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1

North Atlantic Current variability as observed by two decades of XBT measurements  

NASA Astrophysics Data System (ADS)

In the framework of the German contribution to the Ship-of-Opportunity program (SOOP) temperature measurements in the North Atlantic have been carried out since 1988. The timeseries of XBT measurements along the AX-03 line (English channel to Grand Banks, continuing to Halifax or New York) is without major interruptions and will be used to investigate interannual to decadal temperature changes in the highly variable transition region between the subtropical and subpolar gyre. Along the western part of the section changes of the separation latitude of the North Atlantic Current (NAC) are observed, showing a tendency for warmer waters to penetrate farther north between 1999-2006 compared to the period 1988-1998. However, interannual variability is on the same order of magnitude and masks the signal in some years. Based on XBT data only it is impossible to distinguish if the 1999-2006 warming is a trend or decadal variability. The variability in the eastern basin reveals a qualitative similar behavior, although with smaller variability amplitudes. Combining both findings the observations indicate a basinwide northward shift of the NAC and the subtropical gyre until 2006. Heat content changes at the western boundary amount to about 5*109 J/m2, along the eastern boundary to about 2*109 J/m2. Applying XBT fall rate corrections to the original data does not reveal a significant change of the variability behavior.

Hüttl-Kabus, Sabine; Klein, Birgit

2010-05-01

2

Ethiopian decadal climate variability  

NASA Astrophysics Data System (ADS)

Ethiopian decadal climate variability is characterized by application of singular value decomposition to gridded rainfall data over the period 1901-2007. Two distinct modes are revealed with different annual cycles and opposing responses to regional and global forcing. The northern zone that impacts the Nile River and underlies the tropical easterly jet has a unimodal rainy season that is enhanced by Atlantic Multidecadal Oscillation warm phase. This rainfall mode is linked with the Atlantic zonal overturning circulation and exhibits 10-12-year cycles through much of the twentieth century. The southern zone has a bimodal rainy season that is enhanced by Pacific Decadal Oscillation cool phase and the southern meridional overturning circulation. Multiyear wet and dry spells are characterized by sympathetic responses in the near-equatorial trough extending from Central America across the African Sahel to Southeast Asia. The interaction of Walker and Hadley cells over Africa appears to be a key feature that modulates Ethiopian climate at decadal frequency through anomalous north-south displacement of the near-equatorial trough.

Jury, Mark R.

2010-07-01

3

Decadal Variability of the Kuroshio Extension: Observations and an Eddy-Resolving Model Hindcast  

Microsoft Academic Search

Low-frequency variability of the Kuroshio Extension (KE) is studied using observations and a multidec- adal (1950-2003) hindcast by a high-resolution (0.1°), eddy-resolving, global ocean general circulation model for the Earth Simulator (OFES). In both the OFES hindcast and satellite altimeter observations, low-frequency sea surface height (SSH) variability in the North Pacific is high near the KE front. An empirical orthogonal

Bunmei Taguchi; Shang-Ping Xie; Niklas Schneider; Masami Nonaka; Hideharu Sasaki; Yoshikazu Sasai

2007-01-01

4

Decadal variability of heat content in South China Sea inferred from observation data and an ocean data assimilation product  

NASA Astrophysics Data System (ADS)

Using an observation dataset of temperature and the Simple Ocean Data Assimilation (SODA), the decadal variability of upper ocean heat content (0-400 m; hereafter, OHC) in the South China Sea (SCS) was investigated for the period from 1958 to 2007. Decadal variability was identified as the dominant mode of upper OHC besides the seasonal cycle. According to deceasing or increasing OHC, four periods were chosen to discuss detailed processes behind OHC variability in the SCS; the four periods are 1958-1968, 1969-1981, 1982-1992, and 1993-2003. Results show that advection was the major factor for decreasing (increasing) OHC during 1958-1968 (1968-1981). During 1982-1992 and 1993-2003, the net surface heat flux was the main contributor to the variability of OHC besides the advection. The OHC, advection and net surface heat flux had significant rising tendencies during 1992-2003. The spatial characteristics of OHC variability and heat budget in the Luzon Strait, west of Luzon Island, and Xisha warm eddy region were also discussed in this paper.

Song, W.; Lan, J.; Liu, Q.; Wang, D.

2013-08-01

5

Observational evidence of interannual to decadal-scale variability of the subsurface temperature-salinity structure of the world ocean  

Microsoft Academic Search

We present a brief summary of some results describing interannual to decade scale variability of ocean parameters, focusing on subsurface temperature and salinity. We focus attention on the North Atlantic, where it is very clear that a major redistribution of heat and salt has been occurring since 1960, from the sea surface to at least 3000 m depth. We then

Sydney Levitus; John Antonov

1995-01-01

6

Water Tables, Evapotranspiration, and Climate Variability: A Decade of Observations From a Semi-Arid Riparian Ecosystem  

NASA Astrophysics Data System (ADS)

Native (Rio Grande cottonwood) riparian ecosystems in the semi-arid Rio Grande floodplain of central New Mexico are threatened by hydrologic alterations and highly competitive invasive vegetation (saltcedar, Russian olive). Climate change is expected to alter surface runoff in the southwestern United States and exacerbate water scarcity. Depletions are likely to increase in this agricultural riverine corridor downstream of the rapidly growing Albuquerque metropolitan area. Long-term monitoring of shallow alluvial water tables (WTs) and evapotranspiration (ET) in native, non-native, and mixed communities along the river has provided critical information to help understand how water availability affects these ecosystems during a decade of extreme climate variability. Here, we present several observations, with implications for restoration. WTs ranged from several meters depth to flood stage and from relatively stable to highly dynamic, which can influence recruitment of native vegetation and ecosystem functioning. Annual ET declined with deeper WTs across sites, with robust correlations where WTs were dynamic. Riparian communities responded differently to drought cycles and to restorative flooding during peak runoff at the onset of the growing season. Annual ET in a native-dominated system was reduced following removal of non-native understory vegetation, but returned to previous levels when regrowth was left unmanaged. Long-term data are valuable assets that can help optimize efforts to sustain and restore native ecosystems amid the challenges of a changing climate.

Thibault, J. R.; Cleverly, J. R.; Dahm, C.

2009-12-01

7

Multi-decadal variability of flood risk  

NASA Astrophysics Data System (ADS)

Recent research has highlighted the persistence of multi-decadal epochs of enhanced/reduced flood risk across New South Wales (NSW), Australia. Recent climatological studies have also revealed multi-decadal variability in the modulation of the magnitude of El Niño/Southern Oscillation (ENSO) impacts. In this paper, the variability of flood risk across NSW is analysed with respect to the observed modulation of ENSO event magnitude. This is achieved through the use of a simple index of regional flood risk. The results indicate that cold ENSO events (La Niña) are the dominant drivers of elevated flood risk. An analysis of multi-decadal modulation of flood risk is achieved using the inter-decadal Pacific Oscillation (IPO) index. The analysis reveals that IPO modulation of ENSO events leads to multi-decadal epochs of elevated flood risk, however this modulation appears to affect not only the magnitude of individual ENSO events, but also the frequency of their occurrence. This dual modulation of ENSO processes has the effect of reducing and elevating flood risk on multi-decadal timescales. These results have marked implications for achieving robust flood frequency analysis as well as providing a strong example of the role of natural climate variability.

Kiem, Anthony S.; Franks, Stewart W.; Kuczera, George

2003-01-01

8

Investigating decadal variability and trends in the Pacific Decadal Oscillation  

Microsoft Academic Search

Climate indices are of great value to Earth scientists for their ability to characterize important climate features and distill complex spatio-temporal variability into more simple forms. The Pacific Decadal Oscillation (PDO), distinguished by its sudden cold-warm phase shifts, is mainly portrayed as a natural mode of variability, and has been shown to closely relate to the variability of many biological,

C. Bonfils; B. Santer

2009-01-01

9

One Decade of Noctilucent Cloud Observations Above ALOMAR by Lidar: Persistence and Variability at Different Time Scales.  

NASA Astrophysics Data System (ADS)

Noctilucent clouds (NLC) are the visible manifestation of icy particles persistently present in the polar summer mesopause region. Their formation is a rather complicated physical process depending on atmospheric background parameters, such as temperature and water vapor, which are hardly to measure directly at the altitudes of interest. This strong dependence on the atmospheric parameters and the fact that the clouds show variabilities at different time scales from minutes to several years, make NLC an attractive tracer for dynamic processes in the atmosphere. We report on observations of NLC using the ALOMAR Rayleigh/Mie/Raman (RMR) lidar in Northern Norway at 69N from 1997 to 2006. At this latitude NLC occur regularly from the beginning of June to the middle of August. Using the primary wavelength of the lidar at 532nm we have observed NLC signatures covering all local times even during highest solar background conditions. From the vertically resolved volume backscatter coefficient of the NLC particles, cloud parameters like brightness and altitude are derived. Furthermore, NLC occurrence frequencies as function of the cloud brightness are calculated. Investigations of the local time dependencies of cloud occurrence, brightness, and altitude yield a remarkable persistence concerning diurnal and semidiurnal variations. Within our 10-years data set, the year-to-year variations of cloud occurrence and brightness show signatures which we discuss in respect of the solar cycle. Furthermore our data are analyzed regarding a time lag between NLC occurrence/brightness and solar activity, as shown by visual as well as satellite observations. We compare our measurements with results from the Leibniz Institute Middle Atmosphere model (LIMA), a 3D GCM containing the relevant physical and chemical processes, such as dynamics, radiation, chemistry, and transport, including a mesospheric ice module. Spatial and temporal variability is introduced by assimilation of ECMWF data. These capabilities make it very suitable for comparisons with our experimental NLC data at different time scales.

Fiedler, J.; Baumgarten, G.; Berger, U.; von Cossart, G.

2006-12-01

10

An empirical model of decadal ENSO variability  

NASA Astrophysics Data System (ADS)

This paper assesses potential predictability of decadal variations in the El Niño/Southern Oscillation (ENSO) characteristics by constructing and performing simulations using an empirical nonlinear stochastic model of an ENSO index. The model employs decomposition of global sea-surface temperature (SST) anomalies into the modes that maximize the ratio of interdecadal-to-subdecadal SST variance to define low-frequency predictors called the canonical variates (CVs). When the whole available SST time series is so processed, the leading canonical variate (CV-1) is found to be well correlated with the area-averaged SST time series which exhibits a non-uniform warming trend, while the next two (CV-2 and CV-3) describe secular variability arguably associated with a combination of Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) signals. The corresponding ENSO model that uses either all three (CVs 1-3) or only AMO/PDO-related (CVs 2 and 3) predictors captures well the observed autocorrelation function, probability density function, seasonal dependence of ENSO, and, most importantly, the observed interdecadal modulation of ENSO variance. The latter modulation, and its dependence on CVs, is shown to be inconsistent with the null hypothesis of random decadal ENSO variations simulated by multivariate linear inverse models. Cross-validated hindcasts of ENSO variance suggest a potential useful skill at decadal lead times. These findings thus argue that decadal modulations of ENSO variability may be predictable subject to our ability to forecast AMO/PDO-type climate modes; the latter forecasts may need to be based on simulations of dynamical models, rather than on a purely statistical scheme as in the present paper.

Kravtsov, S.

2012-11-01

11

Decadal cyclone variability in the North Atlantic  

Microsoft Academic Search

The unstable midlatitude ocean-atmosphere coupling motivates the definition of two decadal regimes with distinct implications for the North Atlantic cyclone variability. Phases with low (high) decadal variability of the North Atlantic Oscillation, which are connected with an annular (sectoral) spatial scale of the geopotential height teleconnection pattern, are identified as a hemispheric (regional) regime. In the hemispheric regime during a

Ute Luksch; Christoph C. Raible; Richard Blender; Klaus Fraedrich

2005-01-01

12

Decadal Variability in the Large-Scale Sea Surface Height Field of the South Pacific Ocean: Observations and Causes  

Microsoft Academic Search

Large-scale sea surface height (SSH) changes in the extraequatorial South Pacific Ocean are investigated using satellite altimetry data of the past 12 yr. The decadal SSH signals in the 1990s were dominated by an increasing trend in the 30°-50°S band and a decreasing trend in the central South Pacific Ocean poleward of 50°S. In recent years since 2002 there has

Bo Qiu; Shuiming Chen

2006-01-01

13

An empirical model of decadal ENSO variability  

NASA Astrophysics Data System (ADS)

This study assesses potential predictability of decadal variations in the El Niño/Southern Oscillation (ENSO) characteristics by constructing and performing simulations using an empirical nonlinear model of the Niño-3 index. The model employs decomposition of global sea-surface temperature (SST) anomalies into the modes that maximize the ratio of interdecadal-to-subdecadal SST variance to define external predictors called the canonical variates. When the whole available SST time series is so processed, the leading canonical variate (CV-1) is found to be well correlated with the area-averaged SST and exhibit a non-uniform warming trend, while the next two (CV-2 and CV-3) describe secular variability arguably associated with the Atlantic Multidecadal Oscillation (AMO). The corresponding Niño-3 model that uses either all three (CVs 1-3) or only AMO-related (CVs 2 and 3) predictors captures well the observed autocorrelation function, probability density function, and the seasonal dependence of the ENSO, as well as the observed interdecadal modulations of fall/wintertime ENSO variance, the latter being anti-correlated with the AMO. The model predicts a net reduction in ENSO activity by the year 2020. Retroactive ENSO-frequency forecasts possess a useful skill at decadal lead times. The skill is limited chiefly by the lack of predictability of the canonical variates, so that improvements to decadal ENSO forecasts require alternative definitions of the external predictors; the latter may need to be based on simulations of dynamical models, rather than to be computed in a purely statistical fashion as in the present paper. These findings thus argue that decadal modulations of ENSO variability are predictable subject to our ability to forecast AMO-type climate modes.

Kravtsov, Sergey

2010-05-01

14

Anatomy of North Pacific Decadal Variability.  

NASA Astrophysics Data System (ADS)

A systematic analysis of North Pacific decadal variability in a full-physics coupled ocean-atmosphere model is executed. The model is an updated and improved version of the coupled model studied by Latif and Barnett. Evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20-30-yr timescales. The possible mechanisms include a midlatitude gyre ocean-atmosphere feedback loop, stochastic forcing, remote forcing, or sampling error.Decadal variability in the model is expressed most prominently in anomalies of upper-ocean streamfunction, sea surface temperature (SST), and latent surface heat flux in the Kuroshio-Oyashio extension (KOE) region off Japan. The decadal signal off Japan is initiated by changes in strength and position of the Aleutian low. The atmospheric perturbations excite SST anomalies in the central and eastern North Pacific (with opposing signs and canonical structure). The atmospheric perturbations also change the Ekman pumping over the North Pacific, which excites equivalent barotropic Rossby waves that carry thermocline depth perturbations toward the west. This gyre adjustment results in a shift in the border between subtropical and subpolar gyres after about five years. This process consequently excites SST anomalies (bearing the same sign as the central North Pacific) in the KOE region. The SST anomalies are generated by subsurface temperature anomalies that are brought to the surface during winter by deep mixing and are damped by air-sea winter heat exchange (primarily latent heat flux). This forcing of the atmosphere by the ocean in the KOE region is associated with changes of winter precipitation over the northwestern Pacific Ocean. The polarity of SST and Ekman pumping is such that warm central and cool eastern Pacific anomalies are associated with a deep thermocline, a poleward shift of the border between subtropical and subpolar gyres, and warm SST anomalies and an increase of rain in the KOE region.The preponderance of variance at decadal timescales in the KOE results from the integration of stochastic Ekman pumping along Rossby wave trajectories. The Ekman pumping is primarily due to atmospheric variability that expresses itself worldwide including in the tropical Pacific. A positive feedback between the coupled model KOE SST (driven by the ocean streamfunction) and North Pacific Ekman pumping is consistent with the enhanced variance of the coupled model at 20-30-yr periods. However, the time series are too short to unambiguously distinguish this positive feedback hypothesis from sampling variability. No evidence is found for a midlatitude gyre ocean-atmosphere delayed negative feedback loop.Comparisons with available observations confirm the seasonality of the forcing, the up to 5-yr time lag between like-signed central North Pacific and KOE SST anomalies, and the associated damping of SST in the KOE region by the latent heat flux. The coupled model results also suggest that observed SST anomalies in the KOE region may be predictable from the history of the wind-stress curl over the North Pacific.

Schneider, Niklas; Miller, Arthur J.; Pierce, David W.

2002-03-01

15

Deciphering the Role of Climate and Sea-Level Changes on Observed Decadal-Scale Variability in Salt-Marsh Sedimentation.  

NASA Astrophysics Data System (ADS)

We are investigating the controls that climate and local oceanography exert on sedimentation patterns in 4 salt marsh-estuary complexes around Long Island, New York, USA. These systems encompass a variety of physical settings, including a range of tidal conditions, wave fetches, and human influences, but are all located within one climatic regime. Within these settings, we hypothesize that sedimentation patterns in limited-fetch, mesotidal salt marshes are influenced most strongly by sea-level changes, as the system is largely steady-state under high-energy conditions and sedimentation should track the longer-term sea-level transgression. Conversely, sedimentation in microtidal systems with large fetch should better track atmospheric forcings, because marsh-surface accretion largely occurs during episodic wind and storm events. To test this hypothesis, accretion rates (cm/yr) were determined by applying a constant-flux model to profiles of excess 210Pb, which reveals temporal variation in sedimentation. Additionally, we examined the rate of mineral sediment deposition (g/cm2/yr) and rate of organic matter accumulation (g/cm2/yr). These measures yielded a chronology of sedimentation patterns ~100 years long with a temporal resolution of 2-5 years, sufficient for resolving decadal-scale oscillations. Our proxies for sea-level change come from a variety of tide gauges; including the gauge at Battery Park, NYC which covers much of the past century, as well as local tide gauges with records spanning several decades. Proxies used for atmospheric forcings include mean annual winds for the past 50 years, storm histories and Hurrel's index of the North Atlantic Oscillation, which extends for over a century. Initial results reveal clear decadal-scale variability in marsh accretion, with variations ranging 2-3 fold about the long-term mean. These oscillations are very similar in timing and magnitude to those observed for the climate proxies and sea-level records. However, initial results reveal no significant correlation between local climate proxies and tide gauge records at the scale of this study. Therefore, we suspect that independent atmospheric and oceanic drivers of marsh sedimentation exist. The relative importance of these drivers in a particular embayment will likely depend on how characteristics such as the tidal regime, wave climate and human modifications, respond to changes in their physical forcings.

Kolker, A. S.; Goodbred, S. L.; Cochran, J. K.; Beck, A.; Kroboth, T.

2004-12-01

16

Decadal variability in North Atlantic phytoplankton blooms  

NASA Astrophysics Data System (ADS)

The interannual to decadal variability in the timing and magnitude of the North Atlantic phytoplankton bloom is examined using a combination of satellite data and output from an ocean biogeochemistry general circulation model. The timing of the bloom as estimated from satellite chlorophyll data is used as a novel metric for validating the model's skill. Maps of bloom timing reveal that the subtropical bloom begins in winter and progresses northward starting in May in subpolar regions. A transition zone, which experiences substantial interannual variability in bloom timing, separates the two regions. Time series of the modeled decadal (1959-2004) variability in bloom timing show no long-term trend toward earlier or delayed blooms in any of the three regions considered here. However, the timing of the subpolar bloom does show distinct decadal-scale periodicity, which is found to be correlated with the North Atlantic Oscillation (NAO) index. The mechanism underpinning the relationship is identified as anomalous wind-driven mixing conditions associated with the NAO. In positive NAO phases, stronger westerly winds result in deeper mixed layers, delaying the start of the subpolar spring bloom by 2-3 weeks. The subpolar region also expands during positive phases, pushing the transition zone further south in the central North Atlantic. The magnitude of the bloom is found to be only weakly dependent on bloom timing, but is more strongly correlated with mixed layer depth. The extensive interannual variability in the timing of the bloom, particularly in the transition region, is expected to strongly impact the availability of food to higher trophic levels.

Henson, Stephanie A.; Dunne, John P.; Sarmiento, Jorge L.

2009-04-01

17

Intensification of decadal and multi-decadal sea level variability in the western tropical Pacific during recent decades  

NASA Astrophysics Data System (ADS)

Previous studies have linked the rapid sea level rise (SLR) in the western tropical Pacific (WTP) since the early 1990s to the Pacific decadal climate modes, notably the Pacific Decadal Oscillation in the north Pacific or Interdecadal Pacific Oscillation (IPO) considering its basin wide signature. Here, the authors investigate the changing patterns of decadal (10-20 years) and multidecadal (>20 years) sea level variability (global mean SLR removed) in the Pacific associated with the IPO, by analyzing satellite and in situ observations, together with reconstructed and reanalysis products, and performing ocean and atmosphere model experiments. Robust intensification is detected for both decadal and multidecadal sea level variability in the WTP since the early 1990s. The IPO intensity, however, did not increase and thus cannot explain the faster SLR. The observed, accelerated WTP SLR results from the combined effects of Indian Ocean and WTP warming and central-eastern tropical Pacific cooling associated with the IPO cold transition. The warm Indian Ocean acts in concert with the warm WTP and cold central-eastern tropical Pacific to drive intensified easterlies and negative Ekman pumping velocity in western-central tropical Pacific, thereby enhancing the western tropical Pacific SLR. On decadal timescales, the intensified sea level variability since the late 1980s or early 1990s results from the "out of phase" relationship of sea surface temperature anomalies between the Indian and central-eastern tropical Pacific since 1985, which produces "in phase" effects on the WTP sea level variability.

Han, Weiqing; Meehl, Gerald A.; Hu, Aixue; Alexander, Michael A.; Yamagata, Toshio; Yuan, Dongliang; Ishii, Masayoshi; Pegion, Philip; Zheng, Jian; Hamlington, Benjamin D.; Quan, Xiao-Wei; Leben, Robert R.

2013-10-01

18

Decadal-scale climate variability in the tropical and North Pacific during the 1970s and 1980s: Observations and model results  

SciTech Connect

An abrupt change in the large-scale boreal winter circulation pattern over the North Pacific was observed during the mid-1970s. This paper presents a variety of observed data and model results to describe the climate shift, and to understand some of the links within the coupled climate system that produced, it. Five main findings are emphasized: (1) evidence of abrupt, simultaneous, and apparently related changes can be found in many fields and in many model results; the climate shift is not an artifact, (2) over the tropical Pacific the climate change represents a shift in the state of the coupled ocean-atmosphere system, some aspects of which resemble features associated with El Nino episodes. However, the shift in state is not well characterized as due to a change in the frequency of intensity of El Nino episodes; it is better described as a change in background mean state, (3) When forced with observed SSTs, both a very simple atmospheric model and a full general circulation model (GCM) qualitatively simulate aspects of the decadalscale shift over the tropical Pacific, (4) when forced with observed surface wind stress, two ocean models of the tropical Pacific, in which surface heat fluxes are parameterized as Newtonian damping, reproduce some aspects of the near-equatorial decadal SST signal. However, the models do not reproduce the large changes in SST observed at higher latitudes of the tropical Pacific. suggesting that altered surface heat fluxes dominated in producing these changes, and (5) an important new finding of this study is the success of a GCM in reproducing important aspects of the observed mid-1970s shift in winter northern hemisphere circulation. Comparative analyses of the observed and GCM simulated circulation suggest the altered patterns of tropical Pacific SST and convection were important in forcing the changes in the mid-latitude circulation, a finding corroborated by recent GCM experiments. 70 refs., 18 figs.

Graham, N.E. [Scripps Institution of Oceanography, La Jolla, CA (United States)

1994-08-01

19

Contribution of solar radiation to decadal temperature variability over land.  

PubMed

Global air temperature has become the primary metric for judging global climate change. The variability of global temperature on a decadal timescale is still poorly understood. This paper examines further one suggested hypothesis, that variations in solar radiation reaching the surface (Rs) have caused much of the observed decadal temperature variability. Because Rs only heats air during the day, its variability is plausibly related to the variability of diurnal temperature range (daily maximum temperature minus its minimum). We show that the variability of diurnal temperature range is consistent with the variability of Rs at timescales from monthly to decadal. This paper uses long comprehensive datasets for diurnal temperature range to establish what has been the contribution of Rs to decadal temperature variability. It shows that Rs over land globally peaked in the 1930s, substantially decreased from the 1940s to the 1970s, and changed little after that. Reduction of Rs caused a reduction of more than 0.2 °C in mean temperature during May to October from the 1940s through the 1970s, and a reduction of nearly 0.2 °C in mean air temperature during November to April from the 1960s through the 1970s. This cooling accounts in part for the near-constant temperature from the 1930s into the 1970s. Since then, neither the rapid increase in temperature from the 1970s through the 1990s nor the slowdown of warming in the early twenty-first century appear to be significantly related to changes of Rs. PMID:23980136

Wang, Kaicun; Dickinson, Robert E

2013-08-26

20

Contribution of solar radiation to decadal temperature variability over land  

PubMed Central

Global air temperature has become the primary metric for judging global climate change. The variability of global temperature on a decadal timescale is still poorly understood. This paper examines further one suggested hypothesis, that variations in solar radiation reaching the surface (Rs) have caused much of the observed decadal temperature variability. Because Rs only heats air during the day, its variability is plausibly related to the variability of diurnal temperature range (daily maximum temperature minus its minimum). We show that the variability of diurnal temperature range is consistent with the variability of Rs at timescales from monthly to decadal. This paper uses long comprehensive datasets for diurnal temperature range to establish what has been the contribution of Rs to decadal temperature variability. It shows that Rs over land globally peaked in the 1930s, substantially decreased from the 1940s to the 1970s, and changed little after that. Reduction of Rs caused a reduction of more than 0.2 °C in mean temperature during May to October from the 1940s through the 1970s, and a reduction of nearly 0.2 °C in mean air temperature during November to April from the 1960s through the 1970s. This cooling accounts in part for the near-constant temperature from the 1930s into the 1970s. Since then, neither the rapid increase in temperature from the 1970s through the 1990s nor the slowdown of warming in the early twenty-first century appear to be significantly related to changes of Rs.

Wang, Kaicun; Dickinson, Robert E.

2013-01-01

21

A Decade of Satellite Ocean Color Observations *  

NASA Astrophysics Data System (ADS)

After the successful Coastal Zone Color Scanner (CZCS, 1978-1986) demonstration that quantitative estimations of geophysical variables such as chlorophyll a and diffuse attenuation coefficient could be derived from top of the atmosphere radiances, a number of international missions with ocean color capabilities were launched beginning in the late 1990s. Most notable were those with global data acquisition capabilities, i.e., the Ocean Color and Temperature Sensor (OCTS, Japan, 1996-1997), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, United States, 1997-present), two Moderate Resolution Imaging Spectroradiometers (MODIS, United States, Terra/2000-present and Aqua/2002-present), the Global Imager (GLI, Japan, 2002-2003), and the Medium Resolution Imaging Spectrometer (MERIS, European Space Agency, 2002-present). These missions have provided data of exceptional quality and continuity, allowing for scientific inquiries into a wide variety of marine research topics not possible with the CZCS. This review focuses on the scientific advances made over the past decade using these data sets.

McClain, Charles R.

2009-01-01

22

A decade of satellite ocean color observations.  

PubMed

After the successful Coastal Zone Color Scanner (CZCS, 1978-1986) demonstration that quantitative estimations of geophysical variables such as chlorophyll a and diffuse attenuation coefficient could be derived from top of the atmosphere radiances, a number of international missions with ocean color capabilities were launched beginning in the late 1990s. Most notable were those with global data acquisition capabilities, i.e., the Ocean Color and Temperature Sensor (OCTS,Japan, 1996-1997), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, United States, 1997-present), two Moderate Resolution Imaging Spectroradiometers (MODIS, United States, Terra/2000-present and Aqua/2002-present), the Global Imager (GLI, Japan, 2002-2003), and the Medium Resolution Imaging Spectrometer (MERIS, European Space Agency, 2002-present). These missions have provided data of exceptional quality and continuity, allowing for scientific inquiries into a wide variety of marine research topics not possible with the CZCS. This review focuses on the scientific advances made over the past decade using these data sets. PMID:21141028

McClain, Charles R

2009-01-01

23

Observing Variable Stars  

NASA Astrophysics Data System (ADS)

Observing variable stars is one of the major contributions amateur astronomers make to science. There are 36,000 variable stars listed in the General Catalogue of Variable Stars, so it is clearly impossible for the limited number of professional observatories to target even the majority of them. That's where amateur astronomers come in - thousands of them turning their telescopes to the sky every night. Variable star observing is the most popular of "real science" activities for amateurs, and Gerry Good's book provides everything needed. The first part of the book provides a highly detailed account of the various classes of variable star, with examples, illustrations and physical descriptions. The second section covers practical aspects of observing, everything from preparation and planning, through observing techniques, to data management and reduction.

Good, Gerry A.

24

Regional modeling of decadal rainfall variability over the Sahel  

NASA Astrophysics Data System (ADS)

A regional climate model is used to investigate the mechanism of interdecadal rainfall variability, specifically the drought of the 1970s and 1980s, in the Sahel region of Africa. The model is the National Center for Environmental Prediction’s (NCEPs) Regional Spectral Model (RSM97), with a horizontal resolution of approximately equivalent to a grid spacing of 50 km, nested within the ECHAM4.5 atmospheric general circulation model (AGCM), which in turn was forced by observed sea surface temperature (SST). Simulations for the July September season of the individual years 1955 and 1986 produced wet conditions in 1955 and dry conditions in 1986 in the Sahel, as observed. Additional July September simulations were run forced by SSTs averaged for each month over the periods 1950 1959 and the 1978 1987. These simulations yielded wet conditions in the 1950 1959 case and dry conditions in the 1978 1987 case, confirming the role of SST forcing in decadal variability in particular. To test the hypothesis that the SST influences Sahel rainfall via stabilization of the tropospheric sounding, simulations were performed in which the temperature field from the AGCM was artificially modified before it was used to force the regional model. We modified the original 1955 ECHAM4.5 temperature profiles by adding a horizontally uniform, vertically varying temperature increase, taken from the 1986 1955 tropical mean warming in either the AGCM or the NCEP/National Center for Atmospheric Research Reanalysis. When compared to the 1955 simulations without the added tropospheric warming, these simulations show a drying in the Sahel similar to that in the 1986 1955 difference and to the decadal difference between the 1980s and 1950s. This suggests that the tropospheric warming may have been, at least in part, the agent by which the SST increases led to the Sahel drought of the 1970s and 1980s.

Herceg, Deborah; Sobel, Adam H.; Sun, Liqiang

2007-07-01

25

Possible origins of the western pacific warm pool decadal variability  

NASA Astrophysics Data System (ADS)

In this study, the impacts of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on the western Pacific warm pool (WPWP) were investigated. Our results show that the WPWP is linked with the PDO and the AMO at multiple time scales. On the seasonal time scales, the WPWP and the PDO/AMO reinforce each other, while at decadal time scales the forcing roles of the PDO and the AMO dominate. Notably, a positive PDO tends to enlarge the WPWP at both seasonal and decadal time scales, while a positive AMO tends to reduce the WPWP at decadal time scales. Furthermore, the decadal variability of the WPWP can be well predicted based on the PDO and AMO.

Gan, Bolan; Wu, Lixin

2012-01-01

26

Decadal variability of precipitation over Western North America  

USGS Publications Warehouse

Decadal (>7- yr period) variations of precipitation over western North America account for 20%-50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] components. These decadal variations are contributed by fluctuations in precipitation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipitation variations are linked to various decadal atmospheric circulation and SST anomaly patterns where scales range from regional to global scales and that emphasize tropical or extratropical connections, depending upon which precipitation region is considered. Further, wet or dry decades are associated with changes in frequency of at least a few short-period circulation 'modes' such as the Pacific-North American pattern. Precipitation fluctuations over the southwestern United States and the Saskatchewan region of western Canada are associated with extensive shifts of sea level pressure and SST anomalies, suggesting that they are components of low-frequency precipitation variability from global-scale climate proceses. Consistent with the global scale of its pressure and SST connection, the Southwest decadal precipitation is aligned with opposing precipitation fluctuations in northern Africa.Decadal (>7-yr period) variations of precipitation over western North America account for 20%-50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] components. These decadal variations are contributed by fluctuations in precipitation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipitation variations are linked to various decadal atmospheric circulation and SST anomaly patterns where scales range from regional to global scales and that emphasize tropical or extratropical connections, depending upon which precipitation region is considered. Further, wet or dry decades are associated with changes in frequency of at least a few short-period circulation `modes' such as the Pacific-North American pattern. Precipitation fluctuations over the southwestern United States and the Saskatchewan region of western Canada are associated with extensive shifts of sea level pressure and SST anomalies, suggesting that they are components of low-frequency precipitation variability from global-scale climate processes. Consistent with the global scale of its pressure and SST connection, the Southwest decadal precipitation is aligned with opposing precipitation fluctuations in northern Africa.

Cayan, D. R.; Dettinger, M. D.; Diaz, H. F.; Graham, N. E.

1998-01-01

27

South Pacific Ocean controls the phase reversal and periodicity of the decadal and bi-decadal ENSO-like variabilities  

NASA Astrophysics Data System (ADS)

Phase reversal mechanism of the Pacific decadal and bi-decadal ENSO-like variabilities and origins of oceanic signals for the phase reversal are investigated based on a pair of the climate model experiments using MIROC3m and consisting of the control run (CTRL) and the partial blocking run (PB) where model temperature and salinity are restored to their climatological values along 10°S in the South Pacific. In CTRL, the pattern of the Pacific Decadal Oscillations (PDO) with positive anomalies in the tropics and negative anomalies in the North Pacific mid-latitudes is found in the leading mode of the sea surface temperature. On the other hand, in PB, the former tropical signals are not appeared and only the mid-latitude signals are seen. It is robustly demonstrated that oceanic signals of the South Pacific origin are keys in controlling the Pacific ENSO-like variabilities on decadal timescales. By separating oceanic signals in CTRL into decadal and bi-decadal components, we try to identify oceanic physical processes and to explain how the periodicity is determined. Based on statistical analysis and a tracer experiment using an off-line ocean model, it is shown that relatively faster oceanic wave adjustments triggered by changes of wind-stress curl in the South Pacific extra-tropics and slower mean isopycnal advection of subsurface temperature anomalies associated with modification of South Pacific eastern subtropical mode water are essential in the phase reversals of a decadal and bi-decadal variabilities, respectively. The periodicity and frequencies of the variabilities are determined mainly by the transient times of the oceanic subsurface signals from the extra-tropics and mid-latitudes to the tropics. In the last several years, decadal climate predictions are in progress using state-of-the-art climate models at research institutes and centers world-wide towards contributing to the IPCC-AR5. Although predictability of the PDO within several years has been reported, this is not the case for the tropical predictability on a decadal scale. The present study implies that observational data accumulated by ARGO floats which cover the South Pacific Ocean will contribute to further improvement of decadal climate predictions by using the data in initializing climate models.

Tatebe, H.; Imada, Y.; Kimoto, M.; Hasumi, H.

2012-04-01

28

A further assessment of vegetation feedback on decadal Sahel rainfall variability  

NASA Astrophysics Data System (ADS)

The effect of vegetation feedback on decadal-scale Sahel rainfall variability is analyzed using an ensemble of climate model simulations in which the atmospheric general circulation model ICTPAGCM ("SPEEDY") is coupled to the dynamic vegetation model VEGAS to represent feedbacks from surface albedo change and evapotranspiration, forced externally by observed sea surface temperature (SST) changes. In the control experiment, where the full vegetation feedback is included, the ensemble is consistent with the observed decadal rainfall variability, with a forced component 60 % of the observed variability. In a sensitivity experiment where climatological vegetation cover and albedo are prescribed from the control experiment, the ensemble of simulations is not consistent with the observations because of strongly reduced amplitude of decadal rainfall variability, and the forced component drops to 35 % of the observed variability. The decadal rainfall variability is driven by SST forcing, but significantly enhanced by land-surface feedbacks. Both, local evaporation and moisture flux convergence changes are important for the total rainfall response. Also the internal decadal variability across the ensemble members (not SST-forced) is much stronger in the control experiment compared with the one where vegetation cover and albedo are prescribed. It is further shown that this positive vegetation feedback is physically related to the albedo feedback, supporting the Charney hypothesis.

Kucharski, Fred; Zeng, Ning; Kalnay, Eugenia

2013-03-01

29

Sea level trends, interannual and decadal variability in the Pacific Ocean  

NASA Astrophysics Data System (ADS)

Linear trend analysis is commonly applied to quantify sea level change, often over short periods because of limited data availability. However, the linear trend computed over short periods is complicated by large-scale climate variability which can affect regional sea level on interannual to inter-decadal time scales. As a result, the meaning of a local linear sea level trend over the short altimeter era (since 1993; less than 20 years) is unclear, and it is not straightforward to distinguish the regional sea level changes associated with climate change from those associated with natural climate variability. In this study, we use continuous near-global altimeter measurements since 1993 to attempt to separate interannual and decadal sea level variability in the Pacific from the sea level trend. We conclude that the rapid rates of sea level rise in the western tropical Pacific found from a single variable linear regression analysis are partially due to basin-scale decadal climate variability. The negligible sea level rise, or even falling sea level, in the eastern tropical Pacific and US west coast is a result of the combination of decreasing of sea level associated with decadal climate variability and a positive sea level trend. The single variable linear regression analysis only accounts for slightly more than 20% of the observed variance, whereas a multiple variable linear regression including filtered indices of the El Nino-Southern Oscillation and the Pacific Decadal Oscillation accounts for almost 60% of the observed variance.

Zhang, Xuebin; Church, John A.

2012-11-01

30

Quasi-decadal variability of fall extreme wave heights in the western North Pacific  

NASA Astrophysics Data System (ADS)

We present a prominent quasi-decadal variability of fall extreme wave heights (H90, September-November mean of the monthly 90th percentile of significant wave heights) in the western North Pacific (WNP), based on wave reanalysis of the ERA40. It is found by applying an Empirical Orthogonal Function (EOF) analysis to H90 for 1957-2001 that the first EOF mode captures a monopole structure with maximum amplitude in the south of Japan with quasi-decadal variability of approximately 15-year. The quasi-decadal variability is also found partially in H90 observed around southern coast of Japan. By comparing intense tropical cyclone (ITC, with central pressure below 980 hPa) tracks for the decennial periods, we may be able to attribute the quasi-decadal variability of H90 in the WNP to the changes in the ITC tracks around the south of Japan.

Sasaki, W.; Iwasaki, S. I.; Matsuura, T.; Iizuka, S.

2006-05-01

31

Multi-Decadal Variability of Colorado River Basin Streamflow  

NASA Astrophysics Data System (ADS)

Conventional water resource planning and management are based upon the assumption that past run-off records are indicative of future hydrologic conditions. The severe and sustained nature of the recent drought in the Southwestern United States has underscored the limitation of this planning approach. Furthermore, a growing collection of scientific literature indicates that anthropogenic climate change may further dry the region and strain its water resources. Thus, developing tools and strategies to address streamflow variability, is critical for effective water management in regions such as the Colorado River Basin. A crucial first step toward this end is the understanding of streamflow variability at multi-decadal time scales, driven by large scale climate features such as El Nino Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multi-decadal Oscillation (AMO), etc. Here, a systematic analysis of basin-wide natural streamflow and paleo-reconstructed flows in the Colorado River Basin is presented, using time domain principal component analysis (PCA) and spectral methods based on wavelets and a multi-taper method. The dominant patterns of variability are related to global sea surface temperatures (SSTs) to identify potential large scale climate features that drive the variability. Results indicate that the first two PCs explain approximately 60% of the total streamflow variance in the Basin. The first PC, which is a predominantly Upper Basin signal, correlates strongly with Atlantic Ocean SSTs and shows an AMO pattern, while the second PC has distinct ties to the Pacific Ocean, reminiscent of PDO and ENSO patterns. The spectral analyses of the leading PCs indicate strong coherence with the corresponding indices of the aforementioned climate forcings. The spectrum of the first PC displays a strong signal at 10-15 year and 60-70 year periodicities. Spectral analysis of paleo-reconstructed Upper Basin streamflow indicates that these periodicities are modulated, especially the decadal signal being modulated at a 75-year time scale. These results provide insight into the multi-decadal variability of Colorado River streamflow. Furthermore, they will have considerable utility in realistic simulation of near-term streamflows and consequently, efficient planning and management of water resources in the Colorado River Basin.

Nowak, K. C.; Rajagopalan, B.; Hoerling, M.; Zagona, E. A.

2010-12-01

32

Pacific Decadal Variability and Hydrology in the Americas  

NASA Astrophysics Data System (ADS)

The relationship between the hydroclimate of the Americas and slow fluctuations in the sea surface temperatures (SSTs) of the Pacific ocean is examined. As an example of severe societal impact, the Northeast US drought of 1962-1966 is considered, and the pattern and severity of that drought is used as a benchmark to evaluate the current drought in the eastern US. The established relationships between Pacific decadal SST variability and variations in the rainfall, Palmer drought index, and stream flow of the Americas are reviewed. Particular attention is given to 1. data quality and availability, 2. definitional issues with Pacific decadal variability, and 3. possible atmospheric linkages between the Pacific variability and the continental hydrology, including issues of seasonality. The 1962-1966 Northeast US drought is considered as an example of a severe event closely linked to a primary pattern of low frequency Pacific variability. The timing of SST anomalies in the North Pacific were closely linked to the evolution of the drought, and diagnosis of upper level wave energy suggests an atmospheric bridge between the North Pacific and eastern US. During the 1960s drought period, there were also coherent SST anomalies in the western North Atlantic. The possibility that these Atlantic SSTs played a contributing role in the drought is explored.

Barlow, M.

2002-05-01

33

Reading the bass line: How well do moisture-sensitive tree rings track decadal variability?  

NASA Astrophysics Data System (ADS)

Most dendroclimatic studies assess past changes in decadal variability by first reconstructing an annually-resolved target variable, and then applying some form of filter that emphasizes variability within a specific frequency band. We evaluate the ability of a network of tree-ring records along the central Pacific Coast of the United States (hereafter, the CPC) to estimate the behavior of an exceptionally vigorous decadal pattern in winter precipitation. The CPC is one of the few regions in North America where precipitation records exhibited strong variability at decadal timescales during the last century. Fewer than one-quarter of all tree-ring chronologies from this region are good proxies for the decadal pattern, but Monte Carlo analysis demonstrates that the level of similarity observed between the ring-width network and winter precipitation was not likely to occur due to chance. By screening the network to retain those tree-ring chronologies that are optimal predictors of our decadal target, we produce an estimate of that component that is better than those obtained from either projecting the signal over all records or over some function (either the network’s mean or its leading principal component) that describes tree growth across the entire network. Projecting the pattern over the entire length of the tree-ring chronologies indicated that decadal variability in regional precipitation was most vigorous during the mid and late-20th century. Between 1650 and 1930, the amplitude of the decadal pattern was relatively weak and the proxy estimates show a limited number of decadal events separated by longer intervals of lower variance. Our results indicate that strong decadal variability is a relatively new feature of the winter climate of the CPC region, and that this type of behavior has been uncommon for most of the last three and a half centuries. They also provide another example of the benefits of reconstruction approaches that evaluate the ability of proxy records to track climate variability at specific timescales.

St George, S.; Ault, T. R.

2010-12-01

34

Decadal climate variability in the Mediterranean region: roles of large-scale forcings and regional processes  

NASA Astrophysics Data System (ADS)

We analyze decadal climate variability in the Mediterranean region using observational datasets over the period 1850-2009 and a regional climate model simulation for the period 1960-2000, focusing in particular on the winter (DJF) and summer (JJA) seasons. Our results show that decadal variability associated with the winter and summer manifestations of the North Atlantic Oscillation (NAO and SNAO respectively) and the Atlantic Multidecadal Oscillation (AMO) significantly contribute to decadal climate anomalies over the Mediterranean region during these seasons. Over 30% of decadal variance in DJF and JJA precipitation in parts of the Mediterranean region can be explained by NAO and SNAO variability respectively. During JJA, the AMO explains over 30% of regional surface air temperature anomalies and Mediterranean Sea surface temperature anomalies, with significant influence also in the transition seasons. In DJF, only Mediterranean SST still significantly correlates with the AMO while regional surface air temperature does not. Also, there is no significant NAO influence on decadal Mediterranean surface air temperature anomalies during this season. A simulation with the PROTHEUS regional ocean-atmosphere coupled model is utilized to investigate processes determining regional decadal changes during the 1960-2000 period, specifically the wetter and cooler 1971-1985 conditions versus the drier and warmer 1986-2000 conditions. The simulation successfully captures the essence of observed decadal changes. Model set-up suggests that AMO variability is transmitted to the Mediterranean/European region and the Mediterranean Sea via atmospheric processes. Regional feedbacks involving cloud cover and soil moisture changes also appear to contribute to observed changes. If confirmed, the linkage between Mediterranean temperatures and the AMO may imply a certain degree of regional decadal climate predictability. The AMO and other decadal influences outlined here should be considered along with those from long-term increases in greenhouse gas forcings when making regional climate out-looks for the Mediterranean 10-20 years out.

Mariotti, Annarita; Dell'Aquila, Alessandro

2012-03-01

35

Decadal variability in European wet and dry phases  

NASA Astrophysics Data System (ADS)

Climate varies over time and space, triggered by a large variety of processes. At continental and regional scales, numerous long-term changes in climate have been observed with profound direct and indirect influences on natural environments and the human society. This study focuses on the spatio-temporal characteristics and changes of long-lasting dry and wet spells in Europe for 1851-2010. Analysis is done for seven European sub-regions ranging from Northern Europa via Central Europe to the Mediterranean area. The decile indicator is used for precipitation time series to define long-lasting dry and wet phases that may last several months to years. Its calculation is based on three-month precipitation totals. Different decile-based thresholds are used to determine the start and the end of the respective dry or wet phase. They are calculated separately for each of the twelve three-month periods to account for the seasonal precipitation cycle. Links of this precipitation-based indicator to flood events in European catchments are examined. We noticed that during certain times, dry and wet phases, respectively, occur more frequent and last longer than during other times, where almost no event occurs. Considering all of Europe, dry phases were particularly frequent and long between 1880 and 1910, the mid-1940s to mid-1960s and in the mid 1970s, while wet phases showed a peak in occurrence from 1910 to the early 40s, from the mid-1960s to the early 1980s and from 1994 to 2010. The picture changes if individual sub-regions are considered. Opposite sub-regional trends lead to almost negligible or indifferent trends over Europe. Spatial extent and duration of dry phases have decreased noticeably and most pronounced in the second half of the 20th Century, while wet phases show increases in spatial extent and duration from 1851 to the present. Those developments are particularly pronounced in Northern Europe. Opposite trends - particularly for the second half of the 20th century - were noticed for Central Europe and the Mediterranean area. Besides those long-term trends exists a strong inter-decadal variability of the spatial coverage of dry and wet phases, respectively, within all sub-regions, indicating a relation of decile phase occurrence to long-term variations in atmospheric circulation. We explored the relationship between dry and wet phase occurrence and large-scale atmospheric circulation patterns, e.g., Hess-Brezowsky catalogue of circulation types (GWT), North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) and found some links depending on the particular sub-region. Yet, the observed links cannot simply be reduced to simple cause-effect relationships.

Hänsel, Stephanie; Miketta, Wiebke; Matschullat, Jörg

2013-04-01

36

Causes of Decadal Climate Variability over the North Pacific and North America  

Microsoft Academic Search

The cause of decadal climate variability over the North Pacific Ocean and North America is investigated by the analysis of data from a multidecadal integration with a state-of-the-art coupled ocean-atmosphere model and observations. About one-third of the low-frequency climate variability in the region of interest can be attributed to a cycle involving unstable air-sea interactions between the subtropical gyre circulation

M. Latif; T. P. Barnett

1994-01-01

37

Subduction of Decadal North Pacific Temperature Anomalies: Observations and Dynamics  

Microsoft Academic Search

Observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central North Pacific to approximately 188N in the western Pacific. The propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline.

Niklas Schneider; Arthur J. Miller; Michael A. Alexander; Clara Deser

1999-01-01

38

Dynamical and biogeochemical control on the decadal variability of ocean carbon fluxes  

NASA Astrophysics Data System (ADS)

Several recent observation-based studies suggest that ocean anthropogenic carbon uptake has slowed down due to the impact of anthropogenic forced climate change. However, it remains unclear whether detected changes over the recent time period can be attributed to anthropogenic climate change or rather to natural climate variability (internal plus naturally forced variability) alone. One large uncertainty arises from the lack of knowledge on ocean carbon flux natural variability at the decadal time scales. To gain more insights into decadal time scales, we have examined the internal variability of ocean carbon fluxes in a 1000 yr long preindustrial simulation performed with the Earth System Model IPSL-CM5A-LR. Our analysis shows that ocean carbon fluxes exhibit low-frequency oscillations that emerge from their year-to-year variability in the North Atlantic, the North Pacific, and the Southern Ocean. In our model, a 20 yr mode of variability in the North Atlantic air-sea carbon flux is driven by sea surface temperature variability and accounts for ~40% of the interannual regional variance. The North Pacific and the Southern Ocean carbon fluxes are also characterised by decadal to multi-decadal modes of variability (10 to 50 yr) that account for 20-40% of the interannual regional variance. These modes are driven by the vertical supply of dissolved inorganic carbon through the variability of Ekman-induced upwelling and deep-mixing events. Differences in drivers of regional modes of variability stem from the coupling between ocean dynamics variability and the ocean carbon distribution, which is set by large-scale secular ocean circulation.

Séférian, R.; Bopp, L.; Swingedouw, D.; Servonnat, J.

2013-04-01

39

Decadal climate variability over the North Pacific and North America: Dynamics and predictability  

SciTech Connect

The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observation datasets and the output of a state of the art coupled ocean-atmosphere general circulation model that was integrated for 125 years. Both the observations and model results support the picture that the decadal variability in the regional of interest is based on a cycle involving unstable ocean-atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades. The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. 41 refs., 18 figs.

Latif, M. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Barnett, T.P. [Scripps Institution of Oceanography, La Jolla, CA (United States)

1996-10-01

40

The ability of the adjoint technique to recover decadal variability of the North Atlantic circulation  

NASA Astrophysics Data System (ADS)

Different oceanic data assimilation products show rather different decadal-scale variability, in particular for the Atlantic meridional overturning circulation (MOC). In order to understand these differences we evaluate the ability of the adjoint technique to reproduce MOC variability using surface heat flux forcing as the control parameter. We find that in a perfect model framework and for a reasonable weighting the adjoint method is, in principle, successful at reproducing decadal-scale MOC variability if adequate synthetic observations and a priori information of the control parameter are given. Temperature of the upper 1000 m and sea surface height and a priori information about surface heat fluxes contain the most useful information. Using only salinity or only synthetic hydrography below 1000 m, the method fails to converge and to reconstruct MOC variability, given surface heat flux as the only control parameter.

Brüdgam, Michael; Eden, Carsten; Czeschel, Lars; Baehr, Johanna

2013-09-01

41

Evidence for multiple drivers of North Atlantic multi-decadal climate variability  

NASA Astrophysics Data System (ADS)

Observed North Atlantic Ocean surface temperatures have changed in a non-monotonic and non-uniform fashion over the last century. Here we assess the relative roles of greenhouses gases, anthropogenic aerosols, natural forcings and internal variability to the North Atlantic surface temperature decadal fluctuations using multi-model climate simulations driven by estimates of observed external forcings. While the latter are the main source of decadal variability in the tropics and subtropics, there is a large contribution from the unforced component to subpolar Atlantic variations. Reconstruction of forced response patterns suggests that anthropogenic forcings are the main causes of the accelerated warming of the last three decades while internal variability has a dominant contribution to the early 20th-century temperature multi-decadal swings and recent abrupt changes in the subpolar Atlantic. Significant inter-model spread with regard to the spatial response patterns to anthropogenic forcing leads to substantial uncertainty as to robust attribution statements for the mid-to-late 20th century North Atlantic warm and cold periods.

Terray, Laurent

2012-10-01

42

Pacific Decadal Variability: The Tropical Pacific Mode and the North Pacific Mode(.  

NASA Astrophysics Data System (ADS)

Pacific decadal variability is studied in a series of coupled global ocean-atmosphere simulations aided by two `modeling surgery' strategies: partial coupling (PC) and partial blocking (PB). The PC experiments retain full ocean-atmosphere coupling in selected regions, but constrain ocean-atmosphere coupling elsewhere by prescribing the model climatological SST to force the atmospheric component of the coupled system. In PB experiments, sponge walls are inserted into the ocean component of the coupled model at specified latitudinal bands to block the extratropical-tropical oceanic teleconnection.Both modeling and observational studies suggest that Pacific decadal variability is composed of two distinct modes: a decadal to bidecadal tropical Pacific mode (TPM) and a multidecadal North Pacific mode (NPM). The PC and PB experiments showed that the tropical Pacific mode originates predominantly from local coupled ocean-atmosphere interaction within the tropical Pacific. Extratropical-tropical teleconnections, although not a necessary precondition for the genesis of the tropical decadal variability, can enhance SST variations in the Tropics. The decadal memory in the Tropics seems to be associated with tropical higher baroclinic modes. The North Pacific mode originates from local atmospheric stochastic processes and coupled ocean-atmosphere interaction. Atmospheric stochastic forcing can generate a weaker NPM-like pattern in both the atmosphere and ocean, but with no preferred timescales. In contrast, coupled ocean-atmosphere feedback can enhance the variability substantially and generate a basin-scale multidecadal mode in the North Pacific. The multidecadal memory in the midlatitudes seems to be associated with the delayed response of the subtropical/subpolar gyre to wind stress variation in the central North Pacific and the slow growing/decaying of SST anomalies that propagate eastward in the Kuroshio Extension region. Oceanic dynamics, particularly the advection of the mean temperature by anomalous meridional surface Ekman flow and western boundary currents, plays an important role in generating the North Pacific mode.

Wu, L.; Liu, Z.; Gallimore, R.; Jacob, R.; Lee, D.; Zhong, Y.

2003-04-01

43

Decadal Variability in Western North Atlantic SST Recorded in Massive Brain Corals from Bermuda  

Microsoft Academic Search

The history of the North Atlantic Oscillation (NAO) is characterized by variability on time scales of months to decades but low frequency (decadal and multidecadal) variability is especially marked since 1950, leading some to suggest a link to global warming. To address questions concerning the nature and mechanisms of low frequency NAO variability, we have initiated a program to reconstruct

A. L. Cohen; M. S. McCartney; S. R. Smith

2002-01-01

44

Impacts of Pacific Decadal Variability on Marine Ecosystems  

NASA Astrophysics Data System (ADS)

Over the past few decades a wealth of evidence has pointed to important connections between multi-decadal climate changes coherent with North Pacific ecosystem changes. The period from the late 1970's through the mid-1990's, for example, saw sustained high productivity for most Pacific salmon at the northern end of their range coinciding with sustained low productivity for Pacific salmon at the southern end of their range. It is now recognized that this "north-south inverse production pattern" for Pacific salmon played out over much of the 20th Century in response to Pacific climate changes: over multiple decades associated with the Pacific Decadal Oscillation, and from year-to-year associated with the El Nino Southern Oscillation. There is likewise abundant evidence for climate impacts on many other North Pacific marine species from the California Current north to the Bering Sea. In special cases, interdecadal ecosystem changes have been termed "regime shifts", wherein direct and indirect evidence points to large-scale ecosystem restructuring at both lower and upper trophic levels. The growing recognition of climate influences has undoubtedly aided our understanding of variations in Pacific marine ecosystems. In contrast, understanding and predicting ecosystem changes at the time-space scales important to fishery management decisions remains a major challenge.

Mantua, N. J.

2002-05-01

45

Decadal-scale Holocene climate variability in the Nordic seas  

Microsoft Academic Search

Sea-surface temperatures (SST) at decadal resolution have been reconstructed from core MD 95-2011, core MD 99-2269 and core BS88-6-5A based on diatom transfer functions. Core MD 95-2011 is located on the Vöring Plateau (66^o58.18N; 07^o38.36E, 1050 m water depth) along the main axis of the northward flowing warm Atlantic water. It is, therefore, in an ideal position to monitor changes

N. Koc; C. Andersen; J. Andrews; A. Jennings

2003-01-01

46

Two decades of ocean CO2 sink and variability  

Microsoft Academic Search

Atmospheric CO2 has increased at a nearly identical average rate of 3.3 and 3.2 Pg C yr?1 for the decades of the 1980s and the 1990s, in spite of a large increase in fossil fuel emissions from 5.4 to 6.3 Pg C yr?1. Thus, the sum of the ocean and land CO2 sinks was 1 Pg C yr?1 larger in

C. Le Quéré; O. Aumont; L. Bopp; P. Bousquet; P. Ciais; R. Francey; M. Heimann; C. D. Keeling; R. F. Keeling; H. Kheshgi; P. Peylin; S. C. Piper; I. C. Prentice; P. J. Rayner

2003-01-01

47

Patterns of Pacific decadal variability recorded by Indian Ocean corals  

Microsoft Academic Search

We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral ?18O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies,\\u000a we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance\\u000a patterns of the coral time

Traute Crueger; Jens Zinke; Miriam Pfeiffer

2009-01-01

48

The decadal variability of the heat and freshwater content of the subpolar North Atlantic  

NASA Astrophysics Data System (ADS)

During the last five decades striking changes occurred in the freshwater and heat content of the subpolar North Atlantic (SNA). The deep and abyssal waters that originate in this region to feed the lower limb of the AMOC experienced a remarkable decrease in salinities after the late 1960s, linked to a progressive dilution of the system of overflows from the Nordic Seas. A rapid reversal of the freshening trend occurred in the mid-1990s, with a pronounced salinification especially in the eastern SNA; at the same time, the freshening of the overflows slowed to a stop. An intriguing feature of the observational record is the tight co-variability of the freshwater and heat content of the SNA: the long-term freshening was accompanied by a progressive decrease in heat content, and both trends reversed simultaneously after 1995. Here we use a sequence of experiments with high-resolution (1/4°, 1/12°, and 1/20°) ocean-sea ice models to identify the dynamical causes of these decadal changes. Hindcast simulations of the oceanic response to the atmospheric variability 1948-2007 (as given by the "CORE" reanalysis) capture the decadal variability in the integral properties of the SNA as reconstructed from historical salinity and temperature data, and reproduce pertinent observational indices of mid-latitude circulation variability. Analysis of the freshwater and heat budgets shows that the largest contribution to the SNA property changes has been due to variations in the inflow of warm, saline water with the subtropical North Atlantic, with only a minor contribution due to variations in the inflow of cold, fresh waters from the northern basins. The subtropical-subpolar flux variability is not directly related to the AMOC; it can conceptually be understood in terms of the "intergyre-gyre" response to the mid-latitude westerlies associated with the NAO.

Boening, Claus W.; Scheinert, Markus; Behrens, Erik; Biastoch, Arne

2013-04-01

49

Decadal Variability of the Tropical Atlantic Ocean Surface Temperature in Shipboard Measurements and in a Global Ocean-Atmosphere Model  

Microsoft Academic Search

Numerous analyses of relatively short (25-30 years in length) time series of the observed surface temperature of the tropical Atlantic Ocean have indicated the possible existence of decadal timescale variability. It was decided to search for such variability in 100-yr time series of sea surface temperature (SST) measured aboard ships and available in the recently published Global Ocean Surface Temperature

Vikram M. Mehta; Thomas Delworth

1995-01-01

50

Interannual, decadal and multidecadal scale climatic variability and geomorphology  

Microsoft Academic Search

Climatologists have identified and started to explain a range of different modes of climatic variability which seem to be essential components of behaviour of the global climatic system. Of potentially high geomorphological importance are oscillations in climate over interannual to century scales. A range of geomorphological impacts of such climatic oscillations has been recognised, such as alterations in streamflow and

H. A. Viles; A. S. Goudie

2003-01-01

51

Decadal to seasonal variability of Arctic sea ice albedo  

Microsoft Academic Search

A controlling factor in the seasonal and climatological evolution of the sea ice cover is its albedo alpha. Here we analyze Arctic data from the Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder and assess the seasonality and variability of broadband albedo from a 23 year daily record. We produce a histogram of daily albedo over ice covered regions in

S. Agarwal; W. Moon; J. S. Wettlaufer

2011-01-01

52

A Decade of Shear-Wave Splitting Observations in Alaska  

NASA Astrophysics Data System (ADS)

Over the last decade four PASSCAL experiments have been conducted in different regions of Alaska. ARCTIC, BEAAR and MOOS form a north-south transect across the state, from the Arctic Ocean to Price Williams Sound, while the STEEP experiment is currently deployed to the east of that line in the St Elias Mountains of Southeastern Alaska. Shear-wave splitting observations from these networks in addition to several permanent stations of the Alaska Earthquake Information Center were determined in an attempt to understand mantle flow under Alaska in a variety of different geologic settings. Results show two dominant splitting patterns in Alaska, separated by the subducted Pacific Plate. North of the subducted Pacific Plate fast directions are parallel to the trench (along strike of the subducted Pacific Plate) indicating large scale mantle flow in the northeast-southwest direction with higher anisotropy (splitting times) within the mantle wedge. Within or below the Pacific Plate fast directions are normal to the trench in the direction of Pacific Plate convergence. In addition to these two prominent splitting patterns there are several regions that do not match either of these trends. These more complex regions which include the results from STEEP could be due to several factors including effects from the edge of the Pacific Plate. The increase of station coverage that Earthscope will bring to Alaska will aid in developing a more complete model for anisotropy and mantle flow in Alaska.

Bellesiles, A. K.; Christensen, D. H.; Abers, G. A.; Hansen, R. A.; Pavlis, G. L.; Song, X.

2010-12-01

53

Multi-Decadal Rainfall Variability under the South Pacific Convergence Zone from 1570-2005  

NASA Astrophysics Data System (ADS)

The Pacific Ocean Basin undergoes natural climate variability on decadal to multi-decadal timescales. Ocean-atmosphere feedbacks drive a complex cycle in tropical and extra-tropical winds and zonal sea-surface temperatures (SST) resulting in basin-scale climate reorganizations. The Pacific Ocean zonal SST gradient responds to upwelling of cold waters near the equator transported by shallow Pacific Meridional Overturning Circulation (PMOC), which in turn responds to changes in winds. However, the frequency, timing, and magnitude of past decadal changes in the Pacific are largely unknown. To address this question, we developed a U-Th dated, 430-year stable oxygen isotope (?18O) cave record of past precipitation in Vanuatu, a location whose climate is heavily influenced by variability in the South Pacific Convergence Zone (SPCZ). The ?18O-based precipitation record shows repeating cycles that are ~25-50 years in duration and correspond to ~115 mm/month of rainfall change that can occur in as fast as 5 years - a change larger and quicker than the 1976 regime shift. The stalagmite ?18O to rainfall amount conversion is based on the "amount effect" observed at similar tropical sites. The "Little Ice Age" (LIA) section of the record exhibits no trend in precipitation, hence no change in the strength or position of the SPCZ over Vanuatu. This result suggests a disconnection between changes in the SPCZ and the Intertropical Convergence Zone (ITCZ), which does exhibit a southerly shift during the LIA period. Changes in PMOC via ocean-atmosphere feedbacks most likely explain the decadal shifts in SPCZ strength through alteration of the tropical Pacific zonal SST gradient and subsequent trade wind response. Periods of high paleo-rainfall in Vanuatu (strong PMOC, increased zonal SST gradient and increased trade winds) correlate with historical accounts of little to no El Niño activity implying that Pacific Basin mean state regulates interannual variability.

Partin, J. W.; Quinn, T. M.; Shen, C.; Taylor, F. W.; Banner, J. L.; Maupin, C. R.; lin, K.; Sinclair, D. J.; Huh, C.

2011-12-01

54

Decadal variability of NAO during the last millennium inferred from Saharan dust in Alpine ice  

NASA Astrophysics Data System (ADS)

Interannual variability of North African atmospheric dust is strongly linked to drought conditions in the Sahel and to the winter North Atlantic Oscillation (NAO). Dust generation and transport are enhanced during winter NAO(+) phases when the North African dust source regions are controlled by high pressure situations leading to less precipitation, and thus to stronger wind erosion of soil material. However, direct Saharan dust observations are limited to the last decades only. Here, we present a first highly resolved ice core record of Saharan dust from the Alps, spanning the last 1,000 years. We focus thereby on concentrations of Fe, Al, Sr, and Ca which are typical elements present in long-range transported Saharan dust. We show that the mineral dust transport to the Southern Alps is primarily controlled by drought conditions in Northern Africa and by the winter NAO. Mean dust concentrations of the last 20 years are unprecedented in the context of the last 1,000 years. These elevated Saharan dust concentrations are consistent with the observed widespread increase in dustiness and dust storm frequencies over Northern Africa from direct measurements or from satellite based observations over the last decades. In contrast, between AD 1050 and 1400, when persistent arid conditions in the main source regions of dust in Northern Africa were deduced from tree-ring data and linked to a pervasive positive NAO mode over centuries, no according imprint is recorded in the ice core mineral dust record. We assume that the low-frequency variability of the tree-ring based reconstruction of Moroccan droughts (which also form the basis for the NAO reconstruction) is biased by the method applied to remove the non-climatic growth trends from the tree-ring series. Based on the ice core data we suggest that decadal-scale variability of the NAO (Moroccan droughts) prevailed over the last 1,000 years.

Schwikowski, Margit; Sigl, Michael; Gäggeler, Heinz W.; Gabrieli, Jacopo; Barbante, Carlo; Boutron, Claude

2010-05-01

55

Decadal Sea Surface Temperature Variability in the Subtropical South Pacific from 1726 to 1997 A.D.  

NASA Astrophysics Data System (ADS)

We present a 271-year record of Sr/Ca variability in a coral from Rarotonga in the South Pacific gyre. Calibration with monthly sea surface temperature (SST) from satellite and ship measurements made in a grid measuring 1° by 1° over the period from 1981 to 1997 indicates that this Sr/Ca record is an excellent proxy for SST. Comparison with SST from ship measurements made since 1950 in a grid measuring 5° by 5° also shows that the Sr/Ca data accurately record decadal changes in SST. The entire Sr/Ca record back to 1726 shows a distinct pattern of decadal variability, with repeated decadal and interdecadal SST regime shifts greater than 0.75°C. Comparison with decadal climate variability in the North Pacific, as represented by the Pacific Decadal Oscillation index (1900-1997), indicates that several of the largest decadal-scale SST variations at Rarotonga are coherent with SST regime shifts in the North Pacific. This hemispheric symmetry suggests that tropical forcing may be an important factor in at least some of the decadal variability observed in the Pacific Ocean.

Linsley, Braddock K.; Wellington, Gerard M.; Schrag, Daniel P.

2000-11-01

56

Inter-Decadal to Multi-Decadal Sea Surface Temperature Variability in the Southwest Tropical Pacific Since AD 1648  

NASA Astrophysics Data System (ADS)

The southwest tropical Pacific is a region with temporally and spatially sparse sea surface temperature (SST) records that limit investigations of climate variability on interannual to centennial time scales for this region. We present a monthly resolved coral Sr/Ca record from 1648 to 1999 from Amédée Island, New Caledonia (22.48°S, 166.47°E), and reconstruct SST variability in the southwest Pacific for the past 350 years. The coral Sr/Ca record was assembled from two 3-m long coeval cores from the same massive Porites lutea coral colony. The chronology is based on annual density-band counting, cross- correlation of the two intracolony coral Sr/Ca records, and 11 230Th dates with 2? precision of ±1.1 to 16.5 years. The intracolony coral Sr/Ca variations are reproducible for more than three centuries (average monthly misfit error = ±0.015 mmol/mol; ~0.28°C), and the intracolony variations are coherent from interannual to centennial periodicities. The SST reconstructed from coral Sr/Ca shows a cooling trend from AD 1740 to 1815, a cold 19th century (~0.6°C with respect to AD 1967 to 1992), followed by a warming trend into the 20th century. Many of the cold events in the coral Sr/Ca record coincide with large volcanic eruptions (e.g., Tambora AD 1815 and Krakatau AD 1883). Spectral analysis reveals the record is dominated by modulating inter-decadal (14 to 21 years) periodicities and quasi-persistent multi-decadal (24 to 38 years) periodicities that do not exhibit coherence with the Pacific Decadal Oscillation (PDO) or the Inter-decadal Pacific Oscillation (IPO). Wavelet analysis reveals that the inter-decadal periodicities coincide with large volcanic eruptions, and the 55- to 70-year periodicities are coeval with volcanic cooling and warming trends in the 19th and 20th centuries. The multi-decadal periodicities may be a harmonic of the modulating inter-decadal periodicities or may represent an independent mode not previously recognized in the southwest Pacific.

Delong, K. L.; Quinn, T. M.; Taylor, F. W.; Lin, K.; Shen, C.

2008-12-01

57

Observed subsurface signature of Southern Ocean decadal sea level rise  

NASA Astrophysics Data System (ADS)

Satellite altimetry data show a strong increase in sea level in various parts of the Southern Ocean over the 1990s. In this paper we examine the causes of the observed sea level rise in the region south of Australia, using 13 years of repeat hydrographic data from the WOCE-SR3 sections, and the SURVOSTRAL XBT and surface salinity data, between Australia and Antarctica. The hydrographic data show a poleward shift in the position of the Subtropical and the Subantarctic Fronts over the period. In the Antarctic Zone, the Antarctic Surface Water has become warmer and fresher, and the Winter Water tongue has become warmer, fresher, thinner and shallower. Increased freshening south of the Polar Front is linked to increased precipitation over the 1990s. Temperature changes over the upper 500 m account for only part of the altimetric sea level rise. The CTD sections show that the deeper layers are also warmer and slightly saltier and the observed sea level can be explained by steric expansion over the upper 2000 m. ENSO variability impacts on the northern part of the section, and a simple Sverdrup transport model shows how large-scale changes in the wind-forcing, related to the Southern Annular Mode, may contribute to the deeper warming to the south.

Morrow, R.; Valladeau, G.; Sallee, J.

2006-12-01

58

Polar Lightning and Decadal-Scale Cloud Variability on Jupiter  

Microsoft Academic Search

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80°N and 74°S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes,

Kevin H. Baines; Amy A. Simon-Miller; Glenn S. Orton; Harold A. Weaver; Allen Lunsford; Thomas W. Momary; John Spencer; Andrew F. Cheng; Dennis C. Reuter; Donald E. Jennings; G. R. Gladstone; Jeffrey Moore; S. Alan Stern; Leslie A. Young; Henry Throop; Padma Yanamandra-Fisher; Brendan M. Fisher; Joseph Hora; Michael E. Ressler

2007-01-01

59

Indian Ocean SST and Indian Summer Rainfall: Predictive Relationships and Their Decadal Variability  

Microsoft Academic Search

The authors examine relationships between Indian Ocean sea surface temperature (SST) variability and the variability of the Indian monsoon, including analysis of potential long-lead predictions of Indian rainfall by regional SST and the influence of ENSO and decadal variability on the stability of the relationships. Using monthly gridded (4 83 48) SST data from the Global Sea-Ice and Sea Surface

Christina Oelfke Clark; Julia E. Cole; Peter J. Webster

2000-01-01

60

Polar lightning and decadal-scale cloud variability on Jupiter.  

PubMed

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter. PMID:17932285

Baines, Kevin H; Simon-Miller, Amy A; Orton, Glenn S; Weaver, Harold A; Lunsford, Allen; Momary, Thomas W; Spencer, John; Cheng, Andrew F; Reuter, Dennis C; Jennings, Donald E; Gladstone, G R; Moore, Jeffrey; Stern, S Alan; Young, Leslie A; Throop, Henry; Yanamandra-Fisher, Padma; Fisher, Brendan M; Hora, Joseph; Ressler, Michael E

2007-10-12

61

Polar Lightning and Decadal-Scale Cloud Variability on Jupiter  

NASA Astrophysics Data System (ADS)

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80°N and 74°S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter.

Baines, Kevin H.; Simon-Miller, Amy A.; Orton, Glenn S.; Weaver, Harold A.; Lunsford, Allen; Momary, Thomas W.; Spencer, John; Cheng, Andrew F.; Reuter, Dennis C.; Jennings, Donald E.; Gladstone, G. R.; Moore, Jeffrey; Stern, S. Alan; Young, Leslie A.; Throop, Henry; Yanamandra-Fisher, Padma; Fisher, Brendan M.; Hora, Joseph; Ressler, Michael E.

2007-10-01

62

Temperature responses to spectral solar variability on decadal time scales  

NASA Astrophysics Data System (ADS)

Two scenarios of spectral solar forcing, namely Spectral Irradiance Monitor (SIM)-based out-of-phase variations and conventional in-phase variations, are input to a time-dependent radiative-convective model (RCM), and to the GISS modelE. Both scenarios and models give maximum temperature responses in the upper stratosphere, decreasing to the surface. Upper stratospheric peak-to-peak responses to out-of-phase forcing are ˜0.6 K and ˜0.9 K in RCM and modelE, ˜5 times larger than responses to in-phase forcing. Stratospheric responses are in-phase with TSI and UV variations, and resemble HALOE observed 11-year temperature variations. For in-phase forcing, ocean mixed layer response lags surface air response by ˜2 years, and is ˜0.06 K compared to ˜0.14 K for atmosphere. For out-of-phase forcing, lags are similar, but surface responses are significantly smaller. For both scenarios, modelE surface responses are less than 0.1 K in the tropics, and display similar patterns over oceanic regions, but complex responses over land.

Cahalan, Robert F.; Wen, Guoyong; Harder, Jerald W.; Pilewskie, Peter

2010-04-01

63

Influence of Decadal Variability of Global Oceans on South Asian Monsoon and ENSO-Monsoon Relation  

NASA Astrophysics Data System (ADS)

This study has investigated the influence of the decadal variability associated with global oceans on South Asian monsoon and El Nino-Southern Oscillation (ENSO)-monsoon relation. The results are based on observational analysis using long records of monsoon rainfall and circulation and coupled general circulation model experiments using the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) version 4 model. The multi-channel singular spectrum analysis (MSSA) of the observed rainfall over India yields three decadal modes. The first mode (52 year period) is associated with the Atlantic Multidecadal Oscillation (AMO), the second one (21 year) with the Pacific Decadal Oscillation (PDO) and the third mode (13 year) with the Atlantic tripole. The existence of these decadal modes in the monsoon was also found in the control simulation of NCAR CCSM4. The regionally de-coupled model experiments performed to isolate the influence of North Pacific and North Atlantic also substantiate the above results. The relation between the decadal modes in the monsoon rainfall with the known decadal modes in global SST is examined. The PDO has significant negative correlation with the Indian Monsoon Rainfall (IMR). The mechanism for PDO-monsoon relation is hypothesized through the seasonal footprinting mechanism and further through Walker and Hadley circulations. The model results also confirm the negative correlation between PDO and IMR and the mechanism through which PDO influences monsoon. Both observational and model analysis show that droughts (floods) are more likely over India than floods (droughts) when ENSO and PDO are in their warm (cold) phase. This study emphasizes the importance of carefully distinguishing the different decadal modes in the SST in the North Atlantic Ocean as they have different impacts on the monsoon. The AMO exhibits significant positive correlation with the IMR while the Atlantic tripole has significant negative correlation with the IMR. The AMO influences the Indian monsoon through atmospheric winds related to high summer North Atlantic Oscillation (NAO) mode leading to enhanced moisture flow over the Indian subcontinent. The Atlantic tripole mode affects the rainfall over India by enhancing the moisture flow through the equatorial westerly winds associated with the NAO. The model also simulates the positive and negative relation of AMO and tripole, respectively, with the monsoon rainfall. The model also indicates the enhanced moisture flow over India related to the positive phase of AMO through the equatorial westerly flow. But, for the tripole mode, the model indicates flow of moisture through the Bay of Bengal in contrast to observations where it is through the Arabian Sea. The reason for the absence of decadal mode in IMR inherent to the Indian Ocean is also explored. The SSA on dipole mode index (DMI) index reveals three modes. The first two modes are related to the biennial and canonical ENSO at interannual timescale while the third mode varies on decadal timescale and is related to PDO. The wind regression pattern associated with the PDO-IOD mode shows northeasterly winds enhancing the southeasterly flow from the southeastern Indian Ocean related to the Indian Ocean dipole (IOD) mode. The model also shows the influence of canonical ENSO and PDO influence on IOD, although the variance explained by PDO mode is lower in the model relative to observations.

Krishnamurthy, Lakshmi

64

Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries  

NASA Astrophysics Data System (ADS)

Observations and reconstructions of decadal-scale climate variability are necessary to place predictions of future global climate change into temporal context (Goddard et al., 2012). This is especially true for decadal-scale climate variability that originates in the Pacific Ocean (Deser et al., 2004; Dong and Lu, 2013). We focus here on the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~ 160° E), a region directly influenced by: the South Pacific Convergence Zone (SPCZ), the West Pacific Warm Pool (WPWP), the Pacific Walker Circulation (PWC), and the Hadley Circulation. We calibrate ?18O variations in a fast growing stalagmite to local rainfall amount and produce a 600 yr record of rainfall variability from the zonally oriented, tropical portion of the SPCZ. We present evidence for large (~ 1.5 m), persistent and decade(s)-long shifts in total annual rainfall amount in the Solomon Islands since 1416 ± 5 CE. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite ?18O record coincide with previously identified decadal shifts in Pacific ocean-atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The 600 yr Solomons stalagmite ?18O record indicates that decadal oscillations in rainfall are a robust characteristic of SPCZ-related climate variability, which has important implications to water resource management in this region.

Maupin, C. R.; Partin, J. W.; Shen, C.-C.; Quinn, T. M.; Lin, K.; Taylor, F. W.; Banner, J. L.; Thirumalai, K.; Sinclair, D. J.

2013-10-01

65

Drivers of annual to decadal streamflow variability in the lower Colorado River Basin  

NASA Astrophysics Data System (ADS)

The Colorado River is the main water supply to the southwest region. As demand reaches the limit of supply in the southwest it becomes increasingly important to understand the dynamics of streamflow in the Colorado River and in particular the tributaries to the lower Colorado River. Climate change may pose an additional threat to the already-scarce water supply in the southwest. Due to the narrowing margin for error, water managers are keen on extending their ability to predict streamflow volumes on a mid-range to decadal scale. Before a predictive streamflow model can be developed, an understanding of the physical drivers of annual to decadal streamflow variability in the lower Colorado River Basin is needed. This research addresses this need by applying multiple statistical methods to identify trends, patterns and relationships present in streamflow, precipitation and temperature over the past century in four contributing watersheds to the lower Colorado River. The four watersheds selected were the Paria, Little Colorado, Virgin/Muddy, and Bill Williams. Time series data over a common period from 1906-2007 for streamflow, precipitation and temperature were used for the initial analysis. Through statistical analysis the following questions were addressed: 1) are there observable trends and patterns in these variables during the past century and 2) if there are trends or patterns, how are they related to each other? The Mann-Kendall test was used to identify trends in the three variables. Assumptions regarding autocorrelation and persistence in the data were taken into consideration. Kendall’s tau-b test was used to establish association between any found trends in the data. Initial results suggest there are two primary processes occurring. First, statistical analysis reveals significant upward trends in temperatures and downward trends in streamflow. However, there appears to be no trend in precipitation data. These trends in streamflow and temperature speak to increasing evaporation and transpiration processes. Second, annual variability in streamflow is not statistically correlated with annual temperature variability but appears to be highly correlated with annual precipitation variability. This implies that on a year-to-year basis, changes in streamflow volumes are directly affected by precipitation and not temperature. Future development of a predictive streamflow model will need to take into consideration these two processes to obtain accurate results. In order to extend predictive skill to the multi-year scale relationships between precipitation, temperature and persistent climate indices such as the Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation and El Nino/Southern Oscillation will need to be examined.

Lambeth-Beagles, R. S.; Troch, P. A.

2010-12-01

66

Decadal variability of the tropical stratosphere: Secondary influence of the El Niño–Southern Oscillation  

Microsoft Academic Search

A decadal variation of tropical lower stratospheric ozone and temperature has previously been identified that correlates positively with the 11 year solar activity cycle. However, the El Niño–Southern Oscillation (ENSO) also influences lower stratospheric ozone and temperature. It is therefore legitimate to ask whether quasi-decadal ENSO variability can contribute to this apparent solar cycle variation, either accidentally because of the

L. L. Hood; B. E. Soukharev; J. P. McCormack

2010-01-01

67

ENSO, Pacific Decadal Variability, and U.S. Summertime Precipitation, Drought, and Stream Flow  

Microsoft Academic Search

The relationship between the three primary modes of Pacific sea surface temperature (SST) variability-the El Niño-Southern Oscillation (ENSO), the Pacific decadal oscillation, and the North Pacific mode-and U.S. warm season hydroclimate is examined. In addition to precipitation, drought and stream flow data are analyzed to provide a comprehensive picture of the lower-frequency components of hydrologic variability.ENSO and the two decadal

M. Barlow; S. Nigam; E. H. Berbery

2001-01-01

68

HERSCHEL OBSERVATIONS OF CATACLYSMIC VARIABLES  

SciTech Connect

We have used the PACS instrument on the Herschel Space Observatory to observe eight cataclysmic variables at 70 and 160 {mu}m. Of these eight objects, only AM Her was detected. We have combined the Herschel results with ground-based, Spitzer, and WISE observations to construct spectral energy distributions for all of the targets. For the two dwarf novae in the sample, SS Cyg and U Gem, we find that their infrared luminosities are completely dominated by their secondary stars. For the two highly magnetic 'polars' in our survey, AM Her and EF Eri, we find that their mid-infrared excesses, previously attributed to circumbinary dust emission, can be fully explained by cyclotron emission. The WISE light curves for both sources show large, orbitally modulated variations that are identically phased to their near-IR light curves. We propose that significant emission from the lowest cyclotron harmonics (n {<=} 3) is present in EF Eri and AM Her. Previously, such emission would have been presumed to be optically thick, and not provide significant orbitally modulated flux. This suggests that the accretion onto polars is more complicated than assumed in the simple models developed for these two sources. We develop a model for the near-/mid-IR light curves for WZ Sge with an L2 donor star that shows that the ellipsoidal variations from its secondary star are detected. We conclude that none of the targets surveyed have dusty circumbinary disks.

Harrison, Thomas E.; Hamilton, Ryan T. [Department of Astronomy, New Mexico State University, Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Tappert, Claus [Departamento de Fisica y Astronomia, Universidad de Valparaiso, Avda. Gran Bretana 1111, Valparaiso (Chile); Hoffman, Douglas I. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Campbell, Ryan K., E-mail: tharriso@nmsu.edu, E-mail: rthamilt@nmsu.edu, E-mail: claus.tappert@uv.cl, E-mail: dhoffman@ipac.caltech.edu, E-mail: Ryan.Campbell@humobldt.edu [Department of Physics and Astronomy, Humboldt State University, 1 Harpst St., Arcata, CA 95521 (United States)

2013-01-01

69

ASSOCIATIONS OF DECADAL TO MULTIDECADAL SEA-SURFACE TEMPERATURE VARIABILITY WITH UPPER COLORADO RIVER FLOW1  

Microsoft Academic Search

The relations of decadal to multidecadal (D2M) variability in global sea-surface temperatures (SSTs) with D2M variability in the flow of the Upper Colorado River Basin (UCRB) are examined for the years 1906- 2003. Results indicate that D2M variability of SSTs in the North Atlantic, North Pacific, tropical Pacific, and Indian Oceans is associated with D2M variability of the UCRB. A

Gregory J. McCabe; Julio L. Betancourt; Hugo G. Hidalgo

70

On the assessment of near-surface global temperature and North Atlantic multi-decadal variability in the ENSEMBLES decadal hindcast  

NASA Astrophysics Data System (ADS)

The ENSEMBLES multi-model and perturbed-parameter decadal re-forecasts are used to assess multi-year forecast quality for global-mean surface air temperature (SAT) and North Atlantic multi-decadal sea surface temperature variability (AMV). Two issues for near-term climate prediction, not discussed so far, are addressed with these two examples: the impact of the choice of the observational reference period, and of the number of years included in the forecast average. Taking into account only years when both observational and model data are available, instead of using the full record, to estimate observed climatologies produces systematically (although not statistically significantly different) higher ensemble-mean correlations and lower root mean square errors in all forecast systems. These differences are more apparent in the second half of the decadal prediction, which suggests an influence of non-stationary long-term trends. Also, as the forecast period averaged increases, the correlation for both global-mean SAT and AMV is generally higher. This also suggests an increasing role for the variable external forcing as when forecast period averaged increases, unpredictable internal variability is smoothed out. The results show that predicting El Niño-Southern Oscillation beyond one year is a hurdle for current global forecast systems, which explains the positive impact of the forecast period averaging. By comparing initialized and uninitialized re-forecasts, the skill assessment confirms that variations of the global-mean SAT are largely controlled by the prescribed variable external forcing. By contrast, the initialization improves the skill of the AMV during the first half of the forecast period. In an operational context, this would lead to improved predictions of the AMV from initializing internal climate fluctuations. The coherence between the multi-model and perturbed-parameter ensemble supports that conclusion for boreal summer and annual means, while the results show less consistency for boreal winter.

García-Serrano, J.; Doblas-Reyes, F. J.

2012-10-01

71

Herschel Observations of Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

We have used the PACS instrument on the Herschel Space Observatory to observe eight cataclysmic variables at 70 and 160 ?m. Of these eight objects, only AM Her was detected. We have combined the Herschel results with ground-based, Spitzer, and WISE observations to construct spectral energy distributions for all of the targets. For the two dwarf novae in the sample, SS Cyg and U Gem, we find that their infrared luminosities are completely dominated by their secondary stars. For the two highly magnetic "polars" in our survey, AM Her and EF Eri, we find that their mid-infrared excesses, previously attributed to circumbinary dust emission, can be fully explained by cyclotron emission. The WISE light curves for both sources show large, orbitally modulated variations that are identically phased to their near-IR light curves. We propose that significant emission from the lowest cyclotron harmonics (n <= 3) is present in EF Eri and AM Her. Previously, such emission would have been presumed to be optically thick, and not provide significant orbitally modulated flux. This suggests that the accretion onto polars is more complicated than assumed in the simple models developed for these two sources. We develop a model for the near-/mid-IR light curves for WZ Sge with an L2 donor star that shows that the ellipsoidal variations from its secondary star are detected. We conclude that none of the targets surveyed have dusty circumbinary disks. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Harrison, Thomas E.; Hamilton, Ryan T.; Tappert, Claus; Hoffman, Douglas I.; Campbell, Ryan K.

2013-01-01

72

Examining the last few decades of global hydroclimate for evidence of anthropogenic change amidst natural variability  

NASA Astrophysics Data System (ADS)

Climate models robustly predict that the deep tropics and mid-latitude-to-subpolar regions will moisten, and the subtropical dry zones both dry and expand, as a consequence of global warming driven by rising greenhouse gases. The models also predict that this transition to a more extreme climatological mean global hydroclimate should already be underway. Given the importance of these predictions it is an imperative that the climate science community assess whether there is evidence within the observational record that they are correct. This task is made difficult by the tremendous natural variability of the hydrological cycle on seasonal to multidecadal timescales. Here we will use instrumental observations, reanalyses, sea surface temperature forced atmosphere models and coupled model simulations, and a variety of methodologies, to attempt to separate global radiatively-forced hydroclimate change from ongoing natural variability. The results will be applied to explain trends and recent events in key regions such as Mexico, the United States and the Mediterranean. It is concluded that the signal of anthropogenic change is small compared to the amplitude of natural variability but that it is a discernible contributor. Globally the evidence reveals that radiatively-forced hydroclimate change is occurring with an amplitude and spatial pattern largely consistent with the predictions by IPCC AR4 models of hydroclimate change to date. However it will also be shown that the radiatively-forced component does not in and of itself provide a useful prediction of near term hydroclimate change because for many regions the amplitude of natural decadal variability is as large or larger. Useful predictions need to account for how natural variability may evolve as well as forced change.

Seager, R.; Naik, N.; Ting, M.; Kushnir, Y.; Kelley, C. P.

2011-12-01

73

The GEOS Association of Variable Star Observers  

NASA Astrophysics Data System (ADS)

(Abstract only) Groupe Européen d'Observation Stellaire (GEOS) is an astronomical association created in the 1970s to promote research among amateurs in Europe. We started in Belgium, France, and Italy, later extended to Spain, Switzerland, and Germany, and more recently, added U.S. amateurs. The basic idea was that amateurs should themselves extract scientific information from their observations (visually at first and later electronically) and publish their results. Some GEOS members have become professional astronomers and the amateur-professional collaboration has strengthened over the years. From the beginning, it has been clear that the study of variable stars is a privileged topic where such projects can develop. Since the 1980s GEOS members have published a number of scientific papers, even in refereed professional journals. Presently, observations are mainly done using CCD cameras though visual measurements still exist. In the past decade our main development has been the creation of a public RR Lyr star maxima database. This is a unique tool for the study of RR Lyr stars, as it enables the user to follow period variations since a star's discovery, some over 100 years ago. In parallel to the database, a project called "GEOS RR Lyr survey" was designed. Its aims include: first, add significantly more maxima timings of the brightest RR Lyr stars essentially using robotic telescopes; second, study fainter understudied stars to refine their period and find new stars which exhibit the so-called Blazhko effect; third, characterize the Blazhko effect, one of our main research topics. Other variable stars are also studied: eclipsing binaries, d Scuti stars, and so on. GEOS has a good cooperation with other variable star associations, mainly BAV and AAVSO.

Hambsch, F.-J.; LeBorgne, J.-F.; Poretti, E.; GEOS association

2012-06-01

74

Decadal Variability in the Terrestrial Carbon Budget Caused by the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation  

Microsoft Academic Search

The terrestrial carbon dioxide (CO2) budget interacts with the Earth's climate system on diurnal to centennial and longer time scales, making it critical for climatic prediction and stabilization. Atmospheric observations and global syntheses of CO2 data indicate that the terrestrial biosphere is one the major sources of interannual variability, but the underlying mechanisms operating on different time-scales and the potential

Akihiko Ito

2011-01-01

75

Prioritizing Global Observations Along Essential Climate Variables  

NASA Astrophysics Data System (ADS)

The Global Climate Observing System (GCOS) Secretariat, housed within the World Meteorological Organization, released in August 2010 updated guidance for priority actions worldwide in support of observations of GCOS Essential Climate Variables (ECVs). This guidance states that full achievement of the recommendations in the 2010 Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (http://www.wmo.int/pages/prog/gcos/Publications/gcos­138.pdf) is required to ensure that countries are able to understand and predict climate change and its impacts and manage their response throughout the 21st century and beyond. GCOS is sponsored by the United Nations and the International Council for Science (ICSU) and is an internationally coordinated network of observing systems and a program of activities that support and improve the network, which is designed to meet evolving national and international requirements for climate observations. One of the main objectives of GCOS is to sustain observations into the future to allow evaluation of how climate is changing, so that informed decisions can be made on prevention, mitigation, and adaptation strategies. GCOS priorities are based on the belief that observations are crucial to supporting the research needed to refine understanding of the climate system and its changes, to initialize predictions on time scales out to decades, and to develop the models used to make these predictions and longer­term scenario-based projections. Observations are also needed to assess social and economic vulnerabilities and to support related actions needed across a broad range of societal sectors by underpinning emerging climate services.

Bojinski, Stephan; Richter, Carolin

2010-12-01

76

Decadal Thermocline Variability in the North Pacific Ocean: Two Pathwaysaround the Subtropical Gyre  

Microsoft Academic Search

Yearly in situ temperature anomaly data in the North Pacific Ocean for 1961-90 have been analyzed along constant-density surfaces (isopycnals) in order to better describe and understand decadal thermocline variability in the region. Various empirical orthogonal function analyses are performed on isopycnals to depict the dominant three-dimensional patterns. The major finding is of two preferential pathways associated with decadal temperature

Rong-Hua Zhang; Zhengyu Liu

1999-01-01

77

Global warming trend without the contributions from decadal variability of the Arctic Oscillation  

NASA Astrophysics Data System (ADS)

Climate change associated with recent global warming is most prominent in the Arctic and subarctic. The Arctic Oscillation (AO) is a dominant atmospheric phenomenon in the Northern Hemisphere. Decadal variability of surface air temperature (SAT) associated with the AO index shows high correlation with recent global warming trend. In this study, the SAT variability in the Northern Hemisphere is separated in contributions from decadal variability by the AO and remaining components.The results indicate that the decadal variability of the AO index shows high correlation with the SAT variation until 1990. The AO index and SAT variabilities show a negative trend during 1949-1969, while the trend is positive during 1969-1989. In addition, the spatial distribution pattern of the SAT linear trend during each period shows the same pattern as AO. However, while the AO index indicates a negative trend, the SAT trend is continuously positive also after 1990. This warming pattern appearing after 1990 is caused by the Arctic amplification.Although the AO has a large amplitude on local scale, the AO is almost dynamically orthogonal to the hemispheric warming component. However, the AO can be related to the decadal variability of the Arctic and subarctic temperature change through the feedbacks by climate sub-systems.

Nagato, Yuta; Tanaka, H. L.

2012-04-01

78

Decadal prediction of observed and simulated sea surface temperatures  

NASA Astrophysics Data System (ADS)

multivariate regression model derived from climate model simulations is shown to produce skillful predictions of unforced, annual mean sea surface temperature variations on multiyear time scales in observations and climate model simulations. Patterns that can be predicted with skill are identified explicitly and shown to arise from a combination of persistence and coupled interactions in the Pacific Ocean. Adding the regression model predictions to an estimate of the response to anthropogenic and natural forcing yields a prediction with higher skill than either alone, demonstrating the contribution of initial condition information to skill on multiyear time scales.

Delsole, Timothy; Jia, Liwei; Tippett, Michael K.

2013-06-01

79

The role of the North Atlantic overturning and deep-ocean for multi-decadal global-mean-temperature variability  

NASA Astrophysics Data System (ADS)

Earth's climate exhibits internal modes of variability on various time scales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC) in the control runs of an ensemble of CMIP5 models. By decomposing global-mean-temperature (GMT) variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade-1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC-deep-ocean system, our results are inconclusive about the role of this feedback in the model ensemble.

Schleussner, C. F.; Runge, J.; Lehmann, J.; Levermann, A.

2013-09-01

80

Response of Tropical Forests to Intense Climate Variability and Rainfall Anomaly over the Last Decade  

NASA Astrophysics Data System (ADS)

During the last decade, strong precipitation anomalies resulted from increased sea surface temperature in the tropical Atlantic, have caused extensive drying trends in rainforests of western Amazonia, exerting water stress, tree mortality, biomass loss, and large-scale fire disturbance. In contrast, there have been no reports on large-scale disturbance in rainforests of west and central Africa, though being exposed to similar intensity of climate variability. Using data from Tropical Rainfall Mapping Mission (TRMM) (1999-2010), and time series of rainfall observations from meteorological stations (1971-2000), we show that both Amazonian and African rainforest experienced strong precipitation anomalies from 2005-2010. We monitored the response of forest to the climate variability by analyzing the canopy water content observed by SeaWinds Ku-band Scatterometer (QSCAT) (1999-2009) and found that more than 70 million ha of forests in western Amazonia experienced a strong water deficit during the dry season of 2005 and a closely corresponding decline in canopy backscatter that persisted until the next major drought in 2010. This decline in backscatter has been attributed to loss of canopy water content and large-scale tree mortality corroborated by ground and airborne observations. However, no strong impacts was observed on tropical forests of Africa, suggesting that the African rainforest may have more resilience to droughts. We tested this hypothesis by examining the seasonal rainfall patterns, maximum water deficit, and the surface temperature variations. Results show that there is a complex pattern of low annual rainfall, moderate seasonality, and lower surface temperature in Central Africa compared to Amazonia, indicating potentially a lower evapotranspiration circumventing strong water deficits

Saatchi, S.; Asefi, S.

2012-04-01

81

Decadal changes in the South Pacific western boundary current system revealed in observations and ocean state estimates  

NASA Astrophysics Data System (ADS)

Observations and ocean state estimates are used to investigate the nature and mechanism of decadal variability in the East Australian Current (EAC) system and South Pacific subtropical gyre. A 62 year record on the Tasmanian continental shelf shows decadal variations of temperature and salinity, as well as a long-term trend, which has been related to wind-driven variations in the poleward extension of the EAC. Repeat expendable bathythermograph lines spanning the last 15 years suggest that low-frequency variations in the transport of the EAC extension and Tasman Front are anticorrelated, but the time series are too short to draw firm conclusions. Here we use two ocean state estimates spanning the past 50 years to diagnose the physical mechanisms and spatial structure of the decadal variability of the South Pacific subtropical gyre. The observations and state estimates paint a consistent picture of the decadal variability of the gyre and EAC system. Strengthening of the basin-wide wind stress curl drives a southward expansion of the subtropical gyre. As the gyre shifts south, the EAC extension pathway is favored at the expense of the Tasman Front, resulting in the observed anticorrelation of the these two major currents. The results suggest that the subtropical gyre and western boundary current respond to decadal variability in basin-scale wind stress curl, consistent with Island Rule dynamics; that strong decadal variability of the South Pacific gyre complicates efforts to infer trends from short-term records; and that wind stress curl changes over the South Pacific basin drive changes in the EAC system that are likely to have implications for marine ecosystems and regional climate.

Hill, K. L.; Rintoul, S. R.; Ridgway, K. R.; Oke, P. R.

2011-01-01

82

Associations of decadal to multidecadal sea-surface temperature variability with Upper Colorado River flow  

USGS Publications Warehouse

The relations of decadal to multidecadal (D2M) variability in global sea-surface temperatures (SSTs) with D2M variability in the flow of the Upper Colorado River Basin (UCRB) are examined for the years 1906-2003. Results indicate that D2M variability of SSTs in the North Atlantic, North Pacific, tropical Pacific, and Indian Oceans is associated with D2M variability of the UCRB. A principal components analysis (with varimax rotation) of detrended and 11-year smoothed global SSTs indicates that the two leading rotated principal components (RPCs) explain 56% of the variability in the transformed SST data. The first RPC (RPC1) strongly reflects variability associated with the Atlantic Multidecadal Oscillation and the second RPC (RPC2) represents variability of the Pacific Decadal Oscillation, the tropical Pacific Ocean, and Indian Ocean SSTs. Results indicate that SSTs in the North Atlantic Ocean (RPC1) explain as much of the D2M variability in global SSTs as does the combination of Indian and Pacific Ocean variability (RPC2). These results suggest that SSTs in all of the oceans have some relation with flow of the UCRB, but the North Atlantic may have the strongest and most consistent association on D2M time scales. Hydroclimatic persistence on these time scales introduces significant nonstationarity in mean annual streamflow, with critical implications for UCRB water resource management. ?? 2007 American Water Resources Association.

McCabe, G. J.; Betancourt, J. L.; Hidalgo, H. G.

2007-01-01

83

Optimal nonlinear excitation of decadal variability of the North Atlantic thermohaline circulation  

NASA Astrophysics Data System (ADS)

Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation (THC) is investigated with a three-dimensional ocean circulation model, using the conditional nonlinear optimal perturbation method. The results show two types of optimal initial perturbations of sea surface salinity, one associated with freshwater and the other with salinity. Both types of perturbations excite decadal variability of the THC. Under the same amplitude of initial perturbation, the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation, suggesting that the THC is more sensitive to freshwater than salinity perturbation. As the amplitude of initial perturbation increases, the decadal variations become stronger for both perturbations. For salinity perturbations, recovery time of the THC to return to steady state gradually saturates with increasing amplitude, whereas this recovery time increases remarkably for freshwater perturbations. A nonlinear (advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability excitation. The results are consistent with previous ones from simple box models, and highlight the importance of nonlinear feedback in decadal THC variability.

Zu, Ziqing; Mu, Mu; Dijkstra, Henk A.

2013-08-01

84

Mesoscale Disturbance and Ecological Response to Decadal Climatic Variability in the American Southwest  

Microsoft Academic Search

Ecological responses to climatic variability in the Southwest include regionally synchronized fires, insect outbreaks, and pulses in tree demography (births and deaths). Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography reveal climatic effects across scales, from annual to decadal, and from local (,102 km2) to mesoscale (10 4-106 km2). Climate-disturbance relations are more variable and complex than previously

Thomas W. Swetnam; Julio L. Betancourt

1998-01-01

85

Interannual and decadal variability of the subsurface thermal structure in the Pacific Ocean: 1961–90  

Microsoft Academic Search

Heat content anomalies are analyzed to understand subsurface variability on both aparticular focus on the evolving basinwide\\u000a patterns and oceanic connections between the extratropics and tropics. Various analyses indicate two distinct modes, one interannual\\u000a and the other decadal, that involve the tropics and the North Pacific subtropical gyre, respectively. Interannual variability\\u000a is associated with El Nio in the tropics, with

R.-H. Zhang; L. M. Rothstein; A. J. Busalacchi

1999-01-01

86

Decadal and long-term sea level variability in the tropical Indo-Pacific Ocean  

NASA Astrophysics Data System (ADS)

In this study, we analysed decadal and long-term steric sea level variations over 1966-2007 period in the Indo-Pacific sector, using an ocean general circulation model forced by reanalysis winds. The simulated steric sea level compares favourably with sea level from satellite altimetry and tide gauges at interannual and decadal timescales. The amplitude of decadal sea level variability (up to ~5 cm standard deviation) is typically nearly half of the interannual variations (up to ~10 cm) and two to three times larger than long-term sea level variations (up to 2 cm). Zonal wind stress varies at decadal timescales in the western Pacific and in the southern Indian Ocean, with coherent signals in ERA-40 (from which the model forcing is derived), NCEP, twentieth century and WASWind products. Contrary to the variability at interannual timescale, for which there is a tendency of El Niño and Indian Ocean Dipole events to co-occur, decadal wind stress variations are relatively independent in the two basins. In the Pacific, those wind stress variations drive Ekman pumping on either side of the equator, and induce low frequency sea level variations in the western Pacific through planetary wave propagation. The equatorial signal from the western Pacific travels southward to the west Australian coast through equatorial and coastal wave guides. In the Indian Ocean, decadal zonal wind stress variations induce sea level fluctuations in the eastern equatorial Indian Ocean and the Bay of Bengal, through equatorial and coastal wave-guides. Wind stress curl in the southern Indian Ocean drives decadal variability in the south-western Indian Ocean through planetary waves. Decadal sea level variations in the south-western Indian Ocean, in the eastern equatorial Indian Ocean and in the Bay of Bengal are weakly correlated to variability in the Pacific Ocean. Even though the wind variability is coherent among various wind products at decadal timescales, they show a large contrast in long-term wind stress changes, suggesting that long-term sea level changes from forced ocean models need to be interpreted with caution.

Nidheesh, A. G.; Lengaigne, Matthieu; Vialard, Jérôme; Unnikrishnan, A. S.; Dayan, H.

2013-07-01

87

Decadal variability of the tropical Atlantic Ocean surface temperature in shipboard measurements and in a Global Ocean-atmosphere model  

SciTech Connect

Numerous analyses of relatively short (25-30 years in length) time series of the observed surface temperature of the tropical Atlantic Ocean have indicated the possible existence of decadal timescale variability. It was decided to search for such variability in 100-yr time series of sea surface temperature (SST) measured aboard ships and available in the recently published Global Ocean Surface Temperature Atlas (GOSTA). Fourier and singular spectrum analyses of the GOSTA SST time series averaged over 11 subregions, each approximately 1 x 10{sup 6}km{sup 2} in area, show that pronounced quasi-oscillatory decadal ({approximately}-20 yr) and multidecadal ({approximately}30-40 yr) timescale variability exists in the GOSTA dataset over the tropical Atlantic. Motivated by the above results, SST variability was investigated in a 200-yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the geophysical Fluid Dynamics Laboratory (GFDL). The second 100 yr of SST in the coupled model`s tropical Atlantic region were analyzed with a variety of techniques. Analyses of SST time series, averaged over approximately the same subregions as the GOSTA time series, showed that the GFDL SST anomalies also undergo pronounced quasi-oscillatory decadal and multidecadal variability but at somewhat shorter timescales than the GOSTA SST anomalies. Further analyses of the horizontal structures of the decadal timescale variability in the GFDL coupled model showed the existence of two types of variability in general agreement with results of the GOSTA SST time series analyses. One type, characterized by timescales between 8 and 11 yr, has high spatial coherence within each hemisphere but not between the two hemispheres of the tropical Atlantic. A second type, characterized by timescales between 12 and 20 yr, has high spatial coherence between the two hemispheres. 31 refs., 14 figs., 3 tabs.

Mehta, V.M. [Goddard Space Flight Center, Greenbelt, MD (United States); Delworth, T. [Geophysical Fluid Dynamics Laboratory, Princeton, NJ (United States)

1995-02-01

88

Interannual to Decadal Variability in Hydroclimatic Data: Analyses and Implications to Water Management  

NASA Astrophysics Data System (ADS)

Analysis of decadal variability in climatic data provides better understanding of climate dynamic system. But, the land surface runoff could exhibit a different signature since it is influenced by the variability on both precipitation and temperature. Understanding the decadal variability is also critical for water infrastructure design and long-term planning. We apply Singular Spectrum Analysis (SSA), a data-driven spectrum analysis tool, on precipitation, temperature and streamflow from HCDN watersheds to identify the dominant frequencies and to estimate the variability associated with them. Hypothesis test against an AR(1) process is carried out via Monte Carolo SSA, which detects an oscillation at 90% confidence. Initial results show that hydroclimatic data reveals inter-annual to decadal oscillation. In order to find out whether streamflow and climatic data reveal significant correlation at a certain frequency, cross spectrum analysis between streamflow and precipitation will be employed. Implications of these analyses in the context of decadal climate predictions and their importance to water management will also be discussed.

Wang, H.; Arumugam, S.; Ranjithan, R. S.

2010-12-01

89

Inter-decadal variability of US westcoast precipitation in a GCM  

SciTech Connect

The wintertime precipitation in the mountains of the western United States during a warm or cool period has a pronounced influence on the streamflow. During a warm year, streamflow at intermediate elevations responds more immediately to precipitation events; during a cold year much of the discharge is delayed until the snow melts in spring and summer. Previous efforts at studying these extremes have been hampered by a limited number and length of observational analyses. In this study, we augment this limited observational record by analyzing a simplified general circulation model (GCM). We first analyze the ability of the model to reproduce major characteristics of warm and cool storms. Then, a longer model run is investigated in order to understand inter-annual and inter-decadal variability of winter-mean precipitation and temperature along the west coast of US In addition to having a self consistent hydrologic budget, this model is able to generate substantial numbers of low frequency events which are quite realistic. The model also has stationary statistics (e.g. no problems due to station moves or missing data).

Chen, Shyh-Chin

1991-12-31

90

The Deep Western Boundary Current southeast of Cape Farewell, Greenland: decadal transport variability from repeat hydrography and satellite altimetry  

NASA Astrophysics Data System (ADS)

Recent decadal changes in the Deep Western Boundary Current (DWBC) transport southeast of Cape Farewell are assessed from hydrographic data (1991-2007), individual direct velocity measurements (2002-2006) and altimetry (1992-2007). Following the approach used in earlier studies, we first determined that the DWBC (?0 >27.80) baroclinic transport (TBC) referenced to 1000 m depth increased by ~2 Sv between the mid-1990s (1994-1997) and 2000s (2000-2007). In the next step, we quantified velocity changes at the reference level (1000 m) by combining estimates of the hydrography-derived velocity changes in the water column and the altimetry-derived velocity changes at the sea surface. The inferred increase in the southward velocity at 1000 m above the DWBC in 1994-2007 indicates that the increase in the DWBC absolute transport was larger than the 2-Sv increase in the DWBC TBC. This result and the observed coherence of the DWBC absolute and baroclinic transport changes between individual observations imply that the DWBC absolute transport variability in the region is underestimated but qualitatively well represented by its baroclinic component on decadal and shorter time scales. The updated historical record of the DWBC TBC (1955-2007) shows distinct decadal variability (±2-2.5 Sv) with the transport minima in the 1950s and mid-1990s, maximum in the early 1980s and moderate-to-high transport in the 2000s. The DWBC TBC decadal variability is consistent with the general pattern of the recent decadal hydrographic and circulation changes in the northern North Atlantic. The DWBC TBC anomalies negatively correlate (R = -0.80, 1955-2007) with thickness anomalies of the Labrador Sea Water (LSW) at its origin implying a close association between the DWBC transport southeast of Cape Farewell and the LSW production in the Labrador Sea. During the recent three decades (late 1970s - late 2000s), the DWBC TBC changes were also in-phase with changes in the strength and zonal extension of the Subpolar Gyre (SPG). In particular, the SPG weakening at shallow levels in the mid-1990s - mid-2000s was accompanied by the DWBC strengthening in the Irminger Sea. The results imply that the decadal changes in the (i) LSW production, (ii) SPG strength and (iii) DWBC transport in the Irminger Sea are linked, representing a complex coherent oceanic response to the decadal variability of the surface forcing.

Sarafanov, Artem; Falina, Anastasia; Mercier, Herlé; Lherminier, Pascale; Sokov, Alexey; Gourcuff, Claire

2010-05-01

91

Climate-informed stochastic hydrological modeling: Incorporating decadal-scale variability using paleo data  

NASA Astrophysics Data System (ADS)

A hierarchical framework for incorporating modes of climate variability into stochastic simulations of hydrological data is developed, termed the climate-informed multi-time scale stochastic (CIMSS) framework. To characterize long-term variability for the first level of the hierarchy, paleoclimate and instrumental data describing the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO) are analyzed. A new paleo IPO-PDO time series dating back 440 yr is produced, combining seven IPO-PDO paleo sources using an objective smoothing procedure to fit low-pass filters to individual records. The paleo data analysis indicates that wet/dry IPO-PDO states have a broad range of run lengths, with 90% between 3 and 33 yr and a mean of 15 yr. Model selection techniques were used to determine a suitable stochastic model to simulate these run lengths. The Markov chain model, previously used to simulate oscillating wet/dry climate states, was found to underestimate the probability of wet/dry periods >5 yr, and was rejected in favor of a gamma distribution. For the second level of the hierarchy, a seasonal rainfall model is conditioned on the simulated IPO-PDO state. Application to two high quality rainfall sites close to water supply reservoirs found that mean seasonal rainfall in the IPO-PDO dry state was 15%-28% lower than the wet state. The model was able to replicate observed statistics such as seasonal and multi-year accumulated rainfall distributions and interannual autocorrelations for the case study sites. In comparison, an annual lag-one autoregressive AR(1) model was unable to adequately capture the observed rainfall distribution within separate IPO-PDO states. Furthermore, analysis of the impact of the CIMSS framework on drought risk analysis found that short-term drought risks conditional on IPO/PDO state were far higher than the traditional AR(1) model.

Henley, B.; Thyer, M.; Kuczera, G.

2012-04-01

92

Decadal and inter-hemispheric variability in polar mesospheric clouds, water vapor, and temperature  

NASA Astrophysics Data System (ADS)

Variability in polar mesospheric clouds (PMCs), temperature, and water vapor over decadal time scales and also between hemispheres was examined using measurements from the Halogen Occultation Experiment (HALOE) covering 1991 to present. HALOE measurements were compared to results from a zonally averaged chemical/dynamics model (CHEM2D). HALOE indicates decadal cycles in temperature, water vapor, and PMCs that are correlated with the 11-year solar cycle. During solar cycle 23, variations in temperature and water vapor were nearly identical in the north and south. Temperatures varied by roughly 5 K at 85 km to 1 K at 30 km, with colder temperatures during solar minimum. Water vapor varied by roughly 30% at 85 km to less than 1% at 30 km, with more water vapor during solar minimum. Solar cycle variations in PMC extinction were roughly 23% in both the south and north, with brighter PMCs occurring during solar minimum. The overall picture given by HALOE is consistent with expectations, where a cooler and wetter mesosphere during solar minimum corresponds to brighter PMCs. CHEM2D confirms the solar cycle variations in temperature indicated by HALOE, but underestimates the observed solar cycle changes in H2O. Comparing southern and northern HALOE measurements reveals warmer temperatures in the south throughout the mesosphere. CHEM2D results show the same pattern, although the model appears to overestimate the magnitude of these north-south differences. HALOE indicates that water vapor is nearly identical in the north and south, while CHEM2D predicts a wetter southern mesosphere. HALOE measurements show that northern PMCs are 30% brighter than southern clouds on average, a difference that must be related to the cooler northern summer mesosphere.

Hervig, Mark; Siskind, Dave

2006-01-01

93

Role of Eurasian snow cover in wintertime circulation: Decadal simulations forced with satellite observations  

NASA Astrophysics Data System (ADS)

We investigate the impact of the Eurasian snow cover extent on the Northern Hemisphere winter circulation by performing a suite of ensemble simulations with the Météo-France "Arpege Climat" atmospheric general circulation model, spanning 2 decades (1979-2000). Observed snow cover derived from satellite infrared and visible imagery has been forced weekly into the model. Variability in autumn-early winter snow cover extent over eastern Eurasia is linked to circulation anomalies over the North Pacific that are influencing the North Atlantic sector in late winter through the development of the Aleutian-Icelandic Low Seesaw teleconnection. The forcing of realistic snow cover in the model augments potential predictability over eastern Eurasia and the North Pacific and improves the hindcast skill score of the Aleutian-Icelandic Low Seesaw teleconnection. Enhanced eastern Eurasia snow cover is associated with an anomalous upper-tropospheric wave train across Eurasia, anomalously high upward wave activity flux, and a displaced stratospheric polar vortex.

Orsolini, Yvan J.; Kvamstø, Nils G.

2009-10-01

94

A decadal microwave record of tropical air temperature from AMSU-A/aqua observations  

NASA Astrophysics Data System (ADS)

Atmospheric temperature is one of the most important climate variables. This observational study presents detailed descriptions of the temperature variability imprinted in the 9-year brightness temperature data acquired by the Advanced Microwave Sounding Unit-Instrument A (AMSU-A) aboard Aqua since September 2002 over tropical oceans. A non-linear, adaptive method called the Ensemble Joint Multiple Extraction has been employed to extract the principal modes of variability in the AMSU-A/Aqua data. The semi-annual, annual, quasi-biennial oscillation (QBO) modes and QBO-annual beat in the troposphere and the stratosphere have been successfully recovered. The modulation by the El Niño/Southern oscillation (ENSO) in the troposphere was found and correlates well with the Multivariate ENSO Index. The long-term variations during 2002-2011 reveal a cooling trend (-0.5 K/decade at 10 hPa) in the tropical stratosphere; the trend below the tropical tropopause is not statistically significant due to the length of our data. A new tropospheric near-annual mode (period ~1.6 years) was also revealed in the troposphere, whose existence was confirmed using National Centers for Environmental Prediction Reanalysis air temperature data. The near-annual mode in the troposphere is found to prevail in the eastern Pacific region and is coherent with a near-annual mode in the observed sea surface temperature over the Warm Pool region that has previously been reported. It remains a challenge for climate models to simulate the trends and principal modes of natural variability reported in this work.

Shi, Yuan; Li, King-Fai; Yung, Yuk L.; Aumann, Hartmut H.; Shi, Zuoqiang; Hou, Thomas Y.

2013-09-01

95

A decadal microwave record of tropical air temperature from AMSU-A/aqua observations  

NASA Astrophysics Data System (ADS)

Atmospheric temperature is one of the most important climate variables. This observational study presents detailed descriptions of the temperature variability imprinted in the 9-year brightness temperature data acquired by the Advanced Microwave Sounding Unit-Instrument A (AMSU-A) aboard Aqua since September 2002 over tropical oceans. A non-linear, adaptive method called the Ensemble Joint Multiple Extraction has been employed to extract the principal modes of variability in the AMSU-A/Aqua data. The semi-annual, annual, quasi-biennial oscillation (QBO) modes and QBO-annual beat in the troposphere and the stratosphere have been successfully recovered. The modulation by the El Niño/Southern oscillation (ENSO) in the troposphere was found and correlates well with the Multivariate ENSO Index. The long-term variations during 2002-2011 reveal a cooling trend (-0.5 K/decade at 10 hPa) in the tropical stratosphere; the trend below the tropical tropopause is not statistically significant due to the length of our data. A new tropospheric near-annual mode (period ~1.6 years) was also revealed in the troposphere, whose existence was confirmed using National Centers for Environmental Prediction Reanalysis air temperature data. The near-annual mode in the troposphere is found to prevail in the eastern Pacific region and is coherent with a near-annual mode in the observed sea surface temperature over the Warm Pool region that has previously been reported. It remains a challenge for climate models to simulate the trends and principal modes of natural variability reported in this work.

Shi, Yuan; Li, King-Fai; Yung, Yuk L.; Aumann, Hartmut H.; Shi, Zuoqiang; Hou, Thomas Y.

2013-02-01

96

Interannual to decadal Gulf Stream variability in an eddy-resolving ocean model  

NASA Astrophysics Data System (ADS)

Meridional shifts of the Gulf Stream (GS) jet on interannual to decadal timescales and the corresponding oceanic changes around the GS are investigated using a near global eddy-resolving ocean model hindcast from 1960 to 2003. The simulated variability in the shifts of the GS jet axis shows good agreement with observations, and lags atmospheric fluctuations characterized by the North Atlantic Oscillation by about 2 years. This lagged response of the GS jet to the atmospheric variations is attributed to the westward propagation of the undulation of the jet axis from 45°W to 75°W, which has a wavelength of about 4000 km and a displacement of 0.5°. The propagation direction and phase speed of about 2.8 cm s-1 are consistent with the thin-jet theory. The shifts of the jet axis in the downstream region are likely induced by wind fluctuations through Ekman convergence over the central North Atlantic. Associated with the northward (southward) shift of the jet axis, sea surface temperature is warming (cooling) around and north of the jet, and the former warming has a deep and meridionally narrow subsurface structure, consistent with the northward shift of the jet. The meridional shifts of the jet accompany coherent meridional shifts of energetic eddy activity regions around the GS. Our numerical results suggest that the GS jet brings the atmospheric signals from the central to the western North Atlantic, and the resultant meridional shift of the jet induces the notable oceanic changes around the GS.

Sasaki, Yoshi N.; Schneider, Niklas

97

Simulated and observed variability in ocean temperature and heat content  

PubMed Central

Observations show both a pronounced increase in ocean heat content (OHC) over the second half of the 20th century and substantial OHC variability on interannual-to-decadal time scales. Although climate models are able to simulate overall changes in OHC, they are generally thought to underestimate the amplitude of OHC variability. Using simulations of 20th century climate performed with 13 numerical models, we demonstrate that the apparent discrepancy between modeled and observed variability is largely explained by accounting for changes in observational coverage and instrumentation and by including the effects of volcanic eruptions. Our work does not support the recent claim that the 0- to 700-m layer of the global ocean experienced a substantial OHC decrease over the 2003 to 2005 time period. We show that the 2003–2005 cooling is largely an artifact of a systematic change in the observing system, with the deployment of Argo floats reducing a warm bias in the original observing system.

AchutaRao, K. M.; Ishii, M.; Santer, B. D.; Gleckler, P. J.; Taylor, K. E.; Barnett, T. P.; Pierce, D. W.; Stouffer, R. J.; Wigley, T. M. L.

2007-01-01

98

Local Interstellar Hydrogen Variability observed by IBEX  

NASA Astrophysics Data System (ADS)

IBEX-LO has enabled us to sample local interstellar neutral hydrogen gas directly. We present a review of these observations. In contrast to observations of interstellar neutral helium, the hydrogen fluxes show substantial variability over the three years of observation. This is because the neutral Hydrogen entering the heliosphere is much more sensitive to solar variability. We explain the variability of this signal, and it's differences from the interstellar helium signal, and how these observations can be used as a constraint of heliospheric models.

Saul, L.; Wurz, P.; Rodriguez, D.; McComas, D.; Fuselier, S.; Möbius, E.; Kucharek, H.; Bzowski

2012-04-01

99

Decadal Air-Sea Interaction in the North Atlantic Based on Observations and Modeling Results.  

National Technical Information Service (NTIS)

The decadal, 12-14 year, cycle observed in the North Atlantic SST and tide gauge data was examined using the NCEP/NCAR reanalyses, COADS data and an ocean model simulation. Besides this decadal mode, a shorter, subdecadal period of about 8 years exists in...

S. Hakkinen

1998-01-01

100

Interannual to decadal summer drought variability over Europe and its relationship to global sea surface temperature  

Microsoft Academic Search

Interannual to decadal variability of European summer drought and its relationship with global sea surface temperature (SST)\\u000a is investigated using the newly developed self calibrated Palmer drought severity index (scPDSI) and global sea surface temperature\\u000a (SST) field for the period 1901–2002. A European drought severity index defined as the average of scPDSI over entire Europe\\u000a shows quasiperiodic variations in the

M. Ionita; G. Lohmann; N. Rimbu; S. Chelcea; M. Dima

2011-01-01

101

Associations of multi-decadal sea-surface temperature variability with US drought  

USGS Publications Warehouse

Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th century, but during the 19th century the tropical Pacific is a more consistent indicator of D2 M drought. The interaction between El Nin??o-Southern Oscillation (ENSO) and the AMO explain a large part of the D2M drought variability in the conterminous US. More modeling studies are needed to reveal possible mechanisms linking low-frequency ENSO variability and the AMO with drought in the conterminous US. ?? 2007 Elsevier Ltd and INQUA.

McCabe, G. J.; Betancourt, J. L.; Gray, S. T.; Palecki, M. A.; Hidalgo, H. G.

2008-01-01

102

Decadal Variability in Western North Atlantic SST Recorded in Massive Brain Corals from Bermuda  

NASA Astrophysics Data System (ADS)

The history of the North Atlantic Oscillation (NAO) is characterized by variability on time scales of months to decades but low frequency (decadal and multidecadal) variability is especially marked since 1950, leading some to suggest a link to global warming. To address questions concerning the nature and mechanisms of low frequency NAO variability, we have initiated a program to reconstruct seasonally resolved, multicentury long records of sea surface temperatures (SSTs) in the western North Atlantic, where a strong correlation with the overlying atmosphere is evident in the record of the past 50 years. Bermuda can be considered the hotspot of the subtropical action center, an ideal location from which to index the subtropical gyre. It is also home to several species of massive reef corals which live 500 to 700 years. We have found that the skeletal density and chemistry of the Bermuda brain coral Diploria labyrinthiformis contains an accurate and continuous record of SST variability on weekly through decadal time scales that can be accessed via a number of analytical techniques. Our field studies show that much of the skeleton of D. labyrinthiformis is accreted during the wintertime, rendering this species an ideal cool season recorder. We used a short record of daily temperatures logged in-situ at the collection site and the 45 year long Hydrographic Station S time series to calibrate the coral proxy records and test their correlation with oceanographic variability over time. Variations in skeletal density and chemistry (d18O) are strongly correlated with the decadal scale oscillations that characterize the past 50 years of recorded SSTs (at hydrographic Station S). Interannual variability, including the NAO switch in the winter of 1995/1996 is captured in the coral's strontium-calcium ratio generated at weekly resolution using an in-situ microbeam analytical technique. Application of these techniques to a 500-year old brain coral sampled from the exposed south shore reefs of Bermuda reveal the history of variability in the subtropical gyre over the past several centuries.

Cohen, A. L.; McCartney, M. S.; Smith, S. R.

2002-05-01

103

Observations of Suspected RR Lyrae Variable Stars  

NASA Astrophysics Data System (ADS)

Our group is working on confirming variability of suspected RR Lyrae variables we have identified, and making follow-up observations of confirmed new variables. We developed a new method of detecting RR Lyrae variable stars using only a single epoch of both photometry and spectroscopy taken from the Sloan Digital Sky Survey (SDSS). The method takes advantage of clear departures from the template norm for stars that have photometry and spectroscopy taken out of phase. Over 1,000 stars have been identified as probable RR Lyrae stars, scattered across the halo and ranging from 14th to 20th magnitude. This paper describes observations taken at McDonald Observatory by undergraduate students as part of this project. We will discuss how and why the method works, and our McDonald observations to confirm variability and obtain full lightcurves.

Bahr, Caleb; Amende, H.; Powell, W., Jr.; Wilhelm, R.

2012-01-01

104

State observers for variable-reluctance motors  

Microsoft Academic Search

A sequence of progressively more complex state observers, each driven by measurements of phase voltages and currents, is developed for variable-reluctance motors. For the simpler observers, the exponential stability of their error dynamics in a neighborhood of the origin is proved. For all observers, the results of numerical or physical experiments are provided to demonstrate the globally stable error dynamics.

A. Lumsdaine; J. H. Lang

1990-01-01

105

Six decades of glacier mass-balance observations: a review of the worldwide monitoring network  

Microsoft Academic Search

Glacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring. It has been recognized as the largest non-steric contributor to the present rise in sea level. Six decades of annual mass-balance data have been compiled and made easily available by the World Glacier Monitoring Service and

M. Zemp; M. Hoelzle; W. Haeberli

2009-01-01

106

Decadal-scale variability of upper ocean heat content in the tropical Pacific  

NASA Astrophysics Data System (ADS)

Decadal-scale variability of upper ocean heat content (OHC) in the tropical Pacific is investigated and is compared with that of ENSO scale. The decadal-scale OHC anomaly with a period of about 13 years shows anticlockwise propagations in the tropical North Pacific like as that of ENSO scale. It is also shown that the entire equatorial OHC anomaly leads Niño-3 index anomaly by about a quarter (about 3 years) of the period of the decadal variability in the tropical Pacific. This time lag of a quarter of the period is consistent with the idea of the ``recharge oscillator'' model for ENSO dynamics. Further it is shown that the magnitude of leading OHC anomalies in the entire equatorial Pacific is linearly related to the subsequent magnitudes of Niño-3 and Niño-3.4 indices. This relationship is also similar with that of ENSO scale, but there are several different points between them. Particularly, in contrast with the ENSO scale, the amplitude is larger in central equatorial Pacific (Niño-3.4 region) than in the eastern region (Niño-3 region).

Hasegawa, Takuya; Hanawa, Kimio

2003-03-01

107

Mesoscale simulations of multi-decadal variability in the wind resource over Korea  

NASA Astrophysics Data System (ADS)

This study investigated multi-decadal variability in the wind resource over the Republic of Korea using the Weather Research and Forecasting (WRF) mesoscale meteorological model. Mesoscale simulations were performed for the period from November 1981 to November 2010. The typical wind climatology over the Korean Peninsula, which is influenced by both continental and oceanic features, was represented by the physics-based mesoscale simulations. Winter had windier conditions with northwesterly flows, whereas less windy with southwesterly flows appeared in summer. The annual mean wind speeds over the Republic of Korea were approximately 2 m s-1 with strong wind in mountainous areas, coastal areas, and islands. The multi-decadal variability in wind speed during the study period was characterized by significant increases (positive trend) over many parts of the study area, even though the various local trends appeared depending on the station locations. The longterm trend in the spatially averaged wind speed was approximately 0.002 m s-1 yr-1. The annual frequency of daily mean wind speeds over 5 m s-1 at the turbine hub height also increased during the study period throughout the Republic of Korea. The present study demonstrates that multi-decadal mesoscale simulations can be useful for climatological assessment of wind energy potential.

Kim, Do-Yong; Kim, Jin-Young; Kim, Jae-Jin

2013-02-01

108

Impacts of multi-scale solar activity on climate. Part II: Dominant timescales in decadal-centennial climate variability  

NASA Astrophysics Data System (ADS)

Part II of this study detects the dominant decadal-centennial timescales in four SST indices up to the 2010/2011 winter and tries to relate them to the observed 11-yr and 88-yr solar activity with the sunspot number up to Solar Cycle 24. To explore plausible solar origins of the observed decadal-centennial timescales in the SSTs and climate variability in general, we design a simple one-dimensional dynamical system forced by an annual cycle modulated by a small-amplitude single- or multi-scale "solar activity." Results suggest that nonlinear harmonic and subharmonic resonance of the system to the forcing and period-doubling bifurcations are responsible for the dominant timescales in the system, including the 60-yr timescale that dominates the Atlantic Multidecadal Oscillation. The dominant timescales in the forced system depend on the system's parameter setting. Scale enhancement among the dominant response timescales may result in dramatic amplifications over a few decades and extreme values of the time series on various timescales. Three possible energy sources for such amplifications and extremes are proposed. Dynamical model results suggest that solar activity may play an important yet not well recognized role in the observed decadal-centennial climate variability. The atmospheric dynamical amplifying mechanism shown in Part I and the nonlinear resonant and bifurcation mechanisms shown in Part II help us to understand the solar source of the multi-scale climate change in the 20th century and the fact that different solar influenced dominant timescales for recurrent climate extremes for a given region or a parameter setting. Part II also indicates that solar influences on climate cannot be linearly compared with non-cyclic or sporadic thermal forcings because they cannot exert their influences on climate in the same way as the sun does.

Weng, Hengyi

2012-07-01

109

Volcanic forcing as a major source of European decadal climate variability during the last millennium  

NASA Astrophysics Data System (ADS)

The spatial and temporal variability of regional temperatures reconstructed for the last millennium is among the most important and debated aspects concerning modern climate research. Especially the magnitude and extent of pre-industrial warm and cold anomalies constrain the range of naturally-forced and internal climate variability which is necessary to estimate the anthropogenic contribution to the 20th Century warming and its possible future implications. The MPI-Earth System Model (ESM) simulation ensemble for the last millennium shows that strong tropical volcanic eruptions (SVE) can trigger decadal and even longer timescale fluctuations in the coupled ocean-atmosphere system. These coherently result in the emergence of winter warm anomalies over continental Europe about one decade after a major eruption ("delayed winter warming"). A key period for the assessment of how the magnitude of the eruption and the background climate conditions can affect the temporal occurrence and the spatial pattern of the delayed winter warming is the early XIX Century period. The close succession of two SVEs in 1809 and in 1815 matched the Dalton minimum of solar activity and dominated the climate evolution over decades. An additional MPI-ESM simulation ensemble consisting of a set of full-forcing experiments for the early XIX Century period and a set of volcanic forcing only experiments simulating the climatic effects of the 1809 and 1815 SVEs under pre-industrial background climate conditions is used here to describe in detail the physical mechanism governing the simulated climate response to SVEs, to individuate its key processes and to assess its dependency on the background conditions. We cross-validate our numerical model results with reconstructed winter surface air temperatures for the European region for the last six Centuries. This corroborates our hypothesis that volcanic forcing was a major source of European regional decadal climate variability during the last millennium. The relative importance of internal and externally driven variability and their possible interference adds complexity to the interpretation of simulated and reconstructed past climate variability.

Zanchettin, D.; Graf, H.; Timmreck, C.; Lorenz, S.; Jungclaus, J. H.

2011-12-01

110

Interannual and decadal-scale variability in winter storms over Switzerland since end of the 19th century  

NASA Astrophysics Data System (ADS)

In Switzerland, damaging and potentially life-threatening high-wind events can often be attributed to mid-latitude winter storms. The scarce availability of long-term atmospheric data series has so far limited the analysis of interannual and in particular decadal-scale changes in hazardous winter storms over Switzerland. In our study, we evaluate this variability on the basis of the Twentieth Century Reanalysis (20CR), a novel global atmospheric reanalysis which extends back to 1871, with 56 realisations for each 6-hourly time step. In the 20CR, only observations of synoptic surface pressure were assimilated and monthly sea surface temperature and sea ice distributions served as boundary conditions. We apply an objective cyclone identification and tracking scheme to the global sea level pressure data of the 20CR ensemble, i.e. to each of the 56 ensemble members. For Switzerland and during almost the whole period available, the 20CR shows relatively small values of the ensemble range (uncertainty), compared to other regions of the world. We use historic wind speed measurements taken at Zurich climate station to evaluate the quality of 20CR wind data over Switzerland, in particular during the first half of the 20th century and earlier when surface pressure observations were sparser. On both interannual and decadal time scales, we find a good agreement between the 20CR and observations, concerning the winter storm variability over Switzerland. One of the main conclusions of our study is that the North Atlantic Oscillation (NAO), regarded as the major anomaly pattern of the North Atlantic/European sector, alone does not necessarily provide a good description of the interannual variability in winter storms over Switzerland. In the 20CR, the year-to-year variability in winter storms over Switzerland is rather associated with a large-scale atmospheric pattern similar to a southeastward displaced NAO-like pattern. Also on shorter (i.e. synoptic) time scales, similar large-scale meteorological conditions were in general conducive to high-wind events in Switzerland, as e.g. during the intense winter storm "Kyrill" in January 2007. A second main conclusion is that since end of the 19th century winter storms over Switzerland have revealed pronounced decadal-scale variability, with periods between approximately 36 to 47 years. We try to understand the physical mechanisms responsible for these decadal-scale winter storm variations over Switzerland e.g. by linking them with variations in the global ocean surface temperatures.

Welker, Christoph; Martius, Olivia

2013-04-01

111

Analysis of air quality variability in Shanghai using AOD and API data in the recent decade  

NASA Astrophysics Data System (ADS)

We use the aerosol optical depth (AOD) measured by the moderate resolution imaging spectrometer (MODIS) onboard the Terra satellite, air pollution index (API) daily data measured by the Shanghai Environmental Monitoring Center (SEMC), and the ensemble empirical mode decomposition (EEMD) method to analyze the air quality variability in Shanghai in the recent decade. The results indicate that a trend with amplitude of 1.0 is a dominant component for the AOD variability in the recent decade. During the World Expo 2010, the average AOD level reduced 30% in comparison to the long-term trend. Two dominant annual components decreased 80% and 100%. This implies that the air quality in Shanghai was remarkably improved, and environmental initiatives and comprehensive actions for reducing air pollution are effective. AOD and API variability analysis results indicate that semi-annual and annual signals are dominant components implying that the monsoon weather is a dominant factor in modulating the AOD and API variability. The variability of AOD and API in selected districts located in both downtown and suburban areas shows similar trends; i.e., in 2000 the AOD began a monotonic increase, reached the maxima around 2006, then monotonically decreased to 2011 and from around 2006 the API started to decrease till 2011. This indicates that the air quality in the entire Shanghai area, whether urban or suburban areas, has remarkably been improved. The AOD improved degrees (IDS) in all the selected districts are (8.6±1.9)%, and API IDS are (9.2±7.1)%, ranging from a minimum value of 1.5% for Putuo District to a maximum value of 22% for Xuhui District.

Zhao, Qing; Gao, Wei; Xiang, Weining; Shi, Runhe; Liu, Chaoshun; Zhai, Tianyong; Huang, Hung-lung Allen; Gumley, Liam E.; Strabala, Kathleen

2013-06-01

112

Greenhouse Warming, Decadal Variability, or El Niño? An Attempt to Understand the Anomalous 1990s  

Microsoft Academic Search

The dominant variability modes in the Tropics are investigated and contrasted with the anomalous situation observed during the last few years. The prime quantity analyzed is anomalous sea surface temperature (SST) in the region 30°S-60°N. Additionally, observed tropical surface wind stress fields were investigated. Further tropical atmospheric information was derived from a multidecadal run with an atmospheric general circulation model

M. Latif; R. Kleeman; C. Eckert

1997-01-01

113

STEREO observations of long period variables  

NASA Astrophysics Data System (ADS)

Observations from the Heliospheric Imagers (HI-1) on both the STEREO spacecrafts have been analysed to search for very long period large amplitude stellar variability, finding six new candidates. A total of 85 objects, mostly previously known Mira variables, were found to show convincing variability on time-scales of over a 100 days. These objects range in peak brightness from about fourth magnitude to 10th magnitude in R and have periods between about 170 and 490 d. There is a period gap between 200 and 300 d where no objects were found and this is discussed. 15 of the Miras in the sample are previously recorded as having variable periods and the possibility for these and two other stars to have undergone a period change or to be irregular is discussed. In addition to the six stars in the sample not previously recorded as variable, another seven are recorded as variable but with no classification. Our period determination is the first to be made for 19 of these 85 stars. The sample represents a set of very long period variables that would be challenging to monitor from the Earth, or even from Earth orbit, owing to their position on the ecliptic plane and that their periods are often close to a year or an integer fraction thereof. The possibility for the new candidates to possess circumstellar shells is discussed.

Wraight, K. T.; Bewsher, D.; White, Glenn J.; Nowotny, W.; Norton, A. J.; Paladini, C.

2012-10-01

114

The influence of decadal-scale variability on trends in long European streamflow records  

NASA Astrophysics Data System (ADS)

This study seeks to provide a long-term context for the growing number of trend analyses which have been applied to river flows in Europe. Most studies apply trend tests to fixed periods, in relatively short (generally 1960s-present) records. This study adopts an alternative "multi-temporal" approach, whereby trends are fitted to every possible combination of start and end years in a record. The method is applied to 132 catchments with long (1932-2004) hydrometric records from northern and central Europe, which were chosen as they are minimally anthropogenically influenced and have good quality data. The catchments are first clustered into five regions, which are broadly homogenous in terms of interdecadal variability of annual mean flow. The multi-temporal trend approach was then applied to regional time series of different hydrological indicators (annual, monthly and high and low flows). The results reveal that the magnitude and even direction of short-term trends are heavily influenced by interdecadal variability. Some short-term trends revealed in previous studies are shown to be unrepresentative of long-term change. For example, previous studies have identified post-1960 river flow decreases in southern and eastern Europe: in parts of eastern Europe, these trends are resilient to study period, extending back to the 1930s; in southern France, longer records show evidence of positive trends which reverse from the 1960s. Recent (post-1960) positive trends in northern Europe are also not present in longer records, due to decadal variations influenced by the North Atlantic Oscillation. The results provide a long-term reference for comparison with published and future studies. The multi-temporal approach advocated here is recommended for use in future trend assessments, to help contextualise short-term trends. Future work should also attempt to explain the decadal-scale variations that drive short-term trends, and thus develop more sophisticated methods for trend detection that take account of interdecadal variability and its drivers.

Hannaford, J.; Buys, G.; Stahl, K.; Tallaksen, L. M.

2013-02-01

115

The Relation between Decadal Variability of Subtropical Mode Water and the North Atlantic Oscillation*.  

NASA Astrophysics Data System (ADS)

The Bermuda station `S' time series has been used to define the variability of subtropical mode water (STMW) from 1954 to 1995. This record, which shows decadal variability at a nominal period of about 12-14 yr, has been used as a baseline for seeking correlation with large-scale atmospheric forcing and with decadal north-south excursions of the Gulf Stream position defined by the subsurface temperature at 200-m depth. A common time period of 1954-89 inclusive, defined by the data sources, shows a high degree of correlation among the STMW potential vorticity (PV), Gulf Stream position, and large-scale atmospheric forcing (buoyancy flux, SST, and sea level pressure). Two pentads with anomalously small and large STMW PV were further studied and composites were made to define a revised North Atlantic Oscillation (NAO) index associated with the decadal forcing. During years of low PV at Bermuda, the NAO index is low, the Gulf Stream is in a southerly position, and the zero wind stress curl latitude is shifted south as are the composite extratropical winter storm tracks, in comparison to the period of high PV at Bermuda. Because the NAO, Gulf Stream separation latitude, and STMW PV variations are in phase with maximum annually averaged correlation at zero year time lag, the authors hypothesize that all must be either coupled with one another or with some other phenomenon that determines the covariability. A mechanism is proposed that could link all of the above together. It relies on the fact that during periods of high STMW PV, associated with a northerly Gulf Stream and a high NAO, one finds enhanced production of mode water in the subpolar gyre and Labrador Sea. Export of the enhanced Labrador Sea Water (LSW) component into the North Atlantic via the Deep Western Boundary Current can influence the separation point of the Gulf Stream in the upper ocean once the signal propagates from the source region to the crossover point with the Gulf Stream. If the SST signal produced by the 100-km shift of the Gulf Stream along a substantial (1000 km) length of its path as it leaves the coast can influence the NAO, a negative feedback oscillation may develop with a timescale proportional to the time delay between the change of phase of the air-sea forcing in the Labrador Basin and the LSW transient at the crossover point. Both a simple mechanistic model as well as a three-layer numerical model are used to examine this feedback, which could produce decadal oscillations given a moderately strong coupling.

Joyce, Terrence M.; Deser, Clara; Spall, Michael A.

2000-07-01

116

Decadal Predictability in the Colorado River Basin Using Observed and Reconstructed Records  

NASA Astrophysics Data System (ADS)

The Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) climate indices have been used extensively in a variety of hydroclimate analyses to investigate decadal predictability of regional climate and water cycle dynamics. One such example shows a strong relationship between the phases of these indices and streamflow at Lee’s Ferry along the Colorado River. With this apparent connection, there is an implication that these indices could be used to forecast the next decade of streamflow at Lee’s Ferry. In this study, PDO and AMO are used to make retrospective forecasts of the 40 most recent ten year running means of Lee’s Ferry streamflow, and we confirm that there is substantially more skill than using the climatology alone. The decadal predictions explain 45% of the observed variance which is statistically significant at the 99% level. Next, we test whether or not this relationship, and the accompanying forecast skill, has been consistent over a longer period of time than the observed record. Existing reconstructions of PDO, AMO and Lee’s Ferry streamflow are used to find that the forecast skill over the reconstructed periods has rarely been as high as what is seen in the observed record. Additionally, a wavelet analysis is performed on the observed and reconstructed time series. The observed records of the three time series all share a dominant multidecadal frequency between 40 and 70 years in length. This might help to explain the skill that is seen in the observed record. However, this multidecadal frequency is not persistent in time for any of the reconstructed time series. Therefore, decadal predictions at Lee’s Ferry may prove to be more difficult than the observed record suggests.

Switanek, M.; Troch, P. A.

2010-12-01

117

Decadal- to centennial-scale tropical Atlantic climate variability across a Dansgaard-Oeschger cycle  

NASA Astrophysics Data System (ADS)

The patterns and forcing mechanisms of climate variability on decadal to centennial time scales represent a major void in our current understanding of Earth's climate system. Furthermore, the response of the low latitudes to abrupt climate change is also not well understood, as most high-resolution paleoclimate studies are from midlatitudes and high latitudes. This study explores the tropical Atlantic response to a Dansgaard-Oeschger cycle (Interstadial 12) using ultra-high resolution (˜2-3 years) foraminiferal census data from Cariaco Basin sediments. The interpretation of the abundance records for the onset of Interstadial 12 is complicated by the competing effects of rising sea level on Ekman-induced upwelling within the Cariaco Basin and migrating Intertropical Convergence Zone-associated variations in trade wind location and fluvial nutrient delivery to the basin. The foraminiferal abundance records for the latter part of the interstadial suggest a southerly shift in the average annual position of the Intertropical Convergence Zone that acted to enhance upwelling and productivity within the Cariaco Basin. Sea level eventually reached a critical point in the transition back to stadial conditions that led to upwelling of nutrient-depleted waters and a decline in productivity within the basin. Spectral analyses of theGlobigerina bulloidesabsolute abundance records reveal significant variability ranging from subdecadal- to centennial-scale. Atlantic multidecadal-scale climate variability is only evident in the warmest interval of Interstadial 12, suggesting that variability on this scale may only operate during warm climate periods, something that has significant implications for modern and near-future climate variability.

Hertzberg, J. E.; Black, D. E.; Peterson, L. C.; Thunell, R. C.; Haug, G. H.

2012-09-01

118

MISR decadal observations of mineral dust: property characterization, and climate applications  

NASA Astrophysics Data System (ADS)

The Multi-angle Imaging SpectroRadiometer (MISR) provides a unique, independent source of data for studying dust emission and transport. MISR's multiple view angles allow the retrieval of aerosol properties over bright surfaces, and such retrievals have been shown to be sensitive to the non-sphericity of dust aerosols over both land and water. MISR stereographic views of thick aerosol plumes allow height and instantaneous winds derivations at spatial resolutions of 1.1 km horizontally and ~200m vertically. We will discuss the radiometric and stereo-retrieval capabilities of MISR specifically for dust, and demonstrate the use of MISR data in conjunction with other available satellite observations for dust property characterization and climate studies. First, we will show that over the Atlantic Ocean, MISR and the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products provide complementary information, characterizing transported desert dust plume extent over water and aerosol optical depth (AOD) evolution. Changes in the MISR-derived non-spherical AOD fraction illustrate the evolution of dust during transport; MISR does not observe changes in dust properties during trans-Atlantic dust events. Next, we will present a satellite prospective on dust climatology in Asian dust sources and discuss MISR's unique strengths as well as current product biases. Combined satellite observations do not show statistically significantly increasing trends in dust amount over the natural deserts in the last decade; natural aerosol loadings seem to be predominantly affected by large-scale climatological factors such as the Arctic Oscillation (AO) and El Niño/Southern Oscillation (ENSO). The reasons for the observed springtime correlation between aerosol loadings and the Nino 3.4 index are analyzed in terms of temperature, precipitation, and wind fields. Finally, we show a climatology of dust plume heights and associated wind speeds in the Bodélé North African source region for all events observed by MISR from March 2000 through March 2010 (over 500 events). Seasonally, the MISR data indicate an increase in both plume heights and wind speeds in the winter and spring seasons, in agreement with the reported increase in dust events during this part of the year. Mean plume heights were found to vary with season from 400 m to 900 m above terrain. Dust plume height variability will be discussed in context of regional dust dynamics.

Kalashnikova, O. V.; Garay, M. J.; Sokolik, I. N.; Kahn, R. A.; Lyapustin, A.; Diner, D. J.; Lee, J. N.; Torres, O.; Leptoukh, G. G.; De La Torre Juarez, M.

2011-12-01

119

Decadal climate variability in the upper North Atlantic detected in an ocean analysis  

NASA Astrophysics Data System (ADS)

An ocean analysis where both surface and subsurface hydrographic temperature data are assimilated into a global ocean model has been produced for the period 1958-1998. The assimilation scheme is a univariate, variational optimum interpolation of temperature only in which the first guess is produced by a global ocean general circulation model with a horizontal resolution of 0.5 degree, 31 levels in the vertical and forced by twice daily NCEP reanalysis. The temperature analysis shows encouraging improvement over a corresponding forced ocean simulation and significantly reduces some of the model errors such as the location and amplitude of the surface temperature front along the Gulf Stream and the vertical thermal structure of the region. Decadal evolution of warm and cold anomalies in the Sea Surface Temperature (SST) and upper Ocean Heat Content (OHC) in the subtropical and subpolar gyres of the North Atlantic is detected and investigated. Conventional EOF analysis shows that an important mode of variability of the wintertime upper ocean climate over the North Atlantic during the period of study is characterized by a tripole pattern both in SST and upper OHC. This mode shows a more complicated pattern with respect to a similar mode detected in the analysis of different available SST products. In our ocean analysis the one sign anomalies characteristic of the subtropical gyre extends northward into the Labrador Sea region. The first EOF of the upper OHC winter anomalies shows a similar pattern and exhibits variability on quasi-decadal time scales as in the case of the SST. Finally, in order to identify possible propagating processes of winter SST and OHC anomalies an Extended EOF analysis will be presented.

Masina, S.; di Pietro, P.; Iovino, D.

2003-04-01

120

Black Sea biogeochemistry: response to decadal atmospheric variability during 1960-2000 inferred from numerical modeling.  

PubMed

The long-term variability of the physical and biochemical structure of oxic and suboxic layers in the Black Sea was studied using a one-dimensional coupled hydrophysical and biogeochemical model. The focus was on the correlation between atmospheric forcing (2 m air temperature and dew point temperature, surface level pressure, surface wind) affected by the North Atlantic Oscillation in and the regional responses. The quality of model performance was demonstrated using observed vertical and temporal distribution of biogeochemical variables. It was shown that during 1960-2000, the long-term variability of simulated winter-mean SST in the Black Sea correlated reasonably well with the variability of 2 m air temperature. Furthermore, the thermal state of the upper ocean impacted largely on the variability of biogeochemical variables, such as oxygen, nitrate and phytoplankton concentration. The tele-connection between North Atlantic Oscillation and Black Sea biogeochemistry was manifested in a different way for the specific time-interval 1960-2000; the corresponding regime shifts were thus associated with the large scale forcing. One such extreme event occurred in 1976 leading to a pronounced shift in the oxygen and hydrogen sulfide state. PMID:22425506

He, Yunchang; Stanev, Emil V; Yakushev, Evgeniy; Staneva, Joanna

2012-03-08

121

Radio Band Observations of Blazar Variability  

NASA Astrophysics Data System (ADS)

The properties of blazar variability in the radio band are studied using the unique combination of temporal resolution from single dish monitoring and spatial resolution from VLBA imaging. Such measurements now available in all four Stokes parameters, together with theoretical simulations, identify the origin of radio band variability and probe the characteristics of the radio jet where the broadband blazar emission originates. Outbursts in total flux density and linear polarization in the optical-to-radio bands are attributed to shocks propagating within the jet spine, in part, based on limited modelling invoking transverse shocks; new radiative transfer simulations allowing for shocks at arbitrary angle to the flow direction confirm this picture by reproducing the observed centimeter-band variations observed more generally, and are of current interest since these shocks may play a role in the ?-ray flaring detected by Fermi. Recent UMRAO multifrequency Stokes V studies of bright blazars identify the spectral variability properties of circular polarization for the first time and demonstrate that polarity flips are relatively common. All-Stokes data are consistent with the production of circular polarization by linear-to-circular mode conversion in a region that is at least partially self-absorbed. Detailed analysis of single-epoch, multifrequency, all-Stokes VLBA observations of 3C 279 support this physical picture and are best explained by emission from an electron-proton plasma.

Aller, Margo F.; Aller, Hugh D.; Hughes, Philip A.

2011-06-01

122

Mesoscale Disturbance and Ecological Response to Decadal Climatic Variability in the American Southwest.  

NASA Astrophysics Data System (ADS)

Ecological responses to climatic variability in the Southwest include regionally synchronized fires, insect outbreaks, and pulses in tree demography (births and deaths). Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography reveal climatic effects across scales, from annual to decadal, and from local (<102 km2) to mesoscale (104-106 km2). Climate-disturbance relations are more variable and complex than previously assumed. During the past three centuries, mesoscale outbreaks of the western spruce budworm (Choristoneura occidentalis) were associated with wet, not dry episodes, contrary to conventional wisdom. Regional fires occur during extreme droughts but, in some ecosystems, antecedent wet conditions play a secondary role by regulating accumulation of fuels. Interdecadal changes in fire-climate associations parallel other evidence for shifts in the frequency or amplitude of the Southern Oscillation (SO) during the past three centuries. High interannual, fire-climate correlations (r = 0.7 to 0.9) during specific decades (i.e., circa 1740-80 and 1830-60) reflect periods of high amplitude in the SO and rapid switching from extreme wet to dry years in the Southwest, thereby entraining fire occurrence across the region. Weak correlations from 1780 to 1830 correspond with a decrease in SO frequency or amplitude inferred from independent tree-ring width, ice core, and coral isotope reconstructions.Episodic dry and wet episodes have altered age structures and species composition of woodland and conifer forests. The scarcity of old, living conifers established before circa 1600 suggests that the extreme drought of 1575-95 had pervasive effects on tree populations. The most extreme drought of the past 400 years occurred in the mid-twentieth century (1942-57). This drought resulted in broadscale plant dieoffs in shrublands, woodlands, and forests and accelerated shrub invasion of grasslands. Drought conditions were broken by the post-1976 shift to the negative SO phase and wetter cool seasons in the Southwest. The post-1976 period shows up as an unprecedented surge in tree-ring growth within millennia-length chronologies. This unusual episode may have produced a pulse in tree recruitment and improved rangeland conditions (e.g., higher grass production), though additional study is needed to disentangle the interacting roles of land use and climate. The 1950s drought and the post-1976 wet period and their aftermaths offer natural experiments to study long-term ecosystem response to interdecadal climate variability.

Swetnam, Thomas W.; Betancourt, Julio L.

1998-12-01

123

Simulated and observed variability in ocean temperature and heat content.  

PubMed

Observations show both a pronounced increase in ocean heat content (OHC) over the second half of the 20th century and substantial OHC variability on interannual-to-decadal time scales. Although climate models are able to simulate overall changes in OHC, they are generally thought to underestimate the amplitude of OHC variability. Using simulations of 20th century climate performed with 13 numerical models, we demonstrate that the apparent discrepancy between modeled and observed variability is largely explained by accounting for changes in observational coverage and instrumentation and by including the effects of volcanic eruptions. Our work does not support the recent claim that the 0- to 700-m layer of the global ocean experienced a substantial OHC decrease over the 2003 to 2005 time period. We show that the 2003-2005 cooling is largely an artifact of a systematic change in the observing system, with the deployment of Argo floats reducing a warm bias in the original observing system. PMID:17578928

Achutarao, K M; Ishii, M; Santer, B D; Gleckler, P J; Taylor, K E; Barnett, T P; Pierce, D W; Stouffer, R J; Wigley, T M L

2007-06-19

124

A model data comparison of different classes of LSW and interannual to decadal variability in a FESOM model setup  

NASA Astrophysics Data System (ADS)

The climate in the Atlantic region is essentially influenced by the Atlantic meridional overturning circulation (AMOC) which carries warm waters into northern latitudes and returns cold deep water southward across the equator. In the Labrador Sea basin a major component of the cold limb of the Atlantic meridional overturning circulation (AMOC) is formed. The intermediate water mass that is part of this deep convection process is the Labrador Sea Water (LSW) which can be separated into two different classes: the deep LSW (dLSW) and the less dense upper LSW (uLSW). Both LSW modes are formed by convection, accompanied by a strong surface cooling during winter conditions, which leads to an increase in the near-surface density and to an unstable stratification and a homogenization of the water column. In this study we simulated the deep-water formation in the Labrador Sea using the Finite-Element Sea-Ice Ocean Model (FESOM) in a global model setup with regional focus on the Labrador Sea and Greenland Sea. We evaluated the capability of the model setup to reproduce a realistic deep water formation in the Labrador Sea by analyzing the modeled Labrador Sea hydrography and we compared the modeled and observational derived dLSW and uLSW layer thicknesses for the time interval 1958-2007. It is shown that the model is able to reproduce different phases in the temporal evolution of the potential density, temperature and salinity, which are known in observational data. Based on composite maps of the thermal and haline contributions to the surface density flux we can prove that the central Labrador Sea in the model is dominated by the thermal contributions of the surface density flux, while the haline contributions are limited to the branch of the Labrador Sea Boundary Current system, where they are dominated from the haline contributions of sea ice melting and formation. Our model results feature a shielding of the central Labrador Sea from the haline contributions by the Labrador Sea Boundary Current system. Furthermore we investigated modes of interannual to decadal variability for the period 1958-2004 and attributed the general variability in the model to the atmospheric forcing and to internal modes of the ocean system. Based on a North Atlantic Deep Water (NADW) index defined for a normal and random forced FESOM run, where the interannual to decadal atmospheric variability in the random forced run is replaced by white noise, we identify modes of interannual to quasi-decadal variability of 7yr and 14yr, respectively. The origin of the 14yr variability is attributed to the atmospheric forcing, while the 7yr variability is linked to internal modes of the ocean. To further isolate the horizontal, but also the vertical variability in the model, we apply a principal oscillation pattern analysis in a three dimensional context. Two exceptional stable interannual modes are captured by the POP analysis and their variability is attributed to a propagating Rossby wave structure.

Scholz, Patrick; Lohmann, Gerrit; Ionita, Monica; Kieke, Dagmar; Rhein, Monika

2013-04-01

125

Variability of the Marine Ecosystem in Response to Climate Changes in the Southeastern Bering Sea Midshelf During the Last Decades  

NASA Astrophysics Data System (ADS)

The climate trends of reducing ice cover and rising temperature in the southeastern Bering Sea have profound impacts on the lower tropic level production and fishery production. To address the issue, a multi-decade modeling of the lower trophic level production was conducted using a vertically 1-D coupled ice-ocean ecosystem model that includes both pelagic (Jin et al., 2006a) and sea ice algal components (Jin et al., 2006b). The model was forced by NCEP reanalysis data. Model results were validated with the following observations: 1) temperature, salinity, fluorometer data at 12m, 24m and 44m at NOAA/PMEL mooring from 1995-2004; 2) daily SeaWiFS chl a data (1997-2005). Interannual variability of the primary production was analyzed and statistical relationship against regional climate index and fisheries index were sought.

Jin, M.; Deal, C.; Wang, J.

2006-12-01

126

Coordinated Multifrequency Observations of Variable Agns  

NASA Astrophysics Data System (ADS)

Our ME measurements of BL Lac objects to date, coordinated with observations in other frequency bands, show positive spectral curvature within the infrared to ultraviolet energy range (Worrall and Bruhweiler 1982). There is evidence that this component is synchrotron radiation. In order to fit the spectral measurements, we find that relativistic beaming is an essential ingredient of simple models not involving electron reacceleration. It is important to discover to what extent this is observationally true of all BL Lac objects, and to then compare with expectations of the distribution in Lorentz factor derived from geometrical arguments. Our sample of BL Lac objects so far numbers 5. There are 17 other BL Lac objects for which IUE observations are listed in the master catalogue. However, many of these objects are so heavily contaminated by a galactic component in the visual and near infrared that the data cannot be usefully employed for our purpose. Also, to our knowledge, the necessary nearly simultaneous coverage in the infrared and visual only exists for 6 of these 17. The near-simultaneity is a vital element, since these active galactic nuclei (AGNs) tend to exhibit different flux variability characteristics in the different available wavebands. We present a target list primarily composed of BL Lac objects, but including 3 QSOs. Conclusions from non-simultaneous multifrequency observations by Malkan and Sargent (1982) suggest that one difference between QSOs and BL Lacs is that the non-thermal infrared to ultraviolet QSO flux does not appear to exhibit curvature. We would like to investigate this more closely, with simultaneous observations. We propose to coordinate all our observations with radio, millimeter, infrared and visual wavelength coverage and have calculated time periods during which this will be possible. Final target selection from our list of visually variable objects will be based on their magnitudes just prior to shift allotment.

Worrall, Diana M.

1984-07-01

127

Decadal and shorter period variability of surf zone water quality at Huntington Beach, California.  

PubMed

The concentration of fecal indicator bacteria in the surf zone at Huntington Beach, CA, varies over time scales that span at least 7 orders of magnitude, from minutes to decades. Sources of this variability include historical changes in the treatment and disposal of wastewater and dry weather runoff, El Niño events, seasonal variations in rainfall, spring-neap tidal cycles, sunlight-induced mortality of bacteria, and nearshore mixing. On average, total coliform concentrations have decreased over the past 43 years, although point sources of shoreline contamination (storm drains, river outlets, and submarine outfalls) continue to cause transiently poor water quality. These transient point sources typically persist for 5-8 yr and are modulated by the phase of the moon, reflecting the influence of tides on the sourcing and transport of pollutants in the coastal ocean. Indicator bacteria are very sensitive to sunlight therefore, the time of day when samples are collected can influence the outcome of water quality testing. These results demonstrate that coastal water quality is forced by a complex combination of local and external processes and raise questions about the efficacy of existing marine bathing water monitoring and reporting programs. PMID:12269739

Boehm, A B; Grant, S B; Kim, J H; Mowbray, S L; McGee, C D; Clark, C D; Foley, D M; Wellman, D E

2002-09-15

128

Evidence for 800 years of North Atlantic multi-decadal variability from a Puerto Rican speleothem  

NASA Astrophysics Data System (ADS)

The long-term behavior of the tropical Atlantic ocean/atmospheric system prior to the 20th century is not well characterized due to a lack of high-resolution proxy records to extend the short instrumental record. Here we present the first reconstruction of rainfall variability for the western tropical Atlantic that spans the past 8 centuries and is derived from the ?18O of speleothem calcite. The ?18O of speleothem calcite at this Puerto Rican location varies primarily in response to changes in the amount of summer-time precipitation. The speleothem documents multi-decadal to centennial length oscillations in ?18O that point to large variations in rainfall that have not been manifest in the short instrumental period. Since AD 1850, variations in ?18O have tracked shifts in the Atlantic Multidecadal Oscillation (AMO). We tentatively suggest that the speleothem ?18O-based rainfall record from Puerto Rico extends the history of the AMO to the 12th century.

Winter, Amos; Miller, Thomas; Kushnir, Yochanan; Sinha, Ashish; Timmermann, Axel; Jury, Mark R.; Gallup, Christina; Cheng, Hai; Edwards, R. Lawrence

2011-08-01

129

Observations of faint eclipsing cataclysmic variables  

NASA Astrophysics Data System (ADS)

We present time-resolved photometry of six faint (V>17mag) cataclysmic variables (CVs); one of them is V849 Oph and the others are identified from the Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139, SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations of these objects were performed at the TÜB?TAK National Observatory (Turkey) between February 2006 and March 2009. We aimed to detect short time scale orbital variability arisen from hot-spot modulation, flickering structures which occur from rapid fluctuations of material transferring from red star to white dwarf and orbital period changes for selected short-period (P<4h) CVs at quiescence. Results obtained from eclipse timings and light curves morphology related to white dwarf stars, accretion disks and hot-spots are discussed for each system. Analysis of the short time coverage of data, obtained for SDSS J1227+5139 indicates a cyclical period change arisen from magnetic activity on the secondary star. Photometric period of SDSS J1607+3623 is derived firstly in this study, while for the other five systems light elements are corrected using the previous and new photometric observations. The nature of SDSS J1457+5148 is not precisely revealed that its light curve shows any periodicity that could be related to the orbital period.

Zengin Çamurdan, D.; ?banog?lu, C.; Çamurdan, C. M.

2010-07-01

130

Interannual Variability and Decadal Trend of Global Fractional Vegetation Cover from 1982 to 2000.  

NASA Astrophysics Data System (ADS)

Fractional vegetation cover (FVC) is one of the most important variables in land surface modeling and also provides a continuous field to complement discrete land cover classification. A global 8-km FVC dataset for 1982-2000 is derived using the NOAA-NASA land Pathfinder normalized difference vegetation index data. The confidence in the dataset is provided by the insensitivity of the algorithm to the data resolution (between 1 and 8 km), the good agreement of the results with the field survey data over Germany, the consistency of the results with previous observational studies over the savannas in North Africa and the forests in Bolivia, and the robustness of the algorithm, as demonstrated by the small interannual variability of FVC over areas where anthropogenic land cover change is expected to be small, based on the 30-m Landsat data analysis. Significant interannual variability is found over shrubland, savanna, and grassland; both positive and negative trends exist over different areas of the same region in many parts of the world. In particular, the trend analysis pinpoints areas with statistically significant trends (i.e., `hotspots') for further study using higher-resolution satellite data and field-survey data.

Zeng, Xubin; Rao, Praveen; Defries, Ruth S.; Hansen, Matthew C.

2003-10-01

131

Interannual Variability and Decadal Trend of Global Fractional Vegetation Cover Since 1982  

NASA Astrophysics Data System (ADS)

Fractional vegetation cover (FVC) is one of the most important variables in land surface modeling and also provides a continuous field to complement discrete land cover classification. A global 8-km FVC dataset from 1982-2000 is derived using the NOAA/NASA land pathfinder normalized difference vegetation index data. The confidence in the dataset is provided by the insensitivity of our algorithm to the data resolution (between 1 km and 8 km), the good agreement of our results with the field survey data over Germany, the consistency of our results with previous observational studies over the savannas in North Africa and the forests in Bolivia, and the robustness of our algorithm as demonstrated by the small interannual variability of FVC over areas where anthropogenic land cover change is expected to be small based on the 30-m Landsat data analysis. Significant interannual variability is found over shrubland, savanna, and grassland, while both positive and negative trends exist over different areas of the same region in many parts of the world. In particular, our trend analysis pinpoints areas with statistically significant trends (i.e., `hotspots') for further study using higher resolution satellite data and field survey data. Additional results using both AVHRR and MODIS data will also be presented.

Zeng, X.

2004-12-01

132

On "observation minus reanalysis" method: A view from multidecadal variability  

NASA Astrophysics Data System (ADS)

The observation minus reanalysis (OMR) method is widely used to investigate the impact of urbanization and land use change on climate. Here we present the OMR trends for the periods of 1979-1998 and 1989-2008 in eastern China, which appear inconsistent for the regions experiencing rapid urbanization during recent decades. Using Ensemble Empirical Mode Decomposition, we extract the secular trend and multidecadal variability (MDV) from the temperature observations at stations and the corresponding reanalysis data for the last century and find that, in general, MDV in the reanalysis data is weaker than that in the station observations. This systematic difference considerably modulates the magnitude of the OMR trends during different periods, leading to inconsistent estimates of the impact of urbanization. After MDV adjustment, the OMR trends for Beijing and Shanghai are consistent for the different periods, about 0.04°C-0.1°C/decade, much smaller than some previous estimates. We caution those using OMR methods to estimate the effect of urbanization and also for those using reanalysis data for a limited period in studies of this kind.

Wang, Jun; Yan, Zhongwei; Jones, Phil D.; Xia, Jiangjiang

2013-07-01

133

Morbidity and mortality in common variable immune deficiency over 4 decades  

PubMed Central

The demographics, immunologic parameters, medical complications, and mortality statistics from 473 subjects with common variable immune deficiency followed over 4 decades in New York were analyzed. Median immunoglobulin levels were IgG, 246 mg/dL; IgA, 8 mg/dL; and IgM, 21 mg/dL; 22.6% had an IgG less than 100 mg/dL. Males were diagnosed earlier (median age, 30 years) than females (median age, 33.5 years; P = .004). Ninety-four percent of patients had a history of infections; 68% also had noninfectious complications: hematologic or organ-specific autoimmunity, 28.6%; chronic lung disease, 28.5%; bronchiectasis, 11.2%; gastrointestinal inflammatory disease, 15.4%; malabsorption, 5.9%; granulomatous disease, 9.7%; liver diseases and hepatitis, 9.1%; lymphoma, 8.2%; or other cancers, 7.0%. Females had higher baseline serum IgM (P = .009) and were more likely to develop lymphoma (P = .04); 19.6% of patients died, a significantly shorter survival than age- and sex-matched population controls (P < .0001). Reduced survival was associated with age at diagnosis, lower baseline IgG, higher IgM, and fewer peripheral B cells. The risk of death was 11 times higher for patients with noninfectious complications (hazard ratio = 10.95; P < .0001). Mortality was associated with lymphoma, any form of hepatitis, functional or structural lung impairment, and gastrointestinal disease with or without malabsorption, but not with bronchiectasis, autoimmunity, other cancers, granulomatous disease, or previous splenectomy.

Resnick, Elena S.; Moshier, Erin L.; Godbold, James H.

2012-01-01

134

Observed Variability of the East Pacific ITCZ  

NASA Astrophysics Data System (ADS)

The location and extent of the ITCZ has been identified for 30 years of satellite data using a statistical model. Satellite 3 hourly IR, daily visual and 12 hourly total precipitable water are used as inputs to the model. The information has been used to produce a full climatology of ITCZ occurrence and variability on synoptic time scales. The ITCZ labels are identified by LIMA (Labeling the ITCZ using a Markov-random field Algorithm), a new probability model which uses satellite data from a given location and information from neighboring pixels (in space and time) to inform the decision on whether a given pixel is classified as ITCZ or non-ITCZ. By this method the algorithm is able to emulate what a human would `see' as organized cloud belonging to the convergence zone and does not include isolated convection which would be picked up from thresholding techniques. This method of identification is particularly useful for examining the dynamical aspects of the observed ITCZ as it can pick up the shape and undulations of the different parts of its lifecycle. The overall climatology of the ITCZ and its intraseasonal characteristics are also obtained and have been compared to alternative identification techniques for validation. A separate tracking algorithm has been created to identify clouds associated with tropical cyclone activity. The information has been used to garner statistics on the interaction between ITCZ and tropical cyclones as well extracting information on the cloud characteristics of the cyclones themselves. The LIMA labels of ITCZ have been used to investigate interaction between the Pacific convective region and other aspects of tropical variability. The impacts of tropical features such as the MJO on the ITCZ shape, extent and convection strength will be shown alongside timeseries analysis for the full length dataset. In addition, interactions between ITCZ and ENSO will be shown along with diagnostics for climatic trends in the structure and occurrence of the convergence zone. The method of detection has the advantage that variability within the labeled zone can be extracted, thus the diurnal cycle of convection as well as relationship to sea surface temperatures have been obtained and will be presented alongside the seasonal variability. Shading is IR satellite for June 7 2002, 06 UTC, resolution of 0.5 degrees, obtained from the HURSAT data base. Black contour is the LIMA label of the location of the ITCZ, showing undulation of the feature. The tropical cyclone is identified by a separate tracking algorithm at a later stage.

Bain, C.; Magnusdottir, G.; de Paz, J. M.; Kramer, J.; Smyth, P.; Stern, H.

2009-12-01

135

Variability in a Multi-Decadal Record of Ocean Acidification in Surface Waters of the U.S. Northeast Shelf  

NASA Astrophysics Data System (ADS)

Multiple shelf-wide surveys of the Northeast Shelf of the United States, from the Gulf of Maine through the Mid-Atlantic Bight, were conducted as part of the NOAA Marine Resources Monitoring, Assessment, and Prediction Program (MARMAP) and the Northeast Monitoring Program (NEMP). Observations including pH, total alkalinity, temperature, and salinity were collected from 1973-1984. These historical data were compared to recent data collected as part of a joint NASA/NOAA project (CliVEC) as part of the NOAA Ocean Acidification Program. A preliminary comparison of the historical surface waters suggests that interannual variability in the carbonate system is approximately equal in magnitude to the expected multi-decadal changes. Where geographically comparable data exist for the MARMAP era and recent surveys, changes appear to be dominated by varying water masses, however salinity normalized DIC in the Mid-Atlantic Bight appears to have increased proportional to other published global averages. Ongoing studies of carbonate chemistry in the region will benefit from the availability of this retrospective baseline of the carbonate system and a greater understanding of the seasonal, interannual, and interdecadal variability. Determining the proximal causes of differences between acidification on the Northeast Shelf and the global average is a necessary component of future ecological modeling studies and regional management in this biologically productive and economically valuable region.

Rebuck, N. D.; Hare, J. A.; Mulholland, M. R.; Bernhardt, P. W.; Staryk, C. J.

2011-12-01

136

Interannual and decadal variability of the Subpolar Gyre and the Meridional Overturning Circulation in the North Atlantic  

NASA Astrophysics Data System (ADS)

Significant changes of the hydrographic properties of the water masses involved in the Meridional Overturning Circulation (MOC) have been observed in the last 60 years. Model studies point out the importance of the mutual interactions between MOC, Subpolar Gyre (SPG) of the North Atlantic and formation of Labrador Sea Water (LSW). On the other hand, circulation and water mass changes of the SPG are apparently closely related to the North Atlantic Oscillation (NAO). However, the relation between water mass changes, the MOC and SPG circulations under the influence of the NAO are still unclear. In this study, a comprehensive dataset of temperature and salinity observations between 1950 and 2007 (including WOD05, HydroBase2, ICES, ARGO, WOCE and CLIVAR), as well as numerical simulations with the global ocean circulation model MPIOM are analysed. Realistic atmospheric data from the National Centers for Environmental Prediction (NCEP) are used to force the model and yield a hindcast of the SPG circulation and hydrography in the last 60 years. This modelled interannual and decadal variability is validated with the observations and quantifies the MOC and SPG changes and their interactions with LSW and with heat and freshwater transports from the subtropics.

Nunez-Riboni, Ismael; Haak, Helmuth; Bersch, Manfred; Jungclaus, Johann

2010-05-01

137

An Observational Study of Cataclysmic Variable Evolution  

NASA Astrophysics Data System (ADS)

In this thesis I present an observational study of the evolution of Cataclysmic Variables (CVs). Disrupted magnetic braking has been the standard paradigm of CV evolution for the past twenty years. Unfortunately, some of its predictions are in strong disagreement with the observations. In recent years, a number of additions/alternatives to the standard model have been proposed. Yet, none have been able to explain all of the features observed in the currently known CV population. The work presented in this thesis is based mainly on a large-scale search for CVs. The primary aim of this project is to resolve the disagreement between theory and observations by eliminating the observational biases of the present CV sample. Here, I use two complementary approaches to search for CVs: (1) from the spectroscopic appearance in the Hamburg Quasar Survey (HQS), and (2) by using a combination of ROSAT and 2MASS archival data. So far, we have discovered 52 new CVs in the HQS and 11 new CVs (the majority of them magnetic) and 1 pre-CV in the ROSAT/2MASS. Follow-up observations of two newly discovered HQS CVs, 1RXS J062518.2+733433 and HS 2331+3905, resulted in the classification of the first as an Intermediate Polar, with P_orb = 283.0 min and P_spin = 19.8 min, and the second as a short orbital period system, P_orb = 81.0 min, harbouring a white dwarf pulsator. In addition, we found that the dominant ~3.5 h radial velocity variation of HS 2331+3905 does not correspond to the orbital period of the system, contrary to all other CVs. Despite its novel selection criterion, the HQS does not provide many short-period CVs -- even though tests with the known CVs included in the survey have shown that it is very sensitive to those objects. The biggest surprise in the new HQS sample is the discovery of many new SW Sex stars. The clustering of SW Sex stars in the 3-4 h period range is probably an important feature in the evolution of CVs that we currently do not understand at all. To improve our chances of understanding what is going on in that period range, we need accurate system parameters for these stars, which is difficult mainly because of their defining characteristics. I have used HST data of one of the sporadic low states of the SW Sex star DW UMa to derive its system parameters. The success of this study is the first step towards the otherwise impossible task of compiling reliable system parameters for the SW Sex stars.

Araujo-Betancor, Sofia

2004-03-01

138

Modeling the Temperature Responses to Spectral Solar Variability on Decadal and Centennial Time Scales  

NASA Astrophysics Data System (ADS)

Atmospheric temperature responses to decadal solar variations are computed for two scenarios of solar spectral irradiance (SSI), SIM-based out-of-phase and proxy-based in-phase variations, using a time-dependent radiative-convective model (RCM), and also GISS modelE (GCM.) For both scenarios and both models, maximum responses occur in upper stratosphere, decreasing downward to the surface. Upper stratospheric temperature peak-to-peak responses to out-of-phase forcing are ~0.6 K in RCM and ~0.9 K over tropics in GCM, ~5x as large as responses to in-phase forcing. Stratospheric responses are in-phase with TSI (Total Solar Irradiance). Modeled upper stratospheric temperature responses to SIM-based forcing are similar to 11-year temperature variations observed with HALOE (Halogen Occultation Experiment). For both RCM and GCM, surface responses to the two scenarios are significantly smaller than stratospheric responses. On centennial timescales, SSI variations are poorly known. However, two scenarios of reconstructed TSI, one based on 11-year cycle with background [Lean 2000] and the other on flux transport with much less background [Wang, Lean, and Sheeley, 2005], provide a potential range of TSI variations. We apply phase relations among different SSI bands both from SIM observations and proxy reconstructions to the two scenarios of historical TSI to derive associated historical SSI, which then drives the RCM. The updated atmosphere and ocean mixed coupled RCM including diffusion to deep-ocean provide a first order estimate of temperature responses to SSI variations on centennial time scales. We discuss potential mechanisms for atmosphere-ocean and stratosphere-troposphere couplings responsible for the climate responses to spectral solar variations.

Cahalan, R. F.; Wen, G.; Pilewskie, P.; Harder, J. W.

2010-12-01

139

Corrected mu_delta for Stars of Hipparcos Catalogue from Independent Latitude Observations over Many Decades  

NASA Astrophysics Data System (ADS)

During the last century, there were many so-called independent latitude (IL) stations with the observations which were included into data of a few international organizations (like Bureau International de l'Heure - BIH, International Polar Motion Service - IPMS) and the Earth rotation programmes for determining the Earth Orientation Parameters - EOP. Because of this, nowadays, there are numerous astrometric ground-based observations (made over many decades) of some stars included in the Hipparcos Catalogue (ESA 1997). We used these latitude data for the inverse investigations - to improve the proper motions in declination ?_{?} of the mentioned Hipparcos stars. We determined the corrections ??_{?} and investigated agreement of our ?_{?} and those from the catalogues Hipparcos and new Hipparcos (van Leeuwen 2007). To do this we used the latitude variations of 7 stations (Belgrade, Blagoveschtschensk, Irkutsk, Poltava, Pulkovo, Warsaw and Mizusawa), covering different intervals in the period 1904.7 - 1992.0, obtained with 6 visual and 1 floating zenith telescopes (Mizusawa). On the other hand, with regard that about two decades have elapsed since the Hipparcos ESA mission observations (the epoch of Hipparcos catalogue is 1991.25), the error of apparent places of Hipparcos stars has increased by nearly 20 mas because of proper motion errors. Also, the mission lasted less than four years which was not enough for a sufficient accuracy of proper motions of some stars (such as double or multiple ones). Our method of calculation, and the calculated ?_{?} for the common IL/Hipparcos stars are presented here. We constructed an IL catalogue of 1200 stars: there are 707 stars in the first part (with at least 20 years of IL observations) and 493 stars in the second one (less than 20 years). In the case of ?_{&delta}; of IL stars observed at some stations (Blagoveschtschensk, Irkutsk, Mizusawa, Poltava and Pulkovo) we find the formal errors less than the corresponding Hipparcos ones and for some of them (stations Blagoveschtschensk and Irkutsk) even less than the new Hipparcos ones.

Damljanovic, G.; Milic, I. S.

2011-06-01

140

On the connection between South Pacific subtropical spiciness anomalies and decadal equatorial variability in an ocean general circulation model  

Microsoft Academic Search

Simulations from a 49-year, realistically forced numerical model experiment indicate that decadal variability of temperature and salinity along the equator originates from subsurface spiciness anomalies in the South Pacific. Through western boundary and interior pathways in the thermocline, the subsurface anomalies in the South Pacific are first transferred westward and then northward, eventually appearing along the equator. The large spiciness

Yiyong Luo; Lewis M. Rothstein; Rong-Hua Zhang; Antonio J. Busalacchi

2005-01-01

141

Decadal variability of the Subtropical Front of the western North Pacific in an eddy-resolving ocean general circulation model  

Microsoft Academic Search

We examined decadal variability of the Subtropical Front (STF) of the western North Pacific by using a North Pacific ocean general circulation model (OGCM), comparing the results of three simulations with different horizontal resolutions. In the long-term mean fields, the eddy-resolving model (10 km) was able to simulate the distributions of the STF and the associated Subtropical Countercurrent (STCC) between

Goro Yamanaka; Hiroshi Ishizaki; Mikitoshi Hirabara; Ichiro Ishikawa

2008-01-01

142

Modeling the Climate Responses to Spectral Solar Variability on Decadal and Centennial Time Scales  

NASA Astrophysics Data System (ADS)

We apply two scenarios of external forcing, namely the SIM-based out-of-phase variations and the proxy-based in-phase variations, as input to a time-dependent radiative-convective model (RCM), and also to the GISS modelE GCM, to compute climate responses to solar variation on decadal time scale. We find that the maximum temperature response occurs in the upper stratosphere, while temperature response decreases downward to the surface for both scenarios, and both models. The upper stratospheric temperature peak-to-peak responses to out-of-phase solar forcing are 0.6 K in RCM and 0.9 K over the tropical region in GCM simulations, a factor of 5 times as large as responses to in-phase solar forcing. Stratospheric responses are in-phase with TSI (Total Solar Irradiance) variations. The modeled upper stratospheric temperature responses to the SORCE SIM observed SSI (Spectral Solar Irradiance) forcing are similar to the HALOE (Halogen Occultation Experiment) observed 11-year temperature variations. Surface responses to the two SSI scenarios are small for both RCM and GCM studies, as compared to the stratospheric responses. Though solar irradiance variations on centennial time scale are not well known, the two sce-narios of reconstructed TSI time series (i.e., the one based on 11-year cycle with background [Lean 2000] and the other one from flux transport that has much less background component [Wang, Lean, and Sheeley, 2005]) provide potential range of variations of TSI on centennial time scale. We apply phase relations among different spectral irradiance bands both from SIM observation and proxy reconstructions to the two scenarios of historical TSI to derive the as-sociated historical SSI. The historical SSI is used to drive the RCM. The updated atmosphere and ocean mixed coupled RCM including diffusion to deep-ocean will provide the first order estimate of temperature response to SSI variation on centennial time scales. We anticipate the stratosphere, troposphere, and ocean surface have different responses to different scenarios of spectral solar forcing on centennial time scale. We further discuss potential mechanisms for atmosphere-ocean and stratosphere-troposphere couplings responsible for the climate response to the solar variations.

Cahalan, Robert; Wen, Guoyong; Pilewskie, Peter; Harder, Jerald

143

History of Amateur Variable Star Observations in Japan  

NASA Astrophysics Data System (ADS)

(Abstract only) Japan has about 100 years of history of variable star observing since Naozo Ichinohe, professional astronomer in Tokyo Observatory, observed d Cep in 1906. The first amateur variable star observer is Yoshihiko Kasai, who began observing variable stars in 1918. I introduce a brief history of Japanese amateur variable star observation, including topics of variable star organizations, nova and supernova hunters, collaborations with the AAVSO and the world, PEP and CCD observations. I also introduce the most active variable star observer, Hiroaki Narumi, who made over 260,000 visual estimates since 1975. VSOLJ was established in 1987 in collaborations with the variable star sections of Nihon Tenmon Kenkyu-kai (NTK) and the Oriental Astronomical Association (OAA). VSOLJ maintains a database of Japanese variable star observations (http://vsolj.cetus-net.org) and publishes the Variable Star Bulletin in English.

Kiyota, S.

2012-06-01

144

Decadal changes in the physical mechanisms of the seasonal cycle of summertime precipitation variability in Korea  

NASA Astrophysics Data System (ADS)

Summertime precipitation variability in Korea has changed significantly in recent years. To understand how the physical mechanisms of summertime precipitation in Korea vary with climate change, we analyzed observed precipitation records for 1996-2008 in comparison with those for 1979-1995 at 61 Korea Meteorological Administration stations distributed over South Korea. We investigated detailed physical changes by extracting space-time structures of the physical mechanisms from the daily NCEP/NCAR reanalysis data over East Asia via cyclostationary EOF (CSEOF) analysis. Due to the change of low-level circulation patterns in the Asian region, the commencement, duration, and retreat of the East Asian monsoon front has varied significantly over recent years. Specifically, the first peak of the bimodal precipitation pattern in Korea has started earlier and significantly increased in intensity. The second peak has broadened in recent years and the typical seasonal period of decreased precipitation has weakened. The strength of the sub-seasonal component of precipitation has increased in recent years due to the strengthening of meridional circulation between the subtropics and the midlatitudes. A conspicuous change in the vertical structure of the sub-seasonal component is observed in recent records. Increased warm and moist advection from the south and decreased cold and dry advection from the north seem to be the primary reasons for such a change. The high-frequency component of summer precipitation with time scales shorter than 10 days is formed by the baroclinic instability observed in recent years. This component has increased by ˜25% due primarily to the strengthened dynamic and thermodynamic processes.

Roh, Joon-Woo; Kim, Kwang-Yul; Jhun, Jong-Ghap

2012-04-01

145

Decreasing the Variability Observed in Urine Analysis  

Microsoft Academic Search

Urine analysis is affected significantly by biological variability. The objective of this study was to study the feasibility of reducing the biological variability of excretion of various analytes in urine, especially albumin in children with diabetes, by mixing small volumes of early morning samples. Twenty-two male children with type 1 diabetes collected early morning aliquots of approximately 10 ml of

Z. K. Shihabi; R. P. Schwartz; M. J. Pugia

2001-01-01

146

Decadal variability and extremes of European winter storm frequency according to the Twentieth Century Reanalysis - a process-oriented analysis  

NASA Astrophysics Data System (ADS)

Winter storms, represented by extensive fields of extreme wind speeds, result from intense extra-tropical cyclones. The most extreme of them cause enormous socio-economical losses over Europe. As part of the MiKlip initiative this study deals with the assessment of decadal variability of synoptic-scale European winter storms in terms of their frequency and analyzes the processes influencing this decadal variability. Analysis subject is the new Twentieth Century Reanalysis (20CR) dataset, spanning the period 1871-2008. The discrete winter storm events are identified by matching the results of two event tracking schemes. One scheme identifies extra-tropical cyclones, based on MSLP and its laplacian, the other is based only on surface wind speeds, thus identifies storm events diagnosed as extensive areas of extreme (× local climatological 98th percentile) wind speeds. Hence, the definition of a European winter storm in the context of this study is an extra-tropical cyclone producing synoptic scale fields of extreme surface winds. Based on this approach, the period of 1871-2008 (ONDJFM) is investigated with respect to decadal variability of extreme winter storms and their frequency. Perennial periods of anomalous high/low European winter storm frequency are analyzed regarding global atmospheric and oceanic conditions - for the latter, taking additionally into account the HadISST1.1 dataset, which was used to force 20CR - and their spatio-temporal evolution. The aim of this analysis step is to reveal some of the physical mechanisms behind decadal variability of winter storm frequency. First results indicate a connection between the North Atlantic meridional SST gradient and decadal extremes of European winter storm frequency, as well as some remote influence from the Pacific basin and the tropics in general.

Kruschke, Tim; Rust, Henning W.; Schyska, Bruno; Wild, Simon; Leckebusch, Gregor C.; Ulbrich, Uwe

2013-04-01

147

Simulating multi-decadal variability of Caspian Sea level changes using regional climate model outputs  

NASA Astrophysics Data System (ADS)

The Caspian Sea is the largest enclosed body of water on earth, covering approximately 4×105 km2 and sharing its coast with five countries (Iran, Azerbaijan, Kazakhstan, Russia and Turkmenistan). Because it has no outlet to the ocean the Caspian Sea level (CSL) has undergone rapid shifts in response to climatic forcings, and these have been devastating for the surrounding countries. In this paper we present the initial results of a modeling effort aimed at building a regional climate model for the Caspian Sea basin suitable to study the response of the CSL to interdecadal climate variability and anthropogenic climate change. Simulations are performed using the International Centre for Theoretical Physics (ICTP) regional climate model RegCM at a 50 km grid spacing for the period 1948 1990. During this period an abrupt shift occurred in the sea level after 1977, when the CSL rose about two meters until the early 1990s. Using a simple equation of hydrologic balance for the Caspian Sea basin to predict the CSL, we show that the model is able to reproduce the observed CSL changes at interannual to multidecadal scales. The correlation coefficient between the simulated and observed annual CSL changes is 0.91 and the model is able to reproduce the abrupt shift in CSL which occurred after 1977. Analysis of the climatologies before and after 1977 indicate that the CSL rise was mostly due to an increase in precipitation over the northern basin and a decrease in evaporation over the sea, primarily during the warm season. We plan to apply our model to the investigation of the response of the CSL to anthropogenic climate forcings.

Elguindi, N.; Giorgi, F.

2006-02-01

148

Decadal and Centennial Variability of Wet and Dry in China since Medieval Warm Period Detected from High Resolution Speleothem Data  

NASA Astrophysics Data System (ADS)

High-resolution ?18O data (yearly) since AD 900 from six caves (Dongge, Furong, Heshang, Wanxiang, Buddha, Shihua) in China was analyzed to detect decadal and centennial variability of wet/dry in the Asian Monsoon region. The empirical mode decomposition method (Huang et al., 1998) was used to obtain trends for the six cave data. The nine-year running average was conducted on the detrened data (??18O, called anomaly) to filter out high-frequency fluctuation such as the interannual variability. Mean values of anomaly for each cave were calculated for 5 periods: (1) medieval warm period (MWD, AD 900 -AD 1100), (2) little ice age phase-1 (LIA-1, AD 1250 - AD 1550), (3) little ice age phase-2 (LIA-2, AD 1550 - AD 1850), (4) modern period-1 (MD-1, AD 1850 - AD 1950), and (5) modern period-2 (MD-2, AD 1950-2000). Anomalies in MWP and LIA-2 has opposite signs: negative anomaly (strong monsoon) in MWP and positive anomaly (weak monsoon) in LIA-2 in (Dongge, Wanxiang) cave data otherwise in (Budda, Furong, Heshang, Shihua) cave data. In LIA-1, all the six caves have positive anomalies (weak monsoon). In MD-1 (AD 1850-AD 1950), all the six caves have negative anomalies; and in MD-2 (AD 1950 - AD 2000), all the caves except Buddha have negative anomalies. It implies strong monsoon with global warming trend. Spectral analysis was also conducted on the detrended data of the six caves. The above observational studies show the following results: (1) Monsoon strength has spatial variations; (2) Stronger monsoon occurred under both warm and cold climatic conditions. One should not use the relationship of warm condition, i.e., stronger summer monsoon to interpret monsoonal climates in short time scales (less than centennial scale); and (3) Monsoon strengthening continues.

Chu, P. C.; Li, H.

2011-12-01

149

Decadal gully development in Northern Ethiopia: Understanding networks, volumes and regional variability from remote sensing data  

NASA Astrophysics Data System (ADS)

Understanding historical and present-day gully development is essential when addressing the causes and consequences of land degradation. For Northern Ethiopia, several reports exist on the severity of gully erosion, yet few studies quantified gully development. In this paper, gully network and volume development were quantified over the period 1963-2010 for an area of 123 km², representative for the regional variability in environmental characteristics. Gully networks were mapped from small-scale aerial photographs and high-resolution satellite images. As only gully length could be accurately defined from the aerial photographs and satellite images, quantifying gully volume development required to establish relations between gully network volume (V) and length (L) (or catchment area, A). Field observations indicated that the lithology and the presence/or absence of check dams or low-active channels were the most important controls of gully cross-sectional shape and size. From the network and volume development over the period 1963-2010, the occurrence of one cut-and-fill cycle is apparent. From a largely low-dynamic gully system in the 1960s, network expansion and increased erosion rates in the 1980s and 1990s caused the drainage density and volume to peak in 1994. The total gully density (Dtotal) was then 2.52 km km-2, coinciding with soil losses of 17.6 ton ha-1 y-1 over the period 1963/1965-1994. By 2010, improved land management and the region-wide implementation of soil and water conservation measures caused 25% the gully network to stabilize, resulting in a recent net infilling of the gully channels. The study validates previous findings that land degradation by gullying was severe in Northern Ethiopia in the second half of the 20th century, but also shows that when proper land management is applied, gullies can be transformed into a linear oasis, which increases the resistance of gullies to further erosion.

Frankl, Amaury; Poesen, Jean; Scholiers, Nelles; Jacob, Miro; Haile, Mitiku; Deckers, Jozef; Nyssen, Jan

2013-04-01

150

Tropical Pacific Forcing of Decadal SST Variability in the Western Indian Ocean over the Past Two Centuries  

Microsoft Academic Search

A 194-year annual record of skeletal d 18 O from a coral growing at Malindi, Kenya, preserves a history of sea surface temperature (SST) change that is coherent with instrumental and proxy records of tropical Pacific climate vari- ability over interannual to decadal periods. This variability is superimposed on a warming of as much as 1.3¡C since the early 1800s.

Julia E. Cole; Robert B. Dunbar; Timothy R. McClanahan; Nyawira A. Muthiga

2000-01-01

151

Can we reconcile our understanding of the atmospheric methane budget over the past decades with atmospheric observations?  

NASA Astrophysics Data System (ADS)

The balance of methane in the atmosphere is determined by surface emission, and losses due to uptake in soils and reaction with the hydroxyl radical. The atmospheric abundance of methane has risen by about a factor of three since pre-industrial times, but the growth rate has decreased substantially since the 1990's. Thus, global atmospheric methane appears to have equilibrated to around 1780 ppb subject to considerable interannual variability, the causes of which are not well-understood. Methane emissions are expected to increase in the future due to increases in fossil fuel use and possible changes in wetlands at high-latitudes, and it is therefore important to test our understanding of the methane budget over the last two decades against network observations of atmospheric methane. Issues of interest are whether we can match the rise in methane over the 1980's, whether we can explain the decrease in growth rate during the 1990's, and whether we are able to simulate the observed interannual variability in the observations. We will show results from a multi-decade model simulation using analyzed meteorology from the ERA-40 reanalysis over this period. New times series of methane sources for 1980 through the early 2000's are used in the simulation. Anthropogenic sources include fossil fuels with a total of 7 fuel-process emission combinations associated with mining, processing, transport and distribution of coal, natural gas and oil; ruminant animals and manure based on regionally-representative profiles of bovine populations ; landfills including the impact of on- site methane capture; and irrigated rice cultivation based on seasonal rice-cropping calendars. Natural sources we include are biomass burning from the GFED emission data base, oceans, termites, and natural wetlands using a multiple-regression model derived from a process-based model. If time permits, we will also show preliminary results of a methane data assimilation using the Cooperative Air-Sampling and GMD network observations, and our new estimates of methane sources.

Bruhwiler, L. M.; Matthews, E.

2007-12-01

152

Lead variability in the western North Atlantic Ocean and central Greenland ice: Implications for the search for decadal trends in anthropogenic emissions  

SciTech Connect

As Patterson and coworkers have shown, most of the lead in the modern ocean and atmosphere is of anthropogenic origin. Reductions in the utilization of leaded gasoline over the past two decades should decrease lead deposition from the atmosphere in remote locations. The search for trends in Pb deposition within a single decade is bedeviled by large-amplitude short-term variability due to the inherent noisiness of the atmosphere/ocean system. The authors find that, over the course of a year, lead concentrations in the surface waters of the western North Atlantic Ocean are variable (order of magnitude). In the western North Atlantic, [sup 210]Pb normalization minimizes this problem because [sup 210]Pb and Pb sources are spatially correlated and continental [sup 210]Pb emissions are constant. It is clear the Pb in surface waters of the western North Atlantic has decreased by a factor of 4 during the 1980s. [sup 210]Pb normalization does not help in the Arctic because stable Pb and [sup 210]Pb are not spatially correlated. Because of the order-of-magnitude variability in Greenland snow Pb linked to annual cycles, any discontinuous time series is likely to be affected by the phenomenon of aliasing. Aliasing makes it difficult to determine if there is a trend in Pb deposition in central Greenland during the 1980s; present evidence suggests that the reduction in Pb concentration in snow during the 1980s is less than a factor of two; certainly quite a bit less than observed in the western North Atlantic and less than the factor of >7 reduction in leaded gasoline utilization in the United States during the decade. Although the authors expect that decadal-scale trends in the 1970s and 1980s are in fact occurring due to the phasing out of leaded gasoline, the reported magnitude of decadal-scale trends should be regarded with some reservation until confirmed by independent samplings.

Boyle, E.A.; Sherrell, R.M. (Massachusetts Institute of Technology, Cambridge, MA (United States)); Bacon, M.P. (Woods Hole Oceanographic Institution, MA (United States))

1994-08-01

153

Variable temperature cold stage for microscope observation  

Microsoft Academic Search

It is considerably important to measure crystallization velocity in vitreous state for understanding of crystallization mechanism and quantitative analysis of crystallization process. For this measurement, a microscope equipped with a variable temperature cold stage is useful to regulate temperature to be constant for a long period because some crystallization takes a long time around glass transition point. However, since conventional

Hirosi Yamada; Minoru Hanaya; Youichi Kanno; Takemitu Kikuchi; Shinji Onodera

1992-01-01

154

Yes, There is a Northern Lesser Antilles Forearc Sliver: Results From a Decade of GPS Observations  

NASA Astrophysics Data System (ADS)

Investigations of the discrepancy between thrust fault earthquake slip vectors and the direction of North American plate convergence and arc-normal trending normal fault systems have led previous workers to suggest that the northern Lesser Antilles arc/forearc (NLAAF) region is subject to strain partitioning and sliver motion with some component of internal deformation. Results from a decade of GPS observations in the northern Lesser Antilles and the British Virgin Islands (BVI) are used to directly constrain estimates of microplate motion. We use the observed GPS velocity field to quantitatively test between three kinematic models for the region: 1) the NLAAF moves with the Caribbean plate and does not show a significant amount of sliver motion, 2) the NLAAF shows rigid sliver motion that differs statistically from Caribbean plate motion, or 3) the NLAAF shows motion consistent with an internally deforming forearc sliver. Our analysis of the GPS data indicates that statistically significant northwest directed motion of a forearc sliver is occurring in the region. The observed velocity field also supports internal deformation in the southern part of the sliver where the majority of the extensional fault systems occur. Boundary parallel motion within the NLAAF ranges from ~1-2 mm/yr in the southern region to ~5 mm/yr in the northern region. These rates are in agreement with past studies of plate convergence and earthquake slip vectors for the central part of the NLAAF, but are slower than past estimates of possible sliver motion in the northern region (BVI) indicating that oblique convergence in this area is only partially partitioned. Our velocity field shows predominantly boundary parallel motion along the arc, while islands in the southern forearc region show predominantly arc- normal strain accumulation of ~3 mm/yr.

Turner, H. L.; Jansma, P. E.; Mattioli, G. S.; Matson, S.; Rodríguez Cesaní, H. M.

2008-12-01

155

Decadal variability of the Indian Ocean cross-equatorial exchange in SODA  

NASA Astrophysics Data System (ADS)

The mean meridional circulation across the equator in the Indian Ocean is characterized by the shallow Cross-Equatorial Cell (CEC). At the western boundary, the Somali Current transports thermocline waters northward which then upwell, mostly off Northeast Africa. The upwelled waters are taking up heat and then exported back southward by southward near-surface Ekman and Sverdrup transports. The CEC is closed by subduction in the southeastern subtropics and includes contributions from the Indonesian Throughflow. In an analysis of output from the SODA assimilation, a decadal slowdown of the different branches of the CEC is demonstrated here.

Schoenefeldt, Rena; Schott, Friedrich A.

2006-04-01

156

Bi-decadal variability excited in the coupled ocean-atmosphere system by strong tropical volcanic eruptions  

NASA Astrophysics Data System (ADS)

Decadal and bi-decadal climate responses to tropical strong volcanic eruptions (SVEs) are inspected in an ensemble simulation covering the last millennium based on the Max Planck Institute—Earth system model. An unprecedentedly large collection of pre-industrial SVEs (up to 45) producing a peak annual-average top-of-atmosphere radiative perturbation larger than -1.5 Wm-2 is investigated by composite analysis. Post-eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean-atmosphere system with an average length of 20-25 years. The study provides a new physically consistent theoretical framework to interpret decadal Northern Hemisphere (NH) regional winter climates variability during the last millennium. The fluctuation particularly involves interactions between the Atlantic meridional overturning circulation and the North Atlantic gyre circulation closely linked to the state of the winter North Atlantic Oscillation. It is characterized by major distinctive details. Among them, the most prominent are: (a) a strong signal amplification in the Arctic region which allows for a sustained strengthened teleconnection between the North Pacific and the North Atlantic during the first post-eruption decade and which entails important implications from oceanic heat transport and from post-eruption sea ice dynamics, and (b) an anomalous surface winter warming emerging over the Scandinavian/Western Russian region around 10-12 years after a major eruption. The simulated long-term climate response to SVEs depends, to some extent, on background conditions. Consequently, ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post-eruption decadal evolution of NH regional winter climates.

Zanchettin, D.; Timmreck, C.; Graf, H.-F.; Rubino, A.; Lorenz, S.; Lohmann, K.; Krüger, K.; Jungclaus, J. H.

2012-07-01

157

Atmospheric Variability of CO2 impact on space observation Requirements  

NASA Astrophysics Data System (ADS)

If International governments are to reduce GHG levels by 80% by 2050, as recommended by most scientific bodies concerned with avoiding the most hazardous changes in climate, then massive investments in infrastructure and new technology will be required over the coming decades. Such an investment will be a huge commitment by governments and corporations, and while it will offer long-term dividends in lower energy costs, a healthier environment and averted additional global warming, the shear magnitude of upfront costs will drive a call for a monitoring and verification system. Such a system will be required to offer accountability to signatories of governing bodies, as well as, for the global public. Measuring the average global distribution of CO2 is straight forward, as exemplified by the long running station measurements managed by NOAA’s Global Monitoring Division that includes the longterm Keeling record. However, quantifying anthropogenic and natural source/sink distributions and atmospheric mixing have been much more difficult to constrain. And, yet, an accurate accounting of all anthropogenic source strengths is required for Global Treaty verification. The only way to accurately assess Global GHG emissions is to construct an integrated system of ground, air and space based observations with extensive chemical modeling capabilities. We look at the measurement requirements for the space based component of the solutions. To determine what space sensor performance requirements for ground resolution, coverage, and revisit, we have analyzed regional CO2 distributions and variability using NASA and NOAA aircraft flight campaigns. The results of our analysis are presented as variograms showing average spatial variability over several Northern Hemispheric regions. There are distinct regional differences with the starkest contrast between urban versus rural and Coastal Asia versus Coastal US. The results suggest specific consequences on what spatial and temporal requirements might need to be for space based observations.

Swanson, A. L.; Sen, B.; Newhart, L.; Segal, G.

2009-12-01

158

Diet restriction and ageing in the dog: major observations over two decades.  

PubMed

This report reviews decade two of the lifetime diet restriction study of the dog. Labrador retrievers (n 48) were paired at age 6 weeks by sex and weight within each of seven litters, and assigned randomly within the pair to control-feeding (CF) or 25 % diet restriction (DR). Feeding began at age 8 weeks. The same diet was fed to all dogs; only the quantity differed. Major lifetime observations included 1.8 years longer median lifespan among diet-restricted dogs, with delayed onset of late life diseases, especially osteoarthritis. Long-term DR did not negatively affect skeletal maturation, structure or metabolism. Among all dogs, high static fat mass and declining lean body mass predicted death, most strongly at 1 year prior. Fat mass above 25 % was associated with increasing insulin resistance, which independently predicted lifespan and chronic diseases. Metabolizable energy requirement/lean body mass most accurately explained energy metabolism due to diet restriction; diet-restricted dogs required 17 % less energy to maintain each lean kilogram. Metabonomics-based urine metabolite trajectories reflected DR-related differences, suggesting that signals from gut microbiota may be involved in the DR longevity and health responses. Independent of feeding group, increased hazard of earlier death was associated with lower lymphoproliferative responses to phytohaemagglutinin, concanavalin A, and pokeweed mitogen; lower total lymphocytes, T-cells, CD4 and CD8 cells; lower CD8 percentages and higher B-cell percentages. When diet group was taken into account, PWM responses and cell counts and percentages remained predictive of earlier death. PMID:18062831

Lawler, Dennis F; Larson, Brian T; Ballam, Joan M; Smith, Gail K; Biery, Darryl N; Evans, Richard H; Greeley, Elizabeth H; Segre, Mariangela; Stowe, Howard D; Kealy, Richard D

2007-12-06

159

RXTE Observations of Magnetic Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

Results from hard X-ray observations with RXTE of 5 Polar systems-V2301 Oph, V1432 Aql, EP Dra, GG Leo and V834 Cen, and an Intermediate Polar TV Col are presented. An improved ephemeris for V2301 Oph using mid-eclipse timings has been derived. V1432 Aql shows structured lightcurve containing several prominent peaks and dips. A likely eclipse of X-ray source in EP Dra is observed for the first time. The X-ray emission in EP Dra and GG Leo is found to be consistent with a single pole accretion. V 834 Cen was observed to be bright during 1996-1998, but was 16 times fainter during 2002 observations. The power spectrum of TV Col shows a significant power at frequencies corresponding to the spin period (1910s) and the binary period (5.5hr) and their side-bands, thereby suggesting that both the stream-fed and disk-fed accretion components are present in TV Col.

Rana, V. R.; Singh, K. P.

2003-03-01

160

FUSE Observations of Luminous Blue Variables  

NASA Astrophysics Data System (ADS)

P-Cygni, AG Carinae, S-Doradus and Eta Carinae were observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. FUSE covers the spectral range 905 to 1187 Angstroms at a resolution of 0.05 Angstroms. In this paper we explore in what way the LBV's are similar and in what way they are different. For Eta Car the observed flux at 1160 A, is 4E-12 erg/cm2/s/A. This is 20X larger than observed by STIS/E140M at the same wavelength through a 0.2"x0.2" aperture. The flux level declines toward the Lyman limit where converging molecular and atomic hydrogen features completely blanket the spectrum. The shape of the spectrum shortward of 1110 Angstroms is dominated by strong absorption bands of interstellar molecular hydrogen. In addition to many strong interstellar atomic species, the spectrum contains several prominent P-Cygni features, including C III 1175, S IV 1063-73, Si III 1113, and N I 1134. The lines are broad with unsaturated absorption troughs, implying that the wind is patchy and/or only partly covers the UV emitting surface. The wind absorption extends to -1000 km/s. The large far ultraviolet flux levels at 1150-1180 A, relative to those observed by HST/STIS, imply that the observed far-UV spectrum is formed in an extended 1-2 arcsec diameter UV scattering envelope. The far-UV spectra of P Cygni and AG Carinae are very similar and indicate a cooler atmosphere than Eta Car and S Dor. There is very good agreement between the FUSE spectrum of P Cygni and a model atmosphere computed by Hillier with his code CMFGEN. This work has been supported in part by NASA grants NAG5-8631 to Catholic University of America and NAS5-32985 to Johns Hopkins University.

Iping, R. C.; Sonneborn, G.

2001-12-01

161

Oxygen minimum zone of the open Arabian Sea: variability of oxygen and nitrite from daily to decadal time scales  

NASA Astrophysics Data System (ADS)

The oxygen minimum zone (OMZ) of the Arabian Sea is the thickest of the three oceanic OMZs, which is of global biogeochemical significance because of denitrification in the upper part leading to N2 and N2O production. The residence time of the OMZ water is believed to be less than a decade. The upper few hundred meters of this zone are nearly anoxic but non-sulfidic and still support animal (metazoan) pelagic life, possibly as a result of episodic injections of O2 by physical processes. The very low O2 values obtained with the new STOX sensor in the eastern tropical South Pacific probably also characterize the Arabian Sea OMZ, but there is no apparent reason as to why the temporal trends of the historic data should not hold. We report on discrete measurements of dissolved O2 and NO2-, besides temperature and salinity, made between 1959 and 2004 well below the tops of the sharp pycno- and oxyclines near 150, 200, 300, 400, and 500 m depth. We assemble nearly all O2 determinations (originally, 849 values, 695 in the OMZ) by the visual endpoint detection of the iodometric Winkler procedure, which in our data base yields about 0.04 mL L-1 (∼2 ?M) O2 above the endpoint from modern automated titration methods. We find 632 values acceptable (480 from 150 stations in the OMZ). The data are grouped in zonally-paired boxes of 1° lat. and 2° long. centered at 8°, 10°, 12°, 15°, 18°, 20°, and 21° N along 65° E and 67° E. The latitudes of 8-12° N, outside the OMZ, are only treated in passing. The principal results are as follows: (1) an O2 climatology for the upper OMZ reveals a marked seasonality at 200 to 500 m depth with O2 levels during the northeast monsoon and spring intermonsoon season elevated over those during the southwest monsoon season (median difference, 0.08 mL L-1 [3.5 ?M]). The medians of the slopes of the seasonal regressions of O2 on year for the NE and SW monsoon seasons are -0.0043 and -0.0019 mL L-1 a-1, respectively (-0.19 and -0.08 ?M a-1; n = 10 and 12, differing at p = 0.01); (2) four decades of statistically significant decreases of O2 between 15° and 20° N but a trend to a similar increase near 21° N are observed. The balance of the mechanisms that more or less annually maintain the O2 levels are still uncertain. At least between 300 and 500 m the annual reconstitution of the decrease is inferred to be due to lateral, isopycnal re-supply of O2, while at 200 (250?) m it is diapycnal, most likely by eddies. Similarly, recent models show large vertical advection of O2 well below the pycno-cum-oxycline. The spatial (within drift stations) and temporal (daily) variability in hydrography and chemistry is large also below the principal pycnocline. The seasonal change of hydrography is considerable even at 500 m. There is no trend in the redox environment for a quarter of a century at a GEOSECS station near 20° N. In the entire OMZ the slopes on year within seasons for the quite variable NO2- (taken as an indicator of active denitrification) do not show a clear pattern. Also, future O2 or nutrient budgets for the OMZ should not be based on single cruises or sections obtained during one season only. Steady state cannot be assumed any longer for the intermediate layers of the central Arabian Sea.

Banse, K.; Naqvi, S. W. A.; Narvekar, P. V.; Postel, J. R.; Jayakumar, D. A.

2013-09-01

162

Trend, decadal and interannual variability in annual rainfall of subequatorial and tropical North Africa (1900-1994)  

NASA Astrophysics Data System (ADS)

Annual rainfall anomalies over subequatorial and northern tropical Africa are analysed for interannual and interdecadal variability over the time interval 1900-1994. Then, the main modes of variation in the annual rainfall field are related to the same frequencies of variation in several SST indexes chosen in key-areas. First, empirical orthogonal function (EOF) analysis is performed on the annual rainfall anomalies field for extracting the main dominant spatio-temporal modes, and leading principal components are analysed through multi-singular spectrum analysis (M-SSA). Regional rainfall anomaly indices, constructed from EOF analysis and describing, respectively, the temporal variability of Sahel, Guinea Gulf area, equatorial East Africa and Gabon-Congo area, are analysed individually through Monte Carlo SSA for assessing the level of significance of spectral peaks. Low-frequency variability, strongest north of 5°N, is a combination of a non-linear trend mixed with an irregular oscillation near 25-40 years. Together, these modes contribute about 35-40 per cent of the Sahelian regional variance and about 15-20 per cent of the Guinean one. The low-frequency variability shows weak negative values till 1915-1920, then positive ones till 1967-1970, with a relative minimum near 1940-1945, and lastly, strong negative values. This behaviour must be placed in a larger context of at least Atlantic-basin scale, or at a global scale in which the strongest signal seems to be the reversing of the interhemispheric thermal gradient around 1970. A quasi-decadal pulse (near 12-13 years) is also observed over Sahel and explains about 12-14 per cent of the regional rainfall index variance. Even if associated SSA components are not significant when a red noise null-hypothesis is considered, some physical consistency is found between this mode and a similar oscillation concerning the thermal gradient between tropical northern and equatorial Atlantic. At the interannual scale, significant oscillations of 5.1-5.8 years (quasi-quinquennial oscillation - QQO) (contributing less than 5 per cent of the Sahelian variance to almost 20 per cent of the East African one), and of 3.2-3.6 years (quasi-triennial oscillation - QTO) (explaining from 5 to 10 per cent of the Sahelian variance to 20-25 per cent of the East African one) are the first ones before quasi-biennial oscillations (2.0-2.8 years) which explain in general less than 5 per cent of the variance and at maximum, near 10 per cent of the variance in Equatorial Africa. The QQO and QTO seem to be modulated frequencies of the same phenomenon connected to central and eastern tropical Pacific (CETP): (i) QQO, which is characterized by an out-of-phase pattern between East Africa (more/less rainfall than normal when CETP and western Indian Ocean is anomalously warm/cold) and central Africa seems to be associated mainly with in-phase behaviour between the CETP and western Indian Ocean. The relation is stable during the twentieth century; (ii) QTO, which is characterized by an in-phase pattern from East Africa to the Sahel (less/more rainfall when CETP is anomalously warm/cold) seems to be related only to CETP and this relation is strongest at the end of the period (after 1960-1970). Relationships between QQO and QTO of rainfall with the same oscillations of the Atlantic SST index are weak.

Moron, Vincent

1997-06-01

163

Interannual-to-decadal variability of the stratosphere during the 20th century: ensemble simulations with a chemistry-climate model  

Microsoft Academic Search

Interannual-to-decadal variability in stratospheric ozone and climate have a number of common sources, such as variations in solar irradiance, stratospheric aerosol loading due to volcanic eruptions, El Niño Southern Oscillation variability and the quasi-biennial oscillation (QBO). Currently available data records as well as model simulations addressing stratospheric chemical climate variability mostly cover only the past few decades, which is often

A. M. Fischer; M. Schraner; E. Rozanov; P. Kenzelmann; C. Schnadt Poberaj; D. Brunner; A. Lustenberger; B. P. Luo; G. E. Bodeker; T. Egorova; W. Schmutz; T. Peter; S. Brönnimann

2008-01-01

164

How does natural climate variability on decadal timescales affect timeseries analysis?  

NASA Astrophysics Data System (ADS)

The world meteorological organization (WMO) defined the classical length of climate analysis to be 30 years. Even if this definition allows the uniformity of climate studies, such 30 years period might not be appropriate for different reasons. One example is the presence of non-stationary processes in a time-serie such as the solar cycle or the NAO. Another example is the computational constraints inherent to convection resolving climate simulation that often results in shorter time period integrations. To identify the minimum length required for climate integrations, it is essential to know the uncertainty related to the natural climate variability. The objective of this study is to assess this uncertainty of using a time-limited period for climate analysis with an application to precipitation in Belgium. The precipitation weather generator approach is used for the production of synthetic time-series from which the time-average and the return value are derived. The weather generator integrates three main components, i) a 5th order Markov that models the occurrence of dry, wet and extremely wet days, ii) a gamma generalized linear model that reproduces the amplitude of wet events and iii) a gamma Pareto generalized linear model that reproduces the amplitude of extreme events. These three models use quasi-periodic signal derived from an empirical mode decomposition analysis, as predictors to reproduce cycle signal such as solar cycle, NAO, ENSO, etc... From these models 10000 synthetic time-series are produced allowing the derivation of the uncertainty of the time-averaged and the return value of precipitation. This method has been applied to evaluate the uncertainty related to natural climate variability over a 10 years period. It was found that it represents 10% and 20% of respectively the time-averaged and the return value of daily precipitation in Belgium.

Brisson, E.; van Lipzig, N. P. M.

2012-04-01

165

Multi-decadal variability of ice extent in the Barents Sea  

Microsoft Academic Search

The European Arctic has been explored and commercially exploited for more than 400 years. In 1596, Willem Barentsz sailed the northern Barents Sea reporting on sea-ice extent and on the large number of whales found along the ice edge. By the early 17th century, an extensive and sophisticated whaling industry had developed in northern Spitzbergen. The whale hunters systematically observed

T. Vinje; R. Colony

2003-01-01

166

Multi-decadal-scale records of North Atlantic climate variability during the last and present interglacials and preceding glacial terminations.  

NASA Astrophysics Data System (ADS)

High-resolution records of natural interglacial climate variability can provide knowledge if the currently ongoing climate change and variability are part of or are already beyond the natural state. Warmer-than-present climatic conditions, a reduced Greenland Ice Sheet and higher sea level are some of the features the Last Interglacial (LIG, MIS5e; 129-115 kyr) climate has in common with numerous model projections of our future climate (Otto-Bliesner et al., 2006; Koop et al., 2009). Establishing multi-decadal resolution records of past North Atlantic climate variability hence contributes to a better understanding of the ocean and climate sensitivity of the wider North Atlantic region. We present palaeoceanographic time series of surface ocean climatology from Ocean Drilling Program (ODP) Site 976 in the Alboran Sea, westernmost Mediterranean that span the LIG and Present Interglacial (PIG, Holocene, 11-0 kyr). The site receives North Atlantic climate signals through the atmosphere and with the advection of Atlantic inflow waters which in connection with the high rate of sediment deposition underscores the exceptional quality of the site to monitor North Atlantic climate variability at multi-decadal resolution (60-90 yrs). Sea surface temperature (SST) time series derived from Mg/Ca ratios and stable isotope records (?18O, ?13C) of the planktonic foraminifera Globigerina bulloides are presented. Mg/Ca data display similar SST for the climatic optima PIG and LIG. The records compare well with speleothem and ice core palaeoclimatic profiles, confirming that Site 976 palaeo-profiles reflect climate of the North Atlantic region. The close link between SSTMg-Caand the LIG ?18O record from the Antro del Corchia speleothem in northern Italy highlights the strong connection between marine and terrestrial climatology during that time indicating a farfield contribution of atmospheric signals. Comparison with SST and benthic ?13C records at North Atlantic sites instructs on regional climatological offsets and AMOC stability and variability. Correlation with atmospheric data (ice core palaeo-CO2, ?13Catm) links the North Atlantic climate variability documented in Site 976 with ocean-to-air gas exchanges that were driven by AMOC variability. This is a contribution of the European Commission FP7 Collaborative Project "Past4Future".

Jimenez-Amat, Patricia; Zahn, Rainer

2013-04-01

167

Long-term trend and decadal variability of the southward penetration of the East Australian Current  

NASA Astrophysics Data System (ADS)

Observations from a long-term ocean station off eastern Tasmania show that the southward penetration of the East Australian Current (EAC) has increased over the past 60 years. Changes in temperature and salinity are highly correlated at timescales greater than seasonal, with long-term trends which differ markedly from global ocean values. The data show that the region has become both warmer and saltier with mean trends of 2.28°C/century and 0.34 psu/century over the 1944-2002 period which corresponds to a poleward advance of the EAC of ~350-km. These trends are not directly forced by global surface fluxes but primarily result from changes in the EAC. The summertime trends in temperature and salinity are greater than in winter - there is an augmented summer pulse of warm, high salinity subtropical water associated with the EAC.

Ridgway, K. R.

2007-07-01

168

Decadal changes in surface air temperature variability and cold surge characteristics over northeast Asia and their relation with the Arctic Oscillation for the past three decades (1979-2011)  

NASA Astrophysics Data System (ADS)

Decadal changes in surface air temperature (SAT) variability and cold surge characteristics over Northeast Asia during late winter (January-March) are analyzed for the past three decades. Power spectrum analysis of SAT reveals that the low-frequency variabilities with a period longer than 10 days are significantly enhanced, while the high-frequency variabilities with a period shorter than 10 days are weakened in the 1980s and 2000s. Moreover, cold surges were stronger and lasted longer during the 1980s and 2000s compared to those that occurred in the 1990s. Here, we propose that large-scale atmospheric conditions manifested by a different phase of the Arctic Oscillation (AO) provide preconditioning for a cold surge event, which showed a prominent decadal fluctuation. The more (less) frequent strong and long-lasting cold surge occurrences in the 1980s and 2000s (1990s) are preceded by the more dominant negative (positive) phase of the AO. Lag-composite analyses for cold surge events categorized by the AO phases indicate that stronger and longer-lasting cold air advection dominates at the lower-level, when upper-level wave train and coastal trough are developed over East Asia under the strong negative AO phase. These results suggest that the decadal changes in SAT variability and cold surge characteristics are strongly associated with the decadal changes in the phase distribution of the AO.

Woo, Sung-Ho; Kim, Baek-Min; Jeong, Jee-Hoon; Kim, Seong-Joong; Lim, Gyu-Ho

2012-09-01

169

Coupled decadal variability of the North Atlantic Oscillation, regional rainfall and karst spring discharges in the Campania region (southern Italy)  

NASA Astrophysics Data System (ADS)

Thus far, studies on climate change have focused mainly on the variability of the atmospheric and surface components of the hydrologic cycle, investigating the impact of this variability on the environment, especially with respect to the risks of desertification, droughts and floods. Conversely, the impacts of climate change on the recharge of aquifers and on the variability of groundwater flow have been less investigated, especially in Mediterranean karst areas whose water supply systems depend heavily upon groundwater exploitation. In this paper, long-term climatic variability and its influence on groundwater recharge were analysed by examining decadal patterns of precipitation, air temperature and spring discharges in the Campania region (southern Italy), coupled with the North Atlantic Oscillation (NAO). The time series of precipitation and air temperature were gathered over 90 yr, from 1921 to 2010, using 18 rain gauges and 9 air temperature stations with the most continuous functioning. The time series of the winter NAO index and of the discharges of 3 karst springs, selected from those feeding the major aqueducts systems, were collected for the same period. Regional normalised indexes of the precipitation, air temperature and karst spring discharges were calculated, and different methods were applied to analyse the related time series, including long-term trend analysis using smoothing numerical techniques, cross-correlation and Fourier analysis. The investigation of the normalised indexes highlighted the existence of long-term complex periodicities, from 2 to more than 30 yr, with differences in average values of up to approximately ±30% for precipitation and karst spring discharges, which were both strongly correlated with the winter NAO index. Although the effects of the North Atlantic Oscillation (NAO) had already been demonstrated in the long-term precipitation and streamflow patterns of different European countries and Mediterranean areas, the results of this study allow for the establishment of a link between a large-scale atmospheric cycle and the groundwater recharge of carbonate karst aquifers. Consequently, the winter NAO index could also be considered as a proxy to forecast the decadal variability of groundwater flow in Mediterranean karst areas.

De Vita, P.; Allocca, V.; Manna, F.; Fabbrocino, S.

2012-05-01

170

Late Holocene (0-1.2 ka BP) centennial to decadal time scales surface and deep water variability in the North Atlantic  

NASA Astrophysics Data System (ADS)

The subpolar North Atlantic is a key region for understanding climate variability, as it is one of the world's main localities of deepwater formation. On decadal to multidecadal time-scales two interrelated modes of natural climate variability have been identified that contribute to changes observed in the recent North Atlantic climate system (mostly through their impact on the Atlantic Meridional Overturning Circulation, AMOC): the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO). The Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) have often been highlighted as a good example of the impact of climate oscillations on society. Although the causality of these intervals still remains controversial, a commonly cited explanation is a weak solar trigger which was amplified and transmitted globally through positive feedbacks, possibly including some internal climatic modes (such as the NAO/AMO) and the AMOC. In this study, sediment cores RAPiD-35-25B and RAPiD-17-5P recovered from the Eirik Drift (south of Greenland) and Björn Drift (Iceland Basin) respectively, are used to produce multi-proxy reconstructions of some of the main constituents of the AMOC at sub-decadal to multidecadal resolution during the last 1.2 ka BP. Near-bottom flow speed reconstructions based on the sortable silt mean grain size proxy show multidecadal variability in both of the Nordic Overflows. In particular, the Iceland Scotland Overflow Water vigour presents a range of decadal to centennial periodicities similar to the AMO (55 years) and deVries solar cycles (200 years). Additionally, surface water reconstructions from multi-species planktonic foraminiferal ?18O, Mg/Ca and assemblage counts reveal changes in the properties of the North Atlantic Current and summer season stratification of the upper water column in the Eastern Labrador Sea, with a possible common link to changes in Subpolar Gyre dynamics. As yet, no clear consensus has emerged as to the processes and mechanisms that govern Late Holocene climate variability at decadal to cenntennial time scales and such understanding remains essential to reduce uncertainty in climate prediction under anthropogenic forcing.

Moffa Sanchez, P.; Hall, I. R.; Barker, S.; Thornalley, D. J.

2011-12-01

171

The Recognition of Multi-Decadal Scale Climate Variability in the Paleo-record over the Past 1000 Years  

NASA Astrophysics Data System (ADS)

Proxy reconstructions of climate from tree rings, corals, stalagmites, sclerosponges, and deep-sea sediments show multi-decadal climate variability preserved in records extending back at least 1000 years. Most of these records appear to show a strong correlation with indices such as the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO) over the period of the instrumental record (~1850-present). The repeated recognition of these signals in a number of different archives and geographical locations throughout the Atlantic (Cape Verde Islands, Gulf of Guinea, Puerto Rico, Cariaco Basin , South Florida, and the Bahamas) strongly suggests that these signals are real and have climatic significance. The AMO and NAO climate signals are manifested in these indices through (i) the direct effect of water temperature and salinity on the growth rate of trees and corals and (ii) temperature and salinity influences on the incorporation of geochemical proxies, such as the Mg/Ca, Sr/Ca, and oxygen isotopic ratios, into the skeletons of different carbonate producing organisms. In many areas these relationships are complex and there is often considerable local variability in the response of corals and trees, particularly in the growth rate related parameters. Prior to the instrumental period, the tree-ring index compiled by (Gray et al., 2004, GRL,31) has been taken as the principal reconstruction of the AMO. While most of the marine records examined appear to correlate with the tree-ring record during the instrumental period, there are significant discrepancies prior to 1850. This raises many questions about the stationarity and persistence of the AMO and the suitability of individual archives such as tree rings for these modes.

Swart, Peter; Waite, Amanda; Rosenheim, Brad; Moses, Chris

2010-05-01

172

Long-Term Solar Irradiance Variability: 1984-1989 Observations.  

National Technical Information Service (NTIS)

Long-term variability in the total solar irradiance has been observed in the Earth Radiation Budget Experiment (ERBE) solar monitor measurements. The monitors have been used to measure the irradiance from the Earth Radiation Budget Satellite (ERBS) and th...

R. B. Lee

1990-01-01

173

Einstein X-ray observations of cataclysmic variables  

SciTech Connect

Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.

Mason, K.O.; Cordova, F.A.

1982-01-01

174

GALEX observations of quasar variability in the ultraviolet  

NASA Astrophysics Data System (ADS)

Aims: Using archival observations recorded over a 5+ year timeframe with the NASA GALaxy Evolution eXplorer (GALEX) satellite, we present a study of the ultraviolet (UV) variability of 4360 quasars of redshifts up to z = 2.5 that have optical counterparts in the Sloan Digital Sky Survey DR5 spectroscopic catalog of Schneider et al. (2007, AJ, 134, 102). The observed changes in both the far UV (FUV: 1350-1785 Å) and near UV (NUV: 1770-2830 Å) AB magnitudes as a function of time may help differentiate between models of the emission mechanisms thought to operate in these active galaxies. Methods: A list of NUV and FUV variable quasars was derived from the UV light-curves of sources with 5 or more observational visits by GALEX that spanned a time-frame > 3 months. By measuring the error in the derived mean UV magnitude from the series of GALEX observations for each source, quasars whose UV variability was greater than the 3-? variance from the mean observed value were deemed to be (intrinsically) UV variable. This conservative selection criterion (which was applied to both FUV and NUV observations) resulted in identifying 550 NUV and 371 FUV quasars as being statistically significant UV variable objects. Results: Following the work of Vanden Berk et al. (2004, ApJ, 601, 692), we have performed a structure function (SF) analysis of these data to search for possible correlations between UV variability and parameters such as rest frame time-lag, redshift, luminosity and radio loudness. Firstly, we observe that the amplitudes of variability as a function of time-lag for both the NUV and FUV data are far larger than those observed at visible wavelengths. Secondly, the levels of FUV variability are greater than those observed in the NUV for a given value of time-lag. Also, the amplitudes of both the NUV and FUV variability of quasars increase as a function of rest frame time-lag, irrespective of the value of quasar redshift, for time-lags <200 days. For time-lags >300 days there is a pronounced rollover in the NUV SF for all redshift values, which is also observed (with a lower signiÞcance) in the FUV variability data. Although we find no strong relationship between UV variability and redshift, our data do show that higher redshift quasars appear to be more variable than their low redshift counterparts. Our data also show that, for all values of time-lag, the more luminous quasars tend to be slightly less UV variable, with perhaps the exception of FUV variable quasars for short time-lags. Although our data sample is small, we find that radio-loud quasars are marginally more variable than radio quiet ones by a factor ~2 in the NUV and by a factor 1 - 3 in the FUV. Therefore, our present observations support the notion in which the radio properties of quasars have a limited influence on the observed UV variability of these objects. In summation, our present analysis favors a quasar model in which UV variability is mainly due to stochastic changes in the underlying continuum level, rather than models that favor gravitational microlensing or discrete-event processes.

Welsh, B. Y.; Wheatley, J. M.; Neil, J. D.

2011-03-01

175

More Bang for the Buck: Lessons from a Decade of Keck Mainland Observing Operations  

NASA Astrophysics Data System (ADS)

Most astronomers love observing remotely because they can gather their data while avoiding the inconvenience of traveling to the telescope; however, running a true, facility-class remote observing system can impose a significant burden on the observatory support staff. Although usage of the remote observing capability at Hawaii's W. M. Keck Observatory has risen substantially in the nine years since we began allowing astronomers to observe from California and elsewhere, Keck's system has evolved over time to provide better operational performance with less manpower. This talk will describe improvements to our system in several key areas: scheduling remote observing requests; maintaining the virtual servers used by remote observers; monitoring the health and safety of equipment at remote observing stations; and abandoning the distinction between "local" and "remote" observing. These measures have substantially lessened the effort required to operate the system, provided new capabilities for training and troubleshooting by the technical staff, and enhanced the convenience and reliability of the system for observers and support staff at the remote sites.

Wirth, Gregory D.; Kibrick, Robert I.; Goodrich, Robert W.; Lyke, James E.; Mader, Jeff A.

2011-03-01

176

A Decade of Global CO2 Observations from the Satellite Instrument SCIAMACHY  

NASA Astrophysics Data System (ADS)

CO2 is the most important anthropogenic greenhouse gas. Its global increasing concentration in the Earth's atmosphere is the main driver for global warming. However, in spite of its importance, there are still large uncertainties on its sources and sinks: What is their global distribution? What is their temporal evolution? How will they behave in a changing climate? Satellite measurements, if accurate and precise enough, have the potential to reduce such surface flux uncertainties. SCIAMACHY started its operation in 2002 with the launch of ENVISAT. Roughly one decade later ESA declared end of the mission due to the unexpected loss of ENVISAT. SCIAMACHY was the first and during seven years the only satellite instruments which was able to measure the CO2 mixing ratio (XCO2) with large sensitivity also in the boundary layer. Therefore, SCIAMACHY measurements are essential to create a consistent long term climate data record of XCO2 measurements. We will present two datasets (WFMD and BESD) each of which covering the full SCIAMACHY time series. Analyses of the datasets in respect to land-atmosphere interactions and long term trends will be part of the presentation.

Reuter, Maximilian; Schneising, Oliver; Hilker, Michael; Buchwitz, Michael; Heymann, Jens; Bovensmann, Heinrich; Burrows, John P.

2013-04-01

177

Decadal variability of rainfall in the Sahel: results from the coupled GENESIS-IBIS atmosphere-biosphere model  

Microsoft Academic Search

In this study we investigate the impact of large-scale oceanic forcing and local vegetation feedback on the variability of the Sahel rainfall using a global biosphere-atmosphere model, the coupled GENESIS-IBIS model, running at two different resolutions. The observed global sea surface temperature in the twentieth century is used as the primary model forcing. Using this coupled global model, we experiment

G. Wang; E. A. B. Eltahir; J. A. Foley; D. Pollard; S. Levis

2004-01-01

178

Multi-decadal variability and trends in the temperature of the northwest European continental shelf: A model-data synthesis  

NASA Astrophysics Data System (ADS)

We examine the trends and variability in temperature of the northwest European shelf seas over the period 1960-2004 using four approaches: a regional model simulation (using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System; POLCOMS), in situ multi-annual timeseries observations, satellite remote sensed (AVHRR) sea surface temperature (SST), and an analysis of data held in an international database at the International Council for the Exploration of the Sea (ICES). We focus on variability for the full period and trends from 1985 to 2004, being limited by the length of model simulation and the availability of satellite data. We find that all data sources give a consistent picture, with both trends and variability being intensified on-shelf and north of ˜48°N. The model and AVHRR SST show statistically significant warming trends in large areas of this region that are clearly distinguishable from both model/observation error and natural variability on these timescales. This 'signal to noise ratio' is substantially reduced when near bottom temperatures are considered in the model. The long timeseries at Port Erin (Isle of Man) shows that the variation in trend is well represented by the model and that the warming trend in the period 1985-2004 is substantially larger and of longer duration than previous peaks in 20-year trends since 1914.We find that the SST trends are greater in the model and satellite observations than the air temperature trends in the ERA40 re-analysis used for forcing; the net sea to air heat flux is ˜20% less in 1985-2004 than 1960-1984 (including shortwave, longwave, sensible and latent components). This is partly compensated by a ˜9% reduction in advective warming. The model shows the trends in seasonally stratified regions are greater at the surface than at depth, indicating an increase in this stratification. While this pattern is also seen in the annual trends from the ICES data analysis, the lack of seasonal resolution hampers a quantitative corroboration.The model is seen to have good skill in reproducing both the trends and variability, but tends to underestimate the trends. The modelled variability is overestimated in some coastal and open ocean regions and underestimated elsewhere, while the phase of this variability is generally well represented. Generally the model performance is better on-shelf than in the open ocean.

Holt, Jason; Hughes, Sarah; Hopkins, Joanne; Wakelin, Sarah L.; Penny Holliday, N.; Dye, Stephen; González-Pola, César; Hjøllo, Solfrid Sætre; Mork, Kjell Arne; Nolan, Glen; Proctor, Roger; Read, Jane; Shammon, Theresa; Sherwin, Toby; Smyth, Tim; Tattersall, Graham; Ward, Ben; Wiltshire, Karen Helen

2012-11-01

179

A decade-long climatology of terdiurnal tides using TIMED/SABER observations  

NASA Astrophysics Data System (ADS)

In this paper, we globally characterize the solar terdiurnal tide in the 80-110 km region of Earth's atmosphere through analysis of 10 years of temperature measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics spacecraft. The Sun-synchronous ("migrating") component (TW3), which is longitude-independent and achieves maximum amplitudes of order of 5 K (10 K) at 90 km (110 km), not too different than the 7-15 K amplitudes that are typical of the migrating diurnal and semidiurnal tides in this region. Significant longitude variability (˜ 20-25%) in terdiurnal temperature amplitudes also exists, which is decomposed into zonal wave number components. The largest of these (TE1, TW4, and TW5) reveal distinct seasonal-latitudinal and height versus latitude patterns and interannual consistency. In addition, it is demonstrated that these particular components vary in ways that suggest that they originate from nonlinear interactions between diurnal and semidiurnal tides, specifically between DE3 and SW2 for TE1, between DW2 and SW2 for TW4, and between DW1 and SW4 for TW5. We also demonstrate that the terdiurnal tides derived here are not influenced to any significant degree by aliasing due to the presence of other waves.

Moudden, Y.; Forbes, J. M.

2013-07-01

180

A likelihood-based comparison of CMIP5 decadal experiment runs with observations from the Atmospheric Infrared Sounder  

NASA Astrophysics Data System (ADS)

In Braverman, Cressie, and Teixeira (2011) we introduced a new method for assessing the consistency between climate model simulations and observational time series. The method uses a moving-block bootstrap to simulate the probability density function (pdf) of a statistic from a model-generated time series. The pdf evaluated at the value of a statistic computed from the observations can be thought of as an empirical likelihood. If the climate models are all considered to be equally likely a priori, then posterior probabilities of the models given the observational statistics are proportional to the likelihoods. These posterior probabilities given an indication of which models are most consistent with the observed data record. We have applied this method to CNRM-CM5 and CanCM4 runs from the CMIP5 decadal experiment suite using observations from NASA's AIRS instrument. In this talk, we report the results of these comparisons.

Braverman, A. J.; Cressie, N.; Teixeira, J.

2011-12-01

181

Bimodality, regime shifts, and decadal variability in the QBO and the NH stratospheric winter vortex as seen in model ensembles.  

NASA Astrophysics Data System (ADS)

The stratospheric Northern Hemisphere (NH) winter mean vortex alternates between a strong and a weak state which is manifested in a statistically significant bimodal distribution. In the end of the 1970s a regime change took place increasing the probability of the strong phase relative to the weak phase (Christiansen 2003). Christiansen (2010) found a strong coincidence between strong (weak) vortex winters and the westerly (easterly) QBO phase. This work also demonstrated that the change of the vortex in the late 1970s can be related to a change in the QBO. However, this change in the QBO can be random process simply related to the annual sampling of the QBO. In this paper we investigate the connection between the decadal variability of the vortex and the QBO in historical CMIP5 and CCMVal2 experiments. The CMIP5 archive contains both models with and without a spontaneously generated QBO. Additionally, the CCMVal2 archive includes models with prescribed QBOs. Preliminary results indicate that models with prescribed or spontaneously generated QBOs do show realistic bimodal behaviour of the QBO. While the strength of the variability of the vortex in the models is realistic there is in general little bimodality. We also find that the connection between QBO and the NH vortex is weaker in the models than in the reanalysis. References: Christiansen, B., Evidence for nonlinear climate change: Two stratospheric regimes and a regime shift. J. Climate, 16, 3681-3689, 2003. Christiansen, B., Stratospheric bimodality: Can the equatorial QBO explain the regime behavior of the NH winter vortex? J. Climate, 23, 3953-3966, 2010.

Christiansen, Bo

2013-04-01

182

Coupled decadal variability of the North Atlantic Oscillation, regional rainfall and spring discharges in the Campania region (Southern Italy)  

NASA Astrophysics Data System (ADS)

Climate change is one of the issues most debated by the scientific community with a special focus to the combined effects of anthropogenic modifications of the atmosphere and the natural climatic cycles. Various scenarios have been formulated in order to forecast the global atmospheric circulation and consequently the variability of the global distribution of air temperature and rainfall. The effects of climate change have been analysed with respect to the risks of desertification, droughts and floods, remaining mainly limited to the atmospheric and surface components of the hydrologic cycle. Consequently the impact of the climate change on the recharge of regional aquifers and on the groundwater circulation is still a challenging topic especially in those areas whose aqueduct systems depend basically on springs or wells, such as the Campania region (Southern Italy). In order to analyse the long-term climatic variability and its influence on groundwater circulation, we analysed decadal patterns of precipitation, air temperature and spring discharges in the Campania region (Southern Italy), coupled with the North Atlantic Oscillation (NAO). The time series of precipitation and air temperature were gathered over 90 yr, in the period from 1921 to 2010, choosing 18 rain gauges and 9 air temperature stations among those with the most continuous functioning as well as arranged in a homogeneous spatial distribution. Moreover, for the same period, we gathered the time series of the winter NAO index (December to March mean) and of the discharges of the Sanità spring, belonging to an extended carbonate aquifer (Cervialto Mount) located in the central-eastern area of the Campania region, as well as of two other shorter time series of spring discharges. The hydrogeological features of this aquifer, its relevance due to the feeding of an important regional aqueduct system, as well as the unique availability of a long-lasting time series of spring discharges, allowed us to consider it as an ideal test site, representative of the other carbonate aquifers in the Campania region. The time series of regional normalised indexes of mean annual precipitation, mean annual air temperature and mean annual effective precipitation, as well as the time series of the normalised annual discharge index were calculated. Different methods were applied to analyse the time series: long-term trend analysis, through smoothing numerical techniques, cross-correlation and Fourier analysis. The investigation of the normalised indexes has highlighted long-term complex periodicities, strongly correlated with the winter NAO index. Moreover, we also found robust correlations among precipitation indexes and the annual discharge index, as well as between the latter and the NAO index itself. Although the effects of the North Atlantic Oscillation had already been proved on long-term precipitation and streamflow patterns of different European countries and Mediterranean areas, the results obtained appear original because they establish a link between a large-scale atmospheric cycle and the groundwater circulation of regional aquifers. Therefore, we demonstrated that the winter NAO index can be considered as an effective proxy to forecast the decadal variability of groundwater circulation in Mediterranean areas and in estimating critical scenarios for the feeding of aqueduct systems.

de Vita, P.; Allocca, V.; Manna, F.; Fabbrocino, S.

2011-12-01

183

Observations of Acidification in the Weddell Sea on a Decadal Time Scale  

NASA Astrophysics Data System (ADS)

The amount of anthropogenic CO2 (Cant) that entered the Weddell Sea between 1992 and 2008 is assessed using the extended multiple linear regression method (eMLR). Two multiple linear regressions for total dissolved inorganic carbon (CT) were conducted independently for two data sets from 1992 and 2008. Subtracting these two relations leads to an estimate of anthropogenic carbon (?CT) accumulated in the considered time span assuming that the underlying natural correlations between the input parameters and CT do not change with time. In the Warm Deep Water (WDW) and in the Weddell Sea Bottom Water (WSBW) ?CT values are insignificant, whereas values as high as 8~?mol kg-1 are observed at the shelf. ?CT concentrations in the surface layer vary with latitude between 2 and 11~?mol kg-1. Weak intrusion of anthropogenic CO2 into Weddell Sea Deep Water (WSDW) was demonstrated, ?CT yields 1.5 - 2~?mol kg-1. That more Cant is found in the WSDW than in the WSBW is surprising, but can be explained by the more intense ventilation of the WSDW from east of the Weddell Gyre. The invasion of Cant provokes a shift in the equilibria of the carbonate system, resulting in acidification and reduction of CO32-. The mean decrease of pH in the upper 200~m layer is 0.016. Further effects are decrease of the calcite and aragonite saturation states. Our results indicate a slower decrease of aragonite of surface waters in the Weddell Sea than recent model-based estimates.

Hauck, J.; Hoppema, M.; Völker, C.; Bellerby, R. G.; Wolf-Gladrow, D.

2008-12-01

184

Observed climate variability and change in Urmia Lake Basin, Iran  

NASA Astrophysics Data System (ADS)

This paper analyzes climate variability and change in the Urmia Lake Basin, northwest of Iran. Annual average of the following data time series has been analyzed by statistical methods: dry bulb temperature, maximum and minimum temperature, precipitation, and number of rainy and snowy days. We have also used mean monthly temperature and precipitation data for analysis of drought spells for the period 1964-2005 to find out whether fluctuations in the lake level are attributable to natural drought. Our results indicate that mean precipitation has decreased by 9.2 % and the average maximum temperature has increased by 0.8°C over these four decades. The seasonal changes are particularly visible in winter and spring. Results of the Palmer Drought Severity Index show that on average, drought episodes have hit the Urmia Lake Basin every 5 years and most of them reached severe levels, but recent droughts have become more intense and last longer.

Delju, A. H.; Ceylan, A.; Piguet, E.; Rebetez, M.

2013-01-01

185

Observing Blazar Variability: The GTN-AAVSO Collaboration  

Microsoft Academic Search

The NASA\\/EPO group at Sonoma State University is creating the GLAST Ground-Based Telescope Network (GTN). The GTN is a series of telescopes and observers which will support the science and education goals of NASA's Gamma-Ray Large Area Space Telescope. The GTN is a collaboration with the American Association of Variable Star Observers (AAVSO), other amateurs, schools, and professionals. GLAST will

G. Spear; A. Price; P. Plait; T. Graves; L. Cominsky; J. Mattei

2004-01-01

186

Einstein X-Ray Observations of Cataclysmic Variables.  

National Technical Information Service (NTIS)

Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrum...

K. O. Mason F. A. Cordova

1982-01-01

187

High nutrient pulses, tidal mixing and biological response in a small California estuary: Variability in nutrient concentrations from decadal to hourly time scales  

Microsoft Academic Search

Elkhorn Slough is a small estuary in Central California, where nutrient inputs are dominated by runoff from agricultural row crops, a golf course, and residential development. We examined the variability in nutrient concentrations from decadal to hourly time scales in Elkhorn Slough to compare forcing by physical and biological factors. Hourly data were collected using in situ nitrate analyzers and

Jane M. Caffrey; Thomas P. Chapin; Hans W. Jannasch; John C. Haskins

2007-01-01

188

Spatio-temporal variability in Ebro river basin (NE Spain): Global SST as potential source of predictability on decadal time scales  

NASA Astrophysics Data System (ADS)

Spatio-temporal variability and predictability in Ebro river basin is investigated. Basque-Cantabrian, Pyrenees and Southern Mediterranean regions are differentiated. At decadal time scales SST anomalies are a significant source of predictability for the streamflow. At interannual time scales ARMA modelling provides potential skill in forecasting. Basin-specific hydroclimatic predictions are provided for the Ebro River.

Gámiz-Fortis, S. R.; Hidalgo-Muñoz, J. M.; Argüeso, D.; Esteban-Parra, M. J.; Castro-Díez, Y.

2011-11-01

189

Dynamics and variability of the plasmasphere observed from synchronous orbit  

SciTech Connect

The behavior of the cold ions in the outer plasmasphere is studied using data obtained with the magnetospheric plasma analyzers from multiple geosynchronous satellites. Dense (10-100 cm{sup {minus}3}), cold ({approx}1 eV) regions of plasma are often observed at geosynchronous orbit; in this study the authors refer to these as plasmaspheric intervals. The duration, local time of observation, density variability, and temperature behavior within these regions often depend in a systematic way on geomagnetic and substorm activity. With increasing geomagnetic activity (as indicated by Kp) the plasmaspheric regions are generally observed over shorter durations and at earlier local times. With increasing substorm activity (as indicated by geosynchronous energetic electron injections) the density becomes increasingly variable in these regions. Occasionally, up to order-of-magnitude density variations are observed over several minute timescales corresponding to regions with physical dimensions on the order of 1000 km or less. The appearance of these short-duration, cold-plasma intervals is strongly correlated with energetic ion and electron signatures both at the spacecraft making the plasmaspheric observations and at other spacecraft observing simultaneously in the midnight region. Such energetic particle signatures are indicative of the growth and expansive phase of geomagnetic substorms. The authors conclude that the appearance of these short-duration, plasmaspheric intervals is due to a reconfiguration of the duskside magnetosphere during geomagnetic substorms.

Moldwin, M.B.; Thomsen, M.F.; McComas, D.J.; Reeves, G.D.

1994-11-01

190

Low-frequency eddy modulations in the Hawaiian Lee Countercurrent: Observations and connection to the Pacific Decadal Oscillation  

NASA Astrophysics Data System (ADS)

Interannual-to-decadal time scale eddy variability in the Hawaiian Lee Countercurrent (HLCC) band is investigated using the available sea surface height, sea surface temperature, and surface wind stress data sets. In the HLCC band of 17°N-21.7°N and 170E°-160°W, the prevailing interannual eddy kinetic energy (EKE) signals show enhanced eddy activities in 1993-1998 and 2002-2006, and subpar eddy activities in 1999-2001 and 2007-2009. These interannual EKE signals exhibit little connection to the zonal HLCC velocity changes generated by the dipolar wind stress curl forcing in the immediate lee of the island of Hawaii. Instead, they are highly correlated to the time series of the Pacific Decadal Oscillation (PDO) index. Through a budget analysis for the meridional temperature gradient along the HLCC, we find that during the positive phase of the PDO index, the surface heat flux forcing induces cold (warm) sea surface temperature (SST) anomalies to the north (south) of the HLCC, intensifying the vertical shear between the surface, eastward-flowing HLCC and the subsurface, westward-flowing North Equatorial Current (NEC). This increased vertical shear enhances the baroclinic instability of the HLCC-NEC system and leads to a higher regional EKE level. The opposite processes occur when the PDO switches to a negative phase with the resulting lowered EKE level along the HLCC band. Compared to the surface heat flux forcing, the Ekman flux convergence forcing is found to play a minor role in modifying the meridional SST changes along the HLCC band.

Yoshida, Sachiko; Qiu, Bo; Hacker, Peter

2011-12-01

191

Decadal time scale variability recorded in the Quelccaya summit ice core ?18O isotopic ratio series and its relation with the sea surface temperature  

NASA Astrophysics Data System (ADS)

The spectral characteristics of the ?18O isotopic ratio time series of the Quelccaya ice cap summit core are investigated with the multi taper method (MTM), the singular spectrum analysis (SSA) and the wavelet transform (WT) techniques for the 500 y long 1485-1984 period. The most significant (at the 99.8% level) cycle according to the MTM F-test has a period centered at 14.4 y while the largest variance explaining oscillation according to the SSA technique has a period centered at 12.9 y. The stability over time of these periods is investigated by performing evolutive MTM and SSA on the 500 y long ?18O series with a 100 y wide moving window. It is shown that the cycles with largest amplitude and that the oscillations with largest extracting variance have corresponding periods aggregated around 13.5 y that are very stable over the period between 1485 and 1984. The WT of the same isotopic time series reveals the existence of a main oscillation around 12 y which are also very stable in time. The relation between the isotopic data at Quelccaya and the annual sea surface temperature (SST) field anomalies is then evaluated for the overlapping 1919-1984 period. Significant global correlation and significant coherency at 12.1 y are found between the isotopic series and the annual global sea surface temperature (GSST) series. Moreover, the correlation between the low (over 8 y) frequency component of the isotopic time series and the annual SST field point out significant values in the tropical North Atlantic. This region is characterized by a main SST variability at 12.8 y. The Quelccaya ?18O isotopic ratio series may therefore be considered as a good recorder of the tropical North Atlantic SSTs. This may be explained by the following mechanism: the water vapor amount evaporated by the tropical North Atlantic is function of the SST. So is the water vapor ?18O isotopic ratio. This water vapor is advected during the rainy season by northeast winds and precipitates at the Quelccaya summit with its tropical North Atlantic isotopic signature. It is also suggested from this described stability of the decadal time scale variability observed in the Quelccaya isotopic series, that the decadal time scale GSST variability was also stable during the last five centuries.

Mélice, J. L.; Roucou, P.

192

Anne S. Young: Professor and Variable Star Observer Extraordinaire  

NASA Astrophysics Data System (ADS)

One of the original eight members of the AAVSO, but not well known today, was Professor Anne Sewell Young of Mount Holyoke College. Miss Young taught there for thirty-seven years, and trained many women astronomers during the first third of the 20th century. This paper will attempt to present her life as an inspiring teacher, as well as a contributor of more than 6,500 variable star observations to the AAVSO.

Bracher, K.

2012-06-01

193

Modelled and observed variability in atmospheric vertical temperature structure  

Microsoft Academic Search

Realistic simulation of the internal variability of the climate system is important both for climate change detection and\\u000a as an indicator of whether the physics of the climate system is well-represented in a climate model. In this work zonal mean\\u000a atmospheric temperatures from a control run of the second Hadley Centre coupled GCM are compared with gridded radiosonde observations\\u000a for

N. P. Gillett; M. R. Allen; S. F. B. Tett

2000-01-01

194

Observed small spatial scale and seasonal variability of the CO2-system in the Southern Ocean  

NASA Astrophysics Data System (ADS)

The considerable uncertainties in the carbon budget of the Southern Ocean are largely attributed to unresolved variability, in particular at seasonal time scale and small spatial scale (~ 100 km). In this study, the variability of surface pCO2 and DIC at seasonal and small-spatial scales is examined using a dataset of surface drifters including ~ 80 000 measurements at high spatio-temporal resolution. On spatial scales of 100 km, we find gradients ranging from 5 to 50 ? atm for pCO2 and 2 to 30 ? mol kg-1 for DIC, with highest values in energetic and frontal regions. This result is supported by a second estimate obtained with SST satellite images and local DIC/SST relationships derived from drifters observations. We find that dynamical processes drives the variability of DIC at small spatial scale in most regions of the Southern Ocean, the cascade of large-scale gradients down to small spatial scales leading to gradients up to 15 ? mol kg-1 over 100 km. Although the role of biological activity is more localized, it enhances the variability up to 30 ? mol kg-1 over 100 km. The seasonal cycle of surface DIC is reconstructed following Mahadevan et al. (2011), using an annual climatology of DIC and a monthly climatology of mixed layer depth. This method is evaluated using drifters observations and proves to be a reasonable first-order estimate of the seasonality in the Southern Ocean, which could be used to validate models simulations. We find that small spatial scales structures are a non negligible source of variability for DIC, with amplitudes of about a third of the variations associated with the seasonality and up to 10 times the magnitude of large-scale gradients. The amplitude of small-scale variability reported here should be kept in mind when inferring temporal changes (seasonality, inter-annual variability, decadal trends) of the carbon budget from low resolution observations and models.

Resplandy, L.; Boutin, J.; Merlivat, L.

2013-08-01

195

Variability of extratropical ozone stratosphere-troposphere exchange using microwave limb sounder observations  

NASA Astrophysics Data System (ADS)

The extratropical stratosphere-troposphere exchange (STE) of ozone from 2005 to 2010 is estimated by combining Microwave Limb Sounder ozone observations and MERRA reanalysis meteorological fields in an established direct diagnostic framework. The multiyear mean ozone STE is 275 Tg yr-1 and 214 Tg yr-1 in the Northern and Southern Hemispheres, respectively. The year-to-year variability is greater in the Northern Hemisphere, where the difference between the highest and the lowest annual flux is 15% of the multiyear mean compared with 6% in the Southern Hemisphere. Variability of lower stratospheric ozone and variability of the net mass flux both contribute to interannual variability in the Northern Hemisphere ozone flux. The flux across the extratropical 380 K surface determines the amount of flux across the extratropical tropopause, and the greatest seasonal variability of the 380 K ozone flux occurs in the late winter/early spring, around the time of greatest flux. Both the mass flux and the ozone mixing ratios on the 380 K surface show recurring spatial patterns, but interannual variability of these quantities and their alignment contribute to the ozone flux variability. The spatial and temporal variability are not well represented when zonal and/or monthly mean fields are used to calculate the ozone STE, although this results in a small high bias of the seasonal amplitude and annual magnitude. If the climatological variability over these 6 years is representative, the estimated number of years required to detect a 2 - 3% decade-1 trend in ozone STE using this diagnostic is 35 - 39 years.

Olsen, Mark A.; Douglass, Anne R.; Kaplan, Trevor B.

2013-01-01

196

Simulating Lake-Groundwater Interactions During Decadal Climate Cycles: Accounting For Variable Lake Area In The Watershed  

NASA Astrophysics Data System (ADS)

The volume and extent of a lake within the topo-bathymetry of a watershed can change substantially during wetter and drier climate cycles, altering the interaction of the lake with the groundwater flow system. Lake Starr and other seepage lakes in the permeable sandhills of central Florida are vulnerable to climate changes as they rely exclusively on rainfall and groundwater for inflows in a setting where annual rainfall and recharge vary widely. The groundwater inflow typically arrives from a small catchment area bordering the lake. The sinkhole origin of these lakes combined with groundwater pumping from underlying aquifers further complicate groundwater interactions. Understanding the lake-groundwater interactions and their effects on lake stage over multi-decadal climate cycles is needed to manage groundwater pumping and public expectation about future lake levels. The interdependence between climate, recharge, changing lake area and the groundwater catchment pose unique challenges to simulating lake-groundwater interactions. During the 10-year study period, Lake Starr stage fluctuated more than 13 feet and the lake surface area receded and expanded from 96 acres to 148 acres over drier and wetter years that included hurricanes, two El Nino events and a La Nina event. The recently developed Unsaturated Zone Flow (UZF1) and Lake (LAK7) packages for MODFLOW-2005 were used to simulate the changing lake sizes and the extent of the groundwater catchment contributing flow to the lake. The lake area was discretized to occupy the largest surface area at the highest observed stage and then allowed to change size. Lake cells convert to land cells and receive infiltration as receding lake area exposes the underlying unsaturated zone to rainfall and recharge. The unique model conceptualization also made it possible to capture the dynamic size of the groundwater catchment contributing to lake inflows, as the surface area and volume of the lake changed during the study period. Groundwater flows simulated using daily time steps over a 10-year period were used to describe the relationship between climate, the size of the groundwater catchment, and the relative importance of groundwater inflow to the lake water budget. Modeling approaches used in this study should be applicable to other surface-water bodies such as wetlands and playa lakes. Lake Starr watershed (depressions from sinkholes)

Virdi, M. L.; Lee, T. M.

2009-12-01

197

ROTSE-III observation of a Cataclysmic Variable new outburst  

NASA Astrophysics Data System (ADS)

Further to ATel#2126, we report on an outburst of the Cataclysmic Variable (CV) and probable dwarf nova ROTSE3 J203224.8+602837 in unfiltered CCD images with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory, Texas. The transient, located at RA: 20:32:25.01 Dec +60:28:36.59 (J2000.0; uncertainty ~1"), was observed at mag 16.6 on Oct. 2.10 UT, at mag 16.7 on Oct. 03.11 UT, and at mag 16.8 on Oct.

Ferrante, F. V.; Dhungana, Govinda; Kehoe, R.; Zheng, W.

2013-10-01

198

Two propensity score-based strategies for a three-decade observational study: investigating psychotropic medications and suicide risk.  

PubMed

The US Food and Drug Administration issued separate warnings for suicidality with antidepressants and antiepileptic drugs in the past 5 years. This study describes methods for examining the association of these agents with suicide attempts and suicide deaths in more broadly generalizable samples than examined by the US Food and Drug Administration. An observational study of mood disorders was examined that includes three decades of prospective assessments. Because of sample size differences, two distinct longitudinal implementations of the propensity adjustment are used in separate analyses of antidepressants and antiepileptic drugs. Propensity score quintile-stratified safety analyses were used with the large antidepressant data set; whereas, propensity score matched safety analyses were used with the smaller antiepileptic drug data because stratification was not feasible. In each case, mixed-effects survival models compared the safety of participants when receiving the respective class of medication to periods when they did not receive that medication. When participants were more severely ill, they were significantly more likely to receive either class of psychotropics. Propensity quintile-stratified safety analyses found that risk of suicide attempts or suicides was significantly reduced when participants received antidepressants. In contrast, propensity score matched safety analyses found neither significant risk nor protection from suicidality among participants receiving antiepileptics. PMID:22865578

Leon, Andrew C; Demirtas, Hakan; Li, Chunshan; Hedeker, Donald

2012-08-03

199

Temporal variability of Mrk 421 from XMM-Newton observations  

NASA Astrophysics Data System (ADS)

We present the results of a detailed spectral and temporal analysis of the currently available XMM-Newton observations of the bright BL Lac object Mrk 421 using mainly the EPIC-PN data. The source was found in various intensity states differing by up to a factor of five in count rates. In general, the source is more variable and shows a harder spectrum during higher intensities than when it is in lower states. The spectrum is very complex and cannot be fitted adequately by a broken power law or a continuously curved model. We find that the flux variations on time scales of ga few thousand seconds are associated with significant and sometimes very complex spectral changes. The spectral variability rate is not the same in all cases and is correlated with the source flux state: the spectral variations per unit time increase with the source flux. The Cross-Correlation analysis shows that the soft and hard band light curves are often well correlated near zero lag, in other cases the hard band variations lead the soft band variations by typically ~ 5 min, in two cases we find the soft band leading the hard band variations. The delays appear to be correlated to the flares' duration: the shorter the flare, the smaller the delay.

Brinkmann, W.; Papadakis, I. E.; den Herder, J. W. A.; Haberl, F.

2003-05-01

200

Interannual to Decadal Variability in Climate and the Glacier Mass Balance in Washington, Western Canada, and Alaska*.  

NASA Astrophysics Data System (ADS)

The authors examine the net winter, summer, and annual mass balance of six glaciers along the northwest coast of North America, extending from Washington State to Alaska. The net winter (NWB) and net annual (NAB) mass balance anomalies for the maritime glaciers in the southern group, located in Washington and British Columbia, are shown to be positively correlated with local precipitation anomalies and storminess (defined as the rms of high-passed 500-mb geopotential anomalies) and weakly and negatively correlated with local temperature anomalies. The NWB and NAB of the maritime Wolverine glacier in Alaska are also positively correlated with local precipitation, but they are positively correlated with local winter temperature and negatively correlated with local storminess. Hence, anomalies in mass balance at Wolverine result mainly from the change in moisture that is being advected into the region by anomalies in the averaged wintertime circulation rather than from a change in storminess. The patterns of the wintertime 500-mb circulation and storminess anomalies associated with years of high NWB in the southern glacier group are similar to those associated with low NWB years at the Wolverine glacier, and vice versa.The decadal ENSO-like climate phenomenon discussed by Zhang et al. has a large impact on the NWB and NAB of these maritime glaciers, accounting for up to 35% of the variance in NWB. The 500-mb circulation and storminess anomalies associated with this decadal ENSO-like mode resemble the Pacific-North American pattern, as do 500-mb composites of years of extreme NWB of South Cascade glacier in Washington and of Wolverine glacier in Alaska. Hence, the decadal ENSO-like mode affects precipitation in a crucial way for the NWB of these glaciers. Specifically, the decadal ENSO-like phenomenon strongly affects the storminess over British Columbia and Washington and the moisture transported by the seasonally averaged circulation into maritime Alaska. In contrast, ENSO is only weakly related to NWB of these glaciers because (i) the large-scale circulation anomalies associated with ENSO do not produce substantial anomalies in moisture advection into Alaska, and (ii) the storminess and precipitation anomalies associated with ENSO are far to the south of the southern glacier group.Finally, the authors discuss the potential for short-term climate forecasts of the mass balance for the maritime glaciers in the northwest of North America.

Bitz, C. M.; Battisti, D. S.

1999-11-01

201

EINSTEIN observations of BY Draconis variables and RS CVn binaries  

SciTech Connect

Observations of five BY Draconis variables and four RS Canum Venaticorum systems with the Einstein observatory are presented. All nine stars were detected. Although the BY Draconis stars have an average x-ray luminosity one to two orders of magnitude lower than the RS CVn binaries, at least three of these systems fit the L/sub x//L/sub bol/-vs-period relation first described by Walter and Bowyer for RS CVn's. Since one of the BY Draconis stars is almost certainly single, this result lends strong support to the suggestion that rapid rotation, and not duplicity, is the determining factor in defining the level of stellar activity in such stars. In addition, the x-ray data are consistent with the suggestion, made by Vogt and Fekel, that the BY Draconis stars are in the final stages of pre-main-sequence evolution.

Caillault, J.

1982-03-01

202

Monitoring ? Scuti Variables with Coordinated Observing of Small Telescopes  

NASA Astrophysics Data System (ADS)

Beginning with a Research Experience for Teachers (RET) program this past summer a research effort has been started that will allow undergraduates to collaborate with high school students in monitoring a number of bright variable stars of the ? Scuti variety. This program will make use of the Brigham Young University 16" David Derrick Telescope and 8" Ferdinand Feghoot Telescope along with a new 10" Meade LX-200 installed at Payson High School. The initial targets for this program include DQ Cephei, DX Ceti, V474 Monocerotis, V376 Persei, ? Scuti, and V966 Herculis. Spectroscopic follow-up observations will be made at the 1.2-m Telescope of the Dominion Astrophysical Observatory in Victoria, B.C., Canada. We hope this program will lay the ground work for additional small telescopes at high schools throughout Utah. Preliminary results will be presented. Research Partially supported by NSF REU Program PHY-9988852

Hintz, E.; Jeffery, E.; Walter, L.

2001-12-01

203

Observed Variables Are Indeed More Mysterious than Commonly Supposed  

ERIC Educational Resources Information Center

The author comments on an article about psychometrics titled "Latent Variable Theory" by Denny Borsboom and printed elsewhere in this issue. The author states that Borsboom's conclusion that all variables should be considered latent until proven otherwise is sound, and that his basis for conclusion rests on the relation between the variable…

Howell, Roy D.

2008-01-01

204

Observed Variables Are Indeed More Mysterious than Commonly Supposed  

ERIC Educational Resources Information Center

|The author comments on an article about psychometrics titled "Latent Variable Theory" by Denny Borsboom and printed elsewhere in this issue. The author states that Borsboom's conclusion that all variables should be considered latent until proven otherwise is sound, and that his basis for conclusion rests on the relation between the variable…

Howell, Roy D.

2008-01-01

205

Variability in MLT dynamics and species concentrations as observed by WINDII  

Microsoft Academic Search

Airglow variability is a topic that has been studied for decades but an understanding of the role of the dynamical influence underlying this variability has only been achieved recently. The UARS dynamics instruments, HRDI (High Resolution Doppler Imager) and WINDII (WIND Imaging Interferometer) have been instrumental in providing this understanding, because they measure both winds and emission rates, and so

Gordon G. Shepherd; Shengpan Zhang; Xialong Wang

1999-01-01

206

Stretched-grid Model Intercomparison Project: decadal regional climate simulations with enhanced variable and uniform-resolution GCMs  

Microsoft Academic Search

Summary  Variable-resolution GCMs using a global stretched-grid (SG) with enhanced resolution over the region(s) of interest is an\\u000a established approach to regional climate modeling providing an efficient means for regional down-scaling to mesoscales. This\\u000a approach has been used since the early-mid 90s by the French, U.S., Canadian, Australian and other climate modeling groups\\u000a along with, or as an alternative to, the

M. Fox-Rabinovitz; J. Cote; B. Dugas; M. Deque; J. L. McGregor; A. Belochitski

2008-01-01

207

K-band Observations of Sub-Gap Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

We present K-band spectroscopy of short period, ``sub-gap'' cataclysmic variable (CV) systems obtained using ISAAC on the VLT. We show the infrared spectra (IR) for nine systems below the 2-3 hour period gap: V2051 Oph, V436 Cen, EX Hya, VW Hyi, Z Cha, WX Hyi, V893 Sco, RZ Leo, and TY PsA. We are able to clearly detect the secondary star in all but WX Hyi, V893 Sco, and TY PsA. We present the first direct detection of the secondary stars of V2051 Oph, 436 Cen, and determine new spectral classifications for EX Hya, VW Hyi, Z Cha, and RZ Leo. We find that the CO band strengths of all but Z Cha appear normal for their spectral types, in contrast to their longer period cousins above the period gap. This brings the total number of CVs with moderate resolution (R ? 2000) IR spectroscopy to forty-eight systems: six pre-CVs, thirty-one non-magnetic systems, and eleven magnetic or partially magnetic systems. We discuss the trends seen in the IR abundance patterns thus far, and highlight a potential link between anomalous abundances seen in the IR with the C IV/N V anomaly seen in the ultraviolet. We present a compilation of all systems with sufficient resolution IR observations to assess the CO band strengths, and, by proxy, obtain an estimate on the C abundance on the secondary star.

Hamilton, Ryan T.; Harrison, T. E.; Tappert, C.; Howell, S. B.

2011-01-01

208

Observed and simulated multidecadal variability in the Northern Hemisphere  

Microsoft Academic Search

Analyses of proxy based reconstructions of surface temperatures during the past 330 years show the existence of a distinct\\u000a oscillatory mode of variability with an approximate time scale of 70 years. This variability is also seen in instrumental\\u000a records, although the oscillatory nature of the variability is difficult to assess due to the short length of the instrumental\\u000a record. The

T. L. Delworth; M. E. Mann

2000-01-01

209

Three decades of observed soil acidification in the Calhoun Experimental Forest: Has acid rain made a difference?  

Microsoft Academic Search

Three decades of repeated soil sampling from eight permanent plots at the Calhoun Experimental Forest in South Carolina allowed the authors to estimate the rate of soil acidification, the chemical changes in the soil exchange complex, and the natural and anthropogenic sources of acidity contribution to these processes. During the first 34 yr of loblolly pine (Pinus taeda L.) forest

Daniel Markewitz; Daniel D. Richter; H. Lee Allen; J. Byron Urrego

1998-01-01

210

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis of Multiwavelength Continuum Variability  

NASA Astrophysics Data System (ADS)

This paper combines data from the three preceding papers in order to analyze the multi-wave-band variability and spectral energy distribution of the Seyfert I galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths; The strongest variatIons were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA = 6%) variations (uncorrelated with those at lower energies) were seen at soft gamma ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 A. These data do not probe extreme ultraviolet (1200 A to 0.1 keV) or hard X ray (2-50 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of <~ 0.15 day between 1275 A and the other ultraviolet bands, <~0.3 day between 1275 A and 1.5 keV, and <~1 day between 1275 and 512 A. These tight limits represent more than an order of magnitude improvement over those determined in previous multi wave band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (a <= -2.5). If photons emitted at a "primary" wave band are absorbed by nearby material and "reprocessed" to produce emission at a secondary wave band, causality arguments require that variations in the secondary band follow those in the primary band. The tight interband correlation and limits on the ultraviolet and medium-energy X-ray lags indicate that the reprocessing region is smaller than ~0.15 lt-day in size. After correcting for strong (a factor of ~> 15) line-of-sight absorption, the medium-energy X-ray luminosity variations appear adequate to drive the ultraviolet/optical variations. However the medium-energy X-ray NVA is 2- 4 times that in the ultraviolet, and the single-epoch absorption- corrected X-ray/gamma ray luminosity is only about one third of that of the ultraviolet optical/infrared, suggesting that at most about a third of the total low energy flux could be reprocessed high-energy emission. The strong wavelength dependence of the ultraviolet NVAs is consistent with an origin in an accretion disk, with the variable emission coming from the hotter inner regions and nonvariable emission from the cooler outer regions. These data, when combined with the results of disk fits indicate a boundary between these regions near a radius of order R ~ 0.07 lt-day. No interband lag would be expected, as reprocessing (and thus propagation between regions) need not occur, and the orbital timescale of 1 day is consistent with the observed variability timescale. However, such a model does not immediately explain the good correlation between ultraviolet and X-ray variations.

Edelson, R. A.; Alexander, T.; Crenshaw, D. M.; Kaspi, S.; Malkan, M. A.; Peterson, B. M.; Warwick, R. S.; Clavel, J.; Filippenko, A. V.; Horne, K.; Korista, K. T.; Kriss, G. A.; Krolik, J. H.; Maoz, D.; Nandra, K.; O'Brien, P. T.; Penton, S. V.; Yaqoob, T.; Albrecht, P.; Alloin, D.; Ayres, T. R.; Balonek, T. J.; Barr, P.; Barth, A. J.; Bertram, R.; Bromage, G. E.; Carini, M.; Carone, T. E.; Cheng, F.-Z.; Chuvaev, K. K.; Dietrich, M.; Dultzin-Hacyan, D.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hemar, S.; Ho, L. C.; Huchra, J. P.; Hutchings, J.; Johnson, W. N.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Kovo, O.; Laor, A.; MacAlpine, G. M.; Magdziarz, P.; Martin, P. G.; Matheson, T.; McCollum, B.; Miller, H. R.; Morris, S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike, G.; Pogge, R. W.; Ptak, R. L.; Qian, B.-C.; Recondo-Gonzalez, M. C.; Reichert, G. A.; Rodriguez-Espinoza, J. M.; Rodriguez-Pascual, P. M.; Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Shields, J. C.; Shull, J. M.; Smith, D. A.; Smith, S. M.; Snijders, M. A. J.; Stirpe, G. M.; Stoner, R. E.; Sun, W.-H.; Ulrich, M.-H.; van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Wu, H.; Wurster, J.; Xue, S.-J.; Zdziarski, A. A.; Zheng, W.; Zou, Z.-L.

1996-10-01

211

Interannual relationships between Indian Summer Monsoon and Indo-Pacific coupled modes of variability during recent decades  

NASA Astrophysics Data System (ADS)

Various SST indices in the Indo-Pacific region have been proposed in the literature in light of a long-range seasonal forecasting of the Indian Summer Monsoon (ISM). However, the dynamics associated with these different indices have never been compared in detail. To this end, the present work re-examines the variabilities of ISM rainfall, onset and withdrawal dates at interannual timescales and explores their relationships with El Niño-Southern Oscillation (ENSO) and various modes of coupled variability in the Indian Ocean. Based on recent findings in the literature, five SST indices are considered here: Niño3.4 SST index in December-January both preceding [Nino(-1)] and following the ISM [Nino(0)], South East Indian Ocean (SEIO) SST in February-March, the Indian Ocean Basin (IOB) mode in April-May and, finally, the Indian Ocean Dipole (IOD) averaged from September to November, also, both preceding [IOD(-1)] and following the ISM [IOD(0)]. The respective merits and associated dynamics of the selected indices are compared through various correlation and regression analyses. Our first result is a deceptive one: the statistical relationships with the ISM rainfall at the continental and seasonal scales are modest and only barely significant, particularly for the IOD, IOB and Nino(-1) indices. However, a detailed analysis shows that statistical relationships with the ISM rainfall time series are statistically biased as the ISM rainfall seems to be shaped by much intraseasonal variability, linked in particular to the timing of the onset and withdrawal of the ISM. Surprisingly, analysis within the ISM season shows that Nino(-1), IOB and SEIO indices give rise to prospects of comparatively higher ISM previsibility for both the ISM onset and the amount of rainfall during the second half of the ISM season. The IOD seems to play only a secondary role. Moreover, our work shows that these indices are associated with distinct processes occurring within the Indian Ocean from late boreal winter or early spring onwards. The regression analyses also illustrate that these (local) mechanisms are dynamically and remotely linked to different phases of ENSO in the equatorial Pacific, a result which may have useful implications in terms of forecasting strategies since the choice of the better indices then hinges on the concurrent phasing of the ENSO cycle.

Boschat, Ghyslaine; Terray, Pascal; Masson, Sébastien

2010-08-01

212

Interannual relationships between Indian Summer Monsoon and Indo-Pacific coupled modes of variability during recent decades  

NASA Astrophysics Data System (ADS)

Various SST indices in the Indo-Pacific region have been proposed in the literature in light of a long-range seasonal forecasting of the Indian Summer Monsoon (ISM). However, the dynamics associated with these different indices have never been compared in detail. To this end, the present work re-examines the variabilities of ISM rainfall, onset and withdrawal dates at interannual timescales and explores their relationships with El Niño-Southern Oscillation (ENSO) and various modes of coupled variability in the Indian Ocean. Based on recent findings in the literature, five SST indices are considered here: Niño3.4 SST index in December-January both preceding [Nino(-1)] and following the ISM [Nino(0)], South East Indian Ocean (SEIO) SST in February-March, the Indian Ocean Basin (IOB) mode in April-May and, finally, the Indian Ocean Dipole (IOD) averaged from September to November, also, both preceding [IOD(-1)] and following the ISM [IOD(0)]. The respective merits and associated dynamics of the selected indices are compared through various correlation and regression analyses. Our first result is a deceptive one: the statistical relationships with the ISM rainfall at the continental and seasonal scales are modest and only barely significant, particularly for the IOD, IOB and Nino(-1) indices. However, a detailed analysis shows that statistical relationships with the ISM rainfall time series are statistically biased as the ISM rainfall seems to be shaped by much intraseasonal variability, linked in particular to the timing of the onset and withdrawal of the ISM. Surprisingly, analysis within the ISM season shows that Nino(-1), IOB and SEIO indices give rise to prospects of comparatively higher ISM previsibility for both the ISM onset and the amount of rainfall during the second half of the ISM season. The IOD seems to play only a secondary role. Moreover, our work shows that these indices are associated with distinct processes occurring within the Indian Ocean from late boreal winter or early spring onwards. The regression analyses also illustrate that these (local) mechanisms are dynamically and remotely linked to different phases of ENSO in the equatorial Pacific, a result which may have useful implications in terms of forecasting strategies since the choice of the better indices then hinges on the concurrent phasing of the ENSO cycle.

Boschat, Ghyslaine; Terray, Pascal; Masson, Sébastien

2011-09-01

213

Canonical form observer design for non-linear time-variable systems  

Microsoft Academic Search

An observer of canonical (phase-variable) form for non-linear time-variable systems is introduced. The development of this non-linear time-variable form requires regularity of the non-linear time-variable- observability matrix of the system. From the relationships derived during the development, it follows that a non-linear time-variable observer can be dimensioned by an eigenvalue assignment with respect to the canonical state coordinates if a

D. BESTLE; M. ZEITZ

1983-01-01

214

Sliding modes observers for vehicle dynamics and variable structure automatic systems (SMO-VSAS)  

Microsoft Academic Search

This paper will show how to handle modeling of vehicles to get efficient and good Sliding Mode Observers. A car model with 16 DoF is decomposed for partial state observation with SMO. This decomposition method may lead, in VSAS, to good estimates of different kind variables and inputs (subsystems states, environment and ground variables, interfaces variables, connections and constraint variables).

N. K. M'Sirdi; B. Jaballah; H. Nasser; A. Naamane

2010-01-01

215

Observed intraseasonal thermocline variability in the Bay of Bengal  

NASA Astrophysics Data System (ADS)

The time series of temperature data obtained from moored buoys deployed at 8°N, 12°N, and 15°N along 90°E in the Bay of Bengal (BoB) shows a persistent intraseasonal variability on 30-120 day time scale in three distinct periods 30-70 day, near 90 day, and near 120 day in the thermocline region. The standard deviation of moored buoy temperature data shows that half of the variability in the thermocline region is contributed from the 30-120 day variability. The relative contribution of local Ekman pumping velocity and remote wind forcing from equatorial Indian Ocean (EIO) to the intraseasonal thermocline variability in the BoB is examined using satellite-derived sea surface height anomaly (SSHA), wind and depths of 23° isotherm (D23, proxy for thermocline depth) derived from moored buoys temperature data. The analysis shows that large amplitude intraseasonal oscillations of thermocline—particularly the near 90 day and 120 day variability—could not be explained by local Ekman pumping velocity alone. The SSHA, D23, and wind fields reveal that the first and second baroclinic mode Kelvin and Rossby waves, which are generated remotely by winds from the EIO and eastern BoB, can significantly influence the thermocline variability in the BoB. The near 90 day and 120 day thermocline variability is driven primarily by the variability of equatorial zonal wind stress. While the 30-70 day thermocline variability is affected most by interior Ekman pumping over the Bay, it also appears to be influenced by zonal wind stress in the EIO and alongshore wind stress in the eastern BoB.

Girishkumar, M. S.; Ravichandran, M.; Han, W.

2013-07-01

216

Experimental observation of quantum correlations in modular variables  

NASA Astrophysics Data System (ADS)

We experimentally detect entanglement in modular position and momentum variables of photon pairs which have passed through D-slit apertures. We first employ an entanglement criteria recently proposed in [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.210501 106, 210501 (2011)], using variances of the modular variables. We then propose an entanglement witness for modular variables based on the Shannon entropy and test it experimentally. Finally, we derive criteria for Einstein-Podolsky-Rosen-steering correlations using variances and entropy functions. In both cases, the entropic criteria are more successful at identifying quantum correlations in our data.

Carvalho, M. A. D.; Ferraz, J.; Borges, G. F.; de Assis, P.-L.; Pádua, S.; Walborn, S. P.

2012-09-01

217

Three decades of observed soil acidification in the Calhoun Experimental Forest: Has acid rain made a difference?  

SciTech Connect

Three decades of repeated soil sampling from eight permanent plots at the Calhoun Experimental Forest in South Carolina allowed the authors to estimate the rate of soil acidification, the chemical changes in the soil exchange complex, and the natural and anthropogenic sources of acidity contribution to these processes. During the first 34 yr of loblolly pine (Pinus taeda L.) forest growth, soil pH, decreased by 1 unit in the upper 0- to 15-cm of soils and by 0.4 and 0.3 units in the 15- to 35- and 35- to 60-cm layers, respectively. Throughout the 0- to 60-cm horizon, base cation depletion averaged 1.57 kmol{sub c} ha{sup {minus}1} yr{sup {minus}1} and effective and total acidity increased by 1.26 and 3.28 kmol{sub c} ha{sup {minus}1} yr{sup {minus}1}, respectively. A forest H{sup +} budget estimated for these decades indicated that 38% of soil acidification was due to acid deposition, while 62% of soil acidification was due to acid disposition, while 62% of soil acidification was attributed to the internal functioning of the ecosystem. Soil samples archived during the three-decade experiment also document decreases in soil-adsorbed SO{sub 4}{sup 2{minus}}, presumably in response to decreasing atmospheric inputs in recent years.

Markewitz, D.; Richter, D.D. [Duke Univ., Durham, NC (United States). Nicholas School of the Environment; Allen, H.L. [North Carolina State Univ., Raleigh, NC (United States); Urrego, J.B. [Smurfit-Carton de Colombia, Calli (Colombia). Investigacion Forestal

1998-09-01

218

Interannual and decadal variability of the western Pacific sea surface condition for the years 1787-2000: Reconstruction based on stable isotope record from a Guam coral  

NASA Astrophysics Data System (ADS)

We present a monthly resolved, 213-year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (?18Ocoral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The ?18Ocoral anomaly reflects sea surface temperature (SST) anomaly and sea surface salinity (SSS) anomaly with significant r values of -0.69 and 0.49, respectively, which are strongly linked to oceanographic changes that occur during El Niño-Southern Oscillation (ENSO) warm and cool phases. We identified 46 ENSO warm (El Niño) and 53 cool phases (La Niña) in the coral record, which are consistent with those phases reconstructed by Niño 3.4 SST anomaly. Spectral analyses of the ?18Ocoral anomaly record for the years 1790-1999 identified significant peaks around ˜3 to ˜7 years. These results indicate that the Guam coral has recorded ENSO periodicity. The ?18Ocoral anomaly shows decadal variability of ˜15- to ˜45-year periodicity with significant shifts (<0.2‰) from warmer to cooler condition and vice versa. An accumulative decrease in ?18Ocoral time series may imply ˜0.75°C warming of SST and ˜0.23‰ freshening of seawater ?18O, corresponding to a decrease of SSS by ˜0.85, in the northwestern tropical Pacific over the last 2 centuries.

Asami, Ryuji; Yamada, Tsutomu; Iryu, Yasufumi; Quinn, Terrence M.; Meyer, Christopher P.; Paulay, Gustav

2005-05-01

219

Late summer variability of dissolved organic matter in the Kolyma River observed using satellite imagery  

NASA Astrophysics Data System (ADS)

The Kolyma River basin in northeastern Siberia, one of the six largest river basins draining to the Arctic Ocean, contains vast reserves of carbon in its Pleistocene-aged permafrost soils. Already this region has experienced significant warming over the last few decades and is poised to experience even more dramatic climate change in the near future. Resulting permafrost degradation may cause shifts in riverine biogeochemistry as terrestrial organic matter inputs to adjacent aquatic environments change. Satellite remote sensing offers an opportunity to supplement and extrapolate field-based observations of dissolved organic matter in this expansive and remote region. We present an empirically-derived algorithm that estimates chromophoric dissolved organic matter (CDOM) in the Kolyma River and its major tributaries in the vicinity of Cherskiy, Russia. Field samples from July 2008 and 2009 were regressed against spectral data from Landsat-5 Thematic Mapper (TM) and Landsat-7 Enhanced Thematic Mapper-Plus (ETM+). A combination of band 3 and bands 2:1 resulted in an R2 of 0.78 between in situ CDOM concentrations and satellite-derived predictions. Using the strong correlation between CDOM and dissolved organic carbon (DOC), this algorithm can be used to assess the spatial variability in CDOM and DOC throughout the Kolyma River and its major tributaries during the late-summer period. DOC mapped in July of 2000-2002 and 2004-2009 shows a high degree of interannual variability, with Kolyma River main stem concentrations varying between approximately 3 mg L-1 and 12 mg L-1. The driving forces behind such variability are unclear, but may be most closely related to interannual variability in river discharge.

Griffin, C. G.; Frey, K. E.; Rogan, J.; Holmes, R. M.

2010-12-01

220

Observation of Pluri-Decadal Movement at the NE-Border of the Adria-Plate by Subsurface Long-Base Geodetic Instrumentation and Modeling  

Microsoft Academic Search

The movement of the Adria plate is important in the understanding of the seismicity of Italy and the Dalmatian region. Its northern margin delineates the most seismic area of the Alps and has been hit by destructive earthquakes. The deformation of the margin has been observed over four decades in a natural cave with long-base highly stable and sensitive instruments.

C. Braitenberg; I. Nagy; S. Papacchioli

2004-01-01

221

A new calibration for the Sr/Ca-temperature relationship in sclerosponges reveals synchronous changes in Caribbean specimens indicative of warming and multi-decadal climate variability  

NASA Astrophysics Data System (ADS)

Previous work defined the calibration between the skeletal Sr/Ca ratio of the sclerosponge Ceratoporella nicholsoni and the ambient seawater temperature. However, application of this calibration to records throughout the Caribbean reveals a nearly 4°C warming over the last 150 years, in excess of what one might expect from global climate averages. As the original C. nicholsoni Sr/Ca-temperature relationship was calibrated between 26 and 30°C, it is possible that the relationship differed outside of the examined temperature window. This suspicion is confirmed by the measurement of Sr/Ca ratios from additional specimens of the same species. These show a significantly different slope between Sr/Ca and temperature at lower temperatures (21 to 26°C). Using this information, the calibration equation has been refined and the subsequent reconstructions of temperature are much more realistic, indicating a warming of approximately 1°C over the last 150 years. Applying this new calibration to additional published sclerosponge records of Sr/Ca reveals remarkable agreements between records from the Bahamas and Jamaica, both in amplitude of warming and smaller scale variability. In addition, the depth versus temperature relationship associated with these specimens is preserved. The refined temperature reconstruction of a 600 year record from Exuma Sound, Bahamas, demonstrates the cyclic nature of its variability (~15 and 28 year periodicities). Further use of these data and stable oxygen isotopes to calculate salinity reveals variability on multi-decadal timescales. This includes an approximately 20 year periodicity between 1400 and 1790. From 1790 to 2000, the dominant mode appears to switch to a roughly 60 year periodicity, consistent with that of the Atlantic Multi-decadal Oscillation (AMO).

Waite, A. J.; Swart, P. K.; Rosenheim, B. E.

2009-12-01

222

High nutrient pulses, tidal mixing and biological response in a small California estuary: Variability in nutrient concentrations from decadal to hourly time scales  

USGS Publications Warehouse

Elkhorn Slough is a small estuary in Central California, where nutrient inputs are dominated by runoff from agricultural row crops, a golf course, and residential development. We examined the variability in nutrient concentrations from decadal to hourly time scales in Elkhorn Slough to compare forcing by physical and biological factors. Hourly data were collected using in situ nitrate analyzers and water quality data sondes, and two decades of monthly monitoring data were analyzed. Nutrient concentrations increased from the mid 1970s to 1990s as pastures and woodlands were converted to row crops and population increased in the watershed. Climatic variability was also a significant factor controlling interannual nutrient variability, with higher nutrient concentrations during wet than drought years. Elkhorn Slough has a Mediterranean climate with dry and rainy seasons. Dissolved inorganic nitrogen (DIN) concentrations were relatively low (10-70 ??mol L-1) during the dry season and high (20-160 ??mol L-1) during the rainy season. Dissolved inorganic phosphorus (DIP) concentrations showed the inverse pattern, with higher concentrations during the dry season. Pulsed runoff events were a consistent feature controlling nitrate concentrations during the rainy season. Peak nitrate concentrations lagged runoff events by 1 to 6 days. Tidal exchange with Monterey Bay was also an important process controlling nutrient concentrations, particularly near the mouth of the Slough. Biological processes had the greatest effect on nitrate concentrations during the dry season and were less important during the rainy season. While primary production was enhanced by nutrient pulses, chlorophyll a concentrations were not. We believe that the generally weak biological response compared to the strong physical forcing in Elkhorn Slough occurred because the short residence time and tidal mixing rapidly diluted nutrient pulses. ?? 2006 Elsevier Ltd. All rights reserved.

Caffrey, J. M.; Chapin, T. P.; Jannasch, H. W.; Haskins, J. C.

2007-01-01

223

Evaluation of a Finite-Element Sea-Ice Ocean Model (FESOM) set-up to study the interannual to decadal variability in the deep-water formation rates  

NASA Astrophysics Data System (ADS)

The characteristics of a global set-up of the Finite-Element Sea-Ice Ocean Model under forcing of the period 1958-2004 are presented. The model set-up is designed to study the variability in the deep-water mass formation areas and was therefore regionally better resolved in the deep-water formation areas in the Labrador Sea, Greenland Sea, Weddell Sea and Ross Sea. The sea-ice model reproduces realistic sea-ice distributions and variabilities in the sea-ice extent of both hemispheres as well as sea-ice transport that compares well with observational data. Based on a comparison between model and ocean weather ship data in the North Atlantic, we observe that the vertical structure is well captured in areas with a high resolution. In our model set-up, we are able to simulate decadal ocean variability including several salinity anomaly events and corresponding fingerprint in the vertical hydrography. The ocean state of the model set-up features pronounced variability in the Atlantic Meridional Overturning Circulation as well as the associated mixed layer depth pattern in the North Atlantic deep-water formation areas.

Scholz, Patrick; Lohmann, Gerrit; Wang, Qiang; Danilov, Sergey

2013-04-01

224

Variability of Attention Processes in ADHD: Observations from the Classroom  

ERIC Educational Resources Information Center

|Objective: Classroom- and laboratory-based efforts to study the attentional problems of children with ADHD are incongruent in elucidating attentional deficits; however, none have explored within- or between-minute variability in the classroom attentional processing in children with ADHD. Method: High and low attention groups of ADHD children…

Rapport, Mark D.; Kofler, Michael J.; Alderson, R. Matt; Timko, Thomas M., Jr.; DuPaul, George J.

2009-01-01

225

Variability of Attention Processes in ADHD: Observations from the Classroom  

ERIC Educational Resources Information Center

Objective: Classroom- and laboratory-based efforts to study the attentional problems of children with ADHD are incongruent in elucidating attentional deficits; however, none have explored within- or between-minute variability in the classroom attentional processing in children with ADHD. Method: High and low attention groups of ADHD children…

Rapport, Mark D.; Kofler, Michael J.; Alderson, R. Matt; Timko, Thomas M., Jr.; DuPaul, George J.

2009-01-01

226

Coupled ocean-atmosphere model system for studies of interannual-to-decadal climate variability over the North Pacific Basin and precipitation over the Southwestern United States  

SciTech Connect

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The ultimate objective of this research project is to make understanding and predicting regional climate easier. The long-term goals of this project are (1) to construct a coupled ocean-atmosphere model (COAM) system, (2) use it to explore the interannual-to-decadal climate variability over the North Pacific Basin, and (3) determine climate effects on the precipitation over the Southwestern United States. During this project life, three major tasks were completed: (1) Mesoscale ocean and atmospheric model; (2) global-coupled ocean and atmospheric modeling: completed the coupling of LANL POP global ocean model with NCAR CCM2+ global atmospheric model; and (3) global nested-grid ocean modeling: designed the boundary interface for the nested-grid ocean models.

Lai, Chung-Chieng A.

1997-10-01

227

Field observations of soil moisture variability across scales  

Microsoft Academic Search

In this study, over 36,000 ground-based soil moisture measurements collected during the SGP97, SGP99, SMEX02, and SMEX03 field campaigns were analyzed to characterize the behavior of soil moisture variability across scales. The field campaigns were conducted in Oklahoma and Iowa in the central USA. The Oklahoma study region is sub-humid with moderately rolling topography, while the Iowa study region is

James S. Famiglietti; Dongryeol Ryu; Aaron A. Berg; Matthew Rodell; Thomas J. Jackson

2008-01-01

228

Observing variable stars at the University of Athens Observatory  

NASA Astrophysics Data System (ADS)

In 1999 the University of Athens installed a 0.4-m Cassegrain telescope (CCT-16, by DFM Engineering) on the roof of the Department of Astrophysics, Astronomy and Mechanics, equipped with a ST-8 CCD camera and Bessel UBVRI filters. Although the telescope was built for educational purposes, we found it can be a perfect research instrument, as we can obtain fine quality light curves of bright variable stars, even from a place close to the city center. Light curves of the ? Scuti star V1162 Ori and of the sdB star PG 1336-018 are presented, showing the ability of a 40-cm telescope to detect negligible luminosity fluctuations of relatively bright variable stars. To date, we succeed in making photometry of stars down to 15th magnitude with satisfactory results. We expect to achieve even better results in the future, as our methods still improve, and as the large number of relatively bright stars gives us the chance to study various fields of CCD photometry of variables.

Gazeas, K.; Manimanis, V. N.; Niarchos, P. G.

229

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. I. Ultraviolet Observations  

NASA Astrophysics Data System (ADS)

We present the results of an intensive ultraviolet monitoring campaign on the Seyfert I galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously With the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days Prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 A went through four significant and well-defined events of duration 2-3 days during the continuous-monitoring period. We find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines.

Crenshaw, D. M.; Rodriguez-Pascual, P. M.; Penton, S. V.; Edelson, R. A.; Alloin, D.; Ayres, T. R.; Clavel, J.; Horne, K.; Johnson, W. N.; Kaspi, S.; Korista, K. T.; Kriss, G. A.; Krolik, J. H.; Malkan, M. A.; Maoz, D.; Netzer, H.; O'Brien, P. T.; Peterson, B. M.; Reichert, G. A.; Shull, J. M.; Ulrich, M.-H.; Wamsteker, W.; Warwick, R. S.; Yaqoob, T.; Balonek, T. J.; Barr, P.; Bromage, G. E.; Carini, M.; Carone, T. E.; Cheng, F.-Z.; Chuvaev, K. K.; Dietrich, M.; Doroshenko, V. T.; Dultzin-Hacyan, D.; Filippenko, A. V.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hutchings, J.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Laor, A.; Leighly, K.; Lyutyi, V. M.; MacAlpine, G. M.; Malkov, Yu. F.; Martin, P. G.; McCollum, B.; Merkulova, N. I.; Metik, L.; Metlov, V. G.; Miller, H. R.; Morris, S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike, G.; Pogge, R. W.; Pronik, I.; Pronik, V. I.; Ptak, R. L.; Recondo-Gonzalez, M. C.; Rodriguez-Espinoza, J. M.; Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Sergeev, S. G.; Smith, S. M.; Snijders, M. A. J.; Sparke, L. S.; Stirpe, G. M.; Stoner, R. E.; Sun, W.-H.; van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Zheng, W.

1996-10-01

230

Stable Auroral Red arc occurrences detected by the Pacific Northwest Laboratory photometer network: A decade of observations, 1978--1988  

SciTech Connect

Using data obtained from a network of all-sky scanning photometers designed to operate routinely for long periods of time, a comprehensive inspection of observations covering the time period 1978--1988 has revealed features that we interpret to be Stable Auroral Red (SAR) arcs during 250 nighttime observing periods. These arcs result from high temperature within the ionospheric electron gas that is maintained by slow leakage of energy from the earth's magnetosphere. A listing of these events, the most complete available for this time interval, is presented for the purpose of complementing observations reported for earlier dates. This listing is composed of location of the observing photometer, date, time, photometric intensity, and location (as defined by the earth's magnetic coordinate system). The intent is to make these observations available to a broad range of researchers and thereby initiate further investigations of these features. 22 refs., 3 figs., 2 tabs.

Slater, D.W.; Kleckner, E.W.

1989-11-01

231

What We Have Learned About Clusters From a Decade of Arcsecond-resolution X-ray Observations  

NASA Astrophysics Data System (ADS)

This talk will briefly review the main findings from Chandra high angular resolution observations of galaxy clusters, emphasizing results on cluster astrophysics. Chandra has discovered shock fronts in merging systems, providing information on the shock Mach number and velocity, and for best-observed shocks, constraining the microphysical properties of the intracluster medium (ICM). Cold fronts, a Chandra discovery, are ubiquitous both in merging clusters and in the cool cores of relaxed systems. They reveal the structure and strength of the intracluster magnetic fields and constrain the ICM viscosity. Combined with radio data, these observations also shed light on the production of ultrarelativistic particles that are known to coexist with thermal plasma. Finally, in nearly all cool cores, Chandra observes cavities in the ICM that are produced by the central AGN. All these phenomena will be extremely interesting for high-resolution SZ studies.

Markevitch, Maxim L.

2012-05-01

232

A Review of Global Terrestrial Evapotranspiration: Observation, Modeling, Climatology, and Climatic Variability  

NASA Astrophysics Data System (ADS)

This review provides a survey of the basic theories, observational methods, satellite retrieval algorithms and land surface models of terrestrial evapotranspiration, E (or ?E, latent heat flux), from a climatic variability perspective. We carefully examine the available observations, advancements in understanding the environmental and biological controls of ?E, and their applications to evaluate satellite algorithms and land surface models. The two basic theories to estimate ?E, Penman-Monteith equation and Monin-Obukhov similarity, are similar because the first is derived from the second under three assumptions that (1) surface energy is balanced, (2) the surface can be regard as a big leaf, and (3) atmospheric transfer coefficients for water and heat are equal. However, practical applications for these two theories differ substantially due to their sensitivity to errors of input data. There are six major methods that could provide continuous ?E observations: (1) eddy covariance, (2) Bowen ratio, (3) weighable lysimeters, (4) scintillometer, (5) surface water budget, and (6) atmosphere water budget. The first two of these methods are widely accepted and deployed to provide high quality ?E data. However, its measurements are of short duration and sparse spatial coverage, and therefore, cannot provide long-term regional or global estimates of ?E. Existing evaluations of satellite remote sensing algorithms and land surface models focus on diurnal and seasonal variation. The capability of satellite algorithms and land surface models in estimating inter-annual or decadal variation of regional ?E is still unknown. Furthermore, as a consequence of the lack of information on how to partition total E into soil evaporation, canopy evaporation and canopy transpiration, results from 10 widely accepted models give simulated ratios of global averaged vegetation transpiration to total E varying from 0.25 to 0.64 with an average of 0.42. This uncertainty therefore limits the capability of land surface models to provide the sensitivities of ?E to precipitation deficit and land cover change. The ?E from existing land surface models appears to be overly sensitive to precipitation deficits. A global average for E derived from surface water balance is about 1.3 mm per day (~38 Wm-2 for ?E). The inter-annual or decadal variations of regional ?E still have large uncertainties, whether derived from observations, satellites remote sensing or land surface models.

Wang, K.; Dickinson, R. E.

2011-12-01

233

KEPLER OBSERVATIONS OF RAPID OPTICAL VARIABILITY IN ACTIVE GALACTIC NUCLEI  

SciTech Connect

Over three quarters in 2010-2011, Kepler monitored optical emission from four active galactic nuclei (AGNs) with {approx}30 minute sampling, >90% duty cycle, and {approx}<0.1% repeatability. These data determined the AGN optical fluctuation power spectral density (PSD) functions over a wide range in temporal frequency. Fits to these PSDs yielded power-law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGNs exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first-order magnetorotational instability theoretical calculations of accretion disk fluctuations.

Mushotzky, R. F.; Edelson, R. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Baumgartner, W. [Laboratory for High Energy Astrophysics, NASA/GSFC, Code 662, Greenbelt, MD 20771 (United States); Gandhi, P., E-mail: richard@astro.umd.edu [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)

2011-12-10

234

Infrared and sub-mm observations of cataclysmic variables  

NASA Astrophysics Data System (ADS)

Although cataclysmic variables (CVs) come in a wide variety of shapes and sizes, the essential ingredients are a compact primary star and a Roche-lobe-filling secondary. In most cases the cool component is a main sequence dwarf, and the compact component a white dwarf (WD). Material from the cool component flows through the inner Lagrangian point via an accretion disc onto the surface of the WD; the flow near the WD is significantly affected by the strength of the magnetic field the WD may have (see Warner for a review of CVs). CVs are characterised by regular eruptions, ranging in energetics and frequency from ‘dwarf novae’, in which eruptions of amplitude ~3-4 mag in the visual occur every few days to weeks, to classical novae (CNe) in which the eruption is explosive, due to thermonuclear runaway (TNR) in material accreted on the surface of the WD (see Bode & Evans for a review of CNe).

Evans, A.

2010-11-01

235

Equatorial F2 characteristic variability: A review of recent observations  

NASA Astrophysics Data System (ADS)

This paper reviews the variability of equatorial/low latitude F2 characteristics with emphasis on the most general results reported by authors. On a general note, diurnal variation of ionospheric F2 layer characteristics coefficient of variability (CV) is characterised by post- and pre-midnight peaks at all seasons, epochs and longitude. The post-midnight peak is greater than pre-midnight peak for all the characteristics considered except h'F2 CV during high solar activity (HSA) possibly due to occurrence of post-sunset pre-reversal enhancement (PRE) in height of reflection prominent during HSA. NmF2 CV is greater than CV of MUF and h'F2. MUF CV and foF2 CV are of the same order of magnitude. While seasonal trend is little or nil in daytime CV of F2 layer characteristics, nighttime CV is greater in general at the equinoxes and June Solstice. Nighttime F2 layer characteristics CV are found to decrease with increasing sunspot. This is not the case with daytime CV. Except for h'F2 CV, daytime CV of F2 layer characteristics are independent of latitude while nighttime CV decreases with latitude. Equatorial stations east (Vanimo, 2.7°S, 141.3°E, dip 22.5°S) and west (Huancayo, 12°S, 75.3°W, dip 1.9°N) of the Greenwich Meridian (GM) have greater nighttime CV than those in the neighbourhood of the GM (Ouagadougou, 12.4°N, 1.5°W, dip 7.6°N) with those stations west of GM having the greatest CV, implying longitudinal effect on CV. During magnetic storms CV are reported to be greater than during quiet periods.

Somoye, E. O.; Akala, A. O.; Adeniji-Adele, R. A.; Iheonu, E. E.; Onori, E. O.; Ogwala, A.

2013-10-01

236

Ultraviolet Observations of Solar Variability from the Solar Dynamics Observatory  

Microsoft Academic Search

The launch of the Solar Dynamics Observatory (SDO) in February 2010 allows for continuous ultraviolet observations of the Sun on all times scales from seconds to years. These variations in the solar plasma cause significant deviations in the Earth and space environments on similar time scales, such as affecting the atmospheric densities and composition of particular atoms, molecules, and ions

Phillip C. Chamberlin

2011-01-01

237

Kepler observations of the variability in B-type stars  

Microsoft Academic Search

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB\\/beta Cephei (beta Cep) hybrids. In all cases,

L. A. Balona; A. Pigulski; P. De Cat; G. Handler; J. Gutiérrez-Soto; C. A. Engelbrecht; F. Frescura; M. Briquet; J. Cuypers; J. Daszynska-Daszkiewicz; P. Degroote; R. J. Dukes; R. A. Garcia; E. M. Green; U. Heber; S. D. Kawaler; H. Lehmann; B. Leroy; J. Molenda-Zaaowicz; C. Neiner; A. Noels; J. Nuspl; R. Østensen; D. Pricopi; I. Roxburgh; S. Salmon; M. A. Smith; J. C. Suárez; M. Suran; R. Szabó; K. Uytterhoeven; J. Christensen-Dalsgaard; H. Kjeldsen; D. A. Caldwell; F. R. Girouard; D. T. Sanderfer

2011-01-01

238

Observational constraints on a variable dark energy model  

SciTech Connect

We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are {omega}{sub m}=0.27{sub -0.02}{sup +0.02} (the present matter content) and w{sub 0}=-1.45{sub -0.60}{sup +0.35} (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objects.

Movahed, M. Sadegh [Department of Physics, Sharif University of Technology, P.O.Box 11365-9161, Tehran (Iran, Islamic Republic of); Institute for Studies in theoretical Physics and Mathematics, P.O.Box 19395-5531, Tehran (Iran, Islamic Republic of); Iran Space Agency, P.O.Box 199799-4313, Tehran (Iran, Islamic Republic of); Rahvar, Sohrab [Department of Physics, Sharif University of Technology, P.O.Box 11365-9161, Tehran (Iran, Islamic Republic of); Institute for Studies in theoretical Physics and Mathematics, P.O.Box 19395-5531, Tehran (Iran, Islamic Republic of)

2006-04-15

239

Decadal variability of East Australian Current transport inferred from repeated high-density XBT transects, a CTD survey and satellite altimetry  

NASA Astrophysics Data System (ADS)

A time series of the net geostrophic transport through the Tasman Sea (representing the flow of the East Australian Current (EAC) Extension) is determined from a full-depth CTD section, 15 years of high-density XBT transects, and satellite altimetry data. A section between Sydney and Wellington (PX34) has been occupied four times per year since 1991 with high resolution XBT sampling. Two methods to infer baroclinic transport from proxy data along the section are presented. The first uses shallow XBT transects to derive geostrophic transport relative to a deep (2000 m) reference level. In the second approach (SynTS) the subsurface temperature and salinity structure are inferred from satellite surface height and temperature fields using a model developed from historical in situ observations. The baroclinic transport is then computed in the usual manner. The methods are validated using both a full-depth CTD occupation of the PX34 section and further transects crossing the EAC in the northern Tasman Sea. There is close agreement between the 49 XBT and SynTS PX34 transport estimates obtained between 1992 and 2006. The time series of transport through the Sydney-Wellington section shows a range of temporal signals from eddyscale, seasonal, interannnual to decadal. In particular, we note that the net EAC flow ranges from 5 Sv in 1995 to a maximum of 16 Sv in 2000/2001. This decadal variation confirms the EAC response to a spin-up of the South Pacific circulation forced by changes in the basin-wide winds and matches the changes in oceanic properties observed in the Tasman Sea.

Ridgway, K. R.; Coleman, R. C.; Bailey, R. J.; Sutton, P.

2008-08-01

240

Source parameter inversion for recent great earthquakes from a decade-long observation of global gravity fields  

NASA Astrophysics Data System (ADS)

We quantify gravity changes after great earthquakes present within the 10 year long time series of monthly Gravity Recovery and Climate Experiment (GRACE) gravity fields. Using spherical harmonic normal-mode formulation, the respective source parameters of moment tensor and double-couple were estimated. For the 2004 Sumatra-Andaman earthquake, the gravity data indicate a composite moment of 1.2 × 1023 N m with a dip of 10°, in agreement with the estimate obtained at ultralong seismic periods. For the 2010 Maule earthquake, the GRACE solutions range from 2.0 to 2.7 × 1022 N m for dips of 12°-24° and centroid depths within the lower crust. For the 2011 Tohoku-Oki earthquake, the estimated scalar moments range from 4.1 to 6.1 × 1022 N m, with dips of 9°-19° and centroid depths within the lower crust. For the 2012 Indian Ocean strike-slip earthquakes, the gravity data delineate a composite moment of 1.9 × 1022 N m regardless of the centroid depth, comparing favorably with the total moment of the main ruptures and aftershocks. The smallest event we successfully analyzed with GRACE was the 2007 Bengkulu earthquake with M0 ~ 5.0 × 1021 N m. We found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events. Deeper sources (i.e., in the upper mantle) could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume, thus reducing the negative gravity component. Focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum.

Han, Shin-Chan; Riva, Riccardo; Sauber, Jeanne; Okal, Emile

2013-03-01

241

Observations of Thermospheric Variability Using UV Remote Sensing  

NASA Astrophysics Data System (ADS)

The NASA TIMED mission has been operating since December 7, 2001. In that short time, this low-budget, small-satellite mission has made great contributions to our understanding of the coupled ionosphere- thermosphere-mesosphere system. Of the four instruments on TIMED, the Global Ultraviolet Imager (GUVI) has as its focus the upper atmosphere - from about 130 km and up to the exobase (over 500 km). In this paper I will provide a brief description of some what GUVI has told us about the mean behavior of the thermosphere and ionosphere and the response of the IT system to high latitude drivers. The data set from GUVI is rich and diverse and much more cna be done with it to improve our understanding of the IT system. While we have a very rudimentary view of the mean behavior of the neutral thermosphere as embodied in the MSIS model, GUVI has demonstrated that the response of the neutral atmosphere to perturbations is complex - in fact, one wonders whether we have seen the quiescent state of the thermosphere, even as we approach solar minimum. Comparisons with MSIS show that significant issues remain. We can test our understanding of the upper atmosphere by evaluating the response to and the recovery from an impulsive event such as a geomagnetic disturbance. To do that we need a global data set of thermospheric observations (i.e. at more than one local solar time). The TIMED satellite enables these studies to some degree as it covers all local solar times in 60 days. Ideally one would simultaneous coverage at at least one more local solar time. That can be achieved by using data from the DMSP SSUSI instruments. TIMED has shown that a very low-cost mission can make a contribution to our understanding of the global IT system. The planned IT Storm Probes and Geospace Electrodynamics Connections (GEC) missions are the only IT mission planned for the next 15 years. These low-cost multi-satellite missions are slated to begin operations in 2016 - at the earliest. The community should note that the combined follow-on to DMSP and NOAA (NPOESS) has little in the way of upper atmospheric or space weather measurements. What will be the legacy of TIMED in such an environment?

Paxton, L. J.

2006-12-01

242

Variability of trace gas concentrations over Asian region: satellite observations vs model  

NASA Astrophysics Data System (ADS)

Nitrogen dioxide (NO_2) and Carbon Monoxide (CO) play a key role in the chemistry of the tropospheric ozone and are emitted mainly by anthropogenic processes. These emissions have been increasing over Asia over the past few years due to rapid economic growth and yet there are very few systematic ground based observations of these species over this region. We have analysed ten years of data from space borne instruments: Global Ozone Monitoring Experiment (GOME), SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and Measurements of Pollution in the Troposphere (MOPITT), which have been measuring the tropospheric abundance of these trace gases. We have examined trends over the period 1996-2008 in NO_2 and CO over a few Indian regions where high economic growth in the present decade is likely to see increased emissions for these species. However, even the highest growth rate of these species seen in the present study, is less when compared with similar polluted regions of China, where a much more rapid increase has been observed. In order to understand the trends and variability in atmospheric trace gas concentrations, one must take into account changes in emissions and transport. Only by assessing the relevance of each of these factors will it be possible to predict future changes with reasonable confidence. To this effect we have used a global chemical transport model, MOZART, to simulate concentrations of NO_2 and CO using the POET (European) and REAS (Asian) emission inventories. These are compared with satellite measurements to study seasonal variations and the discrepancies are discussed. The combined uncertainties of the emission inventory and retrieval of the satellite data could be contributing factors to the discrepancies. It may be thus worthwhile to develop emission inventories for India at a higher resolution to include local level activity data.

Sheel, Varun; Richter, Andreas; Srivastava, Shuchita; Lal, Shyam

2012-07-01

243

Sub-Seasonal Variability of Tropical Rainfall Observed by TRMM and Ground-based Polarimetric Radar  

NASA Astrophysics Data System (ADS)

Studies of tropical precipitation characteristics from the TRMM-LBA and NAME field campaigns using ground-based polarimetric S-band data have revealed significant differences in microphysical processes occurring in the various meteorological regimes sampled in those projects. In TRMM-LMA (January-February 1999 in Brazil; a TRMM ground validation experiment), variability is driven by prevailing low-level winds. During periods of low-level easterlies, deeper and more intense convection is observed, while during periods of low-level westerlies, weaker convection embedded in widespread stratiform precipitation is common. In the NAME region (North American Monsoon Experiment, summer 2004 along the west coast of Mexico), strong terrain variability drives differences in precipitation, with larger drops and larger ice mass aloft associated with convection occurring over the coastal plain compared to convection over the higher terrain of the Sierra Madre Occidental, or adjacent coastal waters. Comparisons with the TRMM precipitation radar (PR) indicate that such sub-seasonal variability in these two regions are not well characterized by the TRMM PR reflectivity and rainfall statistics. TRMM PR reflectivity profiles in the LBA region are somewhat lower than S-Pol values, particularly in the more intense easterly regime convection. In NAME, mean reflectivities are even more divergent, with TRMM profiles below those of S-Pol. In both regions, the TRMM PR does not capture rain rates above 80 mm hr-1 despite much higher rain rates estimated from the S-Pol polarimetric data, and rain rates are generally lower for a given reflectivity from TRMM PR compared to S-Pol. These differences between TRMM PR and S-Pol may arise from the inability of Z-R relationships to capture the full variability of microphysical conditions or may highlight problems with TRMM retrievals over land. In addition to the TRMM-LBA and NAME regions, analysis of sub-seasonal precipitation variability and comparison of TRMM PR statistics with ground-based radar has been extended to other regions of the globe. The Australian Bureau of Meteorology C-band polarimetric radar C-Pol has been collecting data in Darwin, Australia for over a decade. The Darwin region affords the opportunity to look at precipitation characteristics over land and ocean, as well as variability associated with monsoon and break periods over long periods of time. The polarimetric X-band radar XPort was stationed in West Africa at a field site in Benin during the 2006 and 2007 African monsoon periods, where differences in rainfall associated with African Easterly Wave (AEW) passages and non-AEW periods can be examined. Similar comparisons between TRMM PR and ground based polarimetric radars will also be reported for these regions.

Dolan, Brenda; Rutledge, Steven; Lang, Timothy; Cifelli, Robert; Nesbitt, Stephen

2010-05-01

244

Decade Volcanoes  

NSDL National Science Digital Library

In the 1990s, the International Association of Volcanology and Chemistry of the Earth's Interior started the Decade Volcano Project. As part of their work, they designated sixteen volcanoes particularly worthy of study "because of their explosive histories and close proximity to human populations." The group recently teamed up with National Geographic to create a guide to these volcanoes via this interactive map. Navigating through the map, visitors can learn about Mount Rainier, Colima, Galeras, Santorini, and other prominent volcanoes. For each volcano, there's a brief sketch that gives the date of its last eruption, its elevation, nearby population centers, and a photograph. Additionally, visitors can learn more by clicking on the sections titled "Did You Know?" and "Eruption Interactive".

2007-11-02

245

Mixed-Effects Logistic Regression Models for Indirectly Observed Discrete Outcome Variables  

ERIC Educational Resources Information Center

|A well-established approach to modeling clustered data introduces random effects in the model of interest. Mixed-effects logistic regression models can be used to predict discrete outcome variables when observations are correlated. An extension of the mixed-effects logistic regression model is presented in which the dependent variable is a latent…

Vermunt, Jeroen K.

2005-01-01

246

Assessment of variability in continental low stratiform clouds based on observations of radar reflectivity  

Microsoft Academic Search

The variability of overcast low stratiform clouds observed over the ARM Climate Research Facility Southern Great Plains (ACRF SGP) site is analyzed, and an approach to characterizing subgrid variability based on assumed statistical distributions is evaluated. The analysis is based on a vast (>1000 hours) radar reflectivity database collected by the Millimeter-Wave Cloud Radar at ACRF SGP site. The radar

Zena N. Kogan; David B. Mechem; Yefim L. Kogan

2005-01-01

247

Towards the Prediction of Decadal to Centennial Climate Processes in the Coupled Earth System Model  

SciTech Connect

In this proposal, we have made major advances in the understanding of decadal and long term climate variability. (a) We performed a systematic study of multidecadal climate variability in FOAM-LPJ and CCSM-T31, and are starting exploring decadal variability in the IPCC AR4 models. (b) We develop several novel methods for the assessment of climate feedbacks in the observation. (c) We also developed a new initialization scheme DAI (Dynamical Analogue Initialization) for ensemble decadal prediction. (d) We also studied climate-vegetation feedback in the observation and models. (e) Finally, we started a pilot program using Ensemble Kalman Filter in CGCM for decadal climate prediction.

Zhengyu Liu, J. E. Kutzbach, R. Jacob, C. Prentice

2011-12-05

248

Project Jelly-Fish: B.R.N.O. Observations of Semiregular Variable Stars  

NASA Astrophysics Data System (ADS)

Brno Regional Network of Observers (BRNO) is a group which prefers to observe eclipsing binary stars. A team called the Jelly-Fish has been formed within BRNO for the purpose of observing variable stars other than eclipsing binaries. The observations by Jelly-Fish members are predominantly visual; CCD observing has started only recently and such observations are not yet included in our statistics. Jelly-Fish has about twenty members at this moment. This paper presents preliminary results based on Jelly-Fish observations of S Camelopardalis, AU Camelopardalis, WZ Cassiopeiae, RS Cygni, T Persei, RU Persei, and R Ursae Minoris.

Hajek, P.

2006-06-01

249

A new atmospheric proxy for sea level variability in the southeastern North Sea: observations and future ensemble projections  

NASA Astrophysics Data System (ADS)

Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October-March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude.

Dangendorf, Sönke; Wahl, Thomas; Nilson, Enno; Klein, Birgit; Jensen, Jürgen

2013-09-01

250

The American Association of Variable Star Observers: Serving the Research Community in 2010 and Beyond  

NASA Astrophysics Data System (ADS)

The American Association of Variable Star Observers (AAVSO) holds the largest single online database of variable star data in the world, collected from thousands of amateur and professional observers during the past century. One of our core missions is to preserve and distribute these data to the research community in service to the science of variable star astronomy. But as an organization, the AAVSO is much more than a data archive. Our services to the research community include: monitoring for and announcement of major astronomical events like novae and supernovae; organization and management of observing campaigns; support for satellite and other TOO observing programs by the professional community; creation of comparison star sequences and generation of charts for the observer community; and observational and other support for the amateur, professional, and educator communities in all things related to variable stars. As we begin a new century of variable star astronomy we invite you to take advantage of the services the AAVSO can provide, and to become a part of our organization yourselves. In this poster, we highlight some of the most important services the AAVSO can provide to the professional research community, as well as suggest ways in which your research may be enhanced with support from the AAVSO.

Templeton, Matthew R.; Henden, A. A.; Davis, K.; Kinne, R.; Watson, C.; Saladyga, M.; Waagen, E.; Beck, S.; Menali, G.; Price, A.; Turner, R.

2010-05-01

251

Inter-observer Variability of Clinical Criteria in Nursing Home Residents with Suspected UTI  

PubMed Central

We determined the inter-observer variability of clinical criteria for urinary tract infection (UTI) in nursing home residents. Pairs of nursing home staff caring for thirty residents were interviewed at times of suspected UTI. At least one measure from each clinical criteria category was reliably observed by nursing home staff members.

Juthani-Mehta, Manisha; Tinetti, Mary; Perrelli, Eleanor; Towle, Virginia; Van Ness, Peter H.; Quagliarello, Vincent

2009-01-01

252

Comparing variability and trends in observed and modelled global-mean surface temperature  

Microsoft Academic Search

The observed evolution of the global-mean surface temperature over the twentieth century reflects the combined influences of natural variations and anthropogenic forcing, and it is a primary goal of climate models to represent both. In this study we isolate, compare, and remove the following natural signals in observations and in climate models: dynamically induced atmospheric variability, the El Niño-Southern Oscillation,

John C. Fyfe; Nathan P. Gillett; David W. J. Thompson

2010-01-01

253

Observer-based indirect adaptive fuzzy integral sliding mode control with state variable filters  

Microsoft Academic Search

This paper proposes an observer-based indirect adaptive fuzzy integral sliding mode controller with state variable filters for a class of unknown nonlinear dynamic systems that not all the states are available for measurement. First, the fuzzy models for describing the input\\/output behavior of the nonlinear dynamic system are constructed. Next, an observer is applied to estimate the tracking error vector.

Chung-Chun Kung; Ti-Hung Chen

2005-01-01

254

Variability of soft X-ray emission of EX Hydrae observed with Einstein Observatory  

Microsoft Academic Search

The cataclysmic variable star EX Hydrae has been observed with the High Resolution Imager (HRI) and the Imaging Proportional Counter (IPC) onboard the Einstein Observatory. The X-ray position is coincident within 3 arcsec of the optical position as measured on Schmidt survey plates. During a 15 1\\/2 hour observation with IPC a search has been made for a modulation of

A. Kruszewski; R. Mewe; J. Heise; W. van Dijk; T. Chlebowski; R. Bakker

1982-01-01

255

The Study of Resonant Variability Observed in the Massive LMC System BI 108  

NASA Astrophysics Data System (ADS)

The LMC star BI 108 is photometrically variable with the unique light curve: Two strong periods are present in a strict 3:2 resonance, staying coherent over several observing seasons. A spectroscopic data collected at VLT/UVES reveals unexpected and still not fully understood behavior of the system, that has not been observed in any other early-type multiple systems.

Ko?aczkowski, Z.; Mennickent, R.; Rivinius, T.

2010-12-01

256

Seasonal to decadal variations of water vapor in the tropical lower stratosphere observed with balloon-borne cryogenic frost point hygrometers  

NASA Astrophysics Data System (ADS)

We investigated water vapor variations in the tropical lower stratosphere on seasonal, quasi-biennial oscillation (QBO), and decadal time scales using balloon-borne cryogenic frost point hygrometer data taken between 1993 and 2009 during various campaigns including the Central Equatorial Pacific Experiment (March 1993), campaigns once or twice annually during the Soundings of Ozone and Water in the Equatorial Region (SOWER) project in the eastern Pacific (1998-2003) and in the western Pacific and Southeast Asia (2001-2009), and the Ticosonde campaigns and regular sounding at Costa Rica (2005-2009). Quasi-regular sounding data taken at Costa Rica clearly show the tape recorder signal. The observed ascent rates agree well with the ones from the Halogen Occultation Experiment (HALOE) satellite sensor. Average profiles from the recent five SOWER campaigns in the equatorial western Pacific in northern winter and from the three Ticosonde campaigns at Costa Rica (10°N) in northern summer clearly show two effects of the QBO. One is the vertical displacement of water vapor profiles associated with the QBO meridional circulation anomalies, and the other is the concentration variations associated with the QBO tropopause temperature variations. Time series of cryogenic frost point hygrometer data averaged in a lower stratospheric layer together with HALOE and Aura Microwave Limb Sounder data show the existence of decadal variations: The mixing ratios were higher and increasing in the 1990s, lower in the early 2000s, and probably slightly higher again or recovering after 2004. Thus linear trend analysis is not appropriate to investigate the behavior of the tropical lower stratospheric water vapor.

Fujiwara, M.; VöMel, H.; Hasebe, F.; Shiotani, M.; Ogino, S.-Y.; Iwasaki, S.; Nishi, N.; Shibata, T.; Shimizu, K.; Nishimoto, E.; Valverde Canossa, J. M.; Selkirk, H. B.; Oltmans, S. J.

2010-09-01

257

An Intrinsic Short-Term Radio Variability Observed in PKS 1510-089  

NASA Astrophysics Data System (ADS)

We searched a short-term radio variability in an active galactic nucleus, PKS 1510-089. Daily flux monitoring for 143 d at 8.4 GHz was performed, and VLBI observations at 8.4, 22, and 43 GHz were carried out 4 times during the flux monitoring period. As a result, variability with a time scale of 20 to 30 d was detected. The variation patterns were very much alike at three frequencies; moreover, those at 22 and 43 GHz were synchronized. These properties support that this short-term variability is an intrinsic one. The Doppler factor estimated from the variability time scale is 47. Since the Doppler factor is not extraordinary large for AGN, such intrinsic variability with a time scale of less than 30 d would exist in other AGNs.

Kadota, Akiko; Fujisawa, Kenta; Sawada-Satoh, Satoko; Wajima, Kiyoaki; Doi, Akihiro

2012-10-01

258

Decadal Comparison of Plankton Levels  

NSDL National Science Digital Library

The global ocean chlorophyll archive produced by the CZCS was revised using compatible algorithms with SeaWiFS. Both archives were then blended with in situ data to reduce residual errors. This methodology permitted a quantitative comparison of decadal changes in global ocean chlorophyll from the CZCS (1979 - 1986) and SeaWiFS (1997 - 2000) records. Global spatial distributions and seasonal variablility of ocean chlorophyll were similar, but global means decreased over the two observational segments. Major changes were observed regionally: chlorophyll concentrations decreased in the northern high latitudes while chlorophyll in the low latitudes increased. Mid-ocean gyres exhibited limited changes. The overall spatial and seasonal similarity of the two data records suggests that the changes are due to natural variability. These results provide evidence of how the Earths climate may be changing and how ocean biota respond.

Thomson, Joycelyn; Gregg, Watson

2002-08-08

259

X-ray observations of selected cataclysmic variable stars using the Einstein observatory  

Microsoft Academic Search

X-ray observations of twelve cataclysmic variable stars using the Einstein Observatory are reported. Nine of these stars, representing all subclasses of cataclysmic variables, were detected. Their fluxes range from 2 x 10⁻¹³ to 1 x 10⁻¹¹ ergs cm⁻² s⁻¹ in the energy interval 0.16--4.5 keV. The 2 sigma upper limits for the remaining stars, which include the so-called magnetic rotators

F. A. Cordova; K. O. Mason; J. E. Nelson

1981-01-01

260

Argentina's Lost Decade  

Microsoft Academic Search

Argentina suffered a depression in the 1980s that was as severe as the Great Depression experienced in the United States and Germany in the interwar period. Our paper examines this depression from the perspective of growth theory, taking total factor productivity as exogenous. The predictions of the growth model conform rather well with the observations during the “lost decade” years.

Finn E. Kydland; Carlos E. J. M. Zarazaga

2002-01-01

261

Observer Variability of the Breast Imaging Reporting and Data System (BI-RADS) Lexicon for Mammography  

PubMed Central

Aim We aimed to determine the inter- and intra-observer variabilities between breast radiologists and a general radiologist in categorizing mammographic lesions using the Breast Imaging Reporting and Data System (BI-RADS), and to evaluate the effects of the histopathologic results on the variability. Methods Mammograms from 142 women who underwent biopsy were evaluated. 3 breast radiologists (2 with >10 years experience and 1 with 1 year experience) and 1 general radiologist retrospectively reviewed mammograms twice within an 8-week interval. Inter- and intra-observer variabilities were assessed with Cohen's kappa statistic, and the positive predictive value for final assessments was calculated. Results The intra-observer variability for mass and calcification assessments was moderate to almost perfect (kappa values: 0.41–1) for breast imagers and was fair to substantial for the general radiologist (kappa values: 0.21–0.8). Inter-observer agreement between the breast imagers was higher than between the breast and general radiologists. There was no apparent difference in agreement between observers for malignant and benign subgroups. Conclusions The differences in intra- and inter-observer agreement between the breast imagers and the general radiologist affirm the utility of the BI-RADS lexicon. The histopathologic results of the lesions do not affect the agreement. BI-RADS is a simple and adequate tool for assessing mammograms, even after only 1 year of training.

Adibelli, Zehra H.; Ergenc, Ruken; Oztekin, Ozgur; Ecevit, Suheyla; Unal, Gokhan; Abal?, Yusuf

2010-01-01

262

Phase and cycle dependence of the photospheric structure and observable properties of Mira variables.  

NASA Astrophysics Data System (ADS)

Nonlinear pulsation models designed to represent the prototype Mira variable o Ceti have been produced. Both fundamental mode and first-overtone models were examined. The fundamental mode models have light and velocity amplitudes similar to those observed and they exhibit bumps on the rising parts of the light curve and aperiodic motion in the upper layers as found observationally in Mira variables. As first found in previous studies, the first-overtone models were not able to produce the observed velocity amplitudes of Mira variables, largely because of the low gravity of the models. This problem suggests that Miras are fundamental mode pulsators. The effect of radiation pressure acting on H_2_O molecules in the outer stellar layers was examined as a source of driving mass loss. It was found that the radiation force on H_2_O molecules had very little effect on the pulsation and did not lead to any mass loss. A series of photospheric models were made based on the density stratifications of the pulsation models at different phases. Synthetic spectra were computed and these were used to derive monochromatic radii to compare with observations of Mira variables with different periods. The computed radii for ?lambda_=1 at different phases in continuum windows was very close to the Rosseland radii. The general appearance of the synthetic spectra and their variation with phase resembled the observations of Mira variables quite well. The behaviour of absorption line profiles from the moving atmospheres was followed through the different phases and cycles of the different model series. A complex behaviour of some lines with phase is predicted. Better agreement between theoretical and observed spectra, colors and radii of Mira variables can be expected to follow from improvements to the treatment of the molecular line opacity.

Bessell, M. S.; Scholz, M.; Wood, P. R.

1996-03-01

263

Quantitative Comparison of the Variability of Simulated and Observed Hyperspectral Solar Radiance  

NASA Astrophysics Data System (ADS)

Principal component analysis (PCA) is a multivariate spectral decomposition technique that has been used to study the variability of Earth-reflected hyperspectral solar radiances measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) aboard ENVISAT and radiances output by Observation System Simulation Experiments (OSSEs). OSSEs have been used to simulate radiance measurements for the NASA Climate and Absolute Radiance and Refractivity Observatory (CLARREO) hyperspectral shortwave instrument over the twenty-first century. Principal component analysis returns eigenvectors and eigenvalues of the spectral covariance matrix calculated from the spectral radiances. Using PCA, we have identified primary underlying physical variables directly from these reflected radiances. The spectral signatures of the principal components (PCs) reveal that clouds, water vapor, vegetation, and sea ice explain the largest fraction of the SCIAMACHY data variance. Comparing the spectral shapes of the principal components calculated from the OSSEs radiances to the SCIAMACHY PCs shows that the OSSE PCs produce similar results, implying that the OSSE reproduces the observed spectral variability within Earth's climate system. PCA applied to the OSSE spectral radiances can also be used to study how the spatial variability of the dominant spectral variables changes over time. PCA combined with multivariate time series analysis techniques such as Singular Spectrum Analysis and Multichannel Singular Spectrum Analysis, will augment our understanding of the expected temporal variability of these dominant variables over the twenty-first century. We have also evaluated the degree to which the OSSE captures the variability of Earth's climate system with quantitative comparisons of the principal components from the OSSE and SCIAMACHY radiances. The results of this analysis may provide guidance as to the elements of the climate system the simulated radiances need to represent more accurately. These quantitative comparisons between simulated and observed radiances can also be used to directly link model inputs to the dominant spectral variables found from PCA. These links can be used to develop future retrieval algorithms for hyperspectral solar radiance measurements and facilitate attribution of climate variability to physical variables. The results from these analysis techniques provide a better understanding of how characterizing the variability of hyperspectral visible and near infrared imagery will benefit future climate-monitoring satellite missions through climate change detection and attribution.

Roberts, Y.; Pilewskie, P.; Kindel, B. C.; Feldman, D.; Collins, W.

2011-12-01

264

The Nature and Origin of Decadal to Millennial Scale Climate Variability in the Southern Tropics of South America: The Holocene Record of Lago Umayo, Peru  

Microsoft Academic Search

This paper serves two purposes: to review current ideas about the nature and forcing of decadal to millennial scale precipitation\\u000a variation in the southern tropics of South America during the late Quaternary and to present a new methodology for the reconstruction\\u000a of precipitation as applied to a Holocene stable isotopic record of carbonate sediments in a tropical Andean lake, Lago

Paul A. Baker; Sherilyn C. Fritz; Stephen J. Burns; Erik Ekdahl; Catherine A. Rigsby

265

Interannual variability of winter oceanic CO2 and air-sea CO2 flux in the western North Pacific for 2 decades  

Microsoft Academic Search

The 2-decade records of the partial pressure of CO2 in surface waters (pCO2sea) and the resulting air-sea CO2 flux in the extensive subtropical to equatorial area along 137°E in the western North Pacific in winter exhibited significant interannual variations that differed in different regions. The pCO2sea varied largely in the equatorial region of 3°N to 6°N, depending on the oceanographic

Takashi Midorikawa; Masao Ishii; Kazuhiro Nemoto; Hitomi Kamiya; Akira Nakadate; Shinji Masuda; Hidekazu Matsueda; Toshiya Nakano; Hisayuki Y. Inoue

2006-01-01

266

Observed metre scale horizontal variability of elemental carbon in surface snow  

NASA Astrophysics Data System (ADS)

Surface snow investigated for its elemental carbon (EC) concentration, based on a thermal–optical method, at two different sites during winter and spring of 2010 demonstrates metre scale horizontal variability in concentration. Based on the two sites sampled, a clean and a polluted site, the clean site (Arctic Finland) presents the greatest variability. In side-by-side ratios between neighbouring samples, 5 m apart, a ratio of around two was observed for the clean site. The median for the polluted site had a ratio of 1.2 between neighbouring samples. The results suggest that regions exposed to snowdrift may be more sensitive to horizontal variability in EC concentration. Furthermore, these results highlight the importance of carefully choosing sampling sites and timing, as each parameter will have some effect on EC variability. They also emphasize the importance of gathering multiple samples from a site to obtain a representative value for the area.

Svensson, J.; Ström, J.; Hansson, M.; Lihavainen, H.; Kerminen, V.-M.

2013-09-01

267

An Observational and Computational Variable Tagging System for Climate Change Informatics  

NASA Astrophysics Data System (ADS)

As climate change science uses diverse data from observations and computational results to model and validate earth systems from global to local scale, understand complex processes, and perform integrated assessments, adaptable and accessible information systems that integrate these observations and model results are required. The data processing tasks associated with the simultaneous use of observation and modeling data are time-consuming because scientists are typically familiar with one or the other, but rarely both. Each data domain has its own portal, its own metadata formats, and its own query-building methods for obtaining datasets. The exact definition of variables and observational parameters may require substantial searches for unfamiliar topics. The dearth of formal descriptions such as ontologies compounds the problem and negatively impacts the advancement of science for each aspect of studying climate change. Our Observational and Computational Variable Tagging System aims to address these challenges through facilitating the quick identification of datasets of interest across archives by associating variables with tags or keywords from a controlled vocabulary. The prototype currently offers the ability to search by tags, variable names, and annotations. Names, plain text descriptions, units, dimensions, and a link to each dataset are returned. The information is aggregated from various locations at the source of origin. Keywords from NASA’s Global Change Master Directory provide built-in suggestions for tags. These features ensure accuracy and disambiguation. For the target application, the system tags variables and stores data from the Community Climate System Model (CCSM), International Boundary Water Commission, US Geological Survey, National Oceanic and Atmospheric Administration, and NASA. Our tagging system allows users to identify variable names and descriptions of observational and computational data from a single Web interface. Our system provides an easy-to-use cross-referencing tool to help overcome an important barrier to inter-disciplinary research in climate change science. As proof-of-concept, the tagging system targets a use case based on comparison of model results against observational data to validate trends for river stream flows in the forthcoming CCSM4. Existing climate models have no ability to account for damming and other man-made stream flow obstructions. However, observational data report on dammed rivers: there is no account of how an un-managed river would fare. One solution to this problem is to use both observational data and historical portions of model data to find regions where observed stream flow and model results are highly correlated. Based on these regions, an anticipated outcome is model refinement. Another potential outcome is the discovery of un-managed rivers that may be good candidates for correctly predicting stream flow under climate change conditions.

Pouchard, L. C.; Lenhardt, W.; Branstetter, M. L.; Runciman, A.; Wang, D.; Kao, S.; King, A. W.; Climate Change Informatics Team

2010-12-01

268

Sensitivity of Portuguese forest fires to climatic, human, and landscape variables: subnational differences between fire drivers in extreme fire years and decadal averages  

Microsoft Academic Search

Within the changing fire regimes of Portugal, the relative importance of humans and climatic variability for regional fire\\u000a statistics remains poorly understood. This work investigates the statistical relationship between temporal dynamics of fire\\u000a events in Portugal and a set of socioeconomic, landscape, and climatic variables for the time periods of 1980–1990, 1991–2000,\\u000a and extreme fires years. For 10 of 15

Luís Costa; Kirsten Thonicke; Benjamin Poulter; Franz-W. Badeck

269

Variability in Observed and Sensor Based Estimated Optimum N Rates in Corn  

Technology Transfer Automated Retrieval System (TEKTRAN)

Recent research showed that active sensors such as Crop Circle can be used to estimate in-season N requirements for corn. The objective of this research was to identify sources of variability in the observed and Crop Circle-estimated optimum N rates. Field experiments were conducted at two locations...

270

Structure of SST and Surface Wind Variability during Indian Ocean Dipole Mode Events: COADS Observations  

Microsoft Academic Search

A study of the detailed spatiotemporal characteristics of the Indian Ocean dipole (IOD) mode in SST and surface winds using available observations from 1958 till 1997 is reported. The analysis is used to address several of the controversial issues regarding the IOD.One key finding of this study is that interdecadal fluctuations contribute strongly to tropical Indian Ocean (TIO) SST variability;

N. H. Saji; T. Yamagata

2003-01-01

271

California Undercurrent variability and eddy transport estimated from RAFOS float observations  

Microsoft Academic Search

RAFOS float observations collected between 1992 and 2002 were analyzed to identify the seasonal variability of circulation in four geographical boxes which extended along the central and northern California coast and were successively located farther offshore. The mean pressure of the floats was 375 dbar. Poleward flow associated with the California Undercurrent dominated the two boxes closest to shore, extending

Curtis A. Collins; Leonid M. Ivanov; Oleg V. Melnichenko; Newell Garfield

2004-01-01

272

Observed seasonal variability of barrier layer in the Bay of Bengal  

Microsoft Academic Search

The observed formation of barrier layer (BL) and the seasonal variability of BL thickness (BLT) in the Bay of Bengal are examined utilizing the most comprehensive data set. Thick BL (?40 m) first appears in the coastal region of the northeastern bay in June and spreads westward as the summer monsoon progresses. Along the east coast of India the BL

Pankajakshan Thadathil; P. M. Muraleedharan; R. R. Rao; Y. K. Somayajulu; G. V. Reddy; C. Revichandran

2007-01-01

273

Microwave enhancement and variability in the elephant's trunk coronal hole: Comparison with SOHO observations  

Microsoft Academic Search

We report on an investigation of the microwave enhancement and its variability in the elephant's trunk coronal hole observed during the Whole Sun Month campaign (August 10 to September 9, 1996). The microwave images from the Nobeyama radioheliograph were compared with magnetograms and EUV images obtained simultaneously by the Michelson Doppler imager and the extreme ultraviolet imaging telescope (EIT) on

N. Gopalswamy; K. Shibasaki; B. J. Thompson; J. Gurman; C. DeForest

1999-01-01

274

Variable Olivine Detection in Soils at Meridiani Planum From Mars Express OMEGA and MER Opportunity Observations  

Microsoft Academic Search

The Meridiani plains have been characterized spectrally using data collected on the ground by the Opportunity rover and from orbit by the Mars Express OMEGA instrument. Observations completed by the Opportunity rover show that the Meridiani plains are covered by aeolian deposits composed of basaltic sands, gray hematite spherules, and variable amounts of bright dust. Measurements made by the Mössbauer

S. M. Wiseman; R. E. Arvidson; F. Poulet; R. V. Morris; D. W. Ming

2006-01-01

275

VARIABILITY IN OBSERVED AND SENSOR BASED ESTIMATED OPTIMUM N RATES IN CORN  

Technology Transfer Automated Retrieval System (TEKTRAN)

Recent research showed that active sensors such as Crop Circle can be used to estimate in-season N requirements in corn. The objective of this research was to identify the sources of variability in the observed and estimated economic optimum N rates (EONR) using Crop Circle. Field experiments were c...

276

Observations of wind-induced subtidal variability in the Delaware estuary  

Microsoft Academic Search

Sea level and current observations made in the Delaware estuary during autumn of 1982 were examined for evidence of wind-forced subtidal variability. The large subtidal sea level fluctuations at the mouth of the Delaware were found to be forced primarily by the wind stress component over the continental shelf nearly parallel to shore, indicating coastal Ekman transport to the right

Kuo-Chun Wong; Richard W. Garvine

1984-01-01

277

Structured observations of hygiene behaviours in Burkina Faso: validity, variability, and utility.  

PubMed Central

The use of observation techniques has been promoted for the study of hygiene practices; however, questions still remain about the validity and repeatability of such techniques. In this article we compare data on hygiene behaviours obtained from questionnaires with data obtained using a structured observation approach and examine the repeatability of structured observations of behaviours and spot observations of environmental conditions. Poor agreement between questionnaire responses and observations was found for child defecation and stool disposal practices (kappa statistic: 0.25 and 0.28, respectively). There was evidence of over-reporting of "good" behaviours (P < 0.0001). Repeated observations of child defecation and stool disposal behaviours showed better agreement (kappa statistic: 0.76 and 0.62, respectively) based on small sample sizes. These findings suggest that our questionnaire data are less valid than data obtained by direct observation. However, different approaches to questioning may be less prone to over-reporting of "good" behaviours than our approach. Further research into the validity of different forms of question is warranted. Behaviours and conditions related to hygiene vary. Observations may be useful in determining the frequency of different behaviours/conditions in the community. However, individual practices may be too variable to assign individuals to exposed and non-exposed groups for the purpose of identifying links with health outcomes. Further studies on the variability of behaviours and the repeatability of observations are therefore needed.

Curtis, V.; Cousens, S.; Mertens, T.; Traore, E.; Kanki, B.; Diallo, I.

1993-01-01

278

Evaluating the observed variability in hyperspectral Earth-reflected solar radiance  

NASA Astrophysics Data System (ADS)

We explore the potential for directly measured hyperspectral Earth-reflected solar radiances to provide sufficient information to study changes in Earth's climate based on the quantified variability of the data using principal component analysis (PCA) and singular spectrum analysis. To do this we used these two multivariate analysis techniques on Earth-reflected radiances between 300 and 1750 nm measured from space by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument. The spatial and temporal variability of hyperspectral reflected radiances over global, hemispherical, and regional scales was quantified. As few as six components were needed to explain over 99.5% of the variance in all cases studied, with the exception of an Arctic Ocean case in which only four components were needed. Both of these values represent large reductions in dimensionality of the input radiances from 291 spectral bands. PCA facilitated attribution of the dominant spectral patterns extracted to atmospheric and surface variables, including water vapor, clouds, surface albedo, and sea ice. The second most dominant spectral variable, that is, the second principal component, in the Arctic closely resembled sea ice reflectance and followed the temporal behavior of sea ice extent determined from AMSR-E observations. The extraction of the spectral, spatial, and temporal variability in reflected shortwave hyperspectral radiance using multivariate analysis provides an alternate and complementary approach to inverse methods for applying space-based observations to climate studies.

Roberts, Yolanda L.; Pilewskie, Peter; Kindel, Bruce C.

2011-12-01

279

Observation Of New Variable Stars In The Field Of Open Cluster M23  

NASA Astrophysics Data System (ADS)

In 2002 a program of surveying regions containing bright open star clusters was initiated using the observing facilities at Luther College. As part of this program the half degree square field containing open cluster M23 was observed in 2003, 2005 and 2006, resulting in approximately 45,000 2.5-second images, 45,000 3.5-second images and 65,000 5.0-second images. The data set contains images from 94 nights spanning a time range from JD 2452810 to JD 2454005. We have searched for stellar variability on timescales from seconds to years in approximately 1600 stars in this field. Unambiguous variability is apparent in 30 stars ranging in magnitude from about 10 to 17. Twenty-eight of these stars have not been previously reported as variable. Seven of the stars are eclipsing binaries, including two apparent W UMa-type contact binaries and one additional eclipsing binary with a period shorter than 0.6 days. The remaining 23 variables are red pulsating stars with long periods. Most of these stars have amplitudes smaller than two magnitudes and periods between 200 and 400 days. Thus, they are likely Semi-Regular variables. We present celestial coordinates, estimated amplitude and estimated period for each of these stars, as well as several selected light curves. Finally, we have performed low-precision BVRI photometry of the field and have placed most of the observed variables on color magnitude diagrams. We are grateful for support from the Roy J. Carver Charitable Trust and the R. J. McElroy Trust.

Wilkerson, Jeffrey A.; Brown, T. S.; Frank, K. A.; Joshi, U.; Lacoul, B. K.; Rengstorf, N. P.; Schiefelbein, A. M.

2007-05-01

280

Intensive Observations of Cataclysmic, RR Lyr, and High Amplitude delta Scuti (HADS) Variable Stars  

NASA Astrophysics Data System (ADS)

An intensive observing campaign is ongoing to study cataclysmic, RR Lyr (with and without Blazhko effect), and High Amplitude delta Scuti (HADS) variable stars. These observations are based on requests and in collaboration with different organisations (CBA, VSNET, GEOS) and individuals. Observations are taken from my private observatories in Belgium, Chile, and through shared use of an observatory belonging to the AAVSOnet in New Mexico. Examples of individual stars intensively followed-up on are: CD Ind and BW Scl, two cataclysmic variables; NU Aur, an RR Lyr star with strong Blazhko effect; and GSC0762-0110, a HADS star. Many publications in different journals including Astronomy and Astrophysics have already emerged from this research.

Hambsch, F.-J.

2012-06-01

281

Towards identification of relevant variables in the observed aerosol optical depth bias between MODIS and AERONET observations  

NASA Astrophysics Data System (ADS)

Measurements made by satellite remote sensing, Moderate Resolution Imaging Spectroradiometer (MODIS), and globally distributed Aerosol Robotic Network (AERONET) are compared. Comparison of the two datasets measurements for aerosol optical depth values show that there are biases between the two data products. In this paper, we present a general framework towards identifying relevant set of variables responsible for the observed bias. We present a general framework to identify the possible factors influencing the bias, which might be associated with the measurement conditions such as the solar and sensor zenith angles, the solar and sensor azimuth, scattering angles, and surface reflectivity at the various measured wavelengths, etc. Specifically, we performed analysis for remote sensing Aqua-Land data set, and used machine learning technique, neural network in this case, to perform multivariate regression between the ground-truth and the training data sets. Finally, we used mutual information between the observed and the predicted values as the measure of similarity to identify the most relevant set of variables. The search is brute force method as we have to consider all possible combinations. The computations involves a huge number crunching exercise, and we implemented it by writing a job-parallel program.

Malakar, N. K.; Lary, D. J.; Gencaga, D.; Albayrak, A.; Wei, J.

2013-08-01

282

Solar variability observed through changes in solar figure and mean diameter  

NASA Astrophysics Data System (ADS)

The work performed on solar variability during 1989 at (Santa Clara Lab for Experimental Relativity by Astrometry) SCLERA is reviewed. That portion of the SCLERA research program supported by the Department of Energy has been directed toward the detection and monitoring of climatically significant solar variability by accurate measurement of the variability in solar shape and diameter. Observations were obtained in 1989 and results from analysis of earlier observations obtained. Systematic long term changes in the apparent solar diameter and/or radius were detected and these changes were found to strongly correlate with long term changes in solar total irradiance. Additional evidence for gravity mode coupling was found which may be important to understanding neutrino and fusion energy production rates in the solar core. Each of these findings may be important to anticipating future changes in the solar luminosity. Progress was made in setting up an international network based on SCLERA type instruments to improve the coverage and quality of the observations. A proposal is made for the continuation of support from the DOE for further studies relevant to solar variability forecasting.

Hill, Henry A.

1990-01-01

283

Multi-decadal river flows variations in France  

NASA Astrophysics Data System (ADS)

In this article, multi-decadal variations in French hydroclimate are investigated, with a specific focus on river flows. Based on long observed series, it is shown that river flows in France generally exhibit large multi-decadal variations on the historical period, especially in spring. Differences of means between two 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations. Multi-decadal spring river flows variations are associated with variations in spring precipitation and temperature. These multi-decadal variations in precipitation are themselves found to be driven by large-scale atmospheric circulation, more precisely by a multi-decadal oscillation in a sea level pressure dipole between western Europe and the East Atlantic. It is suggested that the Atlantic Multidecadal Variability, the main mode of decadal variability in the North Atlantic/Europe sector, controls those variations in large-scale circulation and is therefore the main ultimate driver of multi-decadal variations in spring river flows. Multi-decadal variations in river flows in other seasons, and in particular summer, are also noted. As they are not associated with significant surface climate anomalies (i.e. temperature, precipitation) in summer, other mechanisms are investigated based on hydrological simulations. The impact of climate variations in spring on summer soil moisture, and the impact of soil moisture in summer on the runoff to precipitation ratio, could potentially play a role in multi-decadal summer river flows variations. The large amplitude of the multi-decadal variations in French river flows suggests that internal variability may play a very important role in the evolution of river flows during the next decades, potentially temporarily limiting, reversing or seriously aggravating the long-term impacts of anthropogenic climate change.

Boé, J.; Habets, F.

2013-09-01

284

Multidecadal Variability Simulated With an Atmospheric General Circulation Model Forced With Observed Sea Surface Temperature  

NASA Astrophysics Data System (ADS)

We investigate the response of an atmospheric general circulation model to observed sea surface temperature for the instrumental period 1856-2000. The model used is the {nderline P}ortable {nderline U}niversity {nderline M}odel of the {nderline A}tmosphere (PUMA) developed at the University of Hamburg for long-term climate studies. When the model is forced with global sea surface temperatures (SSTs) the model interdecadal variability is dominated by the Atlantic Interdecadal Mode (AIM) and its associated teleconnection patterns. The modeled interdecadal variability sea surface patterns are in good agreement with analysis of observational time series in an ensemble mode integration. Positive SST anomalies and a sea level pressure (SLP) dipole pattern dominate the North Atlantic while a strong positive anomaly in SLP is characteristic for the North Pacific Ocean. Although the observational database is short, investigations of the typical AIM patterns before and after the climate shift in the 1970's suggest an oscillatory multidecadal mode rather than a singular event for that period. Additional experiments with ''Atlantic only'' forcing depict strong sensitivities of the relative roles of Atlantic and Pacific SST data initiating variability at multidecadal time scales. Our results have implications for climate predictability on long time scales from observed SST data.

Grosfeld, K.; Rimbu, N.; Lohmann, G.; Lunkeit, F.

2002-12-01

285

Inter- and intra-observer variability in radiologists' assessment of mass similarity on mammograms  

NASA Astrophysics Data System (ADS)

The purpose of this study was to compare the performances of two recently-developed image retrieval methods for mammographic masses, and to investigate the inter- and intra-observer variability in radiologists' assessment of mass similarity. Method 1 retrieved masses that are similar to a query mass from a reference library based on radiologists' margin and shape descriptions and the mass size. Method 2 used computer-extracted features. Two MQSA radiologists participated in an observer study in which they rated the similarity between 100 query masses and the retrieved lesions based on margins, shape, and size. For each query mass, three masses retrieved using Method 1 and three masses retrieved using Method 2 were displayed in random order using a graphical user interface. A nine-point similarity rating scale was used, with a rating of 1 indicating lowest similarity. Each radiologist repeated the readings twice, separated by more than three months, so that intra-observer variability could be studied. Averaged over the two radiologists, two readings, and all masses, the mean similarity ratings were 5.59 and 5.57 for Methods 1 and 2, respectively. The difference between the two methods did not reach significance (p>0.20) for either radiologist. The intra-observer variability was significantly lower than the inter-observer variability, which may indicate that each radiologist may have their image similarity criteria, and the criteria may vary from radiologist to radiologist. The understanding of the trends in radiologists' assessment of mass similarity may guide the development of decision support systems that make use of mass similarity to aid radiologists in mammographic interpretation.

Sahiner, Berkman; Hadjiiski, Lubomir M.; Chan, Heang-Ping; Cui, Jing; Paramagul, Chintana; Nees, Alexis; Helvie, Mark

2009-02-01

286

Estimating river discharge from earth observation measurements of river surface hydraulic variables  

NASA Astrophysics Data System (ADS)

River discharge is a key variable for quantifying the water cycle, its fluxes and stocks at different scales. These scales range from a local scale for the efficient management of water resources to a global scale for the monitoring of climate change. Therefore, developing Earth observation (EO) techniques for the measurement or estimation of river discharge poses a major challenge. A key question deals with the possibility of deriving river discharge values from EO surface variables (width, level, slope, and velocity are the only such variables accessible through EO) without any in situ measurement. Based on a literature study and original investigations, this study explores the possibilities of estimating river discharge from water surface variables. The proposed method relies on limiting assumptions to simplify river flow equations to obtain the values of the hydraulic parameters at a given river station without using ground measurements. Once the hydraulic parameters are identified, the method allows the estimation of the river discharge corresponding to a set of surface measurements of hydraulic variables.

Negrel, J.; Kosuth, P.; Bercher, N.

2011-06-01

287

The three-class ideal observer for univariate normal data: Decision variable and ROC surface properties  

PubMed Central

Although a fully general extension of ROC analysis to classification tasks with more than two classes has yet to be developed, the potential benefits to be gained from a practical performance evaluation methodology for classification tasks with three classes have motivated a number of research groups to propose methods based on constrained or simplified observer or data models. Here we consider an ideal observer in a task with underlying data drawn from three univariate normal distributions. We investigate the behavior of the resulting ideal observer’s decision variables and ROC surface. In particular, we show that the pair of ideal observer decision variables is constrained to a parametric curve in two-dimensional likelihood ratio space, and that the decision boundary line segments used by the ideal observer can intersect this curve in at most six places. From this, we further show that the resulting ROC surface has at most four degrees of freedom at any point, and not the five that would be required, in general, for a surface in a six-dimensional space to be non-degenerate. In light of the difficulties we have previously pointed out in generalizing the well-known area under the ROC curve performance metric to tasks with three or more classes, the problem of developing a suitable and fully general performance metric for classification tasks with three or more classes remains unsolved.

Edwards, Darrin C.; Metz, Charles E.

2012-01-01

288

Observations of high-frequency variability in the chromospherically active star V390 Aurigae  

NASA Astrophysics Data System (ADS)

V390 Aurigae is a rapidly rotating, chromospherically active late-type giant. The X-ray emission from the corona of V390 Aur, observed by the XMM-Newton space observatory, indicates intense flaring activity on this star. Multisite, coordinated high-speed UBVRI photometry of V390 Aur and a reference star was carried out in years 2002-2009 at the Peak Terskol, Crimean and Belogradchik observatories, aimed at finding persistent variability on millisecond-to-subsecond time-scales. We find that variability is peaked at f ˜ 1 Hz, gradually subsiding in the range 0.1-10 Hz, with the peak rms amplitude of 0.005 mag in the UBV bands. We conclude that the light curves of V390 Aur contain microflares that may be responsible for the observed activity on subsecond time-scales, with a relative power of fluctuations reaching (2.1-3.0) × 10-5 in the UBV bands.

Zhilyaev, Boris E.; Verlyuk, Irina A.; Andreev, Maxim V.; Sergeev, Alexandr V.; Lovkaya, Margarita N.; Tsap, Yury T.; Konstantinova-Antova, Renada K.; Antov, Alexandr P.; Bogdanovski, Rumen; Spassov, Borislav; Svyatogorov, Oleg A.; Stetsenko, Kirill O.; Bondar, Arkadii V.; Taradii, Volodymyr K.

2013-10-01

289

First detection of a seasonality of stratomesospheric CO above mid-latitudes via solar FTIR measurements. Analysis of one decade of observations at the NDACC Primary Station Zugspitze  

NASA Astrophysics Data System (ADS)

Model studies revealed that stratomesospheric CO exhibits considerable seasonal and latitudinal variations caused by the competition between downward transport from the thermospheric production region and photochemical loss processes. A sharp latitudinal gradient with highest abundances at the North Pole was found which implies that the mid-latitude region can exhibit strong enhancements of stratomesospheric CO under conditions of large-scale planetary wave activity displacing CO enriched vortex air from North to South. Unfortunately, until now there are not enough continuous long-term measurements of stratomesospheric CO at mid-latitudes to prove this assumption. Velazco et al. [2007] reported ground-based FTIR measurements of stratomesospheric CO partial columns from several sites in the Arctic, northern and southern mid-latitudes, and Antarctica. Unfortunately, this study concluded that, generally, the mid-latitude stations show no significant annual variability of stratomesospheric CO columns. However, already early microwave observations indicated that stratomesospheric CO is about twice as large in mid-latitude winter as in summer [Clancy et al., 1982]. Obviously, there was a technical difficulty with the FTIR inversion of mid-latitude mesospheric CO in the early study by Velazco et al. [2007]. It is one aim of this paper to present a solution to this problem. Therefore, this paper describes an improved retrieval approach for ground-based FTIR stations, that is capable to derive a significant seasonal cycle of stratomesospheric CO at mid-latitudes. Coincident measurements at Zugspitze (2964 m a.s.l.) and Garmisch (744 m a.s.l.) show perfect agreement (R = 0.94) which proves that the new retrieval approach is not limited to high altitude stations, and is thus applicable to all mid-latitude stations. The first long-term series of stratomesospheric CO at mid-latitudes (42.42°N, 10.98°E) derived from ground-based FTIR spectrometry is presented (1999 to 2008). Between November and April the monthly mean time series shows column enhancements by a factor of 2.2 relative to the summer minimum of 1.64E16 cm-2 with a maximum of 3.63E16 cm-2 in February and strong year-to-year variability of up to 32 % (1 sigma). The seasonality agrees very well with the WACCM model [Garcia et al., 2007] which, however, can not reproduce measured year-to-year variability. Pronounced short time enhancements (duration of 1 to 3 days) are observed, which during winter exceed the monthly-mean background seasonality by up to 276 %. Comparison with WACCM and FTIR measurements at high-latitudes [Jones et al., 2007] reveal, that these enhancements reflect inner vortex conditions and are due to transport by planetary waves. References Clancy, R. T., D. O. Muhleman and G. L. Berge (1982), Microwave spectra of terrestrial mesospheric CO, J. Geophys. Res., 87, 5009 - 5014. Garcia, R. R., D. R. Marsh, D. E. Kinnison, B. A. Boville, and F. Sassi (2007), Simulation of secular trends in the middle atmosphere, 1950-2003, J. Geophys. Res., 112, D09301, doi: 10.1029/2006JD007485. Jones, N. B., Y. Kasai, E. Dupuy, Y. Murayama, J. Urban, B. Barret, M. Sinnhuber, A. Kagawa, T. Koshiro, P. Ricaud, and D. Murtagh (2007), Stratomesospheric CO measured by a ground-based Fourier Transform Spectrometer over Poker Flat, Alaska: Comparison with Odin/SMR and a 2-D model, J. Geophys. Res., 112, D20303, doi: 10.1029/2006JD007916. Velazco, V., S. W. Wood, M.Sinnhuber, I. Kramer, N. B. Jones, Y. Kasai, J. Notholt, T. Warneke, T. Blumenstock, F. Hase, F. J. Murcray, and O. Schrems (2007), Annual variation of strato-mesospheric carbon monoxide measured by ground-based Fourier transform infrared spectrometry, Atmos. Chem. Phys., 7, 1305-1312.

Borsdorff, T.; Sussmann, R.; Rettinger, M.

2009-04-01

290

Optical observations of the growth and day-to-day variability of equatorial plasma bubbles  

Microsoft Academic Search

A new narrow-field ionospheric imaging system, the Portable Ionospheric Camera and Small-Scale Observatory, has been installed at the Cerro Tololo Inter-American Observatory near La Serena, Chile (geographic 30.17°S, 289.19°E; geomagnetic 16.72°S, 0.42°E). We present observations of the naturally occurring nightglow emission at 630.0 nm on three consecutive nights demonstrating the day-to-day variability in the occurrence of equatorial plasma bubbles or

J. J. Makela; E. S. Miller

2008-01-01

291

Optical observations of the growth and day-to-day variability of equatorial plasma bubbles  

Microsoft Academic Search

A new narrow-field ionospheric imaging system, the Portable Ionospheric Camera and Small-Scale Observatory, has been installed at the Cerro Tololo Inter-American Observatory near La Serena, Chile (geographic 30.17°S, 289.19°E geomagnetic 16.72°S, 0.42°E). We present observations of the naturally occurring nightglow emission at 630.0 nm on three consecutive nights demonstrating the day-to-day variability in the occurrence of equatorial plasma bubbles or

J. J. Makela; E. S. Miller

2008-01-01

292

Investigation of observed day-to-day variability in September mesopause region tidal-period perturbations  

Microsoft Academic Search

Simultaneous observations of the tidal-period perturbations (diurnal, semidiurnal, .etc) of temperature, zonal wind, and meridional wind in the mesopause region (80km-105km) by the CSU two-beam Na lidar system in Fort Collins, Colorado between UT day 264 and 272, September 2003 (a 9-day continuous campaign) indicate a dramatic day-to-day variability on tidal amplitudes. Further analysis on the dataset with best fit

T. Li; B. P. Williams; C. She; H. Liu

2004-01-01

293

Variability of soft X-ray emission of EX Hydrae observed with Einstein Observatory  

Microsoft Academic Search

The cataclysmic variable EX Hydrae has been observed in X-rays with Einstein Observatory. A 67 min periodic X-ray modulation has been found in the energy range. 1 – 2 keV, whereas the source is approximately constant above 2 keV. The modulation is approx. in phase with the stable 47 min modulation in the optical brightness. The X-ray spectrum changes slightly

A. Kruszewski; R. Mewe; J. Heise; T. Chlebowski; W. van Dijk; R. Bakker

1981-01-01

294

Precise High-cadence Time Series Observations of Five Variable Young Stars in Auriga with MOST  

NASA Astrophysics Data System (ADS)

To explore young star variability on a large range of timescales, we have used the MOST satellite to obtain 24 days of continuous, sub-minute cadence, high-precision optical photometry on a field of classical and weak-lined T Tauri stars (TTSs) in the Taurus-Auriga star formation complex. Observations of AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal brightness fluctuations at the 1%-10% level on timescales of hours to weeks. We have further assessed the variability properties with Fourier, wavelet, and autocorrelation techniques, identifying one significant period per star. We present spot models in an attempt to fit the periodicities, but find that we cannot fully account for the observed variability. Rather, all stars exhibit a mixture of periodic and aperiodic behavior, with the latter dominating stochastically on timescales less than several days. After removal of the main periodicity, periodograms for each light curve display power-law trends consistent with those seen for other young accreting stars. Several of our targets exhibited unusual variability patterns not anticipated by prior studies, and we propose that this behavior originates with the circumstellar disks. The MOST observations underscore the need for investigation of TTS light variations on a wide range of timescales in order to elucidate the physical processes responsible; we provide guidelines for future time series observations. Based on data from the MOST satellite, a Canadian Space Agency mission, jointly operated by Systems Canada Inc. (MSCI), formerly part of Dynacon, Inc., the University of Toronto Institute for Aerospace Studies, and the University of British Columbia with the assistance of the University of Vienna.

Cody, Ann Marie; Tayar, Jamie; Hillenbrand, Lynne A.; Matthews, Jaymie M.; Kallinger, Thomas

2013-03-01

295

Seasonal to decadal variations of water vapor in the tropical lower stratosphere observed with balloon-borne cryogenic frost point hygrometers  

Microsoft Academic Search

We investigated water vapor variations in the tropical lower stratosphere on seasonal, quasi-biennial oscillation (QBO), and decadal time scales using balloon-borne cryogenic frost point hygrometer data taken between 1993 and 2009 during various campaigns including the Central Equatorial Pacific Experiment (March 1993), campaigns once or twice annually during the Soundings of Ozone and Water in the Equatorial Region (SOWER) project

M. Fujiwara; H. Vömel; F. Hasebe; M. Shiotani; S.-Y. Ogino; S. Iwasaki; N. Nishi; T. Shibata; K. Shimizu; E. Nishimoto; J. M. Valverde Canossa; H. B. Selkirk; S. J. Oltmans

2010-01-01

296

Variables  

NSDL National Science Digital Library

This site, presented by Statistics Canada, is a section from "Statistics: Power from Data!" on variable classification. It discusses categorical and numerical variables and their types. The site discusses these variables: nominal, ordinal, numeric, continuous, and discrete. This is a good introductory site for any mathematics classroom studying statistics.

2008-12-25

297

Variability of V4332 Sgr observed in the near-IR  

NASA Astrophysics Data System (ADS)

We carried out near-IR photometric observations of of the enigmatic variable star V4332 Sgr with the 3.8-m United Kingdom Infrared Telescope (UKIRT) and the UKIRT Wide Field Camera (WFCAM) using the near-IR MKO filters Z, Y, J, H and K (effective wavelengths: 0.8717, 1.0305, 1.2483, 1.6313 and 2.2010 microns respectively) on multiple epochs from 25 May to 6 Oct. 2011. The epochs of observations, filters used and the magnitudes estimated (in the UKIRT-WFCAM photometric system) are given in the table below.

Varricatt, W. P.; Wold, T.; Carroll, T.; Ehle, J.; Banerjee, D. P. K.; Ashok, N. M.

2012-04-01

298

Amateur Observing Patterns and Their Potential Impact on Variable Star Science  

NASA Astrophysics Data System (ADS)

In this paper I highlight some trends seen in amateur observations submitted to the AAVSO over the past fifty years. Some systematic trends are noted in both the amount of data submitted and the frequency with which stars are observed. Two trends are evident: the decreasing number of days per year when individual stars are observed, and the overall decreasing number of visual observations submitted. The former is shown through an analysis of data submitted for a number of subclasses of cataclysmic variable, while the latter is generally evident across all variable star types through our overall annual totals. A decrease in nightly coverage may impact the kinds of science that can be done with AAVSO light curves. The decrease in visual observing may result in a loss of long-term coverage that impacts the usability of long-term light curves. I discuss possible impacts on the kinds of science that can be done with AAVSO data and long-term light curves, and suggest ways to address this issue.

Templeton, M. R.

2012-06-01

299

Comparison of precipitation isotope variability across the tropical Pacific in observations and SWING2 model simulations  

NASA Astrophysics Data System (ADS)

the dynamics of the Earth's hydrologic cycle benefits from the use of isotope-equipped global climate models. However, isotope model simulations are not often compared together, along with existing observations, to assess the distribution of simulated stable isotope variability. Here we evaluate the spatial and temporal patterns of tropical Pacific precipitation isotope variability in global climate models from the second Stable Water Isotope Intercomparison Group experiment and in observations. The tropical Pacific is home to many isotope-based proxies of paleoclimatic change, and as such is an important target for such model-data comparisons. We find spatial and temporal examples of precipitation-isotope mismatches, highlighting that factors beyond the amount effect influence precipitation isotope variability across the tropical Pacific. The models that best capture mean annual precipitation in the tropical Pacific are not necessarily the models that best simulate the mean annual stable isotopic composition of precipitation. Nudging with reanalysis winds has a small effect on precipitation ?18O values. Model performance and the strength of the relationship between precipitation and precipitation ?18O values varies between the western, central, and eastern equatorial Pacific. In the majority of the simulations, western equatorial Pacific ?18O values are correlated with large-scale, but not local precipitation, whereas in the central and eastern equatorial Pacific, ?18O values are correlated most strongly with regional precipitation. This comparison provides a cautionary note on using results from a single model to assist in interpretation of paleoclimate proxy records.

Conroy, Jessica L.; Cobb, Kim M.; Noone, David

2013-06-01

300

Inter-observer variability in the measurement of diffuse intrinsic pontine gliomas  

PubMed Central

Diffuse intrinsic pontine glioma (DIPG) is an invasive pediatric brainstem tumor with a poor prognosis. Patients commonly enter investigational trials, many of which use radiographic response as an endpoint for assessing drug efficacy. However, DIPGs are difficult to measure on magnetic resonance imaging (MRI). In this study, we characterized the reproducibility of these commonly performed measurements. Each of four readers measured 50 MRI scans from DIPG patients and inter-observer variability was estimated with descriptive statistics. Results confirmed that there is wide variability in DIPG tumor measurements between readers for all image types. Measurements on FLAIR imaging were most consistent. For patients on clinical trials, measurement of DIPG should be performed by a single reader while comparing prior images side-by-side. Endpoints for clinical trials determining efficacy in this population should also include more objective measures, such as survival, and additional endpoints need to be investigated.

Hayward, Robert M.; Patronas, Nicolas; Baker, Eva H.; Vezina, Gilbert; Albert, Paul S.; Warren, Katherine E.

2008-01-01

301

Inter-observer variability in the measurement of diffuse intrinsic pontine gliomas.  

PubMed

Diffuse intrinsic pontine glioma (DIPG) is an invasive pediatric brainstem tumor with a poor prognosis. Patients commonly enter investigational trials, many of which use radiographic response as an endpoint for assessing drug efficacy. However, DIPGs are difficult to measure on magnetic resonance imaging (MRI). In this study, we characterized the reproducibility of these commonly performed measurements. Each of four readers measured 50 MRI scans from DIPG patients and inter-observer variability was estimated with descriptive statistics. Results confirmed that there is wide variability in DIPG tumor measurements between readers for all image types. Measurements on FLAIR imaging were most consistent. For patients on clinical trials, measurement of DIPG should be performed by a single reader while comparing prior images side-by-side. Endpoints for clinical trials determining efficacy in this population should also include more objective measures, such as survival, and additional endpoints need to be investigated. PMID:18587536

Hayward, Robert M; Patronas, Nicolas; Baker, Eva H; Vézina, Gilbert; Albert, Paul S; Warren, Katherine E

2008-06-28

302

Observed and simulated variability of extreme temperature events over South America  

NASA Astrophysics Data System (ADS)

This invited review paper tends to summarise the results based on the variability of occurrence of temperature extremes in South America. The first thing to note is that there is a geographical imbalance with respect to the number of published studies on temperature extremes. Most of the results come from the southern part of South America, east of the Andes, and a few from the northern part of the continent and for the Altiplano. The workshop organised by the ETCCDMI in Brazil was the first time to have the opportunity to collect information in a regional way and present trends in extreme daily temperatures. A better geographical picture enhanced with more data show significant geographical trends in warm (positive) and cold (negative) nights over Southern South America and over the northern South America coast. All other studies based on smaller regions also agree in finding the most significant trends in the evolution of the minimum temperature, with positive trends in almost all studies on the occurrence of warm nights (or hot extremes of minimum temperature) and negative trend in the cold extremes of the minimum. On the other hand, there is little agreement on the variability of maximum temperature. Generally the maximum temperature in southern South America has decreased, in opposition to the case of northern South America where it has increased. Strong decadal and interannual variability have been found in the occurrence of cold extremes. Reanalysis and climate models underestimate the intensity of extremes, mainly near the Andes. The studies trying to understand the dynamics of the circulation that leads to the occurrence of these extremes are analysed from its occurrence in almost all scales from the synoptic, intraseasonal, seasonal, annual, and multi-year linear trend with different methodologies, also, indentifying the local and remote forcing. A gap was found in studies that relate some specific local forcing (like changes in land use) and compare it with the remote ones. Different aspects of the occurrence of the temperature extremes are still missing in some regions of the continent.

Rusticucci, Matilde

2012-03-01

303

Variability and budget of CO2 in Europe: analysis of the CAATER airborne campaigns - Part 1: Observed variability  

NASA Astrophysics Data System (ADS)

Atmospheric airborne measurements of CO2 are very well suited for estimating the time-varying distribution of carbon sources and sinks at the regional scale due to the large geographical area covered over a short time. We present here an analysis of two cross-European airborne campaigns carried out on 23-26 May 2001 (CAATER-1) and 2-3 October 2002 (CAATER-2) over Western Europe. The area covered during CAATER-1 and CAATER-2 was 4° W to 14° E long; 44° N to 52° N lat and 1° E to 17° E long; 46° N to 52° N lat respectively. High precision in situ CO2, CO and Radon 222 measurements were recorded. Flask samples were collected during both campaigns to cross-validate the in situ data. During CAATER-1 and CAATER-2, the mean CO2 concentration was 370.1 ± 4.0 (1-? standard deviation) ppm and 371.7 ± 5.0 (1-?) ppm respectively. A HYSPLIT back-trajectories analysis shows that during CAATER 1, northwesterly winds prevailed. In the planetary boundary layer (PBL) air masses became contaminated over Benelux and Western Germany by emissions from these highly urbanized areas, reaching about 380 ppm. Air masses passing over rural areas were depleted in CO2 because of the photosynthesis activity of the vegetation, with observations as low as 355 ppm. During CAATER-2, the back-trajectory analysis showed that air masses were distributed among the 4 sectors. Air masses were enriched in CO2 and CO over anthropogenic emission spots in Germany but also in Poland, as these countries have part of the most CO2-emitting coal-based plants in Europe. Simultaneous measurements of in situ CO2 and CO combined with back-trajectories helped us to distinguish between fossil fuel emissions and other CO2 sources. The ?CO/?CO2 ratios (R2 = 0.33 to 0.88, slopes = 2.42 to 10.37), calculated for anthropogenic-influenced air masses over different countries/regions matched national inventories quite well, showing that airborne measurements can help to identify the origin of fossil fuel emissions in the PBL even when distanced by several days/hundreds of kms from their sources. We have compared airborne CO2 observations to nearby ground station measurements and thereby, confirmed that measurements taken in the lower few meters of the PBL (low-level ground stations) are representative of the local scale, while those located in the free troposphere (FT) (moutain stations) are representative of atmospheric CO2 regionally on a scale of a few hundred kilometers. Stations located several 100 km away from each other differ from a few ppm in their measurements indicating the existence of a gradient within the free troposphere. Observations at stations located on top of small mountains may match the airborne data if the sampled air comes from the FT rather than coming up from the valley. Finally, the analysis of the CO2 vertical variability conducted on the 14 profiles recorded in each campaign shows a variability at least 5 to 8 times higher in the PBL (the 1-? standard deviation associated to the CO2 mean of all profiles within the PBL is 4.0 ppm and 5.7 ppm for CAATER-1 and CAATER-2, respectively) than in the FT (within the FT, 1-? is 0.5 ppm and 1.1 ppm for CAATER-1 and CAATER-2, respectively). The CO2 jump between the PBL and the FT equals 3.7 ppm for the first campaign and -0.3 ppm for the second campaign. A very striking zonal CO2 gradient of about 11 ppm was observed in the mid-PBL during CAATER-2, with higher concentrations in the west than in the east. This gradient may originate from differences in atmospheric mixing, ground emission rates or Autumn's earlier start in the west. More airborne campaigns are currently under analysis in the framework of the CARBOEUROPE-IP project to better assess the likelihood of these different hypotheses. In a companion paper (Xueref-Remy et al., 2011, Part 2), a comparison of vertical profiles from observations and several modeling frameworks was conducted for both campaigns.

Xueref-Remy, I.; Messager, C.; Filippi, D.; Pastel, M.; Nedelec, P.; Ramonet, M.; Paris, J. D.; Ciais, P.

2011-06-01

304

Inter- and Intra-Observer Variability in Prostate Definition With Tissue Harmonic and Brightness Mode Imaging  

SciTech Connect

Purpose: The objective of this study was to compare the relative utility of tissue harmonic (H) and brightness (B) transrectal ultrasound (TRUS) images of the prostate by studying interobserver and intraobserver variation in prostate delineation. Methods and Materials: Ten patients with early-stage disease were randomly selected. TRUS images of prostates were acquired using B and H modes. The prostates on all images were contoured by an experienced radiation oncologist (RO) and five equally trained observers. The observers were blinded to information regarding patient and imaging mode. The volumes of prostate glands and areas of midgland slices were calculated. Volumes contoured were compared among the observers and between observer group and RO. Contours on one patient were repeated five times by four observers to evaluate the intraobserver variability. Results: A one-sample Student t-test showed the volumes outlined by five observers are in agreement (p > 0.05) with the RO. Paired Student t-test showed prostate volumes (p = 0.008) and midgland areas (p = 0.006) with H mode were significantly smaller than that with B mode. Two-factor analysis of variances showed significant interobserver variability (p < 0.001) in prostate volumes and areas. Inter- and intraobserver consistency was quantified as the standard deviation of mean volumes and areas, and concordance indices. It was found that for small glands ({<=}35 cc) H mode provided greater interobserver consistency; however, for large glands ({>=}35 cc), B mode provided more consistent estimates. Conclusions: H mode provided superior inter- and intraobserver agreement in prostate volume definition for small to medium prostates. In large glands, H mode does not exhibit any additional advantage. Although harmonic imaging has not proven advantageous for all cases, its utilization seems to be judicious for small prostates.

Sandhu, Gurpreet Kaur, E-mail: Gurpreet.Sandhu2@albertahealthservices.ca [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Dunscombe, Peter [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Meyer, Tyler [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Pavamani, Simon [Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Department of Radiation Oncology, Christian Medical College, Vellore (India); Khan, Rao [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada)

2012-01-01

305

Experimental observations and numerical modeling of coupled microbial and transport processes in variably saturated sand.  

SciTech Connect

An experimental and numerical investigation was conducted to study interactions between microbial dynamics and transport processes in variably saturated porous media. Experiments were conducted with constant, surface-applied water fluxes in duplicate, variably saturated, sand-filled columns that were uniformly inoculated with the bacterium Pseudomonas fluorescens HK44. The permeability of the sand in the columns was reduced by a factor of 45 during one week of growth on glucose. Pressure heads increased (became less negative) at all measured depths, but significant increases in the apparent volumetric water contents were only observed in the upper 5 cm of the columns, corresponding to the areas with the highest concentrations of attached bacteria. A numerical model was used to simulate the experiments. The model accounted for the processes of water flow, solute and bacterial transport, cell growth and accumulation, glucose and oxygen consumption, and gas diffusion and exchange. Observed changes in water content and pressure head were reproduced approximately using fluid-media scaling to account for an apparent surface-tension lowering effect. Reasonable correspondence was obtained between observed and simulated effluent data and final attached biomass concentration distributions using first-order reversible cell attachment and detachment kinetics with attachment rate coefficients based on particle-filtration theory, and time-dependent detachment rate coefficients. The results of this study illustrate the potential importance of using fully coupled multi-fluid flow and multi-component reactive transport equations to model coupled biogeochemical and transport processes in soils.

Rockhold, Mark L.; Yarwood, R R.; Niemet, M R.; Bottomley, Peter J.; Selker, John S.

2005-05-13

306

Optical observations of 22 violently variable extragalactic sources - 1968-1986  

NASA Astrophysics Data System (ADS)

Broadband photographic observations of 22 optically violent variable (OVV) active galactic nuclei are presented. Over 3100 observations made between 1968 and 1986 at Rosemary Hill Observatory are tabulated and displayed graphically. The majority of the observations were made in either the Johnson B system or the international photographic (PG) system. Multicolor data are presented for a few objects. Descriptions of the light curves include the assignment of each OVV to an arbitrary variability subclass. The light curves, some extending over 18 yr, are analyzed for linear trends and underlying structure using linear regression and unequal-interval Fourier transform techniques. The results of the analysis for each of the 22 objects are given, and models of the light variations of 3C 120, 3C 345, and 3C 446 are presented. The models of these light curves show underlying structure with rapid variations superimposed. The time scales seen in the light curves of 3C 120, 3C 345, and 3C 446 are compared with characteristic time scales found in massive-accretion-disk models. The time scales most likely to be responsible for the optical behavior are either the viscous or the thermal time scales.

Webb, James R.; Smith, Alex G.; Leacock, Robert J.; Fitzgibbons, Gregory L.; Gombola, Paul P.; Shepherd, David W.

1988-02-01

307

Optical observations of 22 violently variable extragalactic sources - 1968-1986  

SciTech Connect

Broadband photographic observations of 22 optically violent variable (OVV) active galactic nuclei are presented. Over 3100 observations made between 1968 and 1986 at Rosemary Hill Observatory are tabulated and displayed graphically. The majority of the observations were made in either the Johnson B system or the international photographic (PG) system. Multicolor data are presented for a few objects. Descriptions of the light curves include the assignment of each OVV to an arbitrary variability subclass. The light curves, some extending over 18 yr, are analyzed for linear trends and underlying structure using linear regression and unequal-interval Fourier transform techniques. The results of the analysis for each of the 22 objects are given, and models of the light variations of 3C 120, 3C 345, and 3C 446 are presented. The models of these light curves show underlying structure with rapid variations superimposed. The time scales seen in the light curves of 3C 120, 3C 345, and 3C 446 are compared with characteristic time scales found in massive-accretion-disk models. The time scales most likely to be responsible for the optical behavior are either the viscous or the thermal time scales. 50 references.

Webb, J.R.; Smith, A.G.; Leacock, R.J.; Fitzgibbons, G.L.; Gombola, P.P.

1988-02-01

308

Simultaneous U BV RI observations of the cataclysmic variable AE Aquarii: Temperatures and masses of fireballs  

NASA Astrophysics Data System (ADS)

We report simultaneous multicolour observations in 5 bands (U BV RI) of the flickering variability of the cataclysmic variable AE Aqr. Our aim is to estimate the parameters (colours, temperature, size) of the fireballs that produce the optical flares. The observed rise times of the optical flares are in the interval 220-440 s. We estimate the dereddened colours of the fireballs as (U-B)_0˜ 0.8-1.4, (B-V)_0 ˜ 0.03-0.24, and (V-I)_0 ˜ 0.26-0.78. We find for the fireballs temperatures of 10000-25000 K, masses of (7-90)× 1019 g, and sizes of (3-7)× 109 cm (using a distance of d=86 pc). These values refer to the peak of the flares observed in the U BV RI bands. The data are available upon request from the authors. Based on data collected with the telescopes at Bulgarian National Astronomical Observatory Rozhen and Belogradchick Astronomical Observatory.

Zamanov , R. K.; Latev, G. Y.; Stoyanov, K. A.; Boeva, S.; Spassov, B.; Tsvetkova, S. V.

2012-10-01

309

Spectroscopic observations and Doppler tomography of the short-period cataclysmic variable star V455 And  

NASA Astrophysics Data System (ADS)

We present the results of spectroscopic observations and Doppler tomography of the short-period cataclysmic variable star V455 And. The investigated spectra indicate that the disk in the system periodically changes its size. Besides, we suppose that there is a dense region in the disk, moving in the retrograde precession. This region can periodically amplify shock waves, which may be seen in the light curves of the system. The Doppler tomograms, computed, using the spectra, obtained at different orbital phases, demonstrate different bright regions. This may be an additional argument, supporting the idea of the moving dense region.

Kononov, D. A.; Bisikalo, D. V.; Puzin, V. B.; Zhilkin, A. G.; Sytov, A. Yu.

2013-09-01

310

Temperature variability in X-ray bright points observed with Hinode/XRT  

NASA Astrophysics Data System (ADS)

Aims: We investigate the variability in temperature as a function of time among a sample of coronal X-ray bright points (XBPs). Methods: We analysed a 7-h (17:00-24:00 UT) long time sequence of soft X-ray images observed almost simultaneously in two filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope (XRT) onboard the Hinode mission. We identified and selected 14 XBPs for a detailed analysis. The light curves of XBPs were derived using the SolarSoft library in IDL. The temperature of XBPs was determined using the calibrated temperature response curves of the two filters by means of the intensity ratio method. Results: We find that the XBPs show a high variability in their temperature and that the average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in average X-ray emission. It is evident from the results of time series that the XBP heating rate can be highly variable on short timescales, suggesting that it has a reconnection origin.

Kariyappa, R.; Deluca, E. E.; Saar, S. H.; Golub, L.; Damé, L.; Pevtsov, A. A.; Varghese, B. A.

2011-02-01

311

An overview of an intensive observation period on variability of coastal atmospheric refractivity  

NASA Astrophysics Data System (ADS)

This paper is an overview of an experiment called Variability of Coastal Atmospheric Refractivity (VOCAR). VOCAR was designed to be conducted under a larger program called Coastal Variability Analysis, Measurements, and Prediction and is a multi-year experimental effort to investigate the variability of atmospheric refractivity with emphasis on the coastal zone. The experiment is being conducted jointly with the Naval Air Warfare Center Weapons Division, Point Mugu, CA, the Naval Research Laboratory, and the Naval Postgraduate School. In addition, the National Oceanic and Atmospheric Administration Environmental Technology Laboratory and Penn State University/Applied Research Laboratory are participating in the measurement phase of VOCAR. The propagation measurements being made during VOCAR consist of monitoring signal strength variations of VHF/UHF transmitters in the southern California coastal region. Corresponding meteorological measurements are made during routine, special, and intensive observation periods. During an intensive measurement period from 23 August to 3 September 1993, radio data were collected at two receiver sites and meteorological data were collected from three profiler sites, eight radiosonde sites, three aircraft, and numerous surface weather sites. Samples of the data will be shown.

Paulus, Richard A.

1995-02-01

312

Moisture variability over Indian monsoon regions observed using high resolution radiosonde measurements  

NASA Astrophysics Data System (ADS)

The strong southwesterly and northeasterly flow in the lower troposphere during June–September (southwest, SW) and October–December (northeast, NE) monsoons bring substantial moisture into Indian sector. In this observational study, moisture variability over Hyderabad which is completely influenced by SW monsoon, Chennai influenced by NE monsoon and Gadanki influenced mostly by NE monsoon and partly by SW monsoon is studied. For the first time we have characterized the vertical variations in moisture based on background wind shear. The moisture variability over Indian monsoon region is compared with western Pacific and found that moisture variations are similar to western Pacific except during monsoon season. The correlation between the total precipitable water and water vapor mixing ratio is found maximum in boundary layer (BL) and decreases in free atmosphere. In general, the total precipitable water between the 850 and 600 hPa is found higher than between 900 and 850 hPa. To investigate the origin of air masses, back trajectories were calculated with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and found that wet events are originated from lower altitudes and from the Bay of Bengal. The moisture variability is found the same during both wet and dry spells within the BL but differ significantly in the mid-troposphere suggesting that the moisture above the BL plays significant role in maintaining the precipitation conditions over Indian region.

Basha, Ghouse; Ratnam, M. Venkat

2013-10-01

313

Stable Isotopic Variability in the Carbon Cycle: Reconciling Ocean Model Results with Atmospheric Observations  

NASA Astrophysics Data System (ADS)

In the face of rising sea levels, species extinction, unpredictable precipitation changes, and other potential impacts of anthropogenic climate change, there is a push for the scientific community to expand our current understanding of the major sources and sinks of global warming’s most implicated culprit, CO2. Knowing the mechanisms controlling CO2 sinks and sources will be vital for policy-makers to make informed decisions regarding its mitigation. The stable carbon isotope, 13C, can be used to partition CO2 fluxes into land and ocean components. The major fluxes of this gas (fossil fuel, ocean and land) impose distinctive and predictable fractionation patterns upon the stable isotope ratio, making it an ideal tool for distinguishing between them. One drawback to this method is that photosynthesis and respiration are not contemporaneous, and because the 13C of atmospheric CO2 is being continuously depleted through the burning of 12C-rich fossil fuels (the Suess effect), there is an isotopic “disequilibrium flux” between CO2 moving into and out of the ocean and land reservoirs. In this study, we take a new approach and seek to reconcile independent estimates of time histories of ocean fluxes with atmospheric observations. We use a combination of atmospheric CO2 and 13CO2 data, fossil fuel emission estimates, and recent ocean model results (from two different approaches) for the ocean CO2 flux, within a box-inverse model as well as a 2D transport model. We calculate time series of land flux, disequilibrium flux and photosynthetic fractionation from 1991 through 2008. Our findings reveal that if ocean variability is as small as is suggested by the ocean model, and the isotopic variability is forced into the disequilibrium flux, then the resulting disequilibrium flux has very large interannual variability (~35 PgC‰/yr). While large interannual variability in DIS seems incompatible with the Suess effect alone, it could be explained by interannual variations in the photosynthetic fractionation term, ?ab. Interannual variations in relative strength of C3 and C4 productivity and stomatal conductance could change isotopic disequilibrium over large spatial scales, thus helping to explain the otherwise seemingly incongruent nature of the ocean model results and atmospheric observations. We produce several end-member scenarios, of varying spatial resolutions, in which photosynthetic fractionation and C4 fraction of net ecosystem exchange (NEE) absorb all variability expressed in the disequilibrium flux results. We next compare our estimates of the photosynthetic fractionation and C3/C4 changes with independent climate indicators, such as precipitation and temperature anomalies, drought indices, and soil moisture.

Alden, C. B.; White, J. W.; Miller, J. B.

2009-12-01

314

An observational and modeling study of the regional impacts of climate variability  

NASA Astrophysics Data System (ADS)

Climate variability has large impacts on humans and their agricultural systems. Farmers are at the center of this agricultural network, but it is often agricultural planners---regional planners, extension agents, commodity groups and cooperatives---that translate climate information for users. Global climate models (GCMs) are a leading tool for understanding and predicting climate and climate change. Armed with climate projections and forecasts, agricultural planners adapt their decision-making to optimize outcomes. This thesis explores what GCMs can, and cannot, tell us about climate variability and change at regional scales. The question is important, since high-quality regional climate projections could assist farmers and regional planners in key management decisions, contributing to better agricultural outcomes. To answer these questions, climate variability and its regional impacts are explored in observations and models for the current and future climate. The goals are to identify impacts of observed variability, assess model simulation of variability, and explore how climate variability and its impacts may change under enhanced greenhouse warming. Chapter One explores how well Goddard Institute for Space Studies (GISS) atmospheric models, forced by historical sea surface temperatures (SST), simulate climatology and large-scale features during the exceptionally strong 1997--1999 El Nino Southern Oscillation (ENSO) cycle. Reasonable performance in this 'proof of concept' test is considered a minimum requirement for further study of variability in models. All model versions produce appropriate local changes with ENSO, indicating that with correct ocean temperatures these versions are capable of simulating the large-scale effects of ENSO around the globe. A high vertical resolution model (VHR) provides the best simulation. Evidence is also presented that SST anomalies outside the tropical Pacific may play a key role in generating remote teleconnections even during El Nino events. Based on the results from Chapter One, the analysis is expanded in several ways in Chapter Two. To gain a more complete and statistically meaningful understanding of ENSO, a 25 year time period is used instead of a single event. To gain a fuller understanding of climate variability, additional patterns are analyzed. Finally analysis is conducted at the regional scales that are of interest to farmers and agricultural planners. Key findings are that GISS ModelE can reproduce: (1) the spatial pattern associated with two additional related modes, the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO); (2) rainfall patterns in Indonesia; and (3) dynamical features such as sea level pressure (SLP) gradients and wind in the study regions. When run in coupled mode, the same model reproduces similar modes spatially but with reduced variance and weak teleconnections. Since Chapter Two identified Western Indonesia as the region where GCMs hold the most promise for agricultural applications, in Chapter Three a finer spatial and temporal scale analysis of ENSO's effects is presented. Agricultural decision-making is also linked to ENSO's climate effects. Early rainy season precipitation and circulation, and same-season planting and harvesting dates, are shown to be sensitive to ENSO. The locus of ENSO convergence and rainfall anomalies is shown to be near the axis of rainy season establishment, defined as the 6--8 mm/day isohyet, an approximate threshold for irrigated rice cultivation. As the axis tracks south and east between October and January, so do ENSO anomalies. Circulation anomalies associated with ENSO are shown to be similar to those associated with rainfall anomalies, suggesting that long lead-time ENSO forecasts may allow more adaptation than 'wait and see' methods, with little loss of forecast skill. Additional findings include: (1) rice and corn yields are lower (higher) during dry (wet) trimesters and El Nino (La Nina) years; and (2) a statistically significant negative relationship exists between malaria cases and ENSO. The fi

Horton, Radley M.

315

Overview of observations from the RADAGAST experiment in Niamey, Niger: Meteorology and thermodynamic variables  

SciTech Connect

An overview is presented of the meteorological and thermodynamic data obtained during the RADAGAST experiment in Niamey, Niger, in 2006. RADAGAST (Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data and AMMA STations), combined data from the Atmospheric Radiation Measurement (ARM) Program Mobile Facility (AMF) at Niamey airport with broadband satellite data from the Geostationary Earth Radiation Budget (GERB) instrument on Meteosat-8. The experiment was conducted in collaboration with the African Monsoon Multidisciplinary Analysis (AMMA) project. The focus in this paper is on the variations through the year of key surface and atmospheric variables. The seasonal advance and retreat of the InterTropical Front (ITF) and the seasonal changes in near-surface variables and precipitation in 2006 are discussed and contrasted with the behavior in 2005 and with long-term averages. Observations from the AMF at Niamey airport are used to document the evolution of near-surface variables and of the atmosphere above the site. There are large seasonal changes in these variables, from the arid and dusty conditions typical of the dry season to the much moister and more cloudy wet season accompanying the arrival and intensification of the West African monsoon. Back trajectories show the origin of the air sampled at Niamey and profiles for selected case studies from rawinsondes and from a MicroPulse Lidar at the AMF site reveal details of typical atmospheric structures. Radiative fluxes and divergences are discussed in the second part of this overview and the subsequent papers in this special section explore other aspects of the measurements and of the associated modeling.

Slingo, A.; Bharmal, N.; Robinson, G. J.; Settle, Jeff; Allan, R. P.; White, H. E.; Lamb, Peter J.; Lele, M.; Turner, David D.; McFarlane, Sally A.; Kassianov, Evgueni I.; Barnard, James C.; Flynn, Connor J.; Miller, Mark

2008-10-17

316

Variability and budget of CO2 in Europe: analysis of the CAATER airborne campaigns - Part 1: Observed variability  

NASA Astrophysics Data System (ADS)

Atmospheric airborne measurements of CO2 are very well-suited to estimate the time varying distribution of carbon sources and sinks at the regional scale. We present here an analysis of two cross-European airborne campaigns that have been carried out on 23-26 May 2001 (CAATER 1) and 2-3 October 2002 (CAATER 2) over Western Europe. The area covered during CAATER 1 (respectively CAATER 2) was comprised between longitude 4° W to 14° E and latitude 44° N to 52° N (respectively longitude 1° E to 17° E and latitude 46° N to 52° N). High precision in-situ CO2, CO and Radon 222 measurements have been recorded. Flasks samples have been collected during both campaigns to cross-validate the in-situ data. During CAATER 1 (respectively CAATER 2), the mean CO2 concentration was 370.1±4 ppm (respectively 371.7±5 ppm). A HYSPLIT backtrajectories analysis shows that during CAATER 1, dominant winds were blowing from the north-west. In the planetary boundary layer (PBL) airmasses got contaminated over Benelux and Western Germany by pollution from these high urbanized areas, reaching about 380 ppm. Air masses passing over rural areas are depleted in CO2 because of the photosynthesis activity of the land cover vegetation, as low as 355 ppm. During CAATER 2, the backtrajectory analysis shows that airmasses were distributed among the 4 sectors. Airmasses got enriched in CO2 and CO when passing above polluted spots in Germany but also in Poland, as these countries are known to hold part of the most polluting plants based on coal consumption, the so-called "dirty thirty" from WWF. Simultaneous measurements of in-situ CO2 and CO combined to backtrajectories helped us to discriminate the role of fossil fuel emissions from over CO2 sources. The ?CO/?CO2 ratios (R2=0.33 to 0.88, slopes=2.42 to 10.37), calculated for polluted airmasses originating from different countries/regions, matched quite well national inventories, showing that the airborne measurements can help to identify the role of fossil fuel sources even several days/hundreds of kms further in the PBL. CO2 observations have been compared to surrounding ground stations measurements, confirming that the stations located near the ground (ex. CBW, WES, HUN) are representative of the local scale, while those located in the free troposphere (FT) are representative of atmospheric CO2 on a regional scale of a few hundred kilometers (ex. CMN). Stations located several 100 km away measure CO2 concentrations different from a few ppm, indicating the existence of a gradient of a few ppm in the free troposphere. Observations at stations located on top of small mountains (ex. SCH, PUY) match or not the airborne data whether they sample air from the FT or air coming up from the valley. Finally, the analysis of the CO2 vertical variability conducted on the 14 profiles recorded per campaign shows that is at least 5 to 8 times higher in the PBL (4 ppm and 5.7 ppm for CAATER 1 and CAATER 2, respectively) than in the FT (0.5 ppm and 1.1 ppm for CAATER 1 and CAATER 2, respectively). The CO2 jump between the PBL and the FT equals 3.7 ppm for the first campaign and -0.3 ppm for the second campaign. A very striking zonal CO2 gradient of about 11 ppm could be observed in the mid-troposphere during CAATER 2, with higher concentrations in the West than in the East. This gradient could originate from differences in atmospheric mixing, ground emission rates or a earlier beginning of the Fall in the west. More airborne campaigns are currently under analysis in the framework of the CARBOEUROPE-IP project to better assess the role of these different hypothesis. In a companion paper (Xueref-Remy et al., 2010), a comparison of vertical profiles from observations and several modeling frameworks is conducted for both campaigns. An attempt to calculate CO2 fluxes during CAATER 1 using CO2 and Radon-222 observations and modeling tools is also carried out.

Xueref-Remy, I.; Messager, C.; Filippi, D.; Nedelec, P.; Ramonet, M.; Paris, J. D.; Ciais, P.

2010-02-01

317

Temporal and spatial variabilities of atmospheric polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and polycyclic aromatic hydrocarbons (PAHs) in the Canadian Arctic: results from a decade of monitoring.  

PubMed

The Northern Contaminants Program (NCP) baseline monitoring project was established in 1992 to monitor for persistent organic pollutants (POPs) in Arctic air. Under this project, weekly samples of air were collected at four Canadian and two Russian arctic sites, namely Alert, Nunavut; Tagish, Yukon; Little Fox Lake, Yukon; Kinngait, Nunavut; Dunai Island, Russia and Amderma, Russia. Selected POPs, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides, were analyzed in both the gas and particulate phases. This paper summarizes results obtained from this project in the past 5 years. Temporal trends were developed for atmospheric PCBs and OCs observed at Alert using a digital filtration (DF) technique. It was found that trends developed with 5 years of data (1993-1997) did not differ significantly from those determined with 7 years of data (1993-1999). This implies that with the DF technique, long-term trends can still be developed with less than 10 years of data. An acceleration in decline of OC and PCB air concentrations was noted in 1999 for some compounds, although the reason is unknown. Monitoring efforts must continue to assess the effect of this decline on the long-term trends of POPs in the Canadian Arctic. Occasional high trans-/cis-chlordane ratios and heptachlor air concentrations measured at Alert between 1995 and 1997 suggests sporadic fresh usage of chlordane-based pesticides. However, significant decreasing trends of chlordanes along with their chemical signatures has provided evidence that emission of old soil residues is replacing new usage as an important source to the atmosphere. Measurements of OC air concentrations conducted at Kinngait in 1994-1995 and 2000-2001 indicated faster OC removal at this location than at Alert. This may be attributed to the proximity of Kinngait to temperate regions where both biotic and abiotic degradation rates are faster. The PAH concentrations observed at Alert mimic those at mid-latitudes and are consistent with long-range transport to the Arctic, particularly for the lighter PAHs. A decline in particulate PAH was observed, similar to atmospheric sulphate aerosol and can be attributed to the collapse of industrial activity in the former Soviet Union between 1991 and 1995. Spatial comparisons of OC seasonality at Alert, Tagish, Dunai and Kinngait show elevated air concentrations of some compounds in spring. However, elevated spring concentrations were observed for different compounds at different sites. Potential causes are discussed. Further investigation in the atmospheric flow pattern in spring which is responsible for the transport of POPs into the Arctic is required. OC and PCB air concentrations at Alert were found to be influenced by two climate variation patterns, the North Atlantic Oscillation (NAO) and the Pacific North American (PNA) pattern. Planetary atmospheric patterns must be taken into account in the global prediction and modelling of POPs in the future. PMID:15866271

Hung, H; Blanchard, P; Halsall, C J; Bidleman, T F; Stern, G A; Fellin, P; Muir, D C G; Barrie, L A; Jantunen, L M; Helm, P A; Ma, J; Konoplev, A

2005-04-15

318

Variability of soft X-ray emission of EX Hydrae observed with Einstein Observatory  

NASA Astrophysics Data System (ADS)

The cataclysmic variable EX Hydrae has been observed in X-rays with Einstein Observatory. A 67 min periodic X-ray modulation has been found in the energy range 0.1-2 keV, whereas the source is approximately constant above 2 keV. The modulation is approximately in phase with the stable 47 min modulation in the optical brightness. The X-ray spectrum changes slightly with the 67 min phase but is consistent with a two-component model with constant temperature only changing in relative intensity. Quasi-simultaneous optical observations were also obtained and used to extend the time base of the optical modulation. The result is indicative of a decrease in the 67 min period on a time scale of 3 million yr. The implications for the hypothesis of a nonuniform rotating white dwarf as the origin of the 67 min optical and X-ray modulation are discussed.

Kruszewski, A.; Mewe, R.; Heise, J.; van Dijk, W.; Chlebowski, T.; Bakker, R.

1981-03-01

319

IUE and Voyager Observations of the Unusual Cataclysmic Variable S193  

NASA Astrophysics Data System (ADS)

UV observations of S193 were obtained with Voyager and the IUE satellite during both high and low states of this unusual object. Voyager only detected the source during the high state, where the continuum looks similar to the novalike IX Vela and dwarf novae at outburst. The IUE spectra at the high state show deep absorption lines, but the line ratios are not typical of disk cataclysmic variables at outburst. They are most similar to V795 Her and the SW Sex star PG0859+415. At the low state, only CIV and MgII are in emission, while the deep absorptions at SiIII and NV persist. The spectra at this state are most similar to the intermediate polar candidate H0551-819. The UV observations of S193 provide further circumstantial evidence for the existence of a disk and a magnetic white dwarf in an intermediate polar system.

Szkody, Paula; Garnavich, Peter; Holberg, Jay; Silber, Andrew; Pastwick, Lora

1997-06-01

320

Isoprene and monoterpene emission rate variability: Observations with Eucalyptus and emission rate algorithm development  

NASA Astrophysics Data System (ADS)

Variability in the emission rates of isoprene and monoterpenes from individual leaves of Eucalyptus globulus was investigated with a laboratory gas exchange system and an environmental control leaf cuvette. For individual leaves, with constant environmental conditions, short-term (1 hour) fluctuations in isoprene emission rates were less than 3% while day-to-day fluctuations averaged 14%. Leaf-to-leaf variations were much larger (62%). Fluctuations with time and leaf-to-leaf variability in CO2 assimilation rates were of the same order as isoprene, while monoterpene variations were higher. Leaf age was identified as one of the factors contributing to leaf-to-leaf variability in CO2 assimilation and isoprene and monoterpene emission rates. Monoterpene emission rates were not influenced by light intensity or CO2 mixing ratio. The observed temperature dependence was the same for ?-pinene and 1,8-cineole (an oxygenated monoterpene) and is similar to the temperature dependence of monoterpene emission rates reported by other investigators. Isoprene emissions were slightly dependent on humidity (1-3% increase in emission per 10% increase in relative humidity) and responded only to very low (<100 ppm) or very high (>600 ppm) CO2 mixing ratios. Isoprene emission was associated with the abaxial leaf side, which contains stomatal pores, while monoterpenes were emitted primarily from the adaxial side, which lacks stomatal pores. The temperature and light dependence of isoprene emission closely resembles relationships observed for electron transport in plant chloroplasts. For this reason, we have used a mechanistic electron transport model as the basis for an empirical isoprene emission rate model. The emission rate variation predicted by this model was within 10% of observed values for 62% of the 255 observations at light-saturated conditions and temperatures between 23° and 33°C. The entire data base includes over 600 observations at leaf temperatures ranging between 12° and 50°C and light intensities between 0 and 2000 ?mol m-2 s-1. Nearly two thirds of the emission rates predicted for the entire data base were within a factor of 1.25, and 89% were within a factor of 2. The algorithms developed in this study provide a solid physiological basis for future efforts to model the biogenic flux of isoprene and monoterpenes into the atmosphere.

Guenther, Alex B.; Monson, Russell K.; Fall, Ray

1991-06-01

321

Evaluation of inter-observer variability of bladder boundary delineation on cone-beam CT  

PubMed Central

Background In-room cone-beam computerized tomography (CBCT) imaging is a promising method to reduce setup errors, especially in organs such as the bladder that often have large intrafractional variations due to organ movement. CBCT image quality is limited by low contrast and imaging artifacts, but few data have been reported about inter-observer variability of bladder boundary delineation on CBCT. The aim of this work was to analyze and evaluate the inter-observer contouring uncertainties of bladder boundary delineation on CBCT images in a prospective fashion. Methods Five radiation oncologists contoured 10 bladders using the CBCT datasets of consecutive 10 patients (including 4 females) who were irradiated to the pelvic region. Prostates were also contoured in male patients. Patients who had had prostatectomy were excluded. The coefficient of variation (COV), conformity index (CIgen), and coordinates of center-of-mass (COM) of the bladder and prostate were calculated for each patient. Results The mean COV for the bladder and prostate was 0.08 and 0.20, respectively. The mean CIgen of the bladder and prostate was 0.81 and 0.66, respectively. The root mean square (RMS) of the inter-observer standard deviation (?) of the COM displacement in the left-right (LR) and anterior-posterior (AP) direction was 0.79, 0.87 and 0.54 for the bladder and 0.63, 0.99 and 1.72 for the prostate. Regarding the mean COV and CIgen for the bladder, the differences between males and females were not significant. Conclusions Inter-observer variability for bladder delineation on CBCT images was substantially small regardless of gender. We believe that our results support the applicability of CBCT in adaptive radiotherapy for bladder cancer.

2013-01-01

322

Lack of uniform trends but increasing spatial variability in observed Indian rainfall extremes  

SciTech Connect

Recent studies disagree on how rainfall extremes over India have changed in space and time over the past half century, as well as on whether the changes observed are due to global warming or regional urbanization. Although a uniform and consistent decrease in moderate rainfall has been reported, a lack of agreement about trends in heavy rainfall may be due in part to differences in the characterization and spatial averaging of extremes. Here we use extreme value theory to examine trends in Indian rainfall over the past half century in the context of long-term, low-frequency variability.We show that when generalized extreme value theory is applied to annual maximum rainfall over India, no statistically significant spatially uniform trends are observed, in agreement with previous studies using different approaches. Furthermore, our space time regression analysis of the return levels points to increasing spatial variability of rainfall extremes over India. Our findings highlight the need for systematic examination of global versus regional drivers of trends in Indian rainfall extremes, and may help to inform flood hazard preparedness and water resource management in the region.

Ghosh, Subimal [ORNL; Das, Debasish [ORNL; Kao, Shih-Chieh [ORNL; Ganguly, Auroop R [ORNL

2012-01-01

323

Microwave enhancement and variability in the elephant's trunk coronal hole: Comparison with SOHO observations  

NASA Astrophysics Data System (ADS)

We report on an investigation of the microwave enhancement and its variability in the elephant's trunk coronal hole observed during the Whole Sun Month campaign (August 10 to September 9, 1996). The microwave images from the Nobeyama radioheliograph were compared with magnetograms and EUV images obtained simultaneously by the Michelson Doppler imager and the extreme ultraviolet imaging telescope (EIT) on board the SOHO spacecraft. The combined data set allowed us to understand the detailed structure of the microwave enhancement in the spatial and temporal domains. We find that the radio enhancement is closely associated with the enhanced unipolar magnetic regions underlying the coronal hole. The radio enhancement consists of a smooth component originating from network cell interiors and a compact component associated with network magnetic elements. When a minority polarity is present near a majority polarity element, within the coronal hole, the resulting mixed polarity region is associated with a bright-point-like emission in coronal EUV lines such as the Fe XII 195 Å. These coronal bright points are also observed distinctly in the EIT 304 Å band, but not in microwaves. On the other hand, the lower-temperature line emission (304 Å) and the microwave enhancement are associated with the unipolar magnetic flux elements in the network. We found strong time variability of the radio enhancement over multiple timescales, consistent with the initial results obtained by SOHO instruments. The microwave enhancement is most probably due to temperature enhancement in the chromosphere and may be related to the origin of solar wind.

Gopalswamy, N.; Shibasaki, K.; Thompson, B. J.; Gurman, J.; DeForest, C.

1999-05-01

324

Lack of uniform trends but increasing spatial variability in observed Indian rainfall extremes  

NASA Astrophysics Data System (ADS)

Recent studies disagree on how rainfall extremes over India have changed in space and time over the past half century, as well as on whether the changes observed are due to global warming or regional urbanization. Although a uniform and consistent decrease in moderate rainfall has been reported, a lack of agreement about trends in heavy rainfall may be due in part to differences in the characterization and spatial averaging of extremes. Here we use extreme value theory to examine trends in Indian rainfall over the past half century in the context of long-term, low-frequency variability. We show that when generalized extreme value theory is applied to annual maximum rainfall over India, no statistically significant spatially uniform trends are observed, in agreement with previous studies using different approaches. Furthermore, our space-time regression analysis of the return levels points to increasing spatial variability of rainfall extremes over India. Our findings highlight the need for systematic examination of global versus regional drivers of trends in Indian rainfall extremes, and may help to inform flood hazard preparedness and water resource management in the region.

Ghosh, Subimal; Das, Debasish; Kao, Shih-Chieh; Ganguly, Auroop R.

2012-02-01

325

Evidence for short-term variability of Jupiter's decimetric emission from VLA observations  

NASA Astrophysics Data System (ADS)

Aims. We present the first evidence of short-term variations of Jupiter's radiation-belt emission obtained with interferometric measurements. Over a two-month period of observational time in 2002, the Jovian synchrotron emission was observed with the Very Large Array (VLA). Methods: The images constructed at the wavelength of 6 cm demonstrate significant changes in the spatial structure of the brightness distribution. The comparisons of the two-dimensional maps with another campaign of VLA observations made in May 1997 confirm our discovery of changes in Jupiter's synchrotron emission on a time-scale of days to weeks. Results: For a series of central meridian longitudes (CMLs), the radiation peak near 1.4 RJ was observed to shift back and forth from one side of the planet to the other between October and December 2002. The change in the location of the emission peak was found to be the result of fluctuations in the peak brightness distribution by 10% up to 40%. These fluctuations are too significant to be associated with the small variation of the geometric parameter DE (the declination of the Earth as seen from Jupiter) during the campaign of observations. We have demonstrated that the variability of the synchrotron emission peak was observed when the angular sectors covering the Jupiter SIII longitudes ?III where the field strength along the equatorial magnetic surface is maximum or minimum were monitored. Conclusions: Short-term variations of Jupiter's synchrotron emission are expected to be reported when specific CMLs are observed and changes in the distributions of the 30-40 MeV electron population occur simultaneously. Our discussions led to the conclusion that the short-term variations of Jupiter's Decimetric brightness distribution may be the result of submicrometre charged dust particles undergoing significant electromagnetic perturbations while interacting with the radiation-belt electrons in the Jovian ring's innermost component.

Santos-Costa, D.; Bolton, S. J.; Sault, R. J.

2009-12-01

326

Impact of snow cover on inter-annual variability of the NH winter circulation in an ensemble GCM simulation forced by satellite observations  

NASA Astrophysics Data System (ADS)

The impact of land boundary conditions on predictability from the seasonal to decadal time-scale and on the forcing atmospheric teleconnections is now the focus of renewed attention. In order to investigate the impact of the terrestrial cryosphere on the northern hemisphere winter circulation, we have performed a suite of ensemble simulations with the Meteo-France ARPEGE Climat (V3) GCM, spanning two decades (1979-2000), to attribute circulation anomalies to changes in snow cover extent. Observed snow cover derived from satellite data has been retrieved from the NISDC, and nudged weekly into the GCM. Control simulations with prognostic snow variables have been also performed. Anomalous snow cover extend over Eastern Eurasia is linked with anomalous circulation over the northern Pacific, in particular over the Aleutian sector, and this impact also the North Atlantic in late winter. We find that nudging of realistic snow cover considerably improves the hindcast and the representation of the Aleutian-Icelandic Low Seesaw in the model. We discuss gains in potential predictability in winter, resulting from the snow nudging, and potential for seasonal to decadal predictions.

Orsolini, Y.; Kvamstø, N.

2009-04-01

327

Variability of tidal currents in a wide strait: A comparison between drifter observations and numerical simulations  

NASA Astrophysics Data System (ADS)

The spatial variability of semidiurnal tidal currents throughout the waters of the northwest coast of Canada is investigated by examination of velocities of surface drifters recording half-hourly Loran-C positions. Time series are examined to remove any records with significant inertial currents. The remaining records are segmented into sequential 25-hour blocks, detrended, and analyzed for semidiurnal energy. Tidal current ellipses are computed and compared with two different numerical models: a finite element barotropic simulation, and a finite difference baroclinic simulation that was initialized with horizontally uniform density surfaces. Models and observations show the dominance of negative rotation (clockwise rotary) with the amplification of currents shoreward of the continental slope. In shallow waters both models agree well with the observations. Along the edge of the continental shelf in waters deeper than 200 m the baroclinic model provides better agreement with observations because of its ability to simulate internal tides. However, observations also reveal that internal tidal currents at and seaward of the shelf break may be irregular because of the presence of plumes and jets, and a baroclinic model with horizontally uniform stratification cannot reproduce local features in these jets and plumes. Internal tidal currents in Dixon Entrance exceed those simulated by the baroclinic model by a significant degree. This is likely due to the constraints of the density field used to initialize the model and to terrain smoothing in its 5-km grid.

Crawford, W. R.; Cherniawsky, J. Y.; Cummins, P. F.; Foreman, M. G. G.

1998-06-01

328

Observation of oligotrophic gyre variability in the south Indian Ocean: Environmental forcing and biological response  

NASA Astrophysics Data System (ADS)

Expansion of oligotrophic ocean gyre and widespread reduction of phytoplankton biomass will have severe environmental and ecological effect since phytoplankton accounts for half of the global primary production, which forms the trophic base for marine ecosystem. Analysis of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) derived chlorophyll-a (Chl-a) datasets (1998-2010) suggested significant expansion of South Indian Ocean oligotrophic gyre (SOG) at average annual rate of 4.46%/yr (r=0.66, p=0.013). The annual trend of SOG expansion was accompanied with the significantly declining trend of Chl-a concentration (-1.36%/yr, or -0.0007±0.0001 mg m-3/yr, r=0.76, p=0.002). Environmental parameters such as sea surface temperature (SST) and meridional wind stress (?y) were found to be the most accountable factors controlling the variability of Chl-a/gyre area. Nevertheless, SST was the dominant predictor of biological response (explains more than 60% of Chl-a variability). This study suggests that the observed trend of SOG expansion and accompanied decline in Chl-a concentration is principally due to SST warming (0.05±0.01 °C/yr, r=0.83, p=0.0008) and weakening of wind stress (?) mainly meridional wind stress component, ?y (-0012 Pa/yr, r=0.86, p=0.004). Additionally, the SST trend map showed more than 80% of the SOG area is warming significantly under circumstance of overall gain of net heat flux by the sea surface. Analysis of these climate variables suggests decreased mixing and enhanced stratification in the SOG which reduces nutrient supply to sunlit zone; consequently resulting in low phytoplankton biomass, and gyre expansion. In addition, the sea-level rise observed in SOG (0.48±0.05 cm/yr) is much higher than the global estimates (0.18±0.05 cm/yr) reported in the Intergovernmental Panel on Climate Change report, 2007. The variability in Chl-a concentration was also studied with respect to leading climate oscillators.

Jena, Babula; Sahu, Shanghamitra; Avinash, Kumar; Swain, Debadatta

2013-10-01

329

Video observations of nearshore bar behaviour. Part 2: alongshore non-uniform variability  

NASA Astrophysics Data System (ADS)

A considerable portion of the variability in nearshore sandbars is related to changes in the plan shape of quasi-rhythmic alongshore non-uniform features, such as rip channels and crescentic shapes. These changes may include changes in their alongshore length, cross-shore amplitude and alongshore position. Here, we use complex empirical orthogonal eigenfunction analysis to quantify these changes from a 3.4-year data set of almost daily time-exposure images of the double-barred coast at Noordwijk (Netherlands). The observed alongshore non-uniform features had alongshore lengths between 380 and approximately 3000 m and lifetimes in the order of months, considerably longer than the characteristic time scale of individual wave events. Transitions from one feature to another were mostly gradual, resulting from an alongshore differential growth in amplitude. Abrupt transitions, that is, the existing features disappeared entirely and were subsequently replaced by different features, were barely observed and did not always take place during high-energy wave events. The amplitude of the non-uniform features varied between 0 and 30 m on a weekly to monthly scale, unrelated to variations in the wave height. In addition, the features migrated back and forth along the shore with typical rates of O(10 m/ day) on weekly scales with the rates increasing with an increase in the alongshore component of the wave power. On the whole our observations suggest that alongshore non-uniform sandbar variability is governed by free behaviour rather than by the direct forcing of the prevailing wave conditions.

van Enckevort, I. M. J.; Ruessink, B. G.

2003-03-01

330

HDO in the Mesosphere: Observation and Modeling of [HDO]/[H2O] Variability  

NASA Astrophysics Data System (ADS)

We present 1992-2002 measurements of HDO and H2O at 50-70 km altitude, derived from ground-based ?wave observations at 32°N, 112°W. Observed HDO/H2O ratios show HDO depletions relative to Standard Mean Ocean Water (SMOW) of ? D=-58% to -3%. Large variability of mesospheric ? D is in surprising contrast to stratospheric observations of ? D=-65% to -50% [Moyer et al., 1996], and indicates sensitivity to processes other than the CH4 oxidation that pertains in the stratosphere. We observe anticorrelation of ? D and H2O abundance, contrary to the stratospheric pattern. Observations are of the 225 GHz HDO and 203 GHz H218O lines, corresponding to rotational transitions of these molecules. The 12-meter radio telescope and T=4oK receivers at Kitt Peak, AZ are used in frequency switching mode. HDO and H2O altitude profiles are derived from sensitivity of the line shape to pressure. H218O is used as a proxy for H216O based on theory and available measurements [Kaye, 1987; Rinsland et al., 1991] of [H218O/H216O] = SMOW+/- 5% in the upper stratosphere. Standard theory holds that HDO is preferentially removed from water transported upward through the tropopause due to isotope-dependent freezing [Kaye, 1987], leading to lower stratosphere HDO depletions -65+/-10% [balloon- Rinsland et al., 1991; ATMOS- Moyer et al. 1996]. Depletion is less extreme in the upper stratosphere owing to conversion of CH4 (D/H ~ SMOW) to H2O. We model the photochemistry and conclude the observed mesospheric HDO behavior is driven by differing photolysis rates for HDO and H2O at ? > 175 nm.

Sandor, B. J.; Clancy, R. T.

2002-12-01

331

Impact of snow cover on inter-annual variability of the NH winter circulation in an ensemble GCM simulation forced by satellite observations  

NASA Astrophysics Data System (ADS)

The impact of land boundary conditions on predictability from the seasonal to decadal time-scale and on the forcing atmospheric teleconnections is now the focus of renewed attention. In order to investigate the impact of the terrestrial cryosphere on the northern hemisphere winter circulation, we have performed a suite of ensemble simulations with the Meteo-France ARPEGE Climat (V3) GCM, spanning two decades (1979-2000), to attribute circulation anomalies to changes in snow cover extent. Observed snow cover derived from satellite data has been retrieved from the NISDC, and nudged weekly into the GCM. Control simulations with prognostic snow variables have been also performed. Anomalous snow cover extend over Eastern Eurasia is linked with anomalous circulation over the northern Pacific, in particular over the Aleutian sector, and this impacts also the North Atlantic in late winter. We find that nudging of realistic snow cover considerably improves the hindcast and the representation of the Aleutian-Icelandic Low Seesaw in the model. We also discuss new coupled AOGCM ensemble forecasts aimed at better understanding the role of snow cover variability over Eurasia onto winter climate.

Orsolini, Y.; Kvamsto, N.; Balsamo, G.

2009-09-01

332

Satellite observations indicate substantial spatiotemporal variability in biomass burning NOx emission factors for South America  

NASA Astrophysics Data System (ADS)

Biomass burning is an important contributor to global total emissions of NOx (NO + NO2). Generally bottom-up fire emissions models calculate NOx emissions by multiplying fuel consumption estimates with static biome specific emission factors, defined in units of grams of NO per kilogram of dry matter consumed. Emission factors are a significant source of uncertainty in bottom-up fire emissions modeling because relatively few observations are available to characterize the large spatial and temporal variability of burning conditions. In this paper we use NO2 tropospheric column observations from the Ozone Monitoring Instrument (OMI) from the year 2005 over South America to calculate monthly NOx emission factors for four fire types: deforestation, savanna/grassland, woodland, and agricultural waste burning. In general, the spatial trends in NOx emission factors calculated in this work are consistent with emission factors derived from in situ measurements from the region, but are more variable than published biome specific global average emission factors widely used in bottom up fire emissions inventories such as the Global Fire Emissions Database (GFED) v3. Satellite based NOx emission factors also indicate substantial temporal variability in burning conditions. Overall, we found that deforestation fires have the lowest NOx emission factors, on average 30 % lower than the emission factors used in GFED v3. Agricultural fire NOx emission factors were the highest, on average a factor of 2 higher than GFED v3 values. For savanna, woodland, and deforestation fires early dry season NOx emission factors were a factor of ~1.5-2.0 higher than late dry season emission factors. A minimum in the NOx emission factor seasonal cycle for deforestation fires occurred in August, the time period of severe drought in South America in 2005. Our results support the hypothesis that prolonged dry spells may lead to an increase in the contribution of smoldering combustion from large diameter fuels to total fire emissions, which would lower the overall modified combustion efficiency (MCE) and NOx emission factor, and offset the higher combustion efficiency of dryer fine fuels. We evaluated the OMI derived NOx emission factors with SCIAMACHY NO2 tropospheric column observations and found improved model performance in regions dominated by fire emissions.

Castellanos, P.; Boersma, K. F.; van der Werf, G. R.

2013-08-01

333

RApid Temporal Survey (RATS) - II. Followup observations of four newly discovered short-period variables  

NASA Astrophysics Data System (ADS)

The Rapid Temporal Survey (RATS) is a survey to detect objects whose optical intensity varies on time-scales of less than ~70 min. In our pilot data set taken with the Isaac Newton Telescope and the Wide Field Camera in 2003 November, we discovered nearly 50 new variable objects. Many of these varied on time-scales much longer than 1 h. However, only four objects showed a modulation on a time-scale of 1 h or less. This paper presents followup optical photometry and spectroscopy of these four objects. We find that RATJ0455 + 1305 is a pulsating (on a period of 374 s) subdwarf B star of the EC14026 type. We have modelled its spectrum and determine Teff = 29200 +/- 1900K and logg = 5.2 +/- 0.3 which locates it on the cool edge of the EC14026 instability strip. It has a modulation amplitude which is one of the highest of any known EC14026 star. Based on their spectra, photometric variability and their infrared colours, we find that RATJ0449 + 1756, J0455 + 1254 and J0807 + 1510 are likely to be SX Phe stars - dwarf ? Sct stars. Our results show that our observing strategy is a good method for finding rare pulsating stars.

Ramsay, Gavin; Napiwotzki, Ralf; Hakala, Pasi; Lehto, Harry

2006-09-01

334

An observational study of ice effects on Nelson River estuarine variability, Hudson Bay, Canada  

NASA Astrophysics Data System (ADS)

Many estuaries in high latitude regions are subjected to seasonally ice-covered conditions. However, ice effects on estuarine variability have received limited scientific attention and remain poorly understood. In this paper, an 11-month mooring record is used to examine seasonal variation of estuarine hydrodynamics in the Nelson River estuary (NRE), Hudson Bay (HB), in northern Canada. We show that ice cover strongly affects tidal amplitudes, velocities and phases in the NRE. In the mid-winter, the M2 tidal amplitude and consequently the tidal range are significantly reduced due to under-ice friction in HB, while conversely the M2 tidal velocity is amplified due to reduction of cross-section of the channel by formation of fast ice. A stronger surface seaward residual flow observed in the winter indicates that the formation of fast ice could also enhance the residual circulation. Suspended sediment concentration in the river mouth is reduced, also possibly due to the formation of fast ice that protects shallow nearshore shoals from erosion. This study demonstrates the importance of ice effects on estuarine variability and the complexity of processes in a seasonally ice-covered estuary.

Wang, Ruixue; McCullough, Greg K.; Gunn, Geoffrey G.; Hochheim, Klaus P.; Dorostkar, Abbas; Sydor, Kevin; Barber, David G.

2012-09-01

335

A Survey of Far Ultraviolet Spectroscopic Explorer Observations of Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

During its lifetime, the Far Ultraviolet Spectroscopic Explorer (FUSE) was used to observe 99 cataclysmic variables (CVs) in 211 separate observations. Here, we present a survey of the moderate-resolution (R ~= 10, 000), far-ultraviolet (905-1188 Å), time-averaged FUSE spectra of CVs. The FUSE spectra are morphologically diverse. They show contributions from the accretion disk, the disk chromosphere, disk outflows, and the white dwarf (WD), but the relative contribution of each component varies widely as a function of CV subtype, orbital period and evolutionary state, inclination, mass accretion rate, and magnetic field strength of the WD. The data reveal information about the structure, temperature, density and mass flow rates of the disk and disk winds, the temperature of the WD and the effects of ongoing accretion on its structure, and the long-term response of the systems to disk outbursts. The complete atlas of time-averaged FUSE spectra of CVs is available at the Multimission Archive at Space Telescope Science Institute as a High Level Science Product. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE was operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.

Froning, Cynthia S.; Long, Knox S.; Gänsicke, Boris; Szkody, Paula

2012-03-01

336

Further VLBA observations of SiO masers toward Mira variable stars  

NASA Astrophysics Data System (ADS)

We present the results of continued monitoring of the SiO masers at 7 mm wavelength in several of the Mira variable stars reported in Cotton et al. (2004, A&A, 414, 275) (o Ceti = Mira, U Orionis = U Ori, R Aquarii = R Aqr) over a period of 16 months, extending the observations to several pulsation cycles. The observed size of the maser rings varied by 3-14% with time but show no clear correlation with pulsation phase. In all cases, the SiO masers appear just outside the dense molecular layer indicated by near-IR observations. Rotation (or large scale motion) is possibly detected in o Ceti with a period of 89× sin(i) years. We find linear polarization up to ˜ 60% and at several epochs predominantly tangentially ordered polarization vectors indicate a radial magnetic field direction. Jet-like features are examined in o Ceti and R Aqr and in both cases, the magnetic field appears elongated with the masing structure. This suggests that the dynamic feature in the envelope is dragging the magnetic field or that the gas is constrained to follow magnetic field.

Cotton, W. D.; Vlemmings, W.; Mennesson, B.; Perrin, G.; Coudé du Foresto, V.; Chagnon, G.; Diamond, P. J.; van Langevelde, H. J.; Bakker, E.; Ridgway, S.; McAllister, H.; Traub, W.; Ragland, S.

2006-09-01

337

When should one adjust for measurement error in baseline variables in observational studies?  

PubMed

Previously, we showed that in randomised experiments, correction for measurement error in a baseline variable induces bias in the estimated treatment effect, and conversely that ignoring measurement error avoids bias. In observational studies, non-zero baseline covariate differences between treatment groups may be anticipated. Using a graphical approach, we argue intuitively that if baseline differences are large, failing to correct for measurement error leads to a biased estimate of the treatment effect. In contrast, correction eliminates bias if the true and observed baseline differences are equal. If this equality is not satisfied, the corrected estimator is also biased, but typically less so than the uncorrected estimator. Contrasting these findings, we conclude that there must be a threshold for the true baseline difference, above which correction is worthwhile. We derive expressions for the bias of the corrected and uncorrected estimators, as functions of the correlation of the baseline variable with the study outcome, its reliability, the true baseline difference, and the sample sizes. Comparison of these expressions defines a theoretical decision threshold about whether to correct for measurement error. The results show that correction is usually preferred in large studies, and also in small studies with moderate baseline differences. If the group sample sizes are very disparate, correction is less advantageous. If the equivalent balanced sample size is less than about 25 per group, one should correct for measurement error if the true baseline difference is expected to exceed 0.2-0.3 standard deviation units. These results are illustrated with data from a cohort study of atherosclerosis. PMID:21259307

Walter, Stephen D; Forbes, Andrew; Chan, Siew; Macaskill, Petra; Irwig, Les

2011-01-14

338

Intensification of the regional scale variability of extreme precipitation derived from RCM simulations and observations  

NASA Astrophysics Data System (ADS)

Future climate change patterns are usually derived from ensembles of coarse global climate model simulations (GCMs), for instance within the Coupled Model Intercomparison Project (CMIP) or from regional climate projections at resolutions of some tens of km, for instance for Europe from the ENSEMBLES or PRUDENCE projects. For regions with complex topography like Central Europe the horizontal resolution of these climate projections is still too coarse to resolve the typical topographical length scales, and therefore the impact of the large scale changes with the regional geography cannot be captured adequately. For this task high resolution ensemble simulations with regional climate models (RCMs) are needed. The generation of an ensemble of such high resolution simulations requires great computational efforts. With the RCM COSMO-CLM several simulations with resolutions down to 7 km have been performed, using different driving GCMs and GCM realisations. This ensemble approach is needed to estimate the robustness of the change signals and to account for the uncertainties introduced by differences in the large scale forcing due to the variability of the climate change signals caused by the different GCMs or the natural variability. The focus of the study is on the changes of extreme precipitation for the near future until the middle of the 21st century. An increase of the temporal and spatial variability is found for the precipitation extremes, especially for summer. The change patterns seem to be statistically robust. Based on long-term observation climatologies for the second half of the 20th century, similar structures where found with areas of decrease and increase only a few tens of kilometres apart from each other. The combination of the findings from the RCM projections and observations suggests a continuation of the trends from the recent past into the near future. Possible causes for the horizontally heterogeneous change patterns are related to weather pattern changes. It is discussed to what extend changes in the frequencies of weather conditions, connected to the extremes, or changes in the meteorological characteristics during such conditions are responsible for changes of the extreme precipitation.

Feldmann, H.; Schädler, G.; Panitz, H.-J.

2012-04-01

339

Marine proxy evidence linking decadal North Pacific and Atlantic climate  

NASA Astrophysics Data System (ADS)

Decadal- to multidecadal variability in the extra-tropical North Pacific is evident in 20th century instrumental records and has significant impacts on Northern Hemisphere climate and marine ecosystems. Several studies have discussed a potential linkage between North Pacific and Atlantic climate on various time scales. On decadal time scales no relationship could be confirmed, potentially due to sparse instrumental observations before 1950. Proxy data are limited and no multi-centennial high-resolution marine geochemical proxy records are available from the subarctic North Pacific. Here we present an annually-resolved record (1818-1967) of Mg/Ca variations from a North Pacific/Bering Sea coralline alga that extends our knowledge in this region beyond available data. It shows for the first time a statistically significant link between decadal fluctuations in sea-level pressure in the North Pacific and North Atlantic. The record is a lagged proxy for decadal-scale variations of the Aleutian Low. It is significantly related to regional sea surface temperature and the North Atlantic Oscillation (NAO) index in late boreal winter on these time scales. Our data show that on decadal time scales a weaker Aleutian Low precedes a negative NAO by several years. This atmospheric link can explain the coherence of decadal North Pacific and Atlantic Multidecadal Variability, as suggested by earlier studies using climate models and limited instrumental data.

Hetzinger, S.; Halfar, J.; Mecking, J. V.; Keenlyside, N. S.; Kronz, A.; Steneck, R. S.; Adey, W. H.; Lebednik, P. A.

2012-09-01

340

Observational and Theoretical Constraints on the Formation and Evolution of Cataclysmic Variables in Globular Clusters  

NASA Astrophysics Data System (ADS)

I will present a critical overview of recent theoretical and observational results regarding the formation and evolution of cataclysmic variables (CVs) in globular clusters (GCs). The overarching goal will be to assess whether the properties of the observed cluster CV population are consistent with expectations based on theoretical predictions and/or direct comparisons to the field CV population. As a starting point, I will take an inventory of the known CV population in GCs, compare its properties to the field CV population and consider to what extent selection effects may be responsible for the differences between them. I will also explore whether physical differences (e.g. in metallicity or primary magnetic field strength) can plausibly explain the observational differences between the two populations. I will go on to consider theoretical predictions for the properties of cluster CVs and show that they depend strongly on the adopted binary evolution recipes (such as the treatment of magnetic braking). This implies that disagreements between predictions and observations of cluster binaries need not imply inadequacies in the treatment of dynamical interactions; they may equally well point to problems with binary evolution prescriptions. This is a serious worry: for example, it is well known that the canonical CV evolution scenario is in serious conflict with several key properties of the field CV population. In a cluster setting, the impact of an erroneous prescription would be exacerbated further by the feedback between stellar dynamics and binary evolution. I will finally consider how to move forward. In particular, I will present results from a recent attempt to empirically calibrate the angular momentum loss (AML) law for field CVs. This AML prescription can be implemented in theoretical models. I will also emphasize the potential of GC surveys to provide CV samples at known distances and with well-understood selection effects. In this sense, GC samples can actually be much cleaner than field CV samples.

Knigge, C.

2006-08-01

341

A SURVEY OF FAR ULTRAVIOLET SPECTROSCOPIC EXPLORER OBSERVATIONS OF CATACLYSMIC VARIABLES  

SciTech Connect

During its lifetime, the Far Ultraviolet Spectroscopic Explorer (FUSE) was used to observe 99 cataclysmic variables (CVs) in 211 separate observations. Here, we present a survey of the moderate-resolution (R {approx_equal} 10, 000), far-ultraviolet (905-1188 A), time-averaged FUSE spectra of CVs. The FUSE spectra are morphologically diverse. They show contributions from the accretion disk, the disk chromosphere, disk outflows, and the white dwarf (WD), but the relative contribution of each component varies widely as a function of CV subtype, orbital period and evolutionary state, inclination, mass accretion rate, and magnetic field strength of the WD. The data reveal information about the structure, temperature, density and mass flow rates of the disk and disk winds, the temperature of the WD and the effects of ongoing accretion on its structure, and the long-term response of the systems to disk outbursts. The complete atlas of time-averaged FUSE spectra of CVs is available at the Multimission Archive at Space Telescope Science Institute as a High Level Science Product.

Froning, Cynthia S. [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 593 UCB, Boulder, CO 80309 (United States); Long, Knox S. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gaensicke, Boris [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Szkody, Paula, E-mail: cynthia.froning@colorado.edu, E-mail: long@stsci.edu, E-mail: Boris.Gaensicke@warwick.ac.uk, E-mail: szkody@alicar.astro.washington.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)

2012-03-01

342

Hubble Space Telescope and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

Ultraviolet observations using the Solar Blind Channel on the Hubble Space Telescope provide light curves and low-resolution spectra of three pulsating white dwarfs in the cataclysmic variables SDSS J013132.39-090122.3, SDSS J161033.64-010223.3, and SDSS J220553.98+115553.7. The UV light curves show enhanced pulsation amplitudes over those from simultaneous and previous optical photometry, while the UV-optical spectra are fit with white dwarf temperatures near 15,000 K. These temperatures place the accreting white dwarfs outside the instability zone for noninteracting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555 with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium; and with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instiitute de Astrofisica de Canaries.

Szkody, Paula; Mukadam, Anjum; Gänsicke, Boris T.; Woudt, Patrick A.; Solheim, Jan-Erik; Nitta, Atsuko; Sion, Edward M.; Warner, Brian; Sahu, D. K.; Prabhu, T.; Henden, Arne

2007-04-01

343

Investigating arctic cloud and radiative properties associated with the large-scale climate variability through observations, reanalysis, and mesoscale modeling  

NASA Astrophysics Data System (ADS)

This dissertation examines two decades of Arctic cloud cover data and the variability in Arctic clouds with relation to changes in sea ice using observational and reanalysis data, as well as a state-of-the-art mesoscale model. Decadal length Arctic cloud cover data are examined because of the inherent differences within these measurements that have not been explored in previous research. Cloud cover data are analyzed from regions poleward of 60°N from several sources of visual surface observations including surface remotely sensed measurements at two locations, two spaced-based passive remotely sensed datasets (Advanced Very High Resolution Radiometer Polar Pathfinder extended (APPx) and Television Infrared Observation Satellite Operational Vertical Sounder (TOVS) Polar Pathfinder (TPP)), and one reanalysis dataset (European Center for Medium-Range Weather Forecasting Reanalysis (ERA-40)) are compared. The passive remotely sensed data are sensitive to surface type. Cloud amounts from the APPx and TPP decrease with increases in sea ice concentrations. In comparison to the surface remotely sensed measurements over sea ice, the APPx and TPP cloud amounts are consistently low. The ERA-40 output cloud cover not contain a sharp decrease from water to ice surfaces, and compares reasonably with the remotely sensed surface measurements over sea ice. During the northern hemisphere winter at land stations, the TPP and ERA-40 cloud amounts are similar. This is most likely a result of the ERA-40 model using TOVS irradiances as input data. The APPx and surface cloud amounts are similar during all seasons, but they are not in precise agreement with the TPP/ERA-40 values. Cloud amounts from the ERA-40 are also most similar to surface measurements in regions where radiosonde data are used as input. Cloud radiative forcing calculated from the ERA-40 output is examined with relation to sea ice concentrations using 20 years of data. The radiative effect of clouds varies linearly with sea ice concentrations during the winter and spring. This relationship is most statistically significant in the North Atlantic region, but statistically significant relationships also occurring the northern Pacific. Statistically significant correlations do not occur during the summer months. By calculating differences in cloud amount during low and high sea ice concentration summers, greater cloud cover amounts occur with decreases in sea ice in the Arctic poleward of the Pacific at the 80 percent statistical significant level. In October, clouds are varying with relation to sea ice near the sea ice edge. One-month lag relationships are calculated to examine if the cloud radiative forcing terms are changing before or after changes in sea ice concentration. Changes in the longwave radiative forcing of clouds occurs before changes in sea ice concentrations and surface temperatures in the North Atlantic region. Cloud radiative forcing, sea ice concentrations, and surface temperatures are interrelated in this region, and may be forced by the same physical mechanism. The response of Arctic clouds and surface radiative properties is examined using the polar version of the Weather Research and Forecasting (WRF) regional model over the Laptev Sea. WRF is run for four Septembers and Octobers with anomalously low and high sea ice concentrations. Differences in the surface radiative forcing, cloud radiative forcing, cloud properties and the surface heat budget are examined for the composite low and high years. In both months, there are more clouds during low sea ice years. WRF produces more low-level liquid cloud amount during years without sea ice. The increase in clouds during low sea ice years corresponds with an increase in downwelling longwave radiation, and hence longwave cloud radiative forcing. Increases in downwelling longwave radiation during low sea ice years are canceled by the increased amount of upwelling longwave radiation, which is a result of warmer surface skin temperatures. In September, the decrease in surface albedo associated with sea ice retreat/m

Barton, Neil P.

344

Airborne lidar observations of mid-latitude mid-tropospheric water vapour variability  

NASA Astrophysics Data System (ADS)

Water vapor, a minor constituent of the earth's atmosphere, plays a major role in the radiation budget and the water cycle with important implications for weather and climate. Due to the heterogeneous distribution of its sources, evaporation, and sinks, condensation and precipitation, and due to the complexity of atmospheric motion and mixing, its distribution is highly variable. The complex dynamics of water vapour in the free troposphere spans a range of source and sink processes from convective clouds on the kilometre scale, to cloud systems associated with motions on scales of a thousand or more kilometres, as well as advection of water vapour as a passive tracer outside of clouds. While large-scale advection of water vapour is well represented in general circulation models, the simulations are greatly dependent on the parameterizations of small scale processes. A lack of knowledge of humidity fluctuations on scales smaller than the mesoscale model grid leads to errors in the development of deep convection and increases the prediction uncertainty. This problem can be addressed with the use of stochastic parameterisations that attempt to explicitly describe variability near the model grid length. However, the design and testing of such schemes depends on an accurate characterisation of small-scale variability in nature. The COPS/ETReC 2007 (Convective and Orographically-induced Precipitation Study/European THORPEX Regional Campaign) field experiment conducted in July 2007 over middle and southwest Europe provided an ample set of long-range water vapour differential absorption lidar (DIAL) measurements onboard the DLR Falcon research aircraft. After discarding flights with weak lidar signals or with large data gaps, and after horizontal averaging to a resolution of 2 km to obtain a high signal to noise ratio, we were able to investigate a total of 8 flights with lengths of 225 - 700 km and vertical extents from 2 - 10 km altitude. Most flight segments have a length of 300 km and a vertical range of 4 km. Given the vertical DIAL resolution of 200 m we obtained a total of 98 time series of specific humidity, resulting in a total length of about 38,000 km. The observed humidity distributions are highly non-stationary and intermittent. Hence, second-order statistics and Fourier spectra are inadequate to describe their variability. Instead, horizontal structure functions up to fifth order were computed. They exhibit power-law scaling between about 10 and 100 km in range. The second-order structure function shows scaling exponents equivalent to spectral slopes that vary from around 5/3 in the lower troposphere to 2 at upper levels. In particular, humidity smoothness is found to increase with height, while intermittency decreases. A classification of the data according to whether the series occurred above or below the level of nearby convective cloud tops gives a separation of the scaling exponents in the two air masses. The results are consistent with a water vapour distribution determined at upper levels by a downscale cascade of variance by advective mixing, but increasingly influenced at lower levels by local injection of humidity by moist convection. Our results show that the structure function exponents provide a compact statistical description of moisture variability on scales just below the resolution of weather and climate models. There is hope that this will help improve stochastic model parameterisations.

Kiemle, C.; Fischer, L.; Craig, G. C.

2012-04-01

345

Sensitivity analysis of SCHADEX extreme flood estimations to observed hydro-meteorological variability  

NASA Astrophysics Data System (ADS)

Extreme floods estimation methods are developed since many years within the hydrological and statistical communities. More recently, approaches based on the statistical analysis of flood streamflow samples simulated by rainfall-runoff models which are forced by simulated rainfall spread in the scientific literature. These approaches, called stochastic simulation methods, are typically composed by a probabilistic rainfall model and a rainfall-runoff model. Each of these two models are usually calibrated over observed hydrometeorological series such as daily precipitation series for the probabilistic rainfall models or such as daily streamflow, precipitation and temperature series for the rainfall-runoff models. Since extreme flood observations are by definition particularly rare, the validation of the proposed extreme flood estimations is one of the main critical issues, whatever the method - statistical or physically-based - used. Moreover, the observed hydrometeorological series used for the calibration of the stochastic simulation methods may be subject to significant variability over time, due to global climate oscillations such as El Niño Southern Oscillations for example. If the estimation of total involved uncertainty is a difficult task, investigating to what extent the proposed extreme flood values are dependent on the calibration period is an interesting first step. The general aim of this study is to propose a methodology for performing a sensitivity analysis of extreme flood estimations to the variability of observed series used for the model calibrations in a stochastic simulation framework. The methodology proposed is based on the nonparametric bootstrap concept and consists to perform a set of block-bootstrap experiments, thus generating different sets of observed series sub-samples. The generated observed series sub-samples are then used for the calibration of the different models considered within the stochastic simulation method. The main originality of the proposed approach is the fact that the parameters are not analyzed individually but by block, allowing thus to distinguish between rainfall hazard, catchment saturation hazard and characteristics of the rainfall-runoff transformation. The sensitivity analysis methodology will be tested within the application of the SCHADEX method (Simulation Climato-Hydrologique pour l'Appréciation des Débits EXtrêmes) proposed by Paquet et al. (2006, 2013). SCHADEX is a `semi-continuous' stochastic simulation method (rainfall hazard is simulated at the event-base while the catchment saturation hazard is simulated trough continuous rainfall-runoff modeling), which is currently used at Electricité De France since 2006 for the dam spillway design. The sensitivity analysis of the SCHADEX method will be illustrated over four catchments which are located in different regions of the world and are thus in different hydrometeorological contexts. References: Paquet, E., Gailhard, J. and Garçon, R. (2006), Evolution of the GRADEX method: improvement by atmospheric circulation classification and hydrological modeling, La Houille Blanche, 5, 80-90. doi:10.1051/lhb:2006091. Paquet, E., Garavaglia, F., Gailhard, J. and Garçon, R. (2013), The SCHADEX method: a semi-continuous rainfall-runoff simulation for extreme flood estimation, Journal of Hydrology, under revision.

Brigode, Pierre; Paquet, Emmanuel; Bernardara, Pietro; Gailhard, Joël; Garavaglia, Federico; Ribstein, Pierre

2013-04-01

346

Rates of ingestion and their variability between individual calanoid copepods: Direct observations  

SciTech Connect

The goals of this study were to determine rates of ingestion and fecal pellet release, and their variability, for individual planktonic copepods over extended periods of time (>20 min). Ingestions and rejections of individual cells of the diatom Thalassiosira eccentrica by a adult females of the calanoid Paracalanus aculeatus were directly quantified by observing individual copepods continuously at cell concentrations ranging from 0.1 to 1.2 mm{sup 3} l{sup {minus}1}. Average ingestion rates increased with increasing food concentration, but were not significantly different between 0.3 and 1.0 mm{sup 3} l{sup {minus}1} (9.8 and 32.7 {mu}g Cl{sup {minus}1}) of T.eccentrica. Rates of cell rejections were low and similar at 0.1 and 0.3. but were significantly higher at 1.0 mm{sup 3} l{sup {minus}1}. The coefficients of variation for average ingestion rates of individual copepods hardly differed between food concentrations, ranging from 17 to 22%, and were close to those for average fecal pellet release intervals which ranged from 15 to 21%. A comparison between individuals at each food concentration found no significant differences at 1.0; at 0.1 and 0.3 mm{sup 3} l{sup {minus}1}, respectively, ingestion rates of four out of five females did not differ significantly from each other. Average intervals between fecal pellet releases were similar at 0.3 and 1.0 mm{sup 3} l{sup {minus}1}. Fecal pellet release intervals between individuals were significantly different at each food concentration; these significant differences were attributed to rather narrow ranges of pellet release intervals of each individual female. Potential sources/causes of variability in the sizes and rates of copepods in the ocean are evaluated.

Paffenhoefer, G.A.; Lewis, K.D. [Skidaway Inst. of Oceanography, Savannah, GA (United States); Bundy, M.H. [Skidaway Inst. of Oceanography, Savannah, GA (United States)]|[Alfred-Wegener-Institut fuer Polar- und Meeresforschung, Bremerhaven (Germany). Inst. fuer Fernerkundung (IFE); Metz, C. [Alfred-Wegener-Institut fuer Polar- und Meeresforschung, Bremerhaven (Germany). Inst. fuer Fernerkundung (IFE)

1995-12-01

347

Horizontal variability of aerosol optical properties observed during the ARCTAS airborne experiment  

NASA Astrophysics Data System (ADS)

The properties of tropospheric aerosol and gas vary within a satellite grid cell and between ground-based instruments. This hinders comparison between satellite and suborbital measurements of different spatial scales as well as their applications to climate and air quality studies. This paper quantifies the realistic range of the variability in aerosol optical depth (AOD), its Angstrom exponent, in-situ extinction coefficient and carbon monoxide mixing ratio over horizontal distances of 1-30 km, using measurements from the ARCTAS airborne experiment. The Canada phase in June and July 2008, in which smoke from local forest fires was sampled, likely represents the most heterogeneous of the ambient aerosol environments common over the globe. The relative standard deviation (stdrel) of AOD measured with the 14-channel Ames Airborne Tracking Sunphotometer (AATS-14) has median 19.4% (at 499 nm) among thousands of horizontal 20 km segments. For 6 km segments the analogous median is 9.1%. Another measure of horizontal variability, the autocorrelation (r) of AOD499 across 20 km and 6 km segments is 0.37 and 0.71, respectively. In contrast, the Alaska phase in April 2008, which sampled particles transported from Asia, is presumably among the most homogeneous environments. The median stdrel is 3.0% and r is 0.90, both over 30 km, only slightly different from those for 1 km (stdrel=0.4% and r=1.00). r in the Canada phase is ~0.2 less for in situ extinction coefficient (from a nephelometer and a particle soot absorption photometer) than for the AOD. It is ~0.1 less than for the carbon monoxide mixing ratio. The trends of horizontal variability with distance and aerosol environment are different for the wavelength dependence and the humidity response of light scattering. We discuss challenges in estimating aerosol optical properties, particle size and chemical composition from measurements at a distant location. The statistical parameters thus help interpret existing remote-sensing observations and design future ones.

Shinozuka, Y.; Redemann, J.; Russell, P. B.; Livingston, J. M.; Clarke, A. D.; Podolske, J. R.

2010-12-01

348

Constraints on the Variability of the Tropospheric Methane Abundance on Titan from Cassini VIMS Observations  

NASA Astrophysics Data System (ADS)

Titan's methane cycles between the atmosphere and the surface, similarly to the hydrological cycle on Earth, as its frequently observed clouds and surface fluvial features indicate. With the constant loss of methane due to photolysis, a surface source is needed to preserve the current high methane abundance in the atmosphere. However, no liquid surfaces or active volcanism have been identified so far, so that the surface branch of Titan's hydrological cycle and its interaction with the atmosphere are yet largely unconstrained. The lack of large liquid surfaces and the preferential occurence of the methane clouds in small areas in the south suggest that the methane distribution on Titan's troposphere might be highly variable, confining the clouds to regions near the surface sources. We present Cassini VIMS (Visual and Infrared Mapping Spectrometer) observations of the 0.64µm methane band, and the constraints on the spatial variation of methane abundance derived from it. The depth of the band is sensitive to the methane as well as the scattering of light by the haze, which increases the apparent methane optical depth. In order to separate the effect of variation in the methane abundance to that of the haze, we compare the methane band depth to the haze optical depth. We find that the band increases to the south of Titan's equator, independently from the haze variation. To quantify the methane variation, we reproduce the observed spectra with radiative transfer models based on the haze properties and vertical distribution at the equatorial region derived by the Huygens DISR (Descent Imager and Spectral Radiometer) team. We find that the band is most sensitive to the higher troposphere and the methane abundance at 20-40 km altitude. We present constraints on the latitudinal distribution of haze, tropospheric methane, and discuss their uncertainties.

Paulo, Penteado F.; Griffith, C.; VIMS Team

2006-09-01

349

Observations of variable inter-observer agreement for clinical evaluation of faecal consistency in grow-finishing pigs.  

PubMed

Inter-observer agreement for assessment of faecal consistency in pigs was evaluated using a scoring system with 3 categories. In a pilot study, 3 observers performed an examination of faecal samples post-collection. The samples were obtained from pigs (12-13 weeks old) in 4 herds with a history of diarrhoea associated with Lawsonia intracellularis, Brachyspira spp. and/or Porcine Circovirus Type 2. Observer 1 examined all the faecal samples from the 4 herds. Observer 2 only examined the faecal samples from herds 1 and 2. Observer 3 only examined the faecal samples from herds 3 and 4. We observed a substantial agreement in faecal consistency scores between Observers 1 and 3 (kappa=0.64, 95% CI: 0.51-0.78). In contrast, only a fair agreement was observed between Observers 1 and 2 (kappa=0.24, 95% CI: 0.14-0.34). The variations in inter-observer agreement detected in the current study suggest that misclassification error can be a problem in studies assessing faecal consistency. Solutions may include developing a standardized system for scoring the consistency of pig faeces, calibration when more than one observer is involved in clinical studies and using a more objective measure of faecal consistency. PMID:21183234

Pedersen, Ken Steen; Holyoake, Patricia; Stege, Helle; Nielsen, Jens Peter

2010-12-22

350

Observed and simulated seasonal variability of the AMOC at 26°N and 41°N  

NASA Astrophysics Data System (ADS)

Timeseries of the Atlantic Meridional Overturning (AMOC) have recently become available, but so far no meridional coherence has been documented in these timeseries. Here, we analyze the 26°N RAPID and the 41°N ARGO-based AMOC observations (Cunningham et al., 2007; Willis, 2010) for meridional coherence at seasonal timescales. We use monthly values smoothed by a three month running mean for both timeseries. At present, the 26°N RAPID array is available for five years (04/04 - 06/09) and the 41°N data are available for eight years (01/02 - 09/10). With no obvious relation between the two latitudes, the AMOC and Ekman transport timeseries are dominated by the annual cycle at 26°N and 41°N. However, after subtracting the Ekman transport from the AMOC, we find an inverse seasonal phasing between AMOC-Ekman at 26°N and 41°N. The mean annual cycle of AMOC-Ekman shows a maximum in October and a minimum in March at 26°N, but a maximum in April and a minimum in December at 41°N. We also find this inversely seasonal cycle in the Sverdrup transports calculated from the zonal integral of the wind stress curl using the NCEP reanalysis at both latitudes. We compare our results to a simulation with the high resolution NCEP-forced ocean simulation from the STORM project. We analyze the period that overlaps with the AMOC observations (01/02-12/10). The horizontal resolution of the model is about 10km, and the daily model output is smoothed to three month running means. In the STORM run, we also find inversely phased seasonal cycles in the Sverdrup transports between 26°N and 41°N, and no obvious relation between the Ekman transports. However, for AMOC-Ekman, we find a positive correlation of the 26°N and 41°N timeseries, with the mean seasonal cycles having a maximum in October and a minimum in March and April at both latitudes. A direct comparison shows that the Ekman and Sverdrup transport agree between the model and the observations both at 26°N and at 41°N. For the total AMOC at 26°N, model and observations agree well, whereas for the total AMOC at 41°N, the observational mean seasonal cycle has its maximum in April and the model mean seasonal cycle shows a maximum in October. While further studies are required, our preliminary results suggest a meridionally coherent seasonal cycle in the AMOC, and in turn (potentially) meridionally coherent AMOC variability even at seasonal timescales.

Mielke, C.; Frajka-Williams, E.; Baehr, J.

2012-04-01

351

Multiwavelength observations of flares and variability in the coronae of active binary systems  

NASA Astrophysics Data System (ADS)

I investigate the multi-wavelength properties of stellar flares on active binary systems, concentrating on X- ray/extreme ultraviolet (EUV) and radio observations of thermal and nonthermal coronal plasmas. I examine the frequency of flaring events in active binary systems in the EUV bandpass, and find that they undergo large scale flares ?40% of the time, with a dynamic range between quiescent and flare luminosities less than a factor of ten. Long duration flares lasting days appear to be common, and there is evidence for variability even when no large flares are obvious. Some coronal flares exhibit long rise times, comparable to the decay timescale. Other flare phenomena observed include a slow brightening before the impulsive phase of the flare, and two different timescales during the flare decay. Dramatic abundance and temperature changes are present in coronae during some flares, with enhancements up to a factor of four between quiescent and flaring iron abundances, and evidence for plasma temperatures >50 MK during flares. The distribution of thermal coronal plasma with temperature is bimodal with a peak around 6 8 106K and another at 20 30 106 K. The hotter temperature peak moves to higher temperatures during flares. Highly polarized, highly time-variable emission at 20 cm is due to a coherent emission mechanism, most likely emission at the plasma frequency or second harmonic, and is a common feature of low frequency radio emission on active binary systems. Gyrosynchrotron flares at higher radio frequencies show very little net polarization, in contrast with coherent phenomena which reveal large degrees of polarization. Radio and X-ray flares do show correlations; some patterns are consistent with solar flare multi-wavelength patterns while others are not. This presents a complex view of flaring. Flares demonstrate an increased contrast over the quiescent level at higher X-ray energies, and the flare evolution proceeds at a faster rate at higher energies. The question to what extent the solar-stellar connection holds with regards to the physics of flares is complicated: there is evidence for and against a connection.

Osten, Rachel Ann

2002-08-01

352

Inter-annual Variability of Mars Polar Processes as Observed by OMEGA/Mars Express  

NASA Astrophysics Data System (ADS)

Mars Express has now been operated successfully more than 6 earth years after orbit insertion in late 2003. Thanks to a much longer than expected lifetime of the cryocoolers, which still perform nominally, the coverage of polar regions by OMEGA now spans more than three full Mars years, from Ls 338°, M-year 26 to Ls 85°, M-year 30. Therefore, the South perennial cap (Ls 310° to Ls 0°), the South seasonal cap (Ls 0° to Ls 310°) and the North seasonal cap (Ls 170° to Ls 90°) have been observed over four successive Mars year while the North perennial cap (Ls 90° to Ls 170°) has been observed over three successive martian years. Due to the precession of the pericenter and of the orbit plane of the elliptical orbit of the satellite, the OMEGA imaging spectrometer on board this mission obtained data on polar regions at resolutions ranging from 300 m to 10 km over a wide range of Ls and local times [1, 2, 3, 4, 5]. This provides an excellent data set for comparing the evolution of seasonal caps and the spectral characteristics of the perennial caps over different Martian years. For both the perennial cap and the seasonal cap, the CO2 ice signatures dominate in the South while H2O ice signatures dominate in the North. The lag by a few weeks of the retreat of the seasonal caps observed by OMEGA between different Martian years is consistent with that of the "Crocus lines" derived from TES temperature data in 1999 - 2001 [6], with a possible link with dust storm activity in 2007. The spectral component which is not dominant (H2O in the South, CO2 in the North) shows overall consistency but significant year to year variability. CRISM/MRO observations at a much higher spatial resolution support these conclusions. In late 2009, OMEGA observations of the South cap at the time of minimum extent (Ls 340°) showed a much larger extent of H2O ice signatures compared to what had been observed in early 2004 [1]. As these regions show only weak albedo contrast, the observed variegation is likely linked with subsurface characteristics such as the high thermal inertia of underlying water ice rich layers at very shallow depths. This will be investigated by linking OMEGA observations with radar sounding of the subsurface by MARSIS/Mex [6] and SHARAD depending on the availability of data on regions of interest. [1] J-P. Bibring et al., Nature 428, p. 627 (2004) [2] Y. Langevin et al., Science 307, p. 1581 (2005) [3] Y. Langevin et al., Nature 442, p. 790 (2006) [4] Y. Langevin et al., J. Geophys. Res. 112, E08S12 (2007) [5] F. Schmidt et al., Icarus 200, p. 374 (2008) [5] T. Titus, H. H. Kieffer, abstract #2071, Lunar Planet. Science 33 (2002) [6] R. Jordan et al., Planet. Space Science 57, p. 1975 (2009)

Langevin, Y.; Bibring, J.-P.; Plaut, J.; Vincendon, M.; Gondet, B.; Poulet, F.; Schmidt, F.

2010-05-01

353

Impact of large-scale climate variability and change on crop yields in Africa: An observational assessment  

NASA Astrophysics Data System (ADS)

Assessments of the relationships between climate and agricultural production have progressed from opposite ends of the spatio-temporal spectrum. While studies of global-scale climate-yield relationships have provided estimates of the impact of multi-decadal trends in temperature and precipitation on recent production, studies of local weather impacts on yield have demonstrated the influence of temperature and precipitation variability on plant physiology, particularly with respect to the duration and timing of extremes. At intermediate spatial and temporal scales, somewhat of a gap in understanding exists. Our investigation contributes to better understanding climate-yield relationships at intermediate scales by assessing the impact of climate variability on crop yields at the country to continent scale on interannual to interdecadal timescales. Toward this end, we employ historical climatic data and reported cereal crop yields from the African continent, 1961 to 2009, in conjunction with principal component regression and partial least squares regression. Our results show that a discrete set of spatial patterns of climate variability account for up to half of the year-to-year variability in crop yields over portions of Africa. The impact of this climate variability is particularly strong in Sub-Saharan Africa, where large or prolonged deficits in yields can result in food shortages. The fundamental patterns of variability used to explain yield fluctuations are based on temperature and precipitation, chosen due to their influence on plant physiology; however, the time-varying behavior of the patterns may also be linked to coherent large-scale climate variability through regressions with sea surface temperature, sea level pressure and low-level wind fields. Results are distilled in terms of five UN designated geographic regions of Africa. Implications for short-term food security and future climate change are discussed.

Smoliak, B. V.; Po-Chedley, S.; Cullen, A. C.

2011-12-01

354

Placing the Deep Impact Mission into context: Two decades of observations of 9P/Tempel 1 from McDonald Observatory  

NASA Astrophysics Data System (ADS)

We report on low-spectral resolution observations of Comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7 m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. We found that the comet showed a decrease in gas production from 1983 to 2005, with the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C 3 by 1.8, CH by 1.4 and C 2 by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we find that the gas production rates of OH, NH, C 3, CH and C 2 ratioed to that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. Comet Tempel 1 is a "normal" comet.

Cochran, A. L.; Barker, E. S.; Caballero, M. D.; Györgey-Ries, J.

2009-01-01

355

Variability of internally generated turbulence in an estuary, from 100 days of continuous observations  

NASA Astrophysics Data System (ADS)

We present detailed observations of internally generated turbulence in a sheared, stratified natural flow, as well as an analysis of the external factors leading to its generation and temporal variability. Multi-month time series of vertical profiles of velocity, acoustic backscatter (0.5 Hz), and turbulence parameters were collected with two moored acoustic Doppler current profilers (ADCPs) in the Hudson River estuary, and estuary-long transects of water density were collected 30 times. ADCP backscatter is used for visualization of coherent turbulent structures and evaluation