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1

Observed Decadal Midlatitude and Tropical Atlantic Climate Variability  

E-print Network

associated with the NAO display a coherent seesaw between Iceland and the Azores. This out index and SLP variability over Iceland and the Azores. Based on these findings we hypothesize of opposite polarity situated around the centers of the Icelandic Low and the Azores High. A banded SST

Columbia University

2

Tides and Decadal Variability  

NASA Technical Reports Server (NTRS)

This paper reviews the mechanisms by which oceanic tides and decadal variability in the oceans are connected. We distinguish between variability caused by tides and variability observed in the tides themselves. Both effects have been detected at some level. The most obvious connection with decadal timescales is through the 18.6-year precession of the moon's orbit plane. This precession gives rise to a small tide of the same period and to 18.6-year modulations in the phase and amplitudes of short-period tides. The 18.6-year "node tide" is very small, no more than 2 cm anywhere, and in sea level data it is dominated by the ocean's natural Variability. Some authors have naively attributed climate variations with periods near 19 years directly to the node tide, but the amplitude of the tide is too small for this mechanism to be operative. The more likely explanation (Loder and Garrett, JGR, 83, 1967-70, 1978) is that the 18.6-y modulations in short-period tides, especially h e principal tide M2, cause variations in ocean mixing, which is then observed in temperature and other climatic indicators. Tidally forced variability has also been proposed by some authors, either in response to occasional (and highly predictable) tidal extremes or as a nonlinear low-frequency oscillation caused by interactions between short-period tides. The former mechanism can produce only short-duration events hardly more significant than normal tidal ranges, but the latter mechanism can in principle induce low-frequency oscillations. The most recent proposal of this type is by Keeling and Whorf, who highlight the 1800-year spectral peak discovered by Bond et al. (1997). But the proposal appears contrived and should be considered, in the words of Munk et al. (2002), "as the most likely among unlikely candidates."

Ray, Richard D.

2003-01-01

3

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

NASA Astrophysics Data System (ADS)

Using an observation data set 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 decreasing 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 positive trends during 1992-2003. The spatial characteristics of OHC variability and heat budget in the Luzon Strait, west of Luzon Island, and in the Xisha warm eddy region are also discussed.

Song, Wei; Lan, Jian; Liu, Qinyan; Sui, Dandan; Zeng, Lili; Wang, Dongxiao

2014-02-01

4

Decadal rainfall variability modes in observed rainfall records over East Africa and their relations to historical sea surface temperature changes  

NASA Astrophysics Data System (ADS)

SummaryDetailed knowledge about the long-term interface of climate and rainfall variability is essential for managing agricultural activities in Eastern African countries. To this end, the space-time patterns of decadal rainfall variability modes over East Africa and their predictability potentials using Sea Surface Temperature (SST) are investigated. The analysis includes observed rainfall data from 1920 to 2004 and global SSTs for the period 1950-2004. Simple correlation, trend and cyclical analyses, Principal Component Analysis (PCA) with VARIMAX rotation and Canonical Correlation Analysis (CCA) are employed. The results show decadal signals in filtered observed rainfall record with 10 years period during March-May (MAM) and October-December (OND) seasons. During June-August (JJA), however, cycles with 20 years period are common. Too much/little rainfall received in one or two years determines the general trend of the decadal mean rainfall. CCA results for MAM showed significant positive correlations between the VARIMAX-PCA of SST and the canonical component time series over the central equatorial Indian Ocean. Positive loadings were spread over the coastal and Lake Victoria regions while negative loading over the rest of the region with significant canonical correlation skills. For the JJA seasons, Atlantic SSTs had negative loadings centred on the tropical western Atlantic Ocean associated with the wet/dry regimes over western/eastern sectors. The highest canonical correlation skill between OND rainfall and the Pacific SSTs showed that El Niño/La Niña phases are associated with wet/dry decades over the region.

Omondi, P.; Awange, J. L.; Ogallo, L. A.; Okoola, R. A.; Forootan, E.

2012-09-01

5

Elements of tropical Pacific decadal variability  

E-print Network

and content by: njamin S. Giese (C Chair of Committee) ~ ~(V Gerald R. North (Member) Wilford D. Gardner (Head of Department) ing Chang Co-Chair of Committee) May 2003 Major Subject Oceanography ABSTRACT Elements of Tropical Pacific Decadal.... Tropical Pacific Decadal Variability and the 1976-77 Climate Shift B. Elements of Spiciness Decadal Variability. . . . . . . . C. Elements of Isopycnal Depth Decadal Variability. . . . IV CONCLUSIONS . A. Summary B. Discussion . . C. Future...

Fuckar, Neven-Stjepan

2003-01-01

6

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

7

Re-Examination of the Observed Decadal Variability of Earth Radiation Budget Using Altitude-Corrected ERBE/ERBS Nonscanner WFOV Data  

NASA Technical Reports Server (NTRS)

This paper gives an update on the observed decadal variability of Earth Radiation Budget using the latest altitude-corrected Earth Radiation Budget Experiment (ERBE)/Earth Radiation Budget Satellite (ERBS) Nonscanner Wide Field of View (WFOV) instrument Edition3 dataset. The effects of the altitude correction are to modify the original reported decadal changes in tropical mean (20N to 20S) longwave (LW), shortwave (SW), and net radiation between the 1980s and the 1990s from 3.1/-2.4/-0.7 to 1.6/-3.0/1.4 Wm(sup -2) respectively. In addition, a small SW instrument drift over the 15-year period was discovered during the validation of the WFOV Edition3 dataset. A correction was developed and applied to the Edition3 dataset at the data user level to produce the WFOV Edition3_Rev1 dataset. With this final correction, the ERBS Nonscanner observed decadal changes in tropical mean LW, SW, and net radiation between the 1980s and the 1990s now stand at 0.7/-2.1/1.4 Wm(sup -2), respectively, which are similar to the observed decadal changes in the HIRS Pathfinder OLR and the ISCCP FD record; but disagree with the AVHRR Pathfinder ERB record. Furthermore, the observed interannual variability of near-global ERBS WFOV Edition3_Rev1 net radiation is found to be remarkably consistent with the latest ocean heat storage record for the overlapping time period of 1993 to 1999. Both data sets show variations of roughly 1.5 Wm(sup -2) in planetary net heat balance during the 1990s.

Wong, Takmeng; Wielicki, Bruce A.; Lee, Robert B.; Smith, G. Louis; Bush, Kathryn A.

2005-01-01

8

Variability of Antarctic ozone loss in the last decade (2004-2013): high resolution simulations compared to Aura MLS observations  

NASA Astrophysics Data System (ADS)

A detailed analysis of the polar ozone loss processes during ten recent Antarctic winters is presented with high resolution Mimosa-Chim model simulations and high frequency polar vortex observations from the Aura Microwave Limb Sounder (MLS) instrument. Our model results for the Antarctic winters 2004-2013 show that chemical ozone loss starts in the edge region of the vortex at equivalent latitudes (EqLs) of 65-69° S in mid-June/July. The loss progresses with time at higher EqLs and intensifies during August-September over the range 400-600 K. The loss peaks in late September/early October, where all EqLs (65-83°) show similar loss and the maximum loss (>2 ppmv [parts per million by volume]) is found over a broad vertical range of 475-550 K. In the lower stratosphere, most winters show similar ozone loss and production rates. In general, at 500 K, the loss rates are about 2-3 ppbv sh-1 (parts per billion by volume/sunlit hour) in July and 4-5 ppbv sh-1 in August/mid-September, while they drop rapidly to zero by late September. In the middle stratosphere, the loss rates are about 3-5 ppbv sh-1 in July-August and October at 675 K. It is found that the Antarctic ozone hole (June-September) is controlled by the halogen cycles at about 90-95% (ClO-ClO, BrO-ClO, and ClO-O) and the loss above 700 K is dominated by the NOx cycle at about 70-75%. On average, the Mimosa-Chim simulations show that the very cold winters of 2005 and 2006 exhibit a maximum loss of ~3.5 ppmv around 550 K or about 149-173 DU over 350-850 K and the warmer winters of 2004, 2010, and 2012 show a loss of ~2.6 ppmv around 475-500 K or 131-154 DU over 350-850 K. The winters of 2007, 2008, and 2011 were moderately cold and thus both ozone loss and peak loss altitudes are between these two ranges (3 ppmv around 500 K or 150 ± 10 DU). The modeled ozone loss values are in reasonably good agreement with those estimated from Aura MLS measurements, but the model underestimates the observed ClO, largely due to the slower vertical descent in the model during spring.

Kuttippurath, J.; Godin-Beekmann, S.; Lefèvre, F.; Santee, M. L.; Froidevaux, L.; Hauchecorne, A.

2014-11-01

9

Anatomy of North Pacific Decadal Variability  

Microsoft Academic Search

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

NIKLAS SCHNEIDER; J. MILLER; DAVID W. P IERCE

10

Decadal variability in Floods and Extreme Rainfall  

NASA Astrophysics Data System (ADS)

Decadal variability in climate extremes associated with floods is of particular interest for infrastructure development and for insurance programs. From an analysis of US data we note that changes in insurance rates and in the construction of flood control infrastructure emerge soon after a period where there is a high incidence of regional flooding. This leads to the question of whether there is clustering in the incidence of anomalous flooding (or its absence) at decadal scales. The direct examination of this question from streamflow data is often clouded by the modification of flows by the construction of dams and other infrastructure to control floods, especially over a large river basin. Consequently, we explore the answer to this question through the analysis of both extreme rainfall and flood records. Spectral and time domain methods are used to identify the nature of decadal variability and its potential links to large scale climate.

Lall, Upmanu; Cioffi, Francesco; Devineni, Naresh; Lu, Mengqian

2014-05-01

11

Food Price Volatility and Decadal Climate Variability  

NASA Astrophysics Data System (ADS)

The agriculture system is under pressure to increase production every year as global population expands and more people move from a diet mostly made up of grains, to one with more meat, dairy and processed foods. Weather shocks and large changes in international commodity prices in the last decade have increased pressure on local food prices. This paper will review several studies that link climate variability as measured with satellite remote sensing to food price dynamics in 36 developing countries where local monthly food price data is available. The focus of the research is to understand how weather and climate, as measured by variations in the growing season using satellite remote sensing, has affected agricultural production, food prices and access to food in agricultural societies. Economies are vulnerable to extreme weather at multiple levels. Subsistence small holders who hold livestock and consume much of the food they produce are vulnerable to food production variability. The broader society, however, is also vulnerable to extreme weather because of the secondary effects on market functioning, resource availability, and large-scale impacts on employment in trading, trucking and wage labor that are caused by weather-related shocks. Food price variability captures many of these broad impacts and can be used to diagnose weather-related vulnerability across multiple sectors. The paper will trace these connections using market-level data and analysis. The context of the analysis is the humanitarian aid community, using the guidance of the USAID Famine Early Warning Systems Network and the United Nation's World Food Program in their response to food security crises. These organizations have worked over the past three decades to provide baseline information on food production through satellite remote sensing data and agricultural yield models, as well as assessments of food access through a food price database. Econometric models and spatial analysis are used to describe the connection between shocks and food prices, and to demonstrate the importance of these metrics in overall outcomes in food-insecure communities.

Brown, M. E.

2013-12-01

12

Advances in Understanding Decadal Climate Variability  

NASA Technical Reports Server (NTRS)

Recently, a joint Brazil-France-U.S. program, known as PIRATA (Pilot Research moored Array in the Tropical Atlantic), was proposed to begin the deployment of moored measurement platforms in the tropical Atlantic in order to enhance the existing observational data base and subsequent understanding of the processes by which the ocean and atmosphere couple in key regions of the tropical Atlantic Ocean. Empirical studies have suggested that there are strong relationships between tropical Atlantic upper ocean variability, SST, ocean-atmosphere coupling and regional climate variability. During the early 1980's a coordinated set of surface wind, subsurface thermal structure, and subsurface current observations were obtained as part of the U.S.-France SEQUAL- FOCAL process experiment designed to observe the seasonal response of the tropical Atlantic Ocean to surface forcing. Since that time, however, the observational data base for the tropical Atlantic Ocean has disintegrated to a few shiptracks measuring ocean temperatures and a small collection of tide gauge stations measuring sea level. A more comprehensive set of observations, modeling and empirical studies is now in order to make progress on understanding the regional climate variability. The proposed PIRATA program will use mooring platforms similar to the tropical Pacific Ocean TAO array to measure surface fluxes of momentum and heat and the corresponding changes in the upper ocean thermal structure. It is anticipated that the oceanic data from this monitoring array will also be used in a predictive mode for initialization studies of regional coupled climate models. Of particular interest are zonal and meridional modes of ocean-atmosphere variability within the tropical Atlantic basin that have significant impacts on the regional climate of the bordering continents.

Busalaacchi, Antonio J.

1998-01-01

13

Advances in Understanding Decadal Climate Variability  

NASA Technical Reports Server (NTRS)

Recently, a joint Brazil-France-U.S. program, known as PIRATA (Pilot Research moored Array in the Tropical Atlantic), was proposed to begin the deployment of moored measurement platforms in the tropical Atlantic in order to enhance the existing observational data base and subsequent understanding of the processes by which the ocean and atmosphere couple in key regions of the tropical Atlantic Ocean. Empirical studies have suggested that there are strong relationships between tropical Atlantic upper ocean variability, SST, ocean-atmosphere coupling and regional climate variability. During the early 1980's a coordinated set of surface wind, subsurface thermal structure, and subsurface current observations were obtained as part of the U.S.-France SEQUAL-FOCAL process experiment designed to observe the seasonal response of the tropical Atlantic Ocean to surface forcing. Since that time, however, the observational data base for the tropical Atlantic Ocean has disintegrated to a few ship-tracks measuring ocean temperatures and a small collection of tide gauge stations measuring sea level. A more comprehensive set of observations, modeling and empirical studies is now in order to make progress on understanding the regional climate variability. The proposed PIRATA program will use mooring platforms similar to the tropical Pacific Ocean TAO array to measure surface fluxes of momentum and heat and the corresponding changes in the upper ocean thermal structure. It is anticipated that the oceanic data from this monitoring array will also be used in a predictive mode for initialization studies of regional coupled climate models. Of particular interest are zonal and meridional modes of ocean-atmosphere variability within the tropical Atlantic basin that have significant impacts on the regional climate of the bordering continents.

Busalacchi, Antonio J.

1999-01-01

14

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. PMID:23980136

Wang, Kaicun; Dickinson, Robert E.

2013-01-01

15

Decadal Climate Variability over the North Pacific and North America: Dynamics and Predictability  

Microsoft Academic Search

The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational 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 region of interest

M. Latif; T. P. Barnett

1996-01-01

16

A Decade of Satellite Ocean Color Observations  

NASA Technical Reports Server (NTRS)

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 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

17

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

18

Decadal Variability of West Coast Marine Stratus Clouds  

NASA Astrophysics Data System (ADS)

Low frequency variability of West Coast summertime marine stratus clouds are investigated using six decades of observations at several coastal airport locations. The magnitude and direction of long-term trends in summertime marine stratus occurrence along the California coast depends strongly on the cloud base height threshold used to distinguish low clouds from higher clouds. In this study, marine stratus clouds are defined as having cloud base at or below 1000 meters. Using this threshold, a decreasing trend in marine stratus cloud frequency was found for Southern California during the 1950-2012 period. No significant trends were found in Northern California. When averaged over the summer season, the cloud data reveal that coastal stratus has substantial variation on multi-year time scales with typical changes of 10-15% from year to year and 5-7% from decade to decade. Low stratus cloud cover varies over long distances with coherent anomalies that extend from southern California to Oregon. The most important correlated modes of SST with cloud cover anomalies, via a canonical correlation analysis contains both local and remote SST linkages. The first mode is correlated with the PDO and also to Pacific atmospheric circulation patterns and coastal upwelling. There is also a linkage to sea surface temperature anomalies in the low latitude Pacific, suggesting that tropical-extratropical interactions may be involved in driving West Coast cloud cover.

Iacobellis, S.; Schwartz, R. E.; Gershunov, A.; Cayan, D. R.; Williams, P.

2013-12-01

19

On the decadal and interdecadal variability in the Pacific Ocean  

Microsoft Academic Search

The Pacific decadal and interdecadal oscillation (PDO) has been extensively explored in recent decades because of its profound\\u000a impact on global climate systems. It is a long-lived ENSO-like pattern of Pacific climate variability with a period of 10–30\\u000a years. The general picture is that the anomalously warm (cool) SSTs in the central North Pacific are always accompanied by\\u000a the anomalously

Yang Haijun; Zhang Qiong

2003-01-01

20

Tropical origins of North and South Pacific decadal variability  

Microsoft Academic Search

The origin of the Pacific Decadal Oscillation (PDO), the leading mode of sea surface temperature variability for the North Pacific, is a matter of considerable debate. One paradigm views the PDO as an independent mode centered in the North Pacific, while another regards it as a largely reddened response to El Niño-Southern Oscillation (ENSO) forcing from the tropics. We calculate

Jeremy D. Shakun; Jeffrey Shaman

2009-01-01

21

Decadal and multidecadal climate variability in the eastern United  

E-print Network

36 Decadal and multidecadal climate variability in the eastern United States and North Atlantic Ocean are sensitive to natural climate variabil- ity associated with the North Atlantic Oscillation Atlantic Oscillation, result- ing in wetter, warmer winters in the eastern United States have occurred

22

Variable stars across the observational HR diagram  

E-print Network

An overview of pulsating variable stars across the observational Hertzprung-Russel (HR) diagram is presented, together with a summary of their global properties. The HR diagram is presented with a third colour-coded dimension, visualizing the fraction of variable, the amplitude of variability or the period of variability. The distribution of variable stars in the other observational diagrams, such as the Period-Amplitude diagram, is also presented. Some of the progresses performed in the field of variable stars during the last decade are briefly summarized, and future projects that will improve our knowledge of variable stars are mentioned.

Laurent Eyer; Nami Mowlavi

2007-12-21

23

Tropical Pacific Observing for the Next Decade  

NASA Astrophysics Data System (ADS)

More than 60 scientists and program officials from 13 countries met at the Scripps Institution of Oceanography for the Tropical Pacific Observing System (TPOS) 2020 Workshop. The workshop, although motivated in part by the dramatic decline of NOAA's Tropical Atmosphere Ocean (TAO) buoy reporting from mid-2012 to early 2014 (see http://www.bloomberg.com/news/2014-03-07/aging-el-nino-buoys-getting-fixed-as-weather-forecasts-at-risk.html), evaluated the needs for tropical Pacific observing and initiated efforts to develop a more resilient and integrative observing system for the future.

Legler, David M.; Hill, Katherine

2014-06-01

24

Decadal-Interdecadal SST Variability and Regional Climate Teleconnections  

NASA Technical Reports Server (NTRS)

Dominant modes of decadal and interdecadal SST variability and their impacts on summertime rainfall variability over East Asia and the North America are studied. Two dominant modes of interdecadal SST variability, one associated with El Nino-like warming in the global oceans and one with an east-west seesaw variation in the equatorial Pacific have been identified. The first mode is associated in part with a long-term warming trend in the topical oceans and cooling over the northern Pacific. The second mode suggests an westward shift and strengthening of the Walker circulation from 1960s to the 1980s. Over East Asian, the first SST mode is correlated with reduced rainfall in northern China and excessive rainfall in central China. This SST mode is also associated with the tendency for increased rainfall over the midwest region, and reduced rainfall over the east Coast of the US. The results suggest a teleconnection pattern which links the occurrences of drought and floods over the Asian monsoon and the US summertime time climate. This teleconnection is likely to be associated with decadal variability of the East Asian jetstream, which are affected by strong land surface heating over the Siberian region, as well as El Nino-like SST forcings. The occurrences of major droughts and floods in the East Asian and US continent in recent decades are discussed in light of the above teleconnection patterns.

Lau, William K. M.; Weng, H.; Einaudi, Franco (Technical Monitor)

2001-01-01

25

Decadal climate variability and forced change in the South Europe - Mediterranean Region  

NASA Astrophysics Data System (ADS)

Decadal climate variability in the Mediterranean/South Europe region since 1860 and projected 21st century change are investigated based on observational data and the newly available Coupled Model Intercomparison Project - Phase 5 (CMIP5) experiments. Our results suggest that decadal changes in surface air temperature and related water cycle changes (e.g. evaporation) observed in the region during the period since 1860 have been significantly affected by forcings, be of natural or anthropic origin. Warming has accelerated during the latter half of the 20th century and is projected to further increase due to growing greenhouse gas concentrations. Due to the significant trend, Mediterranean temperature for the coming decade is very likely to be warmer than 1980-2005 and outside the range of variability, with a mean warming of 2 K projected by 2060. Sea-surface evaporation (fresh water deficit) has increased during past decades and future forced increases are expected to exceed variability by 2020-2040 (in the coming decade). By 2071-2100, temperature (sea-surface evaporation and fresh water deficit) mean forced changes are estimated to be 4 (2) times larger than decade-to-decade anomalies due to internal variability. 20th century precipitation variability in the Mediterranean has been largely of internal origin. 20th century simulations and future projections show an increasing impact of external forcings in the form of long-term negative trends over most of the Mediterranean in the midst of internal variability. In JJA, forced precipitation change is projected to exceed internal variability by 2040. More generally, projections indicate that in the 21st century decade-to-decade conditions may still occasionally be wetter than what we have seen during 1980-2005 but there is an overall progressive shift in the odds for conditions to be drier.

Mariotti, Annarita; Pan, Yutong; Zeng, Ning; Alessandri, Andrea

2014-05-01

26

Evidence for atmospheric variability over the Pacific on decadal timescales  

Microsoft Academic Search

An index of Pacific decadal variability based on a multivariate empirical orthogonal function analysis of National Centers for Environmental Prediction reanalysis is used to extract associated signals in satellite-based measurements of atmospheric parameters. This index captures the 1976–1977 “El Niño–Southern Oscillation (ENSO)-like” warming shift of sea surface temperatures (SST) as well as a more recent transition of opposite sign in

R. J. Burgman; A. C. Clement; C. M. Mitas; J. Chen; K. Esslinger

2008-01-01

27

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability  

NASA Technical Reports Server (NTRS)

Based on the 20th century atmospheric reanalysis, winters with more frequent blocking, in a band of blocked latitudes from Greenland to Western Europe, are found to persist over several decades and correspond to a warm North Atlantic Ocean, in-phase with Atlantic multi-decadal ocean variability. Atmospheric blocking over the northern North Atlantic, which involves isolation of large regions of air from the westerly circulation for 5 days or more, influences fundamentally the ocean circulation and upper ocean properties by impacting wind patterns. Winters with clusters of more frequent blocking between Greenland and western Europe correspond to a warmer, more saline subpolar ocean. The correspondence between blocked westerly winds and warm ocean holds in recent decadal episodes (especially, 1996-2010). It also describes much longer-timescale Atlantic multidecadal ocean variability (AMV), including the extreme, pre-greenhouse-gas, northern warming of the 1930s-1960s. The space-time structure of the wind forcing associated with a blocked regime leads to weaker ocean gyres and weaker heat-exchange, both of which contribute to the warm phase of AMV.

Haekkinen, Sirpa; Rhines, Peter B.; Worthlen, Denise L.

2011-01-01

28

Societal Adaptation to Decadal Climate Variability in the United States  

NASA Astrophysics Data System (ADS)

CRCES Workshop on Societal Impacts of Decadal Climate Variability in the United States, 26-28 April 2007, Waikoloa, Hawaii The search for evidence of decadal climatic variability (DCV) has a very long history. In the past decade, a research community has coalesced around a series of roughly biennial workshops that have emphasized description of past DCV events; their causes and their ``teleconnections'' responsible for droughts, floods, and warm and cold spells around the world; and recently, the predictability of DCV events. Researchers studying climate change put great emphasis on prospective impacts, but the DCV community has yet to do so. To begin rectifying this deficiency, a short but ambitious workshop was convened in Waikoloa, near Kona, Hawaii, from 26-28 April 2007. This workshop, sponsored by the Center for Research on the Changing Earth System (CRCES), NOAA, the U.S. Geological Survey, and the U.S. Army Corps of Engineers, brought together climatologists and sectoral specialists representing agriculture, water resources, economics, the insurance industry, and developing country interests.

Rosenberg, Norman J.; Mehta, Vikram M.; Olsen, J. Rolf; von Storch, Hans; Varady, Robert G.; Hayes, Michael J.; Wilhite, Donald

2007-10-01

29

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability  

NASA Technical Reports Server (NTRS)

Atmospheric blocking over the northern North Atlantic involves isolation of large regions of air from the westerly circulation for 5-14 days or more. From a recent 20th century atmospheric reanalysis (1,2) winters with more frequent blocking persist over several decades and correspond to a warm North Atlantic Ocean, in-phase with Atlantic multi-decadal ocean variability (AMV). Ocean circulation is forced by wind-stress curl and related air/sea heat exchange, and we find that their space-time structure is associated with dominant blocking patterns: weaker ocean gyres and weaker heat exchange contribute to the warm phase of AMV. Increased blocking activity extending from Greenland to British Isles is evident when winter blocking days of the cold years (1900-1929) are subtracted from those of the warm years (1939-1968).

Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

2011-01-01

30

Seasonal Dependency of Bi-Decadal Precipitation Variability  

NASA Astrophysics Data System (ADS)

Seasonal dependency of precipitation variability on a bi-decadal timescale and associated atmospheric circulation anomalies over the Pacific Ocean are investigated using NCEP/NCAR reanalysis data for a period from 1949-2001. We estimated bi-decadal variability of precipitation by calculating regression coefficients between the bidecadal filtered (pass-band of 10-30-year periods) reanalysis data and a representative time series of the Bi-Decadal Oscillation (BDO). As the representative BDO time series, we use wintertime North Pacific Index (NPI), which is a sea level pressure time series, averaged over the Aleutian Lows. The regression map reveals a precipitation band with positive regressions across the Tropical Pacific (EQ-20°N) from autumn to spring. The tropical precipitation band is consistent with gauge data and satellite estimates. In winter, more energetic precipitation changes also occur in the mid-latitude North Pacific with the positive regressions over the northern (50°-70°N) North Pacific and negative regressions in the central North Pacific (30°-50°N) as shown by Minobe and Nakanowari (2002, GRL) in addition to the equatorial precipitation change. In order to know the mechanisms of the bi-decadal precipitation changes, we perform a humidity-flux analysis using the reanalysis data. On the bi-decadal time scale, the precipitation anomalies can be approximately explained by the sum of horizontal humidity flux convergence and evaporation anomalies. For the tropical band, the humidity flux convergence has similar amplitudes to the evaporation in autumn and spring seasons, but dominate in winter season. In mid-latitudes, the wintertime precipitation anomalies are well explained by the humidity convergence. The humidity-flux convergences in mid-latitudes are due to anomalous geostrophic winds over climatological humidity gradients, and wind anomalies are essentially non-divergent. On the other hand, humidity-flux convergences in the tropics are resulted from surface wind convergence due to ageostrophic wind components. The difference of the convergence mechanism between mid-latitude and tropics results in that relatively small sea-level pressure anomalies in the tropics yield large humidity-flux convergences. The tropical pressure fluctuations are much smaller than those in mid-latitudes, but cannot be ignored for the bi-decadal precipitation changes.

Nakanowatari, T.; Minobe, S.

2002-12-01

31

Marine-based multi-proxy reconstruction of Atlantic multi-decadal variability  

NASA Astrophysics Data System (ADS)

Atlantic multi-decadal variability (AMV) is known to impact climate globally, and knowledge about the persistence of AMV is important for understanding past and future climate variability, as well as modeling and assessing climate impacts. The short observational data do not significantly resolve multi-decadal variability, but recent paleo-proxy reconstructions show multi-decadal variability in North Atlantic temperature prior to the instrumental record. However, most of these reconstructions are land-based, not necessarily representing sea surface temperature. Proxy records are also subject to dating errors and micro-environmental effects. We extend the record of AMV 90 years past the instrumental record using principle component analysis of five marine-based proxy records to identify the leading mode of variability. The first principal component is consistent with the observed AMV, and multi-decadal variability seems to persist prior to the instrumental record. Thus, we demonstrate that reconstructions of past Atlantic low-frequency variability can be improved by combining marine-based proxies.

Svendsen, Lea; Hetzinger, Steffen; Keenlyside, Noel; Gao, Yongqi

2014-05-01

32

Surface Salinity Variability in the North Atlantic During Recent Decades  

NASA Technical Reports Server (NTRS)

The sea surface salinity (SSS) variability in the North Atlantic is investigated using numerical model simulations for the last 50 years based on atmospheric forcing variability from Comprehensive Atmosphere Ocean Data Set (COADS) and National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) Reanalysis. The largest interannual and longer term variability occurs in two regions: the Labrador Sea and the North Equatorial Countercurrent (NECC) region. In both regions the seasonality of the surface salinity variability is prominent with the maximum standard deviation occurring in the summer/fall period. In the Labrador Sea the summer SSS anomalies far exceed those of wintertime in amplitude. The interannual SSS variability in the subpolar gyre can be attributed to two factors: excess ice melt and heat flux (i.e. deep mixing) variations. On the other hand, heat flux variability can also lead to meridional overturning changes on decadal time scales such that weak overturning is manifested in fresh surface conditions in the subpolar gyre. The overturning changes also influence the NECC region SSS variability. Moreover, the subpolar freshening events are expected to occur during the negative phase of North Atlantic Oscillation which is associated with a weak wintertime surface heat loss in the subpolar gyre. No excess sea ice melt or precipitation is necessary for the formation of the fresh anomalies, because with the lack of wide-spread deep mixing, the fresh water that would be expected based on climatology, would accumulate at the surface. Thus, the fresh water 'conveyor' in the Atlantic operates via the overturning circulation such that deep mixing inserts fresh water while removing heat from the water column.

Haekkinen, Sirpa

2001-01-01

33

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

34

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

35

Pacific decadal variability in the view of linear equatorial wave theory  

NASA Astrophysics Data System (ADS)

It has recently been proposed, within the framework of the linear shallow water equations, that tropical Pacific decadal variability can be accounted for by basin modes with eigenperiods of 10 to 20 years, amplifying a mid- latitude wind forcing with an essentially white spectrum (Cessi and Louazel 2001; Liu 2003). We question this idea here, using a different formalism of linear equatorial wave theory. We compute the Green's function for the wind forced response of a linear equatorial shallow water ocean, and use the results of Cane and Moore (1981) to obtain a compact, closed form expression for the motion of the equatorial thermocline, which applies to all frequencies lower than seasonal. At very low frequencies (decadal timescales), we recover the planetary geostrophic solution used by Cessi and Louazel (2001), as well as the equatorial wave solution of Liu (2003), and give a formal explanation for this convergence. Using this more general solution to explore more realistic wind forcings, we come to a different interpretation of the results. We find that the equatorial thermocline is inherently more sensitive to local than to remote wind forcing, and that planetary Rossby modes only weakly alter the spectral characteristics of the response. Tropical winds are able to generate a strong equatorial response with periods of 10 to 20 years, while midlatitude winds can only do so for periods longer than about 50 years. Since the decadal pattern of observed winds shows similar amplitude for tropical and midlatitude winds, we conclude that the latter are unlikely to be responsible for the observed decadal tropical Pacific SST variability. References : Cane, M. A., and Moore, D. W., 1981: A note on low-frequency equatorial basin modes. J. Phys. Oceanogr., 11(11), 1578 1584. Cessi, P., and Louazel, S., 2001: Decadal oceanic response to stochastic wind forcing. J. Phys. Oceanogr., 31, 3020 3029. Liu, Z., 2003: Tropical ocean decadal variability and resonance of planetary wave basin modes. J. Clim., 16(18), 1539 1550.

Emile-Geay, J. B.; Cane, M. A.

2006-12-01

36

Decade of balloon observations of auroral X-rays  

SciTech Connect

The paper describes balloon observations of bremsstrahlung X-rays carried out by the University of Calgary over the past decade which deal with morphological studies of auroral electron precipitation. The program concentrated on the understanding of the correlation between parent electrons and secondary X-rays, the study of microbursts, east-west and north-south extent of electron precipitation, and precipitation during pulsating auroras.

Venkatesan, D.; Vij, K.K.

1981-01-01

37

Climate variability in the North Atlantic on decadal and multi-decadal time scales: A numerical study  

NASA Astrophysics Data System (ADS)

The goal of this work is to understand the mechanisms that drive the decadal and multi-decadal climate variability in the North Atlantic. Natural climate variability on these particular time scales occupies a central position in discussions of anthropogenic climate changes, but many aspects related, to this issue are still poorly understood. The major tool used in this study is a coupled general circulation model consisting of the NCAR CCM3 and the Miami Isopycnic Coordinate Ocean Model. The simulated decadal variability in the North Atlantic is dominated by a tri-pole pattern in sea surface temperature and a North Atlantic Oscillation (NAO) pattern in sea level pressure. The associated oceanic fluctuations are characterized by a delayed subtropical gyre response to anomalou's NAO surface wind stress forcing and advection of SST anomalies originating near the western boundary into the interior ocean. Separate ocean-alone experiments suggest that the SST variability can not be attributed solely to passive response of the ocean to atmospheric thermal forcing. It is also found that a quasi-oscillatory fluctuation of the thermohaline circulation (THC) in the North Atlantic ocean with an approximate time scale of 30 years is present in the coupled but not in uncoupled simulations. The latter were forced with either Newtonian relaxation boundary conditions (based on a monthly climatology of the atmospheric state variables such as the surface air temperature and surface specific humidity) or with imposed monthly varying heat and fresh water flux conditions. These results suggest that the variability of the THC in this model is neither an ocean internal phenomenon nor a passive response of the ocean to atmospheric forcing. Rather, it is a coupled process involving both the ocean and the atmosphere. The THC oscillation appears to be driven by surface heat flux forcings while the effects of surface fresh water fluxes are secondary. Two delay effects are crucial for maintaining this oscillation. One is the delay of the North Atlantic overturning strength relative to the deep water formation rate in the deep water production region; the other is the delay of the associated SST and surface heat flux anomalies in the sinking region relative to the overturning amplitude itself. The sea surface temperature signal associated with the THC oscillation bears some resemblance to an SST interdecadal pattern extracted from observational data (Kushnir, 1993). Accompanying anomalies of northern hemispheric surface air temperature have positive values over the Pacific and Atlantic Oceans and negative values over the Eurasian and North American continents. In addition to anomalies in sea surface temperature and surface air temperature, there are also variations in atmospheric flow pattern over the North Atlantic, namely, an anomalous northerly flow over the Labrador Sea when the THC circulation is strong.

Cheng, Wei

38

Decadal-scale Holocene climate variability in the Nordic seas  

NASA Astrophysics Data System (ADS)

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 in the northward heat flux to northwestern Europe. Core MD 99-2269 is located in the deep Hunafloi trough, off N Iceland (66^o37.53N; 20^o51.16W, 365 m water depth). Today the core lies under the influence of the Irminger current, but it also may be influenced by the cold East Greenland current (EGC) as the Polar front migrates eastward. Core BS88-6-5A is located on the East Greenland shelf (67^o07.54N; 30^o54.26W, 707 m water depth) and is influenced by the EGC. The cores has been dated by AMS C-14 and Pb 210 isotope profiles. SST variations are estimated by means of 3 different diatom transfer function methods. Results indicate a division of the Holocene into three periods and a climate development in step with the decreasing Northern Hemisphere insolation. However, regional differences between the surface currents occur regarding both timing and magnitude of changes. Superimposed on the general Holocene cooling trend there is a high frequency SST variability, which is in the order of 1--1.5 degrees C for the Vöring Plateau and the East Greenland shelf, and 2.5--3 degrees C for the North Iceland shelf. There is clear evidence for late Holocene climatic events such as the "Little Ice Age" and the "Medieval Warm Period". Timing of late Holocene climatic events at the eastern versus western Nordic Seas will be discussed.

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

2003-04-01

39

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

40

The Nature of the Decadal Variability of Surface Climate Over the North Atlantic Ocean  

E-print Network

The Nature of the Decadal Variability of Surface Climate Over the North Atlantic Ocean #12;iii The Nature of the Decadal Variability of Surface Climate Over the North Atlantic Ocean of the surface climate over the North Atlantic Ocean is investigated using the Fast Ocean Atmosphere Model (FOAM

Wisconsin at Madison, University of

41

Nine decades of decreasing phenotypic variability in Atlantic cod  

E-print Network

survey starting in 1919, monitoring juvenile body size and abundance and (ii) capture­mark­recapture data. Keywords Atlantic cod, body size, capture­mark­recapture, growth, phenotypic variability, stabilizing capture­mark­ recapture data collected on coast

Carlson, Stephanie

42

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

43

Interannual and decadal-scale variability of soil moisture and water resources in Africa  

NASA Astrophysics Data System (ADS)

Within water scarce regions such as the African continent, water availability is a fundamental factor for both ecosystems and human population. In particular the various ecoregions are highly vulnerable to climate change as seen in the recent drought in 2011, which affected the entire East African region and forced severe food crises causing the death of thousands of people. Several climate change scenarios associated with the expected population growth revealed an additional pressure on water availability, water accessibility and water demand in Africa in the future. In order to prevent, adapt and to mitigate climate change impacts (e.g. increasing water scarcity in the future) on soil moisture variability and water resources synthesis of its recent variations are extremely important. Unfortunately, there is currently no synthesis that highlights recent variations of soil moisture and fresh water resources in Africa. The aim of the study is to identify regions with large inter annual variability as well as decadal scale variability (trend, trend changes) of soil moisture and water resources. Hence, especially patterns of soil moisture and water resources variability will be demonstrated and implications in terms of vulnerability will be further discussed. The study comprises three different data sources: point measurements, remote sensing datasets and modelling results. Soil moisture observations from passive microwave radiometry (TRMM, AMSRE-E) and GRACE-derived terrestrial water storage were applied to locate areas which show a large inter annual variability. Supplementary, water level fluctuations from SAR altimetry (LEGOS/GOHS, ENVISAT) and in-situ runoff observations (SA FRIEND) provided by the Global Runoff Data Centre were used to confirm the encountered patterns of soil moisture and water resources variability. The spatial map of inter annual variability was subsequently overlaid by population density and land use data to assess the vulnerability of the African population to climate change. In order to put the findings of the synthesis in an historical perspective and to analyse the decadal scale variability and trends, runoff observations and modelled runoff from LPJML were also used.

Thomas, E.; Jung, M.; Wattenbach, M.; Heinke, J.; Weber, U.

2013-12-01

44

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

45

Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation  

NASA Astrophysics Data System (ADS)

Variability in the Atlantic Meridional Overturning Circulation (AMOC) has been analysed using a 600-year pre-industrial control simulation with the Bergen Climate Model. The typical AMOC variability has amplitudes of 1 Sverdrup (1 Sv = 106 m3 s-1) and time scales of 40-70 years. The model is reproducing the observed dense water formation regions and has very realistic ocean transports and water mass distributions. The dense water produced in the Labrador Sea (1/3) and in the Nordic Seas, including the water entrained into the dense overflows across the Greenland-Scotland Ridge (GSR; 2/3), are the sources of North Atlantic Deep Water (NADW) forming the lower limb of the AMOC's northern overturning. The variability in the Labrador Sea and the Nordic Seas convection is driven by decadal scale air-sea fluxes in the convective region that can be related to opposite phases of the North Atlantic Oscillation. The Labrador Sea convection is directly linked to the variability in AMOC. Linkages between convection and water mass transformation in the Nordic Seas are more indirect. The Scandinavian Pattern, the third mode of atmospheric variability in the North Atlantic, is a driver of the ocean's poleward heat transport (PHT), the overall constraint on northern water mass transformation. Increased PHT is both associated with an increased water mass exchange across the GSR, and a stronger AMOC.

Medhaug, I.; Langehaug, H. R.; Eldevik, T.; Furevik, T.; Bentsen, M.

2012-07-01

46

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

47

Investigating the Forcing and Response in Proxy Records of Multi-Decadal Scale Climate Variability  

Microsoft Academic Search

Multi-decadal climate variability has been detected in both instrumental and proxy climate records and these climate modes have been linked to internal interactions in the climate system, changes in solar irradiance, and episodes of explosive volcanism. We are interested in investigating the links in multi-decadal scale variability between highly resolved proxy records (e.g., tree-rings, speleothems, corals, and lake sediments) and

K. L. Delong; T. M. Quinn; R. Z. Poore; G. T. Mitchum

2007-01-01

48

Decadal variability in coupled sea-ice-thermohaline circulation systems  

SciTech Connect

An interdecadal oscillation in a coupled ocean-ice system was identified in a previous study. This paper extends that study to further examine the stability of the oscillation and the sensitivity of its frequency to various parameters and forcing fields. Three models are used: (i) an analytical box model; (ii) a two-dimensional model for the ocean thermohaline circulation (THC) coupled to a thermodynamic ice model, as in the authors` previous study; and (iii) a three-dimensional ocean general circulation model (OGCM) coupled to a similar ice model. The box model is used to elucidate the essential feedbacks that give rise to this oscillation and to identify the most important parameters and processes that determine the period. The counted model becomes more stable toward low coupling, greater diffusion, and weaker THC feedback. Nonlinear effects in the sea-ice model become important in the higher ocean-ice coupling regime where the effective sea-ice damping associated with this nonlinearity stabilizes the model. The 3D OGCM is used to test this coupled ocean-ice mechanism in a more realistic model setting. This model generates an interdecadal oscillation whose characteristics and phase relations among the model variables are similar to the oscillation obtained in the 2D models. The major difference is that the oscillation frequency is considerably lower. The difference can be explained in terms of the analytical box model solution in which the period of oscillation depends on the rate of anomalous density production by melting/cooling of sea ice per SST anomaly, times the rate of warming/cooling by anomalous THC heat advection per change in density anomaly. The 3D model has a smaller THC response to high-latitude density perturbations than the 2D model, and anomalous velocities in the 3D case tend to follow the mean isotherms so anomalous heat advection is reduced. This slows the ocean-ice feedback process, leading to the longer oscillation period. 36 refs., 27 figs.

Yang, J. [Woods Hole Oceanographic Institution, Woods Hole, MA (United States)] [Woods Hole Oceanographic Institution, Woods Hole, MA (United States); Neelin, J.D. [Univ. of California, Los Angeles, CA (United States)] [Univ. of California, Los Angeles, CA (United States)

1997-12-01

49

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

50

Temperature Responses to Spectral Solar Variability on Decadal Time Scales  

NASA Technical Reports Server (NTRS)

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 approx.0.6 K and approx.0.9 K in RCM and modelE, approx.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 approx.2 years, and is approx.0.06 K compared to approx.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

2010-01-01

51

Decadal variability in biogeochemical models: Comparison with a 50-year ocean colour dataset  

NASA Astrophysics Data System (ADS)

Assessing the skill of biogeochemical models to hindcast past variability is challenging, yet vital in order to assess their ability to predict biogeochemical change. However, the validation of decadal variability is limited by the sparsity of consistent, long-term biological datasets. The Phytoplankton Colour Index (PCI) product from the Continuous Plankton Recorder survey, which has been sampling the North Atlantic since 1948, is an example of such a dataset. Converting the PCI to chlorophyll values using SeaWiFS data allows a direct comparison with model output. Here we validate decadal variability in chlorophyll from the GFDL TOPAZ model. The model demonstrates skill at reproducing interannual variability, but cannot simulate the regime shifts evident in the PCI data. Comparison of the model output, data and climate indices highlights under-represented processes that it may be necessary to include in future biogeochemical models in order to accurately simulate decadal variability in ocean ecosystems.

Henson, Stephanie A.; Raitsos, Dionysios; Dunne, John P.; McQuatters-Gollop, Abigail

2009-11-01

52

Reconstructing the subsurface ocean decadal variability using surface nudging in a perfect model framework  

NASA Astrophysics Data System (ADS)

Initialising the ocean internal variability for decadal predictability studies is a new area of research and a variety of ad hoc methods are currently proposed. In this study, we explore how nudging with sea surface temperature (SST) and salinity (SSS) can reconstruct the three-dimensional variability of the ocean in a perfect model framework. This approach builds on the hypothesis that oceanic processes themselves will transport the surface information into the ocean interior as seen in ocean-only simulations. Five nudged simulations are designed to reconstruct a 150 years "target" simulation, defined as a portion of a long control simulation. The nudged simulations differ by the variables restored to, SST or SST + SSS, and by the area where the nudging is applied. The strength of the heat flux feedback is diagnosed from observations and the restoring coefficients for SSS use the same time-scale. We observed that this choice prevents spurious convection at high latitudes and near sea-ice border when nudging both SST and SSS. In the tropics, nudging the SST is enough to reconstruct the tropical atmosphere circulation and the associated dynamical and thermodynamical impacts on the underlying ocean. In the tropical Pacific Ocean, the profiles for temperature show a significant correlation from the surface down to 2,000 m, due to dynamical adjustment of the isopycnals. At mid-to-high latitudes, SSS nudging is required to reconstruct both the temperature and the salinity below the seasonal thermocline. This is particularly true in the North Atlantic where adding SSS nudging enables to reconstruct the deep convection regions of the target. By initiating a previously documented 20-year cycle of the model, the SST + SSS nudging is also able to reproduce most of the AMOC variations, a key source of decadal predictability. Reconstruction at depth does not significantly improve with amount of time spent nudging and the efficiency of the surface nudging rather depends on the period/events considered. The joint SST + SSS nudging applied everywhere is the most efficient approach. It ensures that the right water masses are formed at the right surface density, the subsequent circulation, subduction and deep convection further transporting them at depth. The results of this study underline the potential key role of SSS for decadal predictability and further make the case for sustained large-scale observations of this field.

Servonnat, Jérôme; Mignot, Juliette; Guilyardi, Eric; Swingedouw, Didier; Séférian, Roland; Labetoulle, Sonia

2014-06-01

53

Reconstructing the subsurface ocean decadal variability using surface nudging in a perfect model framework  

NASA Astrophysics Data System (ADS)

Initialising the ocean internal variability for decadal predictability studies is a new area of research and a variety of ad hoc methods are currently proposed. In this study, we explore how nudging with sea surface temperature (SST) and salinity (SSS) can reconstruct the three-dimensional variability of the ocean in a perfect model framework. This approach builds on the hypothesis that oceanic processes themselves will transport the surface information into the ocean interior as seen in ocean-only simulations. Five nudged simulations are designed to reconstruct a 150 years "target" simulation, defined as a portion of a long control simulation. The nudged simulations differ by the variables restored to, SST or SST + SSS, and by the area where the nudging is applied. The strength of the heat flux feedback is diagnosed from observations and the restoring coefficients for SSS use the same time-scale. We observed that this choice prevents spurious convection at high latitudes and near sea-ice border when nudging both SST and SSS. In the tropics, nudging the SST is enough to reconstruct the tropical atmosphere circulation and the associated dynamical and thermodynamical impacts on the underlying ocean. In the tropical Pacific Ocean, the profiles for temperature show a significant correlation from the surface down to 2,000 m, due to dynamical adjustment of the isopycnals. At mid-to-high latitudes, SSS nudging is required to reconstruct both the temperature and the salinity below the seasonal thermocline. This is particularly true in the North Atlantic where adding SSS nudging enables to reconstruct the deep convection regions of the target. By initiating a previously documented 20-year cycle of the model, the SST + SSS nudging is also able to reproduce most of the AMOC variations, a key source of decadal predictability. Reconstruction at depth does not significantly improve with amount of time spent nudging and the efficiency of the surface nudging rather depends on the period/events considered. The joint SST + SSS nudging applied everywhere is the most efficient approach. It ensures that the right water masses are formed at the right surface density, the subsequent circulation, subduction and deep convection further transporting them at depth. The results of this study underline the potential key role of SSS for decadal predictability and further make the case for sustained large-scale observations of this field.

Servonnat, Jérôme; Mignot, Juliette; Guilyardi, Eric; Swingedouw, Didier; Séférian, Roland; Labetoulle, Sonia

2015-01-01

54

Observations of solar irradiance variability  

NASA Technical Reports Server (NTRS)

High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.01%. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near 0.15/day; their amplitudes about the mean value of 1368.31 watts per square meter approach plus or minus 0.05%. Two large decreases in irradiance of up to 0.2% lasting about one week are highly correlated with the development of sunspot groups. The magnitude and time scale of the irradiance variability suggest that considerable energy storage occurs within the convection zone in solar active regions.

Willson, R. C.; Gulkis, S.; Janssen, M.; Hudson, H. S.; Chapman, G. A.

1981-01-01

55

Surface salinity variability in the northern North Atlantic during recent decades  

E-print Network

Surface salinity variability in the northern North Atlantic during recent decades Sirpa Ha 2002; accepted 15 March 2002; published 18 September 2002. [1] The sea surface salinity (SSS surface salinity variability is prominent with the maximum standard deviation (SD) occurring in the summer

56

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

E-print Network

reflects variability associated with the Atlantic Multidecadal Oscillation and the second RPC (RPC2, with critical implications for UCRB water resource management. (KEY TERMS: Colorado River; Atlantic MultidecadalASSOCIATIONS OF DECADAL TO MULTIDECADAL SEA-SURFACE TEMPERATURE VARIABILITY WITH UPPER COLORADO

57

Holocene Multi-Decadal to Millennial-Scale Hydrologic Variability on the South American Altiplano  

NASA Astrophysics Data System (ADS)

On orbital timescales, lacustrine sediment records in the tropical central Andes show massive changes in lake level due to mechanisms related to global-scale drivers, varying at precessional timescales. Here we use stable isotopic and diatom records from two lakes in the Lake Titicaca drainage basin to reconstruct multi- decadal to millennial scale precipitation variability during the last 7000 to 8000 years. The records are tightly coupled at multi-decadal to millennial scales with each other and with lake-level fluctuations in Lake Titicaca, indicating that the lakes are recording a regional climate signal. A quantitative reconstruction of precipitation from stable isotopic data indicates that the central Andes underwent significant wet to dry alternations at multi- centennial frequencies with an amplitude of 30 to 40% of total precipitation. A strong millennial-scale component, similar in duration to periods of increased ice rafted debris flux in the North Atlantic, is observed in both lake records, suggesting that tropical North Atlantic sea-surface temperature (SST) variability may partly control regional precipitation. No clear relationship is evident between these records and the inferred ENSO history from Lago Pallcacocha in the northern tropical Andes. In the instrumental period, regional precipitation variability on inter-annual timescales is clearly influenced by Pacific modes; for example, most El Ninos produce dry and warm conditions in this part of the central Andes. However, on longer timescales, the control of tropical Pacific modes is less clear. Our reconstructions suggest that the cold intervals of the Holocene Bond events are periods of increased precipitation in the central Andes, thus indicating an anti-phasing of precipitation variation in the southern tropics of South America relative to the Northern Hemisphere monsoon region.

Fritz, S. C.; Baker, P. A.; Ekdahl, E.; Burns, S.

2006-12-01

58

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

NASA Technical Reports Server (NTRS)

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 tide gauge data north of 40N, in the subpolar SST and in the winter North Atlantic Oscillation (NAO) index and in subpolar winter heat flux values. The decadal cycle is a well separated mode in a singular spectrum analysis (SSA) for a time series of SST EOF mode 1 with a center over the Gulf Stream extension. Tide gauge and SST data are consistent in that both show a significant subdecadal periodicity exclusively in the subpolar gyre, but in subtropics the 12-14 year period is the prominent, but nonstationary, decadal signal. The main finding of this study is that this 12-14 year cycle can be constructed based on the leading mode of the surface heat flux. This connection to the surface heat flux implicates the participation of the thermohaline circulation in the decadal cycle. During the cycle starting from the positive index phase of NAO, SST and oceanic heat content anomalies are created in subtropics due to local heat flux and intensification of the thermohaline circulation. The anomalies advect to the subpolar gyre where they are amplified by local heat flux and are part of the negative feedback of thermohaline circulation on itself. Consequently the oceanic thermohaline circulation slows down and the opposite cycle starts. The oscillatory nature would not be possible without the active atmospheric participation in the cycle, because it provides the unstable interaction through heat flux, without it, the oceanic mode would be damped. This analysis suggests that the two principal modes of heat flux variability, corresponding to patterns similar to North Atlantic Oscillation (NAO) and Western Atlantic (WA), are part of the same decadal cycle and an indirect measure of the north-south movement of the storm tracks.

Hakkinen, Sirpa

1998-01-01

59

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

60

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

61

Observations of Interesting Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

Cataclysmic Variables (CVs) comprise one category of active mass transfer binaries containing a white dwarf accreting from an orbiting late main-sequence companion. Undoubtedly, non-magnetic CVs, intermediate polars and polars constitute a powerful probe of the structure of accretion onto white dwarfs and the theories of angular momentum loss, which elucidate the long-term evolution leading to the formation of these short period compact binaries. Combining photometric and spectroscopic data from space and ground telescopes can lead to novel discoveries. The SDSS survey provided a large dataset of spectra of different types of CVs. Followup photometry and spectroscopy is still underway to determine the unique properties of the objects identified as CVs. The Kepler program provided the first look at the variability of CVs over a continuous timescale of months. The extension of the program to the K2 fields allows further sets of CVs to be explored. We present some interesting results for several new CVs found in the SDSS and Kepler surveys which include their behavior during quiescence and outburst. These observations further demonstrate the complexities of CVs. This research was partially funded by CAS visiting scholar grant, NSF grant AST-1008734 and NASA grant HST-GO12870.

Dai, Zhibin; Szkody, Paula; Garnavich, Peter M.; Kennedy, Mark

2015-01-01

62

Decadal change of the surface water pCO2 in the North Pacific: A synthesis of 35 years of observations  

Microsoft Academic Search

Surface water pCO2 data observed over the 3 decades between 1970 and 2004 are analyzed for space and time (mean decadal) variability in thirty-two 10° × 10° box areas over the North Pacific Ocean north of 10°N. During this period, the pCO2 values at SST increased at a mean decadal rate of 12.0 ± 4.8 ?atm decade?1 in all but

Taro Takahashi; Stewart C. Sutherland; Richard A. Feely; Rik Wanninkhof

2006-01-01

63

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

64

Global Climate Signals: Decadal to Secular,and Equatorial SST Variability during the 20th Century  

NASA Astrophysics Data System (ADS)

Global ocean and individual ocean's basin (i.e., Pacific, Indian, and Atlantic) sea surface temperature (SST) and sea level pressure (SLP) are analyzed jointly, using MTM/SVD technique. The full spectrum of global climate signals for the 20th century is thus presented. Climate signals are evidenced with frequencies from secular to inter-annual variability. For the secular signal, conspicuous phase reversals for the three oceans, occur at times when global `climate shifts' have been already identified. This signal seems is consistent with the secular signal in the Atlantic Ocean linked to variability of the thermohaline circulation. Interestingly enough, inter-decadal (ID) signals dominate in the `Indian and Pacific Oceans pair', while quasi-decadal (QD) signals dominate in the `Pacific and Atlantic Oceans pair'. The origins of the ID signals are tied to climate variations in the tropical Indo-Pacific and associated with low-frequency variability of both the winter North Pacific Index (NPI) and the Sub-Arctic Frontal Zone (SAFZ). The QD signal has a strong equatorial signature in the Pacific Ocean, while it is closely tied with inter-hemispheric linkages in the Atlantic Ocean. Its evolution in the tropical Pacific requires coupled Rossby waves dynamics among others. Moreover, significant correlations are found between three well known equatorial SST indices (i.e., IO1 in Indian Ocean, NINO3 in Pacific Ocean, and ATL2 in Atlantic Ocean), and SST time-series obtained by summing-up only global and lead-frequency signals identified in this study: correlations of 0.74, 0.82, and 0.56 respectively. The observed tendency for the three oceans to get simultaneously warmer at the equator from the mid-80s onward has been reproduced by few global coupled models. SST increase might also reflect global and regional signatures of anthropogenic global greenhouse gases. Amplified equatorial SST gradient could have with global societal consequences. The above results should help mitigating societal impacts by using observed specific equatorial SSTs time-series, in a climate change context.

White, W. B.; Tourre, Y. M.

2006-12-01

65

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

66

IUE observations of cataclysmic variable  

NASA Technical Reports Server (NTRS)

Twenty two approved International Ultraviolet Explorer (IUE) programs were studied over a 14 year period. These programs are listed. The observations and subsequent analysis centered on cataclysmic variables (close binaries with a late main sequence star transferring material to a primary white dwarf via an accretion disk). The early studies highlighted the flux distribution of the accretion disk at outburst and quiescence, while later studies accomplished time-resolved observations throughout the orbital cycles, the study of the outflowing winds present at outburst, the study of the white dwarf in those systems with low accretion rate. There are 39 publications resulting from this work which are listed. These results include those for individual systems (Stepanian's star, Lanning 10, AM Her, MV Lyr, TV Col, VW Hyi, T Leo, IR Gem, TT Ari, Z Cam, BV Pup, IP Peg, PG1030+590, V1315 Aql, SW UMa, V426 Oph, WZ Sge, BY Cam, and U Gem) as well as review articles in journals and publications from reviews at meetings that summarize the impact of IUE on the study of accretion disks, white dwarfs, and hot spots resulting from stream impact as well as magnetic accretion columns.

Szkody, Paula

1993-01-01

67

Seasonal to multi-decadal variability of the width of the tropical belt  

NASA Astrophysics Data System (ADS)

An expansion of the tropical belt has been extensively reported in observations, reanalyses, and climate model simulations, but there is a great deal of uncertainty in estimates of the rate of widening as different diagnostics give a wide range of results. This study critically examines robust diagnostics for the width of the tropical belt to explore their seasonality, interannual variability, and multi-decadal trends. These diagnostics are motivated by an exploration of two simple models of the Hadley circulation and subtropical jets. The width based on the latitudes of the maximum tropospheric dry bulk static stability, measuring the difference in potential temperature between the tropopause and the surface, is found to be closely coupled to the width based on the subtropical jet cores on all timescales. In contrast, the tropical belt width and Northern Hemisphere edge latitudes based on the latitudes at which the vertically-averaged streamfunction vanishes, a measure of the Hadley circulation's poleward edges, lags those of the other diagnostics by approximately one month. The tropical belt width varies by up to ten degrees latitude among the diagnostics, with trends in the tropical belt width ranging from -0.5 to 2.0 degrees per decade over the 1979-2012 period. Nevertheless, in agreement with previous studies nearly all diagnostics exhibit a widening trend, although the streamfunction diagnostic exhibits a significantly stronger widening than either the jet or dry bulk stability diagnostics. Finally, GPS radio occultation observations are used to assess the ability of the reanalyses to reproduce the tropical belt width, finding that they better situate the latitudes of maximum bulk stability versus those of the subtropical jets.

Davis, Nicholas Alexander

68

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

69

Decadal climate variability in a coupled atmosphere-ocean climate model of moderate complexity  

Microsoft Academic Search

In this study we determined characteristic temporal modes of atmospheric variability at the decadal and interdecadal timescales. This was done on the basis of 1000 year long integrations of a global coupled atmosphere-ocean climate model of moderate complexity including the troposphere, stratosphere, and mesosphere. The applied model resolves explicitely the basic features of the large-scale long-term atmospheric and oceanic variables.

Dörthe Handorf; Vladimir K. Petoukhov; Klaus Dethloff; Alexey V. Eliseev; Antje Weisheimer; Igor I. Mokhov

1999-01-01

70

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

Microsoft Academic Search

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

Gregory J. McCabe; Julio L. Betancourt; Stephen T. Gray; Michael A. Palecki; Hugo G. Hidalgo

2008-01-01

71

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

72

A mechanism of decadal variability of the sea- ice volume in the Northern Hemisphere  

Microsoft Academic Search

Abstract Along-term simulation performed with a coarse-resolution, global, atmosphere-ocean- sea-ice model displays strong decadal variability of the ,sea-ice volume ,in the Northern Hemisphere,with a significant peak at about ,15-18 years. This model ,results from the coupling of ECBILT, a spectral T21, 3-level quasi-geostrophic atmospheric model, and CLIO, a sea-ice-ocean general circulation model. First, the mechanism underlying the variability of ice

H. Goosse

2001-01-01

73

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.

2013-11-01

74

North Atlantic decadal variability and the formation of tropical storms and hurricanes  

E-print Network

North Atlantic decadal variability and the formation of tropical storms and hurricanes Robert L of 23.5°N and of Atlantic major hurricanes increased between the 1970's/1980's and 1995 implying that tropical storm, and most likely major hurricane, activity may be reduced in the next several

75

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

76

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 timescales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions. We report an inter-annual GMT variability of about ±0.1° C originating solely from natural variability in the model ensemble. By decomposing the 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.

2014-02-01

77

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

78

Variable stars across the observational HR diagram  

Microsoft Academic Search

An overview of pulsating variable stars across the observational Hertzprung-Russel (HR) diagram is presented, together with a summary of their global properties. The HR diagram is presented with a third colour-coded dimension, visualizing the fraction of variable, the amplitude of variability or the period of variability. The distribution of variable stars in the other observational diagrams, such as the Period-Amplitude

Laurent Eyer; Nami Mowlavi

2008-01-01

79

Top-of-atmosphere radiative contribution to unforced decadal global temperature variability in climate models  

NASA Astrophysics Data System (ADS)

recent work has focused on unforced global mean surface air temperature (T) variability associated with the efficiency of heat transport into the deep ocean. Here the relationship between unforced variability in T and the Earth's top-of-atmosphere (TOA) energy balance is explored in preindustrial control runs of the Coupled Model Intercomparison Project Phase 5 multimodel ensemble. It is found that large decadal scale variations in T tend to be significantly enhanced by the net energy flux at the TOA. This indicates that unforced decadal variability in T is not only caused by a redistribution of heat within the climate system but can also be associated with unforced changes in the total amount of heat in the climate system. It is found that the net TOA radiation imbalances result mostly from changes in albedo associated with the Interdecadal Pacific Oscillation that temporarily counteracts the climate system's outgoing longwave (i.e., Stefan-Boltzmann) response to T change.

Brown, Patrick T.; Li, Wenhong; Li, Laifang; Ming, Yi

2014-07-01

80

Interannual variability and decadal trends in carbon exchange at the Harvard Forest EMS site  

NASA Astrophysics Data System (ADS)

The Harvard Forest EMS site in a mixed deciduous forest in central Massachusetts has been measuring carbon, water, and energy fluxes since 1992. Above-ground biomass, litter input, and tree mortality have been measured since 1995. The forest at this site has consistently been a net sink for carbon over the measurement period with annual uptake rates of 1.0 to > 5.Mg-C ha-1y-1. Carbon uptake rates show a significant increasing trend, despite the forest being 75- 110 years old. There were parallel increases in midsummer photosynthetic capacity at high light level (21.5-31.5 mole m-2s-1), woody biomass (101-115 Mg-C ha-1from 1993-2005, mostly due to growth of one species, red oak), and peak leaf area index (4.5-5.5 m2m-2from 1998-2005). These long-term trends were interrupted in 1998 by sharp declines in photosynthetic capacity, net ecosystem exchange (NEE) of CO2, and other parameters, followed by recovery over the next 3 years. The dip in 1998 could not be directly attributed to any one cause, though leaf expansion in the spring appeared to stall during a period of unfavorable weather, and did not recover later in the summer. Annual increment of above-ground woody biomass has followed the trend in NEE with 1 year offset implying that spring wood growth is supplied by carbon fixed in the previous year. An empirical model of carbon fluxes based on mean temperature and light response functions and observed phenology represents the hourly to seasonal patterns in carbon fluxes but can not adequately account for interannual variability or the long-term trends in carbon uptake. A structured ecosystem model (ED2) that represented both canopy-scale physiology and long-term dynamics of tree growth, mortality, and species composition was able to simulate interannual variability over decadal intervals better than the empirical model based on mean responses could. These results imply that direct effects of climate variability only partially account for interannual variability in NEE. Other key factors appear to be indirect effects of climate forcing on leaf biomass and canopy performance, and long term successional trends in species composition and structure. Detection and attribution of the factors that control long-term trends and interannual variability requires continued long-term data records.

Munger, J.. W.; Wofsy, S. C.; Moorcroft, P. R.; Medvigy, D.

2009-04-01

81

Observations of decadal time scale salinity changes in the subtropical thermocline of the North Pacific Ocean  

E-print Network

Observations of decadal time scale salinity changes in the subtropical thermocline of the North Mixed layer Hydrological cycle a b s t r a c t Data from Argo floats indicate that significant salinity decades, including observations obtained as part of the WOCE hydrographic program. Such a salinity

Riser, Stephen C.

82

Assessing decadal-scale variability in surface albedo feedback across the CMIP5 simulations  

NASA Astrophysics Data System (ADS)

Surface albedo feedback (SAF) is one of the strongest positive feedback mechanisms operating in current climate. Previous studies quantify global mean SAF from equilibrium or century-scale climate simulations, but few studies have examined decadal-scale variability in SAF. Here, we apply historical and future climate simulations from the Coupled Model Intercomparison Project version 5 (CMIP5) combined with radiative kernels to quantify temporal variability in SAF. Applying a sorting procedure, we show that variance in SAF decreases during periods of larger global mean temperature change. We examine this relationship for 40 year time periods to determine a minimum temperature change threshold for which the calculated feedback becomes representative of the model's long time scale feedback. Interestingly, initial results using the Community Earth System Model (CESM) indicate that the standard deviation of SAF decreases to about 0.1 (W/m2)/K with a global mean temperature change of about 0.5 K, irrespective of period length and climate state between 1850 and 2300, and continues decreasing rather monotonically with increasing temperature change. Consequently, we determine that periods with global mean temperature change of about 0.5 K or more are needed to eliminate noise in SAF analysis. This also suggests that observations of SAF over such periods may be representative of the actual longer term SAF. Surprisingly, SAF in the CESM simulations remains relatively constant throughout the 21st century under the extreme RCP 8.5 scenario, even toward the end of runs when little seasonal snow and sea-ice remain. We apply simulations extended to 2300 to determine when the SAF strength begins to diminish.

Schneider, A. M.; Flanner, M.

2013-12-01

83

Variability in surface inversion characteristics over India in winter during the recent decades  

NASA Astrophysics Data System (ADS)

The variation in surface inversions during the recent decades over 20 stations in the Indian region is documented. Radiosonde data at 00UTC for the period 1971-2000 has been used to compute the inversion frequency. The depth and strength of the inversions as well as the wind speed through the inversion layer have also been computed. The frequency of inversions at stations north of 20°N is ~20-60% higher than stations located south of 20°N. Moreover, all the stations show frequencies increasing from the 1st to the 3rd decade. Most of the stations show decreasing depth and increasing strength significant at 99% level. With the exception of Nagpur and Hyderabad which show high frequency of very deep inversions increasing from the 1st to the 3rd decade, the decadal variations of inversion depth at most of the other stations show that shallow and moderate inversions occur more frequently than deep or very deep inversions. Decadal variations in inversion strength show weak inversion frequencies decreasing from the 1st to the 3rd decade while moderate/strong inversions occur more frequently at most stations. Frequencies of very strong inversions are low or are absent. Wind speeds are either weak or moderate with frequencies increasing from the 1st to the 3rd decade. Low frequency of strong winds and negligible frequency of very strong winds are observed.

Iyer, U. S.; Nagar, S. G.

2011-02-01

84

Linkage between the Pacific Decadal Oscillation and the low frequency variability of the Pacific Subtropical Cell  

NASA Astrophysics Data System (ADS)

decadal variability of Pacific Subtropical Cell (STC) and its linkages with the Pacific Decadal Oscillation (PDO) are investigated in the present study based on a Simple Ocean Data Assimilation (SODA 2.2.4). It is found that, on decadal time scales, the western boundary and interior pycnocline transports are anticorrelated and the variation of the interior component is more significant, which is consistent with previous studies. The decadal variability of STC in the Northern Hemisphere is found to be strongly associated with PDO. Associated with a positive (negative) phase of PDO, the relaxation (acceleration) of the northeast trades slows down (spins up) the STC within a few years through baroclinic adjustment in conjunction with the subduction of the cold (warm) mixed-layer anomalies in the extratropics. The cold (warm) water is then injected into the thermocline and advected further southwestward to the tropics along the isopycnal surfaces, leading to the slowdown (spin-up) of STC due to zonal pressure gradient change at low latitude. Along with the STC weakening (strengthening), a significant warming (cold) anomaly appears in the tropics and it is advected to the midlatitude by the Kuroshio and North Pacific currents, thus feeding back to the atmosphere over the North Pacific. In contrast to the Northern Hemisphere, it is found the STC in the south only passively responds to the PDO. The mechanism found here highlights the role of the STC advection of extratropical anomalies to the tropics and horizontal gyre advection of the tropical anomalies to the extratropics in decadal variability of the STC and PDO.

Hong, Lingya; Zhang, Liping; Chen, Zhaohui; Wu, Lixin

2014-06-01

85

IUE observations of cataclysmic variables  

NASA Technical Reports Server (NTRS)

The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rats are considered.

Szkody, P.

1982-01-01

86

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

87

Vegetation dynamics and climate variability in West Africa at seasonal- decadal Scales  

NASA Astrophysics Data System (ADS)

New evidence emerged from satellite data analyses and modeling study indicate that patterns of vegetation spatial distribution and vegetation structure are important in the soil-vegetation-atmosphere system (SVAS) and including a fully coupled dynamic vegetation/climate process is of imminent important in increasing our understanding and predictive capabilities of the SVAS. We apply the Simplified Simple Biosphere Model version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID) to investigate the interactions between vegetation dynamics and climate variability for West Africa. The TRIFFID is a dynamic vegetation model, in which the relevant vegetation spatial distribution and structure are modeled based on the surface carbon balance. SSiB4 is a biophysical model based on surface water and energy balance and produces carbon assimilation rate for TRIFFID. The offline SSiB2, which uses specified vegetation spatial distribution and vegetation structure with no inter-annual and decadal variability, and SSiB4/TRIFFID are integrated using the observed precipitation and reanalysis-based meteorological forcing from 1948 to 2006 with 1 degree horizontal resolution over West Africa. West Africa is a diverse climatic and ecosystem region and suffered the most severe and longest drought in the world during the Twentieth Century since the later 1960s. The simulation results indicate that the SSiB4/TRIFFID model was able to produce reasonable vegetation spatial distributions, generally consistent with the products derived from satellites and with the Sahel drought in the 1970s and the 1980s and the partial recovery in the 1990s and the 2000s. The SSiB4/TRIFFID and SSIB2 results show quite different spatial patterns and vegetation structure, which lead to differences in surface net radiation, latent and sensible heat flux partitioning, soil moisture and runoff distribution, and carbon cycles at seasonal and inter-decadal time scales. To investigate the mechanism of dynamic vegetation, water, carbon, and radiation interactions, further analyses are conducted to find relationships between simulated vegetation conditions and environmental conditions. It is found that the vegetation characteristics simulated by SSiB4/TRIFFID responds primarily to five factors: air temperature, atmospheric carbon concentration, soil moisture, carbon assimilation rate, and absorbed photosynthetically active radiation. For instance, in temporal analysis, broad-leaf trees and C4 plants generally negatively correlates with canopy temperature, and positively correlates with soil moisture. In spatial analysis, vegetation positively correlates with soil moisture but negatively correlates with short wave down; meanwhile, broad-leaf tress/C4-plants have positive correlation with long wave down and positive/negative correlation with canopy temperature. Results also indicate that the elevated atmospheric carbon concentration plays an important role in vegetation dynamics at inter-annual and decadal scales.

Xue, Y.; Song, G.; Cox, P.

2011-12-01

88

Rule-based System Architecting of Earth Observing Systems: The Earth Science Decadal Survey  

E-print Network

Rule-based System Architecting of Earth Observing Systems: The Earth Science Decadal Survey Daniel satellite systems, and applies it to the Earth Science Decadal Survey. The architecting problem In 2004, the NASA Office of Earth Science, the National Oceanic and Atmospheric Administration (NOAA

de Weck, Olivier L.

89

Variability of Ocean Heat Uptake: Reconciling Observations and Models  

SciTech Connect

This study examines the temporal variability of ocean heat uptake in observations and in climate models. Previous work suggests that coupled Atmosphere-Ocean General Circulation Models (A-OGCMs) may have underestimated the observed natural variability of ocean heat content, particularly on decadal and longer timescales. To address this issue, we rely on observed estimates of heat content from the 2004 World Ocean Atlas (WOA-2004) compiled by Levitus et al. (2005). Given information about the distribution of observations in WOA-2004, we evaluate the effects of sparse observational coverage and the infilling that Levitus et al. use to produce the spatially-complete temperature fields required to compute heat content variations. We first show that in ocean basins with limited observational coverage, there are important differences between ocean temperature variability estimated from observed and infilled portions of the basin. We then employ data from control simulations performed with eight different A-OGCMs as a test-bed for studying the effects of sparse, space- and time-varying observational coverage. Subsampling model data with actual observational coverage has a large impact on the inferred temperature variability in the top 300 and 3000 meters of the ocean. This arises from changes in both sampling depth and in the geographical areas sampled. Our results illustrate that subsampling model data at the locations of available observations increases the variability, reducing the discrepancy between models and observations.

AchutaRao, K M; Santer, B D; Gleckler, P J; Taylor, K; Pierce, D; Barnett, T; Wigley, T L

2005-05-05

90

Changes of Pacific decadal variability in the twentieth century driven by internal variability, greenhouse gases, and aerosols  

NASA Astrophysics Data System (ADS)

paper explores the contributions of internal variability, greenhouse gases (GHGs), and anthropogenic aerosols (AAs) in driving the magnitude and evolution of Pacific Decadal Variability (PDV) during the twentieth century by analyzing 129 Coupled Model Intercomparison Project Phase 5 model realizations. Evidence shows that PDV phase transition is dominated by internal variability, but it is also significantly affected by external forcing agents such as GHGs and aerosols. The combined effects of GHGs and AAs favor the positive phase of PDV with stronger ocean warming in the tropics than the extratropical Pacific. The GHG forcing induces the increased surface downward longwave radiation, especially over the tropical Pacific, and results in stronger warming in that area. The AA forcing results in a stronger cooling in the North Pacific region, due to the reduced surface downward shortwave radiation via cloud-aerosol interaction: this offsets the substantial warming caused by GHG forcing.

Dong, Lu; Zhou, Tianjun; Chen, Xiaolong

2014-12-01

91

An approach for improving short-term prediction of summer rainfall over North China by decomposing interannual and decadal variability  

NASA Astrophysics Data System (ADS)

A statistical downscaling approach was developed to improve seasonal-to-interannual prediction of summer rainfall over North China by considering the effect of decadal variability based on observational datasets and dynamical model outputs. Both predictands and predictors were first decomposed into interannual and decadal components. Two predictive equations were then built separately for the two distinct timescales by using multivariate linear regressions based on independent sample validation. For the interannual timescale, 850-hPa meridional wind and 500-hPa geopotential heights from multiple dynamical models' hindcasts and SSTs from observational datasets were used to construct predictors. For the decadal timescale, two well-known basin-scale SST decadal oscillation (the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation) indices were used as predictors. Then, the downscaled predictands were combined to represent the predicted/hindcasted total rainfall. The prediction was compared with the models' raw hindcasts and those from a similar approach but without timescale decomposition. In comparison to hindcasts from individual models or their multi-model ensemble mean, the skill of the present scheme was found to be significantly higher, with anomaly correlation coefficients increasing from nearly neutral to over 0.4 and with RMSE decreasing by up to 0.6 mm d-1. The improvements were also seen in the station-based temporal correlation of the predictions with observed rainfall, with the coefficients ranging from -0.1 to 0.87, obviously higher than the models' raw hindcasted rainfall results. Thus, the present approach exhibits a great advantage and may be appropriate for use in operational predictions.

Han, Leqiong; Li, Shuanglin; Liu, Na

2014-03-01

92

Decadal response of the Kuroshio Extension jet to Rossby waves: Observation and thin-jet theory  

NASA Astrophysics Data System (ADS)

This study examines interannual to decadal variability of the Kuroshio Extension (KE) jet using satellite altimeter observations from 1993 to 2010. The leading Empirical Orthogonal Function (EOF) mode of sea level variability in the KE region represents the meridional shift of the KE jet, followed by its strength changes with a few month lag. This result indicates that the latitude changes of the KE jet are a key process in the decadal variability in the KE region. The meridional shift of the KE jet lags atmospheric fluctuations over the eastern North Pacific by about three years. Broad sea level anomalies (SLAs) emerge in the eastern North Pacific 3-4 years before the upstream KE jet shift, and propagate westward along the KE jet axis. It is worth emphasizing that the meridional scale of the SLAs gradually narrows, and their amplitude increases in the course of the propagation. This westward propagation of SLAs with a phase speed of about 5 cm/s is attributed to the westward propagation of the meridional shift of the jet, consistent with the thin-jet theory, whose importance has been suggested by previous numerical studies. In addition, it is revealed that the changes of the meridional scale and amplitude of the SLAs during the propagation are also consistent with the changes of the climatological KE jet structure. Interestingly, the westward propagating signals tend to conserve their quasi-geostrophic potential vorticity anomaly, which may explain the characteristic changes of SLAs during the propagation. After the westward propagating signals of positive (negative) SLAs reach at the east coast of Japan, the upstream KE jet strengthens (weakens) associated with the strength changes of the northern and southern recirculation gyres. This strength change of the KE jet propagates eastward with a phase speed of about 6 cm/s, suggesting an importance of advection of potential vorticity by the current in response to the incoming westward propagating signals along the KE jet axis.Lag regressions of sea level anomalies of the satellite observation onto the KE jet latitude, where negative lag means that the KE jet latitude lags sea level anomalies

Sasaki, Y. N.; Minobe, S.; Schneider, N.

2012-12-01

93

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

94

Decadal Variability of Sea Ice Motion in the Weddell Sea for the Period of 1979 to 2006  

NASA Astrophysics Data System (ADS)

The knowledge and understanding of sea ice drift variability is essential for an assessment of, e.g., varying ice production rates, deformation processes, ice export and also stratification changes in the ocean. The goal of this study is the determination of the decadal variability of sea ice motion in the Weddell Sea and its relation to atmospheric forcing. Yearly and monthly mean drift vector fields for every 10-year period are computed from observations from 1979-2006 and from simulations with the Finite Element Sea ice-Ocean Model (FESOM) for 1948-2008. Ice motion patterns are analysed with respect to the long-term mean in order to identify decadal changes in the typical drift patterns. Observed motion vector fields for Antarctic sea ice are provided by the National Snow and Ice Data Center (NSIDC). The vector fields are created from a combination of satellite data from the 37 GHz and 85 GHz channels of the Scanning Multichannel Microwave Radiometer (SMMR, 1978-1987) and the Special Sensor Microwave/Imager (SSM/I, 1987-2006) as well as from the Advanced Very High Resolution Radiometer (AVHRR, 1981-2000). The gridded data sets have a spatial resolution of 25 km and are available for a temporal resolution of one day. Data from the NCEP/NCAR reanalysis have been used to force the model simulations and are also used to identify the driving forces for ice drift variability.

Schwegmann, S.; Haas, C.; Timmermann, R.; Gerdes, R.; Lemke, P.

2009-04-01

95

Inter-annual variability in atmospheric nitrous oxide over the past two decades  

NASA Astrophysics Data System (ADS)

Nitrous oxide (N2O) concentrations have been steadily increasing in the atmosphere over the past few decades at a rate of approximately 0.3% per year. This trend is of major concern as N2O is both a long-lived greenhouse gas and an Ozone Depleting Substance (ODS). This trend is largely due to the increased input of reactive nitrogen (Nr) to the environment, primarily in N-fertilizers. Before the widespread usage of N-fertilizers, the naturally occurring N2O source was approximately balanced by the atmospheric sink, that is, photochemical destruction in the stratosphere. Super-imposed on the atmospheric trend, is significant inter-annual variability (IAV), which is thought to be mainly determined by inter-annual variations in stratosphere-troposphere exchange. Using global N2O records since the late 1990's (when more than 50 stations are available worldwide), we found significant IAV in the N2O atmospheric growth-rate with a positive anomaly from 1998 to 1999 in the northern hemisphere and a negative anomaly in 2003 in Europe, North America and Asia. To test the influence of the inter-annual variations in emissions versus stratosphere-troposphere exchange on the observed growth-rate, we carried out simulations using the global circulation model, LMDZ4, which was driven using ECMWF reanalysis data and was coupled to emissions estimates from the global eco-system model, Orchidee O-CN and the ocean biogeochemistry model, PISCES, which were also driven by climate data.

Thompson, R. L.; Bousquet, P.; Chevallier, F.; Zaehle, S.; Bopp, L.; Dlugokencky, E.

2012-04-01

96

Footprints of decadal climate variability in ozone at Mauna Loa Observatory  

NASA Astrophysics Data System (ADS)

Ozone is a greenhouse gas that plays a central role in tropospheric chemistry. A 40-year ozone record at Mauna Loa Observatory (MLO, 3.4 km altitude) reveals strikingly different seasonality of ozone trends from those observed at northern mid-latitudes: increasing in fall at MLO but in spring at northern midlatitude remote sites. These changes in seasonal ozone are well reproduced by a chemistry-climate model. We find that the seasonal ozone changes at MLO cannot be accounted for by trends in ozone precursor emissions alone, but reflect decadal shifts in circulation regimes. Specifically, airflow from Eurasia towards Hawaii weakened in spring but strengthened in fall. In spring, the long-term tropical expansion, combined with an early-2000s shift in the Pacific Decadal Oscillation (PDO) towards fewer El Niño events, offsets ozone increases that otherwise would have occurred due to rising Asian emissions. In fall, transport of midlatitude pollution events to MLO has occurred more frequently since the mid-1990s, corresponding with a period of predominantly positive Pacific-North American (PNA) pattern. Our findings highlight the potential for atmospheric ozone measurements at remote sites to document interannual to decadal changes in atmospheric circulation. Decadal shifts in circulation regimes must be considered when attributing ozone changes observed at remote sites to trends in precursor emissions.

Lin, M.; Horowitz, L. W.; Oltmans, S. J.; Fiore, A. M.; Fan, S.

2013-12-01

97

Ocean surface temperature variability: large model-data differences at decadal and longer periods.  

PubMed

The variability of sea surface temperatures (SSTs) at multidecadal and longer timescales is poorly constrained, primarily because instrumental records are short and proxy records are noisy. Through applying a new noise filtering technique to a global network of late Holocene SST proxies, we estimate SST variability between annual and millennial timescales. Filtered estimates of SST variability obtained from coral, foraminifer, and alkenone records are shown to be consistent with one another and with instrumental records in the frequency bands at which they overlap. General circulation models, however, simulate SST variability that is systematically smaller than instrumental and proxy-based estimates. Discrepancies in variability are largest at low latitudes and increase with timescale, reaching two orders of magnitude for tropical variability at millennial timescales. This result implies major deficiencies in observational estimates or model simulations, or both, and has implications for the attribution of past variations and prediction of future change. PMID:25385623

Laepple, Thomas; Huybers, Peter

2014-11-25

98

Interannual to decadal oxygen variability in the mid-depth water masses of the eastern North Atlantic  

NASA Astrophysics Data System (ADS)

The detection of multi-decadal trends in the oceanic oxygen content and its possible attribution to global warming is protracted by the presence of a substantial amount of interannual to decadal variability, which hitherto is poorly known and characterized. Here we address this gap by studying interannual to decadal changes of the oxygen concentration in the Subpolar Mode Water (SPMW), the Intermediate Water (IW) and the Mediterranean Outflow Water (MOW) in the eastern North Atlantic. We use data from a hydrographic section located in the eastern North Atlantic at about 48°N repeated 12 times over a period of 19 years from 1993 through 2011, with a nearly annual resolution up to 2005. Despite a substantial amount of year-to-year variability, we observe a long-term decrease in the oxygen concentration of all three water masses, with the largest changes occurring from 1993 to 2002. During that time period, the trends were mainly caused by a contraction of the subpolar gyre associated with a northwestward shift of the Subpolar Front (SPF) in the eastern North Atlantic. This caused SPMW to be ventilated at lighter densities and its original density range being invaded by subtropical waters with substantially lower oxygen concentrations. The contraction of the subpolar gyre reduced also the penetration of IW of subpolar origin into the region in favor of an increased northward transport of IW of subtropical origin, which is also lower in oxygen. The long-term oxygen changes in the MOW were mainly affected by the interplay between circulation and solubility changes. Besides the long-term signals, mesoscale variability leaves a substantial imprint as well, affecting the water column over at least the upper 1000 m and laterally by more than 400 km. Mesoscale eddies induced changes in the oxygen concentration of a magnitude that can substantially alias analyses of long-term changes based on repeat hydrographic data that are being collected at intervals of typically 10 years.

Stendardo, Ilaria; Kieke, Dagmar; Rhein, Monika; Gruber, Nicolas; Steinfeldt, Reiner

2015-01-01

99

Decadal variability in an OGCM Southern Ocean: Intrinsic modes, forced modes and metastable states  

NASA Astrophysics Data System (ADS)

An ocean general circulation model (OGCM) is used to identify a Southern Ocean southeast Pacific intrinsic mode of low frequency variability. Using CORE data a comprehensive suite of experiments were carried out to elucidate excitation and amplification responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. The Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond to both SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency winds that act to amplify thermocline anomalies propagating downstream from the Pacific. Non-stationary cluster analysis was used to identify the system's dynamical regimes and characterise meta-stability, persistence and transitions between the respective states. This analysis reveals significant trends, indicating fundamental changes to the meta-stability of the ocean dynamics in response to changes in atmospheric forcing. Intrinsic variability in sea-ice concentration was found to be coupled to thermocline processes. Sea-ice variability localised in the Atlantic was most closely associated with high frequency weather forcing. The SAM was associated with a circumpolar sea-ice response whereas ENSO was found to be a major driver of sea-ice variability only in the Pacific. This simulation study identifies plausible mechanisms that determine the predictability of the Southern Ocean climate on multi-decadal timescales.

O'Kane, Terence J.; Matear, Richard J.; Chamberlain, Matthew A.; Risbey, James S.; Sloyan, Bernadette M.; Horenko, Illia

2013-09-01

100

Decadal Variability in an OGCM Southern Ocean: intrinsic modes, forced modes and metastable states  

NASA Astrophysics Data System (ADS)

An Ocean General Circulation Model (OGCM) is used to identify a Southern Ocean southeast Pacific intrinsic mode of low frequency variability. Using CORE data a comprehensive suite of experiments were carried out to elucidate excitation and amplification responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. The Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond to both SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency winds that act to amplify thermocline anomalies propagating downstream from the Pacific. Non-stationary cluster analysis was used to identify the system's dynamical regimes and characterise meta-stability, persistence and transitions between the respective states. This analysis reveals significant trends, indicating fundamental changes to the meta-stability of the ocean dynamics in response to changes in atmospheric forcing. Intrinsic variability in sea-ice concentration was found to be coupled to thermocline processes. Sea-ice variability localised in the Atlantic was most closely associated with high frequency weather forcing. The SAM was associated with a circumpolar sea-ice response whereas ENSO was found to be a major driver of sea-ice variability only in the Pacific. This simulation study identifies plausible mechanisms that determine the predictability of the Southern Ocean climate on multi-decadal timescales.

O'Kane, Terence; Matear, Richard; Chamberlain, Matthew; Risbey, James; Horenko, Illia; Sloyan, Bernadette

2014-05-01

101

Land surface phenological response to decadal climate variability across Australia using satellite remote sensing  

NASA Astrophysics Data System (ADS)

Land surface phenological cycles of vegetation greening and browning are influenced by variability in climatic forcing. Quantitative information on phenological cycles and their variability is important for agricultural applications, wildfire fuel accumulation, land management, land surface modeling, and climate change studies. Most phenology studies have focused on temperature-driven Northern Hemisphere systems, where phenology shows annually reoccurring patterns. Yet, precipitation-driven non-annual phenology of arid and semi-arid systems (i.e. drylands) received much less attention, despite the fact that they cover more than 30% of the global land surface. Here we focused on Australia, the driest inhabited continent with one of the most variable rainfall climates in the world and vast areas of dryland systems. Detailed and internally consistent studies investigating phenological cycles and their response to climate variability across the entire continent designed specifically for Australian dryland conditions are missing. To fill this knowledge gap and to advance phenological research, we used existing methods more effectively to study geographic and climate-driven variability in phenology over Australia. We linked derived phenological metrics with rainfall and the Southern Oscillation Index (SOI). We based our analysis on Enhanced Vegetation Index (EVI) data from the MODerate Resolution Imaging Spectroradiometer (MODIS) from 2000 to 2013, which included extreme drought and wet years. We conducted a continent-wide investigation of the link between phenology and climate variability and a more detailed investigation over the Murray-Darling Basin (MDB), the primary agricultural area and largest river catchment of Australia. Results showed high inter- and intra-annual variability in phenological cycles. Phenological cycle peaks occurred not only during the austral summer but at any time of the year, and their timing varied by more than a month in the interior of the continent. The phenological cycle peak magnitude and integrated greenness were most significantly correlated with monthly SOI within the preceding 12 months. Correlation patterns occurred primarily over north-eastern Australia and within the MDB predominantly over natural land cover and particularly in floodplain and wetland areas. Integrated greenness of the phenological cycles (surrogate of productivity) showed positive anomalies of more than two standard deviations over most of eastern Australia in 2009-2010, which coincided with the transition between the El Niño induced decadal droughts to flooding caused by La Niña. The quantified spatial-temporal variability in phenology across Australia in response to climate variability presented here provides important information for land management and climate change studies and applications.

Broich, M.; Huete, A.; Tulbure, M. G.; Ma, X.; Xin, Q.; Paget, M.; Restrepo-Coupe, N.; Davies, K.; Devadas, R.; Held, A.

2014-05-01

102

Can caves capture decadal climate variability? Evaluating uncertainty in cave speleothem ?18O records using a simple process model  

NASA Astrophysics Data System (ADS)

Speleothem oxygen isotope records in arid regions are typically interpreted as indicators of the total precipitation amount and/or its seasonal balance. Such studies rarely address the potential influence of groundwater mixing processes on oxygen isotope variability of cave dripwater. Here we develop a process model to explore the influence of subsurface processes on dripwater ?18O on sub-decadal to multi-millennial timescales. This model of oxygen isotopes in dripwater and cave calcite is compared to water and stalagmite measurements from Cave of the Bells, Arizona. We simulate moisture flux from surface to cave as a two-layer “leaky-bucket” model. We further develop the model to include a variety of flow paths and times, to represent the cave environment more accurately. We use modern temperature, precipitation amount, and precipitation ?18O data as inputs to the dripwater process model. Model results indicate that cave dripwater ?18O values are most comparable to winter precipitation, which is consistent with observations from within the cave. We show that seasonality and duration of the regional summer monsoon affect how much summer precipitation reaches the cave. We employ a Monte Carlo method to specify statistically realistic ranges for input climate variables and produce time series and variance spectra of cave drips. The spectra of our synthetic ?18O series exhibit a high degree of variance at decadal to multidecadal frequencies, despite being driven by synthetic data that includes only a seasonal cycle. This suggests that some background level of variance in speleothem ?18O records could be due to nonclimatic processes, such as subsurface water storage and mixing. On longer timescales, however, climate variability can overwhelm in situ cave processes as a control on speleothem oxygen isotope variability. Quantifying the degree of variance imparted by nonclimatic processes could be achievable with careful monitoring of the modern system. Interpreting climatic vs. nonclimatic controls on speleothem ?18O variance could also be achieved by replicating records from different caves.

Truebe, S. A.; Ault, T. R.; Cole, J. E.

2010-12-01

103

A Robust Decision-Making Technique for Water Management under Decadal Scale Climate Variability  

NASA Astrophysics Data System (ADS)

Robust decision making, a flexible and dynamic approach to managing water resources in light of deep uncertainties associated with climate variability at inter-annual to decadal time scales, is an analytical framework that detects when a system is in or approaching a vulnerable state. It provides decision makers the opportunity to implement strategies that both address the vulnerabilities and perform well over a wide range of plausible future scenarios. A strategy that performs acceptably over a wide range of possible future states is not likely to be optimal with respect to the actual future state. The degree of success--the ability to avoid vulnerable states and operate efficiently--thus depends on the skill in projecting future states and the ability to select the most efficient strategies to address vulnerabilities. This research develops a robust decision making framework that incorporates new methods of decadal scale projections with selection of efficient strategies. Previous approaches to water resources planning under inter-annual climate variability combining skillful seasonal flow forecasts with climatology for subsequent years are not skillful for medium term (i.e. decadal scale) projections as decision makers are not able to plan adequately to avoid vulnerabilities. We address this need by integrating skillful decadal scale streamflow projections into the robust decision making framework and making the probability distribution of this projection available to the decision making logic. The range of possible future hydrologic scenarios can be defined using a variety of nonparametric methods. Once defined, an ensemble projection of decadal flow scenarios are generated from a wavelet-based spectral K-nearest-neighbor resampling approach using historical and paleo-reconstructed data. This method has been shown to generate skillful medium term projections with a rich variety of natural variability. The current state of the system in combination with the probability distribution of the projected flow ensembles enables the selection of appropriate decision options. This process is repeated for each year of the planning horizon--resulting in system outcomes that can be evaluated on their performance and resiliency. The research utilizes the RiverSMART suite of software modeling and analysis tools developed under the Bureau of Reclamation's WaterSMART initiative and built around the RiverWare modeling environment. A case study is developed for the Gunnison and Upper Colorado River Basins. The ability to mitigate vulnerability using the framework is gauged by system performance indicators that measure the ability of the system to meet various water demands (i.e. agriculture, environmental flows, hydropower etc.). Options and strategies for addressing vulnerabilities include measures such as conservation, reallocation and adjustments to operational policy. In addition to being able to mitigate vulnerabilities, options and strategies are evaluated based on benefits, costs and reliability. Flow ensembles are also simulated to incorporate mean and variance from climate change projections for the planning horizon and the above robust decision-making framework is applied to evaluate its performance under changing climate.

Callihan, L.; Zagona, E. A.; Rajagopalan, B.

2013-12-01

104

Rebuilding Kamchatka Volcanoes: A Decade Of Ground, Air And Spaceborne Observations Of Lava Dome Growth  

NASA Astrophysics Data System (ADS)

From the advent of NASA’s Earth Observing System (EOS) and the launch of the first flagship satellite (Terra) in December 1999, the Kamchatka Peninsula of Russia has been observed frequently. Data from sensors such as MODIS and ASTER have been particularly valuable in capturing processes associated with the large eruptions at Bezymianny (2000, 2005, 2006 and 2007) and Shiveluch (2001, 2004, 2005 and 2007). The high spatial resolution of the ASTER thermal infrared (TIR) sensor (90m/pixel) in conjunction with the relatively rapid revisit time (1-5 days) at the higher latitudes of Kamchatka has been effective in capturing detailed changes in the lava domes, such as following the December 2006 Bezymianny eruption. The temperature distribution of the domes detected from space and airborne TIR data has been used to infer the emplacement of new lava lobes, detect endogenous dome growth and the location of zones of weakness as well as interpreting dome collapse events. The emitted radiance has also been used effectively to model composition, texture and degassing from their surfaces. The success of these satellite-based observations gave rise to a funded NASA program designed to both increase the number of ASTER observations following an eruption and validate the satellite data. The ASTER Urgent Request Protocol has been in place since 2004 and has increased the observational frequency in Kamchatka by 30%. Field campaigns to Bezymianny and Shiveluch were funded by this program and carried out in 2004, 2005 and 2007 in conjunction with the Russian Institute of Volcanology and Seismology (IVS) and the Alaska Volcano Observatory (AVO). They took place following large eruptions and allowed ground- and helicopter-based visible and TIR data to be acquired. Definitive changes were noted on the lava domes, which were linked to the response of the magma system. Although the growth of these two domes has been nearly continuous over the past several decades, each is emplaced in different ways. Bezymianny grows by mostly successively-emplaced, lower aspect lava lobes, whereas Shiveluch tends to grow thicker lobes that are commonly destroyed by explosive events and/or collapse events. The long term synoptic record of thermal infrared observations in Kamchatka helped to reveal this variability, which is linked to the composition, topography and resupply rate at each volcano.

Carter, A. J.; Ramsey, M. S.

2010-12-01

105

Evaluation of a Multi-Decadal Simulation of Stratospheric Ozone by Comparison with Total Ozone Mapping Spectrometer (TOMS) Observations  

NASA Technical Reports Server (NTRS)

One key application of atmospheric chemistry and transport models is prediction of the response of ozone and other constituents to various natural and anthropogenic perturbations. These include changes in composition, such as the previous rise and recent decline in emission of man-made chlorofluorcarbons, changes in aerosol loading due to volcanic eruption, and changes in solar forcing. Comparisons of hindcast model results for the past few decades with observations are a key element of model evaluation and provide a sense of the reliability of model predictions. The 25 year data set from Total Ozone Mapping Spectrometers is a cornerstone of such model evaluation. Here we report evaluation of three-dimensional multi-decadal simulation of stratospheric composition. Meteorological fields for this off-line calculation are taken from a 50 year simulation of a general circulation model. Model fields are compared with observations from TOMS and also with observations from the Stratospheric Aerosol and Gas Experiment (SAGE), Microwave Limb Sounder (MLS), Cryogenic Limb Array Etalon Spectrometer (CLAES), and the Halogen Occultation Experiment (HALOE). This overall evaluation will emphasize the spatial, seasonal, and interannual variability of the simulation compared with observed atmospheric variability.

Douglass, Anne R.; Stolarski, Richard S.; Steenrod, Steven; Pawson, Steven

2003-01-01

106

Evaluation of a Multi-Decadal Siimulation of Stratospheric Ozone by Comparison with Total Ozone Mapping Spectrometer (TOMS) Observations  

NASA Astrophysics Data System (ADS)

One key application of atmospheric chemistry and transport models is prediction of the response of ozone and other constituents to various natural and anthropogenic perturbations. These include changes in composition, such as the previous rise and recent decline in emission of man-made chlorofluorcarbons, changes in aerosol loading due to volcanic eruptions, and changes in solar forcing. Comparisons of hindcast model results for the past few decades with observations are a key element of model evaluation and provide a sense of the reliability of model predictions. The 25-year data set from Total Ozone Mapping Spectrometers is a cornerstone of such model evaluation. Here we report evaluation of a three-dimensional multi-decadal simulation of stratospheric composition. Meteorological fields for this off-line calculation are taken from a 50-year simulation of a general circulation model. Model fields are compared with observations from TOMS and also with observations from the Stratospheric Aerosol and Gas Experiment (SAGE), Microwave Limb Sounder (MLS), Cryogenic Limb Array Etalon Spectrometer (CLAES), and the Halogen Occultation Experiment (HALOE). This overall evaluation will emphasize the spatial, seasonal, and interannual variability of the simulation compared with observed atmospheric variability.

Douglass, A. R.; Stolarski, R. S.; Steenrod, S. D.; Pawson, S.

2003-12-01

107

Cataclysmic variables: Disk characteristics from UV observations  

NASA Technical Reports Server (NTRS)

Low dispersion IUE spectra of 3 cataclysmic variables (V442 Oph, V794 Aq1 and H2215-086) are discussed in terms of current disk models. The range of continuum fluxes, line emission and disk parameters of these three novalike systems are compared with past observations of dwarf novae at outburst and quiescence. Evidence of variability on orbital time scales is presented for V442 Oph and H2215-086.

Szkody, P.

1982-01-01

108

High marsh foraminiferal assemblages' response to intra-decadal and multi-decadal precipitation variability, between 1934 and 2010 (Minho, NW Portugal)  

NASA Astrophysics Data System (ADS)

Foraminiferal assemblages of Caminha tidal marshes have been studied since 2002 revealing a peculiar dominance of brackish species, such as Haplophragmoides manilaensis, Haplophragmoides wilberti, Haplophragmoides sp., Pseudothurammina limnetis and Trochamminita salsa/irregularis in the high marshes of the Minho and the Coura lower estuaries. The assemblage composition reflects low salinity conditions, despite the short distance to the estuarine mouth (~ 4 km). However, in May 2010, the presence of salt marsh species Trochammina inflata and Jadammina macrescens became very significant, likely a result of 5 consecutive dry years and a corresponding salinity rise in sediment pore water. Correspondence analysis (CA) groups the surface samples according to their marsh zone, showing a positive correlation with the submersion time of each sampling point. The brackish and normal salinity foraminiferal species appear separated in the CA. This observation was applied to the top 10 cm of a high marsh sediment core that corresponds to the period of instrumental record of precipitation and river flow in the Minho region. We found that river flow strongly correlates with precipitation in the Lima and Minho basins. The longer precipitation record was, therefore, used to interpret the foraminiferal assemblages' variability. Three main phases were distinguished along ca. 80 years of precipitation data: 1) negative anomalies from 1934 to 1957; 2) positive anomalies from 1958 to 1983; and 3) negative anomalies from 1984 to 2010. This last dryer period exhibits the precipitation maximum and the greatest amplitude of rainfall values. High marsh foraminifera reveals a fast response to these short-term shifts; low salinity species relative abundance increases when precipitation increases over several decades, as well as in the same decade, in the years of heavy rainfall of dryer periods. High marsh foraminifera records the increase of freshwater flooding and seepage by 1) decreasing abundance and 2) increasing the dominance of low salinity species. On the other hand, low precipitation over ca. 5 years increases the assemblage productivity and the relative abundance of normal salinity species. The positive correlation found between winter precipitation and the NAO winter index indicates that the Minho region is a part of the North Atlantic climate dynamics and demonstrates that the foraminiferal record from Caminha high marsh may be applied in high-resolution studies of SW Europe climate evolution.

Fatela, Francisco; Moreno, João; Leorri, Eduardo; Corbett, Reide

2014-10-01

109

Land surface phenological response to decadal climate variability across Australia using satellite remote sensing  

NASA Astrophysics Data System (ADS)

Land surface phenological cycles of vegetation greening and browning are influenced by variability in climatic forcing. Quantitative spatial information on phenological cycles and their variability is important for agricultural applications, wildfire fuel accumulation, land management, land surface modeling, and climate change studies. Most phenology studies have focused on temperature-driven Northern Hemisphere systems, where phenology shows annually recurring patterns. However, precipitation-driven non-annual phenology of arid and semi-arid systems (i.e., drylands) received much less attention, despite the fact that they cover more than 30% of the global land surface. Here, we focused on Australia, a continent with one of the most variable rainfall climates in the world and vast areas of dryland systems, where a detailed phenological investigation and a characterization of the relationship between phenology and climate variability are missing. To fill this knowledge gap, we developed an algorithm to characterize phenological cycles, and analyzed geographic and climate-driven variability in phenology from 2000 to 2013, which included extreme drought and wet years. We linked derived phenological metrics to rainfall and the Southern Oscillation Index (SOI). We conducted a continent-wide investigation and a more detailed investigation over the Murray-Darling Basin (MDB), the primary agricultural area and largest river catchment of Australia. Results showed high inter- and intra-annual variability in phenological cycles across Australia. The peak of phenological cycles occurred not only during the austral summer, but also at any time of the year, and their timing varied by more than a month in the interior of the continent. The magnitude of the phenological cycle peak and the integrated greenness were most significantly correlated with monthly SOI within the preceding 12 months. Correlation patterns occurred primarily over northeastern Australia and within the MDB, predominantly over natural land cover and particularly in floodplain and wetland areas. Integrated greenness of the phenological cycles (surrogate of vegetation productivity) showed positive anomalies of more than 2 standard deviations over most of eastern Australia in 2009-2010, which coincided with the transition from the El Niño-induced decadal droughts to flooding caused by La Niña.

Broich, M.; Huete, A.; Tulbure, M. G.; Ma, X.; Xin, Q.; Paget, M.; Restrepo-Coupe, N.; Davies, K.; Devadas, R.; Held, A.

2014-09-01

110

Dynamical Role of Mode Water Ventilation in Decadal Variability in the Central Subtropical Gyre of the North Pacific*  

E-print Network

Dynamical Role of Mode Water Ventilation in Decadal Variability in the Central Subtropical Gyre and weakening of the STCC because of var- iations in mode water ventilation. The changes in mode water can are characteristic of changes in mode water ventilation. Indeed, this natural mode of STCC variability is excited

Xie, Shang-Ping

111

Interannual variability in solar ultraviolet irradiance over decadal time scales at latitude 55 degrees south.  

PubMed

Ground-based measurements of solar UV spectral irradiance made from Ushuaia, Argentina at latitude 55 degrees S reveal a large degree of variability among corresponding months of different years over the period from September 1990 through April 1998. The magnitude and wavelength dependence of year-to-year changes in monthly spectral UV-B irradiation are consistent with expectations based on the behavior of column ozone and cloudiness. When combined with satellite measurements of column ozone, a regression model fit to the ground-based data set allows estimates of monthly UV-B irradiation over a time frame of two decades, 1978-1998, during several months of the year. Results show a general increase in ground-level irradiation at 305.0 nm from the end of the 1970s to the early 1990s during calendar months from September through December. This is followed by generally smaller irradiances through the middle to late 1990s for all months except November, where the increase continues through the end of the data record. The long-term variability in monthly irradiation over the time period studied is more complicated than can be described by a simple linear trend. PMID:11783932

Frederick, J E; Manner, V W; Booth, C R

2001-12-01

112

Vegetation dynamics contributes to the multi-decadal variability of precipitation in the Amazon region  

NASA Astrophysics Data System (ADS)

Precipitation in most of the Amazon shows multi-decadal fluctuations that were linked to oceanic forcing in the Atlantic. This modeling study shows that vegetation dynamics may play a major role in such low-frequency variability in the Amazon. Despite the large amount of annual precipitation, the presence of a dry season (albeit short) facilitates a strong impact of dynamic vegetation on precipitation persistence in the model. The year-to-year variation of net primary productivity (NPP) is dominated by that of the dry season NPP. As a result, above-normal (below-normal) precipitation in a particular year can enhance (suppress) vegetation growth, leading to widespread increase (decrease) of vegetation density in the subsequent year. Precipitation in the subsequent year is therefore more likely to be above (below) normal. This damping effect of vegetation enhances low-frequency variability of precipitation and leads to recurrent droughts or floods, a result previously considered characteristic of arid and semi-arid regions.

Wang, Guiling; Sun, Shanshan; Mei, Rui

2011-10-01

113

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

114

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

115

Decadal Observations of Cloud Cover and Cloud Top Altitude from MISR  

NASA Astrophysics Data System (ADS)

Cloud cover and cloud top altitude are two critical variables needed in climate research. Long term measurements of these two variables have been jointly summarized by the International Satellite Cloud Climatology Project into a global climatological product, which has been used to gain a better understanding of the role of clouds in climate, as well as in constraining cloud parameterization schemes used in climate models. However, the coarse vertical and horizontal resolution of this product does provide limitations in its applications, as does several unresolved errors in cloud cover and cloud top altitude common to traditional visible-infrared passive sensors. Deriving from its ability to measure any scene from multiple directions, MISR contributes accurate measurements of both cloud cover and cloud top altitude at a high horizontal and vertical spatial resolution at a global scale. Cloud cover is directly calculated from three MISR cloud masks, which are optimally combined to achieve excellent cloud detection performance over all underlying surfaces, including regions traditionally difficult for cloud detection (such as sunglint-contaminated and snow/ice-covered regions). Cloud top altitude from MISR is derived using a stereoscopic technique, whose quality does not rely on the validity of atmospheric temperature profiles used in traditional infrared techniques or radiometric calibration. The joint distribution of MISR-derived cloud cover and cloud top altitude has been summarized in a recently developed MISR product, namely, the Cloud Fraction By Altitude (CFBA) product. CFBA provides monthly global cloud top fractions binned at 500 m altitude intervals (up to 20 km above sea surface level) with a horizontal resolution of 0.5×0.5 latitude/longitude. Amongst all the cloud climatological products from passive remote sensors, CFBA holds the highest vertical resolution. The strategy in developing CFBA will be introduced in the presentation. Decadal observations of cloud cover and cloud top altitude constructed from CFBA at a global scale will highlight unique features exposed over marine stratocumulus regimes, tropical convective zones, and polar regions. In addition, the disparities between CFBA and cloud climatology products from other satellite instruments will be discussed, highlighting the strengths and weaknesses of various techniques, as well as the additional information available when looked at in synergy.

Zhao, G.; di Girolamo, L.; Menzies, A.; Mueller, K. J.

2009-12-01

116

Decadal surface water quality trends under variable climate, land use, and hydrogeochemical setting in Iowa, USA  

USGS Publications Warehouse

Understanding how nitrogen fluxes respond to changes in agriculture and climate is important for improving water quality. In the midwestern United States, expansion of corn cropping for ethanol production led to increasing N application rates in the 2000s during a period of extreme variability of annual precipitation. To examine the effects of these changes, surface water quality was analyzed in 10 major Iowa Rivers. Several decades of concentration and flow data were analyzed with a statistical method that provides internally consistent estimates of the concentration history and reveals flow-normalized trends that are independent of year-to-year streamflow variations. Flow-normalized concentrations of nitrate+nitrite-N decreased from 2000 to 2012 in all basins. To evaluate effects of annual discharge and N loading on these trends, multiple conceptual models were developed and calibrated to flow-weighted annual concentrations. The recent declining concentration trends can be attributed to both very high and very low discharge in the 2000s and to the long (e.g., 8 year) subsurface residence times in some basins. Dilution of N and depletion of stored N occurs in years with high discharge. Reduced N transport and increased N storage occurs in low-discharge years. Central Iowa basins showed the greatest reduction in flow-normalized concentrations, likely because of smaller storage volumes and shorter residence times. Effects of land-use changes on the water quality of major Iowa Rivers may not be noticeable for years or decades in peripheral basins of Iowa, and may be obscured in the central basins where extreme flows strongly affect annual concentration trends.

Green, Christopher T.; Bekins, Barbara A.; Kalkhoff, Stephen J.; Hirsch, Robert M.; Liao, Lixia; Barnes, Kimberlee K.

2014-01-01

117

Decadal Variability and Temperature Trends in the Middle Atmosphere From Historical Rocketsonde Data  

NASA Technical Reports Server (NTRS)

Observational studies were performed using historical rocketsonde data to investigate long-term temperature trends, solar-cycle variations, and interactions between tropical and extratropical latitudes in the middle atmosphere. Evidence from tropical, subtropical, and midlatitude North American rocketsonde stations indicated a consistent downward trend over 25 years, with a solar cycle component superposed. The trend is about -1.4 to -2.0 K per decade and the amplitude of the decadal oscillation is about 1.1 K. Prior to trend derivation it was necessary for us to correct temperatures for aerodynamic heating in the early years. The empirically derived correction profile agrees well with a theoretical profile of Krumins and Lyons. A study was also performed of the correlation between equatorial winds and north polar temperatures in winter, showing that the entire stratospheric wind profile near the equator -- including the quasi-biennial oscillation (QBO) and stratopause semiannual oscillation (SAO) -- is important to the extratropical flow, not merely the QBO component as previously thought. A strong correlation was discovered between winter polar temperatures and equatorial winds in the upper stratosphere during the preceding September, suggesting a role for the second cycle of the SAO.

Dunkerton, Timothy J.

2000-01-01

118

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection  

NASA Astrophysics Data System (ADS)

Time series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW 94 class formed in the period 1989-1994 in the Labrador Sea.

van Aken, Hendrik M.; Femke de Jong, M.; Yashayaev, Igor

2011-05-01

119

Decadal variability of the Tropical Atlantic Ocean Surface Temperature in shipboard measurements and in a Global Ocean-Atmosphere model  

NASA Technical Reports Server (NTRS)

Sea surface temperature (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 Global Ocean Surface Temperature Atlas (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. The second type of variability is considerably weaker than the first. As in the GOSTA time series, the multidecadal variability in the GFDL SST time series has approximately opposite phases between the tropical North and South Atlantic Oceans. Empirical orthogonal function analyses of the tropical Atlantic SST anomalies revealed a north-south bipolar pattern as the dominant pattern of decadal variability. It is suggested that the bipolar pattern can be interpreted as decadal variability of the interhemispheric gradient of SST anomalies. The decadal and multidecadal timescale variability of the tropical Atlantic SST, both in the actual and in the GFDL model, stands out significantly above the background 'red noise' and is coherent within each of the time series, suggesting that specific sets of processes may be responsible for the choice of the decadal and multidecadal timescales. Finally, it must be emphasized that the GFDL coupled ocean-atmosphere model generates the decadal and multidecadal timescale variability without any externally applied force, solar or lunar, at those timescales.

Mehta, Vikram M.; Delworth, Thomas

1995-01-01

120

Stratospheric ozone trends and variability as seen by SCIAMACHY during the last decade  

NASA Astrophysics Data System (ADS)

Vertical profiles of the rate of linear change (trend) in the altitude range 15-50 km are determined from decadal O3 time series obtained from SCIAMACHY/ENVISAT measurements in limb viewing geometry. The trends are calculated by using a multivariate linear regression in the zonal bands 5° S-5° N (tropics), 50-60° N, and 50-60° S (mid- to high latitudes). Seasonal terms, the quasi-biennial oscillation, and solar cycle variations are accounted for in the regression. In the tropics, positive trends between 15 and 30 km and negative trends between 30 and 35 km are identified. Moderately positive O3 trends are found in the upper stratosphere of the tropics and midlatitudes. The explanation favoured for the observed positive and negative trends in the tropical lower and middle stratosphere is NOx chemistry. Comparisons between SCIAMACHY and EOS MLS in the tropics and at midlatitudes show good agreement. In the tropics, measurements from OSIRIS/Odin and SHADOZ are analysed resulting in very similar vertical profiles of the rate of linear change of O3. Observed trends in the stratospheric column derived from integrated SCIAMACHY limb O3 profiles and nadir total columns are found to be consistent.

Gebhardt, C.; Rozanov, A.; Hommel, R.; Weber, M.; Bovensmann, H.; Burrows, J. P.; Degenstein, D.; Froidevaux, L.; Thompson, A. M.

2013-04-01

121

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

122

Wetland inventory and variability over the last two decades at a global scale  

NASA Astrophysics Data System (ADS)

Remote sensing techniques employing visible, infrared, and microwave observations offer varying success in estimating wetlands and inundation extent and in monitoring their natural and anthropogenic variations. Low spatial resolution (e.g., 30 km) limits detection to large wetlands but has the advantage of frequent coverage. High spatial resolution (e.g., 100 m), while providing more environmental information, suffers from poor temporal resolution, with observations for just high/low water or warm/cold seasons. Most existing wetland data sets are limited to a few regions, for specific times in the year. The only global inventories of wetland dynamics over a long period of time is derived from a remote-sensing technique employing a suite of complementary satellite observations: it uses passive microwave land-surface microwave emissivities, scatterometer responses, and visible and near infrared reflectances. Combining observations from different instruments makes it possible to capitalize on their complementary strengths, and to extract maximum information about inundation characteristics. The technique is globally applicable without any tuning for particular environments. The satellite data are used to calculate monthly-mean inundated fractions of equal-area grid cells (0.25°x0.25° at the equator), taking into account the contribution of vegetation to the passive microwave signal (Prigent et al., 2001, 2007). Several adjustments to the initial technique have been applied to account for changes in satellite instruments (Papa et al., 2010). The resulting data set now covers 1993-2008 and has been carefully evaluated. We will present the inter-annual variability of the water surface extents under different environments, and relate these variations to other hydrological variables such as river height, precipitation, water runoff, or Grace data. Natural wetlands are the world's largest methane source and dominate the inter-annual variability of atmospheric methane concentrations, with up to 90% of the global methane flux anomalies related to variations in the wetland extent from some estimation. Our data set quantifying inundation dynamics throughout the world's natural wetlands provides a unique opportunity to reduce uncertainties in the role of natural wetlands in the inter-annual variability of the growth rate of atmospheric methane. Papa, F., C. Prigent, C. Jimenez, F. Aires, and W. B. Rossow, Interannual variability of surface water extent at global scale, 1993-2004, JGR, 115, D12111, doi:10.1029/2009JD012674, 2010. Prigent, C., F. Papa, F. Aires, W. B. Rossow, and E. Matthews, Global inundation dynamics inferred from multiple satellite observations, 1993-2000, JGR, 112, D12107, doi:10.1029/2006JD007847, 2007. Prigent, C., E. Matthews, F. Aires, and W. B. Rossow, Remote sensing of global wetland dynamics with multiple satellite data sets, GRL, 28 , 4631-4634, 2001.

Prigent, C.; Papa, F.; Aires, F.; Rossow, W. B.; Matthews, E.

2011-12-01

123

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

124

Observational constraints on interannual variability projections in CMIP5  

NASA Astrophysics Data System (ADS)

Impacts of climate change are sensitive not only to changes in the mean state but also to potential changes in the internal variability of the climate system at diurnal to interannual and multi-decadal time scales. Internal variability arises from nonlinear interactions and complex feedbacks between ocean, sea ice, atmosphere and land surface without any external forcing. However, an external forcing may change both magnitude, spatial patterns and the time scales of these variations. It is crucial to understand whether and on what temporal and spatial scales internal variability will undergo changes under anthropogenic radiative forcing and to identify the underlying mechanisms. To address these questions, we here use model simulations of the Coupled Model Intercomparison Project Phase 5 database (CMIP5) with historical (1850-2005) - RCP8.5 (2006-2100) concentration pathway. First, we show over which latitudes CMIP5 models simulate robust changes in variability. Second, we explore whether models with low present-day internal variability project changes that substantially differ from those models with high present-day internal variability. Such an inter-model relationship is found over the high-latitudes of both hemispheres. For the regions and seasons, for which a relationship across the multi-model ensemble exists, we use observations and reanalyses, to constrain the model projections. This model constraint is based on the assumption that models with a more realistic representation of present-day variability yield more reliable projections. Once a relationship is identified, physical understanding becomes crucial because it must have a strong physical grounding to justify the constraint. We explore mechanisms that explain the inter-model correlation between current variability and its future change especially at high latitudes. We use a "joint projection" approach, which is based on the fact that multiple climate variables are correlated over different scales in order to understand basic mechanisms and to put forward hypotheses that explain what is observed in multi-model projections. Furthermore, the coupling between variables allows a more precise quantification of these relationships which ultimately should enable us to reduce the uncertainty associated with their joint projections.

Borodina, Aleksandra; Fischer, Erich M.; Knutti, Reto

2014-05-01

125

Relative effects of multi-decadal climatic variability and changes in the mean and variability of climate due to global warming: future streamflows in Britain  

Microsoft Academic Search

Climate change impact assessments conventionally assess just the implications of a change in mean climate due to global warming. This paper compares such effects of such changes with those due to natural multi-decadal variability, and also explores the effects of changing the year-to-year variability in climate as well as the mean. It estimates changes in mean monthly flows and a

Nigel W Arnell

2003-01-01

126

North Pacific Decadal Variability in the GEOS-5 Atmosphere-Ocean Model  

NASA Technical Reports Server (NTRS)

This study examines the mechanisms of the Pacific decadal oscillation (PDO) in the GEOS-5 general circulation model. The model simulates a realistic PDO pattern that is resolved as the first empirical orthogonal function (EOF) of winter sea surface temperature (SST). The simulated PDO is primarily forced by Aleutian low through Ekman transport and surface fluxes, and shows a red spectrum without any preferred periodicity. This differs from the observations, which indicate a greater role of El Nino-Southern Oscillation (ENSO) forcing, and likely reflects the too short time scale of the simulated ENSO. The geostrophic transport in response to the Aleutian low is limited to the Kuroshio-Oyashio Extension, and is unlikely the main controlling factor in this model, although it reinforces the Ekman-induced SST anomalies. The delay between the Aleutian low and the PDO is relatively short (1 year) suggesting that the fast Ekman response (rather than Rossby wave propagation) sets the SST pattern immediately following an Aleutian low fluctuation. The atmospheric feedback (response to the SST) is only about 25 of the forcing and never evolves into an Aleutian low completely, instead projecting onto the North Pacific Oscillation (NPO), a meridional dipole in sea level pressure (SLP). The lack of preferred periodicity and weak atmospheric response bothindicate a coupled oscillation is an unlikely mechanism for the PDO in this model. In agreement with recent studies, the NPO is correlated with the North Pacific Gyre Oscillation (NPGO), which is another leading EOF of the North Pacific SST. A possible connection between the PDO and the NPGO is discussed.

Achuthavarier, Deepthi; Schubert, Siegfried D.; Vikhliaev, Yury V.

2013-01-01

127

Observed cold season changes in a Fennoscandian fell area over the past three decades.  

PubMed

We studied trends and variability in snow and climate characteristics in 1978-2012 in the Värriötunturit fell area, northern Finland. Cold season changes were examined using long-term observational data on snow depths, meteorological data, large-scale climate indices, and reindeer herders' experiences with difficult snow conditions. Snow depths declined, and temperatures increased significantly over the study period, with the largest changes observed in October-December and in April. Snow depths decreased particularly in forests at lower altitudes but not in treeless areas at higher altitudes. Interannual variability (but not the trends) in snow depths could be partially linked to large-scale climate indices. A majority of difficult reindeer grazing conditions were related to deep snow in the winter or spring. Our observations suggest that shortened duration of snow cover may facilitate reindeer grazing, whereas potentially more frequent formation of ice layers and mold growth on pastures in the future is disadvantageous for reindeer husbandry. PMID:25001240

Kivinen, Sonja; Rasmus, Sirpa

2014-07-01

128

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

129

CLARREO Cornerstone of the Earth Observing System: Measuring Decadal Change Through Accurate Emitted Infrared and Reflected Solar Spectra and Radio Occultation  

NASA Technical Reports Server (NTRS)

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is one of four Tier 1 missions recommended by the recent NRC Decadal Survey report on Earth Science and Applications from Space (NRC, 2007). The CLARREO mission addresses the need to provide accurate, broadly acknowledged climate records that are used to enable validated long-term climate projections that become the foundation for informed decisions on mitigation and adaptation policies that address the effects of climate change on society. The CLARREO mission accomplishes this critical objective through rigorous SI traceable decadal change observations that are sensitive to many of the key uncertainties in climate radiative forcings, responses, and feedbacks that in turn drive uncertainty in current climate model projections. These same uncertainties also lead to uncertainty in attribution of climate change to anthropogenic forcing. For the first time CLARREO will make highly accurate, global, SI-traceable decadal change observations sensitive to the most critical, but least understood, climate forcings, responses, and feedbacks. The CLARREO breakthrough is to achieve the required levels of accuracy and traceability to SI standards for a set of observations sensitive to a wide range of key decadal change variables. The required accuracy levels are determined so that climate trend signals can be detected against a background of naturally occurring variability. Climate system natural variability therefore determines what level of accuracy is overkill, and what level is critical to obtain. In this sense, the CLARREO mission requirements are considered optimal from a science value perspective. The accuracy for decadal change traceability to SI standards includes uncertainties associated with instrument calibration, satellite orbit sampling, and analysis methods. Unlike most space missions, the CLARREO requirements are driven not by the instantaneous accuracy of the measurements, but by accuracy in the large time/space scale averages that are key to understanding decadal changes.

Sandford, Stephen P.

2010-01-01

130

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

131

Variability of heat and salinity content in the North Atlantic in the last decade  

NASA Astrophysics Data System (ADS)

The analysis of the heat and salinity contents has been made for the Northern Atlantic for the decade between January 1999 and December 2008. This analysis is based on the Argo profiling data for the upper 2000 m. Basin-averaged values of heat content deviation (HCD) and salinity content deviation (SCD) are robust and stable. The HCD and SCD demonstrate positive trends in the last decade in the upper 2000 m of the North Atlantic. The linear trend of HCD and SCD are (11.14±3.17)×1020 J/yr, and (2.80±1.17)×1013 kg/yr, respectively. Both trends are significant at 95% level of significance.

Ivchenko, V. O.; Wells, N. C.; Aleynik, D. L.; Shaw, A. G. P.

2010-07-01

132

Teleconnections, Midlatitude Cyclones and Aegean Sea Turbulent Heat Flux Variability on Daily Through Decadal Time Scales  

NASA Technical Reports Server (NTRS)

We analyze daily wintertime cyclone variability in the central and eastern Mediterranean during 1958-2001, and identify four distinct cyclone states, corresponding to the presence or absence of cyclones in each basin. Each cyclone state is associated with wind flows that induce characteristic patterns of cooling via turbulent (sensible and latent) heat fluxes in the eastern Mediterranean basin and Aegean Sea. The relative frequency of occurrence of each state determines the heat loss from the Aegean Sea during that winter, with largest heat losses occurring when there is a storm in the eastern but not central Mediterranean (eNOTc), and the smallest occurring when there is a storm in the central but not eastern Mediterranean (cNOTe). Time series of daily cyclone states for each winter allow us to infer Aegean Sea cooling for winters prior to 1985, the earliest year for which we have daily heat flux observations. We show that cyclone states conducive to Aegean Sea convection occurred in 1991/1992 and 1992/1993, the winters during which deep water formation was observed in the Aegean Sea, and also during the mid-1970s and the winters of 1963/1964 and 1968/1969. We find that the eNOTc cyclone state is anticorrelated with the North Atlantic Oscillation (NAO) prior to 1977/1978. After 1977/1978, the cNOTe state is anticorrelated with both the NAO and the North Caspian Pattern (NCP), showing that the area of influence of large scale atmospheric teleconnections on regional cyclone activity shifted from the eastern to the central Mediterranean during the late 1970s. A trend toward more frequent occurrence of the positive phase of the NAO produced less frequent cNOTe states since the late 1970s, increasing the number of days with strong cooling of the Aegean Sea surface waters.

Romanski, Joy; Romanou, Anastasia; Bauer, Michael; Tselioudis, George

2013-01-01

133

Highlights from a Decade of OMI-TOMS Total Ozone Observations on EOS Aura  

NASA Technical Reports Server (NTRS)

Total ozone measurements from OMI have been instrumental in meeting Aura science objectives. In the last decade, OMI has extended the length of the TOMS total ozone record to over 35 years to monitor stratospheric ozone recovery. OMI-TOMS total ozone measurements have also been combined synergistically with measurements from other Aura instruments and MLS in particular, which provides vertically resolved information that complements the total O3 mapping capability of OMI. With this combined approach, the EOS Aura platform has produced more accurate and detailed measurements of tropospheric ozone. This has led in turn to greater understanding of the sources and transport of tropospheric ozone as well as its radiative forcing effect. The combined use of OMI and MLS data was also vital to the analysis of the severe Arctic ozone depletion event of 2011. The quality of OMI-TOMS total O3 data used in these studies is the result of several factors: a mature and well-validated algorithm, the striking stability of the OMI instrument, and OMI's hyperspectral capabilities used to derive cloud pressures. The latter has changed how we think about the effects of clouds on total ozone retrievals. We will discuss the evolution of the operational V8.5 algorithm and provide an overview and motivation for V9. After reviewing results and developments of the past decade, we finally highlight how ozone observations from EOS Aura are playing an important role in new ozone mapping missions.

Haffner, David P.; Bhartia, Pawan K.; McPeters, Richard D.; Joiner, Joanna; Ziemke, Jerald R.; Vassilkov, Alexander; Labow, Gordon J.; Chiou, Er-Woon

2014-01-01

134

Flatfish recruitment response to decadal climatic variability and ocean conditions in the eastern Bering Sea  

Microsoft Academic Search

This paper provides a retrospective analysis of the relationship of physical oceanography and biology and recruitment of three Eastern Bering Sea flatfish stocks: flathead sole (Hippoglossoides elassodon), northern rock sole (Lepidopsetta polyxystra), and arrowtooth flounder (Atheresthes stomias) for the period 1978–1996. Temporal trends in flatfish production in the Eastern Bering Sea are consistent with the hypothesis that decadal scale climate

T. K. Wilderbuer; A. B. Hollowed; W. J. Ingraham; P. D. Spencer; M. E. Conners; N. A. Bond; G. E. Walters

2002-01-01

135

Intra- to Multi-Decadal Temperature Variability over the Continental United States: 1896-2012  

Technology Transfer Automated Retrieval System (TEKTRAN)

The Optimal Ranking Regime (ORR) method was used to identify intra- to multi-decadal (IMD) time windows containing significant ranking sequences in U.S. climate division temperature data. The simplicity of the ORR procedure’s output – a time series’ most significant non-overlapping periods of high o...

136

Watershed-scale response of groundwater recharge to inter-annual and inter-decadal variability in precipitation (Alberta, Canada)  

NASA Astrophysics Data System (ADS)

Groundwater recharge sets a constraint on aquifer water balance in the context of water management. Historical data on groundwater and other relevant hydrological processes can be used to understand the effects of climatic variability on recharge, but such data sets are rare. The climate of the Canadian prairies is characterized by large inter-annual and inter-decadal variability in precipitation, which provides opportunities to examine the response of groundwater recharge to changes in meteorological conditions. A decadal study was conducted in a small (250 km2) prairie watershed in Alberta, Canada. Relative magnitude of annual recharge, indicated by water-level rise, was significantly correlated with a combination of growing-season precipitation and snowmelt runoff, which drives depression-focussed infiltration of meltwater. Annual precipitation was greater than vapour flux at an experimental site in some years and smaller in other years. On average precipitation minus vapour flux was 10 mm y-1, which was comparable to the magnitude of watershed-scale groundwater recharge estimated from creek baseflow. Average baseflow showed a distinct shift from a low value (4 mm y-1) in 1982-1995 to a high value (15 mm y-1) in 2003-2013, indicating the sensitivity of groundwater recharge to a decadal-scale variability of meteorological conditions.

Hayashi, Masaki; Farrow, Christopher R.

2014-12-01

137

Observations on Complexity and Costs for Over Three Decades of Communications Satellites  

NASA Astrophysics Data System (ADS)

This paper takes an objective look at approximately thirty communications satellites built over three decades using a complexity index as an economic model. The complexity index is derived from a number of technical parameters including dry mass, end-of-life- power, payload type, communication bands, spacecraft lifetime, and attitude control approach. Complexity is then plotted versus total satellite cost and development time (defined as contract start to first launch). A comparison of the relative cost and development time for various classes of communications satellites and conclusions regarding dependence on system complexity are presented. Observations regarding inherent differences between commercially acquired systems and those procured by government organizations are also presented. A process is described where a new communications system in the formative stage may be compared against similarly "complex" missions of the recent past to balance risk within allotted time and funds. 1

Bearden, David A.

2002-01-01

138

Mountain Hemlock Growth Responds to Climatic Variability at Annual and Decadal Time Scales  

Microsoft Academic Search

Improved understanding of tree growth responses to climate is needed to model and predict forest ecosystem responses to current and future climatic variability. We used dendroecological methods to study the effects of climatic variability on radial growth of a subalpine conifer, mountain hemlock (Tsuga mertensiana). Tree-ring chronologies were developed for 31 sites, spanning the latitudinal and elevational ranges of mountain

David W. Peterson; David L. Peterson

2001-01-01

139

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

140

Modelling convective severe weather occurrence using observations, reanalysis data and decadal climate predictions  

NASA Astrophysics Data System (ADS)

Observations of local severe convective events can be combined with atmospheric reanalyses to compute severe weather probability as a function of parameters characterizing the local state of the atmosphere. Using ERA-Interim reanalysis data and observations from the European Severe Weather Database, we have investigated several ways to express the probability of large hail, tornadoes, flash floods or wind gusts as a function of parameters such as convective available potential energy, vertical wind shear and precipitation. Our attempts include fitting analytic functions, using smoothers of various kinds, and binning the data within the multidimensional parameter space according to various algorithms. We imposed that any difference between binned observations and the modelled probability function be insignificant at the 95% confidence level. Further tests of robustness of the model were conducted. A probability function fulfilling this criterion was selected and subsequently applied to the ERA-Interim data as well as to predictions of the decadal forecasting system developed in the MiKlip programme. We investigated climatic and modelled past and future trends of severe convective weather. We will present the (preliminary) results of that effort.

Pistotnik, Georg; Groenemeijer, Pieter

2014-05-01

141

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

142

Decadal variability of shallow cells and equatorial sea surface temperature in a numerical model of the Atlantic  

Microsoft Academic Search

The relative role of extraequatorial mechanisms modulating decadal sea surface temperature anomalies (SSTA) in the equatorial Atlantic is investigated using a suite of sensitivity experiments based on an ocean general circulation model. The model is forced by observed wind stress and\\/or computed heat flux from an associated advective atmospheric mixed layer model. In addition, the surface forcing is optionally applied

Jürgen Kröger; Antonio J. Busalacchi; Joaquim Ballabrera-Poy; Paola Malanotte-Rizzoli

2005-01-01

143

Collaborative Research: Separating Forced and Unforced Decadal Predictability in Models and Observations  

SciTech Connect

This report is a progress report of the accomplishments of the research grant “Collaborative Research: Separating Forced and Unforced Decadal Predictability in Models and Observa- tions” during the period 1 May 2011- 31 August 2013. This project is a collaborative one between Columbia University and George Mason University. George Mason University will submit a final technical report at the conclusion of their no-cost extension. The purpose of the proposed research is to identify unforced predictable components on decadal time scales, distinguish these components from forced predictable components, and to assess the reliability of model predictions of these components. Components of unforced decadal predictability will be isolated by maximizing the Average Predictability Time (APT) in long, multimodel control runs from state-of-the-art climate models. Components with decadal predictability have large APT, so maximizing APT ensures that components with decadal predictability will be detected. Optimal fingerprinting techniques, as used in detection and attribution analysis, will be used to separate variations due to natural and anthropogenic forcing from those due to unforced decadal predictability. This methodology will be applied to the decadal hindcasts generated by the CMIP5 project to assess the reliability of model projections. The question of whether anthropogenic forcing changes decadal predictability, or gives rise to new forms of decadal predictability, also will be investigated.

Tippett, Michael K. [Columbia University

2014-04-09

144

Decadal variability of North Atlantic winter cyclone tracks in the 20C Reanalysis and MPI-ESM-LR  

NASA Astrophysics Data System (ADS)

Weather and climate in Central and Western Europe are strongly influenced by extra-tropical cyclones in the North Atlantic region. Therefore, the prediction of cyclones is of great interest. The MiKlip joint project aims at developing a decadal prediction system with Europe as one focus area. As part of MiKlip, this study uses a cyclone tracking identification algorithm based on the Laplacian of sea level pressure to investigate the decadal variability of North Atlantic winter (ONDJFM) cyclone tracks. For this purpose, we develop a set of indices to describe the spatial extent as well as the orientation of the mean path of cyclone tracks and climatological cyclone track densities. Linking these indices to atmospheric and oceanic phenomena, such as the NAO and AMO, we seek to identify physical processes influencing the variability of North Atlantic winter cyclone tracks. We use the Twentieth Century Reanalysis and the HadISST1.1 sea surface temperature datasets to create long-term (1871-2007) index time series and to identify these processes. The results from the reanalysis datasets are compared to decadal hindcasts of the MPI-ESM-LR (contributor to cmip5). First results indicate problems of the model to reproduce the results from the reanalysis dataset.

Schyska, Bruno; Rust, Henning; Kruschke, Tim; Ulbrich, Uwe

2013-04-01

145

Intra-decadal variability in the Ekman heat flux from scatterometer winds  

Microsoft Academic Search

We examine evidences of low frequency variability in the Ekman heat flux due to changes in the global temperature and wind patterns. The 10-year long time series of high resolution surface wind vectors was provided by the European Remote Sensing Satellites 1 and 2. A linear regression of the zonally averaged Ekman heat flux shows a latitudinal trend for the

O. T. Sato; P. S. Polito; W. Timothy Liu

2002-01-01

146

Intra-decadal variability in the Ekman heat flux from scatterometer winds  

Microsoft Academic Search

(1) We examine evidences of low frequency variability in the Ekman heat flux due to changes in the global temperature and wind patterns. The 10-year long time series of high resolution surface wind vectors was provided by the European Remote Sensing Satellites 1 and 2. A linear regression of the zonally averaged Ekman heat flux shows a latitudinal trend for

O. T. Sato; P. S. Polito

2002-01-01

147

Four decades of variability in turbidity in the western Wadden Sea as derived from corrected Secchi disk readings  

NASA Astrophysics Data System (ADS)

The Wadden Sea has undergone many changes of which some (e.g., seagrass disappearance, dredging activities) are thought to have affected the concentrations of suspended particulate matter (SPM) in these waters. Results of previous analyses of long-term variation and trends in SPM are, however, possibly biased by the fact that the data underlying these trends were not corrected for methodological changes in time. In this paper we analyze the variability of Secchi disk measurements recorded at one location in the westernmost part of the Wadden Sea during almost four decades (from 1974 to 2010). The Secchi readings were corrected for varying environmental conditions (solar zenith angle, solar irradiance and sea surface conditions) at the time of observation and then converted to a turbidity proxy that measures the attenuation of light due to suspended and dissolved materials in the water column. We tested a series of hypotheses to describe the seasonal and long-term variations of this turbidity proxy. The best statistical model assumed one common seasonal pattern within the study period and a strong variation in turbidity over the years without any apparent long-term increase or decrease in time (n = 1361; r2 = 0.53). In addition, we found that most of the turbidity variation in this part of the Wadden Sea can be described as a function of SPM, chlorophyll-a, salinity, water temperature, the filter type used for the SPM determinations, and a still unidentified seasonal factor (n = 401; r2 = 0.88). Comparison with annual averaged ADCP-derived SPM concentrations as determined from a ferry sailing across the Marsdiep tidal inlet (1998-2008) showed that the variability in turbidity at the sampling station was indicative for the variation in light attenuation in the westernmost part of the Wadden Sea. Because the intensity of the underwater light-field affects primary productivity, this new and consistent information on long-term variation in turbidity is of profound importance to the assessment of long-term changes and underlying mechanisms of the carrying capacity of the Wadden Sea.

Philippart, Catharina J. M.; Salama, Mhd. Suhyb; Kromkamp, Jacco C.; van der Woerd, Hendrik J.; Zuur, Alain F.; Cadée, Gerhard C.

2013-09-01

148

Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa  

Microsoft Academic Search

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ??2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little

Andrew S. Cohen; Kiram E. Lezzar; Julia Cole; David Dettman; Geoffrey S. Ellis; Meagan Eagle Gonneea; Pierre-Denis Plisnier; Victor Langenberg; Maarten Blaauw; Derrick Zilifi

2006-01-01

149

A Decade of Cassini Radio Science Observations of the Saturn System  

NASA Astrophysics Data System (ADS)

The Cassini Radio Science Subsystem (RSS) on board the Cassini spacecraft has returned a wealth ofinformation about the Saturn system during its first decade of observations. The instrumentation is quite versatile, operating in up to three wavelengths simultaneously (S, X, and Ka bands), and tied to a very stable frequency standard either on board or uplinked to the spacecraft from a maser-controlled transmitter as part of the Deep Space Network. Over the course of the mission so far, dozens of occultations by Saturn's rings have been observed, revealing the detailed structure and scattering properties of the rings at sub-km resolution. A companion set of atmospheric occultations by Saturn and Titan have provided detailed vertical profiles of the temperature of the neutral atmosphere and the electron density of the ionosphere, spanning a range of latitudes and a significant fraction of a Saturn season. Operatin in a bistatic mode, the RSS instrument has transmitted signals to the surface of Titan at the specular point such that the reflected signal is received on the earth, revealing the dielectric properties of Titan's surface. Finally, exquisitely accurate measurements of the gravitationally induced Dopper shift of the RSS transmitted signal have provided measurements of the gravitations fields and probes of the internal structure of several of Saturn's major satellites, most notably indicating the presence of sub-surface oceans on both Titan and Enceladus. During the upcoming three-year finale of the Cassini mission, highlights of the remaining RSS science objectives include high- SNR measurements of the rings at their most favorable geometry of the entire Cassini orbital tour, and a set of close orbital fly-bys of Saturn itself, enabling the determination of the planet's gravitational field to an accuracy comparable to that expected for the Juno mission to Jupiter.

French, R.; Armstrong, J.; Flasar, M.; Iess, L.; Kliore, A.; Marouf, E.; McGhee, C.; Nagy, A.; Rappaport, N.; Schinder, P.; Tortora, P.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischmann, D.; Kahan, D.

2014-04-01

150

Characteristics of intra-, inter-annual and decadal sea-level variability and the role of meteorological forcing: the long record of Cuxhaven  

NASA Astrophysics Data System (ADS)

This paper addresses the role of meteorological forcing on mean sea level (MSL) variability at the tide gauge of Cuxhaven over a period from 1871 to 2008. It is found that seasonal sea level differs significantly from annual means in both variability and trends. The causes for the observed differences are investigated by comparing to changes in wind stress, sea level pressure and precipitation. Stepwise regression is used to estimate the contribution of the different forcing factors to sea level variability. The model validation and sensitivity analyses showed that a robust and timely independent estimation of regression coefficients becomes possible if at least 60 to 80 years of data are available. Depending on the season, the models are able to explain between 54 % (spring, April to June) and 90 % (winter, January to March) of the observed variability. Most parts of the observed variability are attributed to changes in zonal wind stress, whereby the contribution of sea level pressure, precipitation and meridional wind stress is rather small but still significant. On decadal timescales, the explanatory power of local meteorological forcing is considerable weaker, suggesting that the remaining variability is attributed to remote forcing over the North Atlantic. Although meteorological forcing contributes to linear trends in some sub-periods of seasonal time series, the annual long-term trend is less affected. However, the uncertainties of trend estimation can be considerably reduced, when removing the meteorological influences. A standard error smaller than 0.5 mm/year requires 55 years of data when using observed MSL at Cuxhaven tide gauge. In contrast, a similar standard error in the meteorologically corrected residuals is reached after 32 years.

Dangendorf, Sönke; Mudersbach, Christoph; Wahl, Thomas; Jensen, Jürgen

2013-03-01

151

Mechanisms of the Internally Generated Decadal-to-Multidecadal Variability in the Atlantic  

NASA Astrophysics Data System (ADS)

The thesis investigates the physical question of mechanisms of the Atlantic multidecadal variability (AMV) in a new way, using the weather noise forced interactive ensemble. It includes two distinct but closely related components. 1) Verification of the interactive ensemble strategy and justification for the noise forcing. In order to separate the noise from the SST forced response, the SST forced response in the atmospheric GCM (AGCM), forced by the SST from the coupled GCM (CGCM), has to be the same as in the CGCM. To be consistent, the noise should also be the same statistically in the CGCM and AGCM. Comparison of the CGCM and AGCM ensemble shows that these conditions are satisfied. Therefore, the interactive ensemble is an appropriate tool for the investigation, and the "noise" that is diagnosed and used as forcing is appropriate. Our results apply not just to the interactive ensemble, but also have broader implications important for the design of a wide range of climate modeling experiments. 2) Diagnosis of the multidecadal variability in the CGCM simulation. The diagnosis is done using the interactive ensemble CGCM, in which the heat flux, wind stress and fresh water flux weather noise components are applied at the ocean surface in different regions and in different combinations. The interactive ensemble simulations prove that the model's climate variability is predominantly forced by weather noise. The local weather noise forcing is found to be responsible for the SST variability in the Atlantic, with the noise heat flux and noise wind stress playing a critical role, while the noise fresh water flux has negligible impact. The North Atlantic Oscillation (NAO) pattern in the atmosphere, dominated by weather noise, forces the AMV 45-year mode through the noise heat flux and noise wind stress, with the former important in the eastern North Atlantic and the latter along the separated Gulf Stream. The noise wind stress forces the AMV 45-year mode through ocean dynamics, including Rossby waves, ocean gyres and the Atlantic Meridional Overturning Circulation. The atmospheric response to SST, including the SST-forced heat flux and SST-forced wind stress, acts as a damping on the AMV 45-year mode.

Chen, Hua

152

Observing Decadal Trends in Atmospheric Feedbacks and Climate Change with Zeus and CLARREO  

NASA Astrophysics Data System (ADS)

New technologies for observing decadal trends in atmospheric feedbacks and climate change from space have been recently demonstrated via a NASA Instrument Incubator Program (IIP) project of our group and the Anderson Group of Harvard University. Using these new technologies, a mission named Zeus has been proposed to the first NASA Earth Venture Instruments opportunity (EVI-1). Zeus would provide a low cost mechanism to initiate a new era in high spectral resolution IR climate Benchmark and Intercalibration observations, the basis for which has been established by definition of the CLARREO mission in the 2007 NRC "Decadal Survey" and by the Science Definition Team established by NASA LaRC to further the full blown CLARREO mission. Zeus EVI is a low-cost, low-risk, and high-value EVI mission that will deploy an Absolute Radiance Interferometer (ARI) instrument to measure absolute spectrally resolved infrared radiance over much of the Earth-emitted spectrum with ultra-high accuracy (<0.1 K 3-sigma brightness temperature). Zeus makes use of broad spectral coverage (3.7-50 microns) and high spectral resolution (<1 cm-1) to provide benchmark products for climate trending with much higher information content than traditional spectrally-integrated measurements. While ARI requirements for accuracy and spectral properties are demanding, the overall instrument is relatively simple and low-cost because of the limited requirements on spatial sampling (25-100 km nadir-only footprints spaced at < 250 km) and on noise performance (climate products are created by combining many samples). The orbit chosen for Zeus must provide coverage immune to time-of-day sampling errors. Because of its relatively high rate of precession, an attractive baseline option for Zeus EVI is the 51.6 degrees inclination orbit of the International Space Station (ISS). For Zeus deployment on the ISS, higher latitude climate benchmark information will be obtained from operational sounders intercalibrated by Zeus. A key aspect of the Zeus ARI instrument is the On-orbit Verification and Test System (OVTS) for verifying its accuracy by reference to International Standards (SI) and testing on orbit. The OVTS includes an On-orbit Absolute Radiance Standard (OARS), which is a high emissivity cavity blackbody that can be operated over a wide range of temperatures to verify ARI calibration. The OARS uses multiple small phase change cells to establish its fundamental temperature scale to better than 5 mK absolute and a broad-band heated-halo source for monitoring its cavity spectral emissivity throughout the mission. A Quantum Cascade Laser (QCL) is also used by the OVTS to monitor the ARI instrument spectral lineshape and the emissivity of its calibration blackbody relative to that of the OARS. The ARI radiance measurements will also be tested for other systematic errors on orbit (non-linearity, polarization effects, and stray light). Through especially careful attention to accuracy, proven on orbit, Zeus EVI will provide the first irrefutable benchmark measurements of the Earth's emitted spectral radiance with accuracy exceeding 0.1 K 3 sigma. In addition, Zeus will serve as a reference standard for operational advanced sounders and will enable fundamental improvements in our capability to document climate trends and to forecast climate and weather.

Revercomb, H. E.; Best, F. A.; Knuteson, R. O.; Tobin, D. C.; Taylor, J. K.; Gero, P.; Adler, D. P.; Pettersen, C.; Mulligan, M.; Tobin, D. C.

2012-12-01

153

Influence of climate variability versus change at multi-decadal time scales on hydrological extremes  

NASA Astrophysics Data System (ADS)

Recent studies have shown that rainfall and hydrological extremes do not randomly occur in time, but are subject to multidecadal oscillations. In addition to these oscillations, there are temporal trends due to climate change. Design statistics, such as intensity-duration-frequency (IDF) for extreme rainfall or flow-duration-frequency (QDF) relationships, are affected by both types of temporal changes (short term and long term). This presentation discusses these changes, how they influence water engineering design and decision making, and how this influence can be assessed and taken into account in practice. The multidecadal oscillations in rainfall and hydrological extremes were studied based on a technique for the identification and analysis of changes in extreme quantiles. The statistical significance of the oscillations was evaluated by means of a non-parametric bootstrapping method. Oscillations in large scale atmospheric circulation were identified as the main drivers for the temporal oscillations in rainfall and hydrological extremes. They also explain why spatial phase shifts (e.g. north-south variations in Europe) exist between the oscillation highs and lows. Next to the multidecadal climate oscillations, several stations show trends during the most recent decades, which may be attributed to climate change as a result of anthropogenic global warming. Such attribution to anthropogenic global warming is, however, uncertain. It can be done based on simulation results with climate models, but it is shown that the climate model results are too uncertain to enable a clear attribution. Water engineering design statistics, such as extreme rainfall IDF or peak or low flow QDF statistics, obviously are influenced by these temporal variations (oscillations, trends). It is shown in the paper, based on the Brussels 10-minutes rainfall data, that rainfall design values may be about 20% biased or different when based on short rainfall series of 10 to 15 years length, and still 8% for series of 25 years lengths. Methods for bias correction are demonstrated. The definition of "bias" depends on a number of factors, which needs further debate in the hydrological and water engineering community. References: Willems P. (2013), 'Multidecadal oscillatory behaviour of rainfall extremes in Europe', Climatic Change, 120(4), 931-944 Willems, P. (2013). 'Adjustment of extreme rainfall statistics accounting for multidecadal climate oscillations', Journal of Hydrology, 490, 126-133 Willems, P., Olsson, J., Arnbjerg-Nielsen, K., Beecham, S., Pathirana, A., Bülow Gregersen, I., Madsen, H., Nguyen, V-T-V. (2012), 'Impacts of climate change on rainfall extremes and urban drainage', IWA Publishing, 252p., Paperback Print ISBN 9781780401256; Ebook ISBN 9781780401263

Willems, Patrick

2014-05-01

154

Interannual and sub-decadal variability in hydrography and nutrient concentrations in the Cariaco Basin  

NASA Astrophysics Data System (ADS)

The Cariaco Basin is a deep (1400 m) permanently anoxic depression on the Venezuelan continental margin. First studied in the mid-1950s, it is the site of one of the longest time series of biogeochemical data in the ocean and for the past 18 years has been intensively studied by US and Venezuelan scientists through the CARIACO Ocean Times Series program. Although the basin's geochemistry was originally thought to be in steady state, data from CARIACO have demonstrated both long term trends and short term variability in hydrography and nutrients at all depths. These trends are influenced by a number of factors including changes in the position of the ITCZ, the exchange of water between the Caribbean and the Cariaco Basin, and by changes in terrestrial influence. The long term trends include warming of surface waters by more than 1oC in 18 years, increases in surface fCO2 (2.95 +/- 0.43 micro-atmospheres kg-1 y-1) and nDIC (1.89 +/- 0.45 micromole kg-1 y-1), decreases in pH (0.0025 +/- 0.0004 y-1), and shifts in plankton community structure. Short-term variability includes fluctuations in the depth and salinity of Subtropical Underwater and depth of the oxic/anoxic interface, changes in the depth and frequency of intrusions of oxygen-containing water into mid-depths, and episodic transport of terrestrial material into the basin after earthquakes or high precipitation events. Our results show that at least the upper 300-400 m of the water column is periodically (but not continuously) ventilated by water from the open Caribbean. Nutrient concentrations in the deep basin have increased steadily with time in a proportion reflective of the elemental ratios in the settling organic matter, although N:P ratios in the water column (for dissolved ammonium and phosphate in the sulfidic zone the ratio is approximately 16:1) differ from ratios for the accumulating nutrients (11:1) and the settling flux (approximately 5:1 to 12.5:1). This difference is likely due to long-term changes in the source material for remineralization, either because of sizeable ecosystem changes, changes in the relative importance of the terrestrial input of inorganic P or scavenging of P by mineral precipitation near the oxic/anoxic interface.

Scranton, Mary; Taylor, Gordon; Muller-Karger, Frank; Lorenzoni, Laura; Montes, Enrique; Fanning, Kent; Thunell, Robert; Benitez-Nelson, Claudia; Astor, Yrene; Varela, Ramon

2014-05-01

155

Multiwavelength observations of eleven cataclysmic variables  

NASA Technical Reports Server (NTRS)

A study of 11 cataclysmic variables in the UV, optical and IR ranges has indicated that the alpha index of the UV flux distribution for five systems at quiescence is relatively flat and constrained, implying a narrow range in mass transfer rate. This may be correlated with the mechanism for mass transfer in short orbital period systems. Near maximum light, the alpha index is steep and consistent with steady state models.

Szkody, P.

1985-01-01

156

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

157

30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability  

NASA Technical Reports Server (NTRS)

A 30-year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea ice extent decreased by 0.30+0.03 x 10(exp 6) square kilometers per 10 yr from 1972 through 2002, but by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per 10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased. Over the full 30-year period, the Antarctic ice extent decreased by 0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10 yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.

Cavalieri, D. J.; Parkinson, C. L.; Vinnikov, K. Y.

2003-01-01

158

Variability of global net sea-air CO2 fluxes over the last three decades using empirical relationships  

NASA Astrophysics Data System (ADS)

ABSTRACT The interannual variability of net sea-air CO2 flux for the period 1982-2007 is obtained from a diagnostic model using empirical subannual relationships between climatological CO2 partial pressure in surface seawater (pCO2SW) and sea surface temperature (SST), along with interannual changes in SST and wind speed. These optimum subannual relationships show significantly better correlation between pCO2SW and SST than the previous relationships using fixed monthly boundaries. Our diagnostic model yields an interannual variability of +/-0.14 PgC yr-1 (1?) with a 26-year mean of -1.48 PgC yr-1. The greatest interannual variability is found in the Equatorial Pacific, and significant variability is also found at northern and southern high-latitudes, depending in part, on which wind product is used. We provide an assessment of our approach by applying it to pCO2SW and SST output from a prognostic global biogeochemical ocean model. Our diagnostic approach applied to this model output shows reasonable agreement with the prognostic model net sea-air CO2 fluxes in terms of magnitude and phase of variability, suggesting that our diagnostic approach can capture much of the observed variability on regional to global scale. A notable exception is that our approach shows significantly less variability than the prognostic model in the Southern Ocean.

Park, Geun-Ha; Wanninkhof, Rik; Doney, Scott C.; Takahashi, Taro; Lee, Kitack; Feely, Richard A.; Sabine, Christopher L.; Triñanes, Joaquin; Lima, Ivan D.

2010-11-01

159

Decadal Observations of Cloud Cover and Cloud Top Altitude from MISR  

Microsoft Academic Search

Cloud cover and cloud top altitude are two critical variables needed in climate research. Long term measurements of these two variables have been jointly summarized by the International Satellite Cloud Climatology Project into a global climatological product, which has been used to gain a better understanding of the role of clouds in climate, as well as in constraining cloud parameterization

G. Zhao; L. di Girolamo; A. Menzies; K. J. Mueller

2009-01-01

160

Temporal variability and coherence of euphotic zone bacterial communities over a decade in the Southern California Bight  

PubMed Central

Time-series are critical to understanding long-term natural variability in the oceans. Bacterial communities in the euphotic zone were investigated for over a decade at the San Pedro Ocean Time-series station (SPOT) off southern California. Community composition was assessed by Automated Ribosomal Intergenic Spacer Analysis (ARISA) and coupled with measurements of oceanographic parameters for the surface ocean (0–5?m) and deep chlorophyll maximum (DCM, average depth ?30?m). SAR11 and cyanobacterial ecotypes comprised typically more than one-third of the measured community; diversity within both was temporally variable, although a few operational taxonomic units (OTUs) were consistently more abundant. Persistent OTUs, mostly Alphaproteobacteria (SAR11 clade), Actinobacteria and Flavobacteria, tended to be abundant, in contrast to many rarer yet intermittent and ephemeral OTUs. Association networks revealed potential niches for key OTUs from SAR11, cyanobacteria, SAR86 and other common clades on the basis of robust correlations. Resilience was evident by the average communities drifting only slightly as years passed. Average Bray-Curtis similarity between any pair of dates was ?40%, with a slight decrease over the decade and obvious near-surface seasonality; communities 8–10 years apart were slightly more different than those 1–4 years apart with the highest rate of change at 0–5?m between communities <4 years apart. The surface exhibited more pronounced seasonality than the DCM. Inter-depth Bray-Curtis similarities repeatedly decreased as the water column stratified each summer. Environmental factors were better predictors of shifts in community composition than months or elapsed time alone; yet, the best predictor was community composition at the other depth (that is, 0–5?m versus DCM). PMID:23864126

Chow, Cheryl-Emiliane T; Sachdeva, Rohan; Cram, Jacob A; Steele, Joshua A; Needham, David M; Patel, Anand; Parada, Alma E; Fuhrman, Jed A

2013-01-01

161

GINGA and ROSAT observations of the cataclysmic variable S193  

Microsoft Academic Search

The cataclysmic variable S193 was observed with the Ginga and ROSAT satellites, along with ground-based optical observations. The bremsstrahlung temperatures and the column densities derived from these two observations are noticeably different. However, since the observations were separated by 3 yr and took place at different optical magnitudes, it is not clear whether this is related to an intrinsic change

Paula Szkody; Peter Garnavich; Michael Castelaz; F. Makino

1994-01-01

162

Understanding interannual, decadal level variability in paralytic shellfish poisoning toxicity in the Gulf of Maine: The HAB Index  

NASA Astrophysics Data System (ADS)

A major goal in harmful algal bloom (HAB) research has been to identify mechanisms underlying interannual variability in bloom magnitude and impact. Here the focus is on variability in Alexandrium fundyense blooms and paralytic shellfish poisoning (PSP) toxicity in Maine, USA, over 34 years (1978-2011). The Maine coastline was divided into two regions - eastern and western Maine, and within those two regions, three measures of PSP toxicity (the percent of stations showing detectable toxicity over the year, the cumulative amount of toxicity per station measured in all shellfish (mussel) samples during that year, and the duration of measurable toxicity) were examined for each year in the time series. These metrics were combined into a simple HAB Index that provides a single measure of annual toxin severity across each region. The three toxin metrics, as well as the HAB Index that integrates them, reveal significant variability in overall toxicity between individual years as well as long-term, decadal patterns or regimes. Based on different conceptual models of the system, we considered three trend formulations to characterize the long-term patterns in the Index - a three-phase (mean-shift) model, a linear two-phase model, and a pulse-decline model. The first represents a “regime shift” or multiple equilibria formulation as might occur with alternating periods of sustained high and low cyst abundance or favorable and unfavorable growth conditions, the second depicts a scenario of more gradual transitions in cyst abundance or growth conditions of vegetative cells, and the third characterizes a ”sawtooth” pattern in which upward shifts in toxicity are associated with major cyst recruitment events, followed by a gradual but continuous decline until the next pulse. The fitted models were compared using both residual sum of squares and Akaike's Information Criterion. There were some differences between model fits, but none consistently gave a better fit than the others. This statistical underpinning can guide efforts to identify physical and/or biological mechanisms underlying the patterns revealed by the HAB Index. Although A. fundyense cyst survey data (limited to 9 years) do not span the entire interval of the shellfish toxicity records, this analysis leads us to hypothesize that major changes in the abundance of A. fundyense cysts may be a primary factor contributing to the decadal trends in shellfish toxicity in this region. The HAB Index approach taken here is simple but represents a novel and potentially useful tool for resource managers in many areas of the world subject to toxic HABs.

Anderson, Donald M.; Couture, Darcie A.; Kleindinst, Judith L.; Keafer, Bruce A.; McGillicuddy, Dennis J., Jr.; Martin, Jennifer L.; Richlen, Mindy L.; Hickey, J. Michael; Solow, Andrew R.

2014-05-01

163

Empirical temperature-based estimates of variability in the oceanic uptake of CO2 over the past 2 decades  

NASA Astrophysics Data System (ADS)

We infer the year-to-year variability of net global air-sea CO2 fluxes from observed interannual changes in wind speed and estimated differences in CO2 partial pressure between surface seawater (pCO2SW) and the overlying atmosphere. Changes in pCO2SW are estimated from changes in sea surface temperature via seasonal algorithms that relate pCO2SW to sea surface temperature. Our diagnostic model yields an interannual variability of ±0.18 petagrams (1?, Pg = 1015 grams) of carbon per year for the period 1982-2001. El Niño Southern Oscillation-induced changes in the equatorial efflux contribute approximately 70% of the diagnostic modeled global variability. Regional flux anomalies for areas outside the equatorial Pacific are found to neither systematically reinforce nor counteract each other during times of transition from El Niño years to normal years. The interannual variability of ±0.18 Pg C yr-1 obtained in the present work is at the low end of previous estimates that falls in the range of ±0.2 to ±0.5 Pg C yr-1. Of the previous estimates, lower values are generally estimated from global ocean circulation-biogeochemical models, while higher values are derived from atmospheric inversion models constrained by atmospheric CO2 observations. Comparisons of our modeled results with two time series data sets and equatorial Pacific data suggest that our diagnostic model is not able to capture the full range of pCO2SW variations; this is probably due to the inability of the empirical model to fully account for changes in surface pCO2SW related to ocean biological and physical processes. The small interannual variability in our modeled fluxes suggests that observed year-to-year variations in the rate of atmospheric CO2 increase are primarily caused by changes in the rate of CO2 uptake by the land biosphere.

Park, Geun-Ha; Lee, Kitack; Wanninkhof, Rik; Feely, Richard A.

2006-07-01

164

Spectroscopic Observations of Twenty-one Faint Cataclysmic Variables Candidates  

E-print Network

We provide the first minimum light spectroscopic observations for 21 previously known or suspected faint cataclysmic variable candidates. The sources were selected from the Downes et al. (2001) living edition catalog and the identified candidates have minimum light magnitudes of V~18-22. We confirm 15 of the candidates to be cataclysmic variables.

E. Mason; S. B. Howell

2003-03-03

165

Bayesian Network Models for Local Dependence among Observable Outcome Variables  

ERIC Educational Resources Information Center

Bayesian network models offer a large degree of flexibility for modeling dependence among observables (item outcome variables) from the same task, which may be dependent. This article explores four design patterns for modeling locally dependent observations: (a) no context--ignores dependence among observables; (b) compensatory context--introduces…

Almond, Russell G.; Mulder, Joris; Hemat, Lisa A.; Yan, Duanli

2009-01-01

166

The Tropical Ocean-Global Atmosphere observing system: A decade of progress  

Microsoft Academic Search

A major accomplishment of the recently completed Tropical Ocean-Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal-to-interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database.

Michael J. McPhaden; Antonio J. Busalacchi; Robert Cheney; Jean-René Donguy; Kenneth S. Gage; David Halpern; Ming Ji; Paul Julian; Gary Meyers; Gary T. Mitchum; Pearn P. Niiler; Joel Picaut; Richard W. Reynolds; Neville Smith; Kensuke Takeuchi

1998-01-01

167

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

168

Bayesian estimation of nonlinear Markovian variables by partial observation  

NASA Astrophysics Data System (ADS)

A general formulation is made on the Bayesian estimation of the nonlinear Markovian variables, x and y being subject to the master equation. It is assumed that only the variable y can be observed. The evolution equation of the conditional probability density p(x,t|yt',ti<=t'<=t) of x is derived, which forcasts the value of x at the time t upon knowing the observations yt' performed on the variable y in the time interval from the initial time ti to the present time t. The formulation is applied to nonlinear diffusion processes.

Agu, Masahiro; Yamanaka, Kazuo

1983-12-01

169

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

NASA Technical Reports Server (NTRS)

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 ccres of relaxed systems. They reveal the structure and strength of the intracluster magnetic fields and constrain the ICM viscosity a combined with radio data, these observations also shed light on the production of ultra-relativistic 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

2012-01-01

170

Monitoring multi-decadal satellite earth observation of soil moisture using era-land global land water resources dataset  

NASA Astrophysics Data System (ADS)

It has been widely recognized that soil moisture is one of the main drivers of the water, energy and carbon cycles. It is a crucial variable for Numerical Weather Prediction (NWP) and climate projections because it plays a key role in hydro-meteorological processes. A good representation of soil moisture conditions can help improving the forecasting of precipitation, temperature, droughts and floods. For many applications global or continental scale soil moisture maps are needed. As a consequence, a signi?cant amount of studies have been conducted to obtain such information. For that purpose, land surface modeling, remote sensing techniques or a combination of both through Land Data Assimilation Systems are used. Assessing the quality of these products is required and for instance, the release of a new -long term- harmonized soil moisture product (SM-MW hereafter) from remote sensing within the framework of the European Space Agency's Water Cycle Multi-mission Observation Strategy (WACMOS) and Climate Change Initiative (CCI) projects in 2012 (more information at http://www.esa-soilmoisture-cci.org/) triggered several evaluation activities. The typical validation approach for model and satellite based data products is to compare them to in situ observations. However the evaluation of soil moisture products using ground measurements is not trivial. Even if in the recent years huge efforts were made to make such observations available in contrasting biomes and climate conditions, long term and large scale ground measurements networks are still sparse. Additionally, different networks will present different characteristics (e.g. measurement methods, installation depths and modes, calibration techniques, measurement interval, and temporal and spatial coverage). Finally using in situ measurements, the quality of retrieved soil moisture can be accurately assessed for the locations of the stations. That is why it is of interest to conceive new validation methods, complementing the existing soil moisture networks. To do so Land Surface Models (LSM) can be used to upscale the in situ surface soil moisture observations and complete the evaluation of satellite derived products, assuming that land surface models, forced with high quality atmospheric forcing data, adequately capture the soil moisture temporal dynamic. In this study, SM-MW is first evaluated using ground measurements of soil moisture over 2007-2010. Along with SM-MW, soil moisture from two revised re-analyses; ERA-Land, an update of the land surface component of the ERA-Interim reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) and MERRA-Land, an enhanced land surface data product based on MERRA reanalysis by the National Aeronautics and Space Administration (NASA) were evaluated, also. In situ measurements from almost 200 stations from five networks in different countries (USA, Spain, France, China and Australia) were considered. Then soil moisture from ERA-Land, is used to monitor at a global scale the consistency of SM-MW over multi-decadal time period (1980-2010).

Albergel, Clement; Dorigo, Wouter; Balsamo, Gianpaolo; de Rosnay, Patricia; Muñoz-Sabater, Joaquin; Isaksen, Lars; Brocca, Luca; de Jeu, Richard; Wagner, Wolfgang

2014-05-01

171

Comparison of optical observational capabilities for the coming decades: ground versus space  

Microsoft Academic Search

Ground-based adaptive optics (AO) in the infrared has made exceptional advances in approaching space-like image quality at higher collecting area. Optical-wavelength applications are now also growing in scope. We therefore provide here a comparison of the pros and cons of observational capabilities from the ground and from space at optical wavelengths. With an eye towards the future, we focus on

Roeland van der Marel; Remi Soummer; Anton Koekemoer; Harry Ferguson; Marc Postman; Donald T. Gavel; Olivier Guyon; Douglas Simons; Wesley A. Traub

2009-01-01

172

Near-infrared observations of the variable crab nebula  

NASA Astrophysics Data System (ADS)

We present three near-infrared NIR observations of the Crab Nebula obtained with CISCO on the Subaru Telescope and Quick Infrared Camera on the University of HAWAII 88 inch Telescope The observations were performed on 2004 September 2005 February and 2005 October and were coordinated with X-ray observations obtained with the Chandra X-ray observatory within 10 days As shown in previous optical and X-ray monitoring observations outward-moving wisps and variable knots are detected also in our NIR observations The NIR variations are closely correlated with variations in the X-ray observations indicating that both variations are driven by the same physical process We discuss the origin of NIR-emitting particles based on the temporal variations as well as the spectral energy distributions of each variable component

Yamamoto, M.; Mori, K.; Shibata, S.; Tsujimoto, M.; Misawa, T.; Burrows, D.; Kawai, N.

173

Coral luminescence identifies the Pacific Decadal Oscillation as a primary driver of river runoff variability impacting the southern Great Barrier Reef.  

PubMed

The Pacific Decadal Oscillation (PDO) is a large-scale climatic phenomenon modulating ocean-atmosphere variability on decadal time scales. While precipitation and river flow variability in the Great Barrier Reef (GBR) catchments are sensitive to PDO phases, the extent to which the PDO influences coral reefs is poorly understood. Here, six Porites coral cores were used to produce a composite record of coral luminescence variability (runoff proxy) and identify drivers of terrestrial influence on the Keppel reefs, southern GBR. We found that coral skeletal luminescence effectively captured seasonal, inter-annual and decadal variability of river discharge and rainfall from the Fitzroy River catchment. Most importantly, although the influence of El Niño-Southern Oscillation (ENSO) events was evident in the luminescence records, the variability in the coral luminescence composite record was significantly explained by the PDO. Negative luminescence anomalies (reduced runoff) were associated with El Niño years during positive PDO phases while positive luminescence anomalies (increased runoff) coincided with strong/moderate La Niña years during negative PDO phases. This study provides clear evidence that not only ENSO but also the PDO have significantly affected runoff regimes at the Keppel reefs for at least a century, and suggests that upcoming hydrological disturbances and ecological responses in the southern GBR region will be mediated by the future evolution of these sources of climate variability. PMID:24416214

Rodriguez-Ramirez, Alberto; Grove, Craig A; Zinke, Jens; Pandolfi, John M; Zhao, Jian-xin

2014-01-01

174

Coral Luminescence Identifies the Pacific Decadal Oscillation as a Primary Driver of River Runoff Variability Impacting the Southern Great Barrier Reef  

PubMed Central

The Pacific Decadal Oscillation (PDO) is a large-scale climatic phenomenon modulating ocean-atmosphere variability on decadal time scales. While precipitation and river flow variability in the Great Barrier Reef (GBR) catchments are sensitive to PDO phases, the extent to which the PDO influences coral reefs is poorly understood. Here, six Porites coral cores were used to produce a composite record of coral luminescence variability (runoff proxy) and identify drivers of terrestrial influence on the Keppel reefs, southern GBR. We found that coral skeletal luminescence effectively captured seasonal, inter-annual and decadal variability of river discharge and rainfall from the Fitzroy River catchment. Most importantly, although the influence of El Niño-Southern Oscillation (ENSO) events was evident in the luminescence records, the variability in the coral luminescence composite record was significantly explained by the PDO. Negative luminescence anomalies (reduced runoff) were associated with El Niño years during positive PDO phases while positive luminescence anomalies (increased runoff) coincided with strong/moderate La Niña years during negative PDO phases. This study provides clear evidence that not only ENSO but also the PDO have significantly affected runoff regimes at the Keppel reefs for at least a century, and suggests that upcoming hydrological disturbances and ecological responses in the southern GBR region will be mediated by the future evolution of these sources of climate variability. PMID:24416214

Rodriguez-Ramirez, Alberto; Grove, Craig A.; Zinke, Jens; Pandolfi, John M.; Zhao, Jian-xin

2014-01-01

175

Outbreaks of mumps: an observational study over two decades in a single hospital in Korea  

PubMed Central

Purpose The introduction of the mumps vaccine has dramatically reduced the number of mumps cases, but outbreaks have recently occurred among highly vaccinated populations in developed countries. Epidemiological and clinical characteristics of patients with mumps admitted between 1989 and 2012 in a single hospital in Korea are described in the present study. Methods We retrospectively evaluated inpatients with mumps between 1989 and 2012 and outpatients and inpatients with mumps in 2011-2012. Results A total of 152 patients with mumps were admitted between 1989 and 2012, and 163 patients were recorded in 2011-2012. The highest number of admitted cases occurred in 1998 and 2012 (35 and 34 cases, respectively). Among the patients admitted in 2011-2012, the highest frequency was observed among people aged 15-19 years, and low frequency was observed in those aged <4 years and >20 years, compatible to the city data and national data. In patients admitted to our department in 1998 (35 cases) and in 2010-2012 (27 cases), there were significant differences in the mean age and the rate of secondary measles-mumps-rubella (MMR) vaccination, but had similar clinical features, including complications, except aseptic meningitis. Antimumps immunoglobulin (Ig) G was positive in 83% and 100%, and IgM was positive in 67% and 41%, respectively, in the two periods. Conclusion In Korea, recent mumps outbreaks have occurred mainly among secondary school students who received two doses of the MMR vaccine. The vaccinees might have a modified immune reaction to viral insults, manifesting modified epidemiological and clinical features. PMID:25324865

Ryu, Ji-Ung; Kim, Eun-Kyung; Youn, You-Sook; Rhim, Jung-Woo

2014-01-01

176

Observations of variable stars in the globular cluster M80  

NASA Astrophysics Data System (ADS)

Observations of the globular cluster M80 obtained between 1939 and 1987 are examined. The observations have resulted in the discovery of ten variable stars in or near the cluster. The colors and periods of these variable stars are discussed. For the nine stars with known periods, blue light curves are obtained. The light curves of the five variables farthest from the cluster center are obtained. Consideration is given to the shape of the light curve and position in the period-luminosity diagram of V1, a W Virginis star whose light curve and period have not changed over the 50 yrs of observations. Also, the nova T Sco 1860 is discussed, noting the possibility of searching for the nova using modern technology.

Wehlau, Amelia; Butterworth, Steve; Hogg, Helen Sawyer

1990-04-01

177

Comparison of optical observational capabilities for the coming decades: ground versus space  

E-print Network

Ground-based adaptive optics (AO) in the infrared has made exceptional advances in approaching space-like image quality at higher collecting area. Optical-wavelength applications are now also growing in scope. We therefore provide here a comparison of the pros and cons of observational capabilities from the ground and from space at optical wavelengths. With an eye towards the future, we focus on the comparison of a ~30m ground-based telescope with an 8-16m space-based telescope. We review the current state-of-the-art in AO, and summarize the expected future improvements in image quality, field of view, contrast, and low-wavelength cut-off. We discuss the exciting advances in extreme AO for exoplanet studies and explore what the theoretical limitations in achievable contrast might be. Our analysis shows that extreme AO techniques face both fundamental and technological hurdles to reach the contrast of 1E-10 necessary to study an Earth-twin at 10 pc. Based on our assessment of the current state-of-the-art, the ...

Mountain, Matt; Soummer, Remi; Koekemoer, Anton; Ferguson, Harry; Postman, Marc; Gavel, Donald T; Guyon, Olivier; Simons, Douglas; Traub, Wesley A

2009-01-01

178

Bayesian adaptive estimation under a random cost of observation associated with each observable variable #  

E-print Network

Bayesian adaptive estimation under a random cost of observation associated with each observable to Bayesian adaptive estimation. We extend the framework to situations where each observable variable is associated with a certain random cost of observation and consider the goal of maximizing the expected utility

Jyväskylä, University of

179

Bayesian adaptive estimation under a random cost of observation associated with each observable variable  

E-print Network

Bayesian adaptive estimation under a random cost of observation associated with each observable to Bayesian adaptive estimation. We extend the framework to situations where each observable variable is associated with a certain random cost of observation and consider the goal of maximizing the expected utility

Jyväskylä, University of

180

Contrasting aerosol trends over South Asia during the last decade based on MODIS observations  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols over south Asia constitute a major environmental and climate issue. Thus, extensive land and cruise campaigns have been conducted over the area focusing on investigating the aerosol properties and climate implications. Except from the ground-based instrumentation, several studies dealt with analyzing the aerosol properties from space, focusing mainly on the spatial distribution of the aerosol optical depth (AOD) and possible feedbacks of aerosols on the monsoon system. However, except from some works using ground-based instrumentation or satellite observations over a specific region, there is lack of studies dealing with monitoring of the aerosol trend over south Asia. The present work analyzes the variations and trends in aerosol load over south Asia using Terra-MODIS AOD550 data in the period 2000-2009. Overall, an increasing trend of 10.17 % in AOD is found over whole south Asia, which exhibits large spatio-temporal variation. More specifically, the AOD550 increasing trend is more pronounced in winter, and especially over northern India. The present study shows an evidence of a decreasing AOD550 trend over the densely-populated Indo-Gangetic Plains (IGP) during the period April-September, which has never been reported before. This decreasing trend is not statistically significant and leads to an AOD change of -0.01 per year in June, when the dust activity is at its maximum. The AOD decrease seems to be attributed to weakness of dust activity in the northwest of India, closely associated with expansion of the vegetated areas and increase in precipitation over the Thar desert. Similarly, GOCART simulations over south Asia show a pronounced decreasing trend in dust AOD in accordance with MODIS. However, much more analysis and longer dataset are required for establishing this evidence.

Kaskaoutis, D. G.; Kharol, S. K.; Sinha, P. R.; Singh, R. P.; Badarinath, K. V. S.; Mehdi, W.; Sharma, M.

2011-08-01

181

A DECADE OF SOLAR TYPE III RADIO BURSTS OBSERVED BY THE NANCAY RADIOHELIOGRAPH 1998-2008  

SciTech Connect

We present a statistical survey of almost 10,000 radio type III bursts observed by the Nancay Radioheliograph from 1998 to 2008, covering nearly a full solar cycle. In particular, sources sizes, positions, and fluxes were examined. We find an east-west asymmetry in source positions that could be attributed to a 6 Degree-Sign {+-} 1 Degree-Sign eastward tilt of the magnetic field, that source FWHM sizes s roughly follow a solar-cycle-averaged distribution (dN/ds) Almost-Equal-To 14 {nu}{sup -3.3} s {sup -4} arcmin{sup -1} day{sup -1}, and that source fluxes closely follow a solar-cycle-averaged (dN/ds {sub {nu}}) Almost-Equal-To 0.34 {nu}{sup -2.9} S {sup -1.7} {sub {nu}} sfu{sup -1} day{sup -1} distribution (when {nu} is in GHz, s in arcminutes, and S {sub {nu}} in sfu). Fitting a barometric density profile yields a temperature of 0.6 MK, while a solar wind-like ({proportional_to}h {sup -2}) density profile yields a density of 1.2 Multiplication-Sign 10{sup 6} cm{sup -3} at an altitude of 1 R{sub S} , assuming harmonic emission. Finally, we found that the solar-cycle-averaged radiated type III energy could be similar in magnitude to that radiated by nanoflares via non-thermal bremsstrahlung processes, and we hint at the possibility that escaping electron beams might carry as much energy away from the corona as is introduced into it by accelerated nanoflare electrons.

Saint-Hilaire, P. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)] [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Vilmer, N.; Kerdraon, A., E-mail: shilaire@ssl.berkeley.edu [LESIA, Observatoire de Paris, CNRS, UPMC, Universite Paris-Diderot 5 place Jules Janssen, F-92195 Meudon (France)

2013-01-01

182

Trends and variability in East African rainfall and temperature observations  

NASA Astrophysics Data System (ADS)

The economy of East Africa is highly dependent on agriculture, leading to a strong vulnerability of local society to fluctuations in seasonal rainfall amounts, including extreme events. Hence, the knowledge about the evolution of seasonal rainfall under future climate conditions is crucial. Rainfall regimes over East Africa are influenced by multiple factors, including two monsoon systems, several convergence zones and the Rift Valley lakes. In addition, local conditions, like topography, modulate the large-scale rainfall pattern. East African rainfall variability is also influenced by various teleconnections like the Indian Ocean Zonal Mode and El Niño Southern Oscillation. Regarding future climate projections, regional and global climate models partly disagree on the increase or decrease of East African rainfall. The specific aim of the present study is the acquirement of historic data from weather stations in East Africa (Kenya, Tanzania, Ruanda and Uganda), the use of gridded satellite (rainfall) products (ARC2 and TRMM), and three-dimensional atmospheric reanalysis (e.g., ERA-Interim) to quantify climate variability in the recent past and to understand its causes. Climate variability and trends, including changes in extreme events, are evaluated using ETCCDI climate change and standardized precipitation indices. These climate indices are determined in order to investigate the variability of temperature and rainfall and their trends with the focus on most recent decades. In the follow-up, statistical and dynamical analyses are conducted to quantify the local impact of pertinent large-scale modes of climate variability (Indian Ocean Zonal Mode, El Niño Southern Oscillation, Sea Surface Temperature of the Indian Ocean).

Seregina, Larisa; Ermert, Volker; Fink, Andreas H.; Pinto, Joaquim G.

2014-05-01

183

Observational Evidence for a Decade-long climate optimum near the Hesperian/Amazonian Transition  

NASA Astrophysics Data System (ADS)

Hesperian to Amazonian-aged valleys (HAVs) are predominantly found in the southern equatorial and mid-latitudes of Mars and form parallel to dendritic networks. These features record a significant warming of the regional/global climate which may have been associated with outflow channel formation and/or a period of alluvial fan deposition in Margaritifer Terra [1]. HAVs are distinct from older valley networks in both their age and morphology and they provide a window into the past climate conditions and potential water sources which formed them. Using quantitative geomorphic analysis we calculate the expected range of timescales, water volumes, precipitation rates and atmospheric conditions which contributed to HAV formation. In Newton crater (40oS, -159oE) we measured valley widths, depths, slopes and alluvial fan volumes. These observations, when combined with a set of terrestrial sediment transport prediction functions [2,3,4,5], allow us to calculate an expected duration of fluvial activity ranging from 0.1 to 10 years for water-filled channel depths ranging between 20 and 130 cm, and median sediment grain size ranging from 1 mm to 10 cm. The water volume required to form a single HAV in Newton crater ranges between 1.8 and 5.7~km3 based on the Darcy-Weisbach equation [6] in combination with the aforementioned range in channel depths, grain sizes and formation timescales. These results imply water runoff rates of between 1 to 10~cm/day over a typical, 300~km2, drainage area. Such a high runoff rate and short formation time suggest a brief, dramatic regional to global climate excursion. The source of water which formed these features remains unclear, but it must have been released at the aforementioned rates, and was widely distributed within each drainage catchment, and regionally over Newton crater and the southern highlands. HAV formation was likely a two-step process involving, first, the deposition of a 10s of meters thick regional snowpack along topographic highs sourced either from polar ice redistributed during high obliquity, or by one or more outflow channel water release events. The atmospheric temperature gradient required to generate preferential ice deposition on topographic highs implies a much thicker (few hundred millibars [7]) atmosphere. Next, a significant (perhaps, brief) global warming event melted these snowpacks. Likely warming mechanisms include the formation of a ~100 km impact crater or a short-lived SO2 greenhouse generated from a rapid, voluminous volcanic dike injection such as that which formed Sirenum Fossae [8]. [1] Grant, J., & Wilson, S. (2011), Geophys. Res. Lett., 38. [2] Smart, G. (1984), J. Hydraulic Eng., 110, 267-276. [3] Meyer-Peter, E. & Mueller, R. (1948) in Int. Assoc. for Hydraul. Struct. Res., vol. 2, pp. 39-64, Stockholm. [4] Parker, G., Klingeman, P. & McLean, D. (1982) J. Hydraul. Eng., 108(HY4), 544-571. [5] Ribberink, J. S. (1998), Coastal Eng., 34, 59-82. [6] Silberman, E., Einstein, H., Hinds, J., Powell, R., et al. (1963), J. Hydraul. Eng., 89(HY2), 97-143. [7] Wordsworth, R., Forget, F., Millour, E., Head, J., Madeleine, J.-B. & Charnay, B. (submitted), Icarus. [8] Wilson, L., & Head, J. (2002), J. Geophys. Res., 107.

Parsons, R.; Moore, J. M.; Howard, A. D.

2012-12-01

184

Ginga and ROSAT observations of the cataclysmic variable S193  

NASA Technical Reports Server (NTRS)

The cataclysmic variable S193 was observed with the Ginga and ROSAT satellites, along with ground-based optical observations. The bremsstrahlung temperatures and the column densities derived from these two observations are noticeably different. However, since the observations were separated by 3 yr and took place at different optical magnitudes, it is not clear whether this is related to an intrinsic change in the system or to a two component source of X-rays. While the X-ray data are not sufficient to accomplish a detailed analysis for periodicities, the Ginga data place an upper limit of 40% on the amplitude of any sinusoidal modulation.

Szkody, Paula; Garnavich, Peter; Castelaz, Michael; Makino, F.

1994-01-01

185

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

186

Understanding selection effects in observed samples of cataclysmic variables  

NASA Astrophysics Data System (ADS)

Large differences between the properties of the known sample of cataclysmic variable stars (CVs) and the predictions of the theory of binary star evolution have long been recognised. However, because all existing CV samples suffer from strong selection effects, observational bias must be considered before it is possible to tell whether there is an inconsistency, which would imply a failure of the evolutionary model. We have modelled common selection effects and illustrate their influence on observed CV samples.

Pretorius, Magaretha L.; Knigge, Christian; Kolb, Ulrich

2007-08-01

187

Variability of the Mindanao Current: Mooring observation results  

Microsoft Academic Search

Mooring observations were conducted from October 1999 to July 2002 near the east coast of Mindanao Island, the Philippines, (6°50?N, 126°43?E) to observe current variability at the axis of the Mindanao Current (MC). The MC was a strong current with a subsurface velocity maximum exceeding 1.3 m s?1 at approximately 100 m depth. The MC flows shallower than 700 m,

Yuji Kashino; Akio Ishida; Yoshifumi Kuroda

2005-01-01

188

Variability of the Mindanao Current: Mooring observation results  

Microsoft Academic Search

Mooring observations were conducted from October 1999 to July 2002 near the east coast of Mindanao Island, the Philippines, (6°50'N, 126°43'E) to observe current variability at the axis of the Mindanao Current (MC). The MC was a strong current with a subsurface velocity maximum exceeding 1.3 m s-1 at approximately 100 m depth. The MC flows shallower than 700 m,

Yuji Kashino; Akio Ishida; Yoshifumi Kuroda

2005-01-01

189

Variability of Arctic Sea Ice as Determined from Satellite Observations  

NASA Technical Reports Server (NTRS)

The compiled, quality-controlled satellite multichannel passive-microwave record of polar sea ice now spans over 18 years, from November 1978 through December 1996, and is revealing considerable information about the Arctic sea ice cover and its variability. The information includes data on ice concentrations (percent areal coverages of ice), ice extents, ice melt, ice velocities, the seasonal cycle of the ice, the interannual variability of the ice, the frequency of ice coverage, and the length of the sea ice season. The data reveal marked regional and interannual variabilities, as well as some statistically significant trends. For the north polar ice cover as a whole, maximum ice extents varied over a range of 14,700,000 - 15,900,000 sq km, while individual regions experienced much greater percent variations, for instance, with the Greenland Sea having a range of 740,000 - 1,110,000 sq km in its yearly maximum ice coverage. In spite of the large variations from year to year and region to region, overall the Arctic ice extents showed a statistically significant, 2.80% / decade negative trend over the 18.2-year period. Ice season lengths, which vary from only a few weeks near the ice margins to the full year in the large region of perennial ice coverage, also experienced interannual variability, along with spatially coherent overall trends. Linear least squares trends show the sea ice season to have lengthened in much of the Bering Sea, Baffin Bay, the Davis Strait, and the Labrador Sea, but to have shortened over a much larger area, including the Sea of Okhotsk, the Greenland Sea, the Barents Sea, and the southeastern Arctic.

Parkinson, Claire L.

1999-01-01

190

Variability of the Mindanao Current: Mooring observation results  

NASA Astrophysics Data System (ADS)

Mooring observations were conducted from October 1999 to July 2002 near the east coast of Mindanao Island, the Philippines, (6°50'N, 126°43'E) to observe current variability at the axis of the Mindanao Current (MC). The MC was a strong current with a subsurface velocity maximum exceeding 1.3 m s-1 at approximately 100 m depth. The MC flows shallower than 700 m, and there was no evidence of a steady northward current (the Mindanao Undercurrent) at the study location. Compared with the large average velocity, MC variability was low (standard deviation <0.2 m s-1 for all directions). All the observed interannual, seasonal, and intraseasonal variations in the MC were of comparable amplitude. The MC was strong during boreal summers and during the onset of the 2002-03 El Niño. The core velocity of the MC at approximately 100 m was correlated with the sea level difference between Cebu, Philippines and Malakal, Palau.

Kashino, Yuji; Ishida, Akio; Kuroda, Yoshifumi

2005-09-01

191

Cataclysmic variables to be monitored for HST observations  

NASA Astrophysics Data System (ADS)

Drs. Boris Gaensicke (Warwick University), Joseph Patterson (Columbia University, Center for Backyard Astrophysics), and Arne Henden (AAVSO), on behalf of a consortium of 16 astronomers, requested the help of AAVSO observers in monitoring the ~40 cataclysmic variables in support of Hubble Space Telescope observations in the coming months. The HST COS (Cosmic Origins Spectrograph) will be carrying out far-ultraviolet spectroscopy of ~40 CVs sequentially, with the aim to measure the temperatures, atmospheric compositions, rotation rates, and eventually masses of their white dwarfs. The primary purpose of the monitoring is to know whether each target is in quiescence immediately prior to the observation window; if it is in outburst it will be too bright for the HST instrumentation. Based on the information supplied by the AAVSO, the HST scheduling team will make the decision (usually) the evening before the scheduled observing time as to whether to go forward with the HST observations. For CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. B filter would be best for a light curve, although for the magnitude estimates, V would be best. Finder charts may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. If the target is seen in outburst, please contact the AAVSO immediately and post a message to the Observations and Campaigns & Observations Reports forum (http://www.aavso.org/forum). This campaign will run the better part of a year or longer. See full Alert Notice for more details and list of objects.

Waagen, Elizabeth O.

2012-09-01

192

Satellite Observed Variability in Antarctic and Arctic Surface Temperatures and Their Correlation to Open Water Areas  

NASA Technical Reports Server (NTRS)

Recent studies using meterological station data have indicated that global surface air temperature has been increasing at a rate of 0.05 K/decade. Using the same set of data but for stations in the Antarctic and Arctic regions (>50 N) only, the increases in temperature were 0.08, and 0.22 K/decade, when record lengths of 100 and 50 years, respectively, were used. To gain insights into the increasing rate of warming, satellite infrared and passive microwave observations over the Arctic region during the last 20 years were processed and analyzed. The results show that during this period, the ice extent in the Antarctic has been increasing at the rate of 1.2% per decade while the surface temperature has been decreasing at about 0.08 K per decade. Conversely, in the Northern Hemisphere, the ice extent has been decreasing at a rate of 2.8% per decade, while the surface temperatures have been increasing at the rate of 0.38 K per decade. In the Antarctic, it is surprising that there is a short term trend of cooling during a global period of warming. Very large anomalies in open water areas in the Arctic were observed especially in the western region, that includes the Beaufort Sea, where the observed open water area was about 1x10(exp 6) sq km, about twice the average for the region, during the summer of 1998. In the eastern region, that includes the Laptev Sea, the area of open water was also abnormally large in the summer of 1995. Note that globally, the warmest and second warmest years in this century, were 1998 and 1995, respectively. The data, however, show large spatial variability with the open water area distribution showing a cyclic periodicity of about ten years, which is akin to the North Atlantic and Arctic Oscillations. This was observed in both western and eastern regions but with the phase of one lagging the other by about two years. This makes it difficult to interpret what the trends really mean. But although the record length of satellite data is still relatively short and the climate trend difficult to establish, the immediate impact of a continued warming trend may be very profound.

Comiso, Josefino C.; Zukor, Dorothy (Technical Monitor)

2000-01-01

193

Variable-Structure Disturbance Observers for Harmonic Drive Actuators  

Microsoft Academic Search

This paper presents the design of a high-order variable-structure disturbance observer (VSDO) that yields asymptotic estimation of unknown disturbances described by polynomial functions of time with arbitrary degrees. In comparison with conventional VSDO, the high-order VSDO requires a small switching gain for ensuring the existence of a sliding mode, thus diminishing the chattering phenomenon further. Two high-order VSDOs were implemented

Yu-Sheng Lu; Chi-Sheng Hwang

2007-01-01

194

A Preliminary Observational Search for Circumbinary Disks Around Cataclysmic Variables  

E-print Network

Circumbinary (CB) disks have been proposed as a mechanism to extract orbital angular momentum from cataclysmic variables (CVs) during their evolution. As proposed by Taam & Spruit, these disks extend outwards to several a.u. and should be detected observationally via their infrared flux or by absorption lines in the ultraviolet spectra of the CV. We have made use of archival HST/STIS spectra as well as our own near-IR imaging to search for observational evidence of such CB disks in seven CVs. Based on the null result, we place an upper limit on the column density of the disk of N_H~10^17 cm^-2.

K. E. Belle; N. Sanghi; S. B. Howell; J. B. Holberg; P. T. Williams

2004-03-31

195

Decadal- and Centennial-Scale Variability in Sea Surface Temperature in Beppu Bay in Japan During the Last 2900 Years  

NASA Astrophysics Data System (ADS)

We generated 8-year-resolution records of paleotemperatures using UK37? and TEX86 and discuss the decadal and centennial changes in winter and summer sea surface temperatures (SSTs) in Beppu Bay, Kyushu Island, Japan. Beppu Bay is a silled basin filled with oxygen-deficient bottom water. Because of anoxic environment, organic matter is well preserved in sediments and bioturbation is limited. Fourteen piston and gravity cores were retrieved at the center of the basin. Correlation of cores was conducted using sand and silt seams, and the age-depth model was created by wiggle-matching of forty-two AMS radiocarbon dates from bivalve mollusk shells and excess Pb-210 and Cs-137 concentrations. The sedimentation rates were 230-300 cm/ky. TEX86 and UK37? records show different patterns, but both have a similar multi-decadal periodicity. The temperature estimated by TEX86 at the core-top sample is lower than mean annual SST, implying that TEX86 reflects the SST weighted in winter. That by UK37? corresponds to the SST weighted in summer. UK37? shows multi-decadal and centennial-scale variation interrupted by frequent short-term cool periods. The periods corresponded to volcanic eruptions recorded in a Greenland ice core. TEX86 shows multi-decadal variation that is consistent with a proxy PDO record reconstructed from North American tree-rings. Beppu Bay sediments are a good climate archive to provide high-resolution summer and winter SST records in the northwestern Pacific region.

Yamamoto, M.; Kuwae, M.; Abe, M.; Ichikawa, N.

2012-12-01

196

Regional Variability in Tropical Convection: Observations from TRMM.  

NASA Astrophysics Data System (ADS)

Observation of the vertical profile of precipitation over the global Tropics is a key objective of the Tropical Rainfall Measuring Mission (TRMM) because this information is central to obtaining vertical profiles of latent heating. This study combines both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine `wet-season' vertical structures of tropical precipitation across a broad spectrum of locations in the global Tropics. TRMM-PR reflectivity data (2A25 algorithm) were utilized to produce seasonal mean three-dimensional relative frequency histograms and precipitation ice water contents over grid boxes of approximately 5°-10° in latitude and longitude. The reflectivity histograms and ice water contents were then combined with LIS lightning flash densities and 2A25 mean rainfall rates to examine regional relationships between precipitation vertical structure, precipitation processes, and lightning production.Analysis of the reflectivity vertical structure histograms and lightning flash density data reveals that 1) relative to tropical continental locations, wet-season isolated tropical oceanic locations exhibit relatively little spatial (and in some instances seasonal) variability in vertical structure across the global Tropics; 2) coastal locations and areas located within 500-1000 km of a continent exhibit considerable seasonal and spatial variability in mean vertical structure, often resembling `continental' profiles or falling intermediate to that of tropical continental and isolated oceanic regimes; and 3) interior tropical continental locations exhibit marked variability in vertical structure both spatially and seasonally, exhibiting a continuum of characteristics ranging from a near-isolated oceanic profile observed over the central Amazon and India to a more robust continental profile observed over regions such as the Congo and Florida. Examination of regional and seasonal mean conditional instability for a small but representative subset of the geographic locations suggests that tropospheric thermodynamic structure likely plays a significant role in the regional characteristics of precipitation vertical structure and associated lightning flash density.In general, the largest systematic variability in precipitation vertical structure observed between all of the locations examined occurred above the freezing level. It is important that subfreezing temperature variability in the vertical reflectivity structures was well reflected in the seasonal mean lightning flash densities and ice water contents diagnosed for each location. In turn, systematically larger rainfall rates were observed on a pixel-by-pixel basis in locations with larger precipitation ice water content and lightning flash density. These results delineate, in a regional sense, the relative importance of mixed-phase precipitation production across the global Tropics.

Petersen, Walter A.; Rutledge, Steven A.

2001-09-01

197

Observations of ultraviolet variability in RV Tauri stars  

NASA Technical Reports Server (NTRS)

An IUE program to monitor the ultraviolet variability in RV Tauri stars was initiated. The Mg II region was investigated as a potential probe of atmospheric shocks, which are believed to be associated with the pulsational variability of this class of objects. Observations, a description of the spectra, and findings for V Vul and AC Her are presented. The Mg II emission does vary significantly during the cycle; major changes in the emission line strength occur on a time scale much less than 0.2 in phase; and as the UV (and optical) continuum flux increases, the Mg II lines decrease and increased emission may be seen at 2823, 2844, and 2900 A.

Brugel, Edward W.; Cardelli, Jason A.

1988-01-01

198

The Parana paradox: can a model explain the decadal impacts of climate variability and land-cover change?  

NASA Astrophysics Data System (ADS)

Since the 1970s, despite a decrease in rainfall, flow in the Parana river has increased. This paradox is explored using the Ecosystem Demography (ED) model. If there were no change in land cover, the modeled runoff decreased from the 1970s to the 2000s by 11.8% (with 1970 land cover) or 18.8% (with 2008 land cover). When the model is run holding climate constant, the decadal average of the modeled runoff increased by 24.4% (with the 1970s climate) or by 33.6% (with 2000s climate). When the model is run allowing both the actual climate and land-cover changes, the model gives an increase in the decadal average of runoff by 8.5%. This agrees well with 10.5% increase in the actual stream flow as measured at Itaipu. There are three main conclusions from this work. First, the ED model is able to explain a major, paradoxical, reality in the Parana basin. Second, it is necessary to take into account both climate and land use changes when exploring past or future changes in river flows. Third, the ED model, now coupled with a regional climate model (i.e., EDBRAMS), is a sound basis for exploring likely changes in river flows in major South American rivers.

Lee, E.; Moorcroft, P. R.; Livino, A.; Briscoe, J.

2013-12-01

199

Spatial and Temporal Distribution of Strain in the Sevier Desert Region from a Decade of BARGEN Continuous GPS Observations  

NASA Astrophysics Data System (ADS)

A transect of four BARGEN GPS sites from 1997-2000 at latitude 39°N revealed a linear increase in velocity from 0 mm/yr on the Colorado Plateau to ~4 mm/yr in east-central Nevada. These geodetic data, when combined with paleoseismic and neotectonic observations, were used to argue for present-day strain accumulation on the Sevier Desert detachment, a seismically-imaged, low-angle (12°) normal fault that underlies a significant portion of west central Utah [Niemi et al., 2004]. A new GPS velocity solution [Davis et al., 2006], including 5 additional years of observations and a new GPS station in the eastern half of the transect, serves to both clarify and complicate our understanding of the spatial and temporal distribution of strain in this region. Geodetic velocity gradients among the three original eastern sites (from east to west, CAST, SMEL, and FOOT), and including the new site, SPIC, located between CAST and SMEL, continue to suggest a linear strain gradient from the Colorado Plateau to westernmost Utah, on a transect spanning the Wasatch, Sevier Desert, and House Range normal faults. In contrast, the baseline between FOOT and EGAN, which underwent extension from 1997-2000, began to contract in 2000, as site EGAN slowed with respect to the Colorado Plateau. This deviation in velocity continued until 2003, when EGAN began moving westward, and has, as of 2006, returned to near its pre-2000 velocity with respect to the Colorado Plateau. The eastward excursion of GPS site EGAN is not unique, and similar excursions are observed in the time series of all BARGEN GPS sites that lie west of ~114.25°W over the time period 2000-2003 [Davis et al., 2006]. The origin of this velocity anomaly is uncertain, but the magnitude and spatial extent of the excursion, as well as the observation of a deep earthquake swarm (~30-40 km depth) coincident with dramatic motion of GPS site SLID, near Lake Tahoe, in 2003 [Smith et al., 2004] suggest a deep crustal or mantle influence on the observed GPS velocities. Bright, mid-crustal horizontal reflections observed in COCORP reflection seismic data west of 114°W have been postulated to represent a detachment that could accommodate shearing along the base of the crust in Nevada [Hauser et al., 1987], a hypothesis broadly consistent with the observed GPS velocities, with the crust shearing relatively east over the subcrustal lithosphere. A deep observatory in the Sevier Desert region, transecting the Sevier Desert detachment, would complement existing paleoseismic and neotectonic studies, and the decade of BARGEN continuous GPS observations, as well as new GPS data from 8 Earthscope Plate Boundary Observatory sites installed along this transect in the past few years. Key questions that could be assessed with a deep observatory are how slip, and strain, at depth on an inclined fault are reflected in geodetic observations of strain at the surface; whether the state of stress and strain rate on the Sevier Desert detachment change through time, as suggested by long-term periodicity in strain release as recorded in the geologic record, and what effect long-lived velocity excursions, such as observed from 2000-2003, have on the regional stress state, perhaps leading to a clearer understanding of the source of these anomalies, and the aseismic tectonic behavior of the lithosphere.

Niemi, N. A.; Wernicke, B. P.

2007-12-01

200

Subtropical Gyre Variability Observed by Ocean Color Satellites  

NASA Technical Reports Server (NTRS)

The subtropical gyres of the world are extensive, coherent regions that occupy about 40% of the surface of the earth. Once thought to be homogeneous and static habitats, there is increasing evidence that mid-latitude gyres exhibit substantial physical and biological variability on a variety of time scales. While biological productivity within these oligotrophic regions may be relatively small, their immense size makes their total contribution significant. Global distributions of dynamic height derived from satellite altimeter data, and chlorophyll concentration derived from satellite ocean color data, show that the dynamic center of the gyres, the region of maximum dynamic height where the thermocline is deepest, does not coincide with the region of minimum chlorophyll concentration. The physical and biological processes by which this distribution of ocean properties is maintained, and the spatial and temporal scales of variability associated with these processes, are analyzed using global surface chlorophyll-a concentrations, sea surface height, sea surface temperature and surface winds from operational satellite and meteorological sources, and hydrographic data from climatologies and individual surveys. Seasonal and interannual variability in the areal extent of the subtropical gyres are examined using 8 months (November 1996 - June 1997) of OCTS and nearly 5 years (September 1997 - June 02) of SeaWiFS ocean color data and are interpreted in the context of climate variability and measured changes in other ocean properties (i.e., wind forcing, surface currents, Ekman pumping, and vertical mixing). The North Pacific and North Atlantic gyres are observed to be shrinking over this period, while the South Pacific, South Atlantic, and South Indian Ocean gyres appear to be expanding.

McClain, Charles R.; Signorini, Sergio R.; Christian, James R.

2002-01-01

201

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)

SummaryThis paper investigates the spatial and temporal variability of streamflow in the Ebro river basin and its potential predictability. Principal Component Analysis applied to monthly streamflow series from 83 gauging stations distributed through the basin, reveals three homogeneous regions: Basque-Cantabrian, Pyrenees and Southern Mediterranean. Attending to this classification the main characteristic time scales of the maximum monthly streamflows are studied by Singular Spectral Analysis (SSA). Decadal variations in streamflow make particularly large contributions to year-to-year streamflow variance in stations placed in the Basque-Cantabrian and Southern Mediterranean regions, while for the Pyrenees flows the interannual contribution is more important. The predictability of the Ebro flow anomalies has been investigated using a combined methodology: at decadal time scales SST anomalies from several regions provide a significant source of predictability for the Ebro flow, while at interannual time scales autoregressive-moving-average modelling, applied to the time series previously filtered by SSA, is able to provide potential skill in forecasting. For gauging stations associated to the Basque-Cantabrian region significant correlations between the maximum monthly streamflow anomalies and a tripole-like pattern in the North Atlantic SSTs during the previous spring are found. This association is found maximum and stable for the tropical part of the pattern (approximately 0-20°N). For the gauging stations placed to the southeast of basin some influence from the Pacific Decadal Oscillation (PDO) is found. This method allows evaluating, independently, the decadal and interannual predictability of the streamflow series. In addition, the combination of both modelling techniques gives as result a methodology that has the capacity to provide basin-specific hydroclimatic predictions which vary (for the 1990-2003 validation period) between 62% for the Basque-Cantabrian region, 76% for the Southern Mediterranean and 81% for the Pyrenees. In summary, this work shows the existence of a valuable decadal and interannual predictability of the Ebro streamflow, a result which may be useful to water resources management.

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

2011-11-01

202

Sea Ice Variability in the Sea of Okhotsk from Passive Microwave Satellite Observations  

NASA Technical Reports Server (NTRS)

The Sea of Okhotsk, located between 50 and 60 N, is bounded by the Kamchatka Peninsula, Siberia, Sakhalin Island, and the Kuril Island chain and is the largest midlatitude seasonal sea ice zone in the Northern Hemisphere. The winter sea ice cover begins to form in November and expands to cover most of the sea by March. Over the following three months, the ice retreats with only small ice-covered areas remaining by the beginning of June. The sea is ice free or nearly ice free on average for six months of the year, from June through November. The recent compilation of a consistent, long-term record of Northern Hemisphere sea ice extents based on passive microwave satellite observations from the Nimbus 7 Scanning Multichannel Microwave Radiometer and from four Defense Meteorological Satellite Program Special Sensor Microwave Imagers provides the basis for assessing long-term sea ice extent variability in the Sea of Okhotsk. Analysis of this 20-year data record (1979-1998) shows that based on yearly averages the overall extent of the Sea of Okhotsk ice cover is decreasing at the rate of -8.1+/-2.1x10(exp 3) sq km/yr (-17.2%/decade), in contrast to the rate of decrease of -33.3+/-0.7x10(exp 3) sq km/yr (-2.7%/decade) for the Northern Hemisphere as a whole. There is large regional sea ice extent variability of the Arctic ice cover. Two of the nine Arctic regions analyzed, the Bering Sea and the Gulf of St. Lawrence, show increases of 0.8+/-1.4xl0(exp 3) sq km/yr (2.7%/decade) and 1.2+/-0.5xl0(exp 3) sq km/yr (17.1%/decade), respectively. Interestingly, the Sea of Okhotsk and the Gulf of St. Lawrence show about equal percentage changes, but of opposite sign. The Sea of Okhotsk exhibits its greatest percent decrease (-24.3%/decade) during spring (April-June). The year of maximum winter sea ice extent for the Sea of Okhotsk was 1979, whereas the minimum winter sea ice extent occurred in 1984.

Cavalieri, Donald J.; Zukor, Dorothy (Technical Monitor)

2000-01-01

203

Hydrological variability from gauging stations and simulated SWOT data, for major French rivers over the past decades  

NASA Astrophysics Data System (ADS)

This study was carried out in the framework of the program Surface Water and Ocean Topography (SWOT) associated to the National Center of Space Studies (CNES). Basing on discharge measurements, and simulated Surface Water and Ocean Topography (SWOT) data, we have investigated the hydrological variability of the main French rivers (Seine, Loire, Garonne and Rhône) by the use of a minimum, maximum and mean annual discharge analyses, Loess and wavelet approach (continuous wavelet analyses and wavelet coherence analyses). Results show (i) strong coherence between the four watershed discharges, varying between 73% and 92% and (ii) three different periods for hydrological variability: before 1970, between 1970 and 1990, and after 1990. From these results, simulated SWOT data and discharges are compared for these three periods using same analyses. Simulated SWOT data are obtained by re-sampling river discharges from the SWOT crossing time calculated. Simulated SWOT data can reproduce the hydrological variability of rivers despite number of SWOT passages (from two to four). These results are validated by coherence wavelet, which underlines coherence higher than 90% between simulated SWOT data and in-situ discharge. However, the results indicate that simulated SWOT data don't reproduce exactly the minimum and maximum annual discharge: (i) maximum annual SWOT data are underestimated and (ii) minimum annual SWOT data are overestimated

Chevalier, Laetitia; Laignel, Benoit; Turki, Imen; Lyard, Florent; Lion, Christine

2014-05-01

204

Ground based observations of Io plasma torus variability  

NASA Astrophysics Data System (ADS)

Jupiter is not only the largest planet in the Solar System, it also has the largest magnetosphere. Jupiter's innermost Galilean moon, Io, is the most volcanically active body in the Solar System. This volcanic activity produces tenuous atmosphere which escapes, creating the Io plasma torus, a ring of charged particles encircling Jupiter. The Io plasma torus is composed mainly of sulfur and oxygen ions. It is most dense around Io's orbit (5.6 Rj). It's observed in extreme ultraviolet (EUV) emission and in the optical. EUV emission arise from interactions between torus superthermal ("hot") electrons and ions. Optical emission comes from interaction between thermal electrons and sulfur ions. The optical emission trace the densest part of the torus, the EUV trace the hottest part of the torus. In early December, 2013, we observed the Io plasma torus at the McMath-Pierce Solar Telescope using a specially designed coronagraph in support of the JAXA EXtrem ultraviolet spectrosCope for ExophEric Dynamics (EXCEED) mission. EXCEED is observing the Io plasma torus in the EUV in a manner similar to that of the landmark observations made by the Cassini UVIS instrument in 2000. Our ground-based [SII] 6731 angstrom images provide context for the EXCEED observations. The analysis of the 2013 [SII] data is important preparation for analysis of a much larger set of observations recorded between 1997 and 2008. This large set of over 1000 images were recorded during the Galileo tour, the Cassini flyby, and the Ulysses flyby of Jupiter. The images provide context for in-situ observations, EUV images, and several new measurements of the mysterious and variable Jovian magnetospheric "system IV" period. In this work, we'll be presenting a comparison between our results and EXCEED's and the methodology which will be used for the 1000 images.

Pinho Magalhães, Fabíola; Echer, Ezequiel; Demétrio Gonzalez Alarcon, Walter; Lopes, Rosaly; Morgenthaler, Jeffrey; Echer, Mariza P. S.

205

New data-based mechanistic methodology to quantify hydrological & biogeochemical recovery following forest disturbance using observations monitored from sub-hourly to decadal time-scales (Invited)  

NASA Astrophysics Data System (ADS)

Quantifying recovery in hydrological & biogeochemical processes following forest disturbances is difficult given sensitivities of watershed systems to controlling climate dynamics at sub-daily to decadal timescales. Trends associated with forest hydrological & biogeochemical recovery can be difficult to identify where natural climate cycles at seasonal to inter-annual time-scales are present & need to be accounted for. Equally, fundamental relationships between physico-chemical processes within experimental watersheds are often unidentifiable where observations are not undertaken at a sufficiently high sampling rate e.g., sub-hourly (Kirchner et al., 2004 Hydrol Process). Consequently, the study of recovery in hydrological & biogeochemical systems requires robust analysis of both short- & long-term dynamic relationships in watersheds. We newly apply two data-based mechanistic (DBM) approaches to characterise change resulting from forest disturbance & recovery in both: (1) longer-term cycles & trends in biogeochemical variables; & (2) short-term dynamic relationships between biogeochemical & controlling hydro-climatic variables. The Unobserved Components - Dynamic Harmonic Regression (UC-DHR) modeling approach is used to quantify the longer-term trends & cycles (Chappell & Tych, 2012 Hydrol Process), while continuous time transfer function modeling is used to illustrate changes in the short-term (within storm) dynamics over the forest management cycle. The DBM philosophy is appropriate for a new focus on under-studied recovering forests because it first makes no a priori assumptions about processes that need to be described, instead uses information contained in the time-series to derive multiple statistically valid models. In the second stage of the approach only those models that also have robust hydrological &/or geochemical interpretations are accepted for further consideration of the dynamics. This study utilises the longest forest hydrological & associated biogeochemical records available in upland UK, namely those of the Plynlimon & Llyn Brianne experimental catchments, where the authors have recently supplemented these data with continuous 15-minute observations from new biogeochemical sensors. The presentation focuses on the dynamics of biogeochemical variables of hydrogen ion (H+) concentration & load for three reasons: (1) their critical role in ongoing work on stream acidification; (2) the associated threat to stream biodiversity; & (3) their role in the regulation of carbon & nitrogen release into streams. Both DBM approaches have been able to quantify change in hydrological & biogeochemical characteristics (illustrated with H+ time series) through periods demonstrating significant recovery from forest disturbance. These range from the short-term dynamic response characteristics controlling biogeochemical export during storms to inter-annual characteristics of cycles & trends within time-series. The demonstrated ability to identify changes that are greater than calculated simulation uncertainties has the potential to make a significant contribution to emerging global research on quantifying change within recovering forest systems.

Chappell, N. A.; Jones, T.

2013-12-01

206

On the use of Standardized Drought Indices under decadal climate variability: Critical assessment and drought policy implications  

NASA Astrophysics Data System (ADS)

Since the recent High Level Meeting on National Drought Policy held in Geneva in 2013, a greater concern about the creation and adaptation of national drought monitoring systems is expected. Consequently, backed by international recommendations, the use of Standardized Drought Indices (SDI), such as the Standardized Precipitation Index (SPI), as an operational basis of drought monitoring systems has been increasing in many parts of the world. Recommendations for the use of the SPI, and consequently, those indices that share its properties, do not take into account the limitations that this type of index can exhibit under the influence of multidecadal climate variability. These limitations are fundamentally related to the lack of consistency among the operational definition expressed by this type of index, the conceptual definition with which it is associated and the political definition it supports. Furthermore, the limitations found are not overcome by the recommendations for their application. This conclusion is supported by the long-term study of the Standardized Streamflow Index (SSI) in the arid north-central region of Chile, under the influence of multidecadal climate variability. The implications of the findings of the study are discussed with regard to their link to aspects of drought policy in the cases of Australia, the United States and Chile.

Núñez, J.; Rivera, D.; Oyarzún, R.; Arumí, J. L.

2014-09-01

207

Observations of Thermal Flare Plasma with the EUV Variability Experiment  

NASA Astrophysics Data System (ADS)

One of the defining characteristics of a solar flare is the impulsive formation of very high temperature plasma. The properties of the thermal emission are not well understood, however, and the analysis of solar flare observations is often predicated on the assumption that the flare plasma is isothermal. The EUV Variability Experiment (EVE) on the Solar Dynamics Observatory provides spectrally resolved observations of emission lines that span a wide range of temperatures (e.g., Fe XV-Fe XXIV) and allow for thermal flare plasma to be studied in detail. In this paper we describe a method for computing the differential emission measure distribution in a flare using EVE observations and apply it to several representative events. We find that in all phases of the flare the differential emission measure distribution is broad. Comparisons of EVE spectra with calculations based on parameters derived from the Geostationary Operational Environmental Satellites soft X-ray fluxes indicate that the isothermal approximation is generally a poor representation of the thermal structure of a flare.

Warren, Harry P.; Mariska, John T.; Doschek, George A.

2013-06-01

208

Advancing Variable Star Astronomy: The Centennial History of the American Association of Variable Star Observers  

NASA Astrophysics Data System (ADS)

Preface; Part I. Pioneers in Variable Star Astronomy Prior to 1909: 1. The emergence of variable star astronomy - a need for observations; 2. A need for observers; Part II. The Founding of the AAVSO - The William Tyler Olcott Era: 3. The amateur's amateur; 4. Amateurs in the service of science; Part III. The Leon Campbell Era: 5. Leon Campbell to the rescue; 6. Formalizing relationships; 7. The Pickering Memorial Endowment; 8. Fading of the Old Guard; 9. Growing pains and distractions; Part IV. The Service Bureau - The Margaret Mayall Era: 10. Learning about independence; 11. Eviction from Harvard College Observatory; 12. Actions and reactions; 13. In search of a home; 14. Survival on Brattle Street; 15. AAVSO achievements; 16. Breathing room on Concord Avenue; Part V. Analysis and Science: The Janet Mattei Era: 17. The growth of a director; 18. Learning the ropes the hard way; 19. Managing with renewed confidence; 20. Expanding the scientific charter; Part VI. Accelerating Observational Science - The Arne Henden Era: 21. Bridging the gap; 22. Accelerating the science - the Henden era begins; Epilogue; Appendices; Index.

Williams, Thomas R.; Saladyga, Michael

2011-05-01

209

EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae  

E-print Network

We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A) light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with the EUVE satellite. We find that the unique shape of the X-ray light curve is different from previously obtained X-ray light curves of QQ Vul and provides evidence for two-pole accretion. Detailed examination of the photometric data indicates that QQ Vul undergoes a stellar eclipse of the X-ray emitting region, indicative of a high binary inclination. We discuss possible implications for the nature of this system given the observed shape of its EUV and X-ray light curves.

Kunegunda E. Belle; Steve B. Howell; Amy Mills

1999-11-30

210

On the causes of plasmaspheric rotation variability: IMAGE EUV observations  

NASA Astrophysics Data System (ADS)

IMAGE EUV observations demonstrate that the plasmasphere usually does not corotate as assumed in simple convection models, even at low L shells. We carry out a statistical survey of plasmaspheric rotation rates over several months of IMAGE EUV data in 2001, using two different measurement techniques. We test the prevailing hypothesis, that subcorotation is due to enhanced auroral zone Joule heating driving equatorward thermospheric winds, by testing for correlation of rotation rates with several geomagnetic indices. Azimuthal features such as "notches" are tracked in local time over a single pass of the IMAGE satellite, both visually and using an automated cross-correlation routine. Each technique provides an estimate of the plasmasphere's rotation rate. We find a weak correlation between rotation rate and Dst, Kp, AE, the midnight boundary index (MBI), and Joule heating estimates from assimilative mapping of ionospheric electrodynamics (AMIE) at L = 2.5, but not at L = 3.5. In general, lower rotation rates correspond to higher auroral and geomagnetic activity. We also make the first direct observation of plasmaspheric superrotation. The plasmaspheric rotation rate is found to be highly variable on multiday timescales, but the typical state of the plasmasphere is subcorotation, with inferred mean values ranging from 88% to 95% of corotation, depending on L shell. In addition, a statistical analysis shows that rotation rates near dusk are generally lower than those at dawn, suggesting that local time and magnetospheric convection contribute to the variation in rotation rate as well. We conclude that the cause of variability in plasmaspheric rotation rate is a combination of storm phase, local-time-dependent convection, and westward ionospheric drift.

Galvan, David A.; Moldwin, Mark B.; Sandel, Bill R.; Crowley, Geoff

2010-01-01

211

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

212

Evaluating carbon dioxide variability in the Community Earth System Model against atmospheric observations  

NASA Astrophysics Data System (ADS)

Changes in atmospheric CO_2 variability during the 21st century may provide insight on ecosystem responses to climate change and have implications for the design of carbon monitoring programs. We analyzed results from a fully coupled climate-carbon simulation using the Community Earth System Model (CESM1-BGC). We evaluated CO2 simulated for the historical period against surface, aircraft, and column observations. The mean annual cycle in total column atmospheric CO2 was underestimated throughout the northern hemisphere relative to TCCON observations, suggesting that the growing season net flux in the land component of CESM was too weak by 50%. Sampling CESM along HIPPO transects confirmed low growing season uptake, but also showed that spring drawdown in the Northern Hemisphere began too early. The vertical gradients in CESM generally agreed with HIPPO data and with NOAA aircraft profiles outside the growing season, but were too weak during the summer. The seasonal bias suggests that vertical transport in CAM4 (the atmospheric component of CESM) was too weak year round. Model evaluation and improvement based on atmospheric observations is crucial. The simulation of surface exchange and atmospheric transport of CO2 in coupled models such as CESM may help with the design of optimal detection strategies. For example, in the simulations of the 21st century, CESM predicted increases in the mean annual cycle of atmospheric CO2 and larger horizontal gradients. Both north-south and east-west contrasts in CO2 strengthened due to changing patterns in fossil fuel emissions and terrestrial carbon exchange, and northern hemisphere interannual variability increased as well. Our results suggest that using atmospheric observations to gain insight about changing terrestrial and ocean processes over the next several decades may become more challenging as anthropogenic contributions to variability on multiple temporal and spatial scales continue to grow.

Keppel-Aleks, G.; Randerson, J. T.; Lindsay, K. T.; Stephens, B. B.; Moore, J. K.; Doney, S. C.; Thornton, P. E.; Mahowald, N. M.; Hoffman, F. M.; Sweeney, C.; Tans, P. P.; Wennberg, P. O.; Wofsy, S. C.

2012-12-01

213

Interannual and Seasonal Variability of Biomass Burning Emissions Constrained by Satellite Observations  

NASA Technical Reports Server (NTRS)

We present a methodology for estimating the seasonal and interannual variation of biomass burning designed for use in global chemical transport models. The average seasonal variation is estimated from 4 years of fire-count data from the Along Track Scanning Radiometer (ATSR) and 1-2 years of similar data from the Advanced Very High Resolution Radiometer (AVHRR) World Fire Atlases. We use the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data product as a surrogate to estimate interannual variability in biomass burning for six regions: Southeast Asia, Indonesia and Malaysia, Brazil, Central America and Mexico, Canada and Alaska, and Asiatic Russia. The AI data set is available from 1979 to the present with an interruption in satellite observations from mid-1993 to mid-1996; this data gap is filled where possible with estimates of area burned from the literature for different regions. Between August 1996 and July 2000, the ATSR fire-counts are used to provide specific locations of emissions and a record of interannual variability throughout the world. We use our methodology to estimate mean seasonal and interannual variations for emissions of carbon monoxide from biomass burning, and we find that no trend is apparent in these emissions over the last two decades, but that there is significant interannual variability.

Duncan, Bryan N.; Martin, Randall V.; Staudt, Amanda C.; Yevich, Rosemarie; Logan, Jennifer A.

2003-01-01

214

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

215

Regional and landscape-scale variability of Landsat-observed vegetation dynamics in northwest Siberian tundra  

NASA Astrophysics Data System (ADS)

Widespread increases in Arctic tundra productivity have been documented for decades using coarse-scale satellite observations, but finer-scale observations indicate that changes have been very uneven, with a high degree of landscape- and regional-scale heterogeneity. Here we analyze time-series of the Normalized Difference Vegetation Index (NDVI) observed by Landsat (1984-2012), to assess landscape- and regional-scale variability of tundra vegetation dynamics in the northwest Siberian Low Arctic, a little-studied region with varied soils, landscape histories, and permafrost attributes. We also estimate spatio-temporal rates of land-cover change associated with expansion of tall alder (Alnus) shrublands, by integrating Landsat time-series with very-high-resolution imagery dating to the mid-1960s. We compiled Landsat time-series for eleven widely-distributed landscapes, and performed linear regression of NDVI values on a per-pixel basis. We found positive net NDVI trends (‘greening’) in nine of eleven landscapes. Net greening occurred in alder shrublands in all landscapes, and strong greening tended to correspond to shrublands that developed since the 1960s. Much of the spatial variability of greening within landscapes was linked to landscape physiography and permafrost attributes, while between-landscape variability largely corresponded to differences in surficial geology. We conclude that continued increases in tundra productivity in the region are likely in upland tundra landscapes with fine-textured, cryoturbated soils; these areas currently tend to support discontinuous vegetation cover, but are highly susceptible to rapid increases in vegetation cover, as well as land-cover changes associated with the development of tall shrublands.

Frost, Gerald V.; Epstein, Howard E.; Walker, Donald A.

2014-01-01

216

Seasonal to Decadal-Scale Variability in Satellite Ocean Color and Sea Surface Temperature for the California Current System  

NASA Technical Reports Server (NTRS)

Support for this project was used to develop satellite ocean color and temperature indices (SOCTI) for the California Current System (CCS) using the historic record of CZCS West Coast Time Series (WCTS), OCTS, WiFS and AVHRR SST. The ocean color satellite data have been evaluated in relation to CalCOFI data sets for chlorophyll (CZCS) and ocean spectral reflectance and chlorophyll OCTS and SeaWiFS. New algorithms for the three missions have been implemented based on in-water algorithm data sets, or in the case of CZCS, by comparing retrieved pigments with ship-based observations. New algorithms for absorption coefficients, diffuse attenuation coefficients and primary production have also been evaluated. Satellite retrievals are being evaluated based on our large data set of pigments and optics from CalCOFI.

Mitchell, B. Greg; Kahru, Mati; Marra, John (Technical Monitor)

2002-01-01

217

Ionospheric Variability as Observed by the CTECS and CORISS Sensors  

NASA Astrophysics Data System (ADS)

The Compact Total Electron Content Sensor (CTECS) is a GPS radio occultation instrument designed for cubesat platforms that utilizes a COTS receiver, modified firmware, and a custom designed antenna. CTECS was placed on the Pico Satellite Solar Cell Testbed 2 (PSSC2) nanosat that was installed on the Space Shuttle Atlantis (STS-135). PSSC2 was successfully released from the shuttle on 20 July 2011 near 380 km altitude. Because of attitude control and power issues, only 13.5 hours of data was collected during its approximately 5-month mission life. The C/NOFS Occultation Receiver for Ionospheric Sensing and Specification (CORISS) GPS radio occultation sensor on the C/NOFS satellite has collected data nearly continuously from May 2008 to June 2013. Both CTECS and CORISS obtain Total Electron Content and scintillation data. In this presentation the CTECS data is first validated against CORISS and available ground-based observations. Then combining the CTECS and CORISS data, low and mid latitude ionospheric variability including scintillation events is presented.

Bishop, R. L.; Redding, M.; Straus, P. R.

2013-12-01

218

Observed and SST-forced multidecadal variability in global land surface air temperature  

NASA Astrophysics Data System (ADS)

The characteristics of multidecadal variability (MDV) in global land surface air temperature (SAT) are analyzed based on observations. The role of sea surface temperature (SST) variations in generating MDV in land SAT is assessed using atmospheric general circulation model simulations forced by observed SST. MDV in land SAT exhibits regional differences, with amplitude larger than 0.3 °C mainly over North America, East Asia, Northern Eurasia, Northern Africa and Greenland for the study period of 1902-2004. MDV can account for more than 30 % of long-term temperature variation during the last century in most regions, especially more than 50 % in parts of the above-mentioned regions. The SST-forced simulations reproduce the observed feature of zonal mean MDV in land SAT, though with weaker amplitude especially at the northern high-latitudes. Two types of MDV in land SAT, one of 60-year-timescale, mainly observed in the northern mid-high-latitude lands, and another of 20-30-year-timescale, mainly observed in the low-latitude lands, are also well reproduced. The SST-forced MDV accounts for more than 40 % amplitude of observed MDV in most regions. Except for some sporadically distributed regions in central Eurasia, South America and Western Australia, the SST-forced multidecadal variations are well in-phase with observations. The Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation signals are found dominant in MDV of both the observed and SST-forced land SAT, suggesting important roles of these oceanic oscillations in generating MDV in global land SAT.

Gao, L. H.; Yan, Z. W.; Quan, X. W.

2014-03-01

219

Observed and SST-forced multidecadal variability in global land surface air temperature  

NASA Astrophysics Data System (ADS)

The characteristics of multidecadal variability (MDV) in global land surface air temperature (SAT) are analyzed based on observations. The role of sea surface temperature (SST) variations in generating MDV in land SAT is assessed using atmospheric general circulation model simulations forced by observed SST. MDV in land SAT exhibits regional differences, with amplitude larger than 0.3 °C mainly over North America, East Asia, Northern Eurasia, Northern Africa and Greenland for the study period of 1902-2004. MDV can account for more than 30 % of long-term temperature variation during the last century in most regions, especially more than 50 % in parts of the above-mentioned regions. The SST-forced simulations reproduce the observed feature of zonal mean MDV in land SAT, though with weaker amplitude especially at the northern high-latitudes. Two types of MDV in land SAT, one of 60-year-timescale, mainly observed in the northern mid-high-latitude lands, and another of 20-30-year-timescale, mainly observed in the low-latitude lands, are also well reproduced. The SST-forced MDV accounts for more than 40 % amplitude of observed MDV in most regions. Except for some sporadically distributed regions in central Eurasia, South America and Western Australia, the SST-forced multidecadal variations are well in-phase with observations. The Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation signals are found dominant in MDV of both the observed and SST-forced land SAT, suggesting important roles of these oceanic oscillations in generating MDV in global land SAT.

Gao, L. H.; Yan, Z. W.; Quan, X. W.

2015-01-01

220

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

221

Final Report for UW-Madison Portion of DE-SC0005301, "Collaborative Project: Pacific Decadal Variability and Central Pacific Warming El Niño in a Changing Climate"  

SciTech Connect

This project funded two efforts at understanding the interactions between Central Pacific ENSO events, the mid-latitude atmosphere, and decadal variability in the Pacific. The first was an investigation of conditions that lead to Central Pacific (CP) and East Pacific (EP) ENSO events through the use of linear inverse modeling with defined norms. The second effort was a modeling study that combined output from the National Center for Atmospheric Research (NCAR) Community Atmospheric Model (CAM4) with the Battisti (1988) intermediate coupled model. The intent of the second activity was to investigate the relationship between the atmospheric North Pacific Oscillation (NPO), the Pacific Meridional Mode (PMM), and ENSO. These two activities are described herein.

Vimont, Daniel [University of Wisconsin - Madison

2014-06-13

222

Six-decade temporal change and seasonal decomposition of climate variables in Lake Dianchi watershed (China): stable trend or abrupt shift?  

NASA Astrophysics Data System (ADS)

Meteorological trend analysis is a useful tool for understanding climate change and can provide useful information on the possibility of future change. Lake Dianchi is the sixth largest freshwater body in China with serious eutrophication. Algal blooms outbreak was proven to be closely associated with some climatic factors in Lake Dianchi. It is therefore essential to explore the trends of climatic time series to understand the mechanism of climate change on lake eutrophication. We proposed an integrated method of Mann-Kendall (MK) test, seasonal-trend decomposition using locally weighted regression (LOESS) (STL), and regime shift index (RSI) to decompose the trend analysis and identify the stable and abrupt changes of some climate variables from 1951 to 2009. The variables include mean air temperature (Tm), maximum air temperatures (Tmax), minimum air temperatures (Tmin), precipitation (Prec), average relative humidity (Hum), and average wind speed (Wind). The results showed that (a) annual Tm, Tmax, and Tmin have a significant increasing trend with the increasing rates of 0.26, 0.15and 0.43 °C per decade, respectively; (b) annual precipitation has an insignificant decreasing trend with the decreasing rate of 3.17 mm per decade; (c) annual Hum has a significant decreasing trend in all seasons; and (d) there are two turning points for temperature rise around 1980 and 1995 and two abrupt change periods for precipitation with the extreme points appearing in 1963 and 1976. Temperature rise and precipitation decline in summer and autumn as well as wind speed decrease after the 1990s may be an important reason for algal blooms outbreak in Lake Dianchi. This study was expected to provide foundation and reference for regional water resource management.

Zhou, Jing; Liang, Zhongyao; Liu, Yong; Guo, Huaicheng; He, Dan; Zhao, Lei

2015-01-01

223

Modelling variability in black hole binaries: linking simulations to observations  

NASA Astrophysics Data System (ADS)

Black hole accretion flows show rapid X-ray variability. The power spectral density (PSD) of this is typically fit by a phenomenological model of multiple Lorentzians for both the broad-band noise and quasi-periodic oscillations (QPOs). Our previous paper developed the first physical model for the PSD and fit this to observational data. This was based on the same truncated disc/hot inner flow geometry which can explain the correlated properties of the energy spectra. This assumes that the broad-band noise is from propagating fluctuations in mass accretion rate within the hot flow, while the QPO is produced by global Lense-Thirring precession of the same hot flow. Here we develop this model, making some significant improvements. First, we specify that the viscous frequency (equivalently, surface density) in the hot flow has the same form as that measured from numerical simulations of precessing, tilted accretion flows. Secondly, we refine the statistical techniques which we use to fit the model to the data. We re-analyse the PSD from the 1998 rise to outburst of XTE J1550-564 with our new model in order to assess the impact of these changes. We find that the derived outer radii of the hot flow (set by the inner radius of the truncated disc) are rather similar, changing from ˜68 to 13Rg throughout the outburst rise. However, the more physical assumptions of our new model also allow us to constrain the scaleheight of the flow. This decreases as the outer radius of the flow decreases, as expected from the spectral evolution. The spectrum steepens in response to the increased cooling as the truncation radius sweeps in, so gas pressure support for the flow decreases. The new model, PROPFLUC, is publicly available within the XSPEC spectral fitting package.

Ingram, Adam; Done, Chris

2012-01-01

224

Partitioning of Terrestrial ET Variability in the CAM4/CLM4 Climate Model, Contributions to Trends over the Last Two Decades, and Sensitivity to Parameterization Changes  

NASA Astrophysics Data System (ADS)

ET is partitioned into canopy evaporation, transpiration, and soil evaporation. For a realistic climate model simulation, it is important that these terms not only add to a realistic total ET but also individually agree with observations. In this study, CAM4.0 was run 21 years from 1982 to 2002 with a spatial resolution of 1 by 1 degree, forced by prescribed SST. A global monthly ET dataset was produced and compared with observational analyses. The CAM may overestimate the magnitude of global ET flux from too much ground evaporation but its annual cycle was reasonably predicted. Ground evaporation has the highest correlation with total ET variation and is the largest contributor its variability. Changes to the current ET parameterizations are suggested that simulate ET variability and magnitude in better agreement with observations from 64 flux measurement sites over different climate regimes and land covers. Linear trends and their drivers are examined and their change with the suggested parameterizations are analyzed.

Sun, Y.; Dickinson, R. E.

2009-12-01

225

Observing Simulated Cepheid Variable Stars in an Introductory Astronomy Lab.  

ERIC Educational Resources Information Center

Describes an exercise developed by the author to help college students to become familiar with the technique of photoelectric photometry of variable stars and permits each student to work with data he or she has personally obtained. (HM)

Flesch, Terry R.

1979-01-01

226

Ozone column content variability at the Kishinev site from satellite retrievals and ground observations  

NASA Astrophysics Data System (ADS)

It is analyzed variability of the total ozone content (TOC) in column of atmosphere by using ozone retrievals from satellite platform and from direct ground observations at the Kishinev site, Moldova (47.00N; 28.56E). Direct ground observations of the TOC are regular carried out by Atmospheric Research Group (ARG), Institute of Applied Physics at the ground-based solar radiation monitoring station, Kishinev site, by using of hand-held ozonemeter MICROTOPS II. TOC measurements started since 2003. Data of ozone observations are presented at the research group web-site http://arg.phys.asm.md. Satellite TOC dataset at specific coordinates of Kishinev site was derived by using linear interpolation of the parent gridded databases from TOMS (1979-2004) and OMI (2005-2008) observations. It was established that relative difference of TOC between periods from 1979 to 1983 and from 2004 to 2008 was -5.16 %. Data were processed by applying of 5-year averaging "window". For a period from 1979 to 2008 statistical estimation of linear trend of the TOC was -2.08% per decade. Climatic norm of TOC for this period was equal to 335 DU. Variation of ozone column content at Kishinev site shows it seasonal character with maximum of the order of ~378 DU (in March and April) and with minimum of the order of ~289 DU (in October). The largest and lowest range of oscillations of monthly means of the TOC retrieved for Kishinev site from TOMS and OMI observations in the course of the period from 1979 to 2008 were ~ 102 DU (in February) and ~29 DU (in October). Extremely low and high values of the TOC ever registered for Kishinev site from TOMS and OMI observations were ~ 209 DU (on December 1, 1999) and ~ 532 DU (on March 3, 1988). It was shown that ARG ground observations give overestimated TOC values in comparison with the TOMS and OMI observations from satellite platforms. Relative differences or biases (in %) between satellite and ARG ground observations of the TOC at Kishinev site were derived by using of daily means of TOC from the short-long series of simultaneous measurements for respective pairs: TOMS vs ARG (2003-2005) and OMI vs ARG(2004-2008). These differences were -1.85% (or -6 DU) for pair TOMS-ARG and -2.15% (or -7 DU) for pair OMI-ARG observations. It should be noted that derived correlation coefficients for sets of TOMS-ARG and OMI-ARG observations of daily means of TOC were ~0.981 and ~0.992, respectively.

Aculinin, Alexandr; Smicov, Vladimir

2010-05-01

227

Influence of Surface Roughness Spatial Variability and Temporal Dynamics on the Retrieval of Soil Moisture from SAR Observations  

PubMed Central

Radar-based surface soil moisture retrieval has been subject of intense research during the last decades. However, several difficulties hamper the operational estimation of soil moisture based on currently available spaceborne sensors. The main difficulty experienced so far results from the strong influence of other surface characteristics, mainly roughness, on the backscattering coefficient, which hinders the soil moisture inversion. This is especially true for single configuration observations where the solution to the surface backscattering problem is ill-posed. Over agricultural areas cultivated with winter cereal crops, roughness can be assumed to remain constant along the growing cycle allowing the use of simplified approaches that facilitate the estimation of the moisture content of soils. However, the field scale spatial variability and temporal variations of roughness can introduce errors in the estimation of soil moisture that are difficult to evaluate. The objective of this study is to assess the impact of roughness spatial variability and roughness temporal variations on the retrieval of soil moisture from radar observations. A series of laser profilometer measurements were performed over several fields in an experimental watershed from September 2004 to March 2005. The influence of the observed roughness variability and its temporal variations on the retrieval of soil moisture is studied using simulations performed with the Integral Equation Model, considering different sensor configurations. Results show that both field scale roughness spatial variability and its temporal variations are aspects that need to be taken into account, since they can introduce large errors on the retrieved soil moisture values. PMID:22389611

Álvarez-Mozos, Jesús; Verhoest, Niko E.C.; Larrañaga, Arantzazu; Casalí, Javier; González-Audícana, María

2009-01-01

228

Final Progress Report: Collaborative Research: Decadal-to-Centennial Climate & Climate Change Studies with Enhanced Variable and Uniform Resolution GCMs Using Advanced Numerical Techniques  

SciTech Connect

The joint U.S-Canadian project has been devoted to: (a) decadal climate studies using developed state-of-the-art GCMs (General Circulation Models) with enhanced variable and uniform resolution; (b) development and implementation of advanced numerical techniques; (c) research in parallel computing and associated numerical methods; (d) atmospheric chemistry experiments related to climate issues; (e) validation of regional climate modeling strategies for nested- and stretched-grid models. The variable-resolution stretched-grid (SG) GCMs produce accurate and cost-efficient regional climate simulations with mesoscale resolution. The advantage of the stretched grid approach is that it allows us to preserve the high quality of both global and regional circulations while providing consistent interactions between global and regional scales and phenomena. The major accomplishment for the project has been the successful international SGMIP-1 and SGMIP-2 (Stretched-Grid Model Intercomparison Project, phase-1 and phase-2) based on this research developments and activities. The SGMIP provides unique high-resolution regional and global multi-model ensembles beneficial for regional climate modeling and broader modeling community. The U.S SGMIP simulations have been produced using SciDAC ORNL supercomputers. Collaborations with other international participants M. Deque (Meteo-France) and J. McGregor (CSIRO, Australia) and their centers and groups have been beneficial for the strong joint effort, especially for the SGMIP activities. The WMO/WCRP/WGNE endorsed the SGMIP activities in 2004-2008. This project reflects a trend in the modeling and broader communities to move towards regional and sub-regional assessments and applications important for the U.S. and Canadian public, business and policy decision makers, as well as for international collaborations on regional, and especially climate related issues.

Fox-Rabinovitz, M; Cote, J

2009-06-05

229

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

230

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.

231

Direct observation of homoclinic orbits in human heart rate variability  

NASA Astrophysics Data System (ADS)

Homoclinic trajectories of the interbeat intervals between contractions of ventricles of the human heart are identified. The interbeat intervals are extracted from 24-h Holter ECG recordings. Three such recordings are discussed in detail. Mappings of the measured consecutive interbeat intervals are constructed. In the second and in some cases in the fourth iterate of the map of interbeat intervals homoclinic trajectories associated with a hyperbolic saddle are found. The homoclinic trajectories are often persistent for many interbeat intervals, sometimes spanning many thousands of heartbeats. Several features typical for homoclinic trajectories found in other systems were identified, including a signature of the gluing bifurcation. The homoclinic trajectories are present both in recordings of heart rate variability obtained from patients with an increased number of arrhythmias and in cases in which the sinus rhythm is dominant. The results presented are a strong indication of the importance of deterministic nonlinear instabilities in human heart rate variability.

?ebrowski, J. J.; Baranowski, R.

2003-05-01

232

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

233

EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae  

Microsoft Academic Search

We present simultaneous X-ray (lambdapeak~44 Å) and EUV (lambdapeak=89 Å) light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with the EUVE satellite. We find that the unique shape of the X-ray light curve is different from previously obtained X-ray light curves of QQ Vul and provides evidence for two-pole accretion. Detailed examination of the photometric data indicates that

Kunegunda E. Belle; Steve B. Howell; Amy Mills

2000-01-01

234

Variability in Tropical Tropospheric Ozone as Observed by SHADOZ  

NASA Technical Reports Server (NTRS)

The SHADOZ (Southern Hemisphere Additional Ozonesondes) ozone sounding network was initiated in 1998 to improve the coverage of tropical in-situ ozone measurements for satellite validation, algorithm development and related process studies. Over 2000 soundings have been archived at the central website, , for 12 stations: Ascension Island; Nairobi and Malindi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; Natal, Brazil; Paramaribo, Surinam. Some results to date indicate reliability of the measurement and highly variable interactions between ozone and tropical meteorology. For example: 1. By using ECC sondes with similar procedures, 5-10% accuracy and precision (1-sigma) of the sonde total ozone measurement was achieved [Thompson et al., 2003al; 2. Week-to-week variability in tropospheric ozone is so great that statistics are frequently not Gaussian and most stations vary up to a factor of 3 in column amount over the course of a year [Thompson et al., 2002b]. 3. Longitudinal variability in tropospheric ozone profiles is a consistent feature, with a 10- 15 DU column-integrated difference between Atlantic and Pacific sites; this is the cause of the zonal wave-one feature in total ozone [Shiotani, 1992]. The ozone record from Paramaribo, Surinam (6N, 55W) is a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone. Interpretations of SHADOZ time-series and approaches to classification suggested by SHADOZ data over Africa and the Indian Ocean will be described.

Thompson, Anne M.; Witte, Jacquelyn C.; Coetzee, Geert J. R.; Chatfield, Robert B.; Hudson, Robert D.

2004-01-01

235

EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae  

Microsoft Academic Search

We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A)\\u000alight curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with\\u000athe EUVE satellite. We find that the unique shape of the X-ray light curve is\\u000adifferent from previously obtained X-ray light curves of QQ Vul and provides\\u000aevidence for two-pole accretion. Detailed examination of the photometric data

Kunegunda E. Belle; Steve B. Howell; Amy Mills

1999-01-01

236

Outcomes of an International Coordination Workshop to Understand Aerosol Observability Capabilities and Requirements for the Next Decade  

NASA Astrophysics Data System (ADS)

In late April 2010 roughly 15 developers for many of the world’s operational numerical weather prediction centers with aerosol forecasting mandates met with an equal number of representatives of satellite data providers to discuss aerosol observability issues facing the next generation of aerosol forecast and modeling systems. While the last 3 years has seen rapid operational implementation of aerosol and pollution models around the world, the key to further development of these models is aerosol observational data from satellites for model evaluation and data assimilation. However, while the dynamical meteorology community has a well developed near real-time observing system to support forecasting, the aerosol community is only beginning to address the problem. This meeting was the first ever to combine the lead aerosol developers and remote sensing data providers from around the globe in discussing state-of-the-art technologies and operational requirements for aerosol forecasting. Participants included: operational centers representatives of ECMWF, FNMOC, JMA, NCEP, and UKMO; remote sensing data providers from EUMETSAT, ESA, JAXA, NASA, and NOAA NESDIS; and additional developers from NASA GMAO, NGST, NOAA, NRL, and several universities. Indeed, the smooth transition from the NASA EOS/A-Train into the international constellation of multi-model, multi-sensor products which satisfy both research and operational communities will require coordination among all of the above participants. In this paper, we provide an overview of important meeting outcomes that should interest the broader atmospheric composition community, including an overview of future satellite and ground systems and their capabilities, key definitions of operational diction, desires for error metrics, specialized product development, and customer outreach and research product delivery. These outcomes are already effecting CONOPS at major data and forecasting sensors.

Reid, J. S.; Benedetti, A.; Colarco, P. R.; Carmichael, G. R.; Icap Team

2010-12-01

237

Use of Machine Learning Techniques for Iidentification of Robust Teleconnections to East African Rainfall Variability in Observations and Models  

NASA Technical Reports Server (NTRS)

Providing advance warning of East African rainfall variations is a particular focus of several groups including those participating in the Famine Early Warming Systems Network. Both seasonal and long-term model projections of climate variability are being used to examine the societal impacts of hydrometeorological variability on seasonal to interannual and longer time scales. The NASA / USAID SERVIR project, which leverages satellite and modeling-based resources for environmental decision making in developing nations, is focusing on the evaluation of both seasonal and climate model projections to develop downscaled scenarios for using in impact modeling. The utility of these projections is reliant on the ability of current models to capture the embedded relationships between East African rainfall and evolving forcing within the coupled ocean-atmosphere-land climate system. Previous studies have posited relationships between variations in El Niño, the Walker circulation, Pacific decadal variability (PDV), and anthropogenic forcing. This study applies machine learning methods (e.g. clustering, probabilistic graphical model, nonlinear PCA) to observational datasets in an attempt to expose the importance of local and remote forcing mechanisms of East African rainfall variability. The ability of the NASA Goddard Earth Observing System (GEOS5) coupled model to capture the associated relationships will be evaluated using Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations.

Roberts, J. Brent; Robertson, Franklin R.; Funk, Chris

2014-01-01

238

Component noise variables of a light observation helicopter  

NASA Technical Reports Server (NTRS)

A test program was conducted to isolate and evaluate the individual noise sources of a light helicopter. To accomplish this, the helicopter was mounted on a special test rig, at a 6-foot skid height, in a simulated hover. The test rig contained by dynamometer for absorbing engine power and an exhaust silencing system for reducing engine noise. This test set-up allowed the various components of the helicopter to be run and listened to individually or in any combination. The sound pressure level was recorded at a point 200 feet from the helicopter as the component parameters were systematically varied. The tests were conducted in an open area, during the middle of the night, with no wind, and with all other known variables either eliminated or kept as constant as possible.

Robinson, F.

1973-01-01

239

Regional Variability in Tropical Convection: Observations from TRMM  

Microsoft Academic Search

Observation of the vertical profile of precipitation over the global Tropics is a key objective of the Tropical Rainfall Measuring Mission (TRMM) because this information is central to obtaining vertical profiles of latent heating. This study combines both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine `wet-season' vertical structures of tropical precipitation across a broad spectrum

Walter A. Petersen; Steven A. Rutledge

2001-01-01

240

Source Parameter Inversion for Recent Great Earthquakes from a Decade-long Observation of Global Gravity Fields  

NASA Technical Reports Server (NTRS)

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 1.2x10(exp 23)Nm with a dip of 10deg, in agreement with the estimate obtained at ultralong seismic periods. For the 2010 Maule earthquake, the GRACE solutions range from 2.0 to 2.7x10(exp 22)Nm for dips of 12deg-24deg and centroid depths within the lower crust. For the 2011 Tohoku-Oki earthquake, the estimated scalar moments range from 4.1 to 6.1x10(exp 22)Nm, with dips of 9deg-19deg and centroid depths within the lower crust. For the 2012 Indian Ocean strike-slip earthquakes, the gravity data delineate a composite moment of 1.9x10(exp 22)Nm 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 M(sub 0) approx. 5.0x10(exp 21)Nm. 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, Ricccardo; Sauber, Jeanne; Okal, Emile

2013-01-01

241

Insights into mantle structure and flow beneath Alaska based on a decade of observations of shear wave splitting  

NASA Astrophysics Data System (ADS)

shear wave splitting measurements from three Program for Array Seismic Studies of the Continental Lithosphere experiments (Broadband Experiment Across the Alaska Range, Alaska Receiving Cross Transect of the Inner Core, and Multidisciplinary Observations Of Subduction), which form a north/south transect across Alaska, show a remarkably simple pattern of two large anisotropy domains. In the northern domain, extending from the 70 km contour of the subducting Pacific plate north to the Arctic Ocean, fast directions are consistently in the NE-SW direction. These directions are essentially parallel to the absolute plate motion direction in northern Alaska and parallel to the strike of the subducting plate above the mantle wedge, suggesting that they represent some combination of plate-scale asthenospheric flow in the upper mantle and flow along the subducting plate in the mantle wedge. A strong wedge component beneath the Alaska Range is required to explain systematics of splitting delay times. In the southern domain, which extends south from the 70 km depth contour to the subducting plate, fast directions are in the NW-SE direction, a 90° rotation from the northern domain. These fast directions are parallel to the dip of the subducting plate in the direction of convergence and represent entrained flow beneath the subducting slab; the Pacific Plate absolute motion approximately parallels local convergence. Two major factors seem to control flow in these regions, absolute plate motion in the north and the subduction of the Pacific plate in the south, although both subduction-driven wedge flow and absolute plate motion contribute to the southern part of the northern regime.

Perttu, Anna; Christensen, Douglas; Abers, Geoffrey; Song, Xiaodong

2014-11-01

242

Followup Observations of SDSS and CRTS Candidate Cataclysmic Variables  

E-print Network

We present photometry of 11 and spectroscopy of 35 potential cataclysmic variables from the Sloan Digital Sky Survey, the Catalina Real-Time Transient Survey and vsnet-alerts. The photometry results include quasi-periodic oscillations during the decline of V1363 Cyg, nightly accretion changes in the likely Polar (AM Herculis binary) SDSS J1344+20, eclipses in SDSS J2141+05 with an orbital period of 76+/-2 min, and possible eclipses in SDSS J2158+09 at an orbital period near 100 min. Time-resolved spectra reveal short orbital periods near 80 min for SDSS J0206+20, 85 min for SDSS J1502+33, and near 100 min for CSS J0015+26, RXS J0150+37, SDSS J1132+62, SDSS J2154+15 and SDSS J2158+09. The prominent HeII line and velocity amplitude of SDSS J2154+15 are consistent with a Polar nature for this object, while the lack of this line and a low velocity amplitude argue against this classification for RXS J0150+37. Single spectra of 10 objects were obtained near outburst and the rest near quiescence, confirming the dwar...

Szkody, Paula; Howell, Steve B; Landolt, Arlo U; Bond, Howard E; Silva, David R; Vasquez-Soltero, Stephanie

2014-01-01

243

Variable Star Observing with the Bradford Robotic Telescope  

NASA Astrophysics Data System (ADS)

With the recent addition of Johnson BVRI filters on the Bradford Robotic Telescope's 24 sq. arc minute camera, this scope has become a possibility to be considered when monitoring certain stars such as LPVs. This presentation will examine the mechanics of observing with the BRT and show examples of work that has been done by the author and how that data has been reduced using VPhot.

Kinne, Richard C. S.

2011-05-01

244

Generic relationships between observational parameters defining ionospheric variability  

NASA Astrophysics Data System (ADS)

It has long been known that travelling ionospheric disturbances (TIDs) are seen as a tilted descending variation in isolines of constant electron density derived from ionograms. This is the descending phase front of what is actually an ascending TID, as originally noted by Hines. What is less known is that this descent results in a time delay between the motion of the ionosphere at the greatest observed height and the arrival of the disturbance at the base of the layer (typically the F2) which in turn causes a temporary a compression of the layer thickness and a temporary increase in maximum electron density (foF2). The tilt in the descending electron density variation is often used as the identifying mark of a TID. This paper points out that the relationships observed between foF2, descending height and layer thickness is not unique to a TID but is a generic relationship observed whenever ionization is driven up and down magnetic field lines. Examples of this broader relationship are given for the equatorial post sunset rise and fall in electron density and in equatorial and middle latitude variations in ionospheric diurnal patterns which may repeat over a number of days. Such patterns are definitely not caused by TIDs.

Lynn, Kenneth; Heitmann, Andrew; Gardener-Garden, Robert

245

Variable Star Observing with the Bradford Robotic Telescope  

NASA Astrophysics Data System (ADS)

(Abstract only) The Bradford Robotic Telescope (BRT) is a collection of telescopes and other instruments located on Mount Teide, Tenerife, Canary Islands; this resource is available to all for use at no cost (http://www.telescope.org/info/BRT_information). With the recent addition of Johnson BVRI filters on the BRT's 24 square arc minute camera, this telescope has become a resource to be considered when monitoring certain stars such as LPVs. This presentation will examine the mechanics of observing with the BRT and show examples of work that has been done by the author and how those data have been reduced using VPhot.

Kinne, R. C. S.

2012-06-01

246

Interannual Variability of OLR as Observed by AIRS and CERES  

NASA Technical Reports Server (NTRS)

The paper examines spatial anomaly time series of Outgoing Longwave Radiation (OLR) and Clear Sky OLR (OLR(sub CLR)) as determined using observations from CERES Terra and AIRS over the time period September 2002 through June 2011. We find excellent agreement of the two OLR data sets in almost every detail down to the x11deg spatial grid point level. The extremely close agreement of OLR anomaly time series derived from observations by two different instruments implies high stability of both sets of results. Anomalies of global mean, and especially tropical mean, OLR are shown to be strongly correlated with an El Nino index. These correlations explain that the recent global and tropical mean decreases in OLR over the time period studied are primarily the result of a transition from an El Nino condition at the beginning of the data record to La Nina conditions toward the end of the data period. We show that the close correlation of mean OLR anomalies with the El Nino Index can be well accounted for by temporal changes of OLR within two spatial regions, one to the east of, and one to the west of, the NOAA Nino-4 region. Anomalies of OLR in these two spatial regions are both strongly correlated with the El Nino Index as a result of the strong anti-correlation of anomalies of cloud cover and mid-tropospheric water vapor in these two regions with the El Nino Index.

Susskind, Joel; Molnar, Gyula I.; Iredell, Lena F.; Loeb, Norman G.

2012-01-01

247

Demographic Variables for Wild Asian Elephants Using Longitudinal Observations  

PubMed Central

Detailed demographic data on wild Asian elephants have been difficult to collect due to habitat characteristics of much of the species’ remaining range. Such data, however, are critical for understanding and modeling population processes in this endangered species. We present data from six years of an ongoing study of Asian elephants (Elephas maximus) in Uda Walawe National Park, Sri Lanka. This relatively undisturbed population numbering over one thousand elephants is individually monitored, providing cohort-based information on mortality and reproduction. Reproduction was seasonal, such that most births occurred during the long inter-monsoon dry season and peaked in May. During the study, the average age at first reproduction was 13.4 years and the 50th percentile inter-birth interval was approximately 6 years. Birth sex ratios did not deviate significantly from parity. Fecundity was relatively stable throughout the observed reproductive life of an individual (ages 11–60), averaging between 0.13–0.17 female offspring per individual per year. Mortalities and injuries based on carcasses and disappearances showed that males were significantly more likely than females to be killed or injured through anthropogenic activity. Overall, however, most observed injuries did not appear to be fatal. This population exhibits higher fecundity and density relative to published estimates on other Asian elephant populations, possibly enhanced by present range constriction. Understanding the factors responsible for these demographic dynamics can shed insight on the future needs of this elephant population, with probable parallels to other populations in similar settings. PMID:24376581

de Silva, Shermin; Webber, C. Elizabeth; Weerathunga, U. S.; Pushpakumara, T. V.; Weerakoon, Devaka K.; Wittemyer, George

2013-01-01

248

Decadal-scale variability of diffuse CO2 emissions and seismicity revealed from long-term monitoring (1995-2013) at Mammoth Mountain, California, USA  

NASA Astrophysics Data System (ADS)

Mammoth Mountain, California, is a dacitic volcano that has experienced several periods of unrest since 1989. The onset of diffuse soil CO2 emissions at numerous locations on the flanks of the volcano began in 1989-1990 following an 11-month period of heightened seismicity. CO2 emission rates were measured yearly from 1995 to 2013 at Horseshoe Lake (HSL), the largest tree kill area on Mammoth Mountain, and measured intermittently at four smaller degassing areas around Mammoth from 2006 to 2013. The long-term record at HSL shows decadal-scale variations in CO2 emissions with two peaks in 2000-2001 and 2011-2012, both of which follow peaks in seismicity by 2-3 years. Between 2000 and 2004 emissions gradually declined during a seismically quiet period, and from 2004 to 2009 were steady at ~ 100 metric tonnes per day (t d- 1). CO2 emissions at the four smaller tree-kill areas also increased by factors of 2-3 between 2006 and 2011-2012, demonstrating a mountain-wide increase in degassing. Delays between the peaks in seismicity and degassing have been observed at other volcanic and hydrothermal areas worldwide, and are thought to result from an injection of deep CO2-rich fluid into shallow subsurface reservoirs causing a pressurization event with a delayed transport to the surface. Such processes are consistent with previous studies at Mammoth, and here we highlight (1) the mountain-wide response, (2) the characteristic delay of 2-3 years, and (3) the roughly decadal reoccurrence interval for such behavior. Our best estimate of total CO2 degassing from Mammoth Mountain was 416 t d- 1 in 2011 during the peak of emissions, over half of which was emitted from HSL. The cumulative release of CO2 between 1995 and 2013 from diffuse emissions is estimated to be ~ 2-3 Mt, and extrapolation back to 1989 gives ~ 4.8 Mt. This amount of CO2 release is similar to that produced by the mid-sized (VEI 3) 2009 eruption of Redoubt Volcano in Alaska (~ 2.3 Mt over 11 months), and significantly lower than long-term emissions from hydrothermal areas such as Solfatara in Campi Flegrei, Italy (16 Mt over 28 years).

Werner, Cynthia; Bergfeld, Deborah; Farrar, Christopher D.; Doukas, Michael P.; Kelly, Peter J.; Kern, Christoph

2014-12-01

249

Interannual Variability of OLR as Observed by AIRS and CERES  

NASA Technical Reports Server (NTRS)

This paper compares spatial anomaly time series of OLR (Outgoing Longwave Radiation) and OLR(sub CLR) (Clear Sky OLR) as determined using observations from CERES Terra and AIRS over the time period September 2002 through June 2011. Both AIRS and CERES show a significant decrease in global mean and tropical mean OLR over this time period. We find excellent agreement of the anomaly time-series of the two OLR data sets in almost every detail, down to 1 deg X 1 deg spatial grid point level. The extremely close agreement of OLR anomaly time series derived from observations by two different instruments implies that both sets of results must be highly stable. This agreement also validates to some extent the anomaly time series of the AIRS derived products used in the computation of the AIRS OLR product. The paper also examines the correlations of anomaly time series of AIRS and CERES OLR, on different spatial scales, as well as those of other AIRS derived products, with that of the NOAA Sea Surface Temperature (SST) product averaged over the NOAA Nino-4 spatial region. We refer to these SST anomalies as the El Nino Index. Large spatially coherent positive and negative correlations of OLR anomaly time series with that of the El Nino Index are found in different spatial regions. Anomalies of global mean, and especially tropical mean, OLR are highly positively correlated with the El Nino Index. These correlations explain that the recent global and tropical mean decreases in OLR over the period September 2002 through June 2011, as observed by both AIRS and CERES, are primarily the result of a transition from an El Nino condition at the beginning of the data record to La Nina conditions toward the end of the data period. We show that the close correlation of global mean, and especially tropical mean, OLR anomalies with the El Nino Index can be well accounted for by temporal changes of OLR within two spatial regions which lie outside the NOAA Nino-4 region, in which anomalies of cloud cover and mid-tropospheric water vapor are both highly negatively correlated with the El Nino Index. Agreement of the AIRS and CERES OLR(sub CLR) anomaly time series is less good, which may be a result of the large sampling differences in the ensemble of cases included in each OLR(sub CLR) data set.

Susskind, Joel; Molnar, Gyula; Iredell, Lena; Loeb, Norman G.

2012-01-01

250

XMM-Newton Observations of the Cataclysmic Variable GW Lib  

E-print Network

XMM-Newton observations of the accreting, pulsating white dwarf in the quiescent dwarf nova GW Librae were conducted to determine if the non-radial pulsations present in previous UV and optical data affect the X-ray emission. The non-radial pulsations are evident in the simultaneous Optical Monitor data but are not detected in X-ray with an upper limit on the pulsation amplitude of 0.092 mags. The best fits to the X-ray spectrum are with a low temperature diffuse gas model or a multi-temperature cooling flow model, with a strong OVIII line, similar to other short period dwarf novae, but with a lower temperature range than evident in normal short period dwarf novae. The lack of pulsations and the spectrum likely indicate that the boundary layer does not extend to the surface of the white dwarf.

Eric J. Hilton; Paula Szkody; Anjum Mukadam; Koji Mukai; Coel Hellier; Liza van Zyl; Lee Homer

2007-06-22

251

New Spectral Observations of the Variable Galaxy Kaz 163  

NASA Astrophysics Data System (ADS)

Kaz 163 is a close double galaxy. Its southern component S is compact, with a very blue nucleus, in which heated active processes take place. From time to time gas formations are ejected from it, which behave themselves like emission components around the main emission lines H? and H?, around both from their long-wave and short-wave sides. This paper presents the spectral data of new observations, which were carried out with the 2.6m telescope at the Byurakan Astrophysical Observatory in September 2011. During the former observation in October 1981, lines [NII] ?? 6584,6548 were not visible in the spectrum of the component S. In 2001 they were already visible on the spectrum, and on the spectrum obtained in 2011 they already surpassed the intensity of H?. The magnitude of the component S is also changing: its nucleus is very blue and its U-B = -0 m .63. In the soft X-ray spectral range (0.1-2 keV) the flux of the radiation changed by 45% during 55,000 sec, and in the hard one (2-10keV) it changed up to 3.4 times. Photoindices ? for the soft and hard ranges in the spectrum of galaxy S, unlike other objects, do not so much differ from each other. The mean value for the first interval is approximately 2.5 and is equal -2.0 for the second one. On the histogram of redshifts Kaz 163 corresponds to the first big peak of the distribution. It is concluded that the component S of the galaxy Kaz 163 is a NLS1 galaxy, with the development of their evolution, is in the preliminary stage. Component N is a normal elliptical galaxy with no activity.

Karapetyan, Emilia L.

2014-07-01

252

Seasonal variability in global sea level observed with Geosat altimetry  

NASA Technical Reports Server (NTRS)

Time changes in global mesoscale sea level variances were observed with satellite altimetry between November 1986 and March 1988, showing significant, geographically coherent seasonal patterns. The NE Pacific and NE Atlantic variances show the most reliable patterns, higher than their yearly averages in both the fall and winter. The response to wind forcing appears as the major contributor to the NE Pacific and Atlantic signals; errors in the estimated inverse barometer response due to errors in atmospheric pressure, residual orbit errors, and errors in sea state bias are evaluated and found to be negligible contributors to this particular signal. The equatorial regions also show significant seasonal patterns, but the uncertainties in the wet tropospheric correction prevent definitive conclusions. The western boundary current changes are very large but not statistically significant. Estimates of the regression coefficient between sea level and significant wave height, an estimate of the sea state bias correction, range between 2.3 and 2.9 percent and vary with the type of orbit correction applied.

Zlotnicki, V.; Fu, L.-L.; Patzert, W.

1989-01-01

253

Sources of Variability in Gulf of Maine Circulation, and the Observations Needed to  

E-print Network

Sources of Variability in Gulf of Maine Circulation, and the Observations Needed to Model it. James in the Gulf of Maine are then quantified, with an emphasis on variability on timescales longer than tidal and the volume of water entering from the Scotian Shelf to the Gulf of Maine produce roughly comparable amounts

Pringle, James "Jamie"

254

Interdecadal variability of the Pacific Ocean: Model response to observed heat flux and wind stress anomalies  

Microsoft Academic Search

Variability of the Pacific Ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux, wind stress and turbulent kinetic energy TKE over the period 1970-88. The model captures the 1976-1977 winter time climate shift in sea surface temperature, as well as its monthly, seasonal and longer term variability as evidenced

Arthur J Miller; Daniel R Cayan; T. P. Barnett; Josef M Oberhuber

1994-01-01

255

Interdecadal variability of the Pacific Ocean: model response to observed heat flux and wind stress anomalies  

Microsoft Academic Search

Variability of the Pacific Ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux, wind stress and turbulent kinetic energy (TKE) over the period 1970-88. The model captures the 1976-77 winter time climate shift in sea surface temperature, as well as its monthly, seasonal and longer term variability as evidenced

Arthur J Miller; Daniel R Cayan; Tim P Barnett; Nicholas E Graham; Josef M Oberhuber

1994-01-01

256

Modulation of the Pacific Decadal Oscillation on the summer precipitation over East China: a comparison of observations to 600-years control run of Bergen Climate Model  

NASA Astrophysics Data System (ADS)

Observations show that the summer precipitation over East China often goes through decadal variations of opposite sign over North China and the Yangtze River valley (YRV), such as the "southern flood and northern drought" pattern that occurred during the late 1970s-1990s. In this study it is shown that a modulation of the Pacific Decadal Oscillation (PDO) on the summer precipitation pattern over East China during the last century is partly responsible for this characteristic precipitation pattern. During positive PDO phases, the warm winter sea surface temperatures (SSTs) in the eastern subtropical Pacific along the western coast of North American propagate to the tropics in the following summer due to weakened oceanic meridional circulation and the existence of a coupled wind-evaporation-SST feedback mechanism, resulting in a warming in the eastern tropical Pacific Ocean (5°N-20°N, 160°W-120°W) in summer. This in turn causes a zonal anomalous circulation over the subtropical-tropical Pacific Ocean that induces a strengthened western Pacific subtropical high (WPSH) and thus more moisture over the YRV region. The end result of these events is that the summer precipitation is increased over the YRV region while it is decreased over North China. The suggested mechanism is found both in the observations and in a 600-years fully coupled pre-industrial multi-century control simulations with Bergen Climate Model. The intensification of the WPSH due to the warming in the eastern tropical Pacific Ocean was also examined in idealized SSTA-forced AGCM experiments.

Yu, Lei; Furevik, Tore; Otterå, Odd Helge; Gao, Yongqi

2015-01-01

257

Combining Visual and Photoelectric Observations of Semi-Regular Red Variables  

E-print Network

Combining visual observations of SR variables with measurements of them using a photoelectric photometer is discussed then demonstrated using data obtained for the bright, southern SR variable theta Aps. Combining such observations is useful in that it can provide a more comprehensive set of data by extending the temporal coverage of the light curve. Typically there are systematic differences in the visual and photometric datasets that must be corrected for.

T. T. Moon; S. A. Otero; L. L. Kiss

2007-11-30

258

Decades 1 &2 Decades 3 & 4  

E-print Network

Seven Decades of Dad #12;Decades 1 &2 #12;Decades 3 & 4 #12;Decades 5 & 6 #12;FamilyFamilyFamily, China, Prague & Barcelona Palestine, Latvia Have been awed by his persona In Bulgaria & Germany been a great friend to me and my family, while being alwaysa wonderful teacher for the past 26 years

Cushing, Jim. M.

259

Multi-decadal river flow variations in France  

NASA Astrophysics Data System (ADS)

In this article, multi-decadal variations in the 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 in the instrumental period (defined in this study as the period from the late 19th century to the present), especially in spring. Differences of means between 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations. Multi-decadal spring river flow 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 eastern Atlantic. It is suggested that the Atlantic Multidecadal Variability, the main mode of multi-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. Potential 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 flow 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.

2014-02-01

260

Changing trends in the prevalence of blindness and visual impairment in a rural district of India: Systematic observations over a decade  

PubMed Central

Context: Globally, limited data are available on changing trends of blindness from a single region. Aims: To report the changing trends in the prevalence of blindness, visual impairment (VI), and visual outcomes of cataract surgery in a rural district of Andhra Pradesh, India, over period of one decade. Settings and Design: Rural setting; cross-sectional study. Materials and Methods: Using a validated Rapid Assessment of Cataract Surgical Services (RACSS) method, population-based, cross-sectional survey was done in a rural district in the state of Andhra Pradesh, India. Two-stage sampling procedure was used to select participants ?50 years of age. Further, a comparative analysis was done with participants ?50 years from the previously concluded Andhra Pradesh Eye Disease Study (APEDS) study, who belonged to the same district. Statistical Analysis: Done using 11th version of Stata. Results: Using RACSS, 2160/2300 (93.9%) participants were examined as compared with the APEDS dataset (n=521). Age and sex adjusted prevalence of blindness in RACSS and APEDS was 8% (95% CI, 6.9–9.1%) and 11% (95% CI, 8.3–13.7%), while that of VI was 13.6% (95% CI, 12.2–15.1%) and 40.3% (95% CI, 36.1–44.5%), respectively. Cataract was the major cause of blindness in both the studies. There was a significant reduction in blindness following cataract surgery as observed through RACSS (17.3%; 95% CI, 13.5–21.8%) compared with APEDS (34%; 95% CI, 20.9–49.3%). Conclusion: There was a significant reduction in prevalence of blindness and VI in this rural district of India over a decade. PMID:22944766

Khanna, Rohit C; Marmamula, Srinivas; Krishnaiah, Sannapaneni; Giridhar, Pyda; Chakrabarti, Subhabrata; Rao, Gullapalli N

2012-01-01

261

Seasonal to Decadal Variations of Water Vapor in the Tropical Lower Stratosphere Observed with Balloon-Borne Cryogenic Frost Point Hygrometers  

NASA Technical Reports Server (NTRS)

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 (10degN) 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.; Voemel, H.; Hasebe, F.; Shiotani, M.; Ogino, S.-Y.; Iwasaki, S.; Nishi, N.; Shibata, T.; Shimizu, K.; Nishimoto, E.; ValverdeCanossa, J. M.; Selkirk, H. B.; Oltmans, S. J.

2010-01-01

262

Tropical Atlantic influence on Pacific variability and mean state in the 20th century in observations and CMIP5  

NASA Astrophysics Data System (ADS)

This paper investigates the influence of the tropical Atlantic on the tropical Pacific interannual variability and mean state in the 20th century. It is demonstrated that observational datasets show a significant time-delayed impact of the tropical Atlantic on tropical Pacific sea surface temperatures, leading to an anticorrelation between the tropical Atlantic and the eastern Pacific if the Atlantic is leading by about 10 months. This result is robust across different sea surface temperature reconstructions. There is no robust correlation between the tropical Atlantic and the eastern Pacific when the Pacific is leading, although in recent decades a positive correlation between the two basins is more dominant. An analysis of the surface pressure response to the tropical Atlantic indicates an atmospheric bridge and a modification of the Walker Circulation as the likely trigger for the teleconnection, and this result is consistent with recent observational and modelling results for the recent decades. 16 out of the 45 analyzed World Climate Research Program's Coupled Model Intercomparison Project Phase 5 (CMIP5) models show lead-lag correlations broadly similar to the observed, whereas the majority of the models show either too strong correlations when the Pacific is leading or very weak correlations for all lags. The atmospheric bridge mechanism seems also valid in the selected CMIP5 models. In these models a stronger warming of the tropical Atlantic compared to the global mean is associated with a La Nina-like mean state change in the tropical Pacific. However, the ensemble mean of these models still shows a weakly El Nino-like trend, which is associated with a relatively weak Atlantic warming compared to the global mean and the observations

Kucharski, Fred; Syed, Faisal S.; Buran, Ahmad; Farah, Ikram; Gohar, Ali

2014-05-01

263

An objective analysis of the observed spatial structure of the tropical Indian Ocean SST variability  

NASA Astrophysics Data System (ADS)

The observed interannual Indian Ocean sea surface temperature (SST) variability from 1950 to 2008 is analyzed in respect to the spatial structure of the variability. The analysis is based on an objective comparison of the leading empirical orthogonal function modes against the stochastic null hypothesis of spatial red noise (isotropic diffusion). Starting from this red noise assumption, the analysis searches for those structures that are most distinct from the red noise hypothesis. This objective approach will put previously well and less known modes of variability into the context of the multivariate SST variability. The Indian Ocean SST variability is marked by relatively weak SST variability, which is strongly dominated by a basin wide monopole pattern that is caused by different processes. The leading modes of variability are the El Nino Southern Oscillation (ENSO) variability and the warming trend, which both project onto the basin wide monopole structure. Other more characteristic spatial patterns of internal variability are much less dominant in the tropical Indian Ocean, which is quite different from all other ocean basin, where characteristic teleconnection patterns exist. The remaining, ENSO independent, detrended variability is dominated by multi-pole patterns from the southern Indian Ocean reaching into the tropical Indian Ocean, which are probably primarily caused by extra-tropical atmospheric forcings. The large scale tropical Indian Ocean internal variability itself has no dominant structure. The currently often used dipole mode index (DMI) does not appear to present a dominant teleconnection pattern of the Indian Ocean internal SST variability. In the context of the objective analysis presented here, the DMI partly reflects the ENSO variability and is also a representation of the multi-dimensional, chaotic spatial red noise (isotropic diffusion) process. As such the DMI cannot be interpreted as a coherent teleconnection between the two poles.

Dommenget, Dietmar

2011-06-01

264

Interpreting intraseasonal variability of subsurface tracers observed by a profiling float  

NASA Astrophysics Data System (ADS)

Recent developments in autonomous biogeochemical instruments can provide new opportunities for investigating biogeochemical variability at unprecedented temporal resolutions. Early studies indicate the importance of relatively rapid and small-scale processes on biogeochemical variability. This analysis focuses on a profiling float deployed in the eastern subpolar North Pacific, showing significant intraseasonal variability in potential density, oxygen and nitrate. We find substantial variability for all tracers in the main thermocline at a depth of about 150 m, indicating a common mechanism. A strong linear correlation between the intraseasonal variability of isopycnal oxygen and nitrate (on ?? = 26.5 surface) with isopycnal spiciness indicates the role of physical transport and mixing. Power spectrum analysis shows a statistically significant spectral peak of about 1/(18 days) for observed tracers in the main thermocline. This high-frequency variability does not show any significant relationship with independent satellite measures of relevant physical and biological properties. With approximately 5 day sampling periods, this spectral peak could be produced by aliasing of the inertial and tidal frequencies, rather than true intraseasonal variability. The low-frequency component (>30 days) shows the spectral slope of ?-2 consistent with the stochastic null hypothesis. The growing number of autonomous biogeochemical observations will likely open up considerable opportunities for further research, and the analytical approaches in this paper will be useful for a further analysis of temporal variability of biogeochemical tracers.

Takano, Yohei; Ito, Takamitsu; Deutsch, Curtis; Johnson, Kenneth S.

2014-01-01

265

A review of observed variability in the dayside ionosphere of Mars Paul Withers  

E-print Network

spectrum, the meteoroid flux at Mars, remanent magnetism in ancient crustal rocks, and atmospheric dustReview A review of observed variability in the dayside ionosphere of Mars Paul Withers Center by Mars Global Surveyor and Mars Express have greatly increased the number of observations of the martian

Mendillo, Michael

266

EVALUATING CLIMATE VARIABILITY AND CHANGE FROM MODERN AND HISTORICAL SST OBSERVATIONS  

E-print Network

historical and modern observations of sea surface temperature (SST) into homogenous gridded data setsEVALUATING CLIMATE VARIABILITY AND CHANGE FROM MODERN AND HISTORICAL SST OBSERVATIONS Nick A-SME), Keplerlaan 1, 2201 AZ, Noordwijk The Netherlands, Email: Craig.Donlon@esa.int (9) Norwegian Meteorological

Kaplan, Alexey

267

Interannual variability of South Atlantic circulation from 4 years of TOPEX/POSEIDON satellite altimeter observations  

NASA Astrophysics Data System (ADS)

Variability of large-scale and regional South Atlantic circulation is investigated using TOPEX/POSEIDON sea level observations. Interannual variations are identified from empirical orthogonal functions of gridded sea level fields, year-to-year fluctuations of root-mean-square sea level variability, and variability of Agulhas eddies evaluated from the along-track data. Two modes of variability are identified. A basin-scale mode indicates that sea level in the eastern South Atlantic underwent a transition from a state of high sea level and enhanced gyre-scale geostrophic circulation in 1993 and 1994, to a state of lower sea level and more sluggish circulation in 1996. The dominant mode of basin-scale zonal wind has the same temporal signature, suggesting a link between the observed variation of gyre-scale circulation and the regional wind forcing. Time variations of this mode also coincide with a transition from a broad Agulhas eddy corridor observed in 1993 and 1994 to a narrower corridor observed in 1996. The input of salt and vorticity to the South Atlantic subtropical gyre via Agulhas eddies may therefore be partially controlled by interannual variations of the wind-forced, large-scale circulation. A second mode isolates interannual variations in the Brazil-Malvinas Confluence region. During 1993, eddy variability along the Brazil Current extension was relatively strong and variability along the continental slope was weak. The opposite pattern was observed in 1995. These variations may be related to interannual variations of the latitude of the confluence. While variations associated with both modes are smaller than those observed on seasonal timescales, these interannual variations contribute significantly to the total South Atlantic variability.

Witter, Donna L.; Gordon, Arnold L.

1999-09-01

268

X-ray and optical variability of Seyfert 1 galaxies as observed with XMM-Newton  

E-print Network

We have examined simultaneous X-ray and optical light curves of a sample of eight nearby Seyfert 1 galaxies observed using the EPIC X-ray cameras and Optical Monitor on board XMM. The observations span ~1 day and revealed optical variability in four of the eight objects studied. In all cases, the X-ray variability amplitude exceeded that of the optical both in fractional and absolute luminosity terms. No clearly significant correlations were detected between wavebands using cross correlation analysis. We conclude that, in three of the four objects in which optical variability was detected, reprocessing mechanisms between wavebands do not dominate either the optical or X-ray variability on the time-scales probed.

R. Smith; S. Vaughan

2007-01-08

269

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

Microsoft Academic Search

SummaryAim: 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

Zehra H. Adibelli; Ruken Ergenc; Ozgur Oztekin; Suheyla Ecevit; Gokhan Unal

2010-01-01

270

Report on the Photometric Observations of the Variable Stars DH Pegasi, DY Pegasi, and RZ Cephei  

NASA Astrophysics Data System (ADS)

We report 872 observations on two RR Lyrae variable stars, DH Pegasi and RZ Cephei, and on one SX Phoenicis variable, DY Pegasi. This paper discusses the methodology of our measurements, the light curves, magnitudes, epochs, and epoch prediction of the above stars. We also derived the period of DY Pegasi. All measurements and analyses are compared with prior publications and known values from multiple databases.

Abu-Sharkh, I.; Fang, S.; Mehta, S.; Pham, D.

2014-12-01

271

Application of the time-delay integration method: Survey observations of geosynchronous orbit objects and short-term variability observations  

NASA Astrophysics Data System (ADS)

"Time-Delay Integration (TDI)" readout technique has been adopted to a mosaic CCD camera equipped with four fully-depleted CCDs. Optical distortion and image deformation due to the TDI operation are discussed. The manner and advantages of the TDI method in survey observations of geosynchronous orbit objects are summarized. We propose a new TDI application method of getting short-term light curves of artificial space objects. This method of detecting a short-term variability can be applied for a variety of objects, ranging from satellites to stars. It can also be used for the light-curve observations of transient objects which might show short-term variability and of which the precise time information is needed.

Okumura, Shin-ichiro; Yanagisawa, Toshifumi; Nakaya, Hidehiko; Tanaka, Wataru; Nishiyama, Kota; Takahashi, Noritsugu; Yoshikawa, Makoto

2014-12-01

272

Reconstruction of Pacific Decadal Oscillation index using Pacific coral records since 1650  

Microsoft Academic Search

Here we develop a 300-year reconstruction of Pacific Decadal Oscillation (PDO) index from six corals records. Our result suggests that the modern observed PDO index is closely matched by the decadal mode variability of geochemical coral proxies. Comparison of our results with the PDO index from northern mid-high latitude tree rings (D` Arrigo et. al, 2001) indicates that the two

J. Liu; T. Crowley

2006-01-01

273

A review of observational evidence for short and long term ultraviolet flux variability of the Sun  

NASA Technical Reports Server (NTRS)

Observation of the Sun in the 160 to 400 nm wavelength region reveals no significant broadband variation with solar flares, variability associated with the rotation of active regions, and a possible long term change which may be related to the 11 year sunspot cycle or longer. A continuing ultraviolet solar flux variability below 200 nm was observed from 1969 through the present from satellites, which is modulated at solar rotation rates. Recent observations from Nimbus-7 show the solar flux is varying by significant amounts also in the regions from 200 nm up to the Calcium 2 H-line at 396.8 nm. Typically the flux may vary over a solar rotation from about 10 percent at 160 nm to slightly less than 1 percent at the Ca2 K-line. Results of an evaluation of observations from rockets, satellites, and the ground measurements are discussed.

Heath, D. F.

1980-01-01

274

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 (i) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the 20th century reanalysis v2 (20CRv2), (ii) to isolate the high frequency meteorological variability of MSL from longer-term changes, (iii) 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 (iv) 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 to 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. Reference: Dangendorf, S., Wahl, T., Nilson, E., Klein, B., Jensen, J. (2013): A new atmospheric proxy for sea level variability in the southeastern North Sea: observations and future ensemble projections, Climate Dynamics, doi:10.1007/s00382-013-1932-4.

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

2014-05-01

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

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...

277

PRECISE HIGH-CADENCE TIME SERIES OBSERVATIONS OF FIVE VARIABLE YOUNG STARS IN AURIGA WITH MOST  

SciTech Connect

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.

Cody, Ann Marie; Tayar, Jamie; Hillenbrand, Lynne A. [Department of Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Matthews, Jaymie M. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1 (Canada); Kallinger, Thomas, E-mail: amc@ipac.caltech.edu [Institut fuer Astronomie, Universitaet Wien, Tuerkenschanzstrasse 17, A-1180 Vienna (Austria)

2013-03-15

278

In this most recent Chandra observation, we see no significant time variability (right, 0th  

E-print Network

In this most recent Chandra observation, we see no significant time variability (right, 0th order Chandra grating data Line diagnostics The two sources are separated by only 3.5 pixels, which ne the Provosts Office at Swarthmore College and acknowledge support from Chandra grant G09-0019 to West Chester

Cohen, David

279

HF radar observations of small-scale surface current variability in the Straits of Florida  

E-print Network

HF radar observations of small-scale surface current variability in the Straits of Florida A. B-frequency Wellen radar (WERA), transmitting at 16.045 MHz, was deployed along the eastern Florida Shelf current measurements within the radar footprint along the shelf break at 86-m depth. The shallowest ADCP

Miami, University of

280

Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope  

E-print Network

The CAT Imaging Telescope has observed the BL Lac object Markarian 501 between March and August 1997. We report here on the variability over this time including several large flares. We present also preliminary spectra for all these data, for the low emission state, and for the largest flare.

A. Barrau; R. Bazer-Bachi; H. Cabot; L. M. Chounet; G. Debiais; B. Degrange; J. P. Dezalay; A. Djannati-Atai; D. Dumora; P. Espigat; B. Fabre; P. Fleury; G. Fontaine; R. George; C. ghesquiere; P. Goret; C. Gouiffes; I. A. Grenier; L. Iacoucci; S. Le Bohec; I. Malet; C. Meynadier; P. Munz; T. A. Palfrey; E. Pare; Y. Pons; M. Punch; J. Quebert; K. Ragan; C. Renault; M. Rivoal; L. Rob; P. Schovanek; D. Smith; J. P. Tavernet; J. Vrana

1997-10-23

281

EUVE Observations of Two UltraShort Period Magnetic Cataclysmic Variables  

Microsoft Academic Search

We propose to make the first EUVE observations of two newly discovered magnetic cataclysmic variables. The orbital period for one star is poorly defined but appears to be near 80 min, while the other, an eclipsing system, has an orbital period of 98 min. Both systems are interesting in that one shows an 8.45 min periodicity, indicative of a white

Steven B. Howell

1996-01-01

282

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

283

Understanding the Long-Term Spectral Variability of Cygnus X-1 from BATSE and ASM Observations  

NASA Technical Reports Server (NTRS)

We present a spectral analysis of observations of Cygnus X-1 by the RXTE/ASM (1.5-12 keV) and CGRO/BATSE (20-300 keV), including about 1200 days of simultaneous data. We find a number of correlations between intensities and hardnesses in different energy bands from 1.5 keV to 300 keV. In the hard (low) spectral state, there is a negative correlation between the ASM 1.5-12 keV flux and the hardness at any energy. In the soft (high) spectral state, the ASM flux is positively correlated with the ASM hardness (as previously reported) but uncorrelated with the BATSE hardness. In both spectral states, the BATSE hardness correlates with the flux above 100 keV, while it shows no correlation with the flux in the 20-100 keV range. At the same time, there is clear correlation between the BATSE fluxes below and above 100 keV. In the hard state, most of the variability can be explained by softening the overall spectrum with a pivot at approximately 50 keV. The observations show that there has to be another, independent variability pattern of lower amplitude where the spectral shape does not change when the luminosity changes. In the soft state, the variability is mostly caused by a variable hard (Comptonized) spectral component of a constant shape superimposed on a constant soft blackbody component. These variability patterns are in agreement with the dependence of the rms variability on the photon energy in the two states. We interpret the observed correlations in terms of theoretical Comptonization models. In the hard state, the variability appears to be driven mostly by changing flux in seed photons Comptonized in a hot thermal plasma cloud with an approximately constant power supply. In the soft state, the variability is consistent with flares of hybrid, thermal/nonthermal, plasma with variable power above a stable cold disk. Also, based on broadband pointed observations simultaneous with those of the ASM and BATSE, we find the intrinsic bolometric luminosity increases by a factor of approximately 3-4 from the hard state to the soft one, which supports models of the state transition based on a change of the accretion rate.

Zdziarski, Andrzej A.; Poutanen, Juri; Paciesas, William S.; Wen, Linqing; Six, N. Frank (Technical Monitor)

2002-01-01

284

The large-scale spatio-temporal variability of precipitation over Sweden observed from the weather radar network  

NASA Astrophysics Data System (ADS)

Using measurements from the national network of 12 weather radar stations for the last decade (2000-2010), we investigate the large-scale spatio-temporal variability of precipitation over Sweden. These statistics provide useful information to evaluate regional climate models as well as for hydrology and energy applications. A strict quality control is applied to filter out noise and artifacts from the radar data. We focus on investigating four distinct aspects namely, the diurnal cycle of precipitation and its seasonality, the dominant time scale (diurnal vs. seasonal) of variability, precipitation response to different wind directions, and the correlation of precipitation events with the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). When classified based on their intensity, moderate to high intensity events (precipitation > 0.34 mm (3 h)-1) peak distinctly during late afternoon over the majority of radar stations in summer and during late night or early morning in winter. Precipitation variability is highest over the southwestern parts of Sweden. It is shown that the high intensity events (precipitation > 1.7mm (3 h)-1) are positively correlated with NAO and AO (esp. over northern Sweden), while the low intensity events are negatively correlated (esp. over southeastern parts). It is further observed that southeasterly winds often lead to intense precipitation events over central and northern Sweden, while southwesterly winds contribute most to the total accumulated precipitation for all radar stations. Apart from its operational applications, the present study demonstrates the potential of the weather radar data set for studying climatic features of precipitation over Sweden.

Devasthale, A.; Norin, L.

2013-12-01

285

Decadal Prediction Research at NOAA/GFDL  

NASA Astrophysics Data System (ADS)

This paper is concerned with whether climate projections for the next several decades may be enhanced when models are initialized from the observed state of the climate system. Climate projections are started from an arbitrary point in time of a control integration. They are forced by specifying concentrations of greenhouse gases. The model is then integrated into the present and future. However, additional predictability may be obtained due to the low frequency variability of the climate system, especially from the ocean. In order to estimate the state of the climate system an initialization procedure that combines observations with the model needs to be in place. The GFDL Ensemble Coupled Data Assimilation estimates the temporally evolving probability distribution of climate states under an observational constraint. From this system a reanalysis from 1971-2010 is produced and is used to generate initial conditions. Using GFDL's CM2.1 CGCM 10 member ensembles of hindcasts and forecasts starting in January for every year 1971-2009 are run for 10 years.The predictions use the RCP4.5 scenario. Contrasting the uninitialized predictions with the initialized ones gives us an estimate of the role the internal variability may have in additional predictability of the climate system on decadal time scales. Our focus will be mainly on the prediction skill of the ocean. These predictions must be considered in the presence of model error, prediction uncertainty, projection uncertainty, and observational uncertainty.

Rosati, A. J.; Zhang, S.; Delworth, T. L.; Gudgel, R.; Chang, Y.

2010-12-01

286

Observing Campaign on Hubble's First Variable in M31: M31_V1  

NASA Astrophysics Data System (ADS)

An observing campaign is being carried out on M31_V1, the first variable star discovered in M31 by Edwin Hubble. The Hubble Heritage Team, with Dr. Keith Noll (STScI) as P.I., plans to observe M31_V1 with HST, and needs to know the phase of this Cepheid variable. Although basic parameters are known for this star, no recent photometry exists, so observations are required to generate current phase information. In 1925 Edwin Hubble published a note in The Observatory (vol. 48, 139) on "Cepheids in Spiral Nebulae." In 1929, he published a seminal paper in the Astrophysical Journal (vol. 69, 103), "A Spiral Nebula as a Stellar System, Messier 31." This paper discussed in detail the galaxy and the 50 variable stars he found in its outer regions. Hubble remarked that the 40 Cepheids found showed the period-luminosity relationship in a conspicuous manner, enabling distance to the galaxy to be calculated. Furthermore, he said that the results of his calculations supported the value determined by Harlow Shapley of the zero point of the period-luminosity relation. This confirmation of the zero point had significant implications for future extragalactic distance determinations. As the first of the variables on Hubble's list, V1, a Cepheid, is a historical curiosity. M31_V1 is magnitude 19.4V. B-V = +1.28, period is 30.41 days, and amplitude ~ 1.2 magnitudes in B, likely smaller in V. Five nights of data obtained by Arne Henden, AAVSO, show that the variable appears to have peaked on 2010 June 19 at about R=18 and as of July 2 was on its way down. It is recommended that observers use either an Rc filter or observe unfiltered. About an hour or more of exposure per integration will be required to reach S/N = 20, depending on your equipment and sky brightness; multiple exposures and stacking might be necessary to avoid saturating the background. The field is not crowded, and the variable itself is not blended. Contamination from the M31 background should n! ot be prohibitive. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp); Rc magnitudes of comparison stars are in the chart-associated photometry table. An R-band finder chart from the Isaac Newton 2.5-m telescope provided by Arne Henden is available. Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details and links to images and charts.

Waagen, Elizabeth O.

2010-07-01

287

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

288

Quantifying Spatial and Seasonal Variability in Atmospheric Ammonia with In Situ and Space-Based Observations  

NASA Technical Reports Server (NTRS)

Ammonia plays an important role in many biogeochemical processes, yet atmospheric mixing ratios are not well known. Recently, methods have been developed for retrieving NH3 from space-based observations, but they have not been compared to in situ measurements. We have conducted a field campaign combining co-located surface measurements and satellite special observations from the Tropospheric Emission Spectrometer (TES). Our study includes 25 surface monitoring sites spanning 350 km across eastern North Carolina, a region with large seasonal and spatial variability in NH3. From the TES spectra, we retrieve a NH3 representative volume mixing ratio (RVMR), and we restrict our analysis to times when the region of the atmosphere observed by TES is representative of the surface measurement. We find that the TES NH3 RVMR qualitatively captures the seasonal and spatial variability found in eastern North Carolina. Both surface measurements and TES NH3 show a strong correspondence with the number of livestock facilities within 10 km of the observation. Furthermore, we find that TES H3 RVMR captures the month-to-month variability present in the surface observations. The high correspondence with in situ measurements and vast spatial coverage make TES NH3 RVMR a valuable tool for understanding regional and global NH3 fluxes.

Pinder, Robert W.; Walker, John T.; Bash, Jesse O.; Cady-Pereira, Karen E.; Henze, Daven K.; Luo, Mingzhao; Osterman, Gregory B.; Shepard, Mark W.

2011-01-01

289

Spectral variability in Swift and Chandra observations of the Ultraluminous source NGC 55 ULX1  

E-print Network

NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only marginal hints of a limited number of dips in the light curve, previously reported to occur in this source, although the uncertainties due to the low counting statistics of the data are large. The Chandra and Swift spectra showed clearly spectral variability which resembles those observed in other ULXs. We can account for this spectral variability in terms of changes in both the normalization and intrinsic column density of a two-components model consisting of a blackbody (for the soft component) and a multicolour accretion disc (for the hard component). We discuss the possibility that strong outflows ejected by the disc are in part responsible for such spectral changes.

Pintore, F; Zampieri, L; Motta, S; Wolter, A

2015-01-01

290

Observations from earth orbit and variability of the polar aurora on Jupiter  

NASA Technical Reports Server (NTRS)

Spatially resolved spectra of Jupiter taken with the International Ultraviolet Explorer satellite show enhanced emissions from the polar regions at H L-alpha (1216 A) and in the Lyman and Werner bands of H2 (1175-1650 A). Two types of variability in emission brightness have been observed in these aurorae: an increase in the observed emission as the auroral oval rotates with Jupiter's magnetic pole to face toward the earth and a general variation in brightness of more than an order of magnitude under nearly identical observing conditions. In addition, the spectral character of these aurorae (determined by the ratio of H L-alpha to H2 brightnesses) appears variable, indicating that the depth of penetration of the auroral particles is not constant.

Clarke, J. T.; Moos, H. W.; Atreya, S. K.; Lane, A. L.

1980-01-01

291

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

292

Tropical Atlantic influence on Pacific variability and mean state in the twentieth century in observations and CMIP5  

NASA Astrophysics Data System (ADS)

This paper investigates the influence of the tropical Atlantic on the tropical Pacific interannual variability and mean state in the twentieth century. It is demonstrated that observational datasets show a significant time-delayed impact of the tropical Atlantic on tropical Pacific sea surface temperatures, leading to an anticorrelation between the tropical Atlantic and the eastern Pacific if the Atlantic is leading by about 10 months. This result is robust across different sea surface temperature reconstructions. There is no robust correlation between the tropical Atlantic and the eastern Pacific when the Pacific is leading, although in recent decades a positive correlation between the two basins is more dominant. An analysis of the surface pressure response to the tropical Atlantic indicates an atmospheric bridge and a modification of the Walker circulation as the likely trigger for the teleconnection, and this result is consistent with recent observational and modelling results for the recent decades. 30 out of the analyzed 45 World Climate Research Program's Coupled Model Intercomparison Project Phase 5 (CMIP5) models show statistically significant anticorrelations between individual tropical Atantic warm and cold events and the time-lagged eastern Pacific sea surface temperatues. 16 out of the 45 analyzed models fulfill the more stringent criterion of lead-lag correlations between the tropical Atlantic and Pacific similar to the observations. The atmospheric bridge mechanism seems also valid in the selected CMIP5 models. We have identified the tropical Atlantic warm bias present in nearly all models as one potential candidate for the overall weak time-delayed teleconnection between the tropical Atlantic and the Pacific, but also other mean state biases are important. In the selected models a stronger warming of the tropical Atlantic Ocean compared to the global sea surface temperature mean is associated with a La Nina-like mean state change in the tropical Pacific. However, the ensemble mean of these models still shows a weakly El Nino-like trend, which is associated with a relatively weak Atlantic warming compared to the global mean and the observations.

Kucharski, F.; Syed, F. S.; Burhan, A.; Farah, I.; Gohar, A.

2014-07-01

293

Inter-annual variability of dissolved inorganic nitrogen in the Biobío River, Central Chile: an analysis base on a decadal database along with 1-D reactive transport modeling  

NASA Astrophysics Data System (ADS)

Rivers may act as important sinks (filters) or sources for inorganic nutrients between the land and the sea, depending on the biogeochemical processes and nutrient inputs along the river. This study examines the inter-annual variability of dissolved inorganic nitrogen (DIN) seasonal (wet-dry) cycle for the Biobío River, one of the largest and most industrialized rivers of Central Chile (36°45'-38°49' S and 71°00'-73°20' W). Long-term water flow (1990-2012) and water quality datasets (2004-2012) were used along with a one-dimensional reactive transport ecosystem model to evaluate the effects of water flow and N inputs on seasonal pattern of DIN. From 2004 to 2012, annual average nitrate levels significantly increased from 1.73 ± 2.17 ?mol L-1 (upstream of the river) to 18.4 ± 12.7 ?mol L-1 (in the river mouth); while the annual average oxygen concentration decreased from 348 ± 22 to 278 ± 42 ?mol L-1 between upstream and downstream, indicating an additional oxygen consumption. Variability in the mid-section of the river (station BB8) was identified as a major influence on the inter-annual variability and appeared to be the site of a major anthropogenic disturbance. However, there was also an influence of climate on riverine DIN concentrations; high DIN production occurred during wet years, whereas high consumption proceeded during dry years. Extremely reduced river flow and drought during summer also strongly affected the annual DIN concentration, reducing the DIN production. Additionally, summer storm events during drought periods appeared to cause significant runoff resulting in nitrate inputs to the river. The total DIN input reaching the river mouth was 0.159 Gmol yr-1, implying that internal production exceeds consumption processes, and identifying nitrification as one of the predominant processes occurring in the estuary. In the following, the impact on the river of DIN increases as a nutrient source, as well as climate and biogeochemical factors are discussed.

Yévenes, M.; Figueroa, R.; Parra, O.; Farías, L.

2015-01-01

294

Comparison of dynamical model atmospheres of Mira variables with mid-infrared interferometric and spectroscopic observations  

E-print Network

We present a comparison of dynamical model atmospheres with mid-infrared (~11 micron) interferometric and spectroscopic observations of the Mira variable o Cet. The dynamical model atmospheres of Mira variables pulsating in the fundamental mode can fairly explain, without assuming ad-hoc components, the seemingly contradictory mid-infrared spectroscopic and interferometric observations of o Cet: the 11 micron sizes measured in the bandpass without any salient spectral features are about twice as large as those measured in the near-infrared. Our calculations of synthetic spectra show that the strong absorption due to a number of optically thick H2O lines is filled in by the emission of these H2O lines originating in the geometrically extended layers, providing a possible physical explanation for the picture proposed by Ohnaka (2004a) based on a semi-empirical modeling. This filling-in effect results in rather featureless, continuum-like spectra in rough agreement with the observed high-resolution 11 micron spectra, although the models still predict the H2O lines to be more pronounced than the observations. The inverse P-Cyg profiles of some strong H2O lines observed in the 11 micron spectra can also be reasonably reproduced by our dynamical model atmospheres. The presence of the extended H2O layers manifests itself as mid-infrared angular diameters much larger than the continuum diameter. The 11 micron uniform-disk diameters predicted by our dynamical model atmospheres are in fair agreement with those observed with the Infrared Spatial Interferometer (ISI), but still somewhat smaller than the observed diameters. We discuss possible reasons for this discrepancy and problems with the current dynamical model atmospheres of Mira variables.

K. Ohnaka; M. Scholz; P. R. Wood

2005-10-07

295

Spectral Variations of RV Tauri and Semi-Regular Variables Observed with Kepler  

NASA Astrophysics Data System (ADS)

We present ground-based spectra of RV Tauri and Semi-Regular variables taken simultaneously with our Cycle 2 Kepler observations of these objects. Our data set includes the Kepler light curves and spectra taken with the KPNO Coude Feed telescope and, for the fainter objects, the 4-meter Mayall telescope. Our spectral observations cover the region from 3700-5100 angstroms and 6400-9000 angstroms. We have spaced our ground-based observing runs out over a period of 1.5 years to include the twelve months covered by our Cycle 2 Kepler observations. Variations in the continuum, absorption lines and emission features in the spectra of these objects are discussed and compared to their simultaneously observed photometric variations acquired by Kepler. Support for this work is provided by the NSF PAARE program under award AST-0750814 and by NASA under award NNX11AB82G.

Walter, Donald K.; Howell, S. B.; Cash, J. L.

2012-01-01

296

Variability and Predictability of Land-Atmosphere Interactions: Observational and Modeling Studies  

NASA Technical Reports Server (NTRS)

The overall goal of this project is to increase our understanding of seasonal to interannual variability and predictability of atmosphere-land interactions. The project objectives are to: 1. Document the low frequency variability in land surface features and associated water and energy cycles from general circulation models (GCMs), observations and reanalysis products. 2. Determine what relatively wet and dry years have in common on a region-by-region basis and then examine the physical mechanisms that may account for a significant portion of the variability. 3. Develop GCM experiments to examine the hypothesis that better knowledge of the land surface enhances long range predictability. This investigation is aimed at evaluating and predicting seasonal to interannual variability for selected regions emphasizing the role of land-atmosphere interactions. Of particular interest are the relationships between large, regional and local scales and how they interact to account for seasonal and interannual variability, including extreme events such as droughts and floods. North and South America, including the Global Energy and Water Cycle Experiment Continental International Project (GEWEX GCIP), MacKenzie, and LBA basins, are currently being emphasized. We plan to ultimately generalize and synthesize to other land regions across the globe, especially those pertinent to other GEWEX projects.

Roads, John; Oglesby, Robert; Marshall, Susan; Robertson, Franklin R.

2002-01-01

297

Multicolor polarimetric observation of 15 min variability in S5 0716 714  

NASA Astrophysics Data System (ADS)

We present the result of near-infrared and optical observations of the BL Lac object S5 0716+714 carried out by the KANATA telescope (Uemura et al. 2008 in these proceedings). S5 0716+714 has both a long term violent variability and a short-term variability. The shortest time-scale variability, so-called microvariability, provides a clue of the minimum size of the emitting re- gion. Here, we report the detection of 15-min variability in S5 0716+714, which is one of the shortest time-scale in the optical and near-infrared variations observed in blazars. The de- tected microvariation had a small amplitude of 0.06±0.01 mag in V band and a blue color of ?(V - J) = -0.03±0.01. The microvariation has a feature of "bluer-when-brighter" that S5 0716+714 has in the variation time-scale of several hours. We furthermore obtained the tem- poral variation of polarization associated with the microvariation. We revealed that the microvari- ation had a specific polarization component whose polarization degree was higher than that of the overall trend. These results suggest that the microvariability originated from a small and local region where the magnetic field is aligned.

Sasada, M.; Uemura, M.; Arai, A.; Fukazawa, Y.; Kawabata, K. S.; Ohsugi, T.; Yamashita, T.; Isogai, M.; Mizuno, T.; Katagiri, H.; Sato, S.; Kino, M.

298

Hubble Space Telescope and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables  

Microsoft Academic Search

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

Paula Szkody; Anjum Mukadam; Boris T. Gänsicke; Patrick A. Woudt; Jan-Erik Solheim; Atsuko Nitta; Edward M. Sion; Brian Warner; D. K. Sahu; T. Prabhu; Arne Henden

2007-01-01

299

EUVE Observations of the Magnetic Cataclysmic Variable RE1938-461  

Microsoft Academic Search

The magnetic cataclysmic variable RE1938-461 was observed by the \\\\euve\\\\ Deep Survey instrument on July 8--9, 1992, during in-orbit calibration. It was detected in the Lexan\\/boron band (centered at 100 Angstroms) with a quiescent count rate of 0.0062+\\/- 0.0017 s(-1) and was not detected in the aluminum\\/carbon band (centered at 200 Angstroms). In addition, two transient events lasting ~ 1

J. K. Warren; J. V. Vallerga; C. W. Mauche; K. Mukai; O. H. W. Siegmund

1992-01-01

300

Summertime tropospheric ozone variability over the Mediterranean basin observed with IASI  

NASA Astrophysics Data System (ADS)

The Mediterranean basin is one of the most sensitive regions of the world to climate change and air quality issues. The particular dynamical situation of the Mediterranean basin leads to ozone amounts in the lower troposphere of the largest ones in the Northern Hemisphere. Six years of summertime tropospheric ozone observed from IASI from 2007 to 2012 have been analyzed to document the variability of ozone over this region. In the lower troposphere a large West-East gradient is observed with an enhancement of ozone in the Eastern part of the basin. This gradient is explained by (i) the diabatic convection over the Persian Gulf during the Indian Monsoon, which induces an important subsidence of ozone rich air masses from the upper to the lower troposphere over the central Mediterranean basin; (ii) the Etesian winds which set up during summer between the Azores anticyclone to the West and the thalweg of Indian Monsoon to the East, leading to a horizontal advection of potentially ozone rich air masses from the European industrial areas. Concerning the temporal variability of ozone over the basin, the IASI observation analysis shows a summertime maximum in July in the lower troposphere. The high correlation with the 300 hPa potential vorticity indicates that the temporal variability of lower tropospheric ozone is mainly driven by vertical exchanges between the upper and the lower troposphere. Two case studies (June 2008 and June 2009) showing ozone anomalies (positive and negative) will also be presented and related to two particular meteorological situations.

Doche, Clément; Dufour, Gaëlle; Foret, Gilles; Eremenko, Maxim; Cuesta, Juan; Beekmann, Matthias

2014-05-01

301

Observing Campaign to Monitor Magnetically-Active Dwarfs for Long-Term Variability  

NASA Astrophysics Data System (ADS)

Dr. Styliani (Stella) Kafka of the Department of Terrestrial Magnetism, Carnegie Institute of Washington, requests AAVSO observers to perform long-term photometric monitoring on a number of magnetically active dwarf stars, with an observing frequency of one observation every three days taken with one or more filters. When multiple filters are available, the preferred observations are (in order of precedence): Rc, V, Ic, and B. Please observe such that you obtain a signal to noise of at least 50 (100 or higher is preferred). These objects are all nearby dwarfs known or suspected to have magnetic activity, primarily of the UV Ceti (flare star) or BY Draconis subtypes. Long-term photometric monitoring of these objects will be used in conjunction with other multiwavelength observations from ground-based facilities including the Magellan 6.5-meter and DuPont 2.5-meter telescopes in Chile to understand the long-term magnetic activity cycles of these stars. Such a study can reveal information about the physical natures of these stars, but also about their near space environments and habitability for life. These objects are red, and the variability amplitudes are low, often well below 0.1 magnitudes. The long-term variability due to stellar activity cycles may be much lower. Photometric accuracy rather than the number of observations are key to the success of this project. Unaccounted-for atmospheric effects such as extinction will likely overwhelm any long-term signal from these stars. Observers are strongly urged to fully calibrate their systems and to carefully reduce and transform their photometry to standard photometric passbands, including corrections for airmass/atmospheric extinction. Parameters for 40 objects are given. Observations should be submitted to the AAVSO International Database.

Templeton, Matthew R.

2009-10-01

302

Split-beam echosounder observations of natural methane seep variability in the northern Gulf of Mexico  

NASA Astrophysics Data System (ADS)

A method for positioning and characterizing marine gas seeps using an 18-kHz scientific split-beam echosounder (SBES) was developed and applied to SBES data collected in the northern Gulf of Mexico. A total of 161 plumes of presumed methane gas bubbles originating at approximately 1400 m depth were observed over 27 repeat surveys and grouped by proximity into 35 clusters. Profiles of mean target strength per vertical meter were calculated with compensation for SBES beam pattern and geometry of plume axis ensonification. These profiles were used as indicators of the fluxes and fates of gas bubbles acoustically observable at 18 kHz and showed significant variability between repeat observations at time intervals of 1 hour to 7.5 months. The minimum depths of acoustic plume observations averaged 875 m and frequently coincided with increased reverberation in layers of biological scatterers. Minimum depth estimates were limited by the SBES beam pattern in five instances.

Jerram, Kevin

303

LRO/LAMP Observations of Temporal Variability of Lunar Exospheric Helium During June and July 2012  

NASA Astrophysics Data System (ADS)

We have previously reported on observations of the lunar helium exosphere made in January 2012 with the Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph on NASA's Lunar Reconnaissance Orbiter Mission. Those observations, of resonantly scattered He I emission at 584 Å from illuminated atmosphere against the dark lunar surface, were made over the night side of the Moon within 30 degrees of the dawn terminator. During June-July 2012 these observations were repeated, this time including both the dusk and dawn terminators. We find temporal variability of the derived surface He density as well as a strong dawn/dusk asymmetry with the He density on the dawn side approximately a factor of three higher than at corresponding longitudes on the dusk side. We again observe a factor of two decrease in surface density during the passage of the Moon through the Earth's magnetotail.

Feldman, P. D.; Hurley, D. M.; Retherford, K. D.; Gladstone, R.; Stern, S. A.; Pryor, W. R.; Parker, J.

2012-12-01

304

Variability of Atlantic inflow to the Arctic Ocean from summer hydrographic observations in the Nordic Seas and Fram Strait  

NASA Astrophysics Data System (ADS)

Before reaching the Arctic Ocean, warm and salty water masses, originating from the North Atlantic, pass the eastern rims of the Norwegian and Greenland Seas and continue farther to the north through Fram Strait. During its northward advection the Atlantic water (AW) is continuously transformed and its temperature, salinity and heat content changes significantly. A part of the AW heat is released to the atmosphere while a major share is lost due to lateral exchanges and mixing with adjacent water masses. This study addresses summer-to-summer variability, transformation, and circulation patterns of the Atlantic water in the region between the northern Norway and northern Fram Strait. We will present results of the long-term summer measurements in the Norwegian-Atlantic and West Spitsbergen Currents, carried in 1996-2013 by Institute of Oceanology PAS, and compare them to continuous observations from the moored array maintained by Alfred Wegener Institute in the northern Fram Strait, to estimate the impact of seasonal variations on long-term changes in the AW properties. Significant variability over different time scales has been observed in the properties of the AW over the studied period with the warmest AW inflow in late 90s and 2005-2006 and a significant positive trend in AW salinity. Time series of temperature and salinity at the standard hydrographic section at 76°30'N reveal a presence of three 5-6 years long cycles. Spatial distributions of AW properties and geostrophic velocities in the studied region show alternating phases of intensified AW inflow into the Barents Sea and periods of increased northward volume and heat transport through Fram Strait. Using available reanalysis data and meteorological measurements from Svalbard area we will attempt to explain possible links between observed changes and atmospheric forcing. The hydrographic measurements, continued by IO PAS for nearly two decades in the Nordic Seas and Fram Strait, have been strongly supported by Eberhard Fahrbach. His experience and advice significantly helped Polish oceanographers to establish the long-term observational program in the northern polar region, which brought the results presented here.

Beszczynska-Möller, Agnieszka; Walczowski, Waldemar; Fahrbach, Eberhard

2014-05-01

305

Variability of linezolid concentrations after standard dosing in critically ill patients: a prospective observational study  

PubMed Central

Introduction Severe infections in intensive care patients show high morbidity and mortality rates. Linezolid is an antimicrobial drug frequently used in critically ill patients. Recent data indicates that there might be high variability of linezolid serum concentrations in intensive care patients receiving standard doses. This study was aimed to evaluate whether standard dosing of linezolid leads to therapeutic serum concentrations in critically ill patients. Methods In this prospective observational study, 30 critically ill adult patients with suspected infections received standard dosing of 600 mg linezolid intravenously twice a day. Over 4 days, multiple serum samples were obtained from each patient, in order to determine the linezolid concentrations by liquid chromatography tandem mass spectrometry. Results A high variability of serum linezolid concentrations was observed (range of area under the linezolid concentration time curve over 24 hours (AUC24) 50.1 to 453.9 mg/L, median 143.3 mg*h/L; range of trough concentrations (Cmin)?observed for 63% and 50% of the patients, respectively. Finally, potentially toxic levels (defined as AUC24?>?400 mg*h/L and Cmin?>?10 mg/L) were observed for 7 of the patients. Conclusions A high variability of linezolid serum concentrations with a substantial percentage of potentially subtherapeutic levels was observed in intensive care patients. The findings suggest that therapeutic drug monitoring of linezolid might be helpful for adequate dosing of linezolid in critically ill patients. Trial registration Clinicaltrials.gov NCT01793012. Registered 24 January 2013. PMID:25011656

2014-01-01

306

Summertime tropospheric ozone variability over the Mediterranean basin observed with IASI  

NASA Astrophysics Data System (ADS)

The Mediterranean basin is one of the most sensitive regions of the world regarding climate change and air quality. This is partly due to the singular dynamical situation of the Mediterranean basin that leads to among the highest tropospheric ozone concentrations over the Northern Hemisphere. Six years of summertime tropospheric ozone observed by the IASI instrument from 2007 to 2012 have been analysed to document the variability of ozone over this region. The satellite observations have been also examined in parallel with meteorological analyses (from ECMWF) to understand the processes that drive this variability. This work confirmed the presence of a steep west-east ozone gradient in the lower troposphere with the highest concentrations observed over the eastern part of the Mediterranean basin. This gradient is mainly explained by the diabatic convection over the Persian Gulf during the Indian Monsoon, which induces an important subsidence of ozone rich air masses from the upper to the lower troposphere over the central and the eastern Mediterranean basin: IASI observations of ozone concentrations at 3 km height show a clear summertime maximum in July that is well correlated to the maximum of downward transport of rich-ozone air masses from the upper troposphere. Even if this feature is robust over the six analyzed years, we have also investigated monthly ozone anomalies, one positive (June 2008) and one negative (June and July 2009) using daily observations of IASI. We show that the relative position and the strength of the meteorological systems (Azores anticyclone and Middle eastern depression) present over the Mediterranean are key factors to explain both the variability and the anomalies of ozone in the lower troposphere in this region.

Doche, C.; Dufour, G.; Foret, G.; Eremenko, M.; Cuesta, J.; Beekmann, M.; Kalabokas, P.

2014-05-01

307

Summertime tropospheric-ozone variability over the Mediterranean basin observed with IASI  

NASA Astrophysics Data System (ADS)

The Mediterranean basin is one of the most sensitive regions in the world regarding climate change and air quality. This is partly due to the singular dynamical situation of the Mediterranean basin that leads to tropospheric-ozone concentrations that are among the highest over the Northern Hemisphere. Six years of summertime tropospheric ozone observed by the Infrared Atmospheric Sounding Interferometer (IASI) instrument from 2007 to 2012 have been analysed to document the variability of ozone over this region. The satellite observations have been examined together with meteorological analyses (from ECMWF) to understand the processes driving this variability. Our work confirmed the presence of a steep west-east ozone gradient in the lower troposphere with the highest concentrations observed over the eastern part of the Mediterranean basin. This gradient is mainly explained by diabatic convection over the Persian Gulf during the Indian monsoon season, which induces an important subsidence of ozone-rich air masses from the upper to the lower troposphere over the central and the eastern Mediterranean basin. IASI observations of ozone concentrations at a 3 km height show a clear summertime maximum in July that is well correlated to the maximum of downward transport of ozone-rich air masses from the upper troposphere. Even if this feature is robust over the six analysed years, we have also investigated monthly ozone anomalies - one positive (June 2008) and one negative (June and July 2009) - using daily IASI observations. We show that the relative position and the strength of the meteorological systems (Azores anticyclone and Middle Eastern depression) present over the Mediterranean are key factors in explaining both the variability and the anomalies of ozone in the lower troposphere in this region.

Doche, C.; Dufour, G.; Foret, G.; Eremenko, M.; Cuesta, J.; Beekmann, M.; Kalabokas, P.

2014-10-01

308

Inter-observer Variability in Esophageal Body Measurements with High Resolution Manometry among New Physician Users  

PubMed Central

Goals To evaluate inter-observer variability among four new physician users on measures of esophageal body function. Background Esophageal high resolution manometry (HRM) allows observation of esophageal motility via pressure topography plots. Little is known about the inter-observer variability among physicians. Study Two resident and two fellow level physicians each interpreted 10 liquid swallows of 20 esophageal HRM studies (n=200 swallows) using the BioVIEW Analysis Suite (Sandhill Scientific, Inc.). Studies evaluated were from patients referred for evaluation of dysphagia but found to have normal esophageal manometry and complete liquid bolus transit. Physicians received an orientation session and reviewed recent literature. Each physician recorded contractile front velocity (CFV) and distal contractile integral (DCI) for each liquid swallow. STATISTICS: Inter-observer agreements for CFV and DCI were assessed by intraclass correlation (ICC) values. Linear correlations between measurements by two readers were assessed using linear regression modeling techniques. Results CFV and DCI values of up to 200 data points were analyzed. Four reader results for CFV and DCI showed strong agreement although stronger for DCI measures (ICC=0.94; 0.91 - 0.98) in comparison to CFV (ICC=0.79; 0.52 - 0.82). Further correlation was performed with two readers; readers 1 and 2 revealed excellent correlation for DCI (r=0.95, p<0.001) and good correlation for CFV (r=0.61, p<0.001). Conclusions With a thorough orientation session, good to excellent agreement for CFV and DCI measurements can be obtained from new physician users. CFV measures exhibit greater inter-observer variability possibly due to the artifact produced by intraesophageal pressurization. PMID:22647828

Singh, Erick; Rife, Christopher; Clayton, Steven; Naas, Peter; Nietert, Paul; Castell, Donald

2012-01-01

309

Observer variability in pinniped counts: Ground-based enumeration of walruses at haul-out sites  

USGS Publications Warehouse

Pinnipeds are often monitored by counting individuals at haul-out sites, but the often large numbers of densely packed individuals at these sites are difficult to enumerate accurately. Errors in enumeration can induce bias and reduce precision in estimates of population size and trend. We used data from paired observers monitoring walrus haul-outs in Bristol Bay, Alaska, to quantify observer variability and assess its relative importance. The probability of a pair of observers making identical counts was 50 individuals. Mean count differences ranged up to 25% for the largest counts, depending on beach and observers. In at least some cases, there was a clear tendency for counts of one observer to be consistently greater than counts of the other observer in a pair, indicating that counts of at least one of the observers were biased. These results suggest that efforts to improve accuracy of counts will be worthwhile. However, we also found that variation among observers was relatively small compared to variation among visits to a beach so that efforts to account for other sources of variation will be more important.

Udevitz, M.S.; Jay, C.V.; Cody, M.B.

2005-01-01

310

Tidal Variability during Stratospheric Sudden Warmings: Comparison between a Whole Atmosphere Model and Satellite Observations  

NASA Astrophysics Data System (ADS)

We compare results from a whole atmosphere-ionosphere coupled model, GAIA, and from the COSMIC and TIMED/SABER observations during 2008/2009 northern winter season. The GAIA model has assimilated meteorological reanalysis data by a nudging method. The comparison shows general agreements in the major features from the stratosphere to the ionosphere including the growth and decay of the major stratospheric sudden warming (SSW) event in 2009. During the major SSW period, a pronounced semidiurnal variation in the F-region electron density and its local-time phase shift similar to the previous observations are reproduced by the model and COSMIC observation. The model suggests that the TEC variation is caused by an enhanced semidiurnal variation in the EXB drift, which is probably related to an amplified semidiurnal migrating tide (SW2) in the lower thermosphere. The model and TIMED/SABER observation show that the SW2 tide amplifies at low latitudes from the stratosphere to the thermosphere as well as the phase variation. Possible sources of the SW2 variability could be related to the changing background wind and temperature distributions and/or to the stratospheric ozone variability. Cases of other SSWs are also studied.

Jin, H.; Miyoshi, Y.; Pancheva, D.; Mukhtarov, P.; Fujiwara, H.; Shinagawa, H.; Murata, T.

2012-12-01

311

Observed thinning of Totten Glacier is linked to coastal polynya variability  

NASA Astrophysics Data System (ADS)

Analysis of ICESat-1 data (2003-2008) shows significant surface lowering of Totten Glacier, the glacier discharging the largest volume of ice in East Antarctica, and less change on nearby Moscow University Glacier. After accounting for firn compaction anomalies, the thinning appears to coincide with fast-flowing ice indicating a dynamical origin. Here, to elucidate these observations, we apply high-resolution ice-ocean modelling. Totten Ice Shelf is simulated to have higher, more variable basal melting rates. We link this variability to the volume of cold water, originating in polynyas upon sea ice formation, reaching the sub-ice-shelf cavity. Hence, we propose that the observed increased thinning of Totten Glacier is due to enhanced basal melting caused by a decrease in cold polynya water reaching its cavity. We support this hypothesis with passive microwave data of polynya extent variability. Considering the widespread changes in sea ice conditions, this mechanism could be contributing extensively to ice-shelf instability.

Khazendar, A.; Schodlok, M. P.; Fenty, I.; Ligtenberg, S. R. M.; Rignot, E.; van den Broeke, M. R.

2013-12-01

312

A Decade of Growth  

NASA Technical Reports Server (NTRS)

This paper examines the Space Surveillance Network catalog's growth in low Earth orbit (LEO) and the geosynchronous Earth orbit (GEO) over the decade 1990-2000. During this time, innovative space utilization concepts, e.g. the Iridium and Globalstar commercial communication satellite constellations, have increased the public's consciousness of space. At the same time, however, these constellations have increased spatial density per 10 km altitude bin by factors of two and three respectively. While not displaying as spectacular a growth in spatial density, other regions of space have grown steadily in terms of number, mass, size, and operational lifetime. In this work we categorize launch traffic by type (e.g. payload, rocket body, operational debris, fragmentation debris, or anomalous debris), mass, and size so as to present the observed growth numerically, in terms of mass, and in terms of cross-sectional area. GEO traffic is further categorized by operational longitude. Because growth itself defines only the instantaneous environment, we also examine the higher-order derivatives of growth. In addition, we compare the last decade's growth with modeling results to illustrate the subtle effects of inclination, eccentricity, and size, in addition to spatial densities, on estimating the collision probability. We identify those regions of space most subject to accidental collision.

Johnson, Nicholas L.; Anzz-Meador, Phillip D.

2001-01-01

313

Linking optical and infrared observations with gravitational wave sources through variability  

E-print Network

Optical and infrared observations have thus far detected more celestial cataclysms than have been seen in gravity waves (GW). This argues that we should search for gravity wave signatures that correspond to flux variability seen at optical wavelengths, at precisely known positions. There is an unknown time delay between the optical and gravitational transient, but knowing the source location precisely specifies the corresponding time delays across the gravitational antenna network as a function of the GW-to-optical arrival time difference. Optical searches should detect virtually all supernovae that are plausible gravitational radiation sources. The transient optical signature expected from merging compact objects is not as well understood, but there are good reasons to expect detectable transient optical/IR emission from most of these sources as well. The next generation of deep wide-field surveys (for example PanSTARRS and LSST) will be sensitive to subtle optical variability, but we need to fill the ``blin...

Stubbs, Christopher W

2007-01-01

314

Observed snowfall and river discharge trend and low-frequency variability over Alps  

NASA Astrophysics Data System (ADS)

We present a twofold analysis of long-term trend and variability of different factors affecting the hydrological cycle over the Alps in spring. The study is based on datasets derived from observations for the last 150 years. In one case we focus on snowfall flux, which we found shifting between two different regimes in concert with the Atlantic Multidecadal Oscillation. This teleconnection is explained by a mixture of changes in circulation and by local climatic feedbacks. Moreover, we analyzed the timing of the river discharge peaks relative to the main Alpine rivers, finding similar features of low frequency variability, and a common anticipation tendency of more than two weeks per century, probably explained by a change of seasonality of total precipitation.

Zampieri, Matteo; Scoccimarro, Enrico; Gualdi, Silvio

2014-05-01

315

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA: RESULTS FROM THE 2010 OBSERVING SEASON  

SciTech Connect

We present results from a season of observations with the Chinese Small Telescope ARray, obtained over 183 days of the 2010 Antarctic winter. We carried out high-cadence time-series aperture photometry of 9125 stars with i ?< 15.3 mag located in a 23 deg{sup 2} region centered on the south celestial pole. We identified 188 variable stars, including 67 new objects relative to our 2008 observations, thanks to broader synoptic coverage, a deeper magnitude limit, and a larger field of view. We used the photometric data set to derive site statistics from Dome A. Based on two years of observations, we find that extinction due to clouds at this site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time, respectively.

Wang, Lingzhi; Zhu, Zonghong [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Macri, Lucas M.; Wang, Lifan [Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Ashley, Michael C. B.; Lawrence, Jon S.; Luong-Van, Daniel; Storey, John W. V. [School of Physics, University of New South Wales, NSW 2052 (Australia); Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Liu, Qiang; Shang, Zhaohui; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; Zhou, Xu; Zhu, Zhenxi [Chinese Center for Antarctic Astronomy, Nanjing 210008 (China); Pennypacker, Carl R. [Center for Astrophysics, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); York, Donald G., E-mail: wanglingzhi@bao.ac.cn [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

2013-12-01

316

Variability in the Speed of the Brewer-Dobson Circulation as Observed by Aura/MLS  

NASA Technical Reports Server (NTRS)

We use Aura/MLS stratospheric water vapour (H2O) measurements as tracer for dynamics and infer interannual variations in the speed of the Brewer-Dobson circulation (BDC) from 2004 to 2011. We correlate one-year time series of H2O in the lower stratosphere at two subsequent pressure levels (68 hPa, approx.18.8 km and 56 hPa, approx 19.9 km at the Equator) and determine the time lag for best correlation. The same calculation is made on the horizontal on the 100 hPa (approx 16.6 km) level by correlating the H2O time series at the Equator with the ones at 40 N and 40 S. From these lag coefficients we derive the vertical and horizontal speeds of the BDC in the tropics and extra-tropics, respectively. We observe a clear interannual variability of the vertical and horizontal branch. The variability reflects signatures of the Quasi Biennial Oscillation (QBO). Our measurements confirm the QBO meridional circulation anomalies and show that the speed variations in the two branches of the BDC are out of phase and fairly well anti-correlated. Maximum ascent rates are found during the QBO easterly phase. We also find that transport of H2O towards the Northern Hemisphere (NH) is on the average two times faster than to the Southern Hemisphere (SH) with a mean speed of 1.15m/s at 100 hPa. Furthermore, the speed towards the NH shows much more interannual variability with an amplitude of about 21% whilst the speed towards the SH varies by only 10 %. An amplitude of 21% is also observed in the variability of the ascent rate at the Equator which is on the average 0.2mm/s.

Flury, Thomas; Wu, Dong L.; Read, W. G.

2013-01-01

317

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

318

Mechanisms for Diurnal Variability of Global Tropical Rainfall Observed from TRMM  

NASA Technical Reports Server (NTRS)

The behavior and various controls of diurnal variability in tropical-subtropical rainfall are investigated using Tropical Rainfall Measuring Mission (TRMM) precipitation measurements retrieved from the three level-2 TRMM standard profile algorithms for the 1998 annual cycle. Results show that diurnal variability characteristics of precipitation are consistent for all three algorithms, providing assurance that TRMM retrievals are producing consistent estimates of rainfall variability. As anticipated, most ocean areas exhibit more rainfall at night, while over most land areas, rainfall peaks during daytime; however, important exceptions are noted. The dominant feature of the oceanic diurnal cycle is a rainfall maximum in late-evening-early-morning (LE-EM) hours, while over land the dominant maximum occurs in the mid- to late afternoon (MLA). In conjunction with these maxima are pronounced seasonal variations of the diurnal amplitudes. Amplitude analysis shows that the diurnal pattern and its seasonal evolution are closely related to the rainfall accumulation pattern and its seasonal evolution. In addition, the horizontal distribution of diurnal variability indicates that for oceanic rainfall, there is a secondary MLA maximum coexisting with the LE-EM maximum at latitudes dominated by large-scale convergence and deep convection. Analogously, there is a preponderancy for an LE EM maximum over land coexisting with the stronger MLA maximum, although it is not evident that this secondary continental feature is closely associated with the large-scale circulation. Neither of the secondary maxima exhibit phase behavior that can be considered semidiurnal in nature. Diurnal rainfall variability over the ocean associated with large-scale convection is clearly an integral component of the general circulation. Phase analysis reveals differences in regional and seasonal features of the diurnal cycle, indicating that underlying forcing mechanisms differ from place to place. This is underscored by the appearance of secondary ocean maxima in the presence of large-scale convection, along with other important features. Among these, there are clear-cut differences between the diurnal variability of seasonal rainfall over the mid-Pacific and Indian Ocean Basins. The mid-Pacific exhibits double maxima in spring and winter but only LE-EM maxima in summer and autumn, while the Indian Ocean exhibits double maxima in spring and summer and only an LE-EM maximum in autumn and winter. There are also evident daytime maxima within the major large-scale marine stratocumulus regions off the west coasts of continents. The study concludes with a discussion concerning how the observational evidence either supports or repudiates possible forcing mechanisms that have been suggested to explain diurnal rainfall variability.

Yang, Song; Smith, Eric a.

2006-01-01

319

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

320

Observation of the F2-layer variability from the “Alma-Ata” observatory  

NASA Astrophysics Data System (ADS)

Hourly values of the F-region critical frequency, foF2, obtained by ground-based ionosonde method at Alma-Ata station during 1988 1999 are used to study the F2-layer variability in terms of ?foF2 obtained as a relative deviation of the current foF2 values from their background level. It has been found that in comparison with summer and equinox the winter ionosphere is more variable with an increase in the night time ionosphere day-to-day variability. Usually, the relative deviations ?foF2 occurred in the ±20% range, with about 80% of them occurring in the ±10% range. The winter nighttime ?foF2 values usually occurred in the range from -30% to 25%. Examples of the emission rate and rotational temperature for the O2 (0 1) atmospheric band obtained at Almaty using the MORTI instrument over nights of January and May 1999 show that the range of the ?E and ?T deviations like those in the ionosphere are maximum in winter like those in the ionosphere suggesting that the winter mesosphere is also more variable than summer mesosphere. Ionospheric data indicate episodic events of pronounced planetary wave (PW)-like oscillations observed in winter ionosphere. Two of the events, which occurred in the period of December 1994 January 1995 and December 1998, are analysed and revealed planetary-wave (PW) like oscillations in foF2 with periods of 5 14 days. The midnight ionospheric data were compared with available optical data obtained at Almaty employing the MORTI instrument for the period of December 1998 January 1999. The comparison showed that the F2-layer electron density, O2 emission rate and rotational temperatures over the entire period of observations tend to behave similarly, indicating oscillations with a period of about 9 days. NCEP/NCAR-reanalysis temperature and zonal wind at 40N and at 10 hPa pressure level as well as geopotential heights at 1 hPa pressure level (UKMO assimilated data) were analysed to interpret the observed perturbations in the mesosphere and ionosphere. A good coincidence between PW-like oscillations in foF2 and those of geopotential heights for periods of about 5 and 9 14 days has been obtained. The number of geomagnetic storms registered at Alma-Ata has been analysed as a plausible source of the ionosphere variability. Potential mechanisms linking the PW-like activity in the ionosphere with the wave events in the stratosphere/mesosphere have also been discussed.

Gordienko, G. I.; Aushev, V. M.; Fedulina, I. N.; Ryazapova, S. Sh.; Shepherd, M. G.

2005-04-01

321

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

322

Regulation of Ignition and Fire Spread by Climate and Landscape Variables in Boreal Forest Ecosystems Using Satellite Observations  

NASA Astrophysics Data System (ADS)

Burned area records in Alaska indicate an increase over the last several decades. Three of the last ten years are among the largest burned area years in recent history. In the complex framework of boreal ecosystems, fire disturbances directly and indirectly influence carbon emissions, albedo, successional cycles and permafrost thaw. There is still a considerable lack of observations and models to understand the response of these ecosystems to fire. The response of fire disturbance regime to climate warming is also poorly understood. Changes in fire disturbance regime are likely to have an important impact on carbon cycle and ecosystems. Therefore it is particularly important to understand the drivers behind large burned area years in boreal ecosystems. We combined MODIS active fires (MCD14ML) information; MODIS imagery (MOD13A1) and ancillary historic fire perimeter database (Alaska Large Fire Dataset) to produce a dataset of fire spread maps (daily burned area) in Alaska for the period 2001-2011. To achieve this, we performed a spatial interpolation of the MODIS active fires detection dates. Subsequently we apply a spectral index calculated from multitemporal MODIS at 500-meter spatial resolution to remove unburned islands. The output maps provide a spatial and temporally continuous representation of fire progression and a precise identification of ignition and extinction dates for each fire and burned area. We use these fire spread maps to investigate the relationship between day-to-day burned area driver variables including meteorological variables and landscape characteristics (land cover, relief). We found a strong relationship between daily burned area and vapor pressure deficit both for individual fires and for the region as a whole. This spatiotemporal analysis allows a better characterization of fires in Alaska and provides a better understanding into the controls leading to large fires in Alaskan boreal forest ecosystems. The link between daily burned area from the fire spread maps and meteorological and landscape variables allows us to obtain a more precise calculation of daily carbon emissions and regional-scale total carbon emission estimates from wildfires for Alaska. The future integration of bottom-up emissions with measurements being collected in the framework of the Carbon in Arctic Reservoirs Vulnerability Experiment project (CARVE) will contribute to refine emission models.

Sedano, F.; Randerson, J. T.; Miller, C. E.

2012-12-01

323

Quantitative Comparison of the Variability in Observed and Simulated Shortwave Reflectance  

NASA Technical Reports Server (NTRS)

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a climate observation system that has been designed to monitor the Earth's climate with unprecedented absolute radiometric accuracy and SI traceability. Climate Observation System Simulation Experiments (OSSEs) have been generated to simulate CLARREO hyperspectral shortwave imager measurements to help define the measurement characteristics needed for CLARREO to achieve its objectives. To evaluate how well the OSSE-simulated reflectance spectra reproduce the Earth s climate variability at the beginning of the 21st century, we compared the variability of the OSSE reflectance spectra to that of the reflectance spectra measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY). Principal component analysis (PCA) is a multivariate decomposition technique used to represent and study the variability of hyperspectral radiation measurements. Using PCA, between 99.7%and 99.9%of the total variance the OSSE and SCIAMACHY data sets can be explained by subspaces defined by six principal components (PCs). To quantify how much information is shared between the simulated and observed data sets, we spectrally decomposed the intersection of the two data set subspaces. The results from four cases in 2004 showed that the two data sets share eight (January and October) and seven (April and July) dimensions, which correspond to about 99.9% of the total SCIAMACHY variance for each month. The spectral nature of these shared spaces, understood by examining the transformed eigenvectors calculated from the subspace intersections, exhibit similar physical characteristics to the original PCs calculated from each data set, such as water vapor absorption, vegetation reflectance, and cloud reflectance.

Roberts, Yolanda, L.; Pilewskie, P.; Kindel, B. C.; Feldman, D. R.; Collins, W. D.

2013-01-01

324

HST and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables  

E-print Network

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 SDSS013132.39-090122.3, SDSSJ161033.64-010223.3 and SDSSJ220553.98+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 15,000K. These temperatures place the accreting white dwarfs outside the instability zone for non-interacting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs.

Paula Szkody; Anjum Mukadam; Boris T. Gaensicke; Patrick A. Woudt; Jan-Erik Solheim; Atsuko Nitta; Edward M. Sion; Brian Warner; D. K. Sahu; T. Prabhu; Arne Henden

2006-12-19

325

X-ray and optical observations of 2 new cataclysmic variables  

NASA Technical Reports Server (NTRS)

The light curves and spectra of two ultra soft X-ray sources are presented. The sources, WGAJ 1047.1+6335 and WGAJ 1802.1+1804 were discovered during a search using the Rosat position sensitive proportional counter (PSPC). The X-ray spectra of both objects show an unusually strong black body component with respect to the harder bremsstrahlung component. Based on the optical observations and on the analysis of the X-ray data, the two objects are identified with new AM Her type cataclysmic variables.

Singh, K. P.; Szkody, P.; Barrett, P.; Schlegel, E.; White, N. E.; Silber, A.; Fierce, E.; Hoard, D.; Hakala, P. J.; Piirola, V.; Sohl, K.

1996-01-01

326

HST and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables  

E-print Network

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 SDSS013132.39-090122.3, SDSSJ161033.64-010223.3 and SDSSJ220553.98+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 15,000K. These temperatures place the accreting white dwarfs outside the instability zone for non-interacting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs.

Szkody, P; Gänsicke, B T; Woudt, P A; Solheim, J E; Nitta, A; Sion, E M; Warner, B; Sahu, D K; Prabhu, T; Henden, A; Szkody, Paula; Mukadam, Anjum; Gaensicke, Boris T.; Woudt, Patrick A.; Solheim, Jan-Erik; Nitta, Atsuko; Sion, Edward M.; Warner, Brian; Henden, Arne

2006-01-01

327

Seasonal and diurnal variability of the meteor flux at high latitudes observed using PFISR  

NASA Astrophysics Data System (ADS)

We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena; for example, it could be the source of meteoric smoke that is thought to act as condensation nuclei in the formation of ice particles in the polar mesosphere. The observations presented here were performed for full 24-h periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes [Janches, D., Heinselman, C.J., Chau, J.L., Chandran, A., Woodman, R., 2006. Modeling of the micrometeor input function in the upper atmosphere observed by High Power and Large Aperture Radars, JGR, 11, A07317, doi:10.1029/2006JA011628]. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected every day. We show that meteor rates, altitude, and radial velocity distributions have a large seasonal dependence. This seasonal variability can be explained by a change in the relative location of the meteoroid sources with respect to the observer. Our results show that the meteor flux into the upper atmosphere is strongly anisotropic and its characteristics must be accounted for when including this flux into models attempting to explain related aeronomical phenomena. In addition, the measured acceleration and received signal strength distribution do not seem to depend on season; which may suggest that these observed quantities do not have a strong dependence on entry angle.

Sparks, J. J.; Janches, D.; Nicolls, M. J.; Heinselman, C. J.

2009-05-01

328

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

329

Linking optical and infrared observations with gravitational wave sources through variability  

E-print Network

Optical and infrared observations have thus far detected more celestial cataclysms than have been seen in gravity waves (GW). This argues that we should search for gravity wave signatures that correspond to flux variability seen at optical wavelengths, at precisely known positions. There is an unknown time delay between the optical and gravitational transient, but knowing the source location precisely specifies the corresponding time delays across the gravitational antenna network as a function of the GW-to-optical arrival time difference. Optical searches should detect virtually all supernovae that are plausible gravitational radiation sources. The transient optical signature expected from merging compact objects is not as well understood, but there are good reasons to expect detectable transient optical/IR emission from most of these sources as well. The next generation of deep wide-field surveys (for example PanSTARRS and LSST) will be sensitive to subtle optical variability, but we need to fill the ``blind spots'' that exist in the Galactic plane, and for optically bright transient sources. In particular, a Galactic plane variability survey at 2 microns seems worthwhile. Science would benefit from closer coordination between the various optical survey projects and the gravity wave community.

Christopher W. Stubbs

2007-12-16

330

Spectral variability of the ? Sco AB binary system observed with IUE  

NASA Astrophysics Data System (ADS)

We present ultraviolet spectra of the ? Sco AB binary system taken by the International Ultraviolet Explorer during the period from 1979 to 1995. An investigation is carried out on the spectral variability of Mg II k and h emission lines arising from the chromosphere of ? Sco A ( Van der Hucht et al., 1979). There are absorption and emission components on the blue sides of the Mg II k and h lines, which are formed in the cool circumstellar gas shells around two stars ( Bernat and Lambert, 1976). This work is based on calculations of line fluxes and line widths for the aforementioned spectral lines. We found that there is spectral variability for these physical parameters with pulsation phase, which we attribute to the changes of density and temperature of the chromosphere of ? Sco A as a result of the semi-regular pulsation and the variability of mass loss of the red supergiant ( Reimers et al., 2008). The observed values of the k-to-h ratio are approximately one, implying that the k and h emission lines originate from an optically thick atmosphere.

Sanad, M. R.; Bobrowsky, M.

2010-10-01

331

Thermal Evolution and Radiative Output of Solar Flares Observed by the EUV Variability Experiment (EVE)  

NASA Astrophysics Data System (ADS)

This paper describes the methods used to obtain the thermal evolution and radiative output during solar flares as observed by the Extreme ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO). How EVE measurements, due to the temporal cadence, spectral resolution and spectral range, can be used to determine how the thermal plasma radiates at various temperatures throughout the impulsive and gradual phase of flares is presented and discussed in detail. EVE can very accurately determine the radiative output of flares due to pre- and in-flight calibrations. Events are presented that show that the total radiated output of flares depends more on the flare duration than the typical GOES X-ray peak magnitude classification. With SDO observing every flare throughout its entire duration and over a large temperature range, new insights into flare heating and cooling as well as the radiative energy release in EUV wavelengths support existing research into understanding the evolution of solar flares.

Chamberlin, P. C.; Milligan, R. O.; Woods, T. N.

2012-07-01

332

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

333

The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006  

E-print Network

Pluto's two small satellites, temporarily designated S/2005 P 1 and S/2005 P 2, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS). Here we collect together the astrometric positions of these two satellites (henceforth P1 and P2), as well as a single color measurement for each satellite and initial constraints on their photometric variability obtained during these observations. We find that both satellites have essentially neutral (grey) reflectivities, like Charon. We also find that neither satellite exhibited strong photometric variation, which might suggest that P1 and P2 are toward the large end of their allowable size range, and therefore may have far lower reflectivities than Charon.

S. A. Stern; M. J. Mutchler; H. A. Weaver; A. J. Steffl

2006-04-29

334

Debris Disk Variability: Observational Test Bed for Probing Terrestrial Planet Formation  

NASA Astrophysics Data System (ADS)

The newly discovered variable emission by extreme debris disks provides a unique opportunity to learn about asteroid-sized bodies in young exoplanetary systems and to explore planetesimal collisions and their aftermaths during the era of terrestrial planet building. However, the baseline of existing observations is too short to characterize this behavior well. We propose to monitor variations in seven systems where they have already been identified, and to look for them in seven more systems that are likely to behave similarly, selected because their high levels of warm dust point to elevated rates of planetesimal collisions. This program requires 130 hours of observing time and will establish the time-domain study of debris disks as an important heritage of the Spitzer warm mission.

Su, Kate; Rieke, George; Jackson, Alan; Gaspar, Andras; Meng, Huan

2014-12-01

335

Observed and Aogcm Simulated Relationships Between us Wind Speeds and Large Scale Modes of Climate Variability  

NASA Astrophysics Data System (ADS)

Previous research has indicated that large-scale modes of climate variability, such as El Niño - Southern Oscillation (ENSO), the Arctic Oscillation (AO) and the Pacific-North American pattern (PNA), influence the inter-annual and intra-annual variability of near-surface and upper-level wind speeds over the United States. For example, we have shown that rawinsonde derived wind speeds indicate that 90th percentile of wind speeds at 700 hPa over the Pacific Northwest and Southwestern USA are significantly higher under the negative phase of the PNA, and the Central Plains experiences higher wind speeds at 850 hPa under positive phase Southern Oscillation index while the Northeast exhibits higher wind speeds at 850 hPa under positive phase NAO. Here, we extend this research by further investigating these relationships using both reanalysis products and output from coupled atmosphere-ocean general circulation models (AOGCMs) developed for the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). The research presented has two specific goals. First, we evaluate the AOGCM simulations in terms of their ability to represent the temporal and spatial representations of ENSO, the AO, and the PNA pattern relative to historical observations. The diagnostics used include calculation of the power spectra (and thus representation of the fundamental frequencies of variability) and Taylor diagrams (for comparative assessment of the spatial patterns and their intensities). Our initial results indicate that most AOGCMs produce modes that are qualitatively similar to those observed, but that differ slightly in terms of the spatial pattern, intensity of specific centers of action, and variance explained. Figure 1 illustrates an example of the analysis of the frequencies of variability of two climate modes for the NCEP-NCAR reanalysis (NNR) and a single AOGCM (BCC CSM1). The results show a high degree of similarity in the power spectra but for this AOGCM the variance of the PNA associated with high frequencies are amplified relative to those in NNR. Second, we quantify the observed and AOGCM-simulated relationships between ENSO, AO, and PNA indices and zonal and meridional wind components at multiple levels for the contiguous United States. The results are presented in form of maps displaying the strength of the relationship at different timescales, from daily to annual, and at multiple atmospheric levels, from 10m to 500 mb. The results of the analysis are used to provide context for regional wind climate projections based on 21st century AOGCM simulations.

Schoof, J. T.; Pryor, S. C.; Barthelmie, R. J.

2013-12-01

336

Water Cycle Missions for the Next Decade  

NASA Astrophysics Data System (ADS)

The global water cycle describes the circulation of water as a vital and dynamic substance in its liquid, solid, and vapor phases as it moves through the atmosphere, oceans and land. Life in its many forms exists because of water, and modern civilization depends on learning how to live within the constraints imposed by the availability of water. The scientific challenge posed by the need to observe the global water cycle is to integrate in situ and space-borne observations to quantify the key water-cycle state variables and fluxes. The vision to address that challenge is a series of Earth observation missions that will measure the states, stocks, flows, and residence times of water on regional to global scales followed by a series of coordinated missions that will address the processes, on a global scale, that underlie variability and changes in water in all its three phases. The accompanying societal challenge is to foster the improved use of water data and information as a basis for enlightened management of water resources, to protect life and property from effects of extremes in the water cycle. A major change in thinking about water science that goes beyond its physics to include its role in ecosystems and society is also required. Better water-cycle observations, especially on the continental and global scales, will be essential. Water-cycle predictions need to be readily available globally to reduce loss of life and property caused by water-related natural hazards. Building on the 2007 Earth Science Decadal Survey, NASA's Plan for a Climate-Centric Architecture for Earth Observations and Applications from Space , and the 2012 Chapman Conference on Remote Sensing of the Terrestrial Water Cycle, a workshop was held in April 2013 to gather wisdom and determine how to prepare for the next generation of water cycle missions in support of the second Earth Science Decadal Survey. This talk will present the outcomes of the workshop including the intersection between science questions, technology readiness and satellite design optimization. A series of next-generation water cycle mission working groups were proposed and white papers, designed to identify capacity gaps and inform NASA were developed. The workshop identified several visions for the next decade of water cycle satellite observations, and developed a roadmap and action plan for developing the foundation for these missions. Achieving this outcome will result in optimized community investments and better functionality of these future missions, and will help to foster broader range of scientists and professionals engaged in water cycle observation planning and development around the country, and the world.

Houser, P. R.

2013-12-01

337

Observed intraseasonal and seasonal variability of the West India Coastal Current on the continental slope  

NASA Astrophysics Data System (ADS)

We present current data from acoustic Doppler current profilers (ADCPs) moored on the continental slope off the west coast of India. The data were collected at four locations (roughly at Kanyakumari, Kollam, Goa, and Mumbai) extending from ˜ 7° to ˜ 20°N during 2008-2012. The observations show that a seasonal cycle, including an annual cycle, is present in the West India Coastal Current (WICC); this seasonal cycle, which strengthens northward, shows considerable interannual variability and is not as strongly correlated along the coast as in climatologies based on ship drifts or the altimeter. The alongshore decorrelation of the WICC is much stronger at intraseasonal periods, which are evident during the winter monsoon all along the coast. This intraseasonal variability is stronger in the south. A striking feature of the WICC is upward phase propagation, which implies an undercurrent whose depth becomes shallower as the season progresses. There are also instances when the phase propagates downward. At the two southern mooring locations off Kollam and Kanyakumari, the cross-shore current, which is usually associated with eddy-like circulations, is comparable to the alongshore current on occasions. A comparison with data from the OSCAR (Ocean Surface Currents Analyses Real-time) data product shows not only similarities, but also significant differences, particularly in the phase. One possible reason for this phase mismatch between the ADCP current at 48 m and the OSCAR current, which represents the current in the 0-30 m depth range, is the vertical phase propagation. Current products based on Ocean General Circulation Models like ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and GODAS (Global Ocean Data Assimilation System) show a weaker correlation with the ADCP current, and ECCO2 does capture some of the observed variability.

Amol, P.; Shankar, D.; Fernando, V.; Mukherjee, A.; Aparna, S. G.; Fernandes, R.; Michael, G. S.; Khalap, S. T.; Satelkar, N. P.; Agarvadekar, Y.; Gaonkar, M. G.; Tari, A. P.; Kankonkar, A.; Vernekar, S. P.

2014-06-01

338

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

339

Intraseasonal Variability of the Equatorial Indian Ocean Observed from Sea Surface Height, Wind, and Temperature Data  

NASA Technical Reports Server (NTRS)

The forcing of the equatorial Indian Ocean by the highly periodic monsoon wind cycle creates many interesting intraseasonal variabilities. The frequency spectrum of the wind stress observations from the European Remote Sensing Satellite scatterometers reveals peaks at the seasonal cycle and its higher harmonics at 180, 120, 90, and 75 days. The observations of sea surface height (SSH) from the Jason and Ocean Topography Experiment (TOPEX)/Poseidon radar altimeters are analyzed to study the ocean's response. The focus of the study is on the intraseasonal periods shorter than the annual period. The semiannual SSH variability is characterized by a basin mode involving Rossby waves and Kelvin waves traveling back and forth in the equatorial Indian Ocean between 10(deg)S and 10(deg)N. However, the interference of these waves with each other masks the appearance of individual Kelvin and Rossby waves, leading to a nodal point (amphidrome) of phase propagation on the equator at the center of the basin. The characteristics of the mode correspond to a resonance of the basin according to theoretical models. The theory also calls for similar modes at 90 and 60 days.

Fu, Lee-Lueng

2007-01-01

340

A Survey of Far Ultraviolet Spectroscopic Explorer Observations of Cataclysmic Variables  

E-print Network

During its lifetime, the Far Ultraviolet Spectroscopic Explorer (FUSE) was used to observe 99 cataclysmic variables in 211 separate observations. Here, we present a survey of the moderate resolution (R\\simeq10,000), far-ultraviolet (905 - 1188 {\\deg}A), time-averaged FUSE spectra of cataclysmic variables (CVs). The FUSE spectra are morphologically diverse. They show contributions from the accretion disk, the disk chromosphere, disk outflows, and the white dwarf, 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 white dwarf. The data reveal information about the structure, temperature, density and mass flow rates of the disk and disk winds, the temperature of the white dwarf 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 are available at the...

Froning, C S; Gaensicke, B; Szkody, P

2011-01-01

341

SABER Observations of the OH Meinel Airglow Variability Near the Mesopause  

NASA Technical Reports Server (NTRS)

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, one of four on board the TIMED satellite, observes the OH Meinel emission at 2.0 m that peaks near the mesopause. The emission results from reactions between members of the oxygen and hydrogen chemical families that can be significantly affected by mesopause dynamics. In this study we compare SABER measurements of OH Meinel emission rates and temperatures with predictions from a 3-dimensional chemical dynamical model. In general, the model is capable of reproducing both the observed diurnal and seasonal OH Meinel emission variability. The results indicate that the diurnal tide has a large effect on the overall magnitude and temporal variation of the emission in low latitudes. This tidal variability is so dominant that the seasonal cycle in the nighttime emission depends very strongly on the local time of the analysis. At higher latitudes, the emission has an annual cycle that is due mainly to transport of oxygen by the seasonally reversing mean circulation.

Marsh, Daniel R.; Smith, Anne K.; Mlynczak, Martin G.

2005-01-01

342

Observation of soil moisture variability in agricultural and grassland field soils using a wireless sensor network  

NASA Astrophysics Data System (ADS)

Soil moisture dynamics is a key factor of energy and matter exchange between land surface and atmosphere. Therefore long-term observation of temporal and spatial soil moisture variability is important in studying impacts of climate change on terrestrial ecosystems and their possible feedbacks to the atmosphere. Within the framework of the network of terrestrial environmental observatories TERENO we installed at the research farm Scheyern in soils of two fields (of ca. 5 ha size each) the SoilNet wireless sensor network (Biogena et al. 2010). The SoilNet in Scheyern consists of 94 sensor units, 45 for the agricultural field site and 49 for the grassland site. Each sensor unit comprises 6 SPADE sensors, two sensors placed at the depths 10, 30 and 50 cm. The SPADE sensor (sceme.de GmbH, Horn-Bad Meinberg Germany) consists of a TDT sensor to estimate volumetric soil water content from soil electrical permittivity by sending an electromagnetic signal and measuring its propagation time, which depends on the soil dielectric properties and hence on soil water content. Additionally the SPADE sensor contains a temperature sensor (DS18B20). First results obtained from the SoilNet measurements at both fields sites will be presented and discussed. The observed high temporal and spatial variability will be analysed and related to agricultural management and basic soil properties (bulk density, soil texture, organic matter content and soil hydraulic characteristics).

Priesack, Eckart; Schuh, Max

2014-05-01

343

Observed seasonal and intraseasonal variability of the East India Coastal Current on the continental slope  

NASA Astrophysics Data System (ADS)

We present data from three acoustic Doppler current profilers (ADCPs) moored off Cuddalore (12?N), Kakinada (16.5?N), and Gopalpur (19?N) on the continental slope of the western Bay of Bengal and one mooring on the slope of the northern bay (89?E, 19?N; referred to as being located at Paradip). The data were collected during May 2009 to March 2013 and the observations show that the seasonal cycle, which includes the annual cycle, the semi-annual cycle, and a peak around 120 days, dominates the observed variability of the East India Coastal Current (EICC). Spectral analysis suggests that the 120-day peak dominates the seasonal variability at Paradip and is strong at Gopalpur and Kakinada. The annual cycle is coherent along the western boundary of the bay, i.e., the east coast of India, but with significant phase differences between moorings. At the semi-annual and 120-day periods, the alongshore coherence is weaker. Intraseasonal variability is weaker than the seasonal cycle, particularly at Cuddalore and Paradip, and it exhibits seasonality: the strongest intraseasonal variation is during spring (February-April). Peaks around 12 and 20-22 days are also seen at Gopalpur, Kakinada, and Cuddalore. A striking feature of the currents is the upward phase propagation, but there are also instances when phase propagates downward. The much lower vertical phase speed in the top ˜100 m at Cuddalore leads to a distinct undercurrent at this location; at other locations, the undercurrent, though it exists often, is not as striking. During spring, however, the EICC tends to flow poleward (eastward) at Cuddalore, Kakinada, and Gopalpur (Paradip) over the top ˜300 m, which is the maximum depth to which observations were made. The cross-shore component of the EICC is much weaker than the alongshore component at Cuddalore and, except for a few bursts during spring, at Kakinada and Gopalpur. It is only at Paradip, on the slope of the northern boundary, that significant cross-shore flows are seen during spring and the summer monsoon (June-August) and these flows are seen to be associated with eddy-like circulations in the altimeter data. We use the ADCP data to validate popular current data products like OSCAR (Ocean Surface Currents Analyses Real-time), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II), and GODAS (Global Ocean Data Assimilation System). The OSCAR currents at Paradip match the observed currents well, but the correlation is much weaker at the other three locations. Both ECCO2 and GODAS fair poorly, particularly the latter because its variability in this boundary-current regime is extremely weak. Though it performs badly at Paradip, ECCO2 does capture the observed variability on occasions at the other locations.

Mukherjee, A.; Shankar, D.; Fernando, V.; Amol, P.; Aparna, S. G.; Fernandes, R.; Michael, G. S.; Khalap, S. T.; Satelkar, N. P.; Agarvadekar, Y.; Gaonkar, M. G.; Tari, A. P.; Kankonkar, A.; Vernekar, S.

2014-08-01

344

Observations of the Magnetic Cataclysmic Variable VV Puppis with the Far Ultraviolet Spectroscopic Explorer  

E-print Network

We present the first far-ultraviolet (FUV) observations of the magnetic cataclysmic variable VV Puppis, obtained with the Far Ultraviolet Spectroscopic Explorer satellite. In addition, we have obtained simultaneous ground-based optical photometric observations of VV Pup during part of the FUV observation. The shapes of the FUV and optical light curves are consistent with each other and with those of past observations at optical, extreme-ultraviolet, and X-ray wavelengths. Time-resolved FUV spectra during the portion of VV Pup's orbit when the accreting magnetic pole of the white dwarf can be seen show an increasing continuum level as the accretion spot becomes more directly visible. The most prominent features in the spectrum are the O VI 1031.9A, 1037.6A emission lines. We interpret the shape and velocity shift of these lines in the context of an origin in the accretion funnel near the white dwarf surface. A blackbody function with T > 90,000 K provides an adequate fit to the FUV spectral energy distribution of VV Pup.

D. W. Hoard; P. Szkody; R. Ishioka; L. Ferrario; B. T. Gaensicke; G. D. Schmidt; T. Kato; M. Uemura

2002-06-27

345

Observations of the Magnetic Cataclysmic Variable VV Puppis with the Far Ultraviolet Spectroscopic Explorer  

E-print Network

We present the first far-ultraviolet (FUV) observations of the magnetic cataclysmic variable VV Puppis, obtained with the Far Ultraviolet Spectroscopic Explorer satellite. In addition, we have obtained simultaneous ground-based optical photometric observations of VV Pup during part of the FUV observation. The shapes of the FUV and optical light curves are consistent with each other and with those of past observations at optical, extreme-ultraviolet, and X-ray wavelengths. Time-resolved FUV spectra during the portion of VV Pup's orbit when the accreting magnetic pole of the white dwarf can be seen show an increasing continuum level as the accretion spot becomes more directly visible. The most prominent features in the spectrum are the O VI 1031.9A, 1037.6A emission lines. We interpret the shape and velocity shift of these lines in the context of an origin in the accretion funnel near the white dwarf surface. A blackbody function with T > 90,000 K provides an adequate fit to the FUV spectral energy distribution...

Hoard, D W; Ishioka, R; Ferrario, L; Gänsicke, B T; Schmidt, G D; Kato, T; Uemura, M

2002-01-01

346

Decadal Climate Prediction: Challenges and Opportunities  

NASA Astrophysics Data System (ADS)

The scientific understanding of climate change is now sufficiently clear to show that climate change from global warming is already upon us, and the rate of change as projected exceeds anything seen in nature in the past 10,000 years. Uncertainties remain, however, especially regarding how climate will change at regional and local scales where the signal of natural variability is large. Decision makers in diverse arenas, from water mangers in the U.S. Southwest to public health experts in Asia, need to know if the climate events they are seeing are the product of natural variability, and hence can be expected to reverse at some point, or are the result of potentially irreversible anthropogenic climate change. The climate science community will not be able to answer these questions and reduce the uncertainties in near-term climate projections without moving toward high resolution climate system predictions, with a blurring of the distinction between shorter-term predictions and longer-term climate projections. The key is the realization that climate system predictions of natural and forced change, regardless of timescale, will require initialization of coupled general circulation models with the best estimates of the current observed state of the atmosphere, oceans, cryosphere, and land surface, a state influenced both by the current phases of modes of natural variability and by the accumulated impacts to date of anthropogenic radiative forcing. Formidable challenges exist: for instance, what is the best method of initialization given imperfect observations and systematic errors in models, what effect does initialization have on climate predictions, what predictions should be attempted and how would they be verified? Accurate initial conditions for the global oceans are especially important and could conceivably be provided by ARGO floats and existing ocean data assimilation exercises. However, performing hindcasts prior to the ARGO float era of near-global upper ocean salinity and temperature data will remain a significant problem and possibly compromise the development of prediction capacities. Despite such challenges, it needs to be recognized that useful predictions of the evolution of the climate system over the next few years to decades requires initialized projections that exploit the predictive potential contained in both past and future changes in radiative forcing and in slowly evolving phenomena, such as ocean current systems and heat content, that give rise to internal decadal variability. Climate predictions that exploit the full predictive potential of forced and free climate variations will form the raw material for the decision making needed to enable societies to adapt to the climate changes of the next few years to decades.

Hurrell, J. W.

2010-12-01

347

Decadal Climate Prediction: Opportunities and Challenges  

NASA Astrophysics Data System (ADS)

The scientific understanding of climate change is sufficiently clear to show that climate change from global warming is already upon us, and the rate of change as projected exceeds anything seen in nature in the past 10,000 years. Uncertainties remain, however, especially regarding how climate will change at regional and local scales where the signal of natural variability is large. Decision makers in diverse arenas, from water managers in the U.S. Southwest to public health experts in Asia, need to know if the climate events they are seeing are the product of natural variability, and hence can be expected to reverse at some point, or are the result of potentially irreversible anthropogenic climate change. The climate science community will not be able to answer these questions and reduce the uncertainties in near-term climate projections without moving toward high resolution climate system predictions, with a blurring of the distinction between shorter-term predictions and longer-term climate projections. The key is the realization that climate system predictions of natural and forced change, regardless of timescale, will require initialization of coupled general circulation models with the best estimates of the current observed state of the atmosphere, oceans, cryosphere, and land surface, a state influenced both by the current phases of modes of natural variability and by the accumulated impacts to date of anthropogenic radiative forcing. Formidable challenges exist: for instance, what is the best method of initialization given imperfect observations and systematic errors in models, what effect does initialization have on climate predictions, what predictions should be attempted and how would they be verified? Accurate initial conditions for the global oceans are especially important and could conceivably be provided by ARGO floats and existing ocean data assimilation exercises. However, performing hindcasts prior to the ARGO float era of near-global upper ocean salinity and temperature data will remain a significant problem and possibly compromise the development of prediction capacities. Despite such challenges, it needs to be recognized that useful predictions of the evolution of the climate system over the next few years to decades requires initialized projections that exploit the predictive potential contained in both past and future changes in radiative forcing and in slowly evolving phenomena, such as ocean current systems and heat content, that give rise to internal decadal variability. Climate predictions that exploit the full predictive potential of forced and free climate variations will form the raw material for the decision making needed to enable societies to adapt to the climate changes of the next few years to decades.

Hurrell, J. W.

2011-12-01

348

Spatial and temporal variability of satellite-observed Subpolar Front in the East/Japan Sea  

NASA Astrophysics Data System (ADS)

Spatial and temporal variability of the Subpolar Front (SPF) in the East/Japan Sea are examined based on semi-monthly sea-surface-temperature (SST) gradient maps constructed from declouded SST images over the period 1990-1995. Analyses demonstrate that the SPF experiences distinct seasonal fluctuations as well as strong year-to-year variations in terms of frontal strength, position, and zonal range. Elevated variability of the SPF is attributed mainly to mesoscale eddies at the frontal region. The main SPF is not zonal along 40?N but trends from the southwest to the northeast during winter-spring, and from the northwest to the southeast in summer. During summer, the SPF west of 135?E shifts significantly to the north, reaching 41.5?N, which is associated with an enhancement of the East Korea Warm Current (EKWC). However, the surface SPF does not necessarily reflect its subsurface structure. Because of strong baroclinicity in summer, the internal SPF surface is inclined to the south with increasing depth. Northward movement of the western SPF is limited to 20 m depth. Topography may give vorticity constraints on the migration of the SPF, but the maximum SPF is not always located around the shallow Yamato Rise (YR) in the central part of the East/Japan Sea. Relatively strong bathymetrically trapped fronts are confined to the northwestern edge of the YR, within a zonal range of 132.5-134.5?E, where steep bathymetry stabilizes the fronts. Topographic steering of SST fronts is weak at the southeastern portion of the YR. The SPF in the EKWC region (<132?E) is not significantly affected by the bathymetry. Spatial variability of atmospheric wind forcing produces a significant meridional shift of the SPF by generating the northwestern branch of the SPF in November. The strongest frontal zone, of magnitude 0.09C/km, near 138?E shows the largest temporal variability in strength, but the smallest temporal variability in terms of meridional location. A temporal trend of the SPF properties is observed, suggesting that its western (eastern) location migrates to the south (north) reaching -(+)0.1?/year with mean strengthening of 6.8×10-4C/kmyear during the study period.

Park, Kyung-Ae; Ullman, David S.; Kim, Kuh; Yul Chung, Jong; Kim, Kyung-Ryul

2007-04-01

349

Temperature: Decadal Averages Map  

NSDL National Science Digital Library

This interactive map allows students to experiment with decadal average temperature projections. Overall temperatures are expected to rise throughout the century and this tool demonstrates those projected measurements.

Commission, California E.

350

Observing Tropospheric Chemistry and Climate Variables from Geostationary Orbit With SIRAS-G  

NASA Astrophysics Data System (ADS)

Understanding the impact of pollution on regional, continental, and global scales imposes unique challenges for spaceborne observations. The variability in tropospheric chemistry, source strengths, and transport results in sub-hourly temporal variation, and produces small-scale variations in the vertical and horizontal distribution of trace gases. Current spaceborne observation from low earth orbit have demonstrated the capability to measure tropospheric trace gases from space but are limited to a twice daily observation. Improving the depiction of diurnal variations requires observations from geosynchronous orbit. The Spaceborne Infrared Atmospheric Sounder from Geosynchronous Earth Orbit (SIRAS-G) is being developed under the NASA Instrument Incubator Program to meet this need. SIRAS-G will enable high temporal, spatial, and spectral resolution observations of temperature, water, ozone, aerosol, cloud and surface properties, and important trace gas concentrations such as CO, CH4, N2O and SO2. The spaceborne instrument concept measures thermal emission in 2048 spectral channels over the wavelength range from 3.75 to 15 microns with a nominal resolving power of 1400. The constraints imposed on instrument mass, power and volume by a geosynchronous mission drives the instrument design toward more compact, and less complex optical systems. The system employs a wide field-of-view hyperspectral infrared optical system that splits incoming radiation to four separate grating spectrometer channels. Combined with large 2-D infrared detector arrays, this system provides simultaneous high-resolution spectral and spatial imaging over a large region with a nominal 4x4 km ground resolution. The longer observation times from geosynchronous orbit enable the necessary high signal to noise. However, the longer integration time makes the sensor more sensitive to slowly varying platform motion or mechanical disturbances generated by the instrument or spacecraft subsystems. This leads to a spectral registration problem for imaging filter wheel radiometers or Fourier transform spectrometer. The imaging grating spectrometer, by virtue of its simultaneous collection of spectral information, is significantly less sensitive to disturbances.

Johnson, B. R.; Kampe, T. U.

2005-12-01

351

Diurnal and seasonal variability of turbulence parameters observed with Indian mesosphere-stratosphere-troposphere radar  

NASA Astrophysics Data System (ADS)

Seasonal and diurnal variation of turbulence parameters such as refractivity structure constant Cn 2 and eddy dissipation rate ? is presented using the data collected with the Indian mesosphere-stratosphere-troposphere (MST) radar over 3 years. The log Cn 2 values estimated from signal-to-noise ratio (SNR) are found to be in the range of -17 to -19 m-2/3 in the height range of 7.5-21 km. Monthly mean values of log Cn 2 show a maximum variation below 12 km with a magnitude of 12-15 dB during the course of annual cycle. A maximum variability of ˜7-10 dB is observed below 12 km in seasonal mean values of log Cn 2. The diurnal variation of log Cn 2 at different heights is also given. Cn 2 is found to be more in the region of strong shears, generally observed in the boundaries of jet streams. Different methods for the estimation of eddy dissipation rate and their limitations are discussed. For the present study, spectral width method is used after correcting the observed spectral width from beam and shear broadening effects. The observed median log ? is on the order of -3 to -4 m2 s-3. Monthly variation of log ? is found to be ˜5-7 dB. Below 10 km the magnitude of ? is more in the postmonsoon than that observed in other seasons. The interannual variation of ? is less in winter than in other seasons. The diurnal variation of log ? is found to be small in postmonsoon at most of the heights. To facilitate a comparison with the other results, we have estimated the eddy diffusivity K and the inner and outer scales of turbulence. The observed values of Cn 2, ?,K, and the inner and outer scales of turbulence are largely consistent with the results available in the literature.

Narayana Rao, D.; Narayana Rao, T.; Venkataratnam, M.; Thulasiraman, S.; Rao, S. V. B.; Srinivasulu, P.; Rao, P. B.

2001-01-01

352

Diurnal and seasonal variability of turbulence parameters observed with Indian mesosphere-stratosphere-troposphere radar  

NASA Astrophysics Data System (ADS)

Seasonal and diurnal variation of turbulence parameters such as refractivity structure constant Cn2 and eddy dissipation rate ? is presented using the data collected with the Indian mesosphere-stratosphere-troposphere (MST) radar over 3 years. The log Cn2 values estimated from signal-to-noise ratio (SNR) are found to be in the range of -17 to -19 m-2/3 in the height range of 7.5-21 km. Monthly mean values of log Cn2 show a maximum variation below 12 km with a magnitude of 12-15 dB during the course of annual cycle. A maximum variability of ˜7-10 dB is observed below 12 km in seasonal mean values of log Cn2. The diurnal variation of log Cn2 at different heights is also given. Cn2 is found to be more in the region of strong shears, generally observed in the boundaries of jet streams. Different methods for the estimation of eddy dissipation rate and their limitations are discussed. For the present study, spectral width method is used after correcting the observed spectral width from beam and shear broadening effects. The observed median log ? is on the order of -3 to -4 m2 s-3. Monthly variation of log ? is found to be ˜5-7 dB. Below 10 km the magnitude of ? is more in the postmonsoon than that observed in other seasons. The interannual variation of ? is less in winter than in other seasons. The diurnal variation of log ? is found to be small in postmonsoon at most of the heights. To facilitate a comparison with the other results, we have estimated the eddy diffusivity K and the inner and outer scales of turbulence. The observed values of Cn2, ?,K, and the inner and outer scales of turbulence are largely consistent with the results available in the literature.

Rao, D. Narayana; Rao, T. Narayana; Venkataratnam, M.; Thulasiraman, S.; Rao, S. V. B.; Srinivasulu, P.; Rao, P. B.

2001-01-01

353

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

354

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 80% 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, F.; van der Werf, G.

2013-12-01

355

Psychological Variables Potentially Implicated in Opioid-Related Mortality as Observed in Clinical Practice  

PubMed Central

Opioid-related deaths in the United States have become a public health problem, with accidental and unintended overdoses being especially troubling. Screening for psychological risk factors is an important first step in safeguarding against nonadherence practices and identifying patients who may be vulnerable to the risks associated with opioid therapy. Validated screening instruments can aid in this attempt as a complementary tool to clinicians’ assessments. A structured screening is imperative as part of an assessment, as clinician judgment is not the most reliable method of identifying nonadherence. As a complement to formal screening, we present for discussion and possible future study certain psychological variables observed during years of clinical practice that may be linked to medication nonadherence and accidental overdose. These variables include catastrophizing, fear, impulsivity, attention deficit disorders, existential distress, and certain personality disorders. In our experience, chronic pain patients with dual diagnoses may become “chemical copers” as a way of coping with their negative emotion. For these patients, times of stress could lead to accidental overdose. Behavioral, cognitive-behavioral (acceptance and commitment, dialectical behavior), existential (meaning-centered, dignity), and psychotropic therapies have been effective in treating these high-risk comorbidities, while managing expectations of pain relief appears key to preventing accidental overdose. PMID:21668755

Passik, Steven D.; Lowery, Amy

2014-01-01

356

Variability of Soft X-ray Spectral Shape in Blazars Observed by ROSAT  

E-print Network

In paper 1 (Cheng et al. 2001) we have shown that the soft X-ray spectra of two types of Seyfert 1 galaxies statistically vary differently with increasing intensity. In order to understand how the spectrum of blazars changes, the spectral shape variability of 18 blazars observed by ROSAT/PSPC mode are studied by presenting the correlation of Hardness Ratio 1 versus Count Rates (HR1-CTs). According to our criteria, 10 blazars show a positive HR1-CTs relation, and only 2 blazars display an anti-correlation of HR1 versus CTs. The rest 6 blazars do not indicate any clear correlation. From these we can see that most blazars of our sample statistically show a hardening spectrum during overall flux increase, though some vary randomly. By investigating the photon index of these objects and different radiation theories, we argue that the dominance of the synchrotron or inverse Compton emission in the soft X-ray band may interpret the dichotomy of spectral variability well, and that different spectral variations might represent a sequence of synchrotron peaked frequency.

Linpeng Cheng; Yongheng Zhao; Janyan Wei

2001-10-30

357

The Geminga Pulsar: Soft X-Ray Variability and an EUVE Observation  

NASA Technical Reports Server (NTRS)

We observed the Geminga pulsar with the EUVE satellite, detecting pulsed emission in the Deep Survey imager. Joint spectral fits of the EUVE flux with ROSAT PSPC data are consistent with thermal plus power-law models in which the thermal component makes the dominant contribution to the soft X-ray flux seen by EUVE and ROSAT. The data are consistent with blackbody emission of T = (4 - 6) x 10(exp 5) K over most of the surface of the star at the measured parallax distance of 160 pc. Although model atmospheres are more realistic, and can fit the data with effective temperatures a factor of 2 lower, current data would not discriminate between these and blackbody models. We also find evidence for variability of Geminga's soft X-ray pulse shape. Narrow dips in the light curve that were present in 1991 had largely disappeared in 1993/1994, causing the pulsed fraction to decline from 32% to 18%. If the dips are attributed to cyclotron resonance scattering by an e1 plasma on closed magnetic field lines, then the process that resupplies that plasma must be variable.

Halpern, Jules P.; Martin, Christopher; Marshall, Herman L.; Oliversen, Ronald (Technical Monitor)

2001-01-01

358

Ultraviolet, visual, and infrared observations of the WC7 variable HD 193793  

NASA Technical Reports Server (NTRS)

Low-resolution IUE data are used to explore the ultraviolet extinction toward the Wolf-Rayet star HD 193793 and to search for ultraviolet variability that might relate to the infrared variability. High-dispersion IUE observations are used to investigate the nature of the stellar wind of the star and to search for anomalies in the interstellar line spectrum that might be expected to be found toward a star that has recently formed a dust shell. Finally, the ultraviolet and new visual and infrared data are combined to investigate the full energy distribution of this unusual source. The energy distribution is found to extend from 0.12 to 12.5 microns, and the ultraviolet data suggest a normal WC-7 type star. A wind terminal speed of about 3000 km/s is implied by the data, as well as an E(B-V) value of 0.85. The dereddened ultraviolet to visual energy distribution is consistent with a star having effective temperature of about 43,000 K.

Fitzpatrick, E. L.; Savage, B. D.; Sitko, M. L.

1982-01-01

359

Some Statistical Strategies for DAE-seq Data Analysis: Variable Selection and Modeling Dependencies among Observations  

PubMed Central

In DAE (DNA After Enrichment)-seq experiments, genomic regions related with certain biological processes are enriched/isolated by an assay and are then sequenced on a high-throughput sequencing platform to determine their genomic positions. Statistical analysis of DAE-seq data aims to detect genomic regions with significant aggregations of isolated DNA fragments (“enriched regions”) versus all the other regions (“background”). However, many confounding factors may influence DAE-seq signals. In addition, the signals in adjacent genomic regions may exhibit strong correlations, which invalidate the independence assumption employed by many existing methods. To mitigate these issues, we develop a novel Autoregressive Hidden Markov Model (AR-HMM) to account for covariates effects and violations of the independence assumption. We demonstrate that our AR-HMM leads to improved performance in identifying enriched regions in both simulated and real datasets, especially in those in epigenetic datasets with broader regions of DAE-seq signal enrichment. We also introduce a variable selection procedure in the context of the HMM/AR-HMM where the observations are not independent and the mean value of each state-specific emission distribution is modeled by some covariates. We study the theoretical properties of this variable selection procedure and demonstrate its efficacy in simulated and real DAE-seq data. In summary, we develop several practical approaches for DAE-seq data analysis that are also applicable to more general problems in statistics. PMID:24678134

Rashid, Naim U.; Sun, Wei; Ibrahim, Joseph G.

2014-01-01

360

Detecting and Interpreting Variable Interactions in Observational Ornithology Data Daria Sorokina, Rich Caruana, Mirek Riedewald, Wesley M. Hochachka, Steve Kelling  

E-print Network

Detecting and Interpreting Variable Interactions in Observational Ornithology Data Daria Sorokina University, Boston, MA. mirek@ccs.neu.edu §Cornell Lab of Ornithology, Ithaca, NY. {wmh6, stk2}@cornell

Riedewald, Mirek

361

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

362

Time-Variable Gravity from Space: Quarter Century of Observations, Mysteries, and Prospects  

NASA Technical Reports Server (NTRS)

Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth's dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease -- until around 1998, when it switched quite suddenly to an increase trend which has continued to 2001 before sharply turning back to the value which it is "supposed to be"!. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this J2 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution (i.e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

Chao, Benjamin F.; Boy, John-Paul

2003-01-01

363

Observation of Air Pollution and Climate Variables from Geostationary Orbit with SIRAS- G  

NASA Astrophysics Data System (ADS)

Understanding the impact of pollution on regional, continental, and global scales imposes unique challenges for spaceborne observations. The variability in tropospheric chemistry, source strengths, and transport results in sub-hourly temporal variation and produces small-scale variations in the vertical and horizontal distribution of key gases. Current spaceborne observations from low earth orbit have demonstrated the capability to measure key tropospheric trace gases from space but are limited to a twice daily observation. To improve on our understanding of diurnal variations requires observations from geosynchronous orbit. The Spaceborne Infrared Atmospheric Sounder from Geosynchronous Earth Orbit (SIRAS-G) being developed under the NASA Instrument Incubator Program (IIP) will enable high temporal, spatial and spectral resolution observations of temperature, water, ozone, aerosol, cloud and surface properties, and important trace gas concentrations such as CO, CH4, N2O and SO2. The spaceborne instrument concept measures thermal emission in 2048 spectral channels over the wavelength range from 3.75 to 15 microns with a nominal resolving power (?/?) of 1400. A laboratory demonstration instrument has been developed under IIP demonstrates the feasibility of the imaging grating spectrometer for this application. The constraints imposed on instrument mass, power and volume by a geosynchronous mission drives the instrument design toward more compact, and less complex optical systems. The system employs wide field-of-view hyperspectral infrared optical system that splits incoming radiation to separate grating spectrometer channels. Combined with large 2-D infrared detector arrays, this system provides simultaneous high-resolution spectral and spatial imaging over a large region with a nominal 4x4 km ground resolution.

Kampe, T.; Johnson, B.

2006-12-01

364

Registration of ‘Decade’ wheat  

Technology Transfer Automated Retrieval System (TEKTRAN)

'Decade’ (Reg. No. CV-1058, PI 660291) hard red winter (HRW) wheat (Triticum aestivum L.) was developed and released jointly by the Montana and North Dakota Agricultural Experiment Stations in 2010. The name “Decade” denotes the extended time period (1997–2010) during which the Montana State Univers...

365

XMM-Newton and Optical Observations of Cataclysmic Variables from the Sloan Digital Sky Survey  

NASA Astrophysics Data System (ADS)

We report on XMM-Newton and optical results for six cataclysmic variables that were selected from Sloan Digital Sky Survey (SDSS) spectra because they showed strong He II emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able to confirm SDSS J233325.92+152222.1 as an intermediate polar from its strong pulse signature at 21 minutes and its obscured hard X-ray spectrum. Ground-based circular polarization and photometric observations were also able to confirm SDSS J142256.31 - 022108.1 as a polar with a period near 4 hr. Photometry of SDSS J083751.00+383012.5 and SDSS J093214.82+495054.7 solidifies the orbital period of the former as 3.18 hr and confirms the latter as a high-inclination system with deep eclipses.

Hilton, Eric J.; Szkody, Paula; Mukadam, Anjum; Henden, Arne; Dillon, William; Schmidt, Gary D.

2009-03-01

366

XMM-NEWTON AND OPTICAL OBSERVATIONS OF CATACLYSMIC VARIABLES FROM THE SLOAN DIGITAL SKY SURVEY  

SciTech Connect

We report on XMM-Newton and optical results for six cataclysmic variables that were selected from Sloan Digital Sky Survey (SDSS) spectra because they showed strong He II emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able to confirm SDSS J233325.92+152222.1 as an intermediate polar from its strong pulse signature at 21 minutes and its obscured hard X-ray spectrum. Ground-based circular polarization and photometric observations were also able to confirm SDSS J142256.31 - 022108.1 as a polar with a period near 4 hr. Photometry of SDSS J083751.00+383012.5 and SDSS J093214.82+495054.7 solidifies the orbital period of the former as 3.18 hr and confirms the latter as a high-inclination system with deep eclipses.

Hilton, Eric J.; Szkody, Paula; Mukadam, Anjum [Astronomy Department, Box 351580, University of Washington, Seattle, WA 98115 (United States); Henden, Arne; Dillon, William [American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138 (United States); Schmidt, Gary D. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)], E-mail: hilton@astro.washington.edu, E-mail: szkody@astro.washington.edu, E-mail: anjum@astro.washington.edu

2009-03-15

367

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