activity in a single direction around the cylindrical model. The rotor could be terminated by a single-pulse stimulus delivered around the core of the rotor. In conclusion, the simulation results provide the following new insights into the mechanisms of intestinal re-entry: (i) anatomical re-entry is only maintained within a specific range of velocities, outside of which the re-entrant activities become either an ectopic activity or simultaneous activations of the intestinal wall; (ii) a maintained rotor entrained slow waves faster in the antegrade direction than in the retrograde direction. Simulations are shown to be a valuable tool for achieving novel insights into the mechanisms of intestinal slow wave dysrhythmia. Copyright © 2017 Elsevier Ltd. All rights reserved.

Antarctic icequakes triggered by the 2010 Maule earthquake in Chile

NASA Astrophysics Data System (ADS)

Peng, Zhigang; Walter, Jacob I.; Aster, Richard C.; Nyblade, Andrew; Wiens, Douglas A.; Anandakrishnan, Sridhar

2014-09-01

Seismic waves from distant, large earthquakes can almost instantaneously trigger shallow micro-earthquakes and deep tectonic tremor as they pass through Earth's crust. Such remotely triggered seismic activity mostly occurs in tectonically active regions. Triggered seismicity is generally considered to reflect shear failure on critically stressed fault planes and is thought to be driven by dynamic stress perturbations from both Love and Rayleigh types of surface seismic wave. Here we analyse seismic data from Antarctica in the six hours leading up to and following the 2010 Mw 8.8 Maule earthquake in Chile. We identify many high-frequency seismic signals during the passage of the Rayleigh waves generated by the Maule earthquake, and interpret them as small icequakes triggered by the Rayleigh waves. The source locations of these triggered icequakes are difficult to determine owing to sparse seismic network coverage, but the triggered events generate surface waves, so are probably formed by near-surface sources. Our observations are consistent with tensile fracturing of near-surface ice or other brittle fracture events caused by changes in volumetric strain as the high-amplitude Rayleigh waves passed through. We conclude that cryospheric systems can be sensitive to large distant earthquakes.

Ozone perturbations in the Arctic summer lower stratosphere as a reflection of NOX chemistry and planetary scale wave activity

NASA Astrophysics Data System (ADS)

Akiyoshi, H.; Sugita, T.; Kanzawa, H.; Kawamoto, N.

2004-02-01

Ozone concentration perturbations in the high-latitude lower stratosphere in the Northern Hemisphere were observed by Improved Limb Atmospheric Spectrometer (ILAS) after the polar vortex breakdown at the beginning of May 1997 and until the end of June of that same year. Simulations and a passive tracer experiment using the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) nudging chemical transport model (CTM) show that the low-ozone perturbations observed in May were caused by the Arctic polar vortex debris, while those after the end of May resulted from a dynamical elongation due to zonal wave number 2 planetary waves of the low-ozone region in the summer polar stratosphere, which had been developed by the catalytic ozone destruction cycle of NOX. These low-O3 air masses of different origin were advected or elongated from the polar region to the ILAS measurement points. An episodic event of a dynamical O3 perturbation in June 1997 on a chemically induced meridional O3 gradient is described. These results show that a timing of the polar vortex breakdown and activity of planetary waves after the breakdown may affect the O3 background gradient in the summer lower stratosphere at middle and high latitudes.

Shallow water observations of the bottom boundary during an energetic storm

NASA Astrophysics Data System (ADS)

Sheremet, A.; Klammer, H.; Calantoni, J.

2016-12-01

We report high-resolution field observations collected at the U.S. Army Corps of Engineers, Field Research Facility, Duck, NC from 26 January - 10 March 2015. The experiment deployed two instrument arrays near the 6-m and 8-m isobaths that included acoustic Doppler current profilers, acoustic Doppler velocimeters, pressure and CTD sensors to monitor waves, currents, turbulence, temperature, conductivity and suspended sediment concentration at high temporal and vertical resolution. Additionally, munitions, or "targets", were deployed that spanned a range of sizes and densities with munitions mobility and burial monitored continuously at the 8-m array with sector scanning sonars and at the 6-m array with a pencil beam sonar. The roughly 6-week long experiment observed a sequence of at least 10 winter storm events, six of which were characterized by significant wave heights exceeding 2 m at the 8-m instrument array, with peak periods typically around 10 s. During the strongest storm from 10 - 15 February 2015, waves at the 8-m array had peak periods around 14 s and significant wave heights exceeding 2 m for more than 3 days, with significant wave heights exceeding 5 m at the peak of activity. Despite the tremendous amount of hydrodynamic activity bathymetric surveys performed on 16 January 2015 (before) and 17 March 2015 (after) the experiment showed only 5 - 10 cm variation in bed elevation at the 8-m array, suggesting that the local gradients in sediment transport were nearly negligible. Additionally, time series of tilt and heading sensors indicated periods of "jacking" of the instrument frame that was initially moored using four pipes, about 3 m in length, jetted into the seafloor, while some targets were found buried up to 60 cm deep. We will present a detailed analysis of the near-bed hydrodynamics during the most energetic storm and present a simple model to explain the observed burial depths of targets.

Experimental characterization and modelling of non-linear coupling of the lower hybrid current drive power on Tore Supra

NASA Astrophysics Data System (ADS)

Preynas, M.; Goniche, M.; Hillairet, J.; Litaudon, X.; Ekedahl, A.; Colas, L.

2013-01-01

To achieve steady-state operation on future fusion devices, in particular on ITER, the coupling of the lower hybrid wave must be optimized on a wide range of edge conditions. However, under some specific conditions, deleterious effects on the lower hybrid current drive (LHCD) coupling are sometimes observed on Tore Supra. In this way, dedicated LHCD experiments have been performed using the LHCD system of Tore Supra, composed of two different conceptual designs of launcher: the fully active multi-junction (FAM) and the new passive active multi-junction (PAM) antennas. A non-linear interaction between the electron density and the electric field has been characterized in a thin plasma layer in front of the two LHCD antennas. The resulting dependence of the power reflection coefficient (RC) with the LHCD power is not predicted by the standard linear theory of the LH wave coupling. A theoretical model is suggested to describe the non-linear wave-plasma interaction induced by the ponderomotive effect and implemented in a new full wave LHCD code, PICCOLO-2D (ponderomotive effect in a coupling code of lower hybrid wave-2D). The code self-consistently treats the wave propagation in the antenna vicinity and its interaction with the local edge plasma density. The simulation reproduces very well the occurrence of a non-linear behaviour in the coupling observed in the LHCD experiments. The important differences and trends between the FAM and the PAM antennas, especially a larger increase in RC for the FAM, are also reproduced by the PICCOLO-2D simulation. The working hypothesis of the contribution of the ponderomotive effect in the non-linear observations of LHCD coupling is therefore validated through this comprehensive modelling for the first time on the FAM and PAM antennas on Tore Supra.

Comparison of infrared and Raman wave numbers of neat molecular liquids: Which is the correct infrared wave number to use?

NASA Astrophysics Data System (ADS)

Bertie, John E.; Michaelian, Kirk H.

1998-10-01

This paper is concerned with the peak wave number of very strong absorption bands in infrared spectra of molecular liquids. It is well known that the peak wave number can differ depending on how the spectrum is measured. It can be different, for example, in a transmission spectrum and in an attenuated total reflection spectrum. This difference can be removed by transforming both spectra to the real, n, and imaginary, k, refractive index spectra, because both spectra yield the same k spectrum. However, the n and k spectra can be transformed to spectra of any other intensity quantity, and the peak wave numbers of strong bands may differ by up to 6 cm-1 in the spectra of the different quantities. The question which then arises is "which infrared peak wave number is the correct one to use in the comparison of infrared wave numbers of molecular liquids with wave numbers in other spectra?" For example, infrared wave numbers in the gas and liquid phase are compared to observe differences between the two phases. Of equal importance, the wave numbers of peaks in infrared and Raman spectra of liquids are compared to determine whether the infrared-active and Raman-active vibrations coincide, and thus are likely to be the same, or are distinct. This question is explored in this paper by presenting the experimental facts for different intensity quantities. The intensity quantities described are macroscopic properties of the liquid, specifically the absorbance, attenuated total reflectance, imaginary refractive index, k, imaginary dielectric constant, ɛ″, and molar absorption coefficient, Em, and one microscopic property of a molecule in the liquid, specifically the imaginary molar polarizability, αm″, which is calculated under the approximation of the Lorentz local field. The main experimental observations are presented for the strongest band in the infrared spectrum of each of the liquids methanol, chlorobenzene, dichloromethane, and acetone. Particular care was paid to wave number calibration of both infrared and Raman spectra. Theoretical arguments indicate that the peak wave number in the αm″ spectrum is the correct one to use, because it is the only one that reflects the properties of molecules in their local environment in the liquid free from predictable long-range resonant dielectric effects. However, it is found that the comparison with Raman wave numbers is confused when the anisotropic local intermolecular forces and configuration in the liquid are significant. In these cases, the well known noncoincidence of the isotropic and anisotropic Raman scattering is observed, and the same factors lead to noncoincidence of the infrared and Raman bands.

Parametric decay of current-driven Langmuir waves in plateau plasmas: Relevance to solar wind and foreshock events

NASA Astrophysics Data System (ADS)

Sauer, Konrad; Malaspina, David M.; Pulupa, Marc; Salem, Chadi S.

2017-07-01

Langmuir amplitude modulation in association with type III radio bursts is a well-known phenomenon since the beginning of space observations. It is commonly attributed to the superposition of beam-excited Langmuir waves and their backscattered counterparts as a result of parametric decay. The dilemma, however, is the discrepancy between fast beam relaxation and long-lasting Langmuir wave activity. Instead of starting with an unstable electron beam, our focus in this paper is on the nonlinear response of Langmuir oscillations that are driven after beam stabilization by the still persisting current of the (stable) two-electron plasma. The velocity distribution function of the second population forms a plateau (index h) with a point at which ∂fh/∂v ˜0 associated with weak damping over a more or less extended wave number range k. As shown by particle-in-cell simulations, this so-called plateau plasma drives primarily Langmuir oscillations at the plasma frequency (ωe) with k = 0 over long times without remarkable change of the distribution function. These Langmuir oscillations act as a pump wave for parametric decay by which an electron-acoustic wave slightly below ωe and a counterstreaming ion-acoustic wave are generated. Both high-frequency waves have nearly the same amplitude, which is given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in reasonable agreement with solar wind and terrestrial foreshock observations made by the Wind spacecraft.

The Bright Future of Gravitational Wave Astronomy

NASA Astrophysics Data System (ADS)

Gonzalez, Gabriela

2008-04-01

These are exciting times in the search for gravitational waves. Gravitational waves are expected from many different astrophysical sources: brief transients from violent events like supernova explosions and collisions of neutron stars and black holes, coalescence of compact binary systems, continuous waves from rotating systems, and stochastic signals from cosmological origin or unresolved transients. The LIGO gravitational wave detectors have achieved unprecedented sensitivity to gravitational waves, and other detectors around the world are expected to reach similar sensitivities. The LIGO Scientific Collaboration (LSC) has recently completed their most sensitive observation run to date with LIGO and GEO detectors, including several months of joint observations with the European VIRGO detector. The LIGO Laboratory and the LSC, as well as the Virgo Collaboration, are actively preparing for operating enhanced detectors in the very near future. The next decade will see the construction and commissioning of Advanced LIGO and VIRGO, and quite possibly the launch of the space-based LISA mission, starting for sure then, if not earlier, a new era for gravitational wave astronomy. Plans for a world-wide network of ground based detectors involving more detectors in Europe, Japan and Australia are becoming more concrete. The future of gravitational wave astronomy is bright indeed! In this talk, will briefly describe the present status of the ground and space based detector projects and discuss the science we may expect to do with the detectors (and detections!) we will have in the upcoming era of gravitational wave astronomy.

Real time wave forecasting using wind time history and numerical model

NASA Astrophysics Data System (ADS)

Jain, Pooja; Deo, M. C.; Latha, G.; Rajendran, V.

Operational activities in the ocean like planning for structural repairs or fishing expeditions require real time prediction of waves over typical time duration of say a few hours. Such predictions can be made by using a numerical model or a time series model employing continuously recorded waves. This paper presents another option to do so and it is based on a different time series approach in which the input is in the form of preceding wind speed and wind direction observations. This would be useful for those stations where the costly wave buoys are not deployed and instead only meteorological buoys measuring wind are moored. The technique employs alternative artificial intelligence approaches of an artificial neural network (ANN), genetic programming (GP) and model tree (MT) to carry out the time series modeling of wind to obtain waves. Wind observations at four offshore sites along the east coast of India were used. For calibration purpose the wave data was generated using a numerical model. The predicted waves obtained using the proposed time series models when compared with the numerically generated waves showed good resemblance in terms of the selected error criteria. Large differences across the chosen techniques of ANN, GP, MT were not noticed. Wave hindcasting at the same time step and the predictions over shorter lead times were better than the predictions over longer lead times. The proposed method is a cost effective and convenient option when a site-specific information is desired.

Analysis shear wave velocity structure obtained from surface wave methods in Bornova, Izmir

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

Pamuk, Eren, E-mail: eren.pamuk@deu.edu.tr; Akgün, Mustafa, E-mail: mustafa.akgun@deu.edu.tr; Özdağ, Özkan Cevdet, E-mail: cevdet.ozdag@deu.edu.tr

2016-04-18

Properties of the soil from the bedrock is necessary to describe accurately and reliably for the reduction of earthquake damage. Because seismic waves change their amplitude and frequency content owing to acoustic impedance difference between soil and bedrock. Firstly, shear wave velocity and depth information of layers on bedrock is needed to detect this changing. Shear wave velocity can be obtained using inversion of Rayleigh wave dispersion curves obtained from surface wave methods (MASW- the Multichannel Analysis of Surface Waves, ReMi-Refraction Microtremor, SPAC-Spatial Autocorrelation). While research depth is limeted in active source study, a passive source methods are utilized formore » deep depth which is not reached using active source methods. ReMi method is used to determine layer thickness and velocity up to 100 m using seismic refraction measurement systems.The research carried out up to desired depth depending on radius using SPAC which is utilized easily in conditions that district using of seismic studies in the city. Vs profiles which are required to calculate deformations in under static and dynamic loads can be obtained with high resolution using combining rayleigh wave dispersion curve obtained from active and passive source methods. In the this study, Surface waves data were collected using the measurements of MASW, ReMi and SPAC at the İzmir Bornova region. Dispersion curves obtained from surface wave methods were combined in wide frequency band and Vs-depth profiles were obtained using inversion. Reliability of the resulting soil profiles were provided by comparison with theoretical transfer function obtained from soil paremeters and observed soil transfer function from Nakamura technique and by examination of fitting between these functions. Vs values are changed between 200-830 m/s and engineering bedrock (Vs>760 m/s) depth is approximately 150 m.« less

The Major Stratospheric Sudden Warming of January 2013: Analyses and Forecasts in the GEOS-5 Data Assimilation System

NASA Technical Reports Server (NTRS)

Coy, Lawrence; Pawson, Steven

2014-01-01

We examine the major stratosphere sudden warming (SSW) that occurred on 6 January 2013, using output from the NASA Global Modeling and Assimilation Office (GMAO) GEOS-5 (Goddard Earth Observing System) near-real-time data assimilation system (DAS). Results show that the major SSW of January 2013 falls into the vortex splitting type of SSW, with the initial planetary wave breaking occurring near 10 hPa. The vertical flux of wave activity at the tropopause responsible for the SSW occurred mainly in the Pacific Hemisphere, including the a pulse associated with the preconditioning of the polar vortex by wave 1 identified on 23 December 2012. While most of the vertical wave activity flux was in the Pacific Hemisphere, a rapidly developing tropospheric weather system over the North Atlantic on 28 December is shown to have produced a strong transient upward wave activity flux into the lower stratosphere coinciding with the peak of the SSW event. In addition, the GEOS-5 5-day forecasts accurately predicted the major SSW of January 2013 as well as the upper tropospheric disturbances responsible for the warming. The overall success of the 5-day forecasts provides motivation to produce regular 10-day forecasts with GEOS-5, to better support studies of stratosphere-troposphere interaction.

Measurement of electromagnetic waves in ELF and VLF bands to monitor lightning activity in the Maritime Continent

NASA Astrophysics Data System (ADS)

Yamashita, Kozo; Takahashi, Yukihiro; Ohya, Hiroyo; Tsuchiya, Fuminori; Sato, Mitsuteru; Matsumoto, Jun

2013-04-01

Data of lightning discharge has been focused on as an effective way for monitoring and nowcasting of thunderstorm activity which causes extreme weather. Spatial distribution of lightning discharge has been used as a proxy of the presence or absence of deep convection. Latest observation shows that there is extremely huge lightning whose scale is more than hundreds times bigger than that of averaged event. This result indicates that lightning observation should be carried out to estimate not only existence but also scale for quantitative evaluation of atmospheric convection. In this study, lightning observation network in the Maritime Continent is introduced. This network is consisted of the sensors which make possible to measure electromagnetic wave radiated from lightning discharges. Observation frequency is 0.1 - 40 kHz for the measurement of magnetic field and 1 - 40 kHz for that of electric field. Sampling frequency is 100 kHz. Waveform of electromagnetic wave is recorded by personal computer. We have already constructed observation stations at Tainan in Taiwan (23.1N, 121.1E), Saraburi in Thailand (14.5N, 101.0E), and Pontianak in Indonesia (0.0N, 109.4E). Furthermore, we plan to install the monitoring system at Los Banos in Philippines (14.18, 121.25E) and Hanoi in Viet Nam. Data obtained by multipoint observation is synchronized by GPS receiver installed at each station. By using data obtained by this network, location and scale of lightning discharge can be estimated. Location of lightning is determined based on time of arrival method. Accuracy of geolocation could be less than 10km. Furthermore, charge moment is evaluated as a scale of each lightning discharge. It is calculated from electromagnetic waveform in ELF range (3-30 kHz). At the presentation, we will show the initial result about geolocation for source of electromagnetic wave and derivation of charge moment value based on the measurement of ELF and VLF sferics.

Unprecedentedly Strong and Narrow Electromagnetic Emissions Stimulated by High-Frequency Radio Waves in the Ionosphere

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

Norin, L.; Leyser, T. B.; Nordblad, E.

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere.

PubMed

Norin, L; Leyser, T B; Nordblad, E; Thidé, B; McCarrick, M

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Three-component ambient noise beamforming in the Parkfield area

NASA Astrophysics Data System (ADS)

Löer, Katrin; Riahi, Nima; Saenger, Erik H.

2018-06-01

We apply a three-component beamforming algorithm to an ambient noise data set recorded at a seismic array to extract information about both isotropic and anisotropic surface wave velocities. In particular, we test the sensitivity of the method with respect to the array geometry as well as to seasonal variations in the distribution of noise sources. In the earth's crust, anisotropy is typically caused by oriented faults or fractures and can be altered when earthquakes or human activities cause these structures to change. Monitoring anisotropy changes thus provides time-dependent information on subsurface processes, provided they can be distinguished from other effects. We analyse ambient noise data at frequencies between 0.08 and 0.52 Hz recorded at a three-component array in the Parkfield area, California (US), between 2001 November and 2002 April. During this time, no major earthquakes were identified in the area and structural changes are thus not expected. We compute dispersion curves of Love and Rayleigh waves and estimate anisotropy parameters for Love waves. For Rayleigh waves, the azimuthal source coverage is too limited to perform anisotropy analysis. For Love waves, ambient noise sources are more widely distributed and we observe significant and stable surface wave anisotropy for frequencies between 0.2 and 0.4 Hz. Synthetic data experiments indicate that the array geometry introduces apparent anisotropy, especially when waves from multiple sources arrive simultaneously at the array. Both the magnitude and the pattern of apparent anisotropy, however, differ significantly from the anisotropy observed in Love wave data. Temporal variations of anisotropy parameters observed at frequencies below 0.2 Hz and above 0.4 Hz correlate with changes in the source distribution. Frequencies between 0.2 and 0.4 Hz, however, are less affected by these variations and provide relatively stable results over the period of study.

Location of EMIC Wave Events Relative to the Plasmapause: Van Allen Probes Observations

NASA Astrophysics Data System (ADS)

Tetrick, S.; Engebretson, M. J.; Posch, J. L.; Kletzing, C.; Smith, C. W.; Wygant, J. R.; Gkioulidou, M.; Reeves, G. D.; Fennell, J. F.

2015-12-01

Many early theoretical studies of electromagnetic ion cyclotron (EMIC) waves generated in Earth's magnetosphere predicted that the equatorial plasmapause (PP) would be a preferred location for their generation. However, several large statistical studies in the past two decades, most notably Fraser and Nguyen [2001], have provided little support for this location. In this study we present a survey of the most intense EMIC waves observed by the EMFISIS fluxgate magnetometer on the Van Allen Probes-A spacecraft (with apogee at 5.9 RE) from its launch through the end of 2014, and have compared their location with simultaneous electron density data obtained by the EFW electric field instrument and ring current ion flux data obtained by the HOPE and RBSPICE instruments. We show distributions of these waves as a function of distance inside or outside the PP as a function of local time sector, frequency band (H+, He+, or both), and timing relative to magnetic storms and substorms. Most EMIC waves in this data set occurred within 1 RE of the PP in all local time sectors, but very few were limited to ± 0.1 RE, and most of these occurred in the 06-12 MLT sector during non-storm conditions. The majority of storm main phase waves in the dusk sector occurred inside the PP. He+ band waves dominated at most local times inside the PP, and H+ band waves were never observed there. Although the presence of elevated fluxes of ring current protons was common to all events, the configuration of lower energy ion populations varied as a function of geomagnetic activity and storm phase.

Latitudinally dependent Trimpi effects: Modeling and observations

NASA Astrophysics Data System (ADS)

Clilverd, Mark A.; Yeo, Richard F.; Nunn, David; Smith, Andy J.

1999-09-01

Modeling studies show that the exclusion of the propagating VLF wave from the ionospheric region results in the decline of Trimpi magnitude with patch altitude. In large models such as Long Wave Propagation Capability (LWPC) this exclusion does not occur inherently in the code, and high-altitude precipitation modeling can produce results that are not consistent with observations from ground-based experiments. The introduction to LWPC of realistic wave attenuation of the height gain functions in the ionosphere solves these computational problems. This work presents the first modeling of (Born) Trimpi scattering at long ranges, taking into account global inhomogeneities and continuous mode conversion along all paths, by employing the full conductivity perturbation matrix. The application of the more realistic height gain functions allows the prediction of decreasing Trimpi activity with increasing latitude, primarily through the mechanism of excluding the VLF wave from regions of high conductivity and scattering efficiency. Ground-based observations from Faraday and Rothera, Antarctica, in September and October 1995 of Trimpi occurring on the NPM (Hawaii) path provide data that are consistent with these predictions. Latitudinal variations in Trimpi occurrence near L=2.5, with a significant decrease of about 70% occurrence between L=2.4 and L=2.8, have been observed at higher L shell resolution than in previous studies (i.e., 2

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

DOE PAGES

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.; ...

2017-02-24

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

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

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Correlation between core ion energization, suprathermal electron bursts, and broadband ELF plasma waves

NASA Astrophysics Data System (ADS)

Knudsen, David J.; Clemmons, James H.; Wahlund, Jan-Erik

1998-03-01

Observations of the lowest energy or core ions provide a particularly sensitive measure of the early stages of auroral ion energization. Freja satellite observations of 0-20 eV core ions in the topside auroral ionosphere and cusp/cleft show signs of heating within both regions of VLF hiss and broadband ELF plasma waves. However, heating to several eV or more is associated predominantly with the ELF waves. A correlation analysis of wave and core ion data formed from orbital segments shows that, on average, correlations are highest for wave frequencies below several hundred Hz, and less at VLF hiss frequencies. A similar analysis shows a higher correlation between electron precipitation and ion heating for electron energies below several hundred eV (i.e., the energies associated with suprathermal electron bursts) and a lower correlation above the 1 keV energies associated with auroral inverted-V's. Signs of core ion heating begin to appear when wave power at the O+ gyrofrequency exceeds about 10-3(mVm-1)2/Hz, and when the integrated field-aligned electron flux exceeds a few times 107cm-2s-1sr-1. This electron energy flux threshold is at least an order of magnitude lower than previously inferred from earlier studies comparing suprathermal electron fluxes and energetic ions. Almost all observed heating events occur during enhanced or active geomagnetic conditions; i.e., Kp>=4. While the most intense core ion heating is correlated with broadband ELF waves, we also present one example of weak ion heating of a few eV in a region of VLF auroral hiss.

Electromagnetic Waves and Bursty Electron Acceleration: Implications from Freja

NASA Technical Reports Server (NTRS)

Andersson, Laila; Ivchenko, N.; Wahlund, J.-E.; Clemmons, J.; Gustavsson, B.; Eliasson, L.

2000-01-01

Dispersive Alfven wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about I keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). The broadband emissions are observed to become more electrostatic towards higher frequencies. Large-scale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E- and B-field fluctuations below 64 Hz (the dc instrument's upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energization of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvenic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfven waves set up these local field-aligned current regions and in turn trigger more electrostatic emissions during certain conditions. In these regions ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods.

Process Contributions to Cool Java SST Anomalies at the Onset of Positive Indian Ocean Dipole Events

NASA Astrophysics Data System (ADS)

Delman, A. S.; McClean, J.; Sprintall, J.; Talley, L. D.

2016-12-01

The seasonal upwelling region along the south coast of Java is the first area to exhibit the negative SST anomalies associated with positive Indian Ocean Dipole (pIOD) events. The seasonal cooling in austral winter is driven by local wind forcing; however, recent observational studies have suggested that the anomalous Java cooling that starts during May-July of pIOD years is driven largely by intraseasonal wind variability along the equator, which forces upwelling Kelvin waves that propagate to the coast of Java. Using observations and an eddy-active ocean GCM simulation, the impacts of local wind stress and remotely-forced Kelvin waves are assessed and compared to the effects of mesoscale eddies and outflows from nearby Lombok Strait. A Kelvin wave coefficient computed from altimetry data shows anomalous levels of upwelling Kelvin wave activity during May-July of all pIOD years, indicating that Kelvin waves are an important and perhaps necessary precondition for pIOD events. Correlation analyses also suggest that flows through Lombok Strait and winds along the Indonesian Throughflow may be influential, though their impacts are more difficult to isolate. Composite temperature budgets from the ocean GCM indicate that advection and diabatic vertical mixing are the primary mechanisms for anomalous mixed layer cooling south of Java. The advection term is further decomposed by linearly regressing model velocity and temperature anomalies onto indices representing each process. According to this process decomposition, the local wind stress and Kelvin waves together account for most of the anomalous advective cooling, though the anomalous cooling effect of local wind stress may be overestimated in the model due to wind and stratification biases. The process decomposition also shows a very modest warming effect from mesoscale eddies. These results demonstrate both the IOD's resemblance to ENSO in the importance of Kelvin waves for its evolution, and notable differences from ENSO that arise from the complex interplay of local winds, planetary waves, stratification, eddies, and topography in the Indonesian region.

Tsunamis generated by long and thin granular landslides in a large flume

NASA Astrophysics Data System (ADS)

Miller, Garrett S.; Andy Take, W.; Mulligan, Ryan P.; McDougall, Scott

2017-01-01

In this experimental study, granular material is released down slope to investigate landslide-generated waves. Starting with a known volume and initial position of the landslide source, detailed data are obtained on the velocity and thickness of the granular flow, the shape and location of the submarine landslide deposit, the amplitude and shape of the near-field wave, the far-field wave evolution, and the wave runup elevation on a smooth impermeable slope. The experiments are performed on a 6.7 m long 30° slope on which gravity accelerates the landslides into a 2.1 m wide and 33.0 m long wave flume that terminates with a 27° runup ramp. For a fixed landslide volume of 0.34 m3, tests are conducted in a range of still water depths from 0.05 to 0.50 m. Observations from high-speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material, and that only a portion of the landslide (termed the "effective mass") is engaged in activating the leading wave. The wave behavior is highly dependent on the water depth relative to the size of the landslide. In deeper water, the near-field wave behaves as a stable solitary-like wave, while in shallower water, the wave behaves as a breaking dissipative bore. Overall, the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near-field wave amplitude, the far-field amplitude, and the runup of tsunamis generated by granular landslides.

Characterization and diagnostic methods for geomagnetic auroral infrasound waves

NASA Astrophysics Data System (ADS)

Oldham, Justin J.

Infrasonic perturbations resulting from auroral activity have been observed since the 1950's. In the last decade advances in infrasonic microphone sensitivity, high latitude sensor coverage, time series analysis methods and computational efficiency have elucidated new types of auroral infrasound. Persistent periods of infrasonic activity associated with geomagnetic sub-storms have been termed geomagnetic auroral infrasound waves [GAIW]. We consider 63 GAIW events recorded by the Fairbanks, AK infrasonic array I53US ranging from 2003 to 2014 and encompassing a complete solar cycle. We make observations of the acoustic features of these events alongside magnetometer, riometer, and all-sky camera data in an effort to quantify the ionospheric conditions suitable for infrasound generation. We find that, on average, the generation mechanism for GAIW is confined to a region centered about ~60 0 longitude east of the anti-Sun-Earth line and at ~770 North latitude. We note furthermore that in all cases considered wherein imaging riometer data are available, that dynamic regions of heightened ionospheric conductivity periodically cross the overhead zenith. Consistent features in concurrent magnetometer conditions are also noted, with irregular oscillations in the horizontal component of the field ubiquitous in all cases. In an effort to produce ionosphere based infrasound free from the clutter and unknowns typical of geophysical observations, an experiment was undertaken at the High Frequency Active Auroral Research Program [HAARP] facility in 2012. Infrasonic signals appearing to originate from a source region overhead were observed briefly on 9 August 2012. The signals were observed during a period when an electrojet current was presumed to have passed overhead and while the facilities radio transmitter was periodically heating the lower ionosphere. Our results suggest dynamic auroral electrojet currents as primary sources of much of the observed infrasound, with modulation of the electrojets due to energetic particle precipitation, dispersion due to coupling with gravity waves, and reflection and refraction effects in the intervening atmosphere all potential factors in the shaping of the waveforms observed.

Sheaths: A Comparison of Magnetospheric, ICME, and Heliospheric Sheaths

NASA Technical Reports Server (NTRS)

Sibeck, D. G.; Richardson, J. D.; Liu, W.

2007-01-01

When a supersonic flow encounters an obstacles, shocks form to divert the flow around the obstacle. The region between the shock and the obstacle is the sheath, where the supersonic flow is compressed, heated, decelerated, and deflected. Supersonic flows, obstacles, and thus sheaths are observed on many scales throughout the Universe. We compare three examples seen in the heliosphere, illustrating the interaction of the solar wind with obstacles of three very different scales lengths. Magnetosheaths form behind planetary bow shocks on scales ranging from tens to 100 planetary radii. ICME sheath form behind shocks driven by solar disturbances on scale lengths of a few to tens of AU. The heliosheath forms behind the termination shock due to the obstacle presented by the interstellar medium on scale lengths of tens to a hundred AU. Despite this range in scales some common features have been observed. Magnetic holes, possibly due to mirror mode waves, have been observed in all three of these sheaths. Plasma depletion layers are observed in planetary and ICME sheaths. Other features observed in some sheaths are wave activity (ion cyclotron, plasma), energetic particles, transmission of Alfven waves/shocks, tangential discontinuities turbulence behind quasi-parallel shocks, standing slow mode waves, and reconnection on the obstacle boundary. We compare these sheath regions, discussing similarities and differences and how these may relate to the scale lengths of these regions.

Ethanol enhances carbachol-induced protease activation and accelerates Ca2+ waves in isolated rat pancreatic acini.

PubMed

Orabi, Abrahim I; Shah, Ahsan U; Muili, Kamaldeen; Luo, Yuhuan; Mahmood, Syeda Maham; Ahmad, Asim; Reed, Anamika; Husain, Sohail Z

2011-04-22

Alcohol abuse is a leading cause of pancreatitis, accounting for 30% of acute cases and 70-90% of chronic cases, yet the mechanisms leading to alcohol-associated pancreatic injury are unclear. An early and critical feature of pancreatitis is the aberrant signaling of Ca(2+) within the pancreatic acinar cell. An important conductor of this Ca(2+) is the basolaterally localized, intracellular Ca(2+) channel ryanodine receptor (RYR). In this study, we examined the effect of ethanol on mediating both pathologic intra-acinar protease activation, a precursor to pancreatitis, as well as RYR Ca(2+) signals. We hypothesized that ethanol sensitizes the acinar cell to protease activation by modulating RYR Ca(2+). Acinar cells were freshly isolated from rat, pretreated with ethanol, and stimulated with the muscarinic agonist carbachol (1 μM). Ethanol caused a doubling in the carbachol-induced activation of the proteases trypsin and chymotrypsin (p < 0.02). The RYR inhibitor dantrolene abrogated the enhancement of trypsin and chymotrypsin activity by ethanol (p < 0.005 for both proteases). Further, ethanol accelerated the speed of the apical to basolateral Ca(2+) wave from 9 to 18 μm/s (p < 0.0005; n = 18-22 cells/group); an increase in Ca(2+) wave speed was also observed with a change from physiologic concentrations of carbachol (1 μM) to a supraphysiologic concentration (1 mM) that leads to protease activation. Dantrolene abrogated the ethanol-induced acceleration of wave speed (p < 0.05; n = 10-16 cells/group). Our results suggest that the enhancement of pathologic protease activation by ethanol is dependent on the RYR and that a novel mechanism for this enhancement may involve RYR-mediated acceleration of Ca(2+) waves.

Ethanol Enhances Carbachol-induced Protease Activation and Accelerates Ca2+ Waves in Isolated Rat Pancreatic Acini*

PubMed Central

Orabi, Abrahim I.; Shah, Ahsan U.; Muili, Kamaldeen; Luo, Yuhuan; Mahmood, Syeda Maham; Ahmad, Asim; Reed, Anamika; Husain, Sohail Z.

2011-01-01

Alcohol abuse is a leading cause of pancreatitis, accounting for 30% of acute cases and 70–90% of chronic cases, yet the mechanisms leading to alcohol-associated pancreatic injury are unclear. An early and critical feature of pancreatitis is the aberrant signaling of Ca2+ within the pancreatic acinar cell. An important conductor of this Ca2+ is the basolaterally localized, intracellular Ca2+ channel ryanodine receptor (RYR). In this study, we examined the effect of ethanol on mediating both pathologic intra-acinar protease activation, a precursor to pancreatitis, as well as RYR Ca2+ signals. We hypothesized that ethanol sensitizes the acinar cell to protease activation by modulating RYR Ca2+. Acinar cells were freshly isolated from rat, pretreated with ethanol, and stimulated with the muscarinic agonist carbachol (1 μm). Ethanol caused a doubling in the carbachol-induced activation of the proteases trypsin and chymotrypsin (p < 0.02). The RYR inhibitor dantrolene abrogated the enhancement of trypsin and chymotrypsin activity by ethanol (p < 0.005 for both proteases). Further, ethanol accelerated the speed of the apical to basolateral Ca2+ wave from 9 to 18 μm/s (p < 0.0005; n = 18–22 cells/group); an increase in Ca2+ wave speed was also observed with a change from physiologic concentrations of carbachol (1 μm) to a supraphysiologic concentration (1 mm) that leads to protease activation. Dantrolene abrogated the ethanol-induced acceleration of wave speed (p < 0.05; n = 10–16 cells/group). Our results suggest that the enhancement of pathologic protease activation by ethanol is dependent on the RYR and that a novel mechanism for this enhancement may involve RYR-mediated acceleration of Ca2+ waves. PMID:21372126

Modelling the descent of nitric oxide during the elevated stratopause event of January 2013

NASA Astrophysics Data System (ADS)

Orsolini, Yvan J.; Limpasuvan, Varavut; Pérot, Kristell; Espy, Patrick; Hibbins, Robert; Lossow, Stefan; Raaholt Larsson, Katarina; Murtagh, Donal

2017-03-01

Using simulations with a whole-atmosphere chemistry-climate model nudged by meteorological analyses, global satellite observations of nitrogen oxide (NO) and water vapour by the Sub-Millimetre Radiometer instrument (SMR), of temperature by the Microwave Limb Sounder (MLS), as well as local radar observations, this study examines the recent major stratospheric sudden warming accompanied by an elevated stratopause event (ESE) that occurred in January 2013. We examine dynamical processes during the ESE, including the role of planetary wave, gravity wave and tidal forcing on the initiation of the descent in the mesosphere-lower thermosphere (MLT) and its continuation throughout the mesosphere and stratosphere, as well as the impact of model eddy diffusion. We analyse the transport of NO and find the model underestimates the large descent of NO compared to SMR observations. We demonstrate that the discrepancy arises abruptly in the MLT region at a time when the resolved wave forcing and the planetary wave activity increase, just before the elevated stratopause reforms. The discrepancy persists despite doubling the model eddy diffusion. While the simulations reproduce an enhancement of the semi-diurnal tide following the onset of the 2013 SSW, corroborating new meteor radar observations at high northern latitudes over Trondheim (63.4°N), the modelled tidal contribution to the forcing of the mean meridional circulation and to the descent is a small portion of the resolved wave forcing, and lags it by about ten days.

Detection of a strongly negative surface potential at Saturn's moon Hyperion.

PubMed

Nordheim, T A; Jones, G H; Roussos, E; Leisner, J S; Coates, A J; Kurth, W S; Khurana, K K; Krupp, N; Dougherty, M K; Waite, J H

2014-10-28

On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn's small, irregularly shaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS), part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating from the direction of the moon's surface. Plasma wave activity detected by the Radio and Plasma Wave instrument suggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and the Magnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that the moon and the spacecraft were magnetically connected when the field-aligned electron population was observed. We show that this constitutes a remote detection of a strongly negative (∼ -200 V) surface potential on Hyperion, consistent with the predicted surface potential in regions near the solar terminator.

Gravity waves, Tides and Planetary wave characteristics revealed by network of MLT radars over Indian region

NASA Astrophysics Data System (ADS)

Venkat Ratnam, Madineni; Karanam, Kishore Kumar; Sunkara, Eswaraiah; Vijaya Bhaskara Rao, S.; Subrahmanyam, K. V.; Ramanjaneyulu, L.

2016-07-01

Mesosphere and Lower Thermosphere (MLT) mean winds, gravity waves, tidal and planetary wave characteristics are investigated using two years (2013-2015) of advanced meteor radar installed at Tirupathi (13.63oN, 79.4oE), India. The observations reveal the presence of high frequency gravity waves (30-120 minutes), atmospheric tides (diurnal, semi-diurnal and terr-diurnal) along with long period oscillations in both zonal and meridional winds. Background mean zonal winds show clear semi-annual oscillation in the mesosphere, whereas meridional winds are characterized by annual oscillation as expected. Diurnal tide amplitudes are significantly larger (60-80 m/s) than semi-diurnal (10-20 m/s) and terr-diurnal (5-8 m/s) tides and larger in meridional than zonal winds. The measured meridional components are in good agreement with Global Scale Wave Model (GSWM-09) predictions than zonal up to ~90 km in all the seasons, except fall equinox. Diurnal tidal phase matches well than the amplitudes between observations and model predictions. However, no similarity is being found in the semi-diurnal tides between observations and model. The measurements are further compared with nearby Thumba meteor radar (8.5oN, 77oE) observations. Some differences do exist between the measurements from Tirupati and Thumba meteor radar and model outputs at greater heights and the possible reasons are discussed. SVU meteor radar observations clearly showed the dominance of well-known ultra-fast kelvin waves (3.5 days), 5-8 day, 16 day, 27 day, and 30-40 day oscillations. Due to higher meteor count extending up to 110 km, we could investigate the variability of these PWs and oscillations covering wider range (70-110 km) for the first time. Significant change above 100 km is noticed in all the above mentioned PW activity and oscillations. We also used ERA-Interim reanalysis data sets available at 0.125x0.125 degree grids for investigating the characteristics of these PW right from surface to 1 hPa. The presence of these waves and oscillations right from upper troposphere to lower thermosphere simultaneously is noticed. Though these waves are expected to have higher wave number (higher horizontal wave lengths) few important differences are noticed between Tirupati and Thumba, that are separated by only 500 km. The implication of these waves and oscillations on the background atmosphere and vice versa are discussed. Thus, installation of SVU meteor radar made good complementary observations that can be effectively used to investigate vertical and lateral coupling. Role of these tides in modulating the mesopause altitude is further investigated using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on-board Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite. It is found that mesopause altitude is always close to 100 km and is strongly affected by gravity waves, tides and planetary waves.

Tidal-Induced Internal Ocean Waves as an Explanation for Enceladus' Tiger Stripe Pattern and Hotspot Activity

NASA Astrophysics Data System (ADS)

Vermeersen, B. L. A.; Maas, L. R.; van Oers, S.; Rabitti, A.; Jara-Orue, H.

2014-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. Indeed, later Cassini observations have shown that salty water jets originate from the tiger stripes [e.g., Hansen et al., Science, 311, 1422-1425, 2006; Postberg et al., Nature, 474, 620-622, 2011]. More recently, Porco et al. [Astron. J., 148:45, Sep. 2014] and Nimmo et al. [Astron. J., 148:46, Sep. 2014] have reported strong evidence that the geysers are not caused by frictional heating at the surface, but that geysers must originate deeper in Enceladus' interior. Tidal flexing models, like those of Hurford et al., Nature, 447, 292-294, 2007, give a good match for the brightness variations Cassini observes, but they seem to fail to reproduce the exact timing of plume brightening. Although jet activity is thus strongly connected to tidal forcing, another mechanism must be involved as well. Last year, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. The latest observations by Porco et al. and Nimmo et al. seem to be in agreement with this tidal-induced wave attractor phenomenon, both with respect to tiger stripe pattern and with respect to timing of hotspot activity. However, in contrast to the thin ocean/thick ice sheet model as anticipated in Fig. 12 of Porco et al. (2014), our lab experiments suggest that attractors are generated most efficiently at aspect ratio O(1), implying that distance between stripes might actually approximately directly represent local ocean depth in a thin ice sheet/thick ocean setting.

Wave Height and Water Level Variability on Lakes Michigan and St Clair

DTIC Science & Technology

2012-10-01

Observations: http://www.ssec.wisc.edu/sose/glwx_activity.html 4. NASA Atlas of Extratropical Storm Tracks: http://data.giss.nasa.gov/stormtracks...term meteorological, ice, wave, and water level measurements. 15. SUBJECT TERMS Base flood elevation Coastal flood Extratropical storms Great...Box 1027 Detroit, MI 48231-1027 ERDC/CHL TR-12-23 ii Abstract The Great Lakes are subject to coastal flooding as a result of severe storms

Understanding Rossby wave trains forced by the Indian Ocean Dipole

NASA Astrophysics Data System (ADS)

McIntosh, Peter C.; Hendon, Harry H.

2018-04-01

Convective variations over the tropical Indian Ocean associated with ENSO and the Indian Ocean Dipole force a Rossby wave train that appears to emanate poleward and eastward to the south of Australia and which causes climate variations across southern Australia and more generally throughout the Southern Hemisphere extratropics. However, during austral winter, the subtropical jet that extends from the eastern Indian Ocean into the western Pacific at Australian latitudes should effectively prohibit continuous propagation of a stationary Rossby wave from the tropics into the extratropics because the meridional gradient of mean absolute vorticity goes to zero on its poleward flank. The observed wave train indeed exhibits strong convergence of wave activity flux upon encountering this region of vanishing vorticity gradient and with some indication of reflection back into the tropics, indicating the continuous propagation of the stationary Rossby wave train from low to high latitudes is inhibited across the south of Australia. However, another Rossby wave train appears to emanate upstream of Australia on the poleward side of the subtropical jet and propagates eastward along the waveguide of the eddy-driven (sub-polar) jet into the Pacific sector of the Southern Ocean. This combination of evanescent wave train from the tropics and eastward propagating wave train emanating from higher latitudes upstream of Australia gives the appearance of a continuous Rossby wave train propagating from the tropical Indian Ocean into higher southern latitudes. The extratropical Rossby wave source on the poleward side of the subtropical jet stems from induced changes in transient eddy activity in the main storm track of the Southern Hemisphere. During austral spring, when the subtropical jet weakens, the Rossby wave train emanating from Indian Ocean convection is explained more traditionally by direct dispersion from divergence forcing at low latitudes.

Infrasounds and biorhythms of the human brain

NASA Astrophysics Data System (ADS)

Panuszka, Ryszard; Damijan, Zbigniew; Kasprzak, Cezary; McGlothlin, James

2002-05-01

Low Frequency Noise (LFN) and infrasound has begun a new public health hazard. Evaluations of annoyance of (LFN) on human occupational health were based on standards where reactions of human auditory system and vibrations of parts of human body were small. Significant sensitivity has been observed on the central nervous system from infrasonic waves especially below 10 Hz. Observed follow-up effects in the brain gives incentive to study the relationship between parameters of waves and reactions obtained of biorhythms (EEG) and heart action (EKG). New results show the impact of LFN on the electrical potentials of the brain are dependent on the pressure waves on the human body. Electrical activity of circulatory system was also affected. Signals recorded in industrial workplaces were duplicated by loudspeakers and used to record data from a typical LFN spectra with 5 and 7 Hz in a laboratory chamber. External noise, electromagnetic fields, temperature, dust, and other elements were controlled. Results show not only a follow-up effect in the brain but also a result similar to arrhythmia in the heart. Relaxations effects were observed of people impacted by waves generated from natural sources such as streams and waterfalls.

Wind structure and small-scale wind variability in the stratosphere and mesosphere during the November 1980 Energy Budget Campaign

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Carlson, M.; Rees, D.; Offermann, D.; Philbrick, C. R.; Widdel, H. U.

1982-01-01

Rocket observations made from two sites in northern Scandinavia between November 6 and December 1, 1980, as part of the Energy Budget Campaign are discussed. It was found that significant vertical and temporal changes in the wind structure were present and that they coincided with different geomagnetic conditions, that is, quiet and enhanced. Before November 16, the meridional wind component above 60 km was found to be positive (southerly), whereas the magnitude of the zonal wind component increased with altitude. After November 16 the meridional component became negative (northerly), and the magnitude of the zonal wind component was observed to decrease with altitude. Time sections of the perturbations of the zonal wind reveal the presence of vertically propagating waves, suggesting gravity wave activity. The waves are found to increase in wavelength from 3-4 km near 40 km to more than 12 km near 80 km. The observational techniques made use of chaff foil, chemical trails, inflatable spheres, and parachutes.

Differences and Similarities in MaCWAVE Summer and Winter Temperatures and Winds

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Goldberg, R. A.

2008-01-01

Small meteorological rockets released inflatable falling spheres during the MaCWAVE Campaign. The Mountain and Convective Waves Ascending Vertically Experiment (MaCWAVE) was carried out in two parts, a summer sequence from Andoya Rocket Range (69N) during July 2002 to examine convective initiation of gravity waves and a winter sequence from ESRANGE (68N) during January 2003 to examine mountain-terrain initiated gravity waves. The sphere-tracked data provided significant information about the variation of temperature and wind from 70 km and above. The changes observed may be considered akin to tidal motion; unfortunately the launch activity was restricted to 12-hour periods, thus the observation of a full diurnal cycle was not possible. During summer, temperature variation was smaller than that observed during winter when peak to null differences reached 15-20 K at 80-85 km. Variation in the zonal winds varied up to 100+mps in summer and winter. Examination of the times of peak wind vs altitude showed that the peak zonal wind occurred approximately two hours ahead of the peak meridional wind. We provide details about the measurements and observed variations.

Planetary plasma waves

NASA Technical Reports Server (NTRS)

Gurnett, Donald A.

1993-01-01

The primary types of plasma waves observed in the vicinity of the planets Venus, Mars, Earth, Jupiter, Saturn, Uranus, and Neptune are described. The observations are organized according to the various types of plasma waves observed, ordered according to decreasing distance from the planet, starting from the sunward side of the planet, and ending in the region near the closest approach. The plasma waves observed include: electron plasma oscillations and ion acoustic waves; trapped continuum radiation; electron cyclotron and upper hybrid waves; whistler-mode emissions; electrostatic ion cyclotron waves; and electromagnetic ion cyclotron waves.

Spatiotemporal characterization of mTOR kinase activity following kainic acid induced status epilepticus and analysis of rat brain response to chronic rapamycin treatment.

PubMed

Macias, Matylda; Blazejczyk, Magdalena; Kazmierska, Paulina; Caban, Bartosz; Skalecka, Agnieszka; Tarkowski, Bartosz; Rodo, Anna; Konopacki, Jan; Jaworski, Jacek

2013-01-01

Mammalian target of rapamycin (mTOR) is a protein kinase that senses nutrient availability, trophic factors support, cellular energy level, cellular stress, and neurotransmitters and adjusts cellular metabolism accordingly. Adequate mTOR activity is needed for development as well as proper physiology of mature neurons. Consequently, changes in mTOR activity are often observed in neuropathology. Recently, several groups reported that seizures increase mammalian target of rapamycin (mTOR) kinase activity, and such increased activity in genetic models can contribute to spontaneous seizures. However, the current knowledge about the spatiotemporal pattern of mTOR activation induced by proconvulsive agents is rather rudimentary. Also consequences of insufficient mTOR activity on a status epilepticus are poorly understood. Here, we systematically investigated these two issues. We showed that mTOR signaling was activated by kainic acid (KA)-induced status epilepticus through several brain areas, including the hippocampus and cortex as well as revealed two waves of mTOR activation: an early wave (2 h) that occurs in neurons and a late wave that predominantly occurs in astrocytes. Unexpectedly, we found that pretreatment with rapamycin, a potent mTOR inhibitor, gradually (i) sensitized animals to KA treatment and (ii) induced gross anatomical changes in the brain.

Spatiotemporal Characterization of mTOR Kinase Activity Following Kainic Acid Induced Status Epilepticus and Analysis of Rat Brain Response to Chronic Rapamycin Treatment

PubMed Central

Macias, Matylda; Blazejczyk, Magdalena; Kazmierska, Paulina; Caban, Bartosz; Skalecka, Agnieszka; Tarkowski, Bartosz; Rodo, Anna; Konopacki, Jan; Jaworski, Jacek

2013-01-01

Mammalian target of rapamycin (mTOR) is a protein kinase that senses nutrient availability, trophic factors support, cellular energy level, cellular stress, and neurotransmitters and adjusts cellular metabolism accordingly. Adequate mTOR activity is needed for development as well as proper physiology of mature neurons. Consequently, changes in mTOR activity are often observed in neuropathology. Recently, several groups reported that seizures increase mammalian target of rapamycin (mTOR) kinase activity, and such increased activity in genetic models can contribute to spontaneous seizures. However, the current knowledge about the spatiotemporal pattern of mTOR activation induced by proconvulsive agents is rather rudimentary. Also consequences of insufficient mTOR activity on a status epilepticus are poorly understood. Here, we systematically investigated these two issues. We showed that mTOR signaling was activated by kainic acid (KA)-induced status epilepticus through several brain areas, including the hippocampus and cortex as well as revealed two waves of mTOR activation: an early wave (2 h) that occurs in neurons and a late wave that predominantly occurs in astrocytes. Unexpectedly, we found that pretreatment with rapamycin, a potent mTOR inhibitor, gradually (i) sensitized animals to KA treatment and (ii) induced gross anatomical changes in the brain. PMID:23724051

Sub-seasonal temperature variability in the tropical upper troposphere and lower stratosphere observed with GPS radio occultation

NASA Astrophysics Data System (ADS)

Scherllin-Pirscher, Barbara; Randel, William J.; Kim, Joowan

2017-04-01

We investigate sub-seasonal temperature variability in the tropical upper troposphere and lower stratosphere (UTLS) region using daily gridded fields of GPS radio occultation measurements. The unprecedented vertical resolution (from about 100 m in the troposphere to about 1.5 km in the stratosphere) and high accuracy and precision (0.7 K to 1 K between 8 km and 25 km) make these data ideal for characterizing temperature oscillations with short vertical wavelengths. Long-term behavior of sub-seasonal temperature variability is investigated using the entire RO record from January 2002 to December 2014 (13 years of data). Transient sub-seasonal waves including eastward-propagating Kelvin waves (isolated with space-time spectral analysis) dominate large-scale zonal temperature variability in the tropical tropopause region and in the lower stratosphere. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO). Enhanced wave activity can be found during the westerly shear phase of the QBO. In the tropical tropopause region, however, sub-seasonal waves are highly transient in time. Several peaks of Kelvin-wave activity coincide with short-term fluctuations in tropospheric deep convection, but other episodes are not evidently related. Also, there are no obvious relationships with zonal winds or stability fields near the tropical tropopause. Further investigations of convective forcing and atmospheric background conditions along the waves' trajectories are needed to better understand sub-seasonal temperature variability near the tropopause. For more details, see Scherllin-Pirscher, B., Randel, W. J., and Kim, J.: Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements, Atmos. Chem. Phys., 17, 793-806, doi:10.5194/acp-17-793-2017, 2017. http://www.atmos-chem-phys.net/17/793/2017/acp-17-793-2017.html

Observations of the upper troposphere and lower stratosphere using the urbana coherent-scatter radar

NASA Technical Reports Server (NTRS)

Goss, L. D.; Bowhill, S. A.

1983-01-01

The Urbana coherent-scatter radar was used to observe the upper troposphere and lower stratosphere, and 134 hours of data were collected. Horizontal wind measurements show good agreement with balloon-measured winds. Gravity waves were frequently observed, and were enhanced during convective activity. Updrafts and downdrafts were observed within thunderstorms. Power returns are related to hydrostatic stability, and changes in echo specularity are shown.

ELF waves and ion resonances produced by an electron beam emitting rocket in the ionosphere

NASA Technical Reports Server (NTRS)

Winckler, J. R.; Abe, Y.; Erickson, K. N.

1986-01-01

Results are reported from the ECHO-6 electron-beam-injection experiment, performed in the auroral-zone ionosphere on March 30, 1983 using a sounding rocket equipped with two electron guns and a free-flying plasma-diagnostics instrument package. The data are presented in extensive graphs and diagrams and characterized in detail. Large ELF wave variations, superposed on the strong beam-sector-directed quasi-dc component, are observed in the 100-eV beam-induced plasma when the beam is injected in a transverse spiral, but not when it is injected upward parallel to the magnetic-field line. ELF activity is found to be suppressed whenever the rocket passed through field lines with auroral activity, suggesting that the waves are produced by the interaction of the beam potentials, plasma currents, and return currents neutralizing the accelerator payload.

Charcateristics of Plasma Waves Excited During Gas Release and Plasma Injection Into The Ionosphere

NASA Astrophysics Data System (ADS)

Klos, Z.; Gdalevich, G. L.; Mikhailov, I.

Waves in broad frequency range are generated during the injection of fast plasma as well as release of neutral gas into ionosphere from the spacecraft. The excited wave modes depend on the environmental plasma parameters, geometry of injection as well as on the rate of ionisation of plasma in the stream. The neutral xenon gas was released from the board of the ACTIVE satellite (in 1989) and parallel with the release process the VLF as well as HF waves were diagnosed. On the other hand the xenon plasma from gun generator was injected into the ionosphere from the board of APEX satellite (in 1991) and also broad frequency range of emission was registered. In the present paper are compared the plasma waves characteristics observed in these two types of experiments.

Propagation characteristics of Pc 3 compressional waves generated at the dayside magnetopause

NASA Technical Reports Server (NTRS)

Zhang, X.; Comfort, R. H.; Musielak, Z. E.; Moore, T. E.; Gallagher, D. L.; Green, J. L.

1993-01-01

New, 3D ray tracing of Pc 3 compressional waves from the magnetosheath reveals that the magnetosphere can present a major propagation barrier to the penetration of these waves to the plasmasphere. This barrier is the ion-ion cutoff between the He(+) and O(+) gyroresonances. As a result of the frequency-dependent location of this cutoff, the magnetosphere behaves like a filter for Pc 3 compressional waves, and only low-frequency components of Pc 3 compressional waves can penetrate to inner magnetosphere. Results are in agreement with previous satellite observations. This 'filter action' strongly depends on the relative concentration of He(+) and O(+) and is therefore sensitive to solar and magnetic activity. Ray-tracing results are based on a cold plasma dispersion relation, a semiempirical model of plasma density, and the Mead-Fairfield (1975) magnetic field model.

The Grand Banks ERS-1 SAR wave spectra validation experiment

NASA Technical Reports Server (NTRS)

Vachon, P. W.; Dobson, F. W.; Smith, S. D.; Anderson, R. J.; Buckley, J. R.; Allingham, M.; Vandemark, D.; Walsh, E. J.; Khandekar, M.; Lalbeharry, R.

1993-01-01

As part of the ERS-1 validation program, the ERS-1 Synthetic Aperture Radar (SAR) wave spectra validation experiment was carried out over the Grand Banks of Newfoundland (Canada) in Nov. 1991. The principal objective of the experiment was to obtain complete sets of wind and wave data from a variety of calibrated instruments to validate SAR measurements of ocean wave spectra. The field program activities are described and the rather complex wind and wave conditions which were observed are summarized. Spectral comparisons with ERS-1 SAR image spectra are provided. The ERS-1 SAR is shown to have measured swell and range traveling wind seas, but did not measure azimuth traveling wind seas at any time during the experiment. Results of velocity bunching forward mapping and new measurements of the relationship between wind stress and sea state are also shown.

Large-scale dynamics of the stratosphere and mesosphere during the MAP/WINE campaign winter 1983 to 1984 in comparison with other winters

NASA Technical Reports Server (NTRS)

Petzoldt, K.

1989-01-01

For the MAP/WINE winter temperature and wind measurements of rockets were combined with SSU radiances (Stratospheric Sounder Unit onboard the NOAA satellites) and stratopause heights from the Solar Mesosphere Explorer (SME) to get a retrieved data set including all available information. By means of this data set a hemispheric geopotential height, temperature and geostrophic wind fields eddy transports for wave mean flow interaction and potential vorticity for the interpretation of nonlinear wave breaking could be computed. Wave reflection at critical lines was investigated with respect of stratospheric warmings. The meridional gradient of the potential vorticity and focusing of wave activity is compared with derived data from satellite observations during other winters.

Synaptically activated Ca2+ waves in layer 2/3 and layer 5 rat neocortical pyramidal neurons

PubMed Central

Larkum, Matthew E; Watanabe, Shigeo; Nakamura, Takeshi; Lasser-Ross, Nechama; Ross, William N

2003-01-01

Calcium waves in layer 2/3 and layer 5 neocortical somatosensory pyramidal neurons were examined in slices from 2- to 8-week-old rats. Repetitive synaptic stimulation evoked a delayed, all-or-none [Ca2+]i increase primarily on the main dendritic shaft. This component was blocked by 1 mm (R,S)-α-methyl-4-carboxyphenylglycine (MCPG), 10 μm ryanodine, 1 mg ml−1 internal heparin, and was not blocked by 400 μm internal Ruthenium Red, indicating that it was due to Ca2+ release from internal stores by inositol 1,4,5-trisphosphate (IP3) mobilized via activation of metabotropic glutamate receptors. Calcium waves were initiated on the apical shaft at sites between the soma to around the main branch point, mostly at insertion points of oblique dendrites, and spread in both directions along the shaft. In the proximal dendrites the peak amplitude of the resulting [Ca2+]i change was much larger than that evoked by a train of Na+ spikes. In distal dendrites the peak amplitude was comparable to the [Ca2+]i change due to a Ca2+ spike. IP3-mediated Ca2+ release also was observed in the presence of the metabotropic agonists t-ACPD and carbachol when backpropagating spikes were generated. Ca2+ entry through NMDA receptors was observed primarily on the oblique dendrites. The main differences between waves in neocortical neurons and in previously described hippocampal pyramidal neurons were, (a) Ca2+ waves in L5 neurons could be evoked further out along the main shaft, (b) Ca2+ waves extended slightly further out into the oblique dendrites and (c) higher concentrations of bath-applied t-ACPD and carbachol were required to generate Ca2+ release events by backpropagating action potentials. PMID:12692172

Wave front sensing for next generation earth observation telescope

NASA Astrophysics Data System (ADS)

Delvit, J.-M.; Thiebaut, C.; Latry, C.; Blanchet, G.

2017-09-01

High resolution observations systems are highly dependent on optics quality and are usually designed to be nearly diffraction limited. Such a performance allows to set a Nyquist frequency closer to the cut off frequency, or equivalently to minimize the pupil diameter for a given ground sampling distance target. Up to now, defocus is the only aberration that is allowed to evolve slowly and that may be inflight corrected, using an open loop correction based upon ground estimation and refocusing command upload. For instance, Pleiades satellites defocus is assessed from star acquisitions and refocusing is done with a thermal actuation of the M2 mirror. Next generation systems under study at CNES should include active optics in order to allow evolving aberrations not only limited to defocus, due for instance to in orbit thermal variable conditions. Active optics relies on aberration estimations through an onboard Wave Front Sensor (WFS). One option is using a Shack Hartmann. The Shack-Hartmann wave-front sensor could be used on extended scenes (unknown landscapes). A wave-front computation algorithm should then be implemented on-board the satellite to provide the control loop wave-front error measure. In the worst case scenario, this measure should be computed before each image acquisition. A robust and fast shift estimation algorithm between Shack-Hartmann images is then needed to fulfill this last requirement. A fast gradient-based algorithm using optical flows with a Lucas-Kanade method has been studied and implemented on an electronic device developed by CNES. Measurement accuracy depends on the Wave Front Error (WFE), the landscape frequency content, the number of searched aberrations, the a priori knowledge of high order aberrations and the characteristics of the sensor. CNES has realized a full scale sensitivity analysis on the whole parameter set with our internally developed algorithm.

Propagating Neural Source Revealed by Doppler Shift of Population Spiking Frequency

PubMed Central

Zhang, Mingming; Shivacharan, Rajat S.; Chiang, Chia-Chu; Gonzalez-Reyes, Luis E.

2016-01-01

Electrical activity in the brain during normal and abnormal function is associated with propagating waves of various speeds and directions. It is unclear how both fast and slow traveling waves with sometime opposite directions can coexist in the same neural tissue. By recording population spikes simultaneously throughout the unfolded rodent hippocampus with a penetrating microelectrode array, we have shown that fast and slow waves are causally related, so a slowly moving neural source generates fast-propagating waves at ∼0.12 m/s. The source of the fast population spikes is limited in space and moving at ∼0.016 m/s based on both direct and Doppler measurements among 36 different spiking trains among eight different hippocampi. The fact that the source is itself moving can account for the surprising direction reversal of the wave. Therefore, these results indicate that a small neural focus can move and that this phenomenon could explain the apparent wave reflection at tissue edges or multiple foci observed at different locations in neural tissue. SIGNIFICANCE STATEMENT The use of novel techniques with an unfolded hippocampus and penetrating microelectrode array to record and analyze neural activity has revealed the existence of a source of neural signals that propagates throughout the hippocampus. The source itself is electrically silent, but its location can be inferred by building isochrone maps of population spikes that the source generates. The movement of the source can also be tracked by observing the Doppler frequency shift of these spikes. These results have general implications for how neural signals are generated and propagated in the hippocampus; moreover, they have important implications for the understanding of seizure generation and foci localization. PMID:27013678

Synconset Waves and Chains: Spiking Onsets in Synchronous Populations Predict and Are Predicted by Network Structure

PubMed Central

Raghavan, Mohan; Amrutur, Bharadwaj; Narayanan, Rishikesh; Sikdar, Sujit Kumar

2013-01-01

Synfire waves are propagating spike packets in synfire chains, which are feedforward chains embedded in random networks. Although synfire waves have proved to be effective quantification for network activity with clear relations to network structure, their utilities are largely limited to feedforward networks with low background activity. To overcome these shortcomings, we describe a novel generalisation of synfire waves, and define ‘synconset wave’ as a cascade of first spikes within a synchronisation event. Synconset waves would occur in ‘synconset chains’, which are feedforward chains embedded in possibly heavily recurrent networks with heavy background activity. We probed the utility of synconset waves using simulation of single compartment neuron network models with biophysically realistic conductances, and demonstrated that the spread of synconset waves directly follows from the network connectivity matrix and is modulated by top-down inputs and the resultant oscillations. Such synconset profiles lend intuitive insights into network organisation in terms of connection probabilities between various network regions rather than an adjacency matrix. To test this intuition, we develop a Bayesian likelihood function that quantifies the probability that an observed synfire wave was caused by a given network. Further, we demonstrate it's utility in the inverse problem of identifying the network that caused a given synfire wave. This method was effective even in highly subsampled networks where only a small subset of neurons were accessible, thus showing it's utility in experimental estimation of connectomes in real neuronal-networks. Together, we propose synconset chains/waves as an effective framework for understanding the impact of network structure on function, and as a step towards developing physiology-driven network identification methods. Finally, as synconset chains extend the utilities of synfire chains to arbitrary networks, we suggest utilities of our framework to several aspects of network physiology including cell assemblies, population codes, and oscillatory synchrony. PMID:24116018

Internal Waves and Wave Attractors in Enceladus' Subsurface Ocean

NASA Astrophysics Data System (ADS)

van Oers, A. M.; Maas, L. R.; Vermeersen, B. L. A.

2016-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. In 2013, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. Numerical simulations show the persistence of wave attractors for a range of ocean shapes and stratifications. The intensification of the wave field near the location of the surface reflections of wave attractors has been numerically and experimentally confirmed. We measured the forces a wave attractor exerts on a solid surface, near a reflection point. These reflection points would correspond to the location of the tiger stripes. Combining experiments and numerical simulations we conclude that (1) wave attractors can exist in Enceladus' subsurface sea, (2) their shape can be matched to the tiger stripes, (3) the wave attractors cause a localized force at the water-ice boundaries, (4) this force could have been large enough to contribute to fracturing the ice and (5) the wave attractors localize energy (and particles) and cause dissipation along its path, helping explain Enceladus' enigmatic heat output at the tiger stripes.

Change in Job Strain as a Predictor of Change in Insomnia Symptoms: Analyzing Observational Data as a Non-randomized Pseudo-Trial.

PubMed

Halonen, Jaana I; Lallukka, Tea; Pentti, Jaana; Stenholm, Sari; Rod, Naja H; Virtanen, Marianna; Salo, Paula; Kivimäki, Mika; Vahtera, Jussi

2017-01-01

To examine whether change in job strain leads to change in insomnia symptoms. Among 24873 adults (82% women, mean age 44 years) who participated in a minimum of three consecutive study waves (2000-2012), job strain was assessed at the first and second wave and insomnia symptoms at all three waves. We analyzed observational data as a "pseudo-trial" including participants with no job strain in the first wave and no insomnia symptoms in the first and second wave (n = 7354) to examine whether the onset of job strain between the first and second waves predicted the onset of insomnia symptoms in the third wave. We used a corresponding approach, including those with job strain in the first wave and insomnia symptoms in the first and second wave (n = 2332), to examine whether the disappearance of job strain between the first two waves predicted remission of insomnia symptoms in the third wave. The onset of job strain predicted the onset of subsequent insomnia symptoms after adjustment for sex, age, marital status, education, smoking, physical activity, alcohol consumption, body mass index, and comorbidities (odds ratio compared to no onset of job strain 1.32, 95% CI 1.16-1.51). The disappearance of job strain was associated with lower odds of repeated insomnia symptoms (odds ratio compared to no disappearance of job strain 0.78, 95% CI 0.65-0.94). Further adjustment for shift work or sleep apnea did not change these associations. These results suggest that job strain is a modifiable risk factor for insomnia symptoms. © Sleep Research Society 2016. Published by Oxford University Press [on behalf of the Sleep Research Society].

Change in Job Strain as a Predictor of Change in Insomnia Symptoms: Analyzing Observational Data as a Non-randomized Pseudo-Trial

PubMed Central

Lallukka, Tea; Pentti, Jaana; Stenholm, Sari; Rod, Naja H.; Virtanen, Marianna; Salo, Paula; Kivimäki, Mika; Vahtera, Jussi

2017-01-01

Abstract Study objectives: To examine whether change in job strain leads to change in insomnia symptoms. Methods: Among 24873 adults (82% women, mean age 44 years) who participated in a minimum of three consecutive study waves (2000–2012), job strain was assessed at the first and second wave and insomnia symptoms at all three waves. We analyzed observational data as a “pseudo-trial” including participants with no job strain in the first wave and no insomnia symptoms in the first and second wave (n = 7354) to examine whether the onset of job strain between the first and second waves predicted the onset of insomnia symptoms in the third wave. We used a corresponding approach, including those with job strain in the first wave and insomnia symptoms in the first and second wave (n = 2332), to examine whether the disappearance of job strain between the first two waves predicted remission of insomnia symptoms in the third wave. Results: The onset of job strain predicted the onset of subsequent insomnia symptoms after adjustment for sex, age, marital status, education, smoking, physical activity, alcohol consumption, body mass index, and comorbidities (odds ratio compared to no onset of job strain 1.32, 95% CI 1.16–1.51). The disappearance of job strain was associated with lower odds of repeated insomnia symptoms (odds ratio compared to no disappearance of job strain 0.78, 95% CI 0.65–0.94). Further adjustment for shift work or sleep apnea did not change these associations. Conclusions: These results suggest that job strain is a modifiable risk factor for insomnia symptoms. PMID:28364463

Observations and Simulations of the Impact of Wave-Current Interaction on Wave Direction in the Surf Zone

NASA Astrophysics Data System (ADS)

Hopkins, Julia; Elgar, Steve; Raubenheimer, Britt

2017-04-01

Accurately characterizing the interaction of waves and currents can improve predictions of wave propagation and subsequent sediment transport in the nearshore. Along the southern shoreline of Martha's Vineyard, MA, waves propagate across strong tidal currents as they shoal, providing an ideal environment for investigating wave-current interaction. Wave directions and mean currents observed for two 1-month-long periods in 7- and 2-m water depths along 11 km of the Martha's Vineyard shoreline have strong tidal modulations. Wave directions shift by as much as 70 degrees over a tidal cycle in 7 m depth, and by as much as 25 degrees in 2 m depth. The magnitude of the tidal modulations in the wave field decreases alongshore to the west, consistent with the observed decrease in tidal currents from 2.1 to 0.2 m/s. The observations are reproduced accurately by a numerical model (SWAN and Deflt3D-FLOW) that simulates waves and currents over the observed bathymetry. Model simulations with and without wave-current interaction and tidal depth changes demonstrate that the observed tidal modulations of the wave field primarily are caused by wave-current interaction and not by tidal changes to water depths over the nearby complex shoals. Sediment transport estimates from simulated wave conditions using a range of tidal currents and offshore wave fields indicate that the modulation of the wave field at Martha's Vineyard can impact the direction of wave-induced alongshore sediment transport, sometimes driving transport opposing the direction of the offshore incident wave field. As such, the observations and model simulations suggest the importance of wave-current interaction to tidally averaged transport in mixed-energy wave-and-current nearshore environments. Supported by ASD(R&E), NSF, NOAA (Sea Grant), and ONR.

A Continuum Model of Actin Waves in Dictyostelium discoideum

PubMed Central

Khamviwath, Varunyu; Hu, Jifeng; Othmer, Hans G.

2013-01-01

Actin waves are complex dynamical patterns of the dendritic network of filamentous actin in eukaryotes. We developed a model of actin waves in PTEN-deficient Dictyostelium discoideum by deriving an approximation of the dynamics of discrete actin filaments and combining it with a signaling pathway that controls filament branching. This signaling pathway, together with the actin network, contains a positive feedback loop that drives the actin waves. Our model predicts the structure, composition, and dynamics of waves that are consistent with existing experimental evidence, as well as the biochemical dependence on various protein partners. Simulation suggests that actin waves are initiated when local actin network activity, caused by an independent process, exceeds a certain threshold. Moreover, diffusion of proteins that form a positive feedback loop with the actin network alone is sufficient for propagation of actin waves at the observed speed of . Decay of the wave back can be caused by scarcity of network components, and the shape of actin waves is highly dependent on the filament disassembly rate. The model allows retraction of actin waves and captures formation of new wave fronts in broken waves. Our results demonstrate that a delicate balance between a positive feedback, filament disassembly, and local availability of network components is essential for the complex dynamics of actin waves. PMID:23741312

Peripheral vasomotor activity assessment using a continuous wavelet analysis on webcam photoplethysmographic signals.

PubMed

Bousefsaf, F; Maaoui, C; Pruski, A

2016-11-25

Vasoconstriction and vasodilation phenomena reflect the relative changes in the vascular bed. They induce particular modifications in the pulse wave magnitude. Webcams correspond to remote sensors that can be employed to measure the pulse wave in order to compute the pulse frequency. Record and analyze pulse wave signal with a low-cost webcam to extract the amplitude information and assess the vasomotor activity of the participant. Photoplethysmographic signals obtained from a webcam are analyzed through a continuous wavelet transform. The performance of the proposed filtering technique was evaluated using approved contact probes on a set of 12 healthy subjects after they perform a short but intense physical exercise. During the rest period, a cutaneous vasodilation is observable. High degrees of correlation between the webcam and a reference sensor were obtained. Webcams are low-cost and non-contact devices that can be used to reliably estimate both heart rate and peripheral vasomotor activity, notably during physical exertion.

A two dimension model of the uterine electrical wave propagation.

PubMed

Rihana, S; Lefrançois, E; Marque, C

2007-01-01

The uterus, usually quiescent during pregnancy, exhibits forceful contractions at term leading to delivery. These contractions are caused by the synchronized propagation of electrical waves from the pacemaker cells to its neighbors inducing the whole coordinated contraction of the uterus wall leading to labor. In a previous work, we simulate the electrical activity of a single uterine cell by a set of ordinary differential equations. Then, this model has been used to simulate the electrical activity propagation. In the present work, the uterine cell tissue is assumed to have uniform and isotropic propagation, and constant electrical membrane properties. The stability of the numerical solution imposes the choice of a critical temporal step. A wave starts at a pacemaker cell; this electrical activity is initiated by the injection of an external stimulation current to the cell membrane. We observe synchronous wave propagation for axial resistance values around 0.5 GOmega or less and propoagation blocking for values greater than 0.7 GOmega. We compute the conduction velocity of the excitation, for different axial resistance values, and obtain a velocity about 10 cm/sec, approaching the one described by the literature for the rat at end of term.

Generation of EMIC Waves Observed by Van Allen Probes at Low L-shells of Earth's Magnetosphere

NASA Astrophysics Data System (ADS)

Gamayunov, K. V.; Zhang, J.; Saikin, A.; Rassoul, H.

2017-12-01

In a multi-ion magnetospheric plasma, where the major species are H+, He+, and O+, the He-band of electromagnetic ion cyclotron (EMIC) waves is the dominant band observed in the inner magnetosphere, and waves are generally quasi-field-aligned inside the geostationary orbit. Almost all the satellite-based studies of EMIC waves before Van Allen Probes, however, have not reported waves below L 3.5. There is probably only one exception from the Akebono satellite where both the H-band and He-band EMIC waves were observed at L 2. The situation has changed dramatically after two Van Allen Probes spacecraft were launched on 30 August, 2012, and many EMIC wave events have been observed below L=4. The Van Allen Probes observations confirm that the He-band of EMIC waves is a dominant band in the inner magnetosphere, but the observation of the He-band waves below L=4 is a new and quite unexpected result compared to our knowledge about EMIC waves before the Van Allen Probes era. In addition, observations show that almost all the He-band EMIC waves are linearly polarized in the region L < 4. This result is also new and unexpected. Here we will present an observational test of the generation mechanism for the He-band EMIC waves observed by Van Allen Probes at L 2.8 on 18 March, 2013. All the plasma parameters, DC magnetic field, and energetic ion distribution functions will be taken from the Van Allen Probes observations during the EMIC wave event to calculate growth rates of EMIC waves. We will then identify the energetic ions responsible for instability, frequencies and normals generated, and physical mechanism of instability.

Modulation of chorus intensity by ULF waves deep in the inner magnetosphere

DOE PAGES

Xia, Zhiyang; Chen, Lunjin; Dai, Lei; ...

2016-09-05

Previous studies have shown that chorus wave intensity can be modulated by Pc4-Pc5 compressional ULF waves. In this paper, we present Van Allen Probes observation of ULF wave modulating chorus wave intensity, which occurred deep in the magnetosphere. The ULF wave shows fundamental poloidal mode signature and mirror mode compressional nature. The observed ULF wave can modulate not only the chorus wave intensity but also the distribution of both protons and electrons. Linear growth rate analysis shows consistence with observed chorus intensity variation at low frequency (f <~ 0.3f ce), but cannot account for the observed higher-frequency chorus waves, includingmore » the upper band chorus waves. This suggests the chorus waves at higher-frequency ranges require nonlinear mechanisms. Finally, in addition, we use combined observations of Radiation Belt Storm Probes (RBSP) A and B to verify that the ULF wave event is spatially local and does not last long.« less

Arguments for fundamental emission by the parametric process L yields T + S in interplanetary type III bursts. [langmuir, electromagnetic, ion acoustic waves (L, T, S)

NASA Technical Reports Server (NTRS)

Cairns, I. H.

1984-01-01

Observations of low frequency ion acoustic-like waves associated with Langmuir waves present during interplanetary Type 3 bursts are used to study plasma emission mechanisms and wave processes involving ion acoustic waves. It is shown that the observed wave frequency characteristics are consistent with the processes L yields T + S (where L = Langmuir waves, T = electromagnetic waves, S = ion acoustic waves) and L yields L' + S proceeding. The usual incoherent (random phase) version of the process L yields T + S cannot explain the observed wave production time scale. The clumpy nature of the observed Langmuir waves is vital to the theory of IP Type 3 bursts. The incoherent process L yields T + S may encounter difficulties explaining the observed Type 3 brightness temperatures when Langmuir wave clumps are incorporated into the theory. The parametric process L yields T + S may be the important emission process for the fundamental radiation of interplanetary Type 3 bursts.

Wave Processes in Arctic Seas, Observed from TerraSAR-X

DTIC Science & Technology

2015-09-30

in order to improve wave models as well as ice models applicable to a changing Arctic wave/ and ice climate . This includes observation and...fields retrieved from the TS-X image swaths. 4. “Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling”, by...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. “Wave Processes in Arctic Seas, Observed from TerraSAR-X

An integrated sea monitoring system based on a X-band wave radar to support the removal activities of the Costa Concordia wreck.

NASA Astrophysics Data System (ADS)

Gozzini, Bernardo; Serafino, Francesco; Lugni, Claudio; Antonini, Andrea; Costanza, Letizia; Orlandi, Andrea; Arturi, Daniele; Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Ortolani, Alberto; Brandini, Carlo

2013-04-01

The planning and management of different types of operations at sea requires a number of sea state data as much in real-time as possible, for rapid and effective response to different situations. This need is particularly strong in emergency management practices, in accidents due to man-made or natural causes, that require the planning of civil protection activities (such as search-and-rescue, cleaning of pollution, ship recovery), transport planning etc. The use of X-band radar technology nowadays provides great advantages over traditional in-situ and satellite-based techniques for sea state measuring, to update information on waves and currents over a sea area with high spatial and temporal resolution. Other advantages include a good spatial coverage around the area of interest, the flexibility of use, the capacity to provide, on-demand and when necessary, complementary information (possible oil spills detection, integration with VTS, etc.). X-band coastal radars (so-called "wave-radars") are widely used in the monitoring of large marine areas, in integration with in-situ measurements, satellites and other radar types (HF), as a key element of the observational component of present operational oceanography systems. Outside of these systems, the use of this technology to support emergency management practices is very promising for both the quality and quantity of available parameters, and for an easy integration with all other available monitoring and forecasting tools. A case study particularly relevant is offered by the presence of the Costa Concordia ship near the Giglio Island. The management of this disaster has requested at an early stage a large number of data to support the monitoring of marine environment around the ship, e.g. to optimally plan water samples. In the next and present phase, to support the highly risky and costly activities linked to the wreck removal, which are extremely sea-state dependent, the installation of a wave-radar allows to detect, in real-time and with high revisiting time, waves and currents in the area surrounding the wreck. In addition wave spectra measures allow to check the reliability of present wave forecasting models, which are unlikely to represent the local and coastal scales of interest and therefore require a continuous process of verification, calibration and quality control. Similar considerations can be made for the reconstruction of marine currents at a local scale, whose uncertainty is inherently greater. The integration of X-band radar data with in-situ data has allowed to optimally calibrate the data itself (especially for what concerns the significant wave height) and to provide a local scale observation system which proved to be fundamental to support the work of continuous sea state monitoring and forecasting around the area of the disaster. The observation system at Giglio is a kind of laboratory unique in its kind, to test the reliability of the wave and hydrodynamic models at a local scale, to assess our present ability to use X-band radars for emergency management activities, and to evaluate the response capacity of such practices to the actual needs of involved stakeholders and private users.

Optimizing an ELF/VLF Phased Array at HAARP

NASA Astrophysics Data System (ADS)

Fujimaru, S.; Moore, R. C.

2013-12-01

The goal of this study is to maximize the amplitude of 1-5 kHz ELF/VLF waves generated by ionospheric HF heating and measured at a ground-based ELF/VLF receiver. The optimization makes use of experimental observations performed during ELF/VLF wave generation experiments at the High-frequency Active Auroral Research Program (HAARP) Observatory in Gakona, Alaska. During these experiments, the amplitude, phase, and propagation delay of the ELF/VLF waves were carefully measured. The HF beam was aimed at 15 degrees zenith angle in 8 different azimuthal directions, equally spaced in a circle, while broadcasting a 3.25 MHz (X-mode) signal that was amplitude modulated (square wave) with a linear frequency-time chirp between 1 and 5 kHz. The experimental observations are used to provide reference amplitudes, phases, and propagation delays for ELF/VLF waves generated at these specific locations. The presented optimization accounts for the trade-off between duty cycle, heated area, and the distributed nature of the source region in order to construct a "most efficient" phased array. The amplitudes and phases generated by modulated heating at each location are combined in post-processing to find an optimal combination of duty cycle, heating location, and heating order.

The Influence of Planetary Waves on Polar Mesospheric Clouds

NASA Astrophysics Data System (ADS)

France, J. A.; Randall, C. E.; Harvey, L.; Siskind, D. E.; Lumpe, J. D.; Bailey, S. M.; Carstens, J. N.; Russell, J. M., III

2016-12-01

Polar mesospheric clouds (PMCs) form as a result of low temperatures and enhanced water vapor near the polar summer mesospause. These conditions occur as a result of upwelling associated with the upper branch of the gravity wave-driven global residual circulation, and are sensitive to changes in planetary wave breaking in the winter hemisphere through interhemispheric coupling (IHC). Observations by the Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite show an anomalous decline in northern hemisphere PMCs in August 2014. The decline is attributed to IHC triggered by planetary wave activity in the Antarctic stratosphere. The results indicate that the IHC in 2014 occurred via a pathway that previous studies have not emphasized. Based on Aura Microwave Limb Sounder data, we suggest that shifts in zonal winds in the summer stratosphere triggered a circulation change that led to the observed PMC decline. We also show that the 5-day planetary wave modulates the response to IHC, in that PMCs persist in the trough when zonal mean temperatures are too high to support PMCs, and are absent in the ridge when mean temperatures are low enough to support PMCs.

Variability of ULF wave power at the magnetopause: a study at low latitude with Cluster data

NASA Astrophysics Data System (ADS)

Cornilleau-Wehrlin, N.; Grison, B.; Belmont, G.; Rezeau, L.; Chanteur, G.; Robert, P.; Canu, P.

2012-04-01

Strong ULF wave activity has been observed at magnetopause crossings since a long time. Those turbulent-like waves are possible contributors to particle penetration from the Solar Wind to the Magnetosphere through the magnetopause. Statistical studies have been performed to understand under which conditions the ULF wave power is the most intense and thus the waves can be the most efficient for particle transport from one region to the other. Clearly the solar wind pressure organizes the data, the stronger the pressure, the higher the ULF power (Attié et al 2008). Double STAR-Cluster comparison has shown that ULF wave power is stronger at low latitude than at high latitude (Cornilleau-Wehrlin et al, 2008). The different studies performed have not, up to now, shown a stronger power in the vicinity of local noon. Nevertheless under identical activity conditions, the variability of this power, even at a given location in latitude and local time is very high. The present work intends at understanding this variability by means of the multi spacecraft mission Cluster. The data used are from spring 2008, while Cluster was crossing the magnetopause at low latitude, in particularly quite Solar Wind conditions. The first region of interest of this study is the sub-solar point vicinity where the long wavelength surface wave effects are most unlikely.

Model of electron lifetimes inside the plasmasphere calculated using a CRRES derived hiss wave amplitude model

NASA Astrophysics Data System (ADS)

Orlova, Ksenia; Spasojevic, Maria; Shprits, Yuri

Particle populations in the inner magnetosphere can change by orders of magnitude on very short time scales. For the last decade observations and theoretical computations showed that resonant interaction of electrons with various plasma waves plays an important role in acceleration and loss mechanisms. Using data from the CRRES plasma wave experiment, we develop quadratic fits to the mean of the wave amplitude squared for plasmaspheric hiss as a function of geomagnetic activity (Kp) and magnetic latitude (lambda) for the dayside (6

Very low frequency earthquakes in Tohoku-Oki recorded by short-period ocean bottom seismographs

NASA Astrophysics Data System (ADS)

Takahashi, H.; Hino, R.; Ohta, Y.; Uchida, N.; Suzuki, S.; Shinohara, M.; Nakatani, Y.; Matsuzawa, T.

2017-12-01

Various kind of slow earthquakes have been found along many plate boundary zones in the world (Obara, and Kato, 2016). In the Tohoku subduction zone where slow event activities have been considered insignificant, slow slip events associated with low frequency tremors were identified prior to the 2011 Tohoku-Oki earthquake based on seafloor geodetic and seismographical observations. Recently very low frequency earthquakes (VLFEs) have been discovered by inspecting onshore broad-band seismograms. Although the activity of the detected VLFEs is low and the VLFEs occurred in the limited area, VLFEs tends to occur successively in a short time period. In this study, we try to characterize the VLFEs along the Japan Trench based on the seismograms obtained by the instruments deployed near the estimated epicenters.Temporary seismic observations using Ocean Bottom Seismometers (OBSs) have been carried out several times after the 2011 Tohoku-Oki earthquake, and several VLFE activities were observed during the deployments of the OBSs. Amplitudes of horizontal component seismograms of the OBSs grow shortly after the estimated origin times of the VLFEs identified by the onshore seismograms, even though the sensors are 4.5 Hz geophones. It is difficult to recognize evident onsets of P or S waves, correspondence between order of arrivals of discernible wave packets and their amplitudes suggests that these wave packets are seismic signals radiated from the VLFE sources. The OBSs detect regular local earthquakes of the similar magnitudes as the VLFEs. Signal powers of the possible VLFE seismograms are comparable to the regular earthquakes in the frequency range < 1 Hz, while significant deficiency of higher frequency components are observed.

A Catalog of Coronal "EIT Wave" Transients

NASA Technical Reports Server (NTRS)

Thompson, B. J.; Myers, D. C.

2005-01-01

SOHO Extreme Ultraviolet Imaging Telescope (EIT) data have been visually searched for coronal "EIT wave" transients over the period beginning 24 March 1997 extending through 24 June 1998. The dates covered start at the beginning of regular high-cadence (more than 1 image every 20 minutes) observations, ending at the 4-month interruption of SOHO observations in mid-1998. 176 events are included in this catalog. The observations range from "candidate" events, which were either weak or had insufficient data coverage, to events which were well-defined and were clearly distinguishable in the data. Included in the catalog are times of the EIT images in which the events are observed, diagrams indicating the observed locations of the wavefronts and associated active regions, and the speeds of the wavefronts. The measured speeds of the wavefronts varied from less than 50 to over 700 km/sec with "typical" speeds of 200-400 Msec.

Development of Electric Field and Plasma Wave Investigations for Future Space Weather Missions: ERG, SCOPE, and beyond

NASA Astrophysics Data System (ADS)

Kasaba, Y.; Kumamoto, A.; Ono, T.; Misawa, H.; Kojima, H.; Yagitani, S.; Kasahara, Y.; Ishisaka, K.

2009-04-01

The electric field and plasma wave investigation is important for the clarification of global plasma dynamics and energetic processes in the planetary Magnetospheric studies. We have several missions which will contribute those objectives. the small-sized radiation belt mission, ERG (Energization and Radiation in Geospace), the cross-scale formation flight mission, SCOPE, the BepiColombo mission to Mercury, and the small-sized and full-scale Jovian mission in future. Those will prevail the universal plasma mechanism and processes in the space laboratory. The main purposes of electric field and plasma wave observation for those missions are: (1) Examination of the theories of high-energy particle acceleration by plasma waves, (2) identification of the origin of electric fields in the magnetosphere associated with cross-scale coupling processes, (3) diagnosis of plasma density, temperature and composition, and (4) investigation of wave-particle interaction and mode conversion processes. Simultaneous observation of plasma waves and energetic particles with high resolution will enable us to investigate the wave-particle interaction based on quasi-linear theory and non-linear models. In this paper, we will summarize the current plan and efforts for those future activities. In order to achieve those objectives, the instrument including sensitive sensors (the long wire / stem antennae, the search-coil / loop antennae) and integrated receiver systems are now in development, including the direct identification of nonlinear wave-particle interactions associated will be tried by Wave-particle Correlator. And, as applications of those development, we will mention to the space interferometer and the radar sounder technologies.

Low-frequency electromagnetic plasma waves at comet P/Grigg-Skjellerup: Overview and spectral characteristics

NASA Technical Reports Server (NTRS)

Glassmeier, Karl-Heinz; Neubauer, Fritz M.

1993-01-01

Large-amplitude electromagnetic plasma waves are one of the dominant features of the solar wind-comet interaction. Wave characteristics strongly depend on parameters such as the solar wind flow and Alfven velocities and the angle between flow and interplanetary magnetic field as well as the production rate. With respect to the latter the flyby of the spacecraft Giotto at comet P/Griff-Skjellerup provides a unique possibility to study such waves in further detail. Pickup ion-related wave signatures have been observed up to a distance of 600,000 km from the nucleus. Peak spectral power in the spacecraft frame of reference occurs at frequencies mainly somewhat below the water group ion gyrofrequency. From this the waves are determined to be mainly left-hand polarized waves, causing one-sided pitch angle diffusion outbound. The wave activity strongly increases close to the comet; upstream it exhibits a quadratic dependence on the water group pickup ion free energy. Furthermore, a phenomenological study of the wave characteristics provides a unique description of the fine-structure of the interaction region. Indications of steepened magnetosonic waves have been found in the outbound magnetosheath region.

Two dimensional kinetic analysis of electrostatic harmonic plasma waves

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

Fonseca-Pongutá, E. C.; Ziebell, L. F.; Gaelzer, R.

2016-06-15

Electrostatic harmonic Langmuir waves are virtual modes excited in weakly turbulent plasmas, first observed in early laboratory beam-plasma experiments as well as in rocket-borne active experiments in space. However, their unequivocal presence was confirmed through computer simulated experiments and subsequently theoretically explained. The peculiarity of harmonic Langmuir waves is that while their existence requires nonlinear response, their excitation mechanism and subsequent early time evolution are governed by essentially linear process. One of the unresolved theoretical issues regards the role of nonlinear wave-particle interaction process over longer evolution time period. Another outstanding issue is that existing theories for these modes aremore » limited to one-dimensional space. The present paper carries out two dimensional theoretical analysis of fundamental and (first) harmonic Langmuir waves for the first time. The result shows that harmonic Langmuir wave is essentially governed by (quasi)linear process and that nonlinear wave-particle interaction plays no significant role in the time evolution of the wave spectrum. The numerical solutions of the two-dimensional wave spectra for fundamental and harmonic Langmuir waves are also found to be consistent with those obtained by direct particle-in-cell simulation method reported in the literature.« less

Contribution of the ULF wave activity to the global recovery of the outer radiation belt during the passage of a high-speed solar wind stream observed in September 2014

NASA Astrophysics Data System (ADS)

Dal Lago, A.; Da Silva, L. A.; Alves, L. R.; Dallaqua, R.; Marchezi, J.; Medeiros, C.; Souza, V. M. C. E. S.; Koga, D.; Jauer, P. R.; Vieira, L.; Rockenbach, M.; Mendes, O., Jr.; De Nardin, C. M.; Sibeck, D. G.

2016-12-01

The interaction of the solar wind with the Earth's magnetosphere can either increase or decrease the relativistic electron population in the outer radiation belt. In order to investigate the contribution of the ULF wave activity to the global recovery of the outer radiation belt relativistic electron population, we searched the Van Allen data for a period in which we can clearly distinguish the enhancement of the fluxes from the background. The complex solar wind structure observed from September 12-24, 2014, which resulted from the interaction of two coronal mass ejections (CMEs) and a high-speed stream, presented such a scenario. The CMEs are related to the dropout of the relativistic electron population followed by several days of low fluxes. The global recovery started during the passage of the high-speed stream that was associated with the occurrence of substorms that persisted for several days. Here we estimate the contribution of ULF wave-particle interactions to the enhancement of the relativistic electron fluxes. Our approach is based on estimates of the ULF wave radial diffusion coefficients employing two models: (a) an analytic expression presented by Ozeke et al. (2014); and (b) a simplified model based on the solar wind parameters. The preliminary results, uncertainties and future steps are discussed in details.

Observation of Chorus Waves by the Van Allen Probes: Dependence on Solar Wind Parameters and Scale Size

NASA Technical Reports Server (NTRS)

Aryan, Homayon; Sibeck, David; Balikhin, Michael; Agapitov, Oleksiy; Kletzing, Craig

2016-01-01

Highly energetic electrons in the Earths Van Allen radiation belts can cause serious damage to spacecraft electronic systems and affect the atmospheric composition if they precipitate into the upper atmosphere. Whistler mode chorus waves have attracted significant attention in recent decades for their crucial role in the acceleration and loss of energetic electrons that ultimately change the dynamics of the radiation belts. The distribution of these waves in the inner magnetosphere is commonly presented as a function of geomagnetic activity. However, geomagnetic indices are nonspecific parameters that are compiled from imperfectly covered ground based measurements. The present study uses wave data from the two Van Allen Probes to present the distribution of lower band chorus waves not only as functions of single geomagnetic index and solar wind parameters but also as functions of combined parameters. Also the current study takes advantage of the unique equatorial orbit of the Van Allen Probes to estimate the average scale size of chorus wave packets, during close separations between the two spacecraft, as a function of radial distance, magnetic latitude, and geomagnetic activity, respectively. Results show that the average scale size of chorus wave packets is approximately 13002300 km. The results also show that the inclusion of combined parameters can provide better representation of the chorus wave distributions in the inner magnetosphere and therefore can further improve our knowledge of the acceleration and loss of radiation belt electrons.

Spatial gravity wave characteristics obtained from multiple OH(3-1) airglow temperature time series

NASA Astrophysics Data System (ADS)

Wachter, Paul; Schmidt, Carsten; Wüst, Sabine; Bittner, Michael

2015-12-01

We present a new approach for the detection of gravity waves in OH-airglow observations at the measurement site Oberpfaffenhofen (11.27°E, 48.08°N), Germany. The measurements were performed at the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) during the period from February 4th, 2011 to July 6th, 2011. In this case study the observations were carried out by three identical Ground-based Infrared P-branch Spectrometers (GRIPS). These instruments provide OH(3-1) rotational temperature time series, which enable spatio-temporal investigations of gravity wave characteristics in the mesopause region. The instruments were aligned in such a way that their fields of view (FOV) formed an equilateral triangle in the OH-emission layer at a height of 87 km. The Harmonic Analysis is applied in order to identify joint temperature oscillations in the three individual datasets. Dependent on the specific gravity wave activity in a single night, it is possible to detect up to four different wave patterns with this method. The values obtained for the waves' periods and phases are then used to derive further parameters, such as horizontal wavelength, phase velocity and the direction of propagation. We identify systematic relationships between periods and amplitudes as well as between periods and horizontal wavelengths. A predominant propagation direction towards the East and North-North-East characterizes the waves during the observation period. There are also indications of seasonal effects in the temporal development of the horizontal wavelength and the phase velocity. During late winter and early spring the derived horizontal wavelengths and the phase velocities are smaller than in the subsequent period from early April to July 2011.

Studying the influence of strong meteorological disturbances in the Earth's lower atmosphere on variations of ionospheric parameters in the Asian region of Russia

NASA Astrophysics Data System (ADS)

Chernigovskaya, Marina; Kurkin, Vladimir; Orlov, Igor; Oinats, Alexey; Sharkov, Eugenii

2010-05-01

Short-period temporal variations of ionospheric parameters were analyzed to study probabilities of manifestation of strong meteorological disturbances in the Earth's lower atmosphere in variations of upper atmosphere parameters in a zone far removed from a disturbance source. In the analysis, we used data on maximum observed frequencies (MOF) of oblique sounding (OS) signals along Norilsk-Irkutsk, Magadan-Irkutsk, and Khabarovsk-Irkutsk paths in East Siberia and the Far East. These data were obtained during solar minimum at equinoxes (March, September) in 2008-2009. Analyzing effects of wave disturbances in ionospheric parameters, we take into account helio-geomagnetic and meteorological conditions in regions under study to do an effective separation between disturbances associated with magnetospheric-ionospheric coupling and those induced by the influence of the lower atmosphere on the upper one. The frequency analysis we conducted revealed time intervals with higher intensity of short-period oscillations which may have been interpreted as manifestation of large-scale traveling ionospheric disturbances (TIDs) whose sources were internal gravity waves (IGWs) with periods of 1-5 hours. The complex analysis of helio-geomagnetic, ionospheric, and atmospheric data as well as data on tropical cyclones established that the detected TIDs were unrelated to helio-geomagnetic disturbances (2008-2009 exhibited solar minimum and quiet geomagnetic conditions). The analysis of other potential sources of the observed short-period wave disturbances shows that observed TIDs do not always coincide in time with passage of local meteorological fronts through the region of subionospheric points of OS paths and are not associated with passage of solar terminator. An attempt was made to connect a number of detected TIDs with ionospheric responses to tropical cyclones (TC) which were in active phase in the north-west of the Pacific Ocean during the periods considered. A considerable increase in energy of short-period wave disturbances was observed along Khabarovsk-Irkutsk, Magadan-Irkutsk, and Norilsk-Irkutsk paths during the active tropical cyclogenesis in September 2008-2009. Intensity of the observed TIDs decreased as midpoints of OS paths moved westward away from potential IGW sources. Ionospheric responses to wave disturbance propagation from the same IGW sources differ in the OS paths under analysis. This must be associated with different geometry of the OS paths as well as with the fact that the IGW source under consideration changes in intensity and its coordinates (stages and motion paths of tropical cyclones) during TC development. Thus there is an angular dependence between the wave disturbance propagation direction and the line connecting midpoints of the OS paths. Velocities of wave disturbance propagation (~90-170 m/s) were measured from the delay period of TIDs passage in regions of midpoints of spaced-apart OS paths. Short-period TIDs can also be observed at spring equinox in March 2008-2009 under quiet helio-geomagnetic conditions and in the absence of active tropical cyclones in the north-west of the Pacific Ocean, but TIDs energy is much lower than that in autumn. Authors note it was not possible to identify potential IGW sources for some TIDs within the scope of this work. These TIDs may be related to ionospheric responses to seasonal transitions in the upper atmosphere dynamic regime during the equinoxes under study. Further systematic investigations in this area of study are required to store statistics of observations of ionospheric responses to strong meteorological disturbances. The study was supported by the RFBR grant № 09-05-00760.

Neutrophils establish rapid and robust WAVE complex polarity in an actin-dependent fashion.

PubMed

Millius, Arthur; Dandekar, Sheel N; Houk, Andrew R; Weiner, Orion D

2009-02-10

Asymmetric intracellular signals enable cells to migrate in response to external cues. The multiprotein WAVE (also known as SCAR or WASF) complex activates the actin-nucleating Arp2/3 complex [1-4] and localizes to propagating "waves," which direct actin assembly during neutrophil migration [5, 6]. Here, we observe similar WAVE complex dynamics in other mammalian cells and analyze WAVE complex dynamics during establishment of neutrophil polarity. Earlier models proposed that spatially biased generation [7] or selection of protrusions [8] enables chemotaxis. These models require existing morphological polarity to control protrusions. We show that spatially biased generation and selection of WAVE complex recruitment also occur in morphologically unpolarized neutrophils during development of their first protrusions. Additionally, several mechanisms limit WAVE complex recruitment during polarization and movement: Intrinsic cues restrict WAVE complex distribution during establishment of polarity, and asymmetric intracellular signals constrain it in morphologically polarized cells. External gradients can overcome both intrinsic biases and control WAVE complex localization. After latrunculin-mediated inhibition of actin polymerization, addition and removal of agonist gradients globally recruits and releases the WAVE complex from the membrane. Under these conditions, the WAVE complex no longer polarizes, despite the presence of strong external gradients. Thus, actin polymer and the WAVE complex reciprocally interact during polarization.

Influence of El Niño and Indian Ocean Dipole on sea level variability in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Sreenivas, P.; Gnanaseelan, C.; Prasad, K. V. S. R.

2012-01-01

Zonally oscillating seasonal equatorial winds generate pairs of upwelling and downwelling Kelvin waves in the Equatorial Indian Ocean, which then advance in to the coastal Bay of Bengal. The first (second) equatorial upwelling Kelvin wave has its origin in the western (eastern) basin, whereas the downwelling Kelvin waves originate in the central basin. The observed interannual variability of these Kelvin waves is highly governed by the associated zonal wind changes in the central and eastern equatorial Indian Ocean during the anomalous years. The second downwelling (upwelling) Kelvin wave is absent (weak) during El Niño (La Niña) years, whereas the second upwelling Kelvin wave strengthened during El Niño years both in the equatorial Indian Ocean and Bay of Bengal. The large scale off equatorial Rossby waves occasionally feedback the equatorial Kelvin waves, which then strengthen the Bay of Bengal coastal Kelvin waves. The coastal Kelvin waves and the associated radiated Rossby waves from east play a dominant role in the mesoscale eddy generation in Bay of Bengal. The analysis of cyclogenesis characteristics in the bay over the past 65 years revealed that the active (suppressed) phases of cyclogenesis are coinciding with the downwelling (upwelling) planetary waves which influence the cyclone heat potential by altering the thermocline depth.

Cavitation cluster dynamics in shock-wave lithotripsy: part 1. Free field.

PubMed

Arora, M; Junge, L; Ohl, C D

2005-06-01

The spatiotemporal dynamics of cavitation bubble growth and collapse in shock-wave lithotripsy in a free field was studied experimentally. The lithotripter was equipped with two independently triggerable layers of piezoceramics. The front and back layers generated positive pressure amplitudes of 30 MPa and 15 MPa, respectively, and -10 MPa negative amplitude. The time interval between the launch of the shock waves was varied from 0 and 0.1 s, covering the regimens of pulse-modification (regimen A, delay 0 to 4 micros), shock wave-cavitation cluster interaction (B, 4 micros to 64 micros) and shock wave-gas bubble interaction (C, 256 micros to 0.1 s). The time-integrated cavitation activity was most strongly influenced in regimen A and, in regimen B, the spatial distribution of bubbles was altered, whereas enhancement of cavitation activity was observed in regimen C. Quantitative measurements of the spatial- and time-integrated void fractions were obtained with a photographic and light-scattering technique. The preconditions for a reproducible experiment are explained, with the existence of two distinct types of cavitation nuclei, small particles suspended in the liquid and residuals of bubbles from prior cavitation clusters.

Gravitational astrophysics

NASA Astrophysics Data System (ADS)

Hendry, Martin; Woan, Graham

2007-02-01

Like the surface of a busy swimming pool, spacetime is awash with waves generated by the local and distant motions of mass and, in principle, much of this activity can be reconstructed by analysing the waveforms. However, instrumentation with a reasonable chance of directly detecting these gravitational waves has only become available within the past year, with the LIGO detectors now running at design sensitivity. Here we review the burgeoning field of observational gravitational astrophysics: using gravitational wave detectors as telescopes to help answer a wide range of astrophysical questions from neutron-star physics to cosmology. The next generation of ground-based telescopes should be able to make extensive gravitational observations of some of the more energetic events in our local universe. Looking only slightly further ahead, the space-based LISA observatory will reveal the gravitational universe in phenomenal detail, supplying high-quality data on perhaps thousands of sources, and tackling some of the most fascinating questions in contemporary astronomy.

Multi Station Frequency Response and Polarization of ELF/VLF Signals Generated via Ionospheric Modification

NASA Astrophysics Data System (ADS)

Maxworth, Ashanthi; Golkowski, Mark; University of Colorado Denver Team

2013-10-01

ELF/VLF wave generation via HF modulated ionospheric heating has been practiced for many years as a unique way to generate waves in the ELF/VLF band (3 Hz - 30 kHz). This paper presents experimental results and associated theoretical modeling from work performed at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. An experiment was designed to investigate the modulation frequency dependence of the generated ELF/VLF signal amplitudes and polarization at multiple sites at distances of 37 km, 50 km and 99 km from the facility. While no difference is observed for X mode versus O mode modulation of the heating wave, it is found that ELF/VLF amplitude and polarization as a function of modulated ELF/VLF frequency is different for each site. An ionospheric heating code is used to determine the primary current sources leading to the observations.

Slow waves, sharp waves, ripples, and REM in sleeping dragons.

PubMed

Shein-Idelson, Mark; Ondracek, Janie M; Liaw, Hua-Peng; Reiter, Sam; Laurent, Gilles

2016-04-29

Sleep has been described in animals ranging from worms to humans. Yet the electrophysiological characteristics of brain sleep, such as slow-wave (SW) and rapid eye movement (REM) activities, are thought to be restricted to mammals and birds. Recording from the brain of a lizard, the Australian dragon Pogona vitticeps, we identified SW and REM sleep patterns, thus pushing back the probable evolution of these dynamics at least to the emergence of amniotes. The SW and REM sleep patterns that we observed in lizards oscillated continuously for 6 to 10 hours with a period of ~80 seconds. The networks controlling SW-REM antagonism in amniotes may thus originate from a common, ancient oscillator circuit. Lizard SW dynamics closely resemble those observed in rodent hippocampal CA1, yet they originate from a brain area, the dorsal ventricular ridge, that has no obvious hodological similarity with the mammalian hippocampus. Copyright © 2016, American Association for the Advancement of Science.

Modeling of Mutiscale Electromagnetic Magnetosphere-Ionosphere Interactions near Discrete Auroral Arcs Observed by the MICA Sounding Rocket

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Lynch, K. A.; Fernandes, P. A.; Miceli, R.; Hampton, D. L.; Michell, R. G.; Samara, M.

2012-12-01

The MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) sounding rocket was launched from Poker Flat on February 19, 2012. The rocket was aimed into the system of discrete auroral arcs and during its flight it detected small-scale electromagnetic disturbances with characteristic features of dispersive Alfvén waves. We report results from numerical modeling of these observations. Our simulations are based on a two-fluid MHD model describing multi-scale interactions between magnetic field-aligned currents carried by shear Alfven waves and the ionosphere. The results from our simulations suggest that the small-scale electromagnetic structures measured by MICA indeed can be interpreted as dispersive Alfvén waves generated by the active ionospheric response (ionopspheric feedback instability) inside the large-scale downward magnetic field-aligned current interacting with the ionosphere.

Imaging San Jacinto Fault damage zone structure using dense linear arrays: application of ambient noise tomography, Rayleigh wave ellipticity, and site amplification

NASA Astrophysics Data System (ADS)

Wang, Y.; Lin, F. C.; Allam, A. A.; Ben-Zion, Y.

2017-12-01

The San Jacinto fault is presently the most seismically active component of the San Andreas Transform system in Southern California. To study the damage zone structure, two dense linear geophone arrays (BS and RR) were deployed across the Clark segment of the San Jacinto Fault between Anza and Hemet during winter 2015 and Fall 2016, respectively. Both arrays were 2 km long with 20 m station spacing. Month-long three-component ambient seismic noise data were recorded and used to calculate multi-channel cross-correlation functions. All three-component noise records of each array were normalized simultaneously to retain relative amplitude information between different stations and different components. We observed clear Rayleigh waves and Love waves on the cross-correlations of both arrays at 0.3 - 1 s period. The phase travel times of the Rayleigh waves on both arrays were measured by frequency-time analysis (FTAN), and inverted for Rayleigh wave phase velocity profiles of the upper 500 m depth. For both arrays, we observe prominent asymmetric low velocity zones which narrow with depth. At the BS array near the Hemet Stepover, an approximately 250m wide slow zone is observed to be offset by 75m to the northeast of the surface fault trace. At the RR array near the Anza segment of the fault, a similar low velocity zone width and offset are observed, along with a 10% across-fault velocity contrast. Analyses of Rayleigh wave ellipticity (H/V ratio), Love wave phase travel times, and site amplification are in progress. By using multiple measurements from ambient noise cross-correlations, we can obtain strong constraints on the local damage zone structure of the San Jacinto Fault. The results contribute to improved understanding of rupture directivity, maximum earthquake magnitude and more generally seismic hazard associated with the San Jacinto fault zone.

Onboard software of Plasma Wave Experiment aboard Arase: instrument management and signal processing of Waveform Capture/Onboard Frequency Analyzer

NASA Astrophysics Data System (ADS)

Matsuda, Shoya; Kasahara, Yoshiya; Kojima, Hirotsugu; Kasaba, Yasumasa; Yagitani, Satoshi; Ozaki, Mitsunori; Imachi, Tomohiko; Ishisaka, Keigo; Kumamoto, Atsushi; Tsuchiya, Fuminori; Ota, Mamoru; Kurita, Satoshi; Miyoshi, Yoshizumi; Hikishima, Mitsuru; Matsuoka, Ayako; Shinohara, Iku

2018-05-01

We developed the onboard processing software for the Plasma Wave Experiment (PWE) onboard the Exploration of energization and Radiation in Geospace, Arase satellite. The PWE instrument has three receivers: Electric Field Detector, Waveform Capture/Onboard Frequency Analyzer (WFC/OFA), and the High-Frequency Analyzer. We designed a pseudo-parallel processing scheme with a time-sharing system and achieved simultaneous signal processing for each receiver. Since electric and magnetic field signals are processed by the different CPUs, we developed a synchronized observation system by using shared packets on the mission network. The OFA continuously measures the power spectra, spectral matrices, and complex spectra. The OFA obtains not only the entire ELF/VLF plasma waves' activity but also the detailed properties (e.g., propagation direction and polarization) of the observed plasma waves. We performed simultaneous observation of electric and magnetic field data and successfully obtained clear wave properties of whistler-mode chorus waves using these data. In order to measure raw waveforms, we developed two modes for the WFC, `chorus burst mode' (65,536 samples/s) and `EMIC burst mode' (1024 samples/s), for the purpose of the measurement of the whistler-mode chorus waves (typically in a frequency range from several hundred Hz to several kHz) and the EMIC waves (typically in a frequency range from a few Hz to several hundred Hz), respectively. We successfully obtained the waveforms of electric and magnetic fields of whistler-mode chorus waves and ion cyclotron mode waves along the Arase's orbit. We also designed the software-type wave-particle interaction analyzer mode. In this mode, we measure electric and magnetic field waveforms continuously and transfer them to the mission data recorder onboard the Arase satellite. We also installed an onboard signal calibration function (onboard SoftWare CALibration; SWCAL). We performed onboard electric circuit diagnostics and antenna impedance measurement of the wire-probe antennas along the orbit. We utilize the results obtained using the SWCAL function when we calibrate the spectra and waveforms obtained by the PWE.[Figure not available: see fulltext.

Observations of coarse sediment movements on the mixed beach of the Elwha Delta, Washington

USGS Publications Warehouse

Miller, I.M.; Warrick, J.A.; Morgan, C.

2011-01-01

Mixed beaches, with poorly sorted grains of multiple sizes, are a common and globally distributed shoreline type. Despite this, rates and mechanisms of sediment transport on mixed beaches are poorly understood. A series of tracer deployments using native clasts implanted with Radio Frequency Identifier (RFID) tags was used to develop a better understanding of sediment transport directions and magnitudes on the mixed grain-size beach of the Elwha River delta. Using tracer samples selected to match the distribution of the coarse fraction on the beach we find that all grain sizes, up to large cobbles (128-256 mm), were mobile under most measured wave conditions and move in relationship to the direction of the alongshore component of wave energy as estimated by incident breaking wave angles. In locations where the breaking wave is normal to the shoreline we find that tracers move in both alongshore directions with approximately equal frequency. In locations where breaking waves are oblique to the shoreline we find that alongshore transport is more unidirectional and tracers can approach average velocities of 100. m/day under winter wave conditions. We use the tracer cloud to estimate the beach active width, the mobile layer depth and sediment velocity. Our results suggest that, while sediment velocity increases under increased incident wave angles, the active layer depth and width decrease, reducing sediment flux at the site with the more oblique breaking waves. This result is contrary to what is suggested by traditional wave energy transport models of alongshore sediment transport. ?? 2011 Elsevier B.V.

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

NASA Technical Reports Server (NTRS)

Yamanaka, M. D.

1989-01-01

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

Strong Magnetic Field Fluctuations within Filamentary Auroral Density Cavities Interpreted as VLF Saucer Sources

NASA Technical Reports Server (NTRS)

Knudsen, D. L.; Kabirzadeh, R.; Burchill, J. K.; Pfaff, Robert F.; Wallis, D. D.; Bounds, S. R.; Clemmons, J. H.; Pincon, J.-L.

2012-01-01

The Geoelectrodynamics and Electro-Optical Detection of Electron and SuprathermalIon Currents (GEODESIC) sounding rocket encountered more than 100 filamentary densitycavities associated with enhanced plasma waves at ELF (3 kHz) and VLF (310 kHz)frequencies and at altitudes of 800990 km during an auroral substorm. These cavities weresimilar in size (20 m diameter in most cases) to so-called lower-hybrid cavities (LHCs)observed by previous sounding rockets and satellites; however, in contrast, many of theGEODESIC cavities exhibited up to tenfold enhancements in magnetic wave powerthroughout the VLF band. GEODESIC also observed enhancements of ELF and VLFelectric fields both parallel and perpendicular to the geomagnetic field B0 within cavities,though the VLF E field increases were often not as large proportionally as seen in themagnetic fields. This behavior is opposite to that predicted by previously published theoriesof LHCs based on passive scattering of externally incident auroral hiss. We argue thatthe GEODESIC cavities are active wave generation sites capable of radiating VLF wavesinto the surrounding plasma and producing VLF saucers, with energy supplied by cold,upward flowing electron beams composing the auroral return current. This interpretation issupported by the observation that the most intense waves, both inside and outside cavities,occurred in regions where energetic electron precipitation was largely inhibited orabsent altogether. We suggest that the wave-enhanced cavities encountered by GEODESICwere qualitatively different from those observed by earlier spacecraft because of thefortuitous timing of the GEODESIC launch, which placed the payload at apogee within asubstorm-related return current during its most intense phase, lasting only a few minutes.

Ionospheric disturbances detected by high-resolution GPS-TEC observations after an earthquake and a tornado

NASA Astrophysics Data System (ADS)

Tsugawa, Takuya; Otsuka, Yuichi; Saito, Akinori; Ishii, Mamoru; Nishioka, Michi

Ionospheric disturbances following the 2011 Tohoku earthquake and the 2013 Moore tornado were observed by high-resolution GPS total electron content (TEC) observations using dense GPS receiver networks. After the 2011 Tohoku earthquake, concentric waves with short propagation distance propagated in the radial direction in the propagation velocity of 3,457, 783, 423 m/s for the first, second, third peak, respectively. Following these waves, concentric waves with long propagation distance appeared to propagate at the velocity of 138-288 m/s. In the vicinity of the epicenter, sudden TEC depletions and short-period oscillations with a period of approximately 4 minutes were also observed. The center of these ionospheric variations, termed the "ionospheric epicenter", corresponded to the tsunami source. Comparing to the results of a numerical simulation using non-hydrostatic compressible atmosphere-ionosphere model, the first peak of circular wave would be caused by the acoustic waves generated from the propagating Rayleigh wave. The second and third waves would be caused by atmospheric gravity waves excited in the lower ionosphere due to the acoustic wave propagations from the tsunami source. The fourth and following waves are considered to be caused by the atmospheric gravity waves induced by the wavefronts of traveling tsunami. After the EF5 tornado hit Moore, Oklahoma, USA, on 20 May 2013, clear concentric waves and short-period oscillations were observed. These concentric waves were non-dispersive waves with a horizontal wavelength of approximately 120 km and a period of approximately 13 minutes. They were observed for more than seven hours throughout North America. TEC oscillations with a period of approximately 4 minutes were also observed in the south of Moore for more than eight hours. Comparison between the GPS-TEC observations and the infrared cloud images from the GOES satellite indicates that the concentric waves and the short-period oscillations would be caused by supercell-induced atmospheric gravity waves and acoustic resonances, respectively. In this presentation, we will introduce the observational results of these ionospheric disturbances and discuss about the mechanism of concentric waves and short-period oscillations observed in both events.

Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding

NASA Astrophysics Data System (ADS)

Baumgarten, Kathrin; Gerding, Michael; Baumgarten, Gerd; Lübken, Franz-Josef

2018-01-01

Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh-Mie-Raman (RMR) lidar at Kühlungsborn (54° N, 12° E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4-8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave-wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

Temporal variability in wind-wave climate and its validation with ESSO-NIOT wave atlas for the head Bay of Bengal

NASA Astrophysics Data System (ADS)

Patra, Anindita; Bhaskaran, Prasad K.

2017-08-01

The head Bay region bordering the northern Bay of Bengal is a densely populated area with a complex geomorphologic setting, and highly vulnerable to extreme water levels along with other factors like sea level rise and impact of tropical cyclones. The influence of climate change on wind-wave regime from this region of Bay of Bengal is not known well and that requires special attention, and there is a need to perform its long-term assessment for societal benefits. This study provides a comprehensive analysis on the temporal variability in domain averaged wind speed, significant wave height (SWH) utilizing satellite altimeter data (1992-2012) and mean wave period using ECMWF reanalysis products ERA-Interim (1992-2012) and ERA-20C (1992-2010) over this region. The SWH derived from WAVEWATCH III (WW3) model along with the ERA-Interim reanalysis supplements the observed variability in satellite altimeter observations. Further, the study performs an extensive error estimation of SWH and mean wave period with ESSO-NIOT wave atlas that shows a high degree of under-estimation in the wave atlas mean wave period. Annual mean and wind speed maxima from altimeter show an increasing trend, and to a lesser extent in the SWH. Interestingly, the estimated trend is higher for maxima compared to the mean conditions. Analysis of decadal variability exhibits an increased frequency of higher waves in the present decade compared to the past. Linear trend analysis show significant upswing in spatially averaged ERA-20C mean wave period, whereas the noticed variations are marginal in the ERA-Interim data. A separate trend analysis for the wind-seas, swell wave heights and period from ERA-20C decipher the fact that distant swells governs the local wind-wave climatology over the head Bay region, and over time the swell activity have increased in this region.

Investigation of electrostatic waves in the ion cyclotron range of frequencies in L-4 and ACT-1

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

Ono, Masayuki

Electrostatic waves in the ion cyclotron range of frequencies (ICRF) were studied in the Princeton L-4 and ACT-1 devices for approximately ten years, from 1975 to 1985. The investigation began in the L-4 linear device, looking for the parametric excitation of electrostatic ion cyclotron waves in multi-ion-species plasmas. In addition, this investigation verified multi-ion-species effects on the electrostatic ion cyclotron wave dispersion religion including the ion-ion hybrid resonance. Finite-Larmor-radius modification of the wave dispersion relation was also observed, even for ion temperatures of T{sub i} {approx} 1/40 eV. Taking advantage of the relatively high field and long device length ofmore » L-4, the existence of the cold electrostatic ion cyclotron wave (CES ICW) was verified. With the arrival of the ACT-1 toroidal device, finite-Larmor-radius (FLR) waves were studied in a relatively collisionless warm-ion hydrogen plasma. Detailed investigations of ion Bernstein waves (IBW) included the verification of mode-transformation in their launching, their wave propagation characteristics, their absorption, and the resulting ion heating. This basic physics activity played a crucial role in developing a new reactor heating concept termed ion Bernstein wave heating. Experimental research in the lower hybrid frequency range confirmed the existence of FLR effects near the lower hybrid resonance, predicted by Stix in 1965. In a neon plasma with a carefully placed phased wave exciter, the neutralized ion Bernstein wave was observed for the first time. Using a fastwave ICRF antenna, two parasitic excitation processes for IBW -- parametric instability and density-gradient-driven excitation -- were also discovered. In the concluding section of this paper, a possible application of externally launched electrostatic waves is suggested for helium ash removal from fusion reactor plasmas.« less

Investigation of electrostatic waves in the ion cyclotron range of frequencies in L-4 and ACT-1

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

Ono, Masayuki.

Electrostatic waves in the ion cyclotron range of frequencies (ICRF) were studied in the Princeton L-4 and ACT-1 devices for approximately ten years, from 1975 to 1985. The investigation began in the L-4 linear device, looking for the parametric excitation of electrostatic ion cyclotron waves in multi-ion-species plasmas. In addition, this investigation verified multi-ion-species effects on the electrostatic ion cyclotron wave dispersion religion including the ion-ion hybrid resonance. Finite-Larmor-radius modification of the wave dispersion relation was also observed, even for ion temperatures of T[sub i] [approx] 1/40 eV. Taking advantage of the relatively high field and long device length ofmore » L-4, the existence of the cold electrostatic ion cyclotron wave (CES ICW) was verified. With the arrival of the ACT-1 toroidal device, finite-Larmor-radius (FLR) waves were studied in a relatively collisionless warm-ion hydrogen plasma. Detailed investigations of ion Bernstein waves (IBW) included the verification of mode-transformation in their launching, their wave propagation characteristics, their absorption, and the resulting ion heating. This basic physics activity played a crucial role in developing a new reactor heating concept termed ion Bernstein wave heating. Experimental research in the lower hybrid frequency range confirmed the existence of FLR effects near the lower hybrid resonance, predicted by Stix in 1965. In a neon plasma with a carefully placed phased wave exciter, the neutralized ion Bernstein wave was observed for the first time. Using a fastwave ICRF antenna, two parasitic excitation processes for IBW -- parametric instability and density-gradient-driven excitation -- were also discovered. In the concluding section of this paper, a possible application of externally launched electrostatic waves is suggested for helium ash removal from fusion reactor plasmas.« less

Internal waves interacting with particles in suspension

NASA Astrophysics Data System (ADS)

Micard, Diane

2016-04-01

Internal waves are produced as a consequence of the dynamic balance between buoy- ancy and gravity forces when a particle of fluid is vertically displaced in a stable stratified environment. Geophysical systems such as ocean and atmosphere are naturally stratified and therefore suitable for internal waves to propagate. Furthermore, these two environ- ments stock a vast amount of particles in suspension, which present a large spectrum of physical properties (size, density, shape), and can be organic, mineral or pollutant agents. Therefore, it is reasonable to expect that internal waves will have an active effect over the dynamics of these particles. In order to study the interaction of internal waves and suspended particles, an ide- alized experimental setup has been implemented. A linear stratification is produced in a 80×40×17 cm3 tank, in which two dimensional plane waves are created thanks to the inno- vative wave generator GOAL. In addition, a particle injector has been developed to produce a vertical column of particles within the fluid, displaying the same two-dimensional sym- metry as the waves. The particle injector allows to control the volumic fraction of particles and the size of the column. The presence of internal waves passing through the column of particles allowed to observe two main effects: The column oscillates around an equilibrium position (which is observed in both, the contours an the interior of the column), and the column is displaced as a whole. The column is displaced depending on the characteristics of the column, the gradient of the density, and the intensity and frequency of the wave. When displaced, the particles within the column are sucked towards the source of waves. The direction of the displacement of the column is explained by computing the effect of the Lagrangian drift generated by the wave over the time the particles stay in the wave beam before settling.

Plasma Waves and Structures Associated with Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Ergun, R.; Wilder, F. D.; Ahmadi, N.; Goodrich, K.; Holmes, J.; Newman, D. L.; Burch, J.; Torbert, R. B.; Le Contel, O.; Giles, B. L.; Strangeway, R. J.; Lindqvist, P. A.

2017-12-01

Space observations of magnetic reconnection indicate a variety of plasma wave modes and structures in the vicinity of the electron diffusion region including electromagnetic whistler waves, quasi-electrostatic whistler waves, electron phase-space holes, double layers, electron acoustic waves, lower hybrid waves, upper hybrid waves, and electromagnetic drift waves. These waves and plasma structures are seen in magnetotail reconnection and subsolar reconnection. The MMS mission has the unique ability to unequivocally identify the electron diffusion region and distinguish waves in the EDR from those in the extended separatrix. Such a distinction is critical since some of the observed waves may be involved the reconnection process while others may result from subsequent or associated events and do not directly influence the reconnection process. For example, some of the largest amplitude (> 100 mV/m) electrostatic waves have been identified as electron acoustic waves and upper hybrid waves. These waves are likely generated as a result of reconnection and do not appear to strongly influence the reconnection process. On the other hand, large-amplitude electrostatic whistler waves have been observed very near the X-line, are seen in simulations, and may be participating in reconnection physics. Electromagnetic drift waves almost always appear in cases of asymmetric reconnection and may lead to a more turbulent process. We summarize wave observations by MMS and discuss the relative their possible role in magnetic reconnection physics, concentrating on recent magnetotail observations.

Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)

USGS Publications Warehouse

Pollitz, F.F.

2008-01-01

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long-period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ???40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at peni ods 27-100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three-dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.

Impact of mitochondrial Ca2+ cycling on pattern formation and stability.

PubMed

Falcke, M; Hudson, J L; Camacho, P; Lechleiter, J D

1999-07-01

Energization of mitochondria significantly alters the pattern of Ca2+ wave activity mediated by activation of the inositol (1,4,5) trisphosphate (IP3) receptor (IP3R) in Xenopus oocytes. The number of pulsatile foci is reduced and spiral Ca2+ waves are no longer observed. Rather, target patterns of Ca2+ release predominate, and when fragmented, fail to form spirals. Ca2+ wave velocity, amplitude, decay time, and periodicity are also increased. We have simulated these experimental findings by supplementing an existing mathematical model with a differential equation for mitochondrial Ca2+ uptake and release. Our calculations show that mitochondrial Ca2+ efflux plays a critical role in pattern formation by prolonging the recovery time of IP3Rs from a refractory state. We also show that under conditions of high energization of mitochondria, the Ca2+ dynamics can become bistable with a second stable stationary state of high resting Ca2+ concentration.

Diffraction-Induced Bidimensional Talbot Self-Imaging with Full Independent Period Control

NASA Astrophysics Data System (ADS)

Guillet de Chatellus, Hugues; Romero Cortés, Luis; Deville, Antonin; Seghilani, Mohamed; Azaña, José

2017-03-01

We predict, formulate, and observe experimentally a generalized version of the Talbot effect that allows one to create diffraction-induced self-images of a periodic two-dimensional (2D) waveform with arbitrary control of the image spatial periods. Through the proposed scheme, the periods of the output self-image are multiples of the input ones by any desired integer or fractional factor, and they can be controlled independently across each of the two wave dimensions. The concept involves conditioning the phase profile of the input periodic wave before free-space diffraction. The wave energy is fundamentally preserved through the self-imaging process, enabling, for instance, the possibility of the passive amplification of the periodic patterns in the wave by a purely diffractive effect, without the use of any active gain.

Diffraction-Induced Bidimensional Talbot Self-Imaging with Full Independent Period Control.

PubMed

Guillet de Chatellus, Hugues; Romero Cortés, Luis; Deville, Antonin; Seghilani, Mohamed; Azaña, José

2017-03-31

We predict, formulate, and observe experimentally a generalized version of the Talbot effect that allows one to create diffraction-induced self-images of a periodic two-dimensional (2D) waveform with arbitrary control of the image spatial periods. Through the proposed scheme, the periods of the output self-image are multiples of the input ones by any desired integer or fractional factor, and they can be controlled independently across each of the two wave dimensions. The concept involves conditioning the phase profile of the input periodic wave before free-space diffraction. The wave energy is fundamentally preserved through the self-imaging process, enabling, for instance, the possibility of the passive amplification of the periodic patterns in the wave by a purely diffractive effect, without the use of any active gain.

Singing comet changes its song

NASA Astrophysics Data System (ADS)

Volwerk, M.; Goetz, C.; Delva, M.; Richter, I.; Tsurutani, B. T.; Eriksson, A.; Odelstad, E.; Meier, P.; Nilsson, H.; Glassmeier, K.-H.

2017-09-01

The singing comet was discovered at the beginning of the Rosetta mission around comet 67P/Churyumov-Gerasimenko. Large amplitude compressional waves with frequencies between 10 and 100 mHz were observed. When the comet became more active this signal was no longer measured. During the so-called tail excursion, late in the mission after perihelion, with again a less active comet, the singing was observed again and interestingly, going from 26 March to 27 March 2016 the character of the singing changed.

In situ Observations of Magnetosonic Waves Modulated by Background Plasma Density

NASA Astrophysics Data System (ADS)

Yu, X.; Yuan, Z.; Huang, S.; Wang, D.; Funsten, H. O.

2017-12-01

We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with 'ring' distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate the amplitudes of magnetosonic waves through controlling the wave growth rates.

Local vertical motions and kinetic temperature from AE-C as evidence for aurora-induced gravity waves

NASA Technical Reports Server (NTRS)

Spencer, N. W.; Theis, R. F.; Wharton, L. E.; Carignan, G. R.

1976-01-01

In situ measurements of local vertical neutral particle motions have been made using the Neutral Atmosphere Temperature Instrument (NATE) on Atmosphere Explorer-C from observations of the direction of flow of neutral particles into the antechamber of the sensor (mass spectrometer). Values ranging from a few to more than 80 meters per second have been observed. The data show vertical motions greater than a few meters per second to be present most of the time, the magnitude being a function of many factors including magnetic activity, location, and magnetic storm history. In a specific case, it is concluded that the observed vertical motions and kinetic temperature are evidence of a travelling disturbance originating as a gravity wave in the auroral zone.

Near Surface Seismic Hazard Characterization in the Presence of High Velocity Contrasts

NASA Astrophysics Data System (ADS)

Gribler, G.; Mikesell, D.; Liberty, L. M.

2017-12-01

We present new multicomponent surface wave processing techniques that provide accurate characterization of near-surface conditions in the presence of large lateral or vertical shear wave velocity boundaries. A common problem with vertical component Rayleigh wave analysis in the presence of high contrast subsurface conditions is Rayleigh wave propagation mode misidentification due to an overlap of frequency-phase velocity domain dispersion, leading to an overestimate of shear wave velocities. By using the vertical and horizontal inline component signals, we isolate retrograde and prograde particle motions to separate fundamental and higher mode signals, leading to more accurate and confident dispersion curve picks and shear wave velocity estimates. Shallow, high impedance scenarios, such as the case with shallow bedrock, are poorly constrained when using surface wave dispersion information alone. By using a joint inversion of dispersion and horizontal-to-vertical (H/V) curves within active source frequency ranges (down to 3 Hz), we can accurately estimate the depth to high impedance boundaries, a significant improvement compared to the estimates based on dispersion information alone. We compare our approach to body wave results that show comparable estimates of bedrock topography. For lateral velocity contrasts, we observe horizontal polarization of Rayleigh waves identified by an increase in amplitude and broadening of the horizontal spectra with little variation in the vertical component spectra. The horizontal spectra offer a means to identify and map near surface faults where there is no topographic or clear body wave expression. With these new multicomponent active source seismic data processing and inversion techniques, we better constrain a variety of near surface conditions critical to the estimation of local site response and seismic hazards.

The Role of Localized Compressional Ultra-low Frequency Waves in Energetic Electron Precipitation

NASA Astrophysics Data System (ADS)

Rae, I. Jonathan; Murphy, Kyle R.; Watt, Clare E. J.; Halford, Alexa J.; Mann, Ian R.; Ozeke, Louis G.; Sibeck, David G.; Clilverd, Mark A.; Rodger, Craig J.; Degeling, Alex W.; Forsyth, Colin; Singer, Howard J.

2018-03-01

Typically, ultra-low frequency (ULF) waves have historically been invoked for radial diffusive transport leading to acceleration and loss of outer radiation belt electrons. At higher frequencies, very low frequency waves are generally thought to provide a mechanism for localized acceleration and loss through precipitation into the ionosphere of radiation belt electrons. In this study we present a new mechanism for electron loss through precipitation into the ionosphere due to a direct modulation of the loss cone via localized compressional ULF waves. We present a case study of compressional wave activity in tandem with riometer and balloon-borne electron precipitation across keV-MeV energies to demonstrate that the experimental measurements can be explained by our new enhanced loss cone mechanism. Observational evidence is presented demonstrating that modulation of the equatorial loss cone can occur via localized compressional wave activity, which greatly exceeds the change in pitch angle through conservation of the first and second adiabatic invariants. The precipitation response can be a complex interplay between electron energy, the localization of the waves, the shape of the phase space density profile at low pitch angles, ionospheric decay time scales, and the time dependence of the electron source; we show that two pivotal components not usually considered are localized ULF wave fields and ionospheric decay time scales. We conclude that enhanced precipitation driven by compressional ULF wave modulation of the loss cone is a viable candidate for direct precipitation of radiation belt electrons without any additional requirement for gyroresonant wave-particle interaction. Additional mechanisms would be complementary and additive in providing means to precipitate electrons from the radiation belts during storm times.

Concentrated energy addition for active drag reduction in hypersonic flow regime

NASA Astrophysics Data System (ADS)

Ashwin Ganesh, M.; John, Bibin

2018-01-01

Numerical optimization of hypersonic drag reduction technique based on concentrated energy addition is presented in this study. A reduction in wave drag is realized through concentrated energy addition in the hypersonic flowfield upstream of the blunt body. For the exhaustive optimization presented in this study, an in-house high precision inviscid flow solver has been developed. Studies focused on the identification of "optimum energy addition location" have revealed the existence of multiple minimum drag points. The wave drag coefficient is observed to drop from 0.85 to 0.45 when 50 Watts of energy is added to an energy bubble of 1 mm radius located at 74.7 mm upstream of the stagnation point. A direct proportionality has been identified between energy bubble size and wave drag coefficient. Dependence of drag coefficient on the upstream added energy magnitude is also revealed. Of the observed multiple minimum drag points, the energy deposition point (EDP) that offers minimum wave drag just after a sharp drop in drag is proposed as the most optimum energy addition location.

Electromagnetic ion cyclotron waves stimulated by modest magnetospheric compressions

NASA Technical Reports Server (NTRS)

Anderson, B. J.; Hamilton, D. C.

1993-01-01

AMPTE/CCE magnetic field and particle data are used to test the suggestion that increased hot proton temperature anisotropy resulting from convection during magnetospheric compression is responsible for the enhancement in Pc 1 emission via generation of electromagnetic ion cyclotron (EMIC) waves in the dayside outer equatorial magnetosphere. The relative increase in magnetic field is used to gauge the strength of the compression, and an image dipole model is used to estimate the motion of the plasma during compression. Proton data are used to analyze the evolution of the proton distribution and the corresponding changes in EMIC wave activity expected during the compression. It is suggested that enhancements in dynamic pressure pump the energetic proton distributions in the outer magnetosphere, driving EMIC waves. Waves are expected to be generated most readily close to the magnetopause, and transient pressure pulses may be associated with bursts of EMIC waves, which would be observed on the ground in association with ionospheric transient signatures.

Anomalous Signal Detection in ELF Band Electromagnetic Wave using Multi-layer Neural Network with Wavelet Decomposition

NASA Astrophysics Data System (ADS)

Itai, Akitoshi; Yasukawa, Hiroshi; Takumi, Ichi; Hata, Masayasu

It is well known that electromagnetic waves radiated from the earth's crust are useful for predicting earthquakes. We analyze the electromagnetic waves received at the extremely low frequency band of 223Hz. These observed signals contain the seismic radiation from the earth's crust, but also include several undesired signals. Our research focuses on the signal detection technique to identify an anomalous signal corresponding to the seismic radiation in the observed signal. Conventional anomalous signal detections lack a wide applicability due to their assumptions, e.g. the digital data have to be observed at the same time or the same sensor. In order to overcome the limitation related to the observed signal, we proposed the anomalous signals detection based on a multi-layer neural network which is trained by digital data observed during a span of a day. In the neural network approach, training data do not need to be recorded at the same place or the same time. However, some noises, which have a large amplitude, are detected as the anomalous signal. This paper develops a multi-layer neural network to decrease the false detection of the anomalous signal from the electromagnetic wave. The training data for the proposed network is the decomposed signal of the observed signal during several days, since the seismic radiations are often recorded from several days to a couple of weeks. Results show that the proposed neural network is useful to achieve the accurate detection of the anomalous signal that indicates seismic activity.

Rogue run-up events at the North Sea coast

NASA Astrophysics Data System (ADS)

Didenkulova, Ira; Blossier, Brice; Daly, Christopher; Herbst, Gabriel; Senichev, Dmitry; Winter, Christian

2015-04-01

On the 1st of January, 1995, the Statoil-operated "Draupner" platform located in the North Sea recorded the so-called "New Year wave". Since then, rogue waves have been the topic of active scientific discussions and investigations. Waves of extreme height appearing randomly at the sea surface have been measured in both deep and shallow waters and have been involved in a number of ship accidents. Nowadays rogue waves are frequently recorded all over the world with several different instruments (range finders installed on offshore platforms, deployed buoys, radars including SAR, etc.). Rogue wave also occur at the coast, where they appear as either sudden flooding of coastal areas or high splashes over steep banks or sea walls. These waves are especially dangerous for beach users and lead regularly to human injuries and fatalities. Despite numerous reports of human accidents, coastal rogue waves have not yet been recorded experimentally. In this paper we discuss the recording of rogue wave events at German North Sea coasts by using high-resolution beach cameras. The recorded rogue waves are observed during different tide levels and different weather conditions. Possible mechanisms of their generation are discussed.

Formation of ECR Plasma in a Dielectric Plasma Guide under Self-Excitation of a Standing Ion-Acoustic Wave

NASA Astrophysics Data System (ADS)

Balmashnov, A. A.; Kalashnikov, A. V.; Kalashnikov, V. V.; Stepina, S. P.; Umnov, A. M.

2018-01-01

The formation of a spatially localized plasma with a high brightness has been experimentally observed in a dielectric plasma guide under the electron cyclotron resonance discharge at the excitation of a standing ion-acoustic wave. The results obtained show the possibility of designing compact high-intensity radiation sources with a spectrum determined by the working gas or gas mixture type, high-intensity chemically active particle flow sources, and plasma thrusters for correcting orbits of light spacecraft.

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.

Wave2 activates serum response element via its VCA region and functions downstream of Rac.

PubMed

Ishiguro, Kazuhiro; Cao, Zhifang; Ilasca, Marco Lopez; Ando, Takafumi; Xavier, Ramnik

2004-12-10

WAVE2 is a member of the WASP/WAVE family of protein effectors of actin reorganization and cell movement. In this report, we demonstrate that WAVE2 overexpression induces serum response element (SRE) activation through serum response factor. A WAVE2 mutant lacking the VCA region did not induce SRE activation and actin polymerization. WAVE2-induced SRE activation was blocked by exposure of cells to Latrunculin A, or overexpression of actin mutant R62D. The DeltaVCA mutant inhibited Rac V12-induced SRE activation, suggesting that WAVE2 lies downstream of Rac. Similar deletion of the VCA domain of WASP attenuated Cdc42 V12-mediated SRE activation, suggesting that WAVE2 acts in relation to Rac as WASP acts in relation to Cdc42. WAVE2 overexpression did not activate NF-kappaB.

Observations of height-dependent pressure-perturbation structure of a strong mesoscale gravity wave

NASA Technical Reports Server (NTRS)

Starr, David O'C.; Korb, C. L.; Schwemmer, Geary K.; Weng, Chi Y.

1992-01-01

Airborne observations using a downward-looking, dual-frequency, near-infrared, differential absorption lidar system provide the first measurements of the height-dependent pressure-perturbation field associated with a strong mesoscale gravity wave. A pressure-perturbation amplitude of 3.5 mb was measured within the lowest 1.6 km of the atmosphere over a 52-km flight line. Corresponding vertical displacements of 250-500 m were inferred from lidar-observed displacement of aerosol layers. Accounting for probable wave orientation, a horizontal wavelength of about 40 km was estimated. Satellite observations reveal wave structure of a comparable scale in concurrent cirrus cloud fields over an extended area. Smaller-scale waves were also observed. Local meteorological soundings are analyzed to confirm the existence of a suitable wave duct. Potential wave-generation mechanisms are examined and discussed. The large pressure-perturbation wave is attributed to rapid amplification or possible wave breaking of a gravity wave as it propagated offshore and interacted with a very stable marine boundary layer capped by a strong shear layer.

Observation and Modeling of Storm Generated Acoustic Waves in the Ionosphere Revealed in a Dense Network of GPS Receivers

NASA Astrophysics Data System (ADS)

Walterscheid, R. L.; Azeem, S. I.

2017-12-01

Acoustic waves generated in the lower atmosphere may become an important source of variably in the upper atmosphere. Although they are excited with small amplitudes they are minimally subject to viscous dissipation and may reach significant amplitudes at F-region altitudes. A number of studies in the 1970s showed clear signatures in ionosonde data in the infrasonic period range attributable to thunder storm activity. We have examined Total Electron Content data from a dense network of over 4000 ground-based GPS receivers over the continental United States during an outbreak of severe weather, including tornados, over Kansas in May 2015. A sequence of GPS TEC images showed clear Traveling Ionospheric Disturbances (TIDs) in the form of concentric rings moving outward from the center of the storm region. The characteristics of the disturbance (phase speed and frequency) were consistent with acoustic waves in the infrasonic range. We have modeled the disturbance by including a tropospheric heat source representing latent heat release from a large thunderstorm. The disturbance at ionospheric altitudes resembles the observed disturbance in terms of phase speed, frequency and horizontal wavelength. We conclude that the observed TIDs in TEC were caused by an acoustic wave generated by deep convection.

Behavior of ectopic surface: effects of β-adrenergic stimulation and uncoupling

PubMed Central

Arutunyan, Ara; Pumir, Alain; Krinsky, Valentin; Swift, Luther; Sarvazyan, Narine

2011-01-01

By using both experimental and theoretical means, we have addressed the progression of ectopic activity from individual cardiac cells to a multicellular two-dimensional network. Experimental conditions that favor ectopic activity have been created by local perfusion of a small area of cardiomyocyte network (I-zone) with an isoproterenol-heptanol containing solution. The application of this solution initially slowed down and then fully blocked wave propagation inside the I-zone. After a brief lag period, ectopically active cells appeared in the I-zone, followed by evolution of the ectopic clusters into slowly propagating waves. The changing pattern of colliding and expanding ectopic waves confined to the I-zone persisted for as long as the isoproterenol-heptanol environment was present. On restoration of the control environment, the ectopic waves from the I-zone broke out into the surrounding network causing arrhythmias. The observed sequence of events was also modeled by FitzHugh-Nagumo equations and included a cell’s arrangement of two adjacent square regions of 20 × 20 cells. The control zone consisted of well-connected, excitable cells, and the I-zone was made of weakly coupled cells (heptanol effect), which became spontaneously active as time evolved (isoproterenol effect). The dynamic events in the system have been studied numerically with the use of a finite difference method. Together, our experimental and computational data have revealed that the combination of low coupling, increased excitability, and spatial heterogeneity can lead to the development of ectopic waves confined to the injured network. This transient condition appears to serve as an essential step for the ectopic activity to “mature” before escaping into the surrounding control network. PMID:12893638

Behavior of ectopic surface: effects of beta-adrenergic stimulation and uncoupling.

PubMed

Arutunyan, Ara; Pumir, Alain; Krinsky, Valentin; Swift, Luther; Sarvazyan, Narine

2003-12-01

By using both experimental and theoretical means, we have addressed the progression of ectopic activity from individual cardiac cells to a multicellular two-dimensional network. Experimental conditions that favor ectopic activity have been created by local perfusion of a small area of cardiomyocyte network (I-zone) with an isoproterenol-heptanol containing solution. The application of this solution initially slowed down and then fully blocked wave propagation inside the I-zone. After a brief lag period, ectopically active cells appeared in the I-zone, followed by evolution of the ectopic clusters into slowly propagating waves. The changing pattern of colliding and expanding ectopic waves confined to the I-zone persisted for as long as the isoproterenol-heptanol environment was present. On restoration of the control environment, the ectopic waves from the I-zone broke out into the surrounding network causing arrhythmias. The observed sequence of events was also modeled by FitzHugh-Nagumo equations and included a cell's arrangement of two adjacent square regions of 20 x 20 cells. The control zone consisted of well-connected, excitable cells, and the I-zone was made of weakly coupled cells (heptanol effect), which became spontaneously active as time evolved (isoproterenol effect). The dynamic events in the system have been studied numerically with the use of a finite difference method. Together, our experimental and computational data have revealed that the combination of low coupling, increased excitability, and spatial heterogeneity can lead to the development of ectopic waves confined to the injured network. This transient condition appears to serve as an essential step for the ectopic activity to "mature" before escaping into the surrounding control network.

Geospace ionosphere research with a MF/HF radio instrument on a cubesat

NASA Astrophysics Data System (ADS)

Kallio, E. J.; Aikio, A. T.; Alho, M.; Fontell, M.; van Gijlswijk, R.; Kauristie, K.; Kestilä, A.; Koskimaa, P.; Makela, J. S.; Mäkelä, M.; Turunen, E.; Vanhamäki, H.

2016-12-01

Modern technology provides new possibilities to study geospace and its ionosphere, using spacecraft and and computer simulations. A type of nanosatellites, CubeSats, provide a cost effective possibility to provide in-situ measurements in the ionosphere. Moreover, combined CubeSat observations with ground-based observations gives a new view on auroras and associated electromagnetic phenomena. Especially joint and active CubeSat - ground based observation campaigns enable the possibility of studying the 3D structure of the ionosphere. Furthermore using several CubeSats to form satellite constellations enables much higher temporal resolution. At the same time, increasing computation capacity has made it possible to perform simulations where properties of the ionosphere, such as propagation of the electromagnetic waves in the medium frequency, MF (0.3-3 MHz) and high frequency, HF (3-30 MHz), ranges is based on a 3D ionospheric model and on first-principles modelling. Electromagnetic waves at those frequencies are strongly affected by ionospheric electrons and, consequently, those frequencies can be used for studying the plasma. On the other hand, even if the ionosphere originally enables long-range telecommunication at MF and HF frequencies, the frequent occurrence of spatiotemporal variations in the ionosphere disturbs communication channels, especially at high latitudes. Therefore, study of the MF and HF waves in the ionosphere has both a strong science and technology interests. We present computational simulation results and measuring principles and techniques to investigate the arctic ionosphere by a polar orbiting CubeSat whose novel AM radio instrument measures HF and MF waves. The cubesat, which contains also a white light aurora camera, is planned to be launched in 2017 (http://www.suomi100satelliitti.fi/eng). We have modelled the propagation of the radio waves, both ground generated man-made waves and space formed space weather related waves, through the 3D arctic ionosphere with (1) a new 3D ray tracing model and (2) a new 3D full kinetic electromagnetic simulation. These simulations are used to analyse the origin of the radio waves observed by the MH/HF radio instrument and, consequently, to derive information about the 3D ionosphere and its spatial and temporal variations.

A Discrete Electromechanical Model for Human Cardiac Tissue: Effects of Stretch-Activated Currents and Stretch Conditions on Restitution Properties and Spiral Wave Dynamics

PubMed Central

Weise, Louis D.; Panfilov, Alexander V.

2013-01-01

We introduce an electromechanical model for human cardiac tissue which couples a biophysical model of cardiac excitation (Tusscher, Noble, Noble, Panfilov, 2006) and tension development (adjusted Niederer, Hunter, Smith, 2006 model) with a discrete elastic mass-lattice model. The equations for the excitation processes are solved with a finite difference approach, and the equations of the mass-lattice model are solved using Verlet integration. This allows the coupled problem to be solved with high numerical resolution. Passive mechanical properties of the mass-lattice model are described by a generalized Hooke's law for finite deformations (Seth material). Active mechanical contraction is initiated by changes of the intracellular calcium concentration, which is a variable of the electrical model. Mechanical deformation feeds back on the electrophysiology via stretch-activated ion channels whose conductivity is controlled by the local stretch of the medium. We apply the model to study how stretch-activated currents affect the action potential shape, restitution properties, and dynamics of spiral waves, under constant stretch, and dynamic stretch caused by active mechanical contraction. We find that stretch conditions substantially affect these properties via stretch-activated currents. In constantly stretched medium, we observe a substantial decrease in conduction velocity, and an increase of action potential duration; whereas, with dynamic stretch, action potential duration is increased only slightly, and the conduction velocity restitution curve becomes biphasic. Moreover, in constantly stretched medium, we find an increase of the core size and period of a spiral wave, but no change in rotation dynamics; in contrast, in the dynamically stretching medium, we observe spiral drift. Our results may be important to understand how altered stretch conditions affect the heart's functioning. PMID:23527160

A discrete electromechanical model for human cardiac tissue: effects of stretch-activated currents and stretch conditions on restitution properties and spiral wave dynamics.

PubMed

Weise, Louis D; Panfilov, Alexander V

2013-01-01

We introduce an electromechanical model for human cardiac tissue which couples a biophysical model of cardiac excitation (Tusscher, Noble, Noble, Panfilov, 2006) and tension development (adjusted Niederer, Hunter, Smith, 2006 model) with a discrete elastic mass-lattice model. The equations for the excitation processes are solved with a finite difference approach, and the equations of the mass-lattice model are solved using Verlet integration. This allows the coupled problem to be solved with high numerical resolution. Passive mechanical properties of the mass-lattice model are described by a generalized Hooke's law for finite deformations (Seth material). Active mechanical contraction is initiated by changes of the intracellular calcium concentration, which is a variable of the electrical model. Mechanical deformation feeds back on the electrophysiology via stretch-activated ion channels whose conductivity is controlled by the local stretch of the medium. We apply the model to study how stretch-activated currents affect the action potential shape, restitution properties, and dynamics of spiral waves, under constant stretch, and dynamic stretch caused by active mechanical contraction. We find that stretch conditions substantially affect these properties via stretch-activated currents. In constantly stretched medium, we observe a substantial decrease in conduction velocity, and an increase of action potential duration; whereas, with dynamic stretch, action potential duration is increased only slightly, and the conduction velocity restitution curve becomes biphasic. Moreover, in constantly stretched medium, we find an increase of the core size and period of a spiral wave, but no change in rotation dynamics; in contrast, in the dynamically stretching medium, we observe spiral drift. Our results may be important to understand how altered stretch conditions affect the heart's functioning.

A study of the dynamics of the equatorial lower stratosphere by use of ultra-long-duration balloons, 2, Gravity waves

NASA Astrophysics Data System (ADS)

Hertzog, A.; Vial, F.

2001-10-01

This study is the companion paper of Vial et al. [this issue]. A campaign of ultra-long-duration, superpressure balloons in the equatorial lower stratosphere was held in September 1998. By conception these balloons evolve on isopycnic surfaces. Pressure and position were measured every 12 min, which enable to infer the characteristics of gravity waves with periods between 1 hour and 1 day in this region of the atmosphere. The intrinsic-frequency spectra of horizontal wind fluctuations exhibit a -2 slope, while the one associated with vertical-wind fluctuations is flat. Significant inhomogeneity of the wave activity is observed, and the variance of the shortest frequency waves is found to be linked to the position of the balloons with respect to the Intertropical Convergence Zone. On average, the total energy associated with gravity waves in the period range studied in this paper is found to be ˜ 7 J kg-1. Calculations of momentum flux have also been undertaken. It appears that there is an approximate equipartition of flux between eastward and westward propagating gravity waves and that the absolute value of the flux is 8-12 × 10-3 m2 s-2 at 20 km. A larger flux is also observed above convective regions. These values suggest that gravity waves may carry the largest part of the Eliassen-Palm flux required for the driving of the quasi-biennial oscillation.

Time-resolved tomography using acoustic emissions in the laboratory, and application to sandstone compaction

NASA Astrophysics Data System (ADS)

Brantut, Nicolas

2018-02-01

Acoustic emission and active ultrasonic wave velocity monitoring are often performed during laboratory rock deformation experiments, but are typically processed separately to yield homogenised wave velocity measurements and approximate source locations. Here I present a numerical method and its implementation in a free software to perform a joint inversion of acoustic emission locations together with the three-dimensional, anisotropic P-wave structure of laboratory samples. The data used are the P-wave first arrivals obtained from acoustic emissions and active ultrasonic measurements. The model parameters are the source locations and the P-wave velocity and anisotropy parameter (assuming transverse isotropy) at discrete points in the material. The forward problem is solved using the fast marching method, and the inverse problem is solved by the quasi-Newton method. The algorithms are implemented within an integrated free software package called FaATSO (Fast Marching Acoustic Emission Tomography using Standard Optimisation). The code is employed to study the formation of compaction bands in a porous sandstone. During deformation, a front of acoustic emissions progresses from one end of the sample, associated with the formation of a sequence of horizontal compaction bands. Behind the active front, only sparse acoustic emissions are observed, but the tomography reveals that the P-wave velocity has dropped by up to 15%, with an increase in anisotropy of up to 20%. Compaction bands in sandstones are therefore shown to produce sharp changes in seismic properties. This result highlights the potential of the methodology to image temporal variations of elastic properties in complex geomaterials, including the dramatic, localised changes associated with microcracking and damage generation.

Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch

NASA Astrophysics Data System (ADS)

Guerlet, S.; Fouchet, T.; Spiga, A.; Flasar, F. M.; Fletcher, L. N.; Hesman, B. E.; Gorius, N.

2018-01-01

Thermal infrared spectra acquired by Cassini/Composite InfraRed Spectrometer (CIRS) in limb-viewing geometry in 2015 are used to derive 2-D latitude-pressure temperature and thermal wind maps. These maps are used to study the vertical structure and evolution of Saturn's equatorial oscillation (SEO), a dynamical phenomenon presenting similarities with the Earth's quasi-biennal oscillation (QBO) and semi-annual oscillation (SAO). We report that a new local wind maximum has appeared in 2015 in the upper stratosphere and derive the descent rates of other wind extrema through time. The phase of the oscillation observed in 2015, as compared to 2005 and 2010, remains consistent with a ˜15 year period. The SEO does not propagate downward at a regular rate but exhibits faster descent rate in the upper stratosphere, combined with a greater vertical wind shear, compared to the lower stratosphere. Within the framework of a QBO-type oscillation, we estimate the absorbed wave momentum flux in the stratosphere to be on the order of ˜7 × 10-6 N m-2. On Earth, interactions between vertically propagating waves (both planetary and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden our knowledge on waves potentially driving Saturn's equatorial oscillation, we searched for thermal signatures of planetary waves in the tropical stratosphere using CIRS nadir spectra. Temperature anomalies of amplitude 1-4 K and zonal wave numbers 1 to 9 are frequently observed, and an equatorial Rossby (n = 1) wave of zonal wave number 3 is tentatively identified in November 2009.

Electromagnetic Cyclotron Waves in the Solar Wind: Wind Observation and Wave Dispersion Analysis

NASA Technical Reports Server (NTRS)

Jian, L. K.; Moya, P. S.; Vinas, A. F.; Stevens, M.

2016-01-01

Wind observed long-lasting electromagnetic cyclotron waves near the proton cyclotron frequency on 11 March 2005, in the descending part of a fast wind stream. Bi-Maxwellian velocity distributions are fitted for core protons, beam protons, and alpha-particles. Using the fitted plasma parameters we conduct kinetic linear dispersion analysis and find ion cyclotron and/or firehose instabilities grow in six of 10 wave intervals. After Doppler shift, some of the waves have frequency and polarization consistent with observation, thus may be correspondence to the cyclotron waves observed.