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1

Mechanism for decadal climate variability.  

National Technical Information Service (NTIS)

We describe in this paper a mechanism for decadal climate variability that can lead to decadal climate cycles in the North Pacific and North Atlantic Oceans. A hierarchy of numerical models and observations are used to understand the fundamental dynamics ...

M. Latif A. Groetzner M. Muennich E. Maier-Reimer S. Venzke

1996-01-01

2

Global scale decadal climate variability  

Microsoft Academic Search

Analysis of observations and results from a global coupled climate model show that coherent decadal climate variability extends over the entire Pacific basin, is associated with processes in the Atlantic and Indian Ocean regions to contribute to global patterns of decadal climate variability, and encompasses regional decadal mechanisms noted in previous studies. Ocean heat content anomalies embedded in the gyre

Gerald A. Meehl; Julie M. Arblaster; Warren G. Strand

1998-01-01

3

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

NASA Astrophysics Data System (ADS)

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

Hüttl-Kabus, Sabine; Klein, Birgit

2010-05-01

4

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

5

What drives the observed variability and decadal trends in North African dust export?  

NASA Astrophysics Data System (ADS)

African mineral dust aerosol shows significant variability on annual and decadal timescales with no clear indication as to what controls the observed changes, limiting our ability to predict future changes in dust export from this important source region. In this 27-year study (1982-2008), we find a significant 10%-per-decade decrease in dust aerosol optical depth (AOD) over the Atlantic using satellite observations. This trend is largely reproduced by the GEOS-Chem chemical transport model and persists throughout most seasons, both close to source and further downwind. While the large inter-annual variability in Atlantic dust loading results from a combination of transport, precipitation, and surface winds (quantified for each season in this study), the overall downward trend is shown to be almost entirely the result of a stilling of surface winds over source regions in North Africa. An increase in vegetation across the Sahel during this period is found to have a negligible direct effect on dust emission in the model. There is evidence to suggest that changes in the wind, as well as vegetation, are linked to the strength and location of the Inter-Tropical Convergence Zone (ITCZ). If recent research linking anthropogenic aerosol changes in the North Atlantic to changes in the ITCZ are correct, then this implies a significant anthropogenic feedback on 'natural' dust emissions.

Ridley, D. A.; Heald, C. L.

2013-12-01

6

Global scale decadal climate variability  

NASA Astrophysics Data System (ADS)

Analysis of observations and results from a global coupled climate model show that coherent decadal climate variability extends over the entire Pacific basin, is associated with processes in the Atlantic and Indian Ocean regions to contribute to global patterns of decadal climate variability, and encompasses regional decadal mechanisms noted in previous studies. Ocean heat content anomalies embedded in the gyre circulations of the Pacific, Atlantic and Indian Oceans are associated with global decadal timescale “El Niño-like” signals in atmosphere and ocean with consequent global energy balance variations. Large-scale tropical-midlatitude interactions act to replenish the ocean heat content anomalies. Maxima in decadal timescale globally averaged surface temperature occur in conjunction with periodic arrangements of SST anomalies, in association with the heat content anomalies embedded in the various ocean gyre circulations, in a global “El Niño-like” pattern that is highly correlated with such maxima. The decadal timescale in the model is approximately set by the circuit times of the ocean gyre circulations.

Meehl, Gerald A.; Arblaster, Julie M.; Strand, Warren G., Jr.

7

Decadal variability of twentieth-century El Niño and La Niña occurrence from observations and IPCC AR4 coupled models  

NASA Astrophysics Data System (ADS)

This study investigates the decadal variability of El Niño and La Niña occurrence in observations and examines that variability in a set of 20th Century climate simulations (20C3M) of coupled general circulation models (CGCMs) in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4).Wavelet analysis reveals that the observed frequency of El Niño events displays significant decadal variability with a period of about 12 years during 1920-1940, whereas the frequency of La Niña events shows significant decadal variations with a spectral peak at 16 years throughout the 20th century. Moreover, the frequencies of El Niño and La Niña events are influenced by different factors that are responsible for planetary teleconnections. The frequency of El Niño events is related the Atlantic Multidecadal Oscillation (AMO), while that of the La Niña events is associated with the Pacific Decadal Oscillation (PDO). Among the 15 IPCC AR4 CGCMs surveyed, csiro and miroc_medres CGCMs can reproduce the decadal variability of ENSO activity, and simulate partly its relationship with the Pacific and north Atlantic SSTa. These results will help us to further understand the important roles of the North Atlantic and North Pacific in ENSO variations.

Wang, Xin; Wang, Dongxiao; Zhou, Wen

2009-06-01

8

Variability of aerosol optical depth and Angstrom wavelength exponent derived from AERONET observations in recent decades  

NASA Astrophysics Data System (ADS)

Using aerosol loading data from 79 Aerosol Robotic Network (AERONET) stations with observations from more than six years, changes in aerosol optical depth (AOD) and Angstrom wavelength exponent (AWE) were studied. A statistical method was developed to determine whether AOD changes were due to increased background AOD values and/or an increased number of high AOD events. AOD decreased significantly at AERONET sites in northeastern North American and in Western Europe, which was accompanied by decreased AWE. Reduction of AOD there was mainly due to a decreased frequency of high AOD events and an increased frequency of background AOD events. In addition, decreased AOD values for high AOD events also accounted for ~ 16-32% of the AOD reduction. This is indicative of significant meteorological effects on AOD variability. AOD trends in other regions were marginal and most were not significant; however, AOD increased significantly at one site in the Sahel and another in Saudi Arabia, predominantly due to the increased frequency of high AOD events and their average AOD.

Xia, Xiangao

2011-10-01

9

Global patterns of decadal-scale variability observed in sea surface temperature and lower-tropospheric circulation fields  

NASA Astrophysics Data System (ADS)

The global patterns associated with decadal-scale variability (DSV) are examined by a lag correlation technique based on local anomaly indices, using the fields of measured sea surface temperature (SST) and 850 hPa geopotential height for the last 50 years. The three dominant patterns are identified, and the variability is examined; the first spreads over the entire Pacific, which is concurrent with the decadal-scale modulation of the El Niño/Southern Oscillation (DES variability), the second is confined to the local midlatitude North Pacific (LNP variability), and the third extends over the North Atlantic with the decadal North Atlantic Oscillation (NAO) (DNA variability). The global SST pattern of DES variability exhibits large-scale equatorial symmetry in the Pacific, which is similar to that of the Pacific Decadal Oscillation but is distinguished by the signals in the subtropical frontal zones. These SST anomalies are accompanied by anomalous subtropical highs that appear prior to the anomalous depression around Australia. The LNP variability, which is related with the Arctic Oscillation, is characterized by the SST anomalies along the North Pacific subarctic frontal zone moving eastward accompanied by the anomalous Aleutian Low. This variability develops (decays) without (with) coherent variability in the tropics. It shows the 6-year quadrature phase relationship with the DES variability, indicative of an interdecadal variability with a period of 24 years. The DNA variability is featured by the atmospheric NAO and by the SST anomalies in four zonal bands that spread in the North Atlantic from the tropics to high latitudes. This variability is independent of either the DES or LNP variability.

Tomita, Tomohiko; Wang, Bin; Yasunari, Tetsuzo; Nakamura, Hisashi

2001-11-01

10

The role of clouds in driving North Atlantic multi-decadal climate variability in observations and models  

NASA Astrophysics Data System (ADS)

Large scale warming and cooling periods of the North Atlantic is known as the Atlantic Multidecadal Oscillation (AMO). The pattern of warming and cooling in the North Atlantic Ocean over the 20th century that has a characteristic spatial structure with maximum warming in the mid-latitudes and subtropics. This has been most often attributed to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), which in turn affects poleward heat transport. A recent modeling study by Booth et al. (2012), however, suggested that aerosols can explain both the spatial pattern and temporal history of Atlantic SST through indirect effects of aerosols on cloud cover; although this idea is controversial (Zhang et al., 2013). We have found observational evidence that changes in cloud amount can drive SST changes on multi-decadal timescale. We hypothesize that a positive local feedback between SST and cloud radiative effect amplifies SST and gives rise to the observed pattern of SST change. During cool North Atlantic periods, a southward shift of the ITCZ strengthens the trade winds in the tropical North Atlantic and increases low-level cloud cover, which acts to amplify the SST cooling in the North Atlantic. During warm periods in the North Atlantic, the opposite response occurs. We are testing whether the amplitude of this feedback is realistically simulated in the CMIP5 models, and whether inter-model differences in the amplitude of the feedback can explain differences in model simulations of Atlantic multi-decadal variability.

Clement, A. C.; Bellomo, K.; Murphy, L.

2013-12-01

11

Ozone deposition into a boreal forest over a decade of observations: evaluating deposition partitioning and driving variables  

NASA Astrophysics Data System (ADS)

This study scrutinizes a decade-long series of ozone deposition measurements in a boreal forest in search for the signature and relevance of the different deposition processes. The canopy-level ozone flux measurements were analysed for deposition characteristics and partitioning into stomatal and non-stomatal fractions, with the main focus on growing season day-time data. Ten years of measurements enabled the analysis of ozone deposition variation at different time-scales, including daily to inter-annual variation as well as the dependence on environmental variables and concentration of biogenic volatile organic compounds (BVOC-s). Stomatal deposition was estimated by using multi-layer canopy dispersion and optimal stomatal control modelling from simultaneous carbon dioxide and water vapour flux measurements, non-stomatal was inferred as residual. Also, utilising the big-leaf assumption stomatal conductance was inferred from water vapour fluxes for dry canopy conditions. The total ozone deposition was highest during the peak growing season (4 mm s-1) and lowest during winter dormancy (1 mm s-1). During the course of the growing season the fraction of the non-stomatal deposition of ozone was determined to vary from 26 to 44% during day time, increasing from the start of the season until the end of the growing season. By using multi-variate analysis it was determined that day-time total ozone deposition was mainly driven by photosynthetic capacity of the canopy, vapour pressure deficit (VPD), photosynthetically active radiation and monoterpene concentration. The multi-variate linear model explained the high portion of ozone deposition variance on daily average level (R2 = 0.79). The explanatory power of the multi-variate model for ozone non-stomatal deposition was much lower (R2 = 0.38). The set of common environmental variables and terpene concentrations used in multivariate analysis were able to predict the observed average seasonal variation in total and non-stomatal deposition but failed to explain the inter-annual differences, suggesting that some still unknown mechanisms might be involved in determining the inter-annual variability. Model calculation was performed to evaluate the potential sink strength of the chemical reactions of ozone with sesquiterpenes in the canopy air space, which revealed that sesquiterpenes in typical amounts at the site were unlikely to cause significant ozone loss in canopy air space. The results clearly showed the importance of several non-stomatal removal mechanisms. Unknown chemical compounds or processes correlating with monoterpene concentrations, including potentially reactions at the surfaces, contribute to non-stomatal sink term.

Rannik, Ü.; Altimir, N.; Mammarella, I.; Bäck, J.; Rinne, J.; Ruuskanen, T. M.; Hari, P.; Vesala, T.; Kulmala, M.

2012-12-01

12

Decadal variability of the shallow Pacific meridional overturning circulation: Relation to tropical sea surface temperatures in observations and climate change models  

Microsoft Academic Search

In this study, we use existing observational datasets to evaluate 20th century climate simulations of the tropical Pacific. The emphasis of our work is decadal variability of the shallow meridional overturning circulation, which links the tropical and subtropical Pacific Ocean. In observations, this circulation is characterized by equatorward geostrophic volume transport convergence in the interior ocean pycnocline across 9°N and

Dongxiao Zhang; Michael J. McPhaden

2006-01-01

13

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

Microsoft Academic Search

This paper gives an update on the observed decadal variability of the earth radiation budget (ERB) 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 (20°N to 20°S) longwave (LW),

Takmeng Wong; Bruce A. Wielicki; Robert B. Lee; G. Louis Smith; Kathryn A. Bush; Joshua K. Willis

2006-01-01

14

Seasonal to decadal variability of Arctic Ocean heat content: A model-based analysis and implications for autonomous observing systems  

NASA Astrophysics Data System (ADS)

A high-resolution global ocean/sea ice model is used to investigate the modes of Arctic Ocean heat content variability for the period 1968-2007. A rotated empirical orthogonal function analysis is performed on the monthly mean vertically integrated heat content to investigate the mechanisms governing its spatiotemporal variations. In the model, 28% of the heat content variability is driven by the seasonal and interannual fluctuations of the atmospheric heat flux in the seasonally ice free regions. The heat flux variability associated with Atlantic Water advected through Fram Strait drives 31% of the heat content variability. Changes of temperature and circulation drive Fram Strait heat transport variability, and these two effects project on different modes and thus drive heat content variations in different parts of the Eurasian Basin. A second branch of Atlantic Water is modified in the Barents Sea and the variations of the heat flux associated with the Barents Sea water branch penetrating the deep Arctic yield heat content variations in the Eurasian Basin. The effect of the Bering Strait heat flux variations remains limited to the Chukchi Sea. Autonomous observing system may be able to capture the Arctic heat content variability. Sea surface temperature satellite observations combined with temperature profiles of the top 800 m in the deep Arctic covered by sea ice are sufficient to capture most of the variability signal. The results emphasize the crucial need for measurements in the Eurasian Basin.

Lique, Camille; Steele, Michael

2013-04-01

15

An empirical model of decadal ENSO variability  

NASA Astrophysics Data System (ADS)

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

Kravtsov, S.

2012-11-01

16

Ozone deposition into a boreal forest over a decade of observations: evaluating deposition partitioning and driving variables  

NASA Astrophysics Data System (ADS)

This study scrutinizes a decade-long series of ozone deposition measurements in a boreal forest in search for the signature and relevance of the different deposition processes. Canopy-level ozone flux measurements were analysed for deposition characteristics and partitioning into stomatal and non-stomatal fractions, focusing on growing season day-time data. Ten years of measurements enabled the analysis of ozone deposition variation at different time- scales, including daily to inter-annual variation as well as the dependence on environmental variables and concentration of biogenic volatile organic compounds (BVOC-s). Stomatal deposition was estimated by using multi-layer canopy dispersion and optimal stomatal control modelling from simultaneous carbon dioxide and water vapour flux measurements, non-stomatal was inferred as residual. Also, utilising big-leaf assumption stomatal conductance was inferred from water vapour fluxes for dry canopy conditions. The total ozone deposition was highest during the peak growing season (4 mm s-1) and lowest during winter dormancy (1 mm s-1). During the course of the growing season the fraction of the non-stomatal deposition of ozone was determined to vary from 26 to 44% during day time, increasing from the start of the season until the end of the growing season. By using multi-variate analysis it was determined that day-time total ozone deposition was mainly driven by photosynthetic capacity of the canopy, vapour pressure deficit (VPD), photosynthetically active radiation and monoterpene concentration. The multi-variate linear model explained high portion of ozone deposition variance on daily average level (R2 = 0.79). The explanatory power of the multi-variate model for ozone non-stomatal deposition was much lower (R2 = 0.38). Model calculation was performed to evaluate the potential sink strength of the chemical reactions of ozone with sesquiterpenes in the canopy air space, which revealed that sesquiterpenes in typical amounts at the site were unlikely to cause significant ozone loss in canopy air space. This was also confirmed by the statistical analysis that did not link measured sesquiterpene concentration with ozone deposition. It was concluded that chemical reactions with monoterpenes, or other removal mechanisms such as surface reactions, play a role as ozone non-stomatal sink inside canopy.

Rannik, Ü.; Altimir, N.; Mammarella, I.; Bäck, J.; Rinne, J.; Ruuskanen, T. M.; Hari, P.; Vesala, T.; Kulmala, M.

2012-05-01

17

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

18

Multi-decadal climate variability, New South Wales, Australia  

Microsoft Academic Search

Traditional hydrological risk estimation has treated the observations of hydro-climatological extremes as being independent and identically distributed, implying a static climate risk. However, recent research has highlighted the persistence of multi-decadal epochs of distinct climate states across New South Wales (NSW), Australia. Climatological studies have also revealed multi-decadal variability in the magnitude and frequency of El Niño\\/Southern Oscillation (ENSO) impacts.

S. W. Franks

2004-01-01

19

Decadal to multidecadal variability and the climate change background  

Microsoft Academic Search

Three prominent quasi-global patterns of variability and change are observed using the Met Office's sea surface temperature (SST) analysis and almost independent night marine air temperature analysis. The first is a global warming signal that is very highly correlated with global mean SST. The second is a decadal to multidecadal fluctuation with some geographical similarity to the El Niño–Southern Oscillation

David Parker; Chris Folland; Adam Scaife; Jeff Knight; Andrew Colman; Peter Baines; Buwen Dong

2007-01-01

20

Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation.  

PubMed

Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC). Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic (RAPID, at latitude 26.5 degrees N, and MOVE, at latitude 16 degrees N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of +/-1.5-3 Sv (1 Sv = 10(6) m(3) s(-1)) on decadal timescales in the subtropics. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south. PMID:19037313

Biastoch, A; Böning, C W; Lutjeharms, J R E

2008-11-27

21

Tropical origins of North and South Pacific decadal variability  

NASA Astrophysics Data System (ADS)

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 the Southern Hemisphere equivalent of the PDO index based on the leading mode of sea surface temperature variability for the South Pacific and find that it adequately explains the spatial structure of the PDO in the North Pacific. A first-order autoregressive model forced by ENSO is used to reproduce the observed PDO indices in the North and South Pacific. These results highlight the strong similarity in Pacific decadal variability on either side of the equator and suggest it may best be viewed as a reddened response to ENSO.

Shakun, Jeremy D.; Shaman, Jeffrey

2009-10-01

22

Contribution of solar radiation to decadal temperature variability over land.  

PubMed

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

Wang, Kaicun; Dickinson, Robert E

2013-09-10

23

A North Pacific decadal variability in subduction rate  

NASA Astrophysics Data System (ADS)

Analysis of results from a global eddy-resolving general circulation model has revealed the existence of a North Pacific decadal variability in subduction rate. This decadal variability corresponds well with the Pacific Decadal Oscillation (PDO). The zero-lag correlation between the two time series reaches 0.61 for the period of integration (1950-2003), and increases to as high as 0.80 after the climate shift in the mid-1970s. Much of the North Pacific decadal variability in subduction rate is due to changes in winter mixed layer depth, which in turn are closely related to changes in surface wind and heat flux.

Qu, Tangdong; Chen, Ju

2009-11-01

24

Anatomizing the Ocean's role in maintaining the pacific decadal variability  

NASA Astrophysics Data System (ADS)

The role of ocean dynamics in maintaining the Pacific Decadal Variability (PDV) was investigated based on simulation results from the Parallel Ocean Program (POP) ocean general circulation model developed at the Los Alamos National Laboratory (LANL). A long-term control simulation of the LANL-POP model forced by a reconstructed coupled wind stress field over the period 1949-2001 showed that the ocean model not only simulates a reasonable climatology, but also produces a climate variability pattern very similar to observed PDV. In the Equatorial Pacific (EP) region, the decadal warming is confined in the thin surface layer. Beneath the surface, a strong compensating cooling, accompanied by a basin-wide-scale overturning circulation in opposition to the mean flow, occurs in the thermocline layer. In the North Pacific (NP) region, the decadal variability nonetheless exhibits a relatively monotonous pattern, characterized by the dominance of anomalous cooling and eastward flows. A term balance analysis of the perturbation heat budget equation was conducted to highlight the ocean's role in maintaining the PDV-like variability over the EP and NP regions. The analyses showed that strong oceanic adjustment must occur in the equatorial thermocline in association with the anomalous overturning circulation in order to maintain the PDV-like variability, including a flattening of the equatorial thermocline slpoe and an enhancement of the upper ocean's stratification (stability), as the climate shifts from a colder regime toward a warmer one. On the other hand, the oceanic response in the extratropical region seems to be confined to the surface layer, without much participation from the subsurface oceanic dynamics.

Yu, Jia-Yuh; Chang, Cheng-Wei

2014-05-01

25

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

26

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

27

Decadal Scale Variability of the Mesosphere and Lower Thermosphere  

NASA Astrophysics Data System (ADS)

In this paper, we will analyze over two decades of satellite observations to quantify and interpret the decadal-scale variation of temperature, composition, and airglow intensity, including the 11-year solar cycle (SC) and long-term anthropogenic change (AC) induced variability, of the Mesosphere and Lower Thermosphere (MLT). The MLT is an interface and buffer between the Sun, interplanetary space, and the magnetosphere above and the atmosphere below and plays a uniquely important role in the solar-terrestrial system. The MLT sensitivities to solar cycle and anthropogenic activities will be extracted from over 11+ years of TIMED observational data. Additional satellite observations (i.e. COSMIC, CHAMP, HALOE/UARS, SOLSTICE/UARS, SORCE) are used to (1) establish the external solar energy input variabilities, (2) determine differences between the satellite datasets and evaluate potential SABER measurement long-term degradation, and (3) extend the length of data records (up to two solar cycles) to assess how their combination refines our conclusions about SC and AC responses.

Yee, J.

2012-12-01

28

Multi-decadal Atlantic Variability Simulated in CGCMs  

NASA Astrophysics Data System (ADS)

As observations are limited, Coupled General Circulation Models (CGCMs) are currently a necessary tool to study Atlantic Multi-decadal Variability (AMV). While some CGCMs indicate a pronounced multi-decadal signal in Atlantic, the range of simulated variability is wide. To understand these difference, here the mechanisms for AMV is study in various CGCMs. The Atlantic Meridional Overturning Circulation (MOC) plays a prominent role in AMV in most models. It makes a dominant contribution to oceanic heat transport via the northward flow of upper ocean warm water. Correlation analysis shows that in most models variations in the Atlantic MOC (30°N) lead variations in Sea Surface Temperature (SST), with the largest influence in mid-latitudes. Few models shows any relationship between MOC and North Atlantic Oscillation (NAO). The mechanisms for AMV are further investigated in the KCM and MPI models with a 3-dimensional temperature and salinity EOF analysis. In particular, the subsurface variability of North Atlantic and its relation with wind driven circulation in the surface and sinking regions is investigated.

Ba, Jin; Keenlyside, Noel; Park, Wonsun

2010-05-01

29

Decadal record of satellite carbon monoxide observations  

NASA Astrophysics Data System (ADS)

Atmospheric carbon monoxide (CO) distributions are controlled by anthropogenic emissions, biomass burning, transport and oxidation by reaction with the hydroxyl radical (OH). Quantifying trends in CO is therefore important for understanding changes related to all of these contributions. Here we present a comprehensive record of satellite observations from 2000 through 2011 of total column CO using the available measurements from nadir-viewing thermal infrared instruments: MOPITT, AIRS, TES and IASI. We examine trends for CO in the Northern and Southern Hemispheres along with regional trends for Eastern China, Eastern USA, Europe and India. We find that all the satellite observations are consistent with a modest decreasing trend ~ -1 % yr-1 in total column CO over the Northern Hemisphere for this time period and a less significant, but still decreasing trend in the Southern Hemisphere. Although decreasing trends in the United States and Europe have been observed from surface CO measurements, we also find a decrease in CO over E. China that, to our knowledge, has not been reported previously. Some of the interannual variability in the observations can be explained by global fire emissions, but the overall decrease needs further study to understand the implications for changes in anthropogenic emissions.

Worden, H. M.; Deeter, M. N.; Frankenberg, C.; George, M.; Nichitiu, F.; Worden, J.; Aben, I.; Bowman, K. W.; Clerbaux, C.; Coheur, P. F.; de Laat, A. T. J.; Detweiler, R.; Drummond, J. R.; Edwards, D. P.; Gille, J. C.; Hurtmans, D.; Luo, M.; Martínez-Alonso, S.; Massie, S.; Pfister, G.; Warner, J. X.

2013-01-01

30

Decadal Record of Satellite Carbon Monoxide Observations  

NASA Astrophysics Data System (ADS)

Atmospheric carbon monoxide (CO) distributions are controlled by anthropogenic emissions, biomass burning, chemical production, transport and oxidation by reaction with the hydroxyl radical (OH). Quantifying trends in CO is therefore important for understanding changes related to all of these contributions. Here we present a comprehensive record of satellite observations from 2000 through 2011 of total column CO using the available measurements from nadir-viewing thermal infrared instruments: MOPITT, AIRS, TES and IASI. We examine trends for CO in the Northern and Southern hemispheres along with regional trends for E. China, E. USA, Europe and India. Measurement and sampling methods for each of the instruments are discussed, and we show diagnostics for systematic errors in MOPITT trends. We find that all the satellite observations are consistent with a modest decreasing trend around -1%/year in total column CO over the Northern hemisphere for this time period. Decreasing trends in total CO column are observed for the United States, Europe and E. China with more than 2? significance. For India, the trend is also decreasing, but smaller in magnitude and less significant. Decreasing trends in surface CO have also been observed from measurements in the U.S. and Europe. Although less information is available for surface CO in China, there is a decreasing trend reported for Beijing. Some of the interannual variability in the observations can be explained by global fire emissions, and there may be some evidence of the global financial crisis in late 2008 to early 2009. But the overall decrease needs further study to understand the implications for changes in anthropogenic emissions.

Worden, Helen; Deeter, Merritt; Frankenberg, Christian; George, Maya; Nichitiu, Florian; Worden, John; Aben, Ilse; Bowman, Kevin; Clerbaux, Cathy; Coheur, Pierre-Francois; de Laat, Jos; Warner, Juying; Drummond, James; Edwards, David; Gille, John; Hurtmans, Daniel; Ming, Luo; Martinez-Alonso, Sara; Massie, Steven; Pfister, Gabriele

2013-04-01

31

Interannual and Decadal Variability of Summer Rainfall over South America  

NASA Technical Reports Server (NTRS)

Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.

Zhou, Jiayu; Lau, K.-M.

1999-01-01

32

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

33

An oceanic mechanism for decadal variability in the North Pacific  

NASA Astrophysics Data System (ADS)

Many studies have noted decadal scale sea surface temperature (SST) variability in the North Pacific Ocean. The spatial SST pattern has a cold anomaly in the central North Pacific that extends to the Pacific western boundary and resembles a broader and weaker El Nino signal in the tropics. This pattern of variability is often referred to as the Pacific Decadal Oscillation (PDO). Despite extensive research, the nature of the apparent oscillation between warm and cold SST anomalies in the central North Pacific is still surrounded by much uncertainty. A generally agreed upon point is that decadal-scale SST variability appears to be somehow linked to El Nino. However, the mechanism by which such variability is generated, be it an independent dynamical process or a stochastic reddening of other climate signals, is not well understood. Decadal variability in the North Pacific has impacts both locally and remotely. Temperature changes in the North Pacific can have a significant effect on the local ecosystem. Remote effects of the PDO include changes to the surface climate (e.g., temperature and precipitation) in Australia, South and North America, the Russian Far East, much of eastern Asia, and the maritime continent. Improved understanding of decadal variability in the North Pacific could lead to a better understanding of climate variability in these remote regions. Here we use a state-of-the-art high-resolution coupled climate model, HiGEM, to show that anomalous ocean transport in the North Pacific can largely account for the decadal-scale SST variability. We also demonstrate that it is likely that the same mechanism occurs in the real ocean, and therefore that internal ocean dynamics play a key role in regulating decadal-scale variability in the North Pacific.

Dawson, Andrew; Stevens, David; Matthews, Adrian

2013-04-01

34

Decadal variability in historical simulations by coupled climate models in CMIP5  

NASA Astrophysics Data System (ADS)

Climate variability beyond interannual time scales has not been well explored by coupled climate models because of relatively poor simulations and shorter observational record to verify its robustness. However, a newly available historical data assimilation products such as 20CR, newly compiled surface observation datasets such as CRU_TS3.2 and GPCC, paleoclimate records, and improved simulation by coupled climate models provide a new opportunity. In this study, we'll evaluate how well fully coupled climate models in CMIP5 simulate a couple of well known decadal/multi-decadal climate variabilities, such as Pacific Decadal Variability (PDV), Atlantic Multi-decadal oscillation (AMO), and decadal component of North Atlantic Oscillation (NAO). Further, we'll use sets of sensitivity experiments with CESM1 to investigate the anthropogenic causes of these decadal variabilities.

Yoon, J.; Rasch, P. J.

2013-12-01

35

Arctic decadal variability from an idealized atmosphere-ice-ocean model: 2. Simulation of decadal oscillations  

Microsoft Academic Search

A simple model of the Arctic Ocean and Greenland Sea, coupled to a thermodynamic sea ice model and an atmospheric model, has been used to study decadal variability of the Arctic ice-ocean-atmosphere climate system. The motivating hypothesis is that the behavior of the modeled and ultimately the real climate system is auto-oscillatory with a quasi-decadal periodicity. This system oscillates between

Dmitry Dukhovskoy; Mark Johnson; Andrey Proshutinsky

2006-01-01

36

Foraminiferal radiocarbon record of northeast Pacific decadal subsurface variability  

NASA Astrophysics Data System (ADS)

The decadal dynamics of the subsurface North Pacific Ocean are largely inaccessible beyond sparse instrumental observations spanning the last 20 years. Here we present a ˜200 year long record of benthic foraminiferal radiocarbon (?14C), extracted at biennial resolution from the annually laminated sediments at the Santa Barbara Basin (SBB) depocenter (˜600 m). The close match between core top benthic foraminiferal ?14C values and the ?14C of seawater dissolved inorganic carbon (DIC) suggests that benthic foraminifera faithfully capture the bottom water radiocarbon concentrations, as opposed to that of the deeper (>0.5 cm) sediment porewater zone. The full time series of benthic foraminiferal ?14C displays significant variability on decadal timescales, with excursions on the order of 40‰. These excursions are overprinted by a unidirectional trend over the late 20th century that likely reflects the sedimentary incorporation of bomb radiocarbon (via remineralized particulate organic carbon). We isolate this trend by means of a one-dimensional oxidation model, which considers the possible contribution of remineralized particles to the total ambient carbon pool. This oxidation model also considers the possible influence of carbon with a variety of sources (ages). Though variable oxidation of preaged carbon could exert a strong influence on benthic foraminiferal radiocarbon variability, the totality of evidence points to the vertical density structure along the Southern California Margin (SCM) as the primary driver of the SBB benthic foraminiferal ?14C record. For example, intervals characterized by significantly lower ?14C values correspond to periods of enhanced upwelling and subsurface equatorward flow along the SCM.

Roach, Lydia D.; Charles, Christopher D.; Field, David B.; Guilderson, Thomas P.

2013-09-01

37

Observed decadal tropical Pacific-North Atlantic teleconnections  

NASA Astrophysics Data System (ADS)

Observations of the last century are considered to investigate the decadal scale Pacific/North Atlantic teleconnections. By using wavelet analysis we find a significant low-frequency coherency between major indices of climate variability. In particular, at periods between 10 and 20 yr, the North Atlantic Oscillation (NAO) tends to be out of phase with the El Niño/Southern Oscillation (ENSO) (strong Icelandic low during La Niña) and the Pacific Decadal Oscillation (PDO), but in phase with the North Pacific Index (NPI). Hence, the Icelandic low is strong during La Niña, but the Aleutian low is weak. The band-pass SST pattern shows a close relationship between the ``decadal-ENSO'' mode in the Pacific and the sea surface temperature anomaly tripole in the Atlantic, consistent with the low-frequency global teleconnections. The spatial sea level patterns corresponding to the band-pass filtered indices suggest that the Aleutian-Icelandic Low seesaw is a main interbasin link on decadal time scale, consistent with the larger coherency of the NPI with the NAO than with ENSO.

Müller, W. A.; Frankignoul, C.; Chouaib, N.

2008-12-01

38

Predictability of Pacific Decadal Climate Variability and Climate Impacts (Invited)  

NASA Astrophysics Data System (ADS)

Predictability of Pacific sea surface temperature (SST) climate variations and climate impacts on time scales of 1-10 years is discussed, using a global linear inverse model (LIM) as an empirical benchmark for decadal surface temperature forecast skill. Constructed from the observed simultaneous and 1-yr lag covariability statistics of annually averaged sea surface temperature (SST) and surface (2 m) land temperature global anomalies during 1901-2009, the LIM has hindcast skill for leads of 2-5 yr and 6-9 yr comparable to and sometimes even better than skill of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) model hindcasts initialized annually over the period 1960-2000 and has skill far better than damped persistence (e.g., a local univariate AR1 process). Pronounced similarity in geographical variations of skill between LIM and CMIP5 hindcasts suggests similarity in their sources of skill as well, supporting additional evaluation of LIM predictability. For forecast leads above 1-2 yr, LIM skill almost entirely results from three nonorthogonal patterns: one corresponding to the secular trend and two more, each with about 10-yr decorrelation time scales but no trend, that represent most of the predictable portions of the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) indices, respectively. In contrast, for forecasts greater than about two years, ENSO acts as noise and degrades forecast skill. These results suggest that current coupled model decadal forecasts may not yet have much skill beyond that captured by multivariate, predictably linear dynamics. A particular focus will be on the predictability of the PDO, which represents the dominant mode of Pacific decadal SST variability. The PDO is shown to represent a few different physical processes, including wind-driven changes of SSTs that can occur either due to daily weather variability or to tropical forcing, and variations in the North Pacific western boundary current region. These different processes represent increasingly longer time scales but are largely unrelated, and it is their combination that may produce regime-like behavior. The question of whether the PDO represents a response to climate forcing rather than a forcing of climate variability is thus key to an understanding of what impacts, if any, the PDO has on North American climate. Finally, in many disciplines, a climate index such as the PDO is a black box to be used as input for system sensitivity tests. But just because the PDO may represent the most predictable SST variation does not mean that it must always have the greatest climate impact. How climate impact assessment will be improved with an end-to-end approach where neither the climate predictability problem nor the systems sensitivity problem is treated in isolation is an essential but largely unanswered question. That is, rather than ask how sensitive our system is to a pre-specified climate pattern, or what climate patterns are most predictable, it may be better to ask what climate impacts on systems are most predictable.

Newman, M.

2013-12-01

39

Interannual to Decadal Variability of Outflow from the Labrador Sea  

NASA Astrophysics Data System (ADS)

A decade of weak convection in the Labrador Sea associated with decreasing water mass transformation, in combination with advective and eddy fluxes into the convection area, caused significant warming of the deep waters in both the central Labrador Sea and boundary current system along the Labrador shelf break. The connection to the export of Deep Water was studied based on moored current meter stations between 1998 and 2009 at the exit of the Labrador Sea, near the shelf break at 53 ° N. More than 100 year-long current meter records have been analyzed with respect to high frequency variability, decaying from the surface to the bottom layer, and for the annual mean flow, showing intra- to interannual variability but no detectable decadal trend in the strength of the deep and near bottom flow out of the Labrador Sea.

Visbeck, M.; Fischer, J.; Zantopp, R.; Nunes, N.

2010-12-01

40

Decadal variability of the Arctic Ocean thermal structure  

NASA Astrophysics Data System (ADS)

Long-term variability of heat content (HC) in the upper 1,000 m of the Arctic Ocean is investigated using surface and subsurface temperature and current data during 1958-2005 compiled by Simple Ocean Data Assimilation. Annual cycle of the Arctic Ocean HC is controlled primarily by the negative and positive excursions in net upper ocean heat flux, while the inter-annual variability is mainly associated with meridional thermal advection from the North Atlantic Ocean. Variability in HC is experienced as a basin-wide cooling/warming in association with the Arctic Oscillation on a decadal time scale. In the first three dominant modes of Empirical Orthogonal Function, the maximum amplitude of HC variability occurs in the Greenland-Norwegian Sea and Eurasian Basin. In general, HC showed increasing trend during 1958-2005 indicating continuous warming with regional variations in magnitude.

Madhusoodanan, M. S.; Thompson, Bijoy

2011-07-01

41

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

NASA Astrophysics Data System (ADS)

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

Zhang, Xuebin; Church, John A.

2012-11-01

42

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

43

Multi-decadal Variability of the Wind Power Output  

NASA Astrophysics Data System (ADS)

The knowledge of the long-term wind power variability is essential to provide a realistic outlook on the power output during the lifetime of a planned wind power project. In this work, the Power Output (Po) of a market wind turbine is simulated with a daily resolution for the period 1871-2009 at two different locations in Spain, one at the Central Iberian Plateau and another at the Gibraltar Strait Area. This is attained through a statistical downscaling of the daily wind conditions. It implements a Greedy Algorithm as classificator of a geostrophic-based wind predictor, which is derived by considering the SLP daily field from the 56 ensemble members of the longest homogeneous reanalysis available (20CR, 1871-2009). For calibration and validation purposes we use 10 years of wind observations (the predictand) at both sites. As a result, a series of 139 annual wind speed Probability Density Functions (PDF) are obtained, with a good performance in terms of wind speed uncertainty reduction (average daily wind speed MAE=1.48 m/s). The obtained centennial series allow to investigate the multi-decadal variability of wind power from different points of view. Significant periodicities around the 25-yr frequency band, as well as long-term linear trends are detected at both locations. In addition, a negative correlation is found between annual Po at both locations, evidencing the differences in the dynamical mechanisms ruling them (and possible complementary behavior). Furthermore, the impact that the three leading large-scale circulation patterns over Iberia (NAO, EA and SCAND) exert over wind power output is evaluated. Results show distinct (and non-stationary) couplings to these forcings depending on the geographical position and season or month. Moreover, significant non-stationary correlations are observed with the slow varying Atlantic Multidecadal Oscillation (AMO) index for both case studies. Finally, an empirical relationship is explored between the annual Po and the parameters of the Weibull PDF. This allowed us to derive a linear model to estimate the annual power output from those parameters, which results especially useful when no wind power data is available.

Kirchner Bossi, Nicolas; García-Herrera, Ricardo; Prieto, Luis; Trigo, Ricardo M.

2014-05-01

44

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

45

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

46

Interannual and Decadal Variability in the Tropical and Midlatitude Pacific Ocean  

Microsoft Academic Search

Forty-four years of mechanical and expendable bathythermograph observations are assimilated into a general circulation model of the Pacific Ocean. The model is run from 1950 through 1993 with forcing at the surface from observed monthly mean wind stress and temperature. The resulting analysis is used to describe the spatial and temporal patterns of variability at interannual and decadal periods. Interannual

Benjamin S. Giese; James A. Carton

1999-01-01

47

Nine decades of decreasing phenotypic variability in Atlantic cod.  

PubMed

Changes in phenotypic variability in natural populations have received little attention in comparison with changes in mean trait values. This is unfortunate because trait diversity may influence adaptive evolutionary change and population stability. We combine two unique data sets to illuminate complex trait changes in Atlantic cod along the Norwegian Skagerrak coast: (i) an annual beach seine survey starting in 1919, monitoring juvenile body size and abundance and (ii) capture-mark-recapture data from which we estimated selection on juvenile body size and growth. We demonstrate that the variability of juvenile size has been steadily decreasing across nine decades, with no evidence for a similar trend in mean size. We also report that small, slow-growing fish as well as large, fast-growing fish are selected against. Together, these results suggest long-term stabilizing selection acting on Atlantic cod, and emphasize the need for further studies evaluating the full complexity of trait changes in wild populations. PMID:19453620

Olsen, Esben Moland; Carlson, Stephanie M; Gjøsaeter, Jakob; Stenseth, Nils Chr

2009-07-01

48

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

49

Arctic decadal variability from an idealized atmosphere-ice-ocean model: 2. Simulation of decadal oscillations  

NASA Astrophysics Data System (ADS)

A simple model of the Arctic Ocean and Greenland Sea, coupled to a thermodynamic sea ice model and an atmospheric model, has been used to study decadal variability of the Arctic ice-ocean-atmosphere climate system. The motivating hypothesis is that the behavior of the modeled and ultimately the real climate system is auto-oscillatory with a quasi-decadal periodicity. This system oscillates between two circulation regimes: the Anticyclonic Circulation Regime (ACCR) and the Cyclonic Circulation Regime (CCR). The regimes are controlled by the atmospheric heat flux from the Greenland Sea and the freshwater flux from the Arctic Ocean. A switch regulating the intensity of the fluxes between the Arctic Ocean and Greenland Sea that depends on the interbasin gradient of dynamic height is implemented as a delay mechanism in the model. This mechanism allows the model system to accumulate the "perturbation" over several years. After the perturbation has been released, the system returns to its initial state. Solutions obtained from numerical simulations with seasonally varying forcing, for scenarios with high and low interaction between the regions, reproduced the major anomalies in the ocean thermohaline structure, sea ice volume, and freshwater fluxes attributed to the ACCR and CCR.

Dukhovskoy, Dmitry; Johnson, Mark; Proshutinsky, Andrey

2006-06-01

50

Decadal monitoring of variables by the AAVSO community  

NASA Astrophysics Data System (ADS)

The American Association of Variable Stars has been in existence for over 100 years. First performing monitoring and follow-up observations for Harvard College astronomers, the organization has expanded into following thousands of variables with a wide variety of instrumentation, as well as participating in the discovery of transient objects and the data-mining of survey catalogs. Several examples of how long, continuous, homogeneous light curves can yield astrophysical results not possible with short lifetime surveys will be given.

Henden, Arne A.

2014-06-01

51

Observations of secular and decade changes in the earth's rotation  

Microsoft Academic Search

Changes in the length of the day over the past 2700 years are derived from observations of occultations of stars by the moon and observations of solar and lunar eclipses. The data since AD 1600 show that the length of the day fluctuates by about 4 milliseconds on a timescale of decades. The more ancient data indicate that there are

L. V. Morrison; F. R. Stephenson

1986-01-01

52

Causes of decadal climate variability over the North Pacific and North America  

SciTech Connect

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 in the North Pacific and the Aleutian low-pressure system. The existence of this cycle provides a basis for long-range climate forecasting over the western United States at decadal time scales. 17 refs., 5 figs.

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

1994-10-28

53

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

54

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

NASA Astrophysics Data System (ADS)

This study investigates the mechanisms of the internally generated decadal-to-multidecadal time scale SST variability in the Atlantic, including the North Atlantic Tripole variability, the Atlantic Multidecadal Variability and the Tropical Atlantic Variability, on the basis of a 300-year 1990 control simulation (CONTROL) made with CCSM3 and in an interactive ensemble version of CCSM3 (IE-CCSM3: 6 copies of AGCM coupled to the OGCM through the flux coupler). The structures, amplitudes and time scales of these three low frequency modes from CONTROL have properties similar to the observed variability, indicating that CCSM3 is appropriate for studying their mechanisms. These modes are closely related to the variability of the Atlantic Meridional Overturning Circulation (AMOC) on decadal time scales, suggesting that all of these types of variability may be manifestations of a single decadal "mode" of variability. To understand the low frequency modes and their interaction with each other, and the interaction among different oceanic regions, we isolate weather noise forcing from other mechanisms, including the coupled feedback, the gyre circulations, wave dynamics, and AMOC. The weather noise surface fluxes, including the net heat flux, wind stress and freshwater flux, are obtained from CONTROL by removing the SST forced surface fluxes, which are averaged from an ensemble of six AGCMs forced by the CONTROL SST. The IE-CCSM3 simulations in which the specified weather noise forcing is restricted to specific regions or in which the effects of the different specified surface fluxes are isolated are carried out to determine the contributions to the Atlantic decadal modes by region and by forcing type. Our results from the weather noise forced IE-CCSM3 simulations demonstrate that weather noise is responsible for most of decadal variability in the Atlantic and reveal the interactions between the three modes.

Chen, H.; Schneider, E. K.

2011-12-01

55

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

SciTech Connect

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

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

1996-10-01

56

Subduction of Decadal North Pacific Temperature Anomalies: Observations and Dynamics  

Microsoft Academic Search

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

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

1999-01-01

57

Icarus Revisted: Three Decades of Radar Observations of Asteroids  

NASA Technical Reports Server (NTRS)

Three decades after the close encounter of 1566 Icarus, which marked the beginning of asteroid radar astronomy, we had a chance to observe the asteroid afresh by using a more developed radar system, and here we present the results of the study.

Mahapatra, P. R.; Ostro, S. J.; Benner, L. A.; Rosema, K. D.; Jurgens, R. F.; Winkler, R.; Rose, R.; Giorgini, J. D.; Yeomans, D. K.; Slade, M. A.

1998-01-01

58

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

59

Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget  

NASA Technical Reports Server (NTRS)

It is widely assumed that variations in the radiative energy budget at large time and space scales are very small. We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. We demonstrate that the radiation budget changes are caused by changes In tropical mean cloudiness. The results of several current climate model simulations fall to predict this large observed variation In tropical energy budget. The missing variability in the models highlights the critical need to Improve cloud modeling in the tropics to support Improved prediction of tropical climate on Inter-annual and decadal time scales. We believe that these data are the first rigorous demonstration of decadal time scale changes In the Earth's tropical cloudiness, and that they represent a new and necessary test of climate models.

Wielicki, Bruce A.; Wong, Takmeng; Allan, Richard; Slingo, Anthony; Kiehl, Jeffrey T.; Soden, Brian J.; Gordon, C. T.; Miller, Alvin J.; Yang, Shi-Keng; Randall, David R.; Arnold, James E. (Technical Monitor)

2001-01-01

60

Decadal variability of rift propagation on the Amery Ice Shelf  

NASA Astrophysics Data System (ADS)

The Amery Ice Shelf, East Antarctica, features five prominent rifts within 30 km of its calving front. We produce a time series of changes in rift length for the period 2002-2012 using available MODIS and MISR data. We find that all five are actively propagating, but with a complex spatio-temporal pattern of variability in which some rifts propagate in tandem while others appear to tradeoff. Temporal variability in rift propagation is dominated by large episodic bursts. These bursts, analogous to the much smaller propagation events detected from field observations, are not synchronous across all five rifts nor do the timing of propagation events exhibit any correlation with observed proxies for environmental forcing (e.g., atmospheric temperatures, sea-ice extent). However, we find that several propagation events take place after the predicted arrival from tsunamis originating in the Indian Ocean. This is especially apparent following the December 2004 Sumatra earthquake and three other earthquakes in the Sumatra/W. Indonesia area. This connection is bolstered by the observation of similar effects at other ice shelves, e.g., a large iceberg calving after the sudden propagation of two front-initiated rifts at Larsen C after the December 2004 tsunami. In comparing rift propagation at Amery with 61 rifts on 10 other ice shelves, we find that with the exception of the occasional tsunami triggered propagation event, the extreme variability on the Amery Ice Shelf is highly atypical. We postulate that the pronounced activity on the Amery is due to the fact that it last had a large calving event in 1963/64, and is approaching its pre-calved position. This suggests that the AIS is poised for another major calving event and the highly dynamic propagation we observe is the precursor to such an event. That multiple rifts exist and propagate due to structural heterogeneity and shelf geometry also makes these observations relevant to the highly fractured shells of the icy moons, which exhibit a high number of fractures and active surfaces.

Walker, C. C.; Bassis, J. N.; Czerwinski, R. J.; Fricker, H. A.

2012-12-01

61

Warming trends and decadal variability in the Western Mediterranean shelf  

NASA Astrophysics Data System (ADS)

We analyse hydrographic, meteorological and sea level time series in the continental shelves of Málaga Bay and L'Estartit, in the South and North Western Mediterranean. We have detected an important reduction of the warming rates reported for the 90s decade, showing that the warming process of the Mediterranean is superimposed on several years lasting oscillations. These accelerations or interruptions, typically account for a fraction of the total trend, and therefore they are not able to obscure the warming detection if the time series are long enough. On the other hand, they can produce artificial results if the time series are short when compared with the length of these cycles. The warming of the shelf waters, its acceleration during the 90s and the reversal during the beginning of the XXI century, are also observed in air temperature time series along the Spanish Mediterranean. We have also checked the influence of the warming acceleration/disruption on the sea level rise. Mean sea level trends are around 1 mm/yr when long time series are analysed, but shorter time series can result in rising trends as large as 13 mm/yr, for accelerated warming periods, or even no sea level change for reversals of the warming trends. Another factor to study is the influence of the NAO on these warming/cooling periods as well as on the strength of upwelling favourable winds, which could have a great importance on shelf ecosystems.

Vargas-Yáñez, Manuel; xmlns:lnsm="http://www. lexis-nexis. com/lnsm">a Jesús García, M.

2008-09-01

62

Teleconnections force interannual-to-decadal tidal variability in the Lagoon of Venice (northern Adriatic)  

NASA Astrophysics Data System (ADS)

In the present investigation, for the first time, fundamental characteristics of autumn and winter average sequences of sea level heights (SLH) that were recorded in the Lagoon of Venice (northern Adriatic, in the Mediterranean Sea) during the period 1872-2004 are investigated. Interannual-to-decadal variability of Venetian SLH is found to reflect the variability of the most prominent Euro-Atlantic teleconnections (EATs). In particular, the North Atlantic Oscillation (NAO), the East Atlantic/Western Russian, and the Scandinavian patterns are found to contribute to generate the ˜5-year, ˜8-year and ˜22-year peaks that dominate the spectra of seasonal Venetian SLH. Among the possible oceanic and atmospheric phenomena downscaling interannual-to-decadal large-scale atmospheric signals into the observed variability in the Venetian SLH, we explore inverse barometer effect, wind-driven setup, and the thermohaline circulation of both the Adriatic and the Mediterranean seas. All these phenomena are assessed to display some of the typical features of the shared interannual-to-decadal variability of both Venetian SLH and EATs. Our analysis shows also that the decadal variability of winter Venetian SLH is closely linked with variations in solar activity: in particular, the winter SLH multidecadal pattern is found to be correlated, with very high statistical confidence, to the Hale Cycles pattern (˜22 years), which describes the series of sunspot cycles with alternating opposite polarity. The marked signature of Hale Cycles on the leading mode of multidecadal sea level pressure winter variability (which is practically indistinguishable from the inverse wintertime NAO) is also detailed to further support the hypothesis of a Sun-Venetian SLH association.

Zanchettin, D.; Rubino, A.; Traverso, P.; Tomasino, M.

2009-04-01

63

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

Microsoft Academic Search

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

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

2002-01-01

64

Role of Sea Ice in a Mechanism of Arctic Decadal Variability  

NASA Astrophysics Data System (ADS)

This study investigates decadal variability of the Arctic Ocean - Greenland, Iceland, Norwegian Seas atmosphere-ice-ocean system. Based on findings from previous observational and modeling studies of Arctic climate it is assumed that decadal variability in the region is associated with self-sustained oscillations in the climate system. We hypothesize that Arctic variability is regulated by heat and freshwater exchange between the Arctic Ocean and the GIN Sea. The interaction between basins is weak during anticyclonic circulation regimes (low AO/NAO) and strong during cyclonic circulation regimes (high AO/NAO). Regime shifts are controlled by the system itself through oceanic and atmospheric gradients (dynamic height and surface air temperature) that increase during the anticyclonic regime and decrease during the cyclonic regime. A simple model of the Arctic Ocean and Greenland Sea, coupled to a thermodynamic sea ice model and atmospheric model, has been used to investigate a possible mechanism of self-sustained climate oscillation. Periodic solutions obtained from simulations with seasonally varying forcing, for scenarios with high and low interaction between the regions, reproduce major anomalies in the ocean thermohaline structure, sea ice volume, and fresh water fluxes attributed to ACCR and CCR. Role of sea ice in the mechanism of decadal variability is discussed.

Dukhovskoy, D.; Johnson, M.; Proshutinsky, A.

2004-12-01

65

Atmospheric response to the North Atlantic Ocean variability on seasonal to decadal time scales  

NASA Astrophysics Data System (ADS)

The NCEP twentieth century reanalyis and a 500-year control simulation with the IPSL-CM5 climate model are used to assess the influence of ocean-atmosphere coupling in the North Atlantic region at seasonal to decadal time scales. At the seasonal scale, the air-sea interaction patterns are similar in the model and observations. In both, a statistically significant summer sea surface temperature (SST) anomaly with a horseshoe shape leads an atmospheric signal that resembles the North Atlantic Oscillation (NAO) during the winter. The air-sea interactions in the model thus seem realistic, although the amplitude of the atmospheric signal is half that observed, and it is detected throughout the cold season, while it is significant only in late fall and early winter in the observations. In both model and observations, the North Atlantic horseshoe SST anomaly pattern is in part generated by the spring and summer internal atmospheric variability. In the model, the influence of the ocean dynamics can be assessed and is found to contribute to the SST anomaly, in particular at the decadal scale. Indeed, the North Atlantic SST anomalies that follow an intensification of the Atlantic meridional overturning circulation (AMOC) by about 9 years, or an intensification of a clockwise intergyre gyre in the Atlantic Ocean by 6 years, resemble the horseshoe pattern, and are also similar to the model Atlantic Multidecadal Oscillation (AMO). As the AMOC is shown to have a significant impact on the winter NAO, most strongly when it leads by 9 years, the decadal interactions in the model are consistent with the seasonal analysis. In the observations, there is also a strong correlation between the AMO and the SST horseshoe pattern that influences the NAO. The analogy with the coupled model suggests that the natural variability of the AMOC and the gyre circulation might influence the climate of the North Atlantic region at the decadal scale.

Gastineau, Guillaume; D'Andrea, Fabio; Frankignoul, Claude

2013-05-01

66

A decade of multispectral sea surface temperature observations from space  

NASA Astrophysics Data System (ADS)

The National Environmental Satellite and Data Information Service (NESDIS) of NOAA has been producing estimates of Sea Surface Temperature (SST) using high resolution, multispectral infrared data from satellites operationally for over 10 years. This dataset is one of the largest and longest available for studies of a primary climate variable. However, the utility of this dataset for studies of Climate and Global Change remains only marginal because of large biases during volcanic aerosol episodes. In this paper, three criteria are critically examined to assess the quality of the operational multi-spectral SST (MCSST) method. These include: 1) the basic physics of the method, 2) mean differences between satellite and in situ SSTs, and 3) an examination of the time/space variability of the satellite dataset. These criteria are fundamental in the evaluation of data derived from satellite observations for global climate monitoring.

Bates, John J.

1994-03-01

67

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

68

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

NASA Astrophysics Data System (ADS)

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 is based on a cycle involving unstable ocean-atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades.The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. When, for instance, the subtropical ocean gyre is anomalously strong, more warm tropical waters are transported poleward by the Kuroshio and its extension, leading to a positive SST anomaly in the North Pacific. The atmospheric response to this SST anomaly involves a weakened Aleutian low, and the associated fluxes at the air-sea interface reinforce the initial SST anomaly, so that ocean and atmosphere act as a positive feedback system. The anomalous heat flux, reduced ocean mixing in response to a weakened storm track, and anonmalous Ekman heat transport contribute to this positive feedback.The atmospheric response, however, consists also of a wind stress curl anomaly that spins down the subtropical ocean gyre, thereby reducing the poleward heat transport and the initial SST anomaly. The ocean adjusts with some time lag to the change in the wind stress curl, and it is this transient ocean response that allows continuous oscillations. The transient response can be expressed in terms of baroclinic planetary waves, and the decadal timescale of the oscillation is therefore determined to first order by wave timescales. Advection by the mean currents, however, is not negligible.The existence of such a cycle provides the basis of long-range climate forecasting over North America at decadal timescales. At a minimum, knowledge of the present phase of the decadal mode should allow a `now-cast' of expected climate `bias' over North America, which is equivalent to a climate forecast several years ahead.

Latif, M.; Barnett, T. P.

1996-10-01

69

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

70

Polar lightning and decadal-scale cloud variability on Jupiter.  

PubMed

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

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

2007-10-12

71

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

72

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

73

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

Microsoft Academic Search

The Bermuda station ''S'' time series has been used to define the variability of subtropical mode water (STMW) from 1954 to 1995. This record, which shows decadal variability at a nominal period of about 12-14 yr, has been used as a baseline for seeking correlation with large-scale atmospheric forcing and with decadal north-south excursions of the Gulf Stream position defined

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

2000-01-01

74

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

Microsoft Academic Search

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

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

75

Aerosol Variability Observed with Rpas  

NASA Astrophysics Data System (ADS)

To observe the origin, vertical and horizontal distribution and variability of aerosol particles, and especially ultrafine particles recently formed, we plan to employ the remotely piloted aircraft system (RPAS) Carolo-P360 "ALADINA" of TU Braunschweig. The goal of the presented project is to investigate the vertical and horizontal distribution, transport and small-scale variability of aerosol particles in the atmospheric boundary layer using RPAS. Two additional RPAS of type MASC of Tübingen University equipped with turbulence instrumentation add the opportunity to study the interaction of the aerosol concentration with turbulent transport and exchange processes of the surface and the atmosphere. The combination of different flight patterns of the three RPAS allows new insights in atmospheric boundary layer processes. Currently, the different aerosol sensors are miniaturized at the Leibniz Institute for Tropospheric Research, Leipzig and together with the TU Braunschweig adapted to fit into the RPAS. Moreover, an additional meteorological payload for measuring temperature, humidity and turbulence properties is constructed by Tübingen University. Two condensation particle counters determine the total aerosol number with a different lower detection threshold in order to investigate the horizontal and vertical aerosol variability and new particle formation (aerosol particles of some nm diameter). Further the aerosol size distribution in the range from about 0.300 to ~5 ?m is given by an optical particle counter.

Altstädter, B.; Lampert, A.; Scholtz, A.; Bange, J.; Platis, A.; Hermann, M.; Wehner, B.

2013-08-01

76

Decadal variation in the Chandler amplitude and the decadal oscillation in the observed dynamic oblateness J2  

NASA Astrophysics Data System (ADS)

Numerical simulation based on atmospheric angular momentum forcing recovers a distinctive decadal variation in the amplitude of the Chandler Wobble, or the Chandler amplitude (CA) for the period 1976-2010. This decadal variation in the CA qualitatively anti-correlates with the decadal oscillation in the Earth's dynamic oblateness, J2, observed by satellite laser ranging for the same period. This revelation raises more questions than it answers: even though the polar-motion-induced perturbation of J2 depends on and anti-correlates with the CA, it is generically second order as a result of trace invariance in the moment of inertia tensor. Only direct mass redistribution can cause first order variation in J2. The decadal variation in the CA excited by highly irregular atmospheric forcing is unlikely to be by chance, as we find that the autocorrelation of the forcing is strongest at the time lag of ~10 years for the period 1976-2010. The time lag between the two strongest cold ENSO phases during the same period of time is also ~10 years (1987-1997), as indicated in the Southern Oscillation Index. The most conspicuous anomalies in the J2 time series that characterize its decadal variation are closely associated with the two cold phases. Detailed anatomy of the broadband excitation for the Chandler Wobble based on the NCEP atmospheric forcing and ECCO ocean model shows a chaotic phase transition in the Chandler signal during the prolonged cold ENSO phases from 1998-2001. All of this evidence consistently points to a decadal climatology in the rapid mass variations in the Earth's water cycle that at least in significant part contributes to the decadal variations of the CA and J2. Thus, it is dangerous to attribute all decadal variations in the Earth's gravity field to deep core dynamics without considering surface processes.

Fang, M.; Hager, B. H.; Cheng, M.

2011-12-01

77

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

78

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

79

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

80

Multi-decadal variability of the eastern North Atlantic subpolar gyre  

NASA Astrophysics Data System (ADS)

The Extended Ellett Line is a hydrographic section sampling the eastern North Atlantic subpolar gyre from Iceland to Scotland. The section samples the main warm-water path of the Atlantic meridional overturning circulation (AMOC) from the subtropics to the Nordic Seas and the cold-water return flow from the Faroe Bank Channel south of Iceland. Here we present property and circulation variability from 18 annual hydrographic sections since 1996. Uncertainties due to aliasing are examined using float-based products, model output and altimetry. Nearest to Scotland in the Rockall Trough we have 65-years of data showing multi-decadal variability of upper ocean heat and salt anomalies feeding into the Nordic Seas. The amplitude of temperature and salinity changes are 0.5°C and 0.08 (salinity), with highs in the mid-2000s. The anomalies are influenced by the strength of the circulation of the subpolar gyre and indicate large-scale changes. The causes of the observed variability of properties and circulation, the relationships between the basins, and the influence of the AMOC and atmosphere are discussed.

Cunningham, Stuart; Holliday, N. Penny; Johnson, Clare; Gary, Stefan

2014-05-01

81

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

82

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

83

IUE observations of cataclysmic variable  

NASA Astrophysics Data System (ADS)

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

1993-06-01

84

Arctic forcing of decadal variability in the tropical Pacific Ocean in a high-resolution global coupled GCM  

NASA Astrophysics Data System (ADS)

The hypothesis that northern high-latitude atmospheric variability influences decadal variability in the tropical Pacific Ocean by modulating the wind jet blowing over the Gulf of Tehuantepec (GT) is examined using the high-resolution configuration of the MIROC 3.2 global coupled model. The model is shown to have acceptable skill in replicating the spatial pattern, strength, seasonality, and time scale of observed GT wind events. The decadal variability of the simulated GT winds in a 100-year control integration is driven by the Arctic Oscillation (AO). The regional impacts of the GT winds include strong sea surface cooling, increased salinity, and the generation of westward-propagating anticyclonic eddies, also consistent with observations. However, significant nonlocal effects also emerge in concert with the low-frequency variability of the GT winds, including anomalously low upper ocean heat content (OHC) in the central tropical Pacific Ocean. It is suggested that the mesoscale eddies generated by the wind stress curl signature of the GT winds, which propagate several thousand kilometers toward the central Pacific, contribute to this anomaly by strengthening the meridional overturning associated with the northern subtropical cell. A parallel mechanism for the decadal OHC variability is considered by examining the Ekman and Sverdrup transports inferred from the atmospheric circulation anomalies in the northern midlatitude Pacific directly associated with the AO.

Karnauskas, Kristopher B.

2014-06-01

85

Response of Tropical Forests to Intense Climate Variability and Rainfall Anomaly of 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. S.; Asefi Najafabady, S.

2011-12-01

86

Herschel Observations of Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

87

EarthScope's USArray: A Decade of Observations and Results  

NASA Astrophysics Data System (ADS)

EarthScope's USArray observatory provides unprecedented observations of geophysical targets across the contiguous United States through the systematic deployment of seismic, magnetotelluric, and atmospheric instruments. In addition, USArray includes tightly integrated data management and outreach activities. The seismic and atmospheric components of USArray consist of a Transportable Array (TA), Flexible Array (FA), and Reference Network. The TA has now occupied approximately 1700 sites spanning the entire contiguous 48 states, at 70 km inter-station spacing. These stations have provided broadband seismic, barometric pressure and atmospheric infrasound observations. The pool of instruments that comprise the FA have been deployed by numerous individual investigators in dense arrays to investigate local and regional features over time periods ranging from days to years. The Reference Network provides a permanent, stationary foundation for the TA and FA, with approximately 100 broadband stations deployed across the contiguous US at roughly 300 km spacing. The magnetotelluric (MT) component of USArray has provided both fixed and campaign-style long-period magnetotelluric observations at hundreds of locations across the US. Many of the field activities of USArray engaged both students and the public in important ways and this has been a significant component of USArray outreach. The TA alone has engaged well over one hundred students in site reconnaissance activities and placed seismic stations on the property of roughly a thousand different landowners. All data collected by USArray are openly available, most in real time. Many of the observations have also been incorporated into a variety of data products that have been developed to facilitate use of USArray by many different audiences. The scientific community has used USArray data to achieve a wide range of results--some that were anticipated when the facility was proposed and some that were completely unanticipated. Data products such as direct visualizations of seismic wave propagation observed by the TA have been viewed hundreds of thousands of times on the web by the general public. We will provide a brief overview of the deployments and accomplishments of USArray from the past ten years, and an overview of the significant and diverse scientific results that have been achieved. We will touch on some of the technologies and organizational and operational strategies that have enabled the success of USArray. We will conclude with a brief discussion of USArray plans for the next five years.

Woodward, R.; Busby, R. W.; Hafner, K.; Gridley, J. M.; Schultz, A.; Frassetto, A.; Simpson, D. W.

2013-12-01

88

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

89

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

SciTech Connect

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

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

1995-02-01

90

Decadal prediction of observed and simulated sea surface temperatures  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

91

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

92

Decadal variability of circulation in the Arctic Ocean retrieved from climatological data by a variational method  

Microsoft Academic Search

An inverse 3D finite-element ocean circulation model has been designed and used to study variability of the Arctic Ocean circulation in the last 4 decades. We obtained stationary model solutions with the temperature and salinity fields close to the ones given by the Environmental Working Group (EWG) [1998] atlas. Transports at the open boundaries, wind forcing and hydrographic fields are

Dmitri Nechaev; Max Yaremchuk; Motoyoshi Ikeda

2004-01-01

93

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

94

The amplitude of decadal to multidecadal variability in precipitation simulated by state-of-the-art climate models  

NASA Astrophysics Data System (ADS)

We assess the magnitude of decadal to multidecadal (D2M) variability in Climate Model Intercomparison Project 5 (CMIP5) simulations that will be used to understand, and plan for, climate change as part of the Intergovernmental Panel on Climate Change's 5th Assessment Report. Model performance on D2M timescales is evaluated using metrics designed to characterize the relative and absolute magnitude of variability at these frequencies. In observational data, we find that between 10% and 35% of the total variance occurs on D2M timescales. Regions characterized by the high end of this range include Africa, Australia, western North America, and the Amazon region of South America. In these areas D2M fluctuations are especially prominent and linked to prolonged drought. D2M fluctuations account for considerably less of the total variance (between 5% and 15%) in the CMIP5 archive of historical (1850-2005) simulations. The discrepancy between observation and model based estimates of D2M prominence reflects two features of the CMIP5 archive. First, interannual components of variability are generally too energetic. Second, decadal components are too weak in several key regions. Our findings imply that projections of the future lack sufficient decadal variability, presenting a limited view of prolonged drought and pluvial risk.

Ault, T. R.; Cole, J. E.; St. George, S.

2012-11-01

95

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

96

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

97

Mechanisms for decadal scale variability in the North Atlantic Ocean circulation in the Bergen Climate Model  

NASA Astrophysics Data System (ADS)

Potential mechanisms for decadal scale variability for the Atlantic Meridional Overturning Circulation (AMOC) and Subpolar Gyre strength have been identified from a 600-year pre-industrial control simulation with the Bergen Climate Model. In short, the variability appears rooted in the atmosphere. The three dominant modes of North Atlantic atmospheric variability - the North Atlantic Oscillation (NAO), the East Atlantic Pattern (EAP) and the Scandinavian Pattern (SP), are all reflected in the ocean circulation. The variable heat flux related to NAO drives convective mixing in the Labrador Sea and thus the formations of upper North Atlantic Deep Water. Negative phases of SP are associated with northerly winds and consequently increased water mass exchange across the Greenland-Scotland Ridge, including more overflow of lower North Atlantic Deep Water and more poleward heat transport with the Atlantic inflow. Finally, the variable deep water properties, together with the EAP, can partly explain the strength of the Subpolar Gyre circulation.

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

2012-04-01

98

Dendrogeomorphically derived slope response to decadal and centennial scale climate variability: Black Mesa, Arizona, USA  

NASA Astrophysics Data System (ADS)

A major impediment to an understanding of the links between climate and landscape change, has been the relatively coarse resolution of landscape response measures (rates of weathering, sediment production, erosion and transport) relative to the higher resolution of the climatic signal (precipitation and temperature on hourly to annual time scales). A combination of high temporal and spatial resolution dendroclimatic and dendrogeomorphic approaches were used to study relationships between climatic variability and hillslope and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, USA Dendrogeomorphic and vegetation evidence from slopes and valley bottoms, including root exposure, bending of trunks, change in plant cover and burial and exhumation of valley bottom trees and shrubs, suggest that the currently observed process of root colonization and rapid breakdown of the weakly cemented bedrock by subaerial weathering, related to periodic dry/wet cycle induced changes in vegetation cover, has lead to a discontinuous, climate-controlled production of sediment from these slopes. High-amplitude precipitation shifts over the last 2000-years may exert the largest control on landscape processes and may be as, or more, important than other hypothesized causal mechanisms (e.g. ENSO frequency and intensity, flood frequency) in eroding slopes and producing sediments that ultimately impact higher order drainages in the region. Current vegetation response to a prolonged drought over the past decade suggests that another major transition, incorporating vegetation change, slope erosion, sediment production and subsequent valley floor deposition, may be in its initial phase.

Scuderi, L. A.; McFadden, L. D.; McAuliffe, J. R.

2008-08-01

99

Upper ocean heat content and surface current variability associated with the Pacific Decadal Oscillation (PDO)  

NASA Astrophysics Data System (ADS)

Changes in the northeast Pacific Ocean during 1993-2004 are examined as an example of upper ocean heat content variability associated with the Pacific Decadal Oscillation (PDO). The leading empirical orthogonal functions (EOF) of both sea surface temperature (SST) and sea surface height (SSH) in this region are highly correlated with the basin-wide PDO index, which transitioned from the warm to the cold phase in 1999. Sea surface velocities (SSV) constructed from satellite-observed SSH, SST, and vector winds indicate that Ekman and gesotrophic components changed with similar magnitudes but different spatial structures. Combining SSV with the SST field, in situ sub-surface temperature data, and surface heat fluxes from an atmospheric model makes it possible to construct an approximate SST budget. The results demonstrate a principal role for anomalous Ekman advection of the mean temperature gradient and relatively smaller contributions from the other terms, which agrees generally with similar analysis by others using an ocean general circulation model.

Lagerloef, Gary S. E.; Springer, Scott

2010-05-01

100

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

101

Changes in Arctic sea ice distribution and variability during the next decades  

NASA Astrophysics Data System (ADS)

The current and future distribution of sea-ice in the Arctic is of interest to various scientific and non-scientific groups e.g. policymakers, fisheries and shipping companies. Their focus is on the development during the next decades. The assessment of Arctic sea-ice is challenging due to internal variability being superimposed on the general trend. On inter-annual and decadal time scales, large patterns such as the Arctic Oscillation and the North Atlantic Oscillation are suspected to play an influencing role. Sea-ice data derived from satellites are limited to the present and the past three decades. To understand the sea-ice variability and its causes, longer time periods need to be considered. General circulation models (GCM) offer the possibility to produce long time series and to extent these into the future by applying greenhouse gas emission scenarios. High spatial resolution is crucial to represent properly the formation and transport of sea-ice as well as the underlying ocean. Within the ACCESS project, a high resolution (0.25°) regional coupled ocean-sea ice model is used to simulate the current and future Arctic sea-ice. We use a specific set-up of the GCM of the Massachusetts Institute of Technology, MITgcm. It uses atmospheric reanalysis data as forcing for hindcasts and validation experiments. In addition, atmospheric output from global coupled GMCs from the coupled model intercomparison projects (CMIP) CMIP3 and CMIP5 are applied to our regional model for downscaling experiments. These downscaling experiments cover a time range of several decades in the past as well as into the future, allowing us high resolution analysis of sea-ice on inter-annual and decadal time scales and to identify its variability.

Riemann-Campe, K.; Gerdes, R.; Castro-Morales, K.; Karcher, M.; Kauker, F.; Köberle, C.; Losch, M.

2012-04-01

102

Behavior of tropopause height and atmospheric temperature in models, reanalyses, and observations: Decadal changes  

NASA Astrophysics Data System (ADS)

We examine changes in tropopause height, a variable that has hitherto been neglected in climate change detection and attribution studies. The pressure of the lapse rate tropopause, pLRT, is diagnosed from reanalyses and from integrations performed with coupled and uncoupled climate models. In the National Centers for Environmental Prediction (NCEP) reanalysis, global-mean pLRT decreases by 2.16 hPa/decade over 1979-2000, indicating an increase in the height of the tropopause. The shorter European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis has a global-mean pLRT trend of -1.13 hPa/decade over 1979-1993. Simulated pLRT trends over the past several decades are consistent with reanalysis results. Superimposed on the overall increase in tropopause height in models and reanalyses are pronounced height decreases following the eruptions of El Chichón and Pinatubo. Interpreting these pLRT results requires knowledge of both T(z), the initial atmospheric temperature profile, and ?T(z), the change in this profile in response to external forcing. T(z) has a strong latitudinal dependence, as does ?T(z) for forcing by well-mixed greenhouse gases and stratospheric ozone depletion. These dependencies help explain why overall tropopause height increases in reanalyses and observations are amplified toward the poles. The pronounced increases in tropopause height in the climate change integrations considered here indicate that even AGCMs with coarse vertical resolution can resolve relatively small externally forced changes in tropopause height. The simulated decadal-scale changes in pLRT are primarily thermally driven and are an integrated measure of the anthropogenically forced warming of the troposphere and cooling of the stratosphere. Our algorithm for estimating pLRT (based on a thermal definition of tropopause height) is sufficiently sensitive to resolve these large-scale changes in atmospheric thermal structure. Our results indicate that the simulated increase in tropopause height over 1979-1997 is a robust, zero-order response of the climate system to forcing by well-mixed greenhouse gases and stratospheric ozone depletion. At the global-mean level, we find agreement between the simulated decadal-scale pLRT changes and those estimated from reanalyses. While the agreement between simulated pLRT changes and those in NCEP is partly fortuitous (due to excessive stratospheric cooling in NCEP), it is also driven by real pattern similarities. Our work illustrates that changes in tropopause height may be a useful "fingerprint" of human effects on climate and are deserving of further attention.

Santer, B. D.; Sausen, R.; Wigley, T. M. L.; Boyle, J. S.; Achutarao, K.; Doutriaux, C.; Hansen, J. E.; Meehl, G. A.; Roeckner, E.; Ruedy, R.; Schmidt, G.; Taylor, K. E.

2003-01-01

103

Regime Change in the Pacific Ocean and the Relative Intensities of Multi-Decadal and Quasi-Centennial Variability  

NASA Astrophysics Data System (ADS)

Fish scales deposited in varves in the Santa Barbara Basin off the coast of California suggest that both Pacific Sardine (Sardinops sagax) and Northern Anchovy (Engraulis mordax) populations vary with common characteristic periodicities of 58, 72-77, and 102-106 years [Baumgartner et al., 1992]. Variability of sardine populations on 30-70 year scales also has been observed since the mid 17th century off the coast of Japan [Yasuda, 1997]. These periodicities in population are thought to be climatically driven. While the 58 year and possibly the 72-77 year "multi-decadal" cycles are observable in modern instrument- derived records of the Pacific Decadal Oscillation (PDO) index, the 102-106 year "quasi-centennial" cycle is less apparent. Recently, Shen et al. [2006] presented a reconstruction of the PDO index since 1470 based on eastern China rainfall in which the quasi-centennial periodicity was more apparent before 1850. Using empirical mode decomposition (EMD, Huang et al., 1998) of the PDO reconstruction, we confirm this result. We then use EMD to analyze a white spruce (Picea glauca) tree ring record from Kobuk/Noatak, Alaska, which correlates with the April PDO index. The results show that multidecadal and quasi-centennial variability in this proxy record were similar in magnitude during the Little Ice Age but that multi-decadal variability dominated during both the Medieval Warm Period and since 1850. Based on this limited analysis, we suggest the possibility that multi-decadal variability in the Pacific Ocean could be enhanced by anthropogenic climate change. Changes in ocean circulation of this type are a major unknown in future climate forecasts. Additionally, we propose that these changes in the dominant periodicities of decadal to centennial variability over time may represent significant changes in Pacific Ocean circulation. Indeed, these regime changes may explain the multi-centennial variability in the covariance of particular Pacific fish populations found by various workers. It is unclear from the limited data available whether the apparent covariance of these shifts with centennial-scale anomalies in solar activity (such as the Medieval Maximum and the Maunder Minimum) are coincidental.

Heavens, N. G.; Yung, Y. L.

2006-12-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

105

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

National Technical Information Service (NTIS)

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

S. Hakkinen

1998-01-01

106

Decadal variability in Gulf of Mexico sea surface temperatures since 1734 CE  

NASA Astrophysics Data System (ADS)

The Gulf of Mexico is a major source of moisture to North America and is a source region for the Gulf Stream, which transports ocean heat northward. Sea surface temperature (SST) variations on centennial to millennial time scales have been documented for this region using paleoceanographic proxies; however, records capable of resolving decadal to subannual variability are lacking. Here we present 274 years of monthly-resolved SST variations derived from records of strontium-to-calcium ratios (Sr/Ca) extracted from four Siderastrea siderea cores recovered from coral colonies within the Dry Tortugas National Park (24°42?N, 82°48?W) in the Gulf of Mexico. We find no significant difference in mean Sr/Ca among these cores and significant correlation between cores (r ? 0.90, p ? 0.05 for monthly). The cross-dated chronology, determined by counting annual bands and correlating Sr/Ca variations, agrees with four 230Th dates within ±2? analytical precision. Calibration and verification of our multi-core coral Sr/Ca record with local temperature records reveals high agreement (Sr/Ca = -0.042 SST + 10.074, R2 = 0.96; ?regression = 0.70°C, 1?), similar to those reported for single cores from this location. We find winter SSTs tend to be more variable than summer SSTs (0.99 and 0.81°C, 1?; respectively) with periodic intervals of 10 to 15 years with cooler summer temperatures. The average reconstructed SST during the Little Ice Age (LIA; 1734-1880 CE) is colder (-0.82°C) than that during the late twentieth century (1971-2000 CE). The amplitude of decadal-scale variability (1 to 2.5°C) in the LIA is larger compared to similar scale variability in the twentieth century. The secular trend and decadal-scale variability in our reconstruction is broadly similar to an ~ decadally-resolved (~12 years/sample) Mg/Ca record from planktic foraminifer in the northern Gulf of Mexico (Richey et al., 2007), thus further confirming the reconstructed patterns of temperature variability in the Gulf of Mexico during the LIA.

DeLong, K. L.; Maupin, C. R.; Flannery, J. A.; Quinn, T. M.; lin, K.; Shen, C.

2012-12-01

107

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

108

Mountain hemlock growth responds to climatic variability at annual and decadal time scales  

USGS Publications Warehouse

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 hemlock in the Pacific Northwest. Factor analysis was used to identify common patterns of inter-annual growth variability among the chronologies, and correlation and regression analyses were used to identify climatic factors associated with that variability. Factor analysis identified three common growth patterns, representing groups of sites with different climate-growth relationships. At high-elevation and midrange sites in Washington and northern Oregon, growth was negatively correlated with spring snowpack depth, and positively correlated with growth-year summer temperature and the winter Pacific Decadal Oscillation index (PDO). In southern Oregon, growth was negatively correlated with spring snowpack depth and previous summer temperature, and positively correlated with previous summer precipitation. At the low-elevation sites, growth was mostly insensitive to annual climatic variability but displayed sensitivity to decadal variability in the PDO opposite to that found at high-elevation sites. Mountain hemlock growth appears to be limited by late snowmelt, short growing seasons, and cool summer temperatures throughout much of its range in the Pacific Northwest. Earlier snowmelt, higher summer temperatures, and lower summer precipitation in southern Oregon produce conditions under which growth is limited by summer temperature and/or soil water availability. Increasing atmospheric CO2 concentrations could produce warmer temperatures and reduced snowpack depths in the next century. Such changes would likely increase mountain hemlock growth and productivity throughout much of its range in Washington and northern Oregon. Increased summer drought stress and reduced productivity would be likely, however, in mountain hemlock forests of southern Oregon and near the species lower elevation limit at some sites.

Peterson, D. W.; Peterson, D. L.

2001-01-01

109

Simulated and observed variability in ocean temperature and heat content  

PubMed Central

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

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

2007-01-01

110

Regional Multi-decadal and Century-scale Internal SSH Variability in CMIP5 Models  

NASA Astrophysics Data System (ADS)

Recent model results of sea surface height projections have been used to estimate local and regional sea level change expected by 2100. The degree to which internal climate variability is superimposed on changes in a warming climate, and on what time scales, is an important aspect of these projections to consider. Internal climate variability, estimated from control-run trends on 20-yr and 100-yr time scales, is shown for an ensemble of CMIP5 models which are due to be published in the next climate assessment report. The internal control-run trend variability on a 20-yr time scale is of the same magnitude regionally as the projected 20-yr change of sea level, whereas for the 100-yr time scale, the internal trend variability is much smaller than for the projections. These estimates of internal variability can be treated as another source of uncertainty for regional and local sea surface height trends; however, for the 100-yr time scale, this is a much smaller uncertainty than the ensemble spread for the projected changes. This high signal-to-noise ratio for regional 100-yr projected trends is applicable to the ocean-only steric and dynamic changes to SSH, and does not include land ice, land water, or elastic earth components. The low signal-to-noise ratio for the 20-yr trends suggest that the models do not have particularly strong predictive capabilities for regional SSH on such short time scales. Applying these internal variability results to the real ocean is problematic in that the internal variability in real-world data is embedded in a warming climate context. Additionally, there is no conclusive evidence that the regional variability for SSH in the real ocean is similar to the models on long time scales, and while inconclusive, comparison to altimeter and reconstruction data shows that the patterns of multi-decadal internal variability are different.

Carson, M. L.; Koehl, A.; Stammer, D.

2013-12-01

111

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

112

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

NASA Astrophysics Data System (ADS)

Variability and predictability of European summer drought conditions during observational period is investigated. The dominat patterns of European drought and their associated large-scale climatic anomalies are identified through canonical correlation analysis (CCA) of the field of self calibrating Palmer Drought Severity Index (PDSI) and global sea surface temperature (SST) anomalies. At interannual time scales we identified patterns of drought variability which are optimally correlated with SST patterns from previous years. The time lag between drought and SST anomaly patterns can provide valuable skill for the prediction of drought conditions over Europe on interannual time scales. Significant lag-correlation between drought patterns and the North Atlantic Oscillation (NAO) suggests that NAO can be used also as a potential predictor of drought European patterns at interannual time scales. The global trend in temperature, the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) play a significant role in establishing the drought conditions over Europe at multidecadal time scales. The influences of these climatic patterns on drought conditions at multidecadal time scales were identified also through CCA. The first PDSI pattern (CCA1) shows a dipole-like structure between the central Europe and the northern part of the Scandinavian Peninsula. The corresponding SST pattern is a mixture between the global SST trend and the abrupt shift in the 1970s. Wet (dry) conditions over central Europe (Scandinavia) are associated with a strong positive SST center south of Greenland and a strong negative center over the European coast and the North Sea. The third mode (CCA3) identifies a multidecadal scale variation, strongly related to summer drought conditions over the southern part of the Scandinavian Peninsula, the south-eastern part of Europe and the western part of Russia. The corresponding SST pattern shows SST anomalies in the Atlantic basin similar to those associated with AMO. The AMO index and the canonical time series associated to CCA3 are significantly correlated. Possible drought conditions over Europe in the next decades based on the relationships between large-scale SST patterns and drought conditions over Europe, established in our study, are discussed.

Ionita, Monica; Lohmann, Gerrit; Rimbu, Norel; Chelcea, Silvia

2010-05-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

115

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

116

Observations of Suspected RR Lyrae Variable Stars  

NASA Astrophysics Data System (ADS)

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

Smith, Stephanie; Powell, W. L.; Wilhelm, R. J.; De Lee, N. M.

2014-01-01

117

Hydrographic variability of Denmark Strait Overflow Water near Cape Farewell with multi-decadal to weekly time scales  

NASA Astrophysics Data System (ADS)

Data in temperature and salinity from near-bottom layer of Denmark Strait Overflow Water in the Irminger Sea near 60°N are presented. These are hydrographic section data from data archives, literature, and CTD observations along the former WOCE AR7E line, as well as data from continuous measurements at two locations. For both salinity and temperature, hydrographic variability was present at all time scales that could be analysed, from multi-decadal to weekly. A mechanistic explanation for the primal cause of the hydrographic variability is still lacking. The direct cause of the observed variability has to be sought in variations of the properties of the source water types involved in the overflow across the sill in Denmark Strait, variations in the mutual ratios of these source water types, and in inhomogeneities in the DSOW layer. The strongest changes occurred at the longest time scales, as is often found for ultimately randomly forced geophysical time series. However, a significant annual cycle of the DSOW, not reported before, was observed at the foot of the East Greenland continental slope, likely a deterministic contribution to the hydrographic variability signal.

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

2012-08-01

118

The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions  

NASA Astrophysics Data System (ADS)

In this study, the effects of volcanic forcing on North Pacific climate variability, on interannual to decadal time scales, are examined using climate model simulations covering the last 600 years. The model used is the Bergen Climate Model, a fully coupled atmosphere-ocean general circulation model. It is found that natural external forcings, such as tropical strong volcanic eruptions (SVEs) and variations in total solar irradiance, play an important role in regulating North Pacific Decadal Variability (NPDV). In response to tropical SVEs the lower stratospheric pole-to-equator temperature gradient is enhanced. The North polar vortex is strengthened, which forces a significant positive Arctic Oscillation. At the same time, dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere. Through positive feedbacks in the troposphere, the surface westerly winds across the central North Pacific are significantly weakened, and positive sea level pressure anomalies are formed in the North Pacific. This anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the North Pacific. As a result of this, warm water converges in the subtropical western North Pacific, where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean. In the eastern and high-latitude North Pacific the ocean loses more heat, and large-scale decreases in sea surface temperatures are found. The overall response of this chain of events is that the North Pacific enters a negative phase of the Pacific decadal oscillation (PDO), and this negative phase of the PDO is maintained for several years. It is thus concluded that the volcanic forcing plays a key role in the phasing of the PDO. The model results furthermore highlight the important role of troposphere-stratosphere coupling, tropical-extratropical teleconnections and extratropical ocean-atmosphere interactions for describing NPDV.

Wang, Tao; Otterå, Odd Helge; Gao, Yongqi; Wang, Huijun

2012-12-01

119

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

Microsoft Academic Search

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

M. Latif; R. Kleeman; C. Eckert

1997-01-01

120

Interannual to decadal variability in circum-Antarctic sea level and transport  

NASA Astrophysics Data System (ADS)

It is known that intra-annual Antarctic sea level variability is highly coherent and represents a barotropic adjustment process associated with wind-driven fluctuations in circumpolar transport. It is also thought that circumpolar transport adjusts to changes in the oceans to the north on multi-century time scales. However, the Antarctic Circumpolar Current is not barotropic, and questions remain about the nature of the variability on intermediate timescales. Here we use multidecadal runs of two eddy-permitting ocean models, together with 50 years of Antarctic tide gauge data, to show three things. 1) The relationship between transport and averaged southern bottom pressure remains the same at period from days to multidecadal. 2) The sea level signal becomes larger than the bottom pressure signal at periods longer than about 4 years. 3) The variability becomes larger than can be explained by wind-driven fluctuations at periods longer than a decade or two. This suggests that longer period variability is dominated by changes in water mass properties, perhaps due to varying freshwater inputs, although the tide gauge measurements may also be influenced by vertical land movement due to changing ice load nearby.

Hughes, C. W.; Williams, J.

2013-12-01

121

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

122

Behavior of tropopause height and atmospheric temperature in models, reanalyses, and observations: Decadal changes  

Microsoft Academic Search

We examine changes in tropopause height, a variable that has hitherto been neglected in climate change detection and attribution studies. The pressure of the lapse rate tropopause, pLRT, is diagnosed from reanalyses and from integrations performed with coupled and uncoupled climate models. In the National Centers for Environmental Prediction (NCEP) reanalysis, global-mean pLRT decreases by 2.16 hPa\\/decade over 1979–2000, indicating

B. D. Santer; R. Sausen; T. M. L. Wigley; J. S. Boyle; K. AchutaRao; C. Doutriaux; J. E. Hansen; G. A. Meehl; E. Roeckner; R. Ruedy; G. Schmidt; K. E. Taylor

2003-01-01

123

Decadal variability and a recent amplification of the summer Beaufort Sea High  

NASA Astrophysics Data System (ADS)

The Beaufort Sea High (BSH), an anti-cyclone over the Beaufort Sea, is an important feature of the summer atmospheric circulation over the Arctic Ocean. For example, years characterized by low Arctic sea ice extent are typically associated with the presence of a stronger BSH; with the opposite occurring during years with high sea ice extent. In this paper, we show that there exists variability on the decadal time scale in the intensity and location of the summer BSH. We also show that there has been a trend towards a stronger summer BSH that began in the late 1990s. This trend is shown to be coincident with a tendency towards a reduction in cyclogenesis during the summer over the Beaufort Sea. We argue that that these trends are the result of a warming of the troposphere in the western Arctic and the concomitant reduction in baroclincity.

Moore, G. W. K.

2012-05-01

124

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

125

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

PubMed

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

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

2012-06-01

126

A decade of high-resolution radio observations of GRS1915+105  

Microsoft Academic Search

The radio emitting X-ray binary GRS1915+105 shows a wide variety of X-ray and radio states. We present a decade of monitoring observations, with the Rossi X-ray Timing Explorer-All Sky Monitor and the Ryle Telescope, in conjunction with high-resolution radio observations using Multi-Element Radio-Linked Interferometer Network and the The Very Long Baseline Array. Linear polarization at 1.4 and 1.6GHz has been

A. Rushton; R. E. Spencer; G. Pooley; S. Trushkin

2010-01-01

127

Satellite Observations to Benefit Science and Society: Recommended Missions for the Next Decade  

NASA Astrophysics Data System (ADS)

Satellite Observations to Benefit Science and Society: Recommended Missions for the Next Decade brings the next ten years into focus for the Earth and environmental science community with a prioritized agenda of space programs, missions, and supporting activities that will best serve scientists in the next decade. These missions will address a broad range of societal needs, such as more reliable weather forecasts, early earthquake warnings, and improved pollution management, benefiting both scientific discovery and the health and well-being of society. Based on the 2007 book, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, this book explores each of the seventeen recommended missions in detail, identifying launch dates, responsible agencies, estimated cost, scientific and public benefits, and more. Printed entirely in color, the book features rich photographs and illustrations, tables, and graphs that will keep the attention of scientists and non-scientists alike.

Committee On Earth Science; Applications From Space

128

Temporal Variability of Observed and Simulated Hyperspectral Earth Reflectance  

NASA Technical Reports Server (NTRS)

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a climate observation system designed to study Earth's climate variability with unprecedented absolute radiometric accuracy and SI traceability. Observation System Simulation Experiments (OSSEs) were developed using GCM output and MODTRAN to simulate CLARREO reflectance measurements during the 21st century as a design tool for the CLARREO hyperspectral shortwave imager. With OSSE simulations of hyperspectral reflectance, Feldman et al. [2011a,b] found that shortwave reflectance is able to detect changes in climate variables during the 21st century and improve time-to-detection compared to broadband measurements. The OSSE has been a powerful tool in the design of the CLARREO imager and for understanding the effect of climate change on the spectral variability of reflectance, but it is important to evaluate how well the OSSE simulates the Earth's present-day spectral variability. For this evaluation we have used hyperspectral reflectance measurements from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), a shortwave spectrometer that was operational between March 2002 and April 2012. To study the spectral variability of SCIAMACHY-measured and OSSE-simulated reflectance, we used principal component analysis (PCA), a spectral decomposition technique that identifies dominant modes of variability in a multivariate data set. Using quantitative comparisons of the OSSE and SCIAMACHY PCs, we have quantified how well the OSSE captures the spectral variability of Earth?s climate system at the beginning of the 21st century relative to SCIAMACHY measurements. These results showed that the OSSE and SCIAMACHY data sets share over 99% of their total variance in 2004. Using the PCs and the temporally distributed reflectance spectra projected onto the PCs (PC scores), we can study the temporal variability of the observed and simulated reflectance spectra. Multivariate time series analysis of the PC scores using techniques such as Singular Spectrum Analysis (SSA) and Multichannel SSA will provide information about the temporal variability of the dominant variables. Quantitative comparison techniques can evaluate how well the OSSE reproduces the temporal variability observed by SCIAMACHY spectral reflectance measurements during the first decade of the 21st century. PCA of OSSE-simulated reflectance can also be used to study how the dominant spectral variables change on centennial scales for forced and unforced climate change scenarios. To have confidence in OSSE predictions of the spectral variability of hyperspectral reflectance, it is first necessary for us to evaluate the degree to which the OSSE simulations are able to reproduce the Earth?s present-day spectral variability.

Roberts, Yolanda; Pilewskie, Peter; Kindel, Bruce; Feldman, Daniel; Collins, William D.

2012-01-01

129

Cassini UVIS observations of Jupiter's auroral variability  

Microsoft Academic Search

The Cassini spacecraft Ultraviolet Imaging Spectrograph (UVIS) obtained observations of Jupiter's auroral emissions in H2 band systems and H Lyman-? from day 275 of 2000 (October 1), to day 81 of 2001 (March 22). Much of the globally integrated auroral variability measured with UVIS can be explained simply in terms of the rotation of Jupiter's main auroral arcs with the

Wayne R. Pryor; A. Ian F. Stewart; Larry W. Esposito; William E. McClintock; Joshua E. Colwell; Alain J. Jouchoux; Andrew J. Steffl; Donald E. Shemansky; Joseph M. Ajello; Robert A. West; Candace J. Hansen; Bruce T. Tsurutani; William S. Kurth; George B. Hospodarsky; Donald A. Gurnett; Kenneth C. Hansen; J. Hunter Waite; Frank J. Crary; David T. Young; Norbert Krupp; John T. Clarke; Denis Grodent; Michele K. Dougherty

2005-01-01

130

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

131

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

NASA Astrophysics Data System (ADS)

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.

2014-03-01

132

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

133

Observations of faint eclipsing cataclysmic variables  

Microsoft Academic Search

We present time-resolved photometry of six faint (V>17mag) cataclysmic variables (CVs); one of them is V849 Oph and the others are identified from the Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139, SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations of these objects were performed at the TÜB?TAK National Observatory (Turkey) between February 2006 and March 2009.

Dicle Zengin Çamurdan; C. Muzaffer Çamurdan

2010-01-01

134

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

135

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

NASA Astrophysics Data System (ADS)

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

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

2003-10-01

136

Geostationary atmospheric composition observations from the NASA Decadal Survey GEO-CAPE mission  

NASA Astrophysics Data System (ADS)

This paper discusses the science definition work that is being performed in preparation for the NASA Decadal Survey GEO-CAPE mission. To serve the atmospheric composition community, GEO-CAPE will make a suite of trace gas and aerosol measurements from geostationary orbit concentrating on North America with high spatiotemporal resolution. This will provide unique insights into pollutant sources, transport, chemical transformations and climate impact. In addition to significantly improved understanding of the underlying processes determining atmospheric composition, GEO-CAPE observations will also find direct societal application for air quality management and forecasting. The paper will also discuss the potential phased implementation of this mission as a series of hosted payloads, and GEO-CAPE as the U.S. contribution to a constellation of geostationary platforms to achieve continuous coverage at northern mid-latitudes by the turn of the decade.

Edwards, D. P.; Jacob, D. J.; Al-Saadi, J. A.; Iraci, L. T.

2012-12-01

137

Interannual to Decadal Variability of Atlantic Water in the Nordic and Adjacent Seas  

NASA Technical Reports Server (NTRS)

Warm salty Atlantic Water is the main source water for the Arctic Ocean and thus plays an important role in the mass and heat budget of the Arctic. This study explores interannual to decadal variability of Atlantic Water properties in the Nordic Seas area where Atlantic Water enters the Arctic, based on a reexamination of the historical hydrographic record for the years 1950-2009, obtained by combining multiple data sets. The analysis shows a succession of four multi-year warm events where temperature anomalies at 100m depth exceed 0.4oC, and three cold events. Three of the four warm events lasted 3-4 years, while the fourth began in 1999 and persists at least through 2009. This most recent warm event is anomalous in other ways as well, being the strongest, having the broadest geographic extent, being surface-intensified, and occurring under exceptional meteorological conditions. Three of the four warm events were accompanied by elevated salinities consistent with enhanced ocean transport into the Nordic Seas, with the exception of the event spanning July 1989-July 1993. Of the three cold events, two lasted for four years, while the third lasted for nearly 14 years. Two of the three cold events are associated with reduced salinities, but the cold event of the 1960s had elevated salinities. The relationship of these events to meteorological conditions is examined. The results show that local surface heat flux variations act in some cases to reinforce the anomalies, but are too weak to be the sole cause.

Carton, James A.; Chepurin, Gennady A.; Reagan, James; Haekkinen, Sirpa

2011-01-01

138

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

139

Decadal to Centennial Variability of Erosion Rates in a Rapidly Degrading Channel Network  

NASA Astrophysics Data System (ADS)

Quantifying short-term spatial variation of rates of vertical land surface change is a challenge in net degradational systems, but this information has the potential to add significantly to our understanding of transport-limited erosional processes acting over long timescales. We have undertaken a dendrogeomorphic approach to assessing denudation rates in a young channel network on the Florida panhandle where unlithified sands and muds are being incised by water supplied from groundwater seepage. The measured exposure of roots for over 500 trees, combined with tree ages, supply surface change rates along a 2 km reach of channel. This number of samples represents all trees greater than 2" diameter from ~1/3 of the valley bottom area within the study section. Tree rings were counted for cores from 33 trees ranging up to ~200 years in age. From these trees an age- diameter relation was determined to estimate ages for the remaining ~500 trees with ~12% standard error. Mean and maximal lengths of root exposure covaried with tree age resulting in characteristic erosion rates valid over decadal to centennial timescales. Three types of surface change rates were measured: vertical motions of the channel bottoms, vertical motions of the valley bottoms, and lateral motions of the channel sidewalls. Their means are 2.8, 1.7, and 7.3 mm/yr, respectively, and support field observations that suggest the valley bottom is denuding by a process independent of the channel lowering. The vertical erosion rates also covary with tree ages in such a way that mean rates decrease by half an order of magnitude for an order of magnitude increase of the averaging timescale. This result is direct evidence for the unsteadiness of sediment transport within the network. Based upon Central-Limit theory, it also suggests that the decorrelation timescale of the sediment transport process is within the range of decades to centuries. The timing of inception for this network is not well constrained. A rough estimate can be made using the total channel length and the erosion rates measured here by assuming that the steephead propagation rate is related to the valley lowering rate through the streamwise valley slope. For a mean valley lowering rate of 2 mm/yr and a slope of 25 m/km, the whole network could have been created in approximately ~100,000 years. This age can be refined with the development of a local erosion rate-erosion duration relationship.

McElroy, B.; Willenbring, J.; Mohrig, D.

2007-12-01

140

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

NASA Astrophysics Data System (ADS)

During the late 1980s and early 1990s, deep water was produced in the Aegean Sea rather than in the Adriatic Sea. The largest production occurred during the winters of 1991/1992 and 1992/1993. This phenomenon, the Eastern Mediterranean Transient (EMT), was due to the confluence of multiple hydrological preconditioning factors and strong atmospheric forcing. This is the only instance of Aegean deep convection which has been observed; however it is thought that similar events have occurred in the past, but with unknown frequency. In a recent paper, we showed that a deviation from the usual pattern of cyclones in the central and eastern Mediterranean basins induced atypical heat advection over the Aegean, producing large turbulent heat losses during the winters of 1991/1992 and 1992/1993 (Romanski et al. 2012)]. Here we extend our analysis to the 1958-2001 period, and connect the presence of cyclones in the central and eastern Mediterranean to characteristic patterns of turbulent heat flux in the eastern Mediterranean and Aegean . We show that the relative frequency of storms in each basin determines the heat loss from the Aegean during that winter. We analyze the wintertime cyclone variability during 1958-2001, discuss the likelihood of atmospheric conditions conducive to deep convection in the Aegean, and link cyclone variability, and Aegean flux variability, to changes in large scale circulation as represented by the North Atlantic Oscillation (NAO) and North Caspian Pattern (NCP) teleconnections. We are thus able to identify other possible occurrences of EMT in the 1958-2001 cyclone record.

Romanski, J.; Romanou, A.; Bauer, M. P.; Tselioudis, G.

2012-12-01

141

Twenty-Four Hour Time Domain Heart Rate Variability and Heart Rate: Relations to Age and Gender Over Nine Decades  

Microsoft Academic Search

Objectives. This study sought to define the effects of age and gender effects on the normal range of time domain heart rate variability (HRV) over nine decades in healthy subjects.Background. Low HRV is considered an independent marker of mortality risk. However, the age-related decline in HRV may limit its predictive value, particularly in the elderly. Delineation of the range of

Ken Umetani; Donald H Singer; Rollin McCraty; Mike Atkinson

1998-01-01

142

Application of EOF\\/CEOF methodology to understand correlation between geomagnetic secular variation and decadal time-variable gravity  

Microsoft Academic Search

In this presentation we discuss the application of EOF and Complex EOF approaches to examine possible correlation between temporal-spatial distributions of the time variable gravity (TVG) and magnetic secular variations (SV) on decadal time scales and longer. The advantage of such approaches is to enable us identifying approximately 3 to 4 EOF\\/CEOF modes that account for the most of the

Z. Wei; W. Kuang; W. Jiang

2006-01-01

143

Spatial variability in subsurface warming over the last three decades; insight from repeated borehole temperature measurements in The Netherlands  

NASA Astrophysics Data System (ADS)

Subsurface temperatures around the world are changing in response to accelerated surface atmospheric temperature (SAT) rise, but are also impacted by other natural and anthropogenic changes in surface environmental conditions which alter the surface energy balance. Improved understanding of the latter influences is important for geothermal climate applications and to generate a comprehensive knowledge-framework of subsurface warming, including inherent spatial variability. Here I examine sixteen wells in a relatively small area in The Netherlands, each with two available temperature logs recorded some three decades apart. Temperature differences of the log pairs reveal marked differences in subsurface warming amongst the wells for this time period. Forward modelling of the observed temperature changes, using surface air temperature (SAT) forcing, shows that a considerable part of this inter-site variability may be caused by inter-site differences in thermal properties and groundwater flow conditions. However, for some of the wells these factors are insufficient, implying contributions from non-SAT-driven changes in ground surface temperature (GST). In one case an anomalous decrease in GST can be linked to back-growth of the canopy after forest cutting. For another well site, GST warming has been less than SAT warming in the absence of apparent changes in surface conditions, indicating local, subtle influences on the surface energy balance independent of SAT. The results demonstrate that repeated borehole temperature logging resolves key uncertainties and ambiguities pertaining to interpretation of individual temperature logs. The study further highlights the importance of establishing high-quality borehole temperature databases, also for these relatively complex settings with dynamic and variable surface conditions.

Kooi, Henk

2008-06-01

144

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

145

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

146

Surface salinity variability in the northern North Atlantic during recent decades  

Microsoft Academic Search

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 the Comprehensive Atmosphere Ocean Data Set (COADS) and National Center for Environmental Prediction\\/National Center for Atmospheric Research (NCEP\\/NCAR) reanalysis. The focus here is the SSS variability in the subpolar region. The seasonality of

Sirpa Häkkinen

2002-01-01

147

On the Contextual Independence of Personality: Teachers' Assessments Predict Directly Observed Behavior after Four Decades  

PubMed Central

The continuity of personality’s association with directly observed behavior is demonstrated across two contexts spanning four decades. During the 1960s, elementary school teachers rated personalities of members of the ethnically diverse Hawaii Personality and Health Cohort (Hampson & Goldberg, 2006). The same individuals were interviewed in a medical clinic over 40 years later. Trained coders viewed video recordings of a subset of these interviews (N = 144, 68 F, 76 M) and assessed the behavior they observed using the Riverside Behavioral Q-sort Version 3.0 (Funder, Furr & Colvin, 2000; Furr, Wagerman & Funder, 2010). Children rated by their teachers as “verbally fluent” (defined as unrestrained talkativeness) showed dominant and socially adept behavior as middle-aged adults. Early “adaptability” was associated with cheerful and intellectually curious behavior, early “impulsivity” was associated with later talkativeness and loud speech, and early rated tendencies to “self-minimize” were related to adult expressions of insecurity and humility.

Nave, Christopher S.; Sherman, Ryne A.; Funder, David C.; Hampson, Sarah E.; Goldberg, Lewis R.

2010-01-01

148

Geomagnetic storms during the last decade: Cluster and Double Star observations (Invited)  

NASA Astrophysics Data System (ADS)

The launch of the Cluster spacecraft almost coincided with one of the largest geomagnetic storm of the last decade, well known as the "Bastille Day" storm, on 14-15 July 2000. Planned on 15 July, the launch was aborted a few minutes before due to a thunderstorm that had hit the Baikonour cosmodrome and made a disruption in the communication lines with the rocket. The launch took place the day after, on 16 July 2000. Our US colleagues had warned us about the storm and recommended not to launch on 15 July. Given the facts that (1) Cluster was built to study the effects of space weather and geomagnetic storms and (2) that the Russian launch authorities were not concerned for the Soyuz rocket, it was decided to go ahead with the launch. The launch was fine and, after a second launch less than a month later, the four Cluster spacecraft were put successfully in their 4x19 RE polar orbit. Since then, Cluster has observed many geomagnetic storms and could observe, for the first time with a constellation of four spacecraft, the dynamics induced in the magnetosphere by coronal mass ejections or interplanetary shocks coming from the Sun. In this talk we will use storms observed by Cluster and Double Star in the last decade to illustrate how the magnetosphere was affected. We have observed large compressions of the magnetosphere, distortions of the polar cusp, acceleration of particles associated with chorus and ULF waves, intensification of the ring current imaged by energetic neutral atom imagers, oxygen outflow from polar regions, and tail current sheet motions.

Escoubet, C.; Taylor, M. G.; Masson, A.; Laakso, H. E.; Liu, Z.; Goldstein, M. L.

2013-12-01

149

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

150

Observed changes in water temperature and ice dynamics at selected lakes of Russia in the past decades  

NASA Astrophysics Data System (ADS)

The potential impacts of climate variability and change on lake hydrology are complex, especially as lakes are an important freshwater resource. The eight largest lakes of Russia contain about 96% of water resources of all lakes over Russia territory. Lakes Ladoga, Onega, Chudsko-Pskovskoe and Ilmen are the largest fresh water lakes of European territory of Russia. The catchment area of Lake Ladoga includes catchments of two other Lakes - Onega and Ilmen. The world's deepest and oldest Lake Baikal is among the four larget lakes of the Asian part of Russia including Lakes Lakes Khanka, Taimyr and closed brackishwater Lake Chany.Variations in air temperature, precipitation, and other meteorological parameters cause direct changes in the hydrological regime of lakes, such as: water level, thermal characteristics, ice events and ice thickness as well as hydrochemical and hydrobiological regimes and the entire lakes ecosystem. However, the response of the individual lakes and lake basins to these changes will depend on the magnitude and nature of regional climate change including peculiarities of the atmospheric circulation manifestation and the specific geomorphologic characteristics of the lakes. The study was based on the data of ice observations on the largest lakes of European Russia (Lakes Ladoga, Onega and Ilmen) and Lakes Baikal, Taimyr and Khanka in the Asian Russia. Observation period varies from 40 years for the Lake Taimyr to 118-116 years for Lakes Ladoga and Onega. Temporal trends have been discovered towards changes in the duration of the complete ice cover and maximum ice thickness on the background of a long-term variability. All observed characteristics of water temperature regime demonstrate the response to changes in air temperature over lakes basins. Mean monthly water temperature increased in Lakes Chany and Baikal by 0.5°C/decade and by 0.3°C/decade in the mentioned lakes of European part of Russia. Water temperature change directly affects lake ice dynamics. This has important implications for aquatic ecosystems' sustainable development and activities on lakes. Maximal ice cover thickness had the most pronounced response to climate warming in winter time during the last decades. All studied lakes exhibited the tendency of reduced ice cover thickness after 1980 by 5-10 cm. The mentioned lakes in the European Russian territory and Lake Baikal show the tendencies to decrease in duration of ice coverage by 10-15 days mainly because of earlier date of ice cover break-up.

Lemeshko, Natalia; Eitzinger, Josef; Kubu, Gerhard

2013-04-01

151

Formation and Variability of the South Pacific Sea Surface Salinity Maximum in Recent Decades  

NASA Astrophysics Data System (ADS)

This study investigates causes for the formation and the variability of the Sea Surface Salinity maximum (SSS>36) centred at 18.4°S-123.8°W in the South Pacific Ocean over the 1990-2011 period at the seasonal timescale and above. We use two monthly gridded products of SSS based on in-situ measurements, high-resolution along-track Voluntary Observing Ships thermosalinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a zonal seasonal cycle of the location of the high (above 36 pss) SSS core barycentre of about 400 km in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show a lower frequency westward shift of the barycentre of 1400 km that could not be linked to the El Nino Southern Oscillation phenomena. In the model, the processes maintaining the 22-year equilibrium of the high salinity in the mixed layer are the surface forcing (~+7 pss/yr), the horizontal salinity advection (~-3.5 pss/yr) and processes occurring at the mixed layer base (~-3.5 pss/yr).

Hasson, A. E.; Delcroix, T. C.; Boutin, J.

2013-12-01

152

Kuroshio Extension Variability and Forcing of the Pacific Decadal Oscillations: Responses and Potential Feedback  

Microsoft Academic Search

A forcing mechanism is sought for the large-scale circulation changes in the Kuroshio Extension region of the western North Pacific Ocean as inferred by TOPEX\\/Poseidon sea surface height (SSH) data. The low- frequency signal of the Kuroshio Extension over the last decade was characterized by a modulation in its zonal mean flow intensity: the mean Kuroshio Extension jet weakened progressively

Bo Qiu

2003-01-01

153

North Pacific carbon cycle response to climate variability on seasonal to decadal timescales  

Microsoft Academic Search

Climate variability drives significant changes in the physical state of the North Pacific, and there may be important impacts of this variability on the upper ocean carbon balance across the basin. We address this issue by considering the response of seven biogeochemical ocean models to climate variability in the North Pacific. The models' upper ocean pCO2 and air-sea CO2 flux

G. A. McKinley; T. Takahashi; E. Buitenhuis; F. Chai; J. R. Christian; S. C. Doney; M.-S. Jiang; K. Lindsay; J. K. Moore; C. Le Quéré; I. Lima; R. Murtugudde; L. Shi; P. Wetzel

2006-01-01

154

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

155

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

156

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation  

Microsoft Academic Search

An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during\\u000a 1963–2003. The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where\\u000a a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1,500 m reproduce well\\u000a those derived from the

Claude Frankignoul; Julie Deshayes; Ruth Curry

2009-01-01

157

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

SciTech Connect

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

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

1994-08-01

158

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

159

A decade of high-resolution radio observations of GRS1915+105  

NASA Astrophysics Data System (ADS)

The radio emitting X-ray binary GRS1915+105 shows a wide variety of X-ray and radio states. We present a decade of monitoring observations, with the Rossi X-ray Timing Explorer-All Sky Monitor and the Ryle Telescope, in conjunction with high-resolution radio observations using Multi-Element Radio-Linked Interferometer Network and the The Very Long Baseline Array. Linear polarization at 1.4 and 1.6GHz has been spatially resolved in the radio jets, on a scale of ~150 mas and at flux densities of a few mJy. Depolarization of the core occurs during radio flaring, associated with the ejection of relativistic knots of emission. We have identified the ejection at four epochs of X-ray flaring. Assuming no deceleration, proper motions of 16.5 to 27 mas per day have been observed, supporting the hypothesis of a varying angle to the line of sight per ejection, perhaps in a precessing jet.

Rushton, A.; Spencer, R. E.; Pooley, G.; Trushkin, S.

2010-02-01

160

Validating Historical and Future GCM Simulations of Climate Moisture Variability with Observed and Dendroclimatic Records  

Microsoft Academic Search

Validating the decadal, multi-decadal or lower frequency climate variability of GCM output is limited by the scarcity of long observational records. Tree-ring proxy data analyses carried out in western North America has proven valuable to quantify natural climate variation over centuries to millennia; therefore, providing a unique opportunity to validate GCMs. Many of the drought events during the 20th century

S. Lapp; J. Barichivich; D. Sauchyn

2007-01-01

161

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

162

Observed variations of cloud fraction and types over Russia in last decades  

NASA Astrophysics Data System (ADS)

Cloudiness changes may mitigate or exacerbate global and local warming. Here, we assess changes of total and low cloud fraction and the occurrence of days with different cloud conditions and different cloud types including convective clouds over Russia from 1965 to 2011 years. Our analysis is based on visual daytime routine observations from almost 500 Russian meteorological stations for the period 1965-2011 and than 1800 stations for the period 1984-2011. In general, cloud fraction tends to increase during the last years. A major increase of total cloud fraction and a decrease of the number of clear days are revealed in spring and autumn mostly due to an increase of the occurrence of convective and non-precipitating stratiform clouds. In contrast, the occurrence of Nimbostratus clouds tends to decrease, which lead to a general decrease of the occurrence of overcast days. In most regions, the ratio between the occurrence of Cumulonimbus and Nimbostratus clouds has increased in last decade compare to previous ones. It worth noting, that for particular stations this redistribution may be associated with observers changes. Over some regions (Ural and the Far East), a decrease of total cloud fraction and an increase of the number of clear days are noted. In addition, we assess possible causes of cloudiness variations. In particular, sensitivity of cloudiness changes to temperature changes were evaluated. The relationship of cloud variations with cyclonic/anticyclonic activity including atmospheric centers of action (Azores and Siberian highs, Aleutian and Icelandic lows) were assessed as well. An overall increase of convective clouds occurrence is an additional and independent evidence for the intensification of convective processes in the last decades over land in the northern midlatitudes. Alongside with an increase of heavy precipitation events, an increase of occurrence of Cumulonimbus clouds leads to lightning occurrence increase and, in turn, leads to an increase of the risk of forest fire initiation. Together with the projected increase of fire danger indices in southern regions of the European Part and Siberia, it can lead to more fire hazardous regional climate. The work has been supported by the grant of the RF President MK-3259.2012.5 and by the Russian Foundation of Basic Research under grant 12-05-00972.

Chernokulsky, Alexander; Akperov, Mirseid; Bulygina, Olga; Mokhov, Igor; Nikitina, Natalia

2013-04-01

163

Decadal change of South China Sea tropical cyclone activity in mid-1990s and its possible linkage with intraseasonal variability  

NASA Astrophysics Data System (ADS)

study focuses on the decadal variability of tropical cyclone (TC) activity over the South China Sea (SCS) since the 1970s and its possible cause behind. It is found that TC activity over the SCS experiences a significant decadal change around the mid-1990s. Compared to the period from the 1970s to the early 1990s, the number of TCs formed in the SCS remarkably increases from the mid-1990s through the 2000s. In particular, this change of TC genesis is closely related to a decadal shift in atmospheric intraseasonal variability (ISV) that occurred in 1994. The ISV on the 30-60 days time scale over the SCS has been increasing since the mid-1990s, and the increased TC frequency after 1994 is attributed primarily to the active convection induced by the enhancement of the SCS ISV. In addition, the TC activities before the mid-1990s are mostly confined within the SCS basin. However, more TCs form over the SCS and move northeastward since the mid-1990s and finally enter the East China Sea and the Philippine Sea. Anomalies of westerly over the northern SCS after 1994 are responsible for the northeastward moving of TCs.

Ha, Yao; Zhong, Zhong; Sun, Yuan; Lu, Wei

2014-05-01

164

Tree-Ring Based Reconstructions of Interannual to Decadal Scale Precipitation Variability for Northeastern Utah Since 1226 A.D.  

NASA Astrophysics Data System (ADS)

Samples from 107 piñon pines (Pinus edulis) at four sites were used to develop a proxy record of annual (June to June) precipitation spanning the 1226 to 2001 AD interval for the Uinta Basin Watershed of northeastern Utah. The reconstruction reveals significant precipitation variability at interannual to decadal scales. Single-year dry events before the instrumental period tended to be more severe than those after 1900. In general, decadal scale dry events were longer and more severe prior to 1900. In particular, dry events in the late 13th, 16th, and 18th Centuries surpass the magnitude and duration of droughts seen in the Uinta Basin after 1900. The last four decades of the 20th Century also represent one of the wettest periods in the reconstruction. The proxy record indicates that the instrumental record (approximately 1900 to the Present) underestimates the potential frequency and severity of severe, sustained droughts in this area, while over representing the prominence of wet episodes. In the longer record, the empirical probability of any decadal scale drought exceeding the duration of the 1954 through 1964 drought is 94 percent, while the probability for any wet event exceeding the duration of the 1965 through 1999 wet spell is only 1 percent. Hence, estimates of future water availability in the Uinta Basin and forecasts for exports to the Colorado River, based on the 1961 to 1990 and 1971 to 2000 "normal" periods, may be overly optimistic.

Gray, Stephen T.; Jackson, Stephen T.; Betancourt, Julio L.

2004-08-01

165

Is decadal-scale variability of middle atmosphere water vapor linked to changes in mesospheric cloud brightness?  

NASA Astrophysics Data System (ADS)

Long-term changes in middle atmosphere water vapor (H2O) have occurred in the upper mesosphere, and should have affected mesospheric ice-cloud (MC) activity (manifested in Noctilucent Clouds/ Polar Mesospheric Clouds and Polar Mesosphere Summertime Echoes). Objections have been raised recently (von Zahn, 2003) against the notion that MC are indicators of mesospheric climate change. It is claimed that the factors of natural variability are too large, and the satellite records are too short, to be able to separately identify the relatively weak `signal' of long-term mesospheric climate change. In this paper we provide a rebuttal to these objections, and address both these issues. We employ satellite observations of MC in both hemispheres, which cover the last 25 years. These SBUV/SBUV-2 data sets provide the clearest evidence to date of long-term increases in UV albedo, as well as solar modulation. For the forcing mechanism(s) we propose that H2O changes at the mesopause are mainly responsible, and are caused by two forcing agents: (1) 11-year solar cycle variations in H2O abundance, and (2) decadal-scale secular increases in H2O. We employ the CARMA microphysical model of MC evolution to study the expected changes in PMC brightness, as a result of these two factors. This study emphasizes the continued importance of MC studies, particularly those that can quantitatively identify the relative importance of the various forcing mechanisms. Reference: von Zahn, U., Are noctilucent clouds truly a "miner's canary" for global change?, EOS Trans. AGU,84, 261,264,2003.

Thomas, G.; Rapp, M.; Olivero, J.; Shettle, E.; Deland, M.

166

Freshwater fluxes in the East Greenland Current: A decade of observations  

NASA Astrophysics Data System (ADS)

Over a decade of mooring measurements in the western Fram Strait at 78°50?N shows that the annual mean liquid freshwater flux (FWF) in the East Greenland Current is relatively constant at -1274 ± 453 km3 yr-1 (-40.4 ± 14.4 mSv) despite the fact that the annual mean total volume transport of the EGC has more than doubled since 2001. This is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest FW content is present on the East Greenland shelf and not in the core of the EGC. In order to capture the FWF on the shelf modeling results of NAOSIM are included showing that a mean contribution of FWF on the shelf of at least -807 ± 357 km3 yr-1 (-25.6 ± 11.3 mSv) should be added to the FWF obtained for the EGC. When compared to the extra input of freshwater required to account for the 1960-1990 freshening of the northern North Atlantic, the observed variations in the 1998-2008 EGC liquid freshwater fluxes are small.

de Steur, L.; Hansen, E.; Gerdes, R.; Karcher, M.; Fahrbach, E.; Holfort, J.

2009-12-01

167

Interannual and Decadal Modulations Recently Observed in the Pacific Storm Track Activity and East Asian Winter Monsoon.  

NASA Astrophysics Data System (ADS)

Interannual variability of the North Pacific storm track observed over 17 recent winters is documented. The local storm track activity is measured by a meridional flux of sensible heat associated with the lower-tropospheric subweekly fluctuations. The interannual variability in the heat flux over the northwestern (NW) Pacific is found to be strongest in midwinter. The first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the NW Pacific, in association with the decadal weakening of the east Asian winter monsoon (Siberian high) and the Aleutian low that occurred in the late 1980s. The most marked signature of this enhancement is that the midwinter minimum in the storm track activity, which had been apparent in the early to mid-1980s, almost disappeared afterward. As opposed to linear theory of baroclinic instability, the enhanced activity occurred despite the weakening of the Pacific jet. As the excessively strong westerlies weakened, the eddy temperature field tended to become better correlated with the eddy meridional and vertical velocities, suggesting that eddy structure tends to become more efficient in converting the mean-flow available potential energy into eddy kinetic energy for growth. The weakened jet also acted to prolong the residence time for migratory eddies in the baroclinic zone, which seemingly overcompensated the effect of the reduced mean-flow baroclinicity but appeared to be of secondary importance. Over the Far East, tropospheric warming to the north of the weakened jet appears to be associated with an anomalous overturning in the thermally direct sense, which is not attributable to the feedback from the concomitant enhancement in the local storm track activity.Over the NW Pacific, the enhanced poleward heat transport by the intensified storm track tended to be compensated by the reduced transport by the weakened monsoonal flow, leaving rather small anomalies in the net transport. Also over the NW Pacific, the weakened monsoonal flow and enhanced storm track activity since the late 1980s led to the reduction in the evaporation and associated latent heat release from the ocean surface and increased precipitation, respectively. The resultant anomalous moisture deficit was compensated by the anomalous moisture transport from the northeastern Pacific, where the enhanced evaporation and reduced precipitation gave rise to an anomalous moisture surplus.

Nakamura, Hisashi; Izumi, Takuya; Sampe, Takeaki

2002-07-01

168

Structure of Interannual-to-Decadal Climate Variability in the Tropical Atlantic Sector  

Microsoft Academic Search

A search for coupled modes of atmosphere-ocean interaction in the tropical Atlantic sector is presented. Previous studies have provided conflicting indications of the existence of coupled modes in this region. The subject is revisited through a rotated principal component analysis performed on datasets spanning the 36-yr period 1958-93. The analysis includes four variables, sea surface temperature, oceanic heat content, wind

Alfredo Ruiz-Barradas; James A. Carton; Sumant Nigam

2000-01-01

169

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

170

A decadal observation of vegetation dynamics using multi-resolution satellite images  

NASA Astrophysics Data System (ADS)

Vegetation cover not just affects the habitability of the earth, but also provides potential terrestrial mechanism for mitigation of greenhouse gases. This study aims at quantifying such green resources by incorporating multi-resolution satellite images from different platforms, including Formosat-2(RSI), SPOT(HRV/HRG), and Terra(MODIS), to investigate vegetation fractional cover (VFC) and its inter-/intra-annual variation in Taiwan. Given different sensor capabilities in terms of their spatial coverage and resolution, infusion of NDVIs at different scales was used to determine fraction of vegetation cover based on NDVI. Field campaign has been constantly conducted on a monthly basis for 6 years to calibrate the critical NDVI threshold for the presence of vegetation cover, with test sites covering IPCC-defined land cover types of Taiwan. Based on the proposed method, we analyzed spatio- temporal changes of VFC for the entire Taiwan Island. A bimodal sequence of VFC was observed for intra-annual variation based on MODIS data, with level around 5% and two peaks in spring and autumn marking the principal dual-cropping agriculture pattern in southwestern Taiwan. Compared to anthropogenic-prone variation, the inter-annual VFC (Aug.-Oct.) derived from HRV/HRG/RSI reveals that the moderate variations (3%) and the oscillations were strongly linked with regional climate pattern and major disturbances resulting from extreme weather events. Two distinct cycles (2002-2005 and 2005-2009) were identified in the decadal observations, with VFC peaks at 87.60% and 88.12% in 2003 and 2006, respectively. This time-series mapping of VFC can be used to examine vegetation dynamics and its response associated with short-term and long-term anthropogenic/natural events.

Chiang, Yang-Sheng; Chen, Kun-Shan; Chu, Chang-Jen

2012-10-01

171

Tropical Climate Variability and the Atlantic Multi-decadal Oscillation from the Geochemistry of Corals and Sclerosponges over the last 500 years  

NASA Astrophysics Data System (ADS)

Observational and model data have shown considerable variability to exist in North Atlantic sea surface temperatures and climate. In particular, several climate oscillations have been documented, including the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO). While the exact forcing of these modes has yet to be defined, they do appear to produce observable climatic variability on multi- decadal time scales. Recent geochemical analyses on climate proxy archives from the western tropical Atlantic have shown variability consistent with that of the AMO. A 300+ year old coral specimen of Montastraea faveolata growing in 6m of water south of Port Everglades, Florida, and a 550+ year old sclerosponge specimen of Ceratoporella nicholsoni collected from 133m of water off of Lee Stocking Island in the Exuma Sound, Bahamas, have been milled at a sub- annual resolution and analyzed for stable C and O isotopes as well as minor element ratios. Salinity calculated from a combination of ?18O and Sr/Ca exhibits similar periodicities to the AMO between ~1700 AD and the present; a rather surprising finding given the significant differences in the local environmental conditions of the two samples. Prior to the 1700s, our sclerosponge record diverges from the AMO record reconstructed from tree rings. Additional analyses from the region will be needed to determine the reasoning for this discrepancy.

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

2008-12-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

173

Characteristics of recent megathrust earthquakes in the decade-long global gravity observations from GRACE  

NASA Astrophysics Data System (ADS)

We report GRACE satellite observations of "ongoing" gravitational potential changes after recent megathrust earthquakes of the 2004 Mw 9.2 Sumatra-Andaman Islands, 2010 Mw 8.8 Maule (Chile), and 2011 Mw 9.0 Tohoku-Oki (Japan) ruptures. The 10-year time-series (since April 2002) of global gravitational potential data are characterized consistently with not only coseismic (episodic) offsets but also postseismic (gradual) relaxation, when localized at the respective area of each earthquake. The recently available Release-05 (RL05) global gravity data (Level-2 data) show ongoing postseismic changes prevailing over other signals and noise, nearly 8 years after the 2004 rupture, and 1 and 2 years after the 2011 and 2010 ruptures, respectively. The abrupt changes in the time-series are consistent with the predicted gravity changes from various seismic solutions, when the centroids locate within the crustal layers (24 km deep or less) with a specific range of compressibility, ruling out the deeper centroid sources. The transient or steady-state changes after all three earthquakes, evident in a decade-long time-series, may imply viscoelastic mantle flow triggered by megathrust ruptures and, ultimately, constrain the asthenosphere rheology and viscosity. For all three megathrust ruptures, the GRACE gravity observations consistently show large-scale interior deformation associated with density change (dilatation). The GRACE observations represent averages over a time window much longer than accessible from seismic data and over a spatial scale much broader than covered by conventional 'geodetic' data. Therefore, GRACE will convey the behavior of the earthquakes on temporal and spatial scales transgressing the seismic and geodetic spectrum. The future GRACE follow-on mission equipped with enhanced instrumentation should allow us to exploit gravitational potential data in the analysis of smaller, and thus more frequent seismic events. Monthly time-series of the GRACE Level-2 (L2) data after applying spatial localization over the earthquake region (solid blue line). The seasonal and inter-seasonal fit was shown in solid red/magenta lines. The data residual (black with error bar) was computed by differencing the data and the fit. The data residuals were subsequently analyzed using the heaviside step and logarithmic functions for delineation of coseismic and postseismic changes, respectively (solid green line). The time-series of exemplary GRACE L2 coefficients at degree 30 containing statistically-significant steps are presented. The RL05 product was used for the data from 2004 to 2012, while RL04 was used in years of 2002 and 2003. Substantial improvement was found in the RL05 products.

Han, S.; Riva, R. E.; Sauber, J. M.; Okal, E.

2012-12-01

174

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

175

Estimates of Surface and Subsurface Forcing for Decadal Sea Surface Temperature Variability in the Mid-Latitude North Pacific  

NASA Astrophysics Data System (ADS)

The upper ocean, atmosphere and their interaction over the North Pacific exhibit pronounced decadal to interdecadal variations. A diagnostic equation for analyzing the heat budget for decadal variability in winter sea surface temperature (SST) is derived that can properly account for subsurface geostrophic advection, and strong seasonal cycle in the depth and temperature of the ocean mixed layer. A model-assimilated ocean dataset, partially validated for the period of the TOPEX/Poseidon mission, is used to evaluate the relative importance of subsurface advection and surface forcing due to wind-induced turbulent heat flux and Ekman advection. For our analysis, two key regions are chosen where decadal SST variance reaches local maxima, centered at 180_?E, 42_?N (Region A) and 155_?W, 35_?N (Region B), respectively. Region B is under the direct influence of the Aleutian Low, where the surface effects are dominant. Region A is part of the Kuroshio-Oyashio Extension, where the winter mixed layer is deep and the subsurface geostrophic advection contributes significantly to low-frequency winter SST variations. Our analysis suggests that anomalous geostrophic advection changes signs north and south 38_?N, presumably as a result of ocean gyre circulation adjustment to wind changes to the east. The surface forcing shows a larger-scale structure covering the entire mid-latitude North Pacific, in response to basin-wide changes in atmospheric circulation.

Tomita, T.; Xie, S.; Nonaka, M.

2002-12-01

176

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

177

Impact of observation-optimized model parameters on decadal predictions: Simulation with a simple pycnocline prediction model  

Microsoft Academic Search

A skillful decadal prediction that foretells varying regional climate conditions over seasonal-interannual to multidecadal time scales is of societal significance. However, predictions initialized from the climate observing system tend to drift away from observed states towards the imperfect model climate due to model biases arising from imperfect model equations, numeric schemes and physical parameterizations, as well as the errors in

S. Zhang

2011-01-01

178

Atmospheric Variability of CO2 impact on space observation Requirements  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

179

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

180

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

NASA Astrophysics Data System (ADS)

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

Ridgway, K. R.

2007-07-01

181

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

NASA Astrophysics Data System (ADS)

The oxygen minimum zone (OMZ) of the Arabian Sea is the thickest of the three oceanic OMZ. It is of global biogeochemical significance because of denitrification in the upper part leading to N2 and N2O production. The residence time of OMZ water is believed to be less than a decade. The upper few hundred meters of this zone are nearly anoxic but non-sulfidic and still support animal (metazoan) pelagic life, possibly as a result of episodic injections of O2 by physical processes. We report on discrete measurements of dissolved O2 and NO2-, temperature and salinity made between 1959 and 2004 well below the tops of the sharp pycnocline and oxycline near 150, 200, 300, 400, and 500 m depth. We assemble nearly all O2 determinations (originally there were 849 values, 695 of which came from the OMZ) by the visual endpoint detection of the iodometric Winkler procedure, which in our data base yields about 0.04 mL L-1 (~ 2 ?M) O2 above the endpoint from modern automated titration methods. We acknowledge that much lower (nanomolar) O2 values have been measured recently with the STOX (Switchable Trace amount OXygen) sensor in the eastern tropical South Pacific, and that similar conditions may also prevail in the Arabian Sea OMZ. In spite of the error in O2 measurements at vanishingly low levels, we argue that the temporal trends of the historic data should still hold. We find 632 values acceptable (480 from 150 stations in the OMZ). The data are grouped in zonally paired boxes of 1° lat. and 2° long. centered at 8, 10, 12, 15, 18, 20, and 21° N along 65 and 67° E. The latitudes of 8-12° N, outside the OMZ, are treated in passing. The principal results are as follows: (1) an O2 climatology for the upper OMZ reveals a marked seasonality at 200 to 500 m depth with O2 levels during the northeast monsoon and spring intermonsoon seasons elevated over those during the southwest monsoon season (median difference, 0.08 mL L-1 [~ 3.5 ?M]). The medians of the slopes of the seasonal regressions of O2 on year for each of the NE and SW monsoon seasons are -0.0043 and -0.0019 mL L-1 a-1, respectively (-0.19 and -0.08 ?M a-1; n = 10 and 12, differing at p = 0.01); (2) four decades of statistically significant decreases of O2 between 15 and 20° N but an opposing trend toward an increase near 21° N are observed. The mechanisms of the balance that more or less annually maintain the O2 levels are still uncertain. At least between 300 and 500 m, the replenishment is inferred to be due to isopycnal re-supply of O2, while at 200 (or 250?) m it is diapycnal, most likely by eddies. Similarly, recent models show large vertical advection of O2 well below the pycnoclines and oxyclines. The NO2- distribution, taken as an indicator of active NO3- reduction, does not show a trend in the redox environment for a quarter of a century at a GEOSECS station near 20° N. In the entire OMZ, the regression slopes on year within seasons for the rather variable NO2- do not present a clear pattern but by other measures tended to an increase of NO2-. Vertical net hauls collect resident animal (metazoan) pelagic life in the NO2- maximum of the OMZ at O2 levels well below the lower limit of the Winkler titration; the extremely low O2 content is inferred from the presence of NO2- believed to be produced through microbial NO3- reduction. Instead of the difficult measurement by the STOX sensor, the relation between the very low O2 inferred from presence of NO2- and mesozooplankton should be studied with 100 to 150 L bottles rather than nets. The spatial (within drift stations) and temporal (daily) variability in hydrography and chemistry is large also below the principal pycnocline. The seasonal change of hydrography is considerable even at 500 m depth. Future O2 or nutrient budgets for the OMZ must not be based on single cruises or sections obtained during one season only. Steady state cannot be assumed any longer for the intermediate layers of the central Arabian Sea.

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

2014-04-01

182

New observations of ultraviolet variability in Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

Observations of ultraviolet variability in Wolf-Rayet stars have been made with the ANS satellite Ultraviolet Photometer Experiment. Significant variations are detected in several of the observed stars, the timescale of the variability ranging from a few minutes to several months.

Burton, W. M.; Evans, R. G.; Patchett, B.; Wu, C.-C.

1978-01-01

183

Asian Monsoon Climate from Tropical Tree Rings: Decadal Scale Variability and Links to Tropical Pacific Sea Surface Temperature.  

NASA Astrophysics Data System (ADS)

Records of climate from the terrestrial tropics for the period before instrumentation are very limited. Tropical tree ring research, particularly in the Asian tropics, has been limited by difficulties ranging from problematic annual ring formation, poor understanding of phenology and physiology of thousands of tree species, complicated forest dynamics factors, and political turmoil and resultant effects on access. The need for understanding the potential range of variability in the monsoon regions of Asia is critical for making sound planning decisions in the face of potential hydrological changes associated with global climate change. A growing body of work from the SSEA-DENDRO (South and Southeast Asian Dendrochronology) project, one component of an NSF-funded project "Tree-Ring Reconstruction of Asian Monsoon Climate Dynamics", is beginning to allow analyses of local and regional climate from Monsoon Asian tree rings. We now have continuous records of 500-plus years, that enable analyses of important time periods such as the Little Ice Age (LIA), while "floating" time series span portions of the Medieval Climate Anomaly (MCA). From these records, we see clear evidence of decadal-scale reduced monsoon strength from India to Thailand for much of the 18th century, and we suggest warm SST anomalies in the eastern tropical Pacific as one of the primary factors. We compare our tree-ring based results with evidence from Speleothem research from northeast India that corroborates the decadal-scale monsoon weakening in the LIA, while revealing increased rainfall during the MCA. The role of SST anomalies in the eastern tropical Pacific is seen as significant, with El Ni?o and La Ni?a like conditions resulting in rainfall reductions and increases, respectively, in the study region. Persistent state changes in the SST fields can result in the kinds of decadal-scale patterns we are seeing in monsoon Asia, with far-reaching influence into the western hemisphere as well. More recently, the effects of shifting ENSO influence on monsoon rainfall from India eastward to Southeast Asia over the past few decades is explored and its significance examined.

Buckley, B. M.; Duangsathaporn, K.; Borgaonkar, H.; Palakit, K.

2006-12-01

184

An 1800-yr record of decadal-scale hydroclimatic variability in the upper Arkansas River basin from bristlecone pine  

USGS Publications Warehouse

Bristlecone pine trees are exceptionally long-lived, and with the incorporation of remnant material have been used to construct multi-millennial length ring-width chronologies. These chronologies can provide valuable information about past temperature and moisture variability. In this study, we outline a method to build a moisture-sensitive bristlecone chronology and assess the robustness and consistency of this sensitivity over the past 1200. yr using new reconstructions of Arkansas River flow (AD 1275-2002 and 1577-2002) and the summer Palmer Drought Sensitivity Index. The chronology, a composite built from parts of three collections in the central Rocky Mountains, is a proxy for decadal-scale moisture variability for the past 18 centuries. Since the sample size is small in some portions of the time series, the chronology should be considered preliminary; the timing and duration of drought events are likely the most robust characteristics. This chronology suggests that the region experienced increased aridity during the medieval period, as did much of western North America, but that the timing and duration of drought episodes within this period were somewhat different from those in other western locations, such as the upper Colorado River basin. ?? 2010 University of Washington.

Woodhouse, C. A.; Pederson, G. T.; Gray, S. T.

2011-01-01

185

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

186

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

187

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

188

Climatic controls of the interannual to decadal variability in Saudi Arabian dust activity: Towards the development of a seasonal prediction tool  

NASA Astrophysics Data System (ADS)

Atmospheric dust significantly influences the climate system, as well as human life in Saudi Arabia. Skillful seasonal prediction of dust activity with climatic variables will help prevent some negative social impacts of dust storms. Yet, the climatic regulators on Saudi Arabian dust activity remain largely unaddressed. Remote sensing and station observations show consistent seasonal cycles in Saudi Arabian dust activity, which peaks in spring and summer. The climatic controls on springtime and summertime Saudi Arabian dust activity during 1975-2010 are studied using observational and reanalysis data. Empirical Orthogonal Function (EOF) of the observed Saudi Arabian dust storm frequency shows a dominant homogeneous pattern across the country, which has distinct interannual and decadal variations, as revealed by the power spectrum. Regression and correlation analyses reveal that Saudi Arabian dust activity is largely tied to precipitation on the Arabian Peninsula in spring and northwesterly (Shamal) wind in summer. On the seasonal-interannual time scale, warm El Niño-Southern Oscillation (ENSO) phase (El Niño) in winter-to-spring inhibits spring dust activity by increasing the precipitation over the Rub'al Khali Desert, a major dust source region on the southern Arabian Peninsula; warm ENSO and warm Indian Ocean Basin Mode (IOBM) in winter-to-spring favor less summer dust activity by producing anomalously low sea-level pressure over eastern north Africa and Arabian Peninsula, which leads to the reduced Shamal wind speed. The decadal variation in dust activity is likely associated with the Atlantic Multidecadal Oscillation (AMO), which impacts Sahel rainfall and North African dust, and likely dust transport to Saudi Arabia. The Pacific Decadal Oscillation (PDO) and tropical Indian Ocean SST also have influence on the decadal variation in Saudi Arabian dust activity, by altering precipitation over the Arabian Peninsula and summer Shamal wind speed. Using eastern tropical Pacific SST as the high-frequency predictor and antecedent accumulated precipitation over the Arabian Peninsula and North Africa as low-frequency predictors, the predicted seasonal dust activity over Saudi Arabia is well correlated with the original time series (correlation above 0.6).

Yu, Y.; Notaro, M.; Liu, Z.; Alkolibi, F.; Fadda, E.; Bakhrjy, F.

2013-12-01

189

Links between the Big Dry in Australia and hemispheric multi-decadal climate variability - implications for water resource management  

NASA Astrophysics Data System (ADS)

Southeast Australia (SEA) experienced a protracted drought during the mid-1990s until early 2010 (known as the Big Dry or Millennium Drought) that resulted in serious environmental, social and economic effects. This paper analyses a range of historical climate data sets to place the recent drought into context in terms of Southern Hemisphere inter-annual to multi-decadal hydroclimatic variability. The findings indicate that the recent Big Dry in SEA is in fact linked to the widespread Southern Hemisphere climate shift towards drier conditions that began in the mid-1970s. However, it is shown that this link is masked because the large-scale climate drivers responsible for drying in other regions of the mid-latitudes since the mid-1970s did not have the same effect on SEA during the mid- to late 1980s and early 1990s. More specifically, smaller-scale synoptic processes resulted in elevated autumn and winter rainfall (a crucial period for SEA hydrology) during the mid- to late 1980s and early 1990s, which punctuated the longer-term drying. From the mid-1990s to 2010 the frequency of the synoptic processes associated with elevated autumn/winter rainfall decreased, resulting in a return to drier than average conditions and the onset of the Big Dry. The findings presented in this paper have marked implications for water management and climate attribution studies in SEA, in particular for understanding and dealing with "baseline" (i.e. current) hydroclimatic risks.

Verdon-Kidd, D. C.; Kiem, A. S.; Moran, R.

2014-06-01

190

Links between the Big Dry in Australia and hemispheric multi-decadal climate variability - implications for water resource management  

NASA Astrophysics Data System (ADS)

Southeast Australia (SEA) experienced a protracted drought during the mid-1990s until early 2010 (known as the Big Dry or Millennium Drought) that resulted in serious environmental, social and economic effects. This paper analyses a range of historical climate data sets to place the recent drought into context in terms of Southern Hemisphere inter-annual to multi-decadal hydroclimatic variability. The findings indicate that the recent Big Dry in SEA is in fact linked to the widespread Southern Hemisphere climate shift towards drier conditions that began in the mid-1970s. However, it is shown that this link is masked because the large-scale climate drivers responsible for drying in other regions of the mid-latitudes since the mid-1970s, did not have the same effect on SEA during the mid to late-1980s and early-1990s. More specifically, smaller-scale synoptic processes resulted in elevated autumn and winter rainfall (a crucial period for SEA hydrology) during the mid to late-1980s and early-1990s, which punctuated the longer term drying. From the mid-1990s to 2010 the frequency of the synoptic processes associated with elevated autumn/winter rainfall decreased, resulting in a return to drier than average conditions and the onset of the Big Dry. The findings presented in this paper have marked implications for water management and climate attribution studies in SEA, in particular for understanding and dealing with "baseline" (i.e. current) hydroclimatic risks.

Verdon-Kidd, D. C.; Kiem, A. S.; Moran, R.

2013-11-01

191

Inter-annual to decadal sea level variability along the Norwegian coast and in the Siberian Seas; a link with the Eastern North Atlantic  

NASA Astrophysics Data System (ADS)

Inter-annual to decadal sea level variations from tide gauge records along the Norwegian coast and in the Siberian Seas are examined for the period 1950 to present. A combination of observations and theory is used to explore the physical mechanisms responsible for the observed sea level variability. Tide gauge records are first grouped into 6 geographical regions: the Norwegian Coast, the Barents Sea, the Kara Sea, the Laptev Sea, the East Siberian Sea, and the Chukchi Sea. Then an average of sea level at tide gauges is computed for each region. All regions exhibit large decadal sea level variations (up to 20 cm). Sea level corrected for the inverse barometer effect is significantly correlated with the Arctic Oscillation index in all regions except in the East Siberian and Chukchi Seas. There is a coherent sea level signal that affects a region extending from Southwest Norway to the Kara Sea. Previous studies have found that sea level variability at the Norwegian coast is related to variations in the Norwegian Atlantic Current (NwAC), which are mainly driven by changes in the wind forcing over the region. Here we show that, apart from the contribution of the NwAC and the local wind, there is an additional contribution to the sea level variability at the Norwegian coast resulting from the poleward propagation of wind-driven sea level variations along the continental slope of the Northeast Atlantic. The fact that sea level variability in both the Barents and the Kara Seas is highly coherent with that in the Norwegian coast suggests propagation of sea level variations further north into these regions. Eastward of the Kara Sea, where the continental shelf is shallower, sea level variations are much larger than in the other regions and they are highly correlated (~0.75) with the local longshore wind.he average of sea level at 8 tide gauge stations on the Norwegian coast (black line) and a reconstruction of sea level (blue line) using a combination of the tide gauge at Newlyn (on the eastern boundary of the North Atlantic) and the longshore wind over the Faroe-Shetland channel and the Norwegian continental shelf. The grey shaded area represents the uncertainty of the time series. A 2-year running mean has been applied to both time series.

Calafat, F. M.; Chambers, D. P.

2012-12-01

192

The reflection of two past outbursts of Sagittarius A* observed by Chandra during the last decade  

NASA Astrophysics Data System (ADS)

The supermassive black hole at the Galactic center, Sagittarius A* has experienced periods of higher activity in the past. The reflection of these past outbursts is observed in the molecular material surrounding the black hole but reconstructing its precise lightcurve is difficult since the distribution of the clouds along the line of sight is poorly constrained.

Clavel, M.; Terrier, R.; Goldwurm, A.; Morris, M. R.; Ponti, G.; Soldi, S.; Trap, G.

2014-05-01

193

Interdecadal-decadal climate variability from multicoral oxygen isotope records in the South Pacific Convergence Zone region since 1650 A.D  

Microsoft Academic Search

In the South Pacific, interdecadal-decadal oceanic and atmospheric variability, referred to as the Interdecadal Pacific Oscillation (IPO), is most pronounced in the South Pacific Convergence Zone (SPCZ) salinity front region. Here we have used annual average oxygen isotope (?18O) time series from five coral cores collected from Fiji and Tonga in this region to construct a Fiji-Tonga Interdecadal-Decadal Pacific Oscillation

Braddock K. Linsley; Peipei Zhang; Alexey Kaplan; Stephen S. Howe; Gerard M. Wellington

2008-01-01

194

High resolution earth observation satellites and services in the next decade a European perspective  

NASA Astrophysics Data System (ADS)

Projects to use very high resolution optical satellite sensor data started in the late 90s and are believed to be the major driver for the commercialisation of earth observation. The global political security situation and updated legislative frameworks created new opportunities for high resolution, dual use satellite systems. In addition to new optical sensors, very high resolution synthetic aperture radars will become in the next few years an important component in the imaging satellite fleet. The paper will review the development in this domain so far, and give perspectives on future emerging markets and opportunities. With dual-use satellite initiatives and new political frameworks agreed between the European Commission and the European Space Agency (ESA), the European market becomes very attractive for both service suppliers and customers. The political focus on "Global Monitoring for Environment and Security" (GMES) and the "European Defence and Security Policy" drive and amplify this demand which ranges from low resolution climate monitoring to very high resolution reconnaissance tasks. In order to create an operational and sustainable GMES in Europe by 2007, the European infrastructure need to be adapted and extended. This includes the ESA SENTINEL and OXYGEN programmes, aiming for a fleet of earth observation satellites and an open and operational earth observation ground segment. The harmonisation of national and regional geographic information is driven by the European Commission's INSPIRE programme. The necessary satellite capacity to complement existing systems in the delivery of space based data required for GMES is currently under definition. Embedded in a market with global competition and in the global political framework of a Global Earth Observation System of Systems, European companies, agencies and research institutions are now contributing to this joint undertaking. The paper addresses the chances, risks and options for the future.

Schreier, Gunter; Dech, Stefan

2005-07-01

195

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

196

Observations of Variable Radio Sources at 2.8 Cm.  

National Technical Information Service (NTIS)

Thirty-one suspected variable radio sources have been observed between July 1966 and October 1967. Definite or possible variations have been detected in 21 of the sources. Some of the observed variations cannot be explained by the theory of an expanding c...

W. J. Medd J. L. Locke B. H. Andrew S. van den Bergh

1968-01-01

197

Dephasing of qubits due to an observable stochastic variable  

NASA Astrophysics Data System (ADS)

Decoherence of qubits under the influence of random phase fluctuations is studied by means of the stochastic Liouville equation, where the phase fluctuations are characterized by means of the Gauss-Markov process and the two-state-jump Markov process. We investigate how an observation of a stochastic variable during the time evolution influences the decoherence of the qubit system. We examine the decays of distinguishability and entanglement of qubit states. It is shown that the decoherence of qubits can be suppressed by the observation of the stochastic variable. It is also found that the suppression of the decoherence does not depend on the observed value.

Ban, Masashi; Kitajima, Sachiko; Shibata, Fumiaki

2013-02-01

198

Quasi-two-day wave structure, interannual variability, and tidal interactions during the 2002-2011 decade  

NASA Astrophysics Data System (ADS)

In this paper we employ Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry temperature measurements from 20 to 120 km and between about ±72° latitude to investigate several aspects of the quasi-two-day wave (QTDW) during the 2002-2011 decade, including interannual variability of its seasonal-latitudinal structure, its penetration into the lower thermosphere, and various wave-wave interactions. We focus on two components of the QTDW: the westward-propagating component with zonal wave number s=3 (TDW3), and the eastward-propagating component with s=-2 (TDE2). TDW3(TDE2) has maximum amplitudes during 2003, 2004, and 2011(2006 and 2011) and both waves have their lowest amplitudes during the deep solar minimum years of 2008-2009. TDW3 and to some degree TDE2 penetrate with significant amplitudes up to 120 km altitude, well into the region where neutral winds generate electric fields through the dynamo mechanism. A new "longitude subdivision method (LSM)" is presented that enhances temporal resolution of TDW3 and enables the determination of 9.6 h and 16 h waves that result from nonlinear interaction between TDW3 and/or TDE2 and diurnal migrating (DW1) and semidiurnal migrating (SW2) tides. Evidence is presented for westward-propagating 9.6 h and 16 h waves with s=5 and s=4, respectively, and a zonally symmetric (s=0) 9.6 h wave. The s=5(s=0) wave only occurs as a result of nonlinear interaction between SW2 and TDW3(TDE2), whereas the s=4 wave can result from interaction of TDW3 with DW1 or of TDE2 with SW2. We payed special attention to possible aliasing between different waves.

Moudden, Y.; Forbes, J. M.

2014-03-01

199

Modes of North Atlantic Decadal Variability in the ECHAM1/LSG Coupled Ocean-Atmosphere General Circulation Model.  

NASA Astrophysics Data System (ADS)

The climate variability in the North Atlantic sector is investigated in a 325-yr integration of the ECHAM1/ LSG coupled ocean-atmosphere general circulation model. At the interannual timescale, the coupled model behaves realistically and sea surface temperature (SST) anomalies arise as a response of the oceanic surface layer to the stochastic forcing by the atmosphere, with the heat exchanges both generating and damping the SST anomalies. In the ocean interior, the temperature spectra are red up to a period of about 20 years, and substantial decadal fluctuations are found in the upper kilometer or so of the water column. Using extended empirical orthogonal function analysis, two distinct quasi-oscillatory modes of ocean-atmosphere variability are identified, with dominant periods of about 20 and 10 years, respectively. The oceanic changes in both modes reflect the direct forcing by the atmosphere through anomalous air-sea fluxes and Ekman pumping, which after some delay affects the intensity of the subtropical and subpolar gyres. The SST is also strongly modulated by the gyre currents. In the thermocline, the temperature and salinity fluctuations are in phase, as if caused by thermocline displacements, and they have no apparent connection with the thermohaline circulation. The 20-yr mode is the most energetic one; it is easily seen in the thermocline and can be found in SST data, but it is not detected in the atmosphere alone. As there is no evidence of positive ocean-atmosphere feedback, the 20-yr mode primarily reflects the passive response of the ocean to atmospheric fluctuations, which may be in part associated with climate anomalies appearing a few years earlier in the North Pacific. The 10-yr mode is more surface trapped in the ocean. Although the mode is most easily seen in the temperature variations of the upper few hundred meters of the ocean, it is also detected in the atmosphere alone and thus appears to be a coupled ocean-atmosphere mode. In both modes, the surface heat flux acts neutrally on the associated SST anomalies once they have been generated, so that their persistence appears to be due in part to an overall adjustment of the air-sea heat exchanges to the SST patterns.

Zorita, Eduardo; Frankignoul, Claude

1997-02-01

200

Interannual and Decadal Variability of Ocean Surface Latent Heat Flux as Seen from Passive Microwave Satellite Algorithms  

NASA Technical Reports Server (NTRS)

Ocean surface turbulent fluxes are critical links in the climate system since they mediate energy exchange between the two fluid systems (ocean and atmosphere) whose combined heat transport determines the basic character of Earth's climate. Deriving physically-based latent and sensible heat fluxes from satellite is dependent on inferences of near surface moisture and temperature from coarser layer retrievals or satellite radiances. Uncertainties in these "retrievals" propagate through bulk aerodynamic algorithms, interacting as well with error properties of surface wind speed, also provided by satellite. By systematically evaluating an array of passive microwave satellite algorithms, the SEAFLUX project is providing improved understanding of these errors and finding pathways for reducing or eliminating them. In this study we focus on evaluating the interannual variability of several passive microwave-based estimates of latent heat flux starting from monthly mean gridded data. The algorithms considered range from those based essentially on SSM/I (e.g. HOAPS) to newer approaches that consider additional moisture information from SSM/T-2 or AMSU-B and lower tropospheric temperature data from AMSU-A. On interannual scales, variability arising from ENSO events and time-lagged responses of ocean turbulent and radiative fluxes in other ocean basins (as well as the extratropical Pacific) is widely recognized, but still not well quantified. Locally, these flux anomalies are of order 10-20 W/sq m and present a relevant "target" with which to verify algorithm performance in a climate context. On decadal time scales there is some evidence from reanalyses and remotely-sensed fluxes alike that tropical ocean-averaged latent heat fluxes have increased 5-10 W/sq m since the early 1990s. However, significant uncertainty surrounds this estimate. Our work addresses the origin of these uncertainties and provides statistics on time series of tropical ocean averages, regional space / time correlation analysis, and separation of contributions by variations in wind and near surface humidity deficit. Comparison to variations in reanalysis data sets is also provided for reference.

Robertson, Franklin R.; Jackson, Darren L.; Wick, Gary A.; Roberts, Brent; Miller, Tim L.

2007-01-01

201

A Decade of Solar Type III Radio Bursts Observed by the Nancay Radioheliograph 1998-2008  

NASA Astrophysics Data System (ADS)

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 degrees eastward tilt of the magnetic field, that source FWHM sizes s roughly follow a solar-cycle-averaged distribution dN/ds = 14 ?-3.3s-4 arcmin-1 day-1, and that source fluxes closely follow a solar-cycle-averaged dN/dS = 0.34 ?-2.9 S-1.7 sfu-1 day-1 distribution (when ? is in GHz, s in arcminutes, and S in sfu). Fitting a barometric density profile yields a temperature of 0.6 MK, while a solar wind-like h-2) density profile yields a density of 1.2 × 106 cm-3 at an altitude of 1 Rs, assuming harmonic emission. Finally, the flux distribution combined with rough radiative efficiency estimates hint at the possibility that escaping electron beams might carry as much energy away from the corona as is introduced into it by nanoflare-accelerated electrons.

Saint-Hilaire, Pascal; Vilmer, N.; Kerdraon, A.

2013-07-01

202

Variability of water mass properties in the last two decades in the South Adriatic Sea with emphasis on the period 2006-2009  

NASA Astrophysics Data System (ADS)

Spatially averaged temperature and salinity profiles from individual cruises between 1990 and 2009 were analysed to outline the temporal evolution of water mass properties in the deep convection site in the South Adriatic Pit (SAP). The long-term variability in thermohaline conditions has been explained and related to a close feedback mechanism between the Ionian and the Adriatic Sea. Prominent influences of the Eastern Mediterranean Transient are manifested in changes in the vertical temperature and salinity patterns in the South Adriatic, and the whole studied period was divided into three stages according to the main thermohaline characteristics: 1990-1995, 1995-2004 and the last period from 2005 onwards. Particular attention was given to data collected during 2006-2009, which permitted us to situate the actual thermohaline properties in the context of the decadal variability. This last period was characterised by a very low production of dense water in the northern basin during 2007, while from winter 2008 high production of North Adriatic Deep Water (NAdDW) and Adriatic Deep Water (AdDW) in the northern and southern basins, respectively, was observed. Finally, we used the Optimum Multiparameter Analysis (OMP) to identify the percentages of the different water masses contained in the SAP, and this highlighted some differences between two recent periods studied (2007 and 2008) and the production of dense waters.

Cardin, Vanessa; Bensi, Manuel; Pacciaroni, Massimo

2011-06-01

203

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

204

One decade of parallel PM10 and PM2.5 measurements in Europe: trends and variability  

NASA Astrophysics Data System (ADS)

The trends and variability of PM10, PM2.5 and PMcoarse concentrations at seven urban and rural background stations in five European countries for the period between 1998 and 2010 were investigated. Collocated or nearby PM measurements and meteorological observations were used in order to construct Generalized Additive Models, which model the effect of each meteorological variable on PM concentrations. In agreement with previous findings, the most important meteorological variables affecting PM concentrations were wind speed, wind direction, boundary layer depth, precipitation, temperature and number of consecutive days with synoptic weather patterns that favor high PM concentrations. Temperature has a negative relationship to PM2.5 concentrations for low temperatures and a positive relationship for high temperatures. The stationary point of this relationship varies between 5 and 15 °C depending on the station. PMcoarse concentrations increase for increasing temperatures almost throughout the temperature range. Wind speed has a monotonic relationship to PM2.5 except for one station, which exhibits a stationary point. Considering PMcoarse, concentrations tend to increase or stabilize for large wind speeds at most stations. It was also observed that at all stations except one, higher PM2.5 concentrations occurred for east wind direction, compared to west wind direction. Meteorologically adjusted PM time series were produced by removing most of the PM variability due to meteorology. It was found that PM10 and PM2.5 concentrations decrease at most stations. The average trends of the raw and meteorologically adjusted data are -0.4 ?g m-3 yr-1 for PM10 and PM2.5 size fractions. PMcoarse have much smaller trends and after averaging over all stations, no significant trend was detected at the 95% level of confidence. It is suggested that decreasing PMcoarse in addition to PM2.5 can result in a faster decrease of PM10 in the future. The trends of the 90th quantile of PM10 and PM2.5 concentrations were examined by quantile regression in order to detect long term changes in the occurrence of very large PM concentrations. The meteorologically adjusted trends of the 90th quantile were significantly larger (as an absolute value) on average over all stations (-0.6 ?g m-3 yr-1).

Barmpadimos, I.; Keller, J.; Oderbolz, D.; Hueglin, C.; Prévôt, A. S. H.

2012-01-01

205

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.

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

2014-01-01

206

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

207

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

208

Genetic variability of microcystin biosynthesis genes in Planktothrix as elucidated from samples preserved by heat desiccation during three decades.  

PubMed

Historic samples of phytoplankton can provide information on the abundance of the toxigenic genotypes of cyanobacteria in dependence on increased or decreased eutrophication. The analysis of a time-series from preserved phytoplankton samples by quantitative PCR (qPCR) extends observation periods considerably. The analysis of DNA from heat-desiccated samples by qPCR can be aggravated by point substitutions or the fragmentation of DNA introduced by the high temperature. In this study, we analyzed whether the heat desiccation of the cellular material of the cyanobacterium Planktothrix sp. introduced potential errors to the template DNA that is used for qPCR within (i) 16S rDNA and phycocyanin genes and (ii) the mcyA gene indicative of the incorporation of either dehydrobutyrine (Dhb) or N-methyl-dehydroalanine (Mdha) in position 7, and (ii) the mcyB gene, which is indicative of homotyrosine (Hty) in position 2 of the microcystin (MC) molecule. Due to high temperature desiccation, the deterioration of the DNA template quality was rather due to fragmentation than due to nucleotide substitutions. By using the heat-desiccated samples of Lake Zürich, Switzerland the abundance of the Dhb, Mdha and Hty genotypes was determined during three decades (1977-2008). Despite major changes in the trophic state of the lake resulting in a major increase of the total Planktothrix population density, the proportion of these genotypes encoding the synthesis of different MC congeners showed high stability. Nevertheless, a decline of the most abundant mcyA genotype indicative of the synthesis of Dhb in position 7 of the MC molecule was observed. This decline could be related to the gradual incline in the proportion of a mutant genotype carrying a 1.8kbp deletion of this gene region. The increase of this mcyA (Dhb) gene deletion mutant has been minor so far, however, and likely did not affect the overall toxicity of the population. PMID:24265798

Ostermaier, Veronika; Christiansen, Guntram; Schanz, Ferdinand; Kurmayer, Rainer

2013-01-01

209

Genetic Variability of Microcystin Biosynthesis Genes in Planktothrix as Elucidated from Samples Preserved by Heat Desiccation during Three Decades  

PubMed Central

Historic samples of phytoplankton can provide information on the abundance of the toxigenic genotypes of cyanobacteria in dependence on increased or decreased eutrophication. The analysis of a time-series from preserved phytoplankton samples by quantitative PCR (qPCR) extends observation periods considerably. The analysis of DNA from heat-desiccated samples by qPCR can be aggravated by point substitutions or the fragmentation of DNA introduced by the high temperature. In this study, we analyzed whether the heat desiccation of the cellular material of the cyanobacterium Planktothrix sp. introduced potential errors to the template DNA that is used for qPCR within (i) 16S rDNA and phycocyanin genes and (ii) the mcyA gene indicative of the incorporation of either dehydrobutyrine (Dhb) or N-methyl-dehydroalanine (Mdha) in position 7, and (ii) the mcyB gene, which is indicative of homotyrosine (Hty) in position 2 of the microcystin (MC) molecule. Due to high temperature desiccation, the deterioration of the DNA template quality was rather due to fragmentation than due to nucleotide substitutions. By using the heat-desiccated samples of Lake Zürich, Switzerland the abundance of the Dhb, Mdha and Hty genotypes was determined during three decades (1977-2008). Despite major changes in the trophic state of the lake resulting in a major increase of the total Planktothrix population density, the proportion of these genotypes encoding the synthesis of different MC congeners showed high stability. Nevertheless, a decline of the most abundant mcyA genotype indicative of the synthesis of Dhb in position 7 of the MC molecule was observed. This decline could be related to the gradual incline in the proportion of a mutant genotype carrying a 1.8kbp deletion of this gene region. The increase of this mcyA (Dhb) gene deletion mutant has been minor so far, however, and likely did not affect the overall toxicity of the population.

Ostermaier, Veronika; Christiansen, Guntram; Schanz, Ferdinand; Kurmayer, Rainer

2013-01-01

210

The ENSO or there and back again. Trying to understand the connection between its decadal variability and processes indexed by PDO, NAO and AMO  

NASA Astrophysics Data System (ADS)

Recent research suggests that decadal variability in ENSO influence not only tropical Pacific SST values but also modulate the rate of change of global temperatures. It may be the main reason for the so called "global warming hiatus" of recent years. This makes it not only an interesting subject of scientific studies but also a subject of interest for general population. Especially predicting average decadal ENSO activity would be important, if it would help predict the rate of global warming on decadal scales. The only hope for such predictions in foreseeable future would come from understanding the relationship of ENSO variability in decadal scales to cycles of natural variability. Several climate indices have quasi-cyclical components of about 60-70 years. The most obvious example is AMO, a proxy for Atlantic meridional overturning circulation (AMOC) variability. However also variability of NAO, the index of atmospheric zonal circulation in the North Atlantic sector, has component of similar period significantly correlated with AMO lagged by about 15 years. Even variability of PDO the index of multidecadal variability in Northern Pacific has a component of similar period and phase as NAO. Then, PDO correlates also with ENSO on decadal scales. Correlation does not imply causation. This raises the question whether there are physical mechanisms behind the correlations. Tropical Pacific temperatures have been shown to influence surface pressure in the North Eastern Pacific influencing zonal circulation which may explain the PDO - NAO "teleconnection". Zonal winds influence the rate of deep water production in Labrador and Greenland seas, which may explain its influence on the rate of change in deep water production (the NAO - AMO correlation lagged by ¼ cycle). AMO being a proxy of AMOC (heat transport from South to North Hemisphere) obviously influences the inter-hemispherical temperature difference. We have recently showed the statistically significant anticorrelation of this NH-SH temperature difference on ENSO, explaining it by the influence on the position of ITCZ and trade winds. We use statistical analysis of climate indices and discuss the underlying physical processes to argue for existence of causal connection between them. This study tries to create a framework for understanding climate variability in Pacific and Atlantic sectors on multidecadal scales as a quasi-cycle of about 65 years involving both ocean and atmospheric circulation involving processes indexed by PDO, NAO, AMO and influencing ENSO variability on decadal scales. We do not believe this is the final word in this field. Rather a good start.

Piskozub, Jacek; Gutowska, Dorota

2014-05-01

211

Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis  

NASA Astrophysics Data System (ADS)

Using new data, we build upon the nearly two-decade long record of observations from Jakobshavn Isbrae to investigate the processes driving its dynamic evolution. While winter flow speed has not increased substantially over the last three winters, there remains a strong seasonal variation in flow speed that coincides with a cycle of summer thinning and winter thickening. We relate changes in glacier speed to geometry through variations in basal traction and horizontal stresses, using ice-flow models constrained by satellite and airborne observations. These results suggest that the bed provides little flow resistance along the main trough within about 20 km of the terminus. While the loss of buttressing from the retreat of grounded and floating ice likely contributed to the initial speedup, other processes are of comparable significance at seasonal to decadal time scales. From analysis of the models, we hypothesize that thinning-induced change in basal effective pressure is the dominant process influencing near-terminus behavior, while diffusive processes drive the upstream response. The apparent need for the terminus to thin to near flotation before it can calve may limit the rate at which retreat occurs. Our analysis of the processes controlling the speed suggests little potential for further large acceleration. Thinning and elevated speeds may continue at rates similar to present, however, putting the glacier on course to retreat to the head of its deep trough in about a century, at which point it likely would stabilize with a thinner terminus.

Joughin, Ian; Smith, Ben E.; Howat, Ian M.; Floricioiu, Dana; Alley, Richard B.; Truffer, Martin; Fahnestock, Mark

2012-06-01

212

Mid-Holocene onset of high-amplitude decadal to centennial scale variability along the Peru Chile Margin  

NASA Astrophysics Data System (ADS)

Understanding the natural climate variations in the eastern tropical Pacific is crucial for predicting the evolution of the El Niño-Southern Oscillation (ENSO) system and for anticipating the ways in which increases in atmospheric CO2 will affect climate. Here we present the first continuous, high-resolution (11-12 yr) climate record across the mid-Holocene transition (10ka-1.4ka) from the Peru-Chile Margin near the epicenter of the modern ENSO system. Although the high productivity of the Peru margin should promote high deposition rates, and the anaerobic bottom water conditions should inhibit sediment mixing by benthic organisms, nearly all sediment cores recovered from this region suffer from major gaps in Holocene sedimentation. Our data comes from a ~5 meter piston core collected from the mid-Peruvian shelf (15° 15"S, 75° 58"W, ~250mwd) in the heart of the oxygen minimum/denitrification zone that provides the first uninterrupted archive of conditions along the Peru-Chile margin. A suite of geochemical proxies allow us to reconstruct sea surface temperature (SST- Uk'37), phytoplankton productivity (C37total and %BSi), and thermocline ventilation (?15N), variables that are tightly correlated to ENSO events today. Despite the observation that the mean late Holocene state of all three variables did not change over the last 10,000 years, our data reveal a dramatic increase in climate variability after the mid Holocene (~5ka); represented by prolonged periods (50-200yrs) of climate extremes, which are absent in the early Holocene. To further investigate these climate extremes we examine benthic foraminiferal assemblages and oxygen isotopes in combination with our other proxy records in selected late Holocene sections. The roughly centennial-scale oscillations do not show typical El Niño-La Niña correlations between proxies. We therefore posit that a significant fraction of super-ENSO variance during the course of the Holocene may originate outside the tropics, through processes that ventilate the subsurface waters of the eastern tropical Pacific and modify its subsurface density structure and nutrient properties. Super-ENSO variability in SST may, however, have modulated the frequency of ENSO events over the Holocene.

Chazen, C. R.; Altabet, M.; Herbert, T. D.

2008-12-01

213

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

214

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

215

Observed low frequency variability of the Brazil Current front  

NASA Astrophysics Data System (ADS)

The Brazil Current is a weak western boundary current, the southwest component of the South Atlantic subtropical gyre, which is the main conduit of upper ocean waters in the region. The objective of this work is to report on observed low frequency variability of the Brazil Current front using satellite-derived sea height anomaly and sea surface temperature observations during the 1993-2008 period. The variability of the front is studied in terms of the separation of the Brazil Current front from the continental shelf break. During the study period, estimates of this parameter vary 6 degrees in latitude, and the mean monthly estimates exhibit a shift to the south of approximately 1.5 degrees. Statistically significant changes are not observed in the geostrophic transport of the Brazil and Malvinas currents, suggesting that the low-frequency changes of the Brazil Current front are governed by different mechanisms than the seasonal variability of these surface currents. Surface drifter trajectories and simulations using synthetic drifters are consistent with the observed shift to the south of the Brazil Current front. Trends of eddy kinetic energy, sea height anomaly, sea surface temperature and wind stress curl are also in agreement with the variability reported here. Wavelet transform analysis revealed interesting changes in the periodicity of the latitude of separation of the Brazil Current front from the continental shelf break, with periods ranging from semiannual to biannual. Longer records, together with comprehensive numerical experiments, will ultimately be needed to determine the origin of these changes.

Goni, Gustavo Jorge; Bringas, Francis; Dinezio, Pedro Nicolas

2011-10-01

216

Observed Low Frequency Variability of the Brazil Current Front  

NASA Astrophysics Data System (ADS)

The Brazil Current is a weak western boundary current, the southwest component of the South Atlantic subtropical gyre, which is the main conduit of upper ocean waters in the region. We report her the observed low frequency variability of the Brazil Current front using satellite-derived sea height anomaly and sea surface temperature observations during the 1993-2008 period. The variability of the front is studied in terms of the separation of the Brazil Current front from the continental shelf break. During the study period, estimates of this parameter indicate a shift to the south of approximately 1.5 degrees. Statistically significant changes are not observed in the geostrophic transport of the Brazil and Malvinas currents suggesting that the low-frequency changes of the Brazil Current front are governed by different mechanisms than the seasonal variability of these surface currents. Surface drifter trajectories as well as simulations using synthetic drifters are consistent with the observed shift to the south of the Brazil Current front. Trends of eddy kinetic energy, sea height anomaly, sea surface temperature and wind stress curl are also in agreement with the variability reported here. Wavelet transform analysis revealed an interesting change in the periodicity of the separation of the Brazil Current front from the continental shelf break from annual to bi-annual during 2003. Longer records together with comprehensive numerical experiments will ultimately be needed to determine the origin of these changes.

Goni, G. J.; Bringas Gutierrez, F.; Di Nezio, P. N.

2012-12-01

217

Sea surface temperature and salinity variability in the Levantine Basin during the last decade, 1996 to 2006  

NASA Astrophysics Data System (ADS)

The reality of global warming since the industrial era is manifested in part by changes in global surface temperatures. Regional temperature increases have also been reported in the Mediterranean Sea, where sea surface temperatures (SSTs) across the Mediterranean as a whole, have been rising about twice as much as those of the global oceans. Here we analyse and compare satellite remote sensing SST data with in-situ data for the period 1996-2006 in the Levantine Basin. Satellite data were collected by the NOAA/NASA Advanced Very High Resolution Radiometers (AVHRR) and processed by the SST Pathfinder program. For our analyses we obtained monthly averaged Level 3, version 5.0, global SST data from the nighttime pass of the satellite at a 4-km resolution and an equal-angle grid of 8192 pixels/360° from January 1996 through December 2006. Monthly quality control flag files for the SST data were also obtained from January 1996 through December 2006 from the same source. Further, 23,000 vertical profiles of temperature and salinity from 160 oceanographic cruises were extracted from the MEDAR/MEDATLAS, WDC-A and the Coriolis databases for the period 1996-2006, in order to study the interannual variability in this basin at the surface layer (0-10m). Annual gridded fields were calculated by averaging the top 10m of the in-situ data, and then interpolated horizontally by the Variational Inverse Method (VIM) and a finite element technique using the SeaDataNet Geostatistical Analysis Tool - DIVA. Satellite SST data indicate that over the last 11 years a general warming has occurred over the Levantine Basin, both at interannual and seasonal time scales. This increase in average SSTs is also seen in the seasonal averages, especially during the spring and summer. Moreover, the averages from the top 10m of in-situ SST, using the relevant data from the above oceanographic databases, show a correlation with the satellite SST data particularly at seasonal time scales. Satellite remote sensing data are thus a very good indicator of environmental conditions. We also analyse in-situ sea surface salinity (SSS) data collected over the same period of time to determine any similarities in the patterns of variability with SSTs. The pattern of SST variability is shared by the patterns of SSS. Therefore, it can be expected that the Levantine Basin has also undergone salinity increases during the last 11 years. Finally, we investigate the variability in regional wind speeds and latent heat fluxes as possible driving mechanisms of the changes observed in SST and SSS. It will be valuable to investigate future trends in SSTs to determine whether the observed patterns of SSTs represent a continued pattern of persistent warming or a new direction for an ever-changing Levantine Basin.

Samuel-Rhoads, Y.; Iona, S.; Zodiatis, G.; Hayes, D.; Gertman, I.; Georgiou, G.

2009-04-01

218

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

219

Solar vs. Tidal Forcing of Centennial to Decadal Scale Variability in Marine Sedimentary Records from the Western Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

Prior studies on Holocene marine sediments from the Antarctic Peninsula, including ODP Site 1098 and USAP N. B. Palmer jumbo piston cores have revealed pronounced multi-century scale variations within a number of paleoenvironmental proxies. In order to fully understand the exact timing of this signal an ultra-high resolution jumbo piston core from the Schollaert Drift was correlated with the well-known Palmer Deep record. A precise and accurate radiocarbon chronology is now available from the former site that utilizes in-situ mollusks, rather than bulk organic matter. The resulting time series spans the last 5000 years over the 20 m length of core NBP99-03 JPC28 and the surface stratigraphy of kasten core NBP01-07 KC8. The corrected and calibrated ages (with an applied reservoir correction of 1170 years) of 10 mollusks dated by the National Ocean Sciences Accelerator Mass Spectrometry Facility and the University of Arizona TAMS facility were used to construct an age-depth profile for JPC28 and KC8. A linear trend (R2 value of 0.993) of the age-depth profile was used to extrapolate the constant time interval between magnetic susceptibility measurements, which were analyzed every 1 cm. Dominant periods in the upper 10 m of the time series were identified using the Arand Spectral Analysis Package (Howell, 2001). This analysis revealed a single pronounced maxima at 160 years, which is inconsistent with the dominant periods found in time series of climate proxies from other sites on the western side of the Antarctic Peninsula. In particular, periods of 200 and 400 years, which are dominant in the Palmer Deep site (Warner and Domack, 2002), are not present in the Schollaert Drift. The spectral peaks derived from the two records are significantly different at the 95% confidence level. The cycles in the Palmer Deep record have been associated with solar variability, where as the 160 year cycle in the Schollaert Drift is close to a 180 year cycle in tidal forces (Keeling and Whorf, 2000). We discuss these alternative forcing mechanisms with respect to: contrasts in regional processes of glacial marine sedimentation, the mechanism whereby the tidal or solar signal is transferred to the sediment column and possible cryptic stratigraphy of the Palmer Deep record (ie. missing time, Nederbragt and Thurow, 2002). Resolution of the correct forcing factor is critical to our ability to hind cast the last 100 years of paleoenvironmental data within these cores and hence to our attempts at recognizing an anthropogenic climate signal in the Antarctic Peninsula region. Howell, P. (2001), ARAND time series and spectral analysis package for the Macintosh, Brown University, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2001-044, NOAA/NGDC Paleoclimatology Program, Boulder, Colo. Keeling, Charles D., and Timothy P. Whorf (2000), The 1,800-year oceanic tidal cycle: A possible cause of rapid climate change, Proc. Natl. Acad. Sci., 97 (8), 3814-3819. Nederbragt, A. J., and Thurow, J. (2002) Sediment color variation and annual accumulation rates in laminated Holocene sediments, Site 1098, Palmer Deep. In Barker, P. F., Camerlenghi, A., Acton, G. D., and Ramsay, A.T.S. (eds), Proc. ODP Sci. Results, 178: College Station TX (Ocean Drilling Program). Warner, Nathaniel R., and E. Domack (2002), Millennial-to decadal-scale paleoenvironmental change during the Holocene in the Palmer Deep, Antarctica, as recorded by particle size analysis, Paleoceanography, 17 (3), 8004, doi:10.1029/2000PA000602.

Kirkwood, G.; Domack, E.; Brachfeld, S.

2004-12-01

220

Evolution of Interannual and Decadal/Interdecadal variability of the SPCZ since the late 18th century using a network of Fiji coral ?18O time-series  

NASA Astrophysics Data System (ADS)

The South Pacific Convergence Zone (SPCZ) region is of high interest due to its impact on tropical rainfall and the export of moisture from the tropics. Documenting the amplitude and periodicity of SPCZ displacements on interannual (mainly influenced by El Niño Southern Oscillation (ENSO)) and decadal/interdecadal (D/I) time-scales is of high importance not only for risk management but also for understanding the dynamics of the SPCZ and for improving General Circulation Model climate predictions. We have generated a unique regional coral ?18O network from the Fiji Islands, which are located just south of the main SPCZ rainfall axis. This network consists of five monthly-resolved coral ?18O time-series from different regions of Fiji. Evaluation of interseries correlation coefficients indicates that ENSO-band (2 to 9 years) and D/I-band (10 to 50 years) ?18O variability is highly reproducible. Correlation to instrumental surface salinity (SSS) data indicates that interannual coral ?18O variability in Fiji is the result of interannual changes in SSS that are coupled to ENSO. The composite reconstruction (arithmetic average of the five Fiji ?18O records), extending from 1790 to 2004 AD, was compared to known climatic indices such as the Southern Oscillation and Interdecadal Pacific Oscillation indices over the 20th century. Pearson Product-Moment correlations between the coral ?18O composite and these target indices of the Pacific basin are r= 0.71 and 0.41 for ENSO and D/I timescales respectively, with p-values better than 0.001. These high values indicate that our Fiji composite ?18O record is suitable for reconstructing past ENSO and D/I variability prior to the instrumental record. Our Fiji ENSO-band and D/I-band reconstructions from the Southwest Pacific also share important similarities with other Pacific coral ?18O records such as the ?18O record from Malo-Channel (Vanuatu). The Fiji composite ?18O reconstruction also correlates negatively with interannual and D/I coral ?18O variability from equatorial sites in the Pacific (e.g. Maiana). Collectively, our results from the SPCZ region reflect the validity of the coral ?18O composite to track regional climatic variability at both interannual and decadal/interdecadal timescales. From the late 18th century to the late 19th century the D/I band dominates the Fiji composite while the ENSO-band amplitude is relatively small. Starting around 1885, this tendency reverses and we observed a drastic decrease in the D/I signal amplitude, with its variance reduced by more than 50%, while the ENSO-band signal increases progressively in amplitude toward the present, reaching unprecedented values during the mid-20th century. This switch around 1885 A.D. is unique over the last 250 years and may correspond to a reorganization of Pacific-wide climate.

Dassie, E. P.; Linsley, B. K.; Correge, T.; Wu, H. C.; Lemley, G. M.; Cabioch, G.

2012-12-01

221

Observations of variable X-ray sources in globular clusters  

NASA Technical Reports Server (NTRS)

The discovery is reported of a variable X-ray source at midgalactic latitude in the globular cluster NGC 1851, and observations are reported which confirm the existence of variable X-ray sources in NGC 7078 and NGC 6441. The new source, designated MX 0513-40, was found to vary in intensity by a factor of at least 5 over a sixteen-day period and to have a hard spectrum as compared to that of the Crab Nebula in the energy range from 1 to 10 keV. The source in NGC 7078 (3U 2131+11) was found to vary by more than a factor of 2 over a 500-day period. Strong evidence of variability is presented for the source in NGC 6441 (3U 1746-37). It is concluded that both MX 0513-40 and 3U 2131+11 are probably stellar objects and are no more than about 160 kpc distant.

Clark, G. W.; Markert, T. H.; Li, F. K.

1975-01-01

222

Interannual/decadal variability in MJO activity as diagnosed in the 40-year NCEP/NCAR reanalysis and simulated in an ensemble of GISST integrations  

SciTech Connect

The Madden-Julian Oscillation (MJO) is the dominant mode of tropical variability at intraseasonal timescales. It displays substantial interannual variability in intensity which may have important implications for the predictability of the coupled system. The reasons for this interannual variability are not understood. The interannual behaviour of the MJO has been diagnosed initially in the 40-year NCEP/NCAR Reanalysis by calculating the variance of the 20-100 day filtered zonal mean zonal wind (10 o N-10 o S averaged) in a 100- day moving window. The results suggest that prior to the mid-1970s the activity of the MJO was consistently lower than during the latter part of the record. This may be related to either inadequacies in the data coverage, particularly over the tropical Indian Ocean prior to the introduction of satellite observations, or to the real effects of a decadal timescale warming in the tropical SSTs. This interdecadal trend is captured by the dominant EOF (explaining 28% of the variance) of the monthly mean SSTs (after removal of the mean seasonal cycle), as used in the NCEP/NCAR Reanalysis for the region of the tropics where the MJO is convectively active (i.e., 60 o E-180 o E, 20 o S-20 o N). During the latter part of 1970?s there was an abrupt change from a predominantly negative PC1 (i.e. colder Indian Ocean) to a positive PC1 (i.e. warmer Indian Ocean), indicative of a general warming of the tropical Indian Ocean by at least 0.5 o K over the last 40 years. However, on interannual timescales, the teleconnection patterns between MJO activity and SST show only a weak, barely significant, influence of El Niño in which the MJO is more active during the cold phase. As well as the NCEP/NCAR Reanalysis, a 4-member ensemble of 45 year integrations with the Hadley Centre climate model (HADAM2a), forced by observed SSTs for 1949-93, has been used to investigate the relationship between MJO activity and SST. HADAM2a is known to give a reasonable simulation of the MJO, and the extended record provided by this ensemble of integrations allows a more robust investigation of the predictability of MJO activity than was possible with the 40-year NCEP/NCAR Reanalysis. The results have shown that, for the uncoupled system, with the atmosphere being driven by imposed SSTs, there is no reproducibility of the activity of the MJO from year to year. The interannual behaviour of the MJO is not controlled by the phase of El Niño and would appear to be mainly chaotic in character. However, the model results have confirmed the low frequency, interdecadal timescale variability of MJO ac-tivity seen in the NCEP/NCAR Reanalysis. The activity of the MJO is consistently lower in all realisations prior to the mid 1970s, suggesting that the MJO may become more active as tropical SSTs become warmer. This result may have implications for the effects of global warming on the coupled atmosphere-ocean system. The implications of these results for the predictability of the tropical ocean-atmosphere system are im-portant since intraseasonal activity in the atmosphere, associated with MJO?s and westerly wind bursts, can have a substantial impact on the Pacific Ocean. As the events in 1997 indicate, MJO activity may have a sig-nificant impact on the magnitude and growth rate of El Niño events. In turn the decadal changes in MJO ac-tivity suggest that if tropical SSTs continue to warm, the activity of the MJO may tend to increase which then might have implications for the future behaviour of El Niño. This work is presented in full by Slingo et al. (1999, Quart. J. Roy. Meteorol. Soc., in press).

Nortley, F; Rowell, D P; Slingo, J M; Sperber, K R

1999-04-21

223

Reassessing regime shifts in the North Pacific: incremental climate change and commercial fishing are necessary for explaining decadal-scale biological variability.  

PubMed

In areas of the North Pacific that are largely free of overfishing, climate regime shifts - abrupt changes in modes of low-frequency climate variability - are seen as the dominant drivers of decadal-scale ecological variability. We assessed the ability of leading modes of climate variability [Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO), Arctic Oscillation (AO), Pacific-North American Pattern (PNA), North Pacific Index (NPI), El Niño-Southern Oscillation (ENSO)] to explain decadal-scale (1965-2008) patterns of climatic and biological variability across two North Pacific ecosystems (Gulf of Alaska and Bering Sea). Our response variables were the first principle component (PC1) of four regional climate parameters [sea surface temperature (SST), sea level pressure (SLP), freshwater input, ice cover], and PCs 1-2 of 36 biological time series [production or abundance for populations of salmon (Oncorhynchus spp.), groundfish, herring (Clupea pallasii), shrimp, and jellyfish]. We found that the climate modes alone could not explain ecological variability in the study region. Both linear models (for climate PC1) and generalized additive models (for biology PC1-2) invoking only the climate modes produced residuals with significant temporal trends, indicating that the models failed to capture coherent patterns of ecological variability. However, when the residual climate trend and a time series of commercial fishery catches were used as additional candidate variables, resulting models of biology PC1-2 satisfied assumptions of independent residuals and out-performed models constructed from the climate modes alone in terms of predictive power. As measured by effect size and Akaike weights, the residual climate trend was the most important variable for explaining biology PC1 variability, and commercial catch the most important variable for biology PC2. Patterns of climate sensitivity and exploitation history for taxa strongly associated with biology PC1-2 suggest plausible mechanistic explanations for these modeling results. Our findings suggest that, even in the absence of overfishing and in areas strongly influenced by internal climate variability, climate regime shift effects can only be understood in the context of other ecosystem perturbations. PMID:23996901

Litzow, Michael A; Mueter, Franz J; Hobday, Alistair J

2014-01-01

224

Building on Decades of Research on the McMurdo Volcanic Group, Antarctica: A Geologic Field Guide to Observation Hill  

NASA Astrophysics Data System (ADS)

Based on more than four decades of research on the rocks of the Erebus Volcanic Province of the McMurdo Volcanic Group, a geologic field guide to the Observation Hill walking tracks near McMurdo Station, Antarctica has been developed. The geologic field guide was an outcome of questions generated by: (1) Teachers participating in the Andrill Research Immersion for Science Educators (ARISE) program; (2) McMurdo Station support staff, as well as (3) Geoscientists with specialties outside volcanology and petrology. Whilst these individuals are acutely aware of the more than a century of references to Observation Hill in exploration literature, there was little in the way of easily-accessible information about the geologic history of Hut Point and Observation Hill, as well as other nearby volcanoes (e.g. Mt. Erebus, White and Black Islands) and larger scale geologic features (e.g. Transantarctic Mountains) that can be seen from the vantage point of Observation Hill. Questions also focused on smaller scale features of the landscape (e.g. patterned ground) and textures and minerals observed in volcanic rocks exposed on the trails. In order to encompass the wide-ranging background of the audience and facilitate access, the field guide will be available in three formats: (1) A downloadable MP3 file, which includes the general information and stop-by- stop information; (2) A double-sided paper brochure that provides a relatively simple, easier-to-digest guide to views and geologic features; (3) A Google Earth Layer that includes access to the MP3 files and the paper brochure, as well as additional geologic information. Links to the field guide can be found at http://www.andrill.org/education.

Pound, K. S.; Panter, K. S.

2008-12-01

225

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

Microsoft Academic Search

We present a monthly resolved, 213-year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (?18Ocoral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The ?18Ocoral

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

2005-01-01

226

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

Microsoft Academic Search

We present a monthly resolved, 213-year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (delta18Ocoral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The delta18Ocoral

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

2005-01-01

227

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

228

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

229

Constraints on Variability of Brightness and Surface Magnetism on Time Scales of Decades to Centuries in the Sun and Sun-Like Stars: A Source of Potential Terrestrial Climate Variability  

NASA Technical Reports Server (NTRS)

These four points summarize our work to date. (1) Conciliation of solar and stellar photometric variability. Previous research by us and colleagues suggested that the Sun might at present be showing unusually low photometric variability compared to other sun-like stars. Those early results would question the suitability of the technique of using sun-like stars as proxies for solar irradiance change on time scales of decades to centuries. However, our results indicate the contrary: the Sun's observed short-term (seasonal) and longterm (year-to-year) brightness variations closely agree with observed brightness variations in stars of similar mass and age. (2) We have demonstrated an inverse correlation between the global temperature of the terrestrial lower troposphere, inferred from the NASA Microwave Sounding Unit (MSU) radiometers, and the total area of the Sun covered by coronal holes from January 1979 to present (up to May 2000). Variable fluxes of either solar charged particles or cosmic rays, or both, may influence the terrestrial tropospheric temperature. The geographical pattern of the correlation is consistent with our interpretation of an extra-terrestrial charged particle forcing. (3) Possible climate mechanism amplifying the impact of solar ultraviolet irradiance variations. The key points of our proposed climate hypersensitivity mechanism are: (a) The Sun is more variable in the UV (ultraviolet) than in the visible. However, the increased UV irradiance is mainly absorbed in the lower stratosphere/upper troposphere rather than at the surface. (b) Absorption in the stratosphere raises the temperature moderately around the vicinity of the tropopause, and tends to stabilize the atmosphere against vertical convective/diffusive transport, thus decreasing the flux of heat and moisture carried upward from surface. (c) The decrease in the upward convection of heat and moisture tends to raise the surface temperature because a drier upper atmosphere becomes less cloudy, which in turn allows more solar radiation to reach the Earth's surface. (4) Natural variability in an ocean-atmosphere climate model. We use a 14-region, 6-layer, global thermo-hydrodynamic ocean-atmosphere model to study natural climate variability. All the numerical experiments were performed with no change in the prescribed external boundary conditions (except for the seasonal cycle of the Sun's tilt angle). Therefore, the observed inter-annual variability is of an internal kind. The model results are helpful toward the understanding of the role of nonlinearity in climate change. We have demonstrated a range of possible climate behaviors using our newly developed ocean-atmosphere model. These include climate configurations with no interannual variability, with multi-year periodicities, with continuous chaos, or with chaotically occuring transitions between two discrete substrates. These possible modes of climate behavior are all possible for the real climate, as well as the model. We have shown that small temporary climate influences can trigger shifts both in the mean climate, and among these different types of behavior. Such shifts are not only theoretically plausible, as shown here and elsewhere; they are omnipresent in the climate record on time scales from several years to the age of the Earth. This has two apparently opposite implications for the possibility of anthropogenic global warming. First, any warming which might occur as a result of human influence would be only a fraction of the small-to-large unpredictable natural changes and changes which result from other external causes. On the other hand, small temporary influences such as human influence do have the potential of causing large permanent shifts in mean climate and interannual variability.

Baliunas, Sallie L.; Sharber, James (Technical Monitor)

2001-01-01

230

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

231

Decadal to millennial-scale variability in sea ice, primary productivity, and Pacific-Water inflow in the Chukchi/East Siberian Sea area (Arctic Ocean)  

NASA Astrophysics Data System (ADS)

Sea-ice is an essential component of the global climate system and, especially, the Polar Oceans. An alarming decrease in term of sea-ice concentration, thickness and duration, has been observed in the Arctic Ocean and its marginal seas over the last 30 years. Thus, understanding the processes controlling modern sea-ice variability and reconstructing paleo-sea-ice extent and variability in polar regions have become of great interest for the international scientific community during the last years. Here, we present new proxy records determined in sediment cores from the East Siberian Sea (RV Polarstern Expedition ARK-XXIII/3 in 2008; Core PS72/350) and from the Chukchi Sea (RV Araon Expedition ARA2B in 2011; Core ARA2B-1A, -1B). These records, including organic-geochemical bulk parameters, specific biomarkers (IP25 and sterols; PIP25; for recent reviews see Stein et al., 2012; Belt and Müller, 2013), biogenic opal, mineralogical data as well as high-resolution XRF scanning data, give new insight into the short-term (decadal-, centennial- to millennial-scale) variability in sea-ice, primary productivity and Pacific-Water inflow during Holocene times. Maximum concentrations of phytoplankton biomarkers and biogenic opal were determined between 8.5 and 4 kyrs. BP, suggesting enhanced primary productivity triggered by increased inflow of nutrient-rich Pacific Water (and/or an increased nutrient input due to an ice-edge position). Short-lived peak values in productivity might be related to strong pulses of Pacific-Water input during this time period (cf., Ortiz et al., 2009). A seasonal sea-ice cover was present in the Chukchi Sea throughout the last 10 kyrs. During the last 3-4 kyrs. BP, the sea-ice cover significantly extended. References Belt, S.T. and Müller, J., 2013. The Arctic sea ice biomarker IP25: a review of current understanding, recommendations for future research and applications in palaeo sea ice reconstructions. Quaternary Science Review 73, 9-25. Ortiz, J. D., Polyak, L., Grebmeier, J. M., Darby, D., Eberl D. D., Naidu, S., Nof, D., 2009. Provenance of Holocene sediment on the Chukchi-Alaskan margin based on combined diffuse spectral reflectance and quantitative X-Ray Diffraction analysis. Global and Planetary Change 68, pp.73-84. Stein, R., Fahl, K., and Müller, J., 2012. Proxy Reconstruction of Cenozoic Arctic Ocean Sea-Ice History - from IRD to IP25. Polarforschung 82, 37-71.

Stein, Ruediger; Fahl, Kirsten; Matthiessen, Jens; Méheust, Marie; Nam, Seung-il; Niessen, Frank; Schade, Inka; Schreck, Michael; Wassmuth, Saskia; Xiao, Xiaotong

2014-05-01

232

Observing Young Variable Stars Using WFCAM at UKIRT  

NASA Astrophysics Data System (ADS)

We present the results from the analysis of 120 epoch time-series photometry of a 1 square degree region of the Lynds 1003 dark cloud in the Cygnus OB7 association. Using the Wide-Field imaging camera (WFCAM) on UKIRT we were able to obtain almost-nightly J,H,K' photometry over three observing seasons of over 100,000 stars with photometric uncertainty better than 0.02 mag in the range J=10-16 mags and better than 0.5 mag down to J=19.5. From the data we establish criteria for determining variability based on the least-varying sources. We report the discovery of both periodic and stochastic variability for a number of young T Tauri stars. We compare statistical properties of known cluster members with the general field population, and discuss physical models for some of the more interesting sources. This work was funded by the NSF REU program.

Rice, Thomas; Aspin, C.; Wolk, S. J.

2011-01-01

233

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

234

Modes of North Atlantic Decadal Variability in the ECHAM1\\/LSG Coupled Ocean-Atmosphere General Circulation Model  

Microsoft Academic Search

The climate variability in the North Atlantic sector is investigated in a 325-yr integration of the ECHAM1\\/ LSG coupled ocean-atmosphere general circulation model. At the interannual timescale, the coupled model behaves realistically and sea surface temperature (SST) anomalies arise as a response of the oceanic surface layer to the stochastic forcing by the atmosphere, with the heat exchanges both generating

Eduardo Zorita; Claude Frankignoul

1997-01-01

235

Solar Plasma Variability Observations from the Solar Dynamics Observatory  

NASA Technical Reports Server (NTRS)

The launch of the Solar Dynamics Observatory (SDO) in February 2010 allows for continuous observations of the Sun on all times scales from seconds to years. These variations in the solar plasma cause significant deviations in the Earth and space environments on similar time scales, such as affecting the atmospheric densities and composition of particular atoms, molecules, and ions in the atmospheres of the Earth and other planets. Presented and discussed will be examples of initial results using the data from SDO that show how we can trace the origins of solar activity from inside the Sun using different wavelengths, and therefore different temperatures (from 50,OOOK to 20MK+) that cover the atmosphere and plasma temperature range of the solar atmosphere. The presentation will emphasize how the Solar Dynamics Observatory (SDO), the first satellite in NASA's Living with a Star program, is going to improve upon current observations and provide further insights into the variable Sun and its Heliospheric influence.

Chamberlin, Phillip C.

2011-01-01

236

Modes of North Atlantic decadal variability in the ECHAM1\\/LSG ocean-atmo-sphere general circulation model  

Microsoft Academic Search

ABSTRACT The climate variability in the North Atlantic sector is investigated,in a 325-yr integration of the ECHAM1I LSG coupled ocean-atmosphere general circulation model. At the interannual timescale, the coupled model behaves,realistically and sea surface temperature,(SST) anomalies,arise as a response,of the oceanic,surface layer to the stochastic forcing by the atmosphere, with the heat exchanges both generating and damping the SST anomalies.

E. Zorita; C. Frankignoul

1997-01-01

237

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

238

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

239

The sensitivity of tree growth to air mass variability and the Pacific Decadal Oscillation in coastal Alabama  

NASA Astrophysics Data System (ADS)

A statistical learning method called random forests is applied to the prediction of transitions between weather regimes of wintertime Northern Hemisphere (NH) atmospheric low-frequency variability. A dataset composed of 55 winters of NH 700-mb geopotential height anomalies is used in the present study. A mixture model finds that the three Gaussian components that were statistically significant in earlier work are robust; they are the Pacific-North American (PNA) regime, its approximate reverse (the reverse PNA, or RNA), and the blocked phase of the North Atlantic Oscillation ( BNAO). The most significant and robust transitions in the Markov chain generated by these regimes are PNA ? BNAO, PNA ? RNA and BNAO ? PNA. The break of a regime and subsequent onset of another one is forecast for these three transitions. Taking the relative costs of false positives and false negatives into account, the random-forests method shows useful forecasting skill. The calculations are carried out in the phase space spanned by a few leading empirical orthogonal functions of dataset variability. Plots of estimated response functions to a given predictor confirm the crucial influence of the exit angle on a preferred transition path. This result points to the dynamic origin of the transitions.

Kondrashov, D.; Shen, J.; Berk, R.; D'Andrea, F.; Ghil, M.

2007-10-01

240

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

NASA Astrophysics Data System (ADS)

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

Boschat, Ghyslaine; Terray, Pascal; Masson, Sébastien

2011-09-01

241

OBSERVATIONS OF THERMAL FLARE PLASMA WITH THE EUV VARIABILITY EXPERIMENT  

SciTech Connect

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.; Doschek, George A. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Mariska, John T. [School of Physics, Astronomy, and Computational Sciences, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States)

2013-06-20

242

Explorin the Ocean-Atmosphere Interaction in Observed Surface Heat Flux Datasets and Coupled Model Forecasts for Recent Decades  

NASA Astrophysics Data System (ADS)

In regions of the Tropical Oceans where upwelling is not important, the dominant forcing of interannual variability is due to the surface heat flux. In order to simulate realistic interannual variability coupled models need to accurately represent the surface heat flux and its interaction with the evolving sea-surface temperature (SST) field. Based on order of magnitude the two dominant surface heat fluxes in the tropics are the solar and latent heat flux. The latter together with the sensible heat flux are due to turbulent processes and hence are known as turbulent fluxes. Here, we compare the turbulent heat fluxes from several observed products with those simulated by two seasonal forecasting systems. The local relationship between SST and turbulent heat fluxes is examined using the feedback parameter as defined by Frankignoul et al (1998). The observed datasets including NCEP/NCAR Reanalysis2 (Kanamitsu et al., 2002), GSSTF2 (Chou et al., 2003), ERA40 (Uppala et al., 2005), OAflux (Yu and Weller, 2007), and HOAPS3 (Andersson et al., 2007) are investigated. This analysis covers the period of 1988-2000. Some notable disagreements are found among these different observational datasets. In the South and the North Subtropical Atlantic, the satellite datasets, GSSTF2 and HOAPS3 indicate that the negative feedback in February-March-April season may be two times as strong as what the reanalysis datasets indicate. In the Subtropical Western North Pacific in the northern summer and fall, relatively weak negative or positive feedback is indicated by both satellite datasets, while the strong negative feedback is indicated by the other datasets. Strong negative feedback in the South Indian Ocean in May-June-July season is indicated by the two satellite datasets, while the other datasets indicate a negative feedback that is less than half as strong. The feedback parameter from two coupled forecast systems, the NCEP CFS (Saha et al., 2006) CGCM and a model based on the ECHAM4.5 AGCM (Roeker et al., 1996) coupled to a mixed layer ocean with Q-flux climatology are examined and compared with the observed datasets. The negative feedback parameters found in the CFS retrospective forecasts tend to be overestimated in the various regions and seasons. This tendency to overestimate the strength of the feedback parameter is found to be most severe around Southeastern marginal seas of Asia in May-June-July and August-September-October seasons and east of Australia in January-February-March. The feedback parameter estimated from the retrospective forecasts by ECHAM4.5 coupled to a mixed layer ocean agrees with the observed estimates, except that the negative feedback parameters are underestimated in regions where strong thermal interaction is expected during winter months.

Lee, D.; Dewitt, D. G.

2008-12-01

243

Field Observations of Soil Moisture Variability across Scales  

NASA Technical Reports Server (NTRS)

In this study, over 36,000 ground-based soil moisture measurements collected during the SGP97, SGP99, SMEX02, and SMEX03 field campaigns were analyzed to characterize the behavior of soil moisture variability across scales. The field campaigns were conducted in Oklahoma and Iowa in the central USA. The Oklahoma study region is sub-humid with moderately rolling topography, while the Iowa study region is humid with low-relief topography. The relationship of soil moisture standard deviation, skewness and the coefficient of variation versus mean moisture content was explored at six distinct extent scales, ranging from 2.5 m to 50 km. Results showed that variability generally increases with extent scale. The standard deviation increased from 0.036 cm3/cm3 at the 2.5-m scale to 0.071 cm3/cm3 at the 50-km scale. The log standard deviation of soil moisture increased linearly with the log extent scale, from 16 m to 1.6 km, indicative of fractal scaling. The soil moisture standard deviation versus mean moisture content exhibited a convex upward relationship at the 800-m and 50-km scales, with maximum values at mean moisture contents of roughly 0.17 cm3/cm3 and 0.19 cm3/cm3, respectively. An empirical model derived from the observed behavior of soil moisture variability was used to estimate uncertainty in the mean moisture content for a fixed number of samples at the 800-m and 50-km scales, as well as the number of ground-truth samples needed to achieve 0.05 cm3/cm3 and 0.03 cm3/cm3 accuracies. The empirical relationships can also be used to parameterize surface soil moisture variations in land surface and hydrological models across a range of scales. To our knowledge, this is the first study to document the behavior of soil moisture variability over this range of extent scales using ground-based measurements. Our results will contribute not only to efficient and reliable satellite validation, but also to better utilization of remotely sensed soil moisture products for enhanced modeling and prediction.

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

2008-01-01

244

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

245

Multi-decadal aerosol variations from 1980 to 2009: a perspective from observations and a global model  

NASA Astrophysics Data System (ADS)

Aerosol variations and trends over different land and ocean regions from 1980 to 2009 are analyzed with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and observations from multiple satellite sensors and available ground-based networks. Excluding time periods with large volcanic influence, aerosol optical depth (AOD) and surface concentration over polluted land regions generally vary with anthropogenic emissions, but the magnitude of this association can be dampened by the presence of natural aerosols, especially dust. Over the 30-year period in this study, the largest reduction in aerosol levels occurs over Europe, where AOD has decreased by 40-60% on average and surface sulfate concentrations have declined by a factor of up to 3-4. In contrast, East Asia and South Asia show AOD increases, but the relatively high level of dust aerosols in Asia reduces the correlation between AOD and pollutant emission trends. Over major dust source regions, model analysis indicates that the change of dust emissions over the Sahara and Sahel has been predominantly driven by the change of near-surface wind speed, but over Central Asia it has been largely influenced by the change of the surface wetness. The decreasing dust trend in the North African dust outflow region of the tropical North Atlantic and the receptor sites of Barbados and Miami is closely associated with an increase of the sea surface temperature in the North Atlantic. This temperature increase may drive the decrease of the wind velocity over North Africa, which reduces the dust emission, and the increase of precipitation over the tropical North Atlantic, which enhances dust removal during transport. Despite significant trends over some major continental source regions, the model-calculated global annual average AOD shows little change over land and ocean in the past three decades, because opposite trends in different land regions cancel each other out in the global average, and changes over large open oceans are negligible. This highlights the necessity for regional-scale assessment of aerosols and their climate impacts, as global-scale average values can obscure important regional changes.

Chin, M.; Diehl, T.; Tan, Q.; Prospero, J. M.; Kahn, R. A.; Remer, L. A.; Yu, H.; Sayer, A. M.; Bian, H.; Geogdzhayev, I. V.; Holben, B. N.; Howell, S. G.; Huebert, B. J.; Hsu, N. C.; Kim, D.; Kucsera, T. L.; Levy, R. C.; Mishchenko, M. I.; Pan, X.; Quinn, P. K.; Schuster, G. L.; Streets, D. G.; Strode, S. A.; Torres, O.; Zhao, X.-P.

2014-04-01

246

Modeling decadal variability of the Baltic Sea: 1. Reconstructing atmospheric surface data for the period 1902–1998  

Microsoft Academic Search

A statistical model is developed to reconstruct atmospheric surface data for the period 1902–1998 to force a coupled sea ice-ocean model of the Baltic Sea. As the response timescale of the Baltic Sea on freshwater inflow is of the order of 30–40 years, climate relevant model studies should cover at least century-long simulations. Such an observational atmospheric data set is

F. Kauker; H. E. M. Meier

2003-01-01

247

Modeling decadal variability of the Baltic Sea: 1. Reconstructing atmospheric surface data for the period 1902-1998  

Microsoft Academic Search

A statistical model is developed to reconstruct atmospheric surface data for the period 1902-1998 to force a coupled sea ice-ocean model of the Baltic Sea. As the response timescale of the Baltic Sea on freshwater inflow is of the order of 30-40 years, climate relevant model studies should cover at least century-long simulations. Such an observational atmospheric data set is

F. Kauker; H. E. M. Meier

2003-01-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

249

Interannual to decadal variability in a control experiment using MIROC4 - a high-resolution AOGCM for the near-term climate prediction  

NASA Astrophysics Data System (ADS)

Preliminary results, especially mean climate and interannual to decadal variability, in a general circulation climate model, Model for Interdisciplinary Research on Climate (MIROC) version 4, are presented. The model is developed by the Center for Climate System Research (CCSR), the University of Tokyo; National Institute for Environmental Studies (NIES); and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). MIROC4 is an updated model from the previous version MIROC3_hires, which was used to contribute to the IPCC AR4. Most of the model components are the same as MIROC3_hires, but the atmospheric component is changed to T213 spectrum model from T106 one to inform adaptation policies for near-term climate changes. The ocean component is the same as that used in MIROC3_hires, whose horizontal resolution is 0.28125° zonally and 0.1875° meridionally, while the latitudinal range where the Gent-McWilliams (GM) parameterization is applied is changed in order to improve the climatological distribution of SST. The other components, sea ice, land surface process, and river routing models, are also same as the previous model. To obtain the radiative balance, parameters associated with radiation, clouds, and aerosols are tuned. Using this model, spin-up and control experiments (120 years) under the condition of year 1950 without flux adjustment were conducted. Globally averaged 2-m temperature (T2) and SST are not drifted, and biases in the SST field, typically warm bias in the high-latitudes and cold bias in the low- and mid-latitudes, are reduced in MIROC4, especially in the Northern Hemisphere. Associated with the reduction of the warm SST bias in the high-latitudes, sea ice in the Northern Hemisphere becomes thicker in MIROC4 than MIROC3_hires. The Atlantic meridional overturning circulation (AMOC) is relatively weak in MIROC4, and mean volume transport of the North Atlantic Deep Water (NADW) is 12-13 Sv (Sv?106 m3/s), which is 1-2 Sv weaker than that obtained by MIROC3_hires. However, the 120-year integration is not enough to spin-up AMOC, and the NADW transport will be greater in the end of the control experiment. Simulated ENSO signal in MIROC4 is improved. The standard deviation of the Niño-3 index in MIROC3_hires was 0.33, but that in MIROC4 it is 0.57 (observation ~ 0.8). Not only the Niño indices, but also distribution of ENSO related fields, e.g. PNA pattern, are better simulated than MIROC3_hires. The time series of PDO obtained as the EOF1 of low-pass filtered (7 years) SST over the Pacific shows that a 20-year variation is dominant, and explains 37% of the total variance in the MIROC4. Its spatial distribution becomes more realistic than that in MIROC3_hires. Currently, only the spin-up and control experiments are finished using MIROC4. We will conduct near-term climate prediction experiments for the coming decades to contribute for CMIP5/IPCC AR5.

Sakamoto, Takashi T.; Komuro, Yoshiki; Ishii, Masayoshi; Tatebe, Hiroaki; Hasegawa, Akira; Shiogama, Hideo; Toyoda, Takahiro; Mori, Masato; Kimoto, Masahide

2010-05-01

250

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

251

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

252

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

USGS Publications Warehouse

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

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

2007-01-01

253

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

SciTech Connect

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

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

1998-09-01

254

Variability of Titan's induced magnetotail: Cassini magnetometer observations  

NASA Astrophysics Data System (ADS)

We study the structure and variability of Titan's magnetotail by analyzing Cassini magnetic field observations from all tail crossings between 2005 and 2013. Titan's magnetotail is strongly affected by fluctuations in the ambient magnetospheric field conditions. Therefore, even Titan flybys with nearly identical trajectories may reveal a completely different location and strength of the perturbations in the moon's tail. Short-scale variations of the ambient magnetospheric field may cause a "fragmentation" of Titan's magnetic lobes, as also seen in Cassini Plasma Spectrometer ion data. By transforming the magnetic field perturbations detected during all available tail crossings to the Draping Coordinate System, we identified the following general characteristics of Titan's plasma interaction: (1) Perpendicular to the background magnetic field and the corotation direction, Titan's magnetotail is confined to a narrow region with a diameter of about 5 Titan radii. Thus, Titan's tail exhibits a rather "flat" structure reminiscent of a delta wing. (2) The plasma incident upon Titan does not possess a significant velocity component along the Saturn-Titan line. (3) The nonzero component of the background field along the corotation direction generates an asymmetry of Titan's magnetotail which clearly manifests in Cassini magnetometer data.

Simon, Sven; Neubauer, Fritz M.; Wennmacher, Alexandre; Dougherty, Michele K.

2014-03-01

255

Atmospheric Variability of CO2 impact on space observation Requirements  

Microsoft Academic Search

If International governments are to reduce GHG levels by 80% by 2050, as recommended by most scientific bodies concerned with avoiding the most hazardous changes in climate, then massive investments in infrastructure and new technology will be required over the coming decades. Such an investment will be a huge commitment by governments and corporations, and while it will offer long-term

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

2009-01-01

256

A Decadal Climate Cycle in the North Atlantic Ocean as Simulated by the ECHO Coupled GCM  

Microsoft Academic Search

In this paper a decadal climate cycle in the North Atlantic that was derived from an extended-range integration with a coupled ocean-atmosphere general circulation model is described. The decadal mode shares many features with the observed decadal variability in the North Atlantic. The period of the simulated oscillation, however, is somewhat longer than that estimated from observations. While the observations

A. Grötzner; M. Latif; T. P. Barnett

1998-01-01

257

Non-stationary relationships between decadal water storage changes over Australia and climate variability of the El Niño Southern Oscillation and Indian Ocean Dipole  

NASA Astrophysics Data System (ADS)

Large-scale ocean-atmosphere interactions are hypothesized as the main drivers of water variations over the Australian continent. This study examines the relative contributions of the large-scale ocean-atmospheric processes in different time-scale variations of terrestrial water storage (TWS) over Australia. The aim is to determine whether the role of main climatic phenomena such as the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on water resources as appears to be a stationary relationship. The main analyses were performed on three decades (1982-2012) of: (i) TWS changes over Australia from the World Wide Water Resources Assessment (W3RA) hydrological model, and (ii) statistically reconstructed TWS changes from the Gravity Recovery And Climate Experiment (GRACE) products. Reconstructions were derived by applying low-degree autoregressive models to relate basin averaged TWS changes, over the nine major river drainage basins of Australia, to input values of precipitation minus evaporation as well as the ENSO and IOD indices. Our results indicate that both intra-annual and seasonal simulation and forecast of TWS water storage changes associated with ENSO cycles have increased during the last two decades of 1990 to 2010. The contribution of IOD to seasonal simulation and forecasts of TWS appears to have increased over the last decade. The long-term influence of IOD in TWS changes, however, appears to have decreased slightly. Our results demonstrate non-stationary behaviour of TWS in terms of variability and predictability due to the ENSO and IOD phenomena. Keywords: Australia; ENSO and IOD in Water Storage; Reconstruction; Non-stationary Impact

Forootan, Ehsan; Kusche, Jürgen; van Dijk, Albert; Awange, Joseph; Schumacher, Maike; Longuevergne, Laurent

2014-05-01

258

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

259

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

260

Two Decades of Global and Regional Sea Level Observation from the ESA Climate Change Initiative Sea Level Project  

NASA Astrophysics Data System (ADS)

Sea level is a very sensitive index of climate change and variability. Sea level integrates the ocean warming, mountain glaciers and ice sheet melting. Understanding the sea level variability and changes implies an accurate monitoring of the sea level variable at climate scales, in addition to understanding the ocean variability and the exchanges between ocean, land, cryosphere, and atmosphere. That is why Sea Level is one of the Essential Climate Variables (ECV) selected in the frame of the ESA Climate Change Initiative (CCI) program. This program aims at providing long-term satellite-based products for climate (ECV products), that should be used by the climate research community. This program has just completed its first phase (Oct. 2010 to Dec. 2013) and will start in February 2014 the second phase of 3 years. The objective of the second phase are similar: to involve the climate research community to refine their needs and collect their feedbacks on product quality, to develop, test and select the best algorithms and standards to generate an updated climate time series and to produce and validate the Sea Level ECV product. This will better answer the climate user needs by improving the quality of the Sea Level products and maintain a sustain service for an up-to-date production. We will firstly present the main achievements of the ESA CCI Sea Level Project. On the one hand, the major steps required to produce the 18 years climate time series (delivered in Sept. 2012) are briefly described: collect and refine the user requirements, development of adapted algorithms for climate applications and specification of the production system. On the other hand, the product characteristics are described as well as the results from product validation, performed by several groups of the ocean and climate modeling community. At last, the work plan and key challenges of the second phase of the project are described.

Larnicol, Gilles; Cazenave, Anny; Ablain, Michael; Legeais, JeanFrancois; Faugere, Yannice; Benveniste, Jerome; Lucas, Bruno; Dinardo, Salvatore; Johannessen, Johnny; Stammer, Detlef; Timms, Gary; Knudsen, Per; Cipollini, Paolo; Roca, Monica; Rudenko, Sergei; Fernandes, Joana; Balmaseda, Magdalena; Guinle, Thierry

2014-05-01

261

CME-driven Shock Simulations and Observations: Variability of SEP Abundances, Mechanisms, and Validation  

NASA Astrophysics Data System (ADS)

In the past decade, much progress has been made by way of satellite observations regarding the origin and acceleration mechanisms of solar energetic particles (SEPs). In comparison, relatively little work has been done on the side of event-based simulations. In particular in the context of developing quantitative models of SEP fluxes and spectra, it is of great concern to understand their intrinsic possible variability, and to address the question whether the prevalence and efficiency of different contributing mechanisms can be estimated or predicted. Using ACE data, we have selected a number of characteristic "energetic storm particle" (ESP) events, i.e., SEP events in which the CME-driven shock passes the spacecraft, to compare observed local proton flux profiles with those obtained from large-scale hybrid simulations (kinetic ions, electron fluid). The events were selected for relatively undisturbed solar wind, isolation from other events, and flux profiles that clearly indicate local shock acceleration. Interestingly, in the sub-MeV range, we find very little variation of peak proton fluxes with shock normal angle. In our simulations we have investigated the role of seed particles, the acceleration processes at oblique shocks, and other effective mechanisms such as mirroring of energetic ions in downstream converging fields. In addition, shock curvature on various scales can play a role. Via direct comparison with the observed events, we discuss the pertinent acceleration mechanisms and the feasibility of predicting their respective, relative importance and occurrence.

Krauss-Varban, D.; Li, Y.; Luhmann, J. G.

2007-12-01

262

Observation of spiciness interannual variability in the Pacific pycnocline  

NASA Astrophysics Data System (ADS)

Monthly gridded fields predominantly based on global Argo in situ temperature and salinity data are used to analyze the density-compensated anomaly of salinity (spiciness anomaly) in the pycnocline of the subtropical and tropical Pacific Ocean between 2004 and 2011. Interannual variability in the formation, propagation and fate of spiciness anomalies are investigated. The spiciness anomalies propagate on the isopycnal surface??= 25.5 along the subtropical-tropical pycnocline advected by the mean currents. They reach the Pacific Western Tropics in about 5-6 years in the Southern Hemisphere and about 7-8 years in the Northern Hemisphere. Their amplitude strongly diminishes along the way and only very weak spiciness anomalies seem to reach the equator in the Western Tropics. A complex-EOF analysis of interannual salinity anomalies on??= 25.5 highlights two dominant modes of variability at interannual scale: i) the former shows a variability of 5-7 years predominant in the Northern Hemisphere, and ii) the latter displays an interannual variability of 2 to 3 years more marked in the Southern Hemisphere. The significant correlation of this second mode with ENSO index suggests that spiciness formation in the southeastern Pacific (SEP) is affected by ENSO tropical interannual variability. A diagnosis of the mechanisms governing the interannual generation of spiciness in the SEP region leads the authors to suggest that the spiciness interannual variability in the sub-surface is linked to the equatorward migration of the isopycnal outcrop line?? = 25.5 into the area of maximum salinity. Quantitative analysis based on Turner angle reveals the dominance of the spiciness injection mechanism occurring through convective mixing at the base of mixed layer.

Kolodziejczyk, Nicolas; Gaillard, Fabienne

2012-12-01

263

Observation of spiciness interannual variability in the Pacific pycnocline  

NASA Astrophysics Data System (ADS)

Monthly gridded fields predominantly based on global Argo in situ temperature and salinity data are used to analyze the density-compensated anomaly of salinity (spiciness anomaly) in the pycnocline of the subtropical and tropical Pacific Ocean between 2004 and 2011. Interannual variability in the formation, propagation and fate of spiciness anomalies are investigated. The spiciness anomalies propagate on the isopycnal surface ?? = 25.5 along the subtropical-tropical pycnocline advected by the mean currents. They reach the Pacific Western Tropics in about 5-6 years in the Southern Hemisphere and about 7-8 years in the Northern Hemisphere. Their amplitude strongly diminishes along the way and only very weak spiciness anomalies seem to reach the equator in the Western Tropics A complex-EOF analysis of interannual salinity anomalies on ?? = 25.5 highlights two dominant modes of variability at interannual scale: i) the former shows a variability of 5-7 years predominant in the Northern Hemisphere, and ii) the latter displays an interannual variability of 2 to 3 years more marked in the Southern Hemisphere. The significant correlation of this second mode with ENSO index suggests that spiciness formation in the South-Eastern Pacific (SEP) is affected by ENSO tropical interannual variability. A diagnosis of the mechanisms governing the interannual generation of spiciness in the SEP region leads the authors to suggest that the spiciness interannual variability in the sub-surface is linked to the equatorward migration of the isopycnal outcrop line ?? = 25.5 into the area of maximum salinity. Quantitative analysis based on Turner angle reveals the dominance of the spiciness injection mechanism occurring through convective mixing at the base of mixed layer.

Kolodziejczyk, Nicolas; Gaillard, Fabienne

2013-04-01

264

Variability of temperature-derived climate indices in the Arctic - Observation and Regional Climate Model  

NASA Astrophysics Data System (ADS)

The Arctic has now generally been accepted as an area very sensitive to climate change. This includes changes in climate extremes. As extreme climate events directly impact on the residents, their investigation is important to understand ecological and societal changes. In this study, the focus is on understanding of the climate variability of extremes on a regional level. The work presented here aims at providing results for temperature-based climate indices over the Arctic. On one hand, it is based on the ERA40 reanalysis data from ECMWF and Russian station data from the "Global Summary of the Day" data set provided by NCDC. On the other hand, output from the regional climate model (RCM) HIRHAM, applied over the Arctic domain, was used. The period 1958-2008 was analyzed. The detailed regional analysis for the Russian Arctic has its background in the EU project CARBO-North (http://www.carbonorth.net/) which aims at quantifying the carbon budget in Northern Russia. Various climate indices were calculated from the data described above. Frost days and growing degree days are presented here, as examples of the analysis. The spatial analysis of frost days over the Arctic domain derived from ERA40 data clearly signs to a warming along the sea ice boundaries in both transition seasons. Over land, few areas with increasing frost days were found. Frost days show a high inter-annual variability; therefore only few significant trends could be calculated. Distinct regional differences in the variability as well as in the amount of frost days are dicussed in the comparison of eastern and western Russian stations. The analysis of frost days calculated from HIRHAM output shows that the model captures both the spatial patterns and the year-to-year variability from the observations, though it overestimates their numbers over most of the model domain. The simulated trends are in adequate agreement with those from the observations. The growing degree days as calculated from ERA40 data reflect the north-south temperature gradient in the Arctic and distinguishes the high mountain ranges in Alaska and eastern Siberia. Positive trends were calculated over most parts of the Arctic and are significant in some areas like northern Alaska and northeastern Canada. This is confirmed by the regional, station based analysis over Russia, though some of the calculated trends are not significant. Growing degree days are systematically underestimated by HIRHAM over the Arctic domain. However, the calculated spatial patterns as well as the trends and decadal-scale variability in the time series are well reproduced.

Matthes, Heidrun; Rinke, Annette; Dethloff, Klaus

2010-05-01

265

Subtropical gyre variability observed by ocean-color satellites  

Microsoft Academic Search

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

Charles R McClain; Sergio R Signorini; James R Christian

2004-01-01

266

Variability of Attention Processes in ADHD: Observations from the Classroom  

ERIC Educational Resources Information Center

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

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

2009-01-01

267

Sea state variability observed by high resolution satellite radar images  

NASA Astrophysics Data System (ADS)

The spatial variability of the wave parameters is measured and investigated using new TerraSAR-X (TS-X) satellite SAR (Synthetic Aperture Radar) images. Wave groupiness, refraction and breaking of individual wave are studied. Space borne SAR is a unique sensor providing two dimensional information of the ocean surface. Due to its daylight, weather independency and global coverage, the TS-X radar is particularly suitable for many ocean and coastal observations and it acquires images of the sea surface with up to 1m resolution; individual ocean waves with wavelength below 30m are detectable. Two-dimensional information of the ocean surface, retrieved using TS-X data, is validated for different oceanographic applications: derivation of the fine resolved wind field (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). The algorithms are capable to take into account fine-scale effects in the coastal areas. This two-dimensional information can be successfully applied to validate numerical models. For this, wind field and sea state information retrieved from SAR images are given as input for a spectral numerical wave model (wind forcing and boundary condition). The model runs and sensitivity studies are carried out at a fine spatial horizontal resolution of 100m. The model results are compared to buoy time series at one location and with spatially distributed wave parameters obtained from SAR. The comparison shows the sensitivity of waves to local wind variations and the importance of local effects on wave behavior in coastal areas. Examples for the German Bight, North Sea and Rottenest Island, Australia are shown. The wave refraction, rendered by high resolution SAR images, is also studied. The wave ray tracking technique is applied. The wave rays show the propagation of the peak waves in the SAR-scenes and are estimated using image spectral analysis by deriving peak wavelength and direction. The changing of wavelength and direction in the rays allows detecting underwater structures (banks, reefs, shallows) and to obtain bathymetry in case a well-developed swell is imaged. Further, wave energy flux propagation towards the coast and its dissipation are obtained using the wave ray technique: wave height and wavelength are derived from TS-X image spectrum. The height of individual breaking waves is obtained from SAR-image signatures and it is compared to the model results and the buoy measurements. The results show some lower amplitude of the breaking waves, when compared to model results in the shoaling zone. This effect could be explained by an actual stronger dissipation than the one given by the model in the investigated area (coral reefs). Wave groups are detected for a cross sea and in storm condition in the ocean. The parameters of the wave groups are investigated and the conditions, which are responsible for their origin, are studied by numerical simulation using spectral wave model.

Pleskachevsky, A.; Lehner, S.

2012-04-01

268

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

269

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

270

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

271

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

272

Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei  

NASA Technical Reports Server (NTRS)

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

Mushotzky, R. F.; Edelson, R.; Baumgartner, W. H.; Gandhi, P.

2012-01-01

273

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

NASA Astrophysics Data System (ADS)

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

Wang, K.; Dickinson, R. E.

2011-12-01

274

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

275

Surface solar radiation variability over Eastern Mediterranean: A high spatial resolution view from satellite and ground-based observations  

NASA Astrophysics Data System (ADS)

Surface Solar Radiation (SSR) has been measured for decades from ground-based observations for several spots around the planet. On the other hand, during the last decades, satellite observations made possible the assessment of the spatial variability of the SSR at a global as well as regional scale. In this study, a detailed view of the SSR spatiotemporal variability is presented at a high spatial resolution, focusing on the region of Eastern Mediterranean. This is a region of particular interest since it is affected by aerosols of various origins (continental, sea, dust and biomass burning particles) and encloses countries with significant socioeconomical changes during the last decades. The SSR satellite data used in this study have been obtained from the Satellite Application Facility on Climate Monitoring (CM SAF) (www.cmsaf.eu). The CM SAF SSR dataset is based on reflections in the visible channel of Meteosat First Generation, has a spatial resolution of 0.03ox0.03o and spans from 1983 to 2005. The satellite observations are validated against ground-based measurements for the city of Thessaloniki, a coastal city of ~1 million inhabitants in northern Greece, situated in the heart of Eastern Mediterranean. Measurements from two pyranometers, an Eppley Precision pyranometer (1983-1992) and a Kipp & Zonen CM-11 pyranometer (1993-2005), both located at the center of the city, were homogenized and a uniform time series for the 23 year period was constructed. SSR was also calculated with the use of MODIS level-2 aerosol and cloud satellite data for the region of Thessaloniki and the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model. These new satellite-based results are compared to both CM SAF and ground-based observations in order to examine whether SBDART and MODIS could be further used for the investigation of the spatial patterns of SSR in the area.

Alexandri, Georgia; Georgoulias, Aristeidis K.; Meleti, Charikleia; Balis, Dimitris

2013-04-01

276

Evidence of the recent decade change in global fresh water discharge and evapotranspiration revealed by reanalysis and satellite observations  

NASA Astrophysics Data System (ADS)

Variations of global evapotranspiration (ET) and fresh water discharge from land to oceans (D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation (Eo). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation.

Seo, K.; Waliser, D. E.; Tian, B.; Kim, B.; Park, S.; Cocke, S.; Ishii, M.

2012-12-01

277

Evidence of the recent decade change in global fresh water discharge and evapotranspiration revealed by reanalysis and satellite observations  

NASA Astrophysics Data System (ADS)

Variations of global evapotranspiration ( ET) and fresh water discharge from land to oceans ( D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation ( E o ). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation.

Seo, Ki-Weon; Waliser, Duane E.; Tian, Baijun; Kim, Baek-Min; Park, Seong-Chan; Cocke, Steve; Sohn, Byung-Ju; Ishii, Masayoshi

2012-05-01

278

Variability in the Io torus as observed by Cassini UVIS  

Microsoft Academic Search

We present observations of the Io torus made by the Cassini Ultraviolet Imaging Spectrograph (UVIS) during the first half (4-Oct-2000-14-Nov-2000) of the inbound leg of the Cassini Jupiter flyby. During this period, 49 rotations of the Jovian magnetosphere were observed, resulting in nearly 2000 spectra, covering a wavelength range of 561-1182Å. The UVIS field of view encompasses the entire Io

A. J. Steffl; F. Bagenal; A. I. F. Stewart; P. A. Delamere

2003-01-01

279

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.

Alvarez-Mozos, Jesus; Verhoest, Niko E.C.; Larranaga, Arantzazu; Casali, Javier; Gonzalez-Audicana, Maria

2009-01-01

280

Observational constraints on pulsars: Location of the emission region and pulse shape stability on decade time scales  

SciTech Connect

Twenty years after their discovery, many basic problems in pulsar physics remain unsolved. Plasma flow patterns along with the associated radio emission and energy loss mechanisms remain a mystery. The dynamical behavior of the neutron star spin rate has been explored via timing analyses but the presence of precession or wandering of the spin axis remain largely unconstrained. The possibility of surface activity such as plate tectonics or volcanism remains open. Observational limits are placed on these phenomena. An introduction is given to pulsars, with an emphasis on the aspects relevant to the remainder of the thesis. The implications of polar cap models are explored within the context of special relativity. Under fairly general conditions, it is found that the suppositions of polar cap models imply a time delay between the centroids of the intensity waveform and the polarization profile with the polarization profile lagging the intensity waveform.

Blaskiewicz, M.M.

1991-01-01

281

Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei  

NASA Astrophysics Data System (ADS)

Over three quarters in 2010-2011, Kepler monitored optical emission from four active galactic nuclei (AGNs) with ~30 minute sampling, >90% duty cycle, and lsim0.1% repeatability. These data determined the AGN optical fluctuation power spectral density (PSD) functions over a wide range in temporal frequency. Fits to these PSDs yielded power-law slopes of -2.6 to -3.3, much steeper than typically seen in the X-rays. We find evidence that individual AGNs exhibit intrinsically different PSD slopes. The steep PSD fits are a challenge to recent AGN variability models but seem consistent with first-order magnetorotational instability theoretical calculations of accretion disk fluctuations.

Mushotzky, R. F.; Edelson, R.; Baumgartner, W.; Gandhi, P.

2011-12-01

282

Infrared and sub-mm observations of cataclysmic variables  

NASA Astrophysics Data System (ADS)

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

Evans, A.

2010-11-01

283

Equatorial F2 characteristic variability: A review of recent observations  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

284

Spatiotemporal Variability and Propagation of Equatorial Noise Observed by Cluster  

NASA Technical Reports Server (NTRS)

We report a multipoint case study of the electromagnetic equatorial noise observed by the Cluster project. High-resolution data were measured in three close points in space located in the morning sector of the outer plasmasphere. We demonstrate a narrow latitudinal extent of the emissions with a typical width of 2 degrees, centered near the minimum-B equator. Power spectra recorded by the different satellites show a complex structure of emission lines whose relative intensities and positions vary at timescales of 1-2 min and/or at spatial scales of tens of wavelengths. These lines do not match harmonics of the local proton cyclotron frequency, as it would be expected if the waves are generated by energetic ions and observed near the source region. We bring observational evidence that the waves propagate with a significant radial component and thus can propagate from a distant generation region located at different radial distances where ion cyclotron frequencies match the observed fine structure.

Santolik, O.; Pickett, J. S.; Gurnett, D. A.; Maksimovic, M.; Cornilleau-Wehrlin, N.

2002-01-01

285

The Semiregular Variable Star Observing Program at Grinnell College  

NASA Astrophysics Data System (ADS)

A large body of photometric and spectroscopic data on 38 semiregular variable stars has been acquired at the Grant O. Gale Observatory of Grinnell College since 1984. This includes V and B band photoelectric photometry, CCD spectroscopic monitoring, and a large set of spectra for RS Cygni. The stars in the program were selected because they had a history of “quiescent episodes” in their pulsations that might be explained as mode switches. Time-dependent Fourier analysis has been applied to the photometric data to reveal the dominant frequency components represented in the light curves and to investigate how the strengths of those components vary - sometimes quite abruptly - over time. The spectroscopic monitoring of the entire set of stars is an ongoing project. The 413 RS Cygni spectra have been used to explore the variation of spectral features with phase. The conspicuous dip near the peak of the RS Cygni light curve does not appear to be associated with obvious variations in the strengths of spectral features.

Cadmus, Robert R.

2014-06-01

286

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

287

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

288

Spectrographic observations of the suspected Delta Scuti variable Beta Ari.  

NASA Astrophysics Data System (ADS)

Three sets of spectra (in all 85 spectra) of the well-known standard and high eccentricity spectroscopic binary star Beta Ari were taken with the Boller and Chivens grating spectrograph applied to the 137 cm reflector of the Merate Astronomical Observatory. The analysis of the radial velocities RV and equivalent widths W? of hydrogen and metal lines shows periodic variations similar to those of some classical Delta Scuti stars. The variations of the asymmetries of the profiles of H and Ca II K lines linked to the variations of the RV seem to recall the Schuster effect observed in classical Cepheids. A periastron effect appears from: (1) increased amplitudes of the RV curves, (2) remarkable variations of the average W? curves, (3) strong positive asymmetry (blue wing larger than red wing) in the H? and Ca II K lines.

di Belgioso, A. B.; Fracassini, M.; Pasinetti, L. E.; Stroppa, P.

1983-07-01

289

One decade of parallel fine (PM2.5) and coarse (PM10-PM2.5) particulate matter measurements in Europe: trends and variability  

NASA Astrophysics Data System (ADS)

The trends and variability of PM10, PM2.5 and PMcoarse concentrations at seven urban and rural background stations in five European countries for the period between 1998 and 2010 were investigated. Collocated or nearby PM measurements and meteorological observations were used in order to construct Generalized Additive Models, which model the effect of each meteorological variable on PM concentrations. In agreement with previous findings, the most important meteorological variables affecting PM concentrations were wind speed, wind direction, boundary layer depth, precipitation, temperature and number of consecutive days with synoptic weather patterns that favor high PM concentrations. Temperature has a negative relationship to PM2.5 concentrations for low temperatures and a positive relationship for high temperatures. The stationary point of this relationship varies between 5 and 15 °C depending on the station. PMcoarse concentrations increase for increasing temperatures almost throughout the temperature range. Wind speed has a monotonic relationship to PM2.5 except for one station, which exhibits a stationary point. Considering PMcoarse, concentrations tend to increase or stabilize for large wind speeds at most stations. It was also observed that at all stations except one, higher PM2.5 concentrations occurred for east wind direction, compared to west wind direction. Meteorologically adjusted PM time series were produced by removing most of the PM variability due to meteorology. It was found that PM10 and PM2.5 concentrations decrease at most stations. The average trends of the raw and meteorologically adjusted data are -0.4 ?g m-3 yr-1 for PM10 and PM2.5 size fractions. PMcoarse have much smaller trends and after averaging over all stations, no significant trend was detected at the 95% level of confidence. It is suggested that decreasing PMcoarse in addition to PM2.5 can result in a faster decrease of PM10 in the future. The trends of the 90th quantile of PM10 and PM2.5 concentrations were examined by quantile regression in order to detect long term changes in the occurrence of very large PM concentrations. The meteorologically adjusted trends of the 90th quantile were significantly larger (as an absolute value) on average over all stations (-0.6 ?g m-3 yr-1).

Barmpadimos, I.; Keller, J.; Oderbolz, D.; Hueglin, C.; Prévôt, A. S. H.

2012-04-01

290

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

291

Spectrographic observations of the suspected Delta Scuti variable Beta Ari  

NASA Astrophysics Data System (ADS)

Three sets of spectra (85 spectra in all) of the well-known standard and high eccentricity spectroscopic binary star Beta Ari are taken with the Boller and Chivens grating spectrograph (29 and 35 A/mm) applied to a 137-cm reflector. The sets were taken during the periastron passage of November 14-15, 1976, after the periastron passage of October 2-3, 1977, and before the apastron passage of November 23, 1977. An analysis of the radial velocities and equivalent widths of hydrogen and metal lines reveals periodic variations similar to those of certain classical Delta Scuti stars. The variations of the asymmetries of the profiles of H and Ca II K lines, linked to the variations of the radial velocities, are thought to suggest the Schuster effect observed in classical Cepheids. There are three indications of a periastron effect. The first is in the increased amplitudes of the radial velocity curves; the second is in the remarkable variations of the averaged equivalent width curves; and the third is in the strong positive asymmetry (with the blue wing larger than the red wing) in the H-gamma and Ca II K lines.

Barbiano di Belgioso, A.; Fracassini, M.; Pasinetti, L. E.; Stroppa, P.

1983-07-01

292

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

293

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

294

Sodium lidar observed variability in mesopause region temperature and horizontal wind: Planetary wave influence and tidal-gravity wave interactions  

NASA Astrophysics Data System (ADS)

The CSU sodium lidar system at Fort Collins, CO (40.6N, 105W), after a decade of mesopause temperature observation was upgraded in 1999 from a one-beam system to a two-beam system, capable of simultaneous and continuous observations of mesopause region temperature, zonal wind, and meridional wind, over full diurnal cycles, weather permitting. The regular observation under this operation mode started in May 2002. The valuable datasets could be used to study not only the tidal day-to-day variability but also planetary waves and gravity waves. Analysis of our longest dataset near fall equinox in 2003 (September 2003 campaign) reveals the dramatic tidal day-to-day variability with 2-fold increase in tidal amplitudes in all three fields during UT day 267 and 268. Further TIME-GCM (Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model) study and comparison between lidar observed temperature and the SABER observed global temperature field suggest that both tidal/planetary wave interactions and tidal/gravity wave interactions play an important role for the tidal amplitude enhancement. Though detailed causes for tidal variability require further study, we have demonstrated that substantial information on MLT dynamics may be obtained from a comprehensive long-period data set. Three near 80hr continuous datasets in consecutive summers of 2002, 2003, 2004 give us the opportunities to study summer quasi-two-day waves (QTD) with the possible modulation of Quasi-Biannual Oscillation (QBO) on QTD wave amplitude. Comparisons between the QTD wave amplitudes of temperature observed by lidar and SABER for all three campaigns show very good agreement. A strong winter mesospheric temperature inversion layer (MIL) was observed by our sodium lidar in December 2004 campaign. Studies of this event reveal the strong MIL which is consistent with mean state and tidal/gravity wave interactions. The observed dramatic tidal amplitude increase in day 338 is the result of such wave-wave interactions.

Li, Tao

295

Ultraviolet observations of extensive variability in the stellar wind of Xi Persei  

NASA Technical Reports Server (NTRS)

A detailed case study of variability in the stellar wind of the O7.5 III star Xi Persei is presented based on 56 high-resolution IUE observations taken between 1978 and 1984. Profile-fitting techniques are described, and possible interpretations for the observed Si IV variability are discussed. The derived properties of the narrow and broad discrete absorption features are given along with other P Cygni profile characteristics, including emission-to-absorption ratios and mass-loss rates. The role of ionization conditions and episodic formation of shells in accounting for the variability is addressed together with some previously reported observations of Xi Per.

Prinja, Raman K.; Howarth, Ian D.; Henrichs, Huib F.

1987-01-01

296

Interannual variability in the atmosphere-biosphere CO2 exchange as simulated by a process-based model for the last decades  

NASA Astrophysics Data System (ADS)

Atmosphere-biosphere CO2 exchange induces not only seasonal oscillation but also interannual change in the atmospheric CO2 concentration. Actually, in 1998, atmospheric CO2 concentration increased at a remarkably high rate, while the growth rate was apparently depressed in 1992 and 1993. Elucidating whether these anomalies were attributable to the ocean or the terrestrial biosphere is an important challenge for carbon cycle researchers. In this study, a process-based model of terrestrial carbon dynamics (Sim-CYCLE) was constructed and used to simulate the terrestrial carbon balance for the period from 1953 to 1999. Climatic variables related to ecosystem processes were derived from the U.S NCEP/NCAR-reanalysis data (T62 spatial resolution), and the Matthews's biome map was adopted. The atmospheric CO2 fertilization effect during the experimental period was also considered in the simulation analysis. Sim-CYCLE includes five carbon compartments (leaves, stems, roots, litter, and humus), and calculates fluxes among them at a monthly step, with taking environmental regulations into account. Accordingly, I could obtain a time-series of net carbon budget, i.e. net ecosystem production (NEP), on the global scale. Through the experimental period, global annual NEP exhibited a considerable interannual variability ranging from +2.0 Pg C in 1971 to ?2.5 Pg C in 1998 (SD 1.1 Pg C yr-1). Tropical ecosystems were most responsible for the interannual variability, especially in such ENSO years as 1973, 1983, and 1998. The estimated NEP anomalies were negatively correlated with surface temperature anomaly, due to the high sensitivity of respiration and decomposition to temperature. Thus, it is inferred that higher temperatures induced by the strong 1997-98 ENSO event would lead to extra CO2 emission and consequently the largest negative NEP anomaly. The estimated responsiveness of terrestrial carbon budget seems enough large to cause anomalies in atmospheric CO2 concentration. However, it should be examined (1) whether the estimated NEP anomalies are consistent with atmospheric observations and oceanic budget, and (2) whether the responsiveness seen in the interannual change is applicable to the future global change.

Ito, A.

2001-05-01

297

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

2014-05-01

298

Decadal Comparison of Plankton Levels  

NSDL National Science Digital Library

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

Thomson, Joycelyn; Gregg, Watson

2002-08-08

299

An Observational Study of Line-Profile Variable B-stars in Multiple Systems  

NASA Astrophysics Data System (ADS)

We present the results of an observational study of the pulsational behavior of the line-profile variable binary components of ? Sco, ? Sco and ? Lup. Our research is situated in the framework of a systematic long-term project targeting line-profile variable B-stars in close binaries, with the aim to search for tidally enhanced oscillations.

Uytterhoeven, K.

2007-03-01

300

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

301

Identification of Variable Stars in COROT's First Main Observing Field (LRc1)  

Microsoft Academic Search

The COROT space mission will monitor several target fields for up to 150 days to perform asteroseismology and to search for extrasolar planets by photometric transits. Variable stars in the target fields are important objects for additional scientific studies but can also disturb the search for planetary transits. A variability characterization of the target fields prior to COROT observations is

C. Karoff; H. Rauer; A. Erikson; H. Voss; P. Kabath; T. Wiese; M. Deleuil; C. Moutou; J. C. Meunier; H. Deeg

2007-01-01

302

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

303

Analysis of AAVSO visual observations of ten small-amplitude red variables  

NASA Astrophysics Data System (ADS)

We have studied the periodicity of the following ten small-amplitude red variables, using Fourier analysis and autocorrelation analysis of AAVSO visual observations: RZ Arietis, Rho Persei, IN Hydrae, FS Comae Berenices, W Bootis, EU Delphini, R Lyrae, U Delphini, W Cygni, and Chi Aquarii. All of the M giants show variability on time scales of several tens of days; the degree of regularity varies from star to star. In addition, most of the stars show variability on time scales of several hundreds of days. The cause of the latter variability is not known.

Percy, John R.; Ralli, Jorge A.; Sen, Li V.

1993-03-01

304

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

305

Decadal time series of tropospheric abundance of N2O isotopomers and isotopologues in the Northern Hemisphere obtained by the long-term observation at Hateruma Island, Japan  

NASA Astrophysics Data System (ADS)

Decadal time series and short-term temporal variations in mixing ratio of atmospheric nitrous oxide (N2O) and abundance of its isotopomers (14N15N16O and 15N14N16O) and isotopologue (14N14N18O) relative to 14N14N16O have been observed for the first time in the Northern Hemisphere at Hateruma Island (HAT), Japan during 1999-2010 by monthly air sampling. Results show that the bulk nitrogen isotope ratio ?15Nbulk decreased at the rate of -0.023 ± 0.006‰ yr-1, although the N2O mixing ratio increased at the rate of about 0.7 nmol mol-1 yr-1 (ppb yr-1) during the period. Isotope budget calculation with the ?15Nbulk trend supports the earlier estimates showing that the isotopically light sources such as agriculture and industry contribute to the increase of atmospheric N2O. However, the rate of decrease of ?15Nbulk is slightly smaller in magnitude than the rates obtained virtually for the 20th century from firn air in polar regions and surface air in the Southern Hemisphere (Tasmania and Antarctica), which suggests greater contribution of 15 N-enriched N2O sources in recent years or in the extra-polar Northern Hemisphere. In contrast, the oxygen isotope ratio (?18O) and intramolecular 15N site preference (SP, difference between isotope ratios at central and terminal nitrogen atoms) of N2O showed no significant trends, contrary to previous reports. Results show that no significant seasonal variation exists in ?15Nbulk, ?18O, and SP of N2O at HAT in the past decade within the limits of our sampling frequency and analytical precision.

Toyoda, Sake; Kuroki, Natsuko; Yoshida, Naohiro; Ishijima, Kentaro; Tohjima, Yasunori; Machida, Toshinobu

2013-04-01

306

Water Cycle Change and the Human Fingerprint on the Water Landscape of the 21st Century: Observations from a Decade of GRACE  

NASA Astrophysics Data System (ADS)

Over the last decade, satellite observations of Earth's water cycle from NASA's GRACE (Gravity Recovery and Climate Experiment) mission, have provided an unprecedented view of global hydrological change and freshwater availability. Since its launch, the mission has helped to confirm that precipitation, evaporation and continental discharge rates are increasing, that the mid-latitudes are drying while the high and low latitudes are moistening, and that the hydrologic extremes of flooding and drought are becoming even more extreme. Importantly, GRACE has exposed the human fingerprint of water management practices such as groundwater use and reservoir storage, which raises many important issues for climate, water, food and economic security. Moreover, the GRACE mission has enabled us to peer beneath Earth's surface and characterize the worldwide depletion of groundwater aquifers, raising significant concerns about the potential for heightened conflict over transboundary water resources. In this talk I review the basics of how the GRACE mission observes terrestrial and global hydrology, what new information the mission has provided since its launch in 2002, and the implications for the future of water availability and sustainable water resources management.

Famiglietti, J. S.

2012-12-01

307

Time series observations of O stars. I - IUE observations of variability in the stellar wind of Zeta Puppis  

NASA Technical Reports Server (NTRS)

Stellar wind variability in Zeta Pup (O4 I(n)f) is described based on 31 high-resolution IUE observations secured over 5 1/2 days in 1989 April. Extensive changes are evident in the absorption regions of Si IV 1393.76, 1402.77A and N IV 1718.55A P Cygni profiles. Both lines exhibit similar patterns of variability, which are characterized by the development and subsequent blueward migration, of discrete absorption components. The formation of four discrete features is identified over about 2.2 days of intensive observations, with a recurrence time of about 15 hr. The time scales, velocities, and accelerations of the progressive absorption enhancements are determined. These changes are accompanied by fluctuations of up to about 200 km/s in the maximum observed blue edge velocities in saturated C IV and N V P Cygni profiles.

Prinja, R. K.; Balona, L. A.; Bolton, C. T.; Crowe, R. A.; Fieldus, M. S.; Fullerton, A. W.; Gies, D. R.; Howarth, I. D.; Mcdavid, D.; Reid, A. H. N.

1992-01-01

308

Interannual-decadal variability of demersal fish assemblages in the Tsushima Warm Current region of the Japan Sea: Impacts of climate regime shifts and trawl fisheries with implications for ecosystem-based management  

Microsoft Academic Search

Data sets for two bottom trawl fisheries, the coastal pair-trawler fishery and offshore single-trawler fishery in the Tsushima Warm Current (TWC) region of the Japan Sea, were compiled and analyzed for the last three decades (1974–2006). These data sets were used to (1) identify and compare the variability in demersal fish assemblages, and (2) relate these to water temperature to

Yongjun Tian; Hideaki Kidokoro; Tadanori Fujino

309

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

310

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

Microsoft Academic Search

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

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

311

Sedimentary records of multidecadal-scale variability of diatom productivity in the Bungo Channel, Japan, associated with the Pacific Decadal Oscillation  

Microsoft Academic Search

In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation\\u000a (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core\\u000a samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux—the best index of fall primary productivity

Michinobu Kuwae; Azumi Yamashita; Yuichi Hayami; Atsushi Kaneda; Takashige Sugimoto; Yoshio Inouchi; Atsuko Amano; Hidetaka Takeoka

2006-01-01

312

The legacy of chlorinated solvents in the Birmingham aquifer, UK: observations spanning three decades and the challenge of future urban groundwater development.  

PubMed

Licensed abstraction well data collected during 1986-2008 from a total of 77 wells mainly located at industrial sites combined with historic land use data from 1975 has allowed insight into the legacy of chlorinated solvent contamination in the Birmingham aquifer that underlies the UK's second largest city. This legacy, expected to be reasonably symptomatic of those occurring in other urban aquifers, was characterised by: dominance of parent solvents, particularly TCE (trichloroethene) that widely exceeded drinking-water quality criteria; greater TCE occurrence in wells in proximity to increased historic land use by the metal/engineering solvent-user industry (the relationship providing a first-pass indicator of future resource development potential); regional groundwater vulnerability controls; well abstraction changes (over months to decades) influential of observed concentration transients and anticipated plume capture or release; persistence of contamination over decades (with less soluble PCE (perchloroethene) showing increased persistence relative to TCE) that was reasonably ascribed to slow contaminant release from DNAPL (dense non-aqueous phase liquid) sources and, or low permeability layers; presence of dechlorination products arising from solvent (bio)degradation, although this key attenuation process appeared to have moderate to weak influence regionally on plumes; and, inadvertent, but significant solvent mass removal from the aquifer by industrial abstractions. Key challenges to realising future urban groundwater development were identified based on the observed legacy and well capture zone simulations. Despite the extensive contamination of the aquifer, it should still be possible to develop wells of high (several megalitres per day) capacity for drinking water supply (or other lower grade uses) without the requirement for solvent treatment. In those areas with higher risk of contamination, our dataset, together with application of emergent risk assessment approaches (that our dataset may serve to validate), could be used to inform potential abstractors as to whether solvent treatment is likely to be required at a particular abstraction site with time. Challenges identified that were relevant to the future development of Birmingham and urban aquifers more generally include the adequacy of groundwater quality monitoring data and uncertainties in contaminant source terms, abstraction well capture zone predictions and plume natural attenuation, in particular degradation rates. The study endorses that despite significant solvent contamination encountered, strategies can, and need, to be increasingly found to reclaim urban aquifer resources and more sustainably meet urban water demands. PMID:23022878

Rivett, Michael O; Turner, Ryan J; Glibbery Née Murcott, Penny; Cuthbert, Mark O

2012-10-01

313

Bayesian ANN estimates of three-class ideal observer decision variables for classification of mammographic masses  

NASA Astrophysics Data System (ADS)

We are using Bayesian artificial neural networks (BANNs) to classify mammographic masses. We investigated whether a BANN can estimate ideal observer decision variables to distinguish malignant, benign, and false-positive computer detections. Five features were calculated for 143 malignant and 125 benign mass lesions, and for 1049 false-positive computer detections, in 596 mammograms randomly divided into a training and testing set. A BANN was trained on the training set features and applied to the testing set features. We then used a known relation between three-class ideal observer decision variables and that used by a two-class ideal observer when two of three classes are grouped into one class, giving one decision variable for distinguishing malignant from non-malignant detections, and a second for distinguishing true-positive from false-positive computer detections. For comparison, we pooled the training data into two classes in the same two ways and trained two-class BANNs for these two tasks. The three-class BANN decision variables were essentially identical in performance to the specifically trained two-class BANNS. This is consistent with the theoretical observation that three-class ideal observer decision variables are directly related to those used by a two-class ideal observer.

Edwards, Darrin C.; Lan, Li; Metz, Charles E.; Giger, Maryellen L.; Nishikawa, Robert M.

2003-05-01

314

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

315

Variable structure sliding mode based unknown input observer for speed identification of brushless DC motors  

Microsoft Academic Search

A variable structure sliding mode unknown input observer (VSSM-UIO) is investigated to estimate the speed of permanent magnet brushless DC motor (BLDC) in this paper, which features in very good robustness to the parameters uncertainty and disturbance. Using the phase voltage mathematical model of BLDC, the observer is deduced by supposing back-EMF as an input disturbance, which has a good

Weisheng Yan; Hai Lin; Ming Wang; Xiaochuan Li; Mei Li; Yintao Wang

2009-01-01

316

Observations of candidate oscillating eclipsing binaries and two newly discovered pulsating variables  

NASA Astrophysics Data System (ADS)

CCD observations of 24 eclipsing binary systems with spectral types ranging between A0-F0, candidate for containing pulsating components, were obtained. Appropriate exposure times in one or more photometric filters were used so that short-periodic pulsations could be detected. Their light curves were analyzed using the Period04 software in order to search for pulsational behaviour. Two new variable stars, namely GSC 2673-1583 and GSC 3641-0359, were discov- ered as by-product during the observations of eclipsing variables. The Fourier analysis of the observations of each star, the dominant pulsation frequencies and the derived frequency spectra are also presented.

Liakos, A.; Niarchos, P.

2009-03-01

317

On the variability of whitecap fraction using satellite-based observations  

NASA Astrophysics Data System (ADS)

Despite decades of effort to accurately quantify whitecap fraction W using in situ photography of the ocean surface, there remains significant scatter in estimates for any given 10 m wind speed (U10). It is believed that the resulting, commonly used, W(U10) parameterizations do not fully account for the true variability in W, by failing to incorporate the impact of the wavefield and other environmental conditions. This paper attests to the variability in whitecap fraction attributed to these additional factors, by analyzing satellite-derived W estimates over the globe for a full year. A comparison is made between the wind speed dependence of satellite estimates and three W(U10) relationships formulated from in situ photographic data. The influence of various secondary factors on W is investigated once the dominant wind speed dependence is accounted for. The W retrieval's sensitivity to secondary forcings is dependent upon microwave frequency; at 37 GHz it varies by up to 25% of the mean at a given wind speed, while at 10 GHz it is a maximum of 8%. This results from a frequency-dependent sensitivity to foam depth; at 10 GHz predominantly foam from active breaking waves is detected, while at 37 GHz thin foam in residual whitecaps is also seen. Principal component analysis is used to rank variables by their success in accounting for variability in W. After wind speed, the most important secondary factor that accounts for variability in W is the wavefield. A wind-wave Reynolds number accounts for almost as much variability in W as wind speed.

Salisbury, Dominic J.; Anguelova, Magdalena D.; Brooks, Ian M.

2013-11-01

318

The observed day-to-day variability of Mars water vapor  

NASA Technical Reports Server (NTRS)

The diurnal variability of atmospheric water vapor as derived from the Viking MAWD data is discussed. The detection of day to day variability of atmospheric water would be a significant finding since it would place constraints on the nature of surface reservoirs. Unfortunately, the diurnal variability seen by the MAWD experiment is well correlated with the occurrence of dust and/or ice hazes, making it difficult to separate real variations from observational effects. Analysis of the day to day variability of water vapor in the Martian atmosphere suggests that the observations are, at certain locations and seasons, significantly affected by the presence of water-ice hazes. Because such effects are generally limited to specific locations, such as Tharsis, Lunae Planum, and the polar cap edge during the spring, the seasonal and latitudinal trends in water vapor that have been previously reported are not significantly affected.

Jakosky, Bruce M.; Lapointe, Michael R.; Zurek, Richard W.

1987-01-01

319

Peaking free variable structure control of uncertain linear systems based on a high-gain observer  

Microsoft Academic Search

An output-feedback model-reference variable structure controller based on a high-gain observer (HGO) is proposed and analyzed. For single-input–single-output (SISO) linear plants with relative degree greater than one, the control law is generated using the HGO signals only to drive the sign function of the variable structure control component while the sign function gain, also called modulation, as well as the

José Paulo Vilela Soares Da Cunha; Ramon R. Costa; Fernando C. Lizarralde; Liu Hsu

2009-01-01

320

Observations of Variability on Synoptic Timescales in the East Pacific ITCZ  

Microsoft Academic Search

Data obtained in the eastern Pacific intertropical convergence zone (ITCZ) during the Tropical Eastern Pacific Process Study (TEPPS) show a 3-6-day variability. The NOAA ship Ronald H. Brown collected surface me- teorological observations, C-band Doppler radar volumes, atmospheric soundings, and rainfall data while on station at 7.88N, 1258W from 8-23 August 1997. The 3-6-day variability was a prominent timescale in

Yolande L. Serra; Robert A. Houze Jr.

2002-01-01

321

Quasi2-day wave and tidal variability observed over Ascension Island during January\\/February 2003  

Microsoft Academic Search

The tidal variability observed in the equatorial mesosphere–lower thermosphere (MLT) region over Ascension Island at a time when a very large quasi-2-day wave was present (January\\/February 2003) has been investigated. The results indicate that two different types of variability of the diurnal tide were present: (i) a change of the diurnal tidal mode when the period of the 2-day wave

Dora V. Pancheva

2006-01-01

322

Temporal variability of the Antarctic Circumpolar Current observed from satellite altimetry  

NASA Technical Reports Server (NTRS)

Sea level measurements by the Seasat altimeter were used to study the temporal variability of the Antarctic Circumpolar Current between July and October 1978. Large-scale zonal coherence in the cross-stream sea level difference was observed, indicating a general increase in the surface geostrophic velocity of the current around the Southern Ocean. The result demonstrates the power of satellite altimetry to monitor the variability of large-scale ocean currents.

Fu, L.-L.; Chelton, D. B.

1984-01-01

323

Temporal variability of the antarctic circumpolar current observed from satellite altimetry.  

PubMed

Sea level measurements by the Seasat altimeter were used to study the temporal variability of the Antarctic Circumpolar Current between July and October 1978. Large-scale zonal coherence in the cross-stream sea level difference was observed, indicating a general increase in the surface geostrophic velocity of the current around the Southern Ocean. The result demonstrates the power of satellite altimetry to monitor the variability of large-scale ocean currents. PMID:17749887

Fu, L L; Chelton, D B

1984-10-19

324

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

325

Multi-decadal river flows variations in France  

NASA Astrophysics Data System (ADS)

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

Boé, J.; Habets, F.

2013-09-01

326

Advances in Understanding Top-of-Atmosphere Radiation Variability from Satellite Observations  

NASA Astrophysics Data System (ADS)

This paper highlights how the emerging record of satellite observations from the Earth Observation System (EOS) and A-Train constellation are advancing our ability to more completely document and understand the underlying processes associated with variations in the Earth's top-of-atmosphere (TOA) radiation budget. Large-scale TOA radiation changes during the past decade are observed to be within 0.5 Wm-2 per decade based upon comparisons between Clouds and the Earth's Radiant Energy System (CERES) instruments aboard Terra and Aqua and other instruments. Tropical variations in emitted outgoing longwave (LW) radiation are found to closely track changes in the El Niño-Southern Oscillation (ENSO). During positive ENSO phase (El Niño), outgoing LW radiation increases, and decreases during the negative ENSO phase (La Niña). The coldest year during the last decade occurred in 2008, during which strong La Nina conditions persisted throughout most of the year. Atmospheric Infrared Sounder (AIRS) observations show that the lower temperatures extended throughout much of the troposphere for several months, resulting in a reduction in outgoing LW radiation and an increase in net incoming radiation. At the global scale, outgoing LW flux anomalies are partially compensated for by decreases in midlatitude cloud fraction and cloud height, as observed by Moderate Resolution Imaging Spectrometer and Multi-angle Imaging SpectroRadiometer, respectively. CERES data show that clouds have a net radiative warming influence during La Niña conditions and a net cooling influence during El Niño, but the magnitude of the anomalies varies greatly from one ENSO event to another. Regional cloud-radiation variations among several Terra and A-Train instruments show consistent patterns and exhibit marked fluctuations at monthly timescales in response to tropical atmosphere-ocean dynamical processes associated with ENSO and Madden-Julian Oscillation.

Loeb, Norman G.; Kato, Seiji; Su, Wenying; Wong, Takmeng; Rose, Fred G.; Doelling, David R.; Norris, Joel R.; Huang, Xianglei

2012-07-01

327

Variability in Rainfall Drop-Size Distributions observed at the Darwin ARM site  

NASA Astrophysics Data System (ADS)

The variability of rainfall drop-size distributions as a function of large-scale atmospheric conditions and cloud/storm characteristics is investigated using observations from the Atmospheric Radiation Measurement (ARM) program's research facility at Darwin, Australia. Drop-size distribution observations are obtained from an impact disdrometer over four years (2006-2010) including the YOTC. The suite of complementary long-term observations from the ARM suite of instruments, including a millimeter cloud radar, micropulse lidar, ceilometers, microwave radiometer, radiosondes, solar and infrared radiometers, etc.provide a means to describe the cloud and storm characteristics and the local atmospheric state and partition the statistics of drop-size distribution observations. Larger-scale precipitation radar and satellite observations will also provide a context for partitioning the drop-size distribution variability at different scales.

Jensen, M. P.; Giangrande, S.; Bartholomew, M. J.

2010-12-01

328

Decadal variability in the abundance of Pacific saury and its response to climatic/oceanic regime shifts in the northwestern subtropical Pacific during the last half century  

NASA Astrophysics Data System (ADS)

Pacific saury ( Cololabis saira) is one of the most important, small-sized, pelagic fishes in the North Pacific. Using correlation analysis and principal component analysis (PCA), we examined the relationships between climatic/oceanographic indices (Asian monsoon index (MOI), Southern Oscillation Index (SOI), North Pacific Index (NPI), Arctic Oscillation Index (AOI), Pacific Decadal Oscillation (PDO) index, air temperature, wind velocity, sea surface temperature (SST), and surface current velocity (SCV) in the Kuroshio axis), and abundance/biological indices of Pacific saury (adult catch, catch per unit effort, i.e., CPUE, condition factor, and body length and larval density) in order to detect the response of Pacific saury abundance to the recent climatic/oceanic regime shifts (1976/1977, 1987/1988, and 1997/1998). Our oceanographic analyses show that notable regime shifts occurred in 1987/1988 and possibly 1997/1998 in the Kuroshio region, while the same kind of regime shift was not readily apparent there in 1976/1977. Results of our oceanographic/biological analyses show that the decadal-scale variation pattern in Pacific saury abundance responded well to the regime shifts of 1987/1988 and 1997/1998. These results indicate that only the regime shifts which occurred in the Kuroshio region can affect Pacific saury abundance. Our results also showed that the abundance and biological indices of saury significantly correlated with both the SSTs in the northwestern Kuroshio waters and the SCV in the Kuroshio axis in winter. These correlations suggest that winter oceanographic conditions in the Kuroshio region strongly affect the early survival process and determine the recruitment success of Pacific saury. The abundance of other major small pelagic species also changed greatly around 1989, suggesting that the regime shift in the late 1980s occurred in the pelagic ecosystem basin. We concluded that Pacific saury could be used as a bio-indicator of regime shifts in the northwestern subtropical Pacific.

Tian, Yongjun; Ueno, Yasuhiro; Suda, Maki; Akamine, Taturo

2004-12-01

329

A general approach to simultaneous model fitting and variable elimination in response models for biological data with many more variables than observations  

Microsoft Academic Search

BACKGROUND: With the advent of high throughput biotechnology data acquisition platforms such as micro arrays, SNP chips and mass spectrometers, data sets with many more variables than observations are now routinely being collected. Finding relationships between response variables of interest and variables in such data sets is an important problem akin to finding needles in a haystack. Whilst methods for

Harri T. Kiiveri

2008-01-01

330

Detecting and Estimating Continuous-Variable Entanglement by Local Orthogonal Observables  

NASA Astrophysics Data System (ADS)

Entanglement detection and estimation are fundamental problems in quantum information science. Compared with discrete-variable states, for which lots of efficient entanglement detection criteria and lower bounds of entanglement measures have been proposed, the continuous-variable entanglement is much less understood. Here we shall present a family of entanglement witnesses based on continuous-variable local orthogonal observables (CVLOOs) to detect and estimate entanglement of Gaussian and non-Gaussian states, especially for bound entangled states. By choosing an optimal set of CVLOOs, our entanglement witness is equivalent to the realignment criterion and can be used to detect bound entanglement of a class of 2+2 mode Gaussian states. Via our entanglement witness, lower bounds of two typical entanglement measures for arbitrary two-mode continuous-variable states are provided.

Zhang, Chengjie; Yu, Sixia; Chen, Qing; Oh, C. H.

2013-11-01

331

New Variable Stars Discovered by the APACHE Survey. I. Results After the First Observing Season  

NASA Astrophysics Data System (ADS)

We present more than 80 new variable stars discovered during the first observing season of the APACHE survey. APACHE is a project aimed at detecting extrasolar planets transiting nearby, bright M dwarfs by using an array of small-aperture telescopes. Despite that the survey is targeted to a well-defined sample of cool stars, we also reduce and analyze data for all the detected field stars. Since July 2012 dozens of different stellar fields have been monitored, leading to the detection of several variables for which we propose a classification and estimate a period, when a periodicity is evident in the data. Thanks to the SuperWASP public archive, we have also retrieved and analyzed photometric data collected by the SWASP survey, which helped us to refine the classification and the period estimation of many variables found in the APACHE database. Some of the variables present peculiarities and thus are discussed separately.

Damasso, M.; Bernagozzi, A.; Bertolini, E.; Calcidese, P.; Carbognani, A.; Cenadelli, D.; Christille, J. M.; Giacibbe, P.; Lanteri, L.; Lattanzi, M. G.; Smart, R.; Sozzetti, A.

2014-06-01

332

Hubble Space Telescope Observations of Ganymede's Time-Variable Auroral Ovals  

NASA Astrophysics Data System (ADS)

We present results of Hubble Space Telescope (HST) observations of Ganymede's auroral ovals obtained during two visits when Ganymede was located at eastern elongation. The observations were obtained on November 19, 2010 and October 1, 2011 and cover five consecutive orbits each. They were designed such that the Jovian magnetic latitudes of Ganymede span the entire possible range, i.e. Ganymede is exposed to the maximum variability of Jupiter's magnetospheric field during each visit. Our analysis shows that the auroral ovals only weakly rock in concert with the time-variable Jovian magnetic field. This weak rocking of the ovals is consistent with shielding of the time-variable field due to electromagnetic induction in a saline subsurface ocean on Ganymede.

Wennmacher, A.; Saur, J.; Duling, S.; Roth, L.; Musacchio, F. M.; Feldman, P. D.; Strobel, D. F.; Retherford, K. D.; McGrath, M. A.

2012-12-01

333

MgII H and K line observations of Delta Scuti variables  

NASA Astrophysics Data System (ADS)

IUE observations of seven Delta Scuti variables and a comparison star are reported with a comparison of the Mg II h and k lines to those of previously observed normal stars. Evident chromospheric emission is observed in three Delta Scuti variables: tau Cyg, beta Cas and rho Pup. Possible emissions are suggested for omega-1 Eri (F2III), iota Cyg, tau Peg, and kappa-2 Boo. Values of the observed emission widths fit well in diagrams of emission width-absolute magnitude, which, if correct, confirms the suggestion by Kondo et al. (1977) of possible evidence of chromospheric emissions in late A stars. A possible relation between emission widths and periods of pulsation is also discussed.

Fracassini, M.; Pasinetti, L. E.

1982-03-01

334

The observed day-to-day variability of Mars atmospheric water vapor  

NASA Astrophysics Data System (ADS)

The present evaluation of Viking water column abundance measurements of the Martian atmosphere notes observed changes to be due to atmospheric water vapor vertical column abundance variations, as well as to apparent changes resulting from abundance changes of atmospheric aerosols, relative vertical distribution changes of water vapor and aerosol, or systematic viewing-geometry variations. Variability noted in several major regions by visible and thermal-IR observations is found to very accurately coincide with the occurrence of water ice clouds and hazes.

Jakosky, B. M.; Zurek, R. W.; La Pointe, M. R.

1988-01-01

335

Intraseasonal variability in the upper layer currents observed in the eastern equatorial Indian Ocean  

Microsoft Academic Search

Direct observations of the upper ocean velocity in the eastern equatorial Indian Ocean by an acoustic Doppler current profiler, from November 2000 to October 2001 on the equator at 90°E, demonstrate that the dominant periods of variability in the upper layer zonal and meridional currents are in intraseasonal frequency bands with periods of 30 to 50 days and 10 to

Yukio Masumoto; Hideaki Hase; Yoshifumi Kuroda; Hiroshi Matsuura; Kensuke Takeuchi

2005-01-01

336

Observations of Novalike Cataclysmic Variables with the Far Ultraviolet Spectroscopic Explorer  

Microsoft Academic Search

Observations at short wavelengths probe the innermost region of cataclysmic variables (CVs), at the zone of interaction between the accretion flow or disk and the boundary layer and\\/or white dwarf. We present new spectra of three CVs (DW UMa, LS Peg, MV Lyr) obtained with the Far Ultraviolet Spectroscopic Explorer satellite. These three systems are members of the novalike class

D. W. Hoard; Paula Szkody; Albert Linnell; K. Long; E. M. Sion; I. Hubeny; C. Knigge

2002-01-01

337

Quality Control and First Insights on the Variability of Surface Wind Observations for North Eastern North America  

NASA Astrophysics Data System (ADS)

Over the last decades, a policy change in energy sources has been fostered in Atlantic Canada. The purpose of this has been to reduce the dependency on energy produced abroad and to propose feasible alternatives with the aim of reducing greenhouse emissions. The region offers a high potential for the development of wind energy facilities and studies within the framework of wind resource assessment are encouraged. Studies of this nature rely on the quality of observational data. Henceforth, it is essential to develop procedures that ensure the reliability of observations before they are subjected to any subsequent analysis. This work summarizes the Quality Control process applied to an observational database of surface wind module and direction in North Eastern North America. The data set consists of 525 stations compiled from three different sources: 344 land sites from Environment Canada (EC; 1940-2009) located in the provinces of Atlantic Canada and Quebec; 40 buoys distributed over the East Coast and the Canadian Great Lakes provided by Fisheries and Oceans Canada (FOC; 1988-2008); and 141 land sites over both Eastern Canada and North Eastern USA provided by the National Center of Atmospheric Research (NCAR; 1975-2010). The process comprises different phases that: 1) unify measurement units and recording times; 2) find accidentally duplicated periods of data within a time series or between different stations; 3) check for physical consistency in the ranges of values; 4) detect time intervals of anomalous low and high variability; and 5) look for long term biases in mean and variance. The temporal extension and resolution of the quality controlled database allows to explore the wind variability at different temporal scales, from daily to multidecadal. This contribution will present a first assessment of the wind field climatology in the region, including a description of long term trends, analogous of wind circulation regimes and their relationship to large scale circulation.

Lucio-Eceiza, E.; González-Rouco, F. J.; Navarro Montesinos, J.; Hidalgo; Jiménez, P.; García-Bustamante, E.; Conte, J.; Casabella, N.; Beltrami, H.

2013-12-01

338

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

339

Linking Temporal and Spatial Variability of Millennial and Decadal-Scale Sediment Yield to Aquatic Habitat in the Columbia River Watershed  

NASA Astrophysics Data System (ADS)

Understanding and predicting the mechanisms, rates and timing of sediment production and storage in the landscape are fundamental problems in the watershed sciences. This is of particular concern given that excess sedimentation is considered a major pollutant to aquatic ecosystems. Rates of sediment delivery to stream networks are characteristically unsteady and non-uniform. Because of this, conventional approaches for predicting sediment yield provide incomplete and often inaccurate information. Terrestrial cosmogenic nuclides (TCNs) provide an estimate of spatially averaged rates of sediment yield from 10^1 to 10^4 km2 and temporally integrated from 10^3 to 10^5 years. Here, I am using TCNs to constrain unsteadiness and non-uniformity of sediment yield within specific catchments of the Columbia River Watershed. This is in combination with GIS analysis (e.g. longitudinal profiles, hypsometric curves, geologic mapping) optically stimulated luminescence (OSL), Carbon-14 (C14) dating of fluvial deposits within the modern and abandoned floodplain, decadal-scale sediment yield river gauge data and rapid geomorphic assessments based on the Fluvial Audit and River Styles frameworks. These methods are employed to address the following three broad questions. 1) How do long-term rates of sediment supply vary spatially and temporally throughout the Columbia River watershed? 2) How have human activities influenced (amplified or dampened) processes of erosion and sediment transport? 3) At what scales do long-term and near-term erosion rates influence aquatic habitat metrics?

Portugal, E. W.; Belmont, P.

2012-12-01

340

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

341

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

342

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

343

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

344

High frequency barotropic ocean variability observed by GRACE and satellite altimetry  

NASA Astrophysics Data System (ADS)

Previous theoretical and model-based studies of the relationship between ocean bottom pressure (pb) and sea level (?) suggest primarily barotropic variability at mid to high latitudes for scales greater than a few hundred kilometers and periods less than a few months. We use 7-day GRACE solutions and equivalent satellite altimetry maps, spatially smoothed over 750 km, to investigate the relation between pb and ?. The observed fields are significantly coherent at high latitudes for periods of ˜14-180 days and mid latitudes for periods of ˜30-100 days. The admittance amplitude between observed pb and ? is close to 1 for higher frequencies and drops off for lower frequencies. The results provide, for the first time, global observational evidence for the barotropic nature of large-scale ocean variability at mid and high latitudes. We also demonstrate that GRACE data contain significant information over the oceans at periods <60 days, i.e., shorter than the nominal monthly time resolution.

Quinn, Katherine J.; Ponte, Rui M.

2012-04-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

346

Observational study on variability between biobanks in the estimation of DNA concentration  

PubMed Central

Background There is little confidence in the consistency of estimation of DNA concentrations when samples move between laboratories. Evidence on this consistency is largely anecdotal. Therefore there is a need first to measure this consistency among different laboratories and then identify and implement remedies. A pilot experiment to test logistics and provide initial data on consistency was therefore conceived. Methods DNA aliquots at nominal concentrations between 10 and 300 ng/?l were dispensed into the wells of 96-well plates by one participant - the coordinating centre. Participants estimated the concentration in each well and returned estimates to the coordinating centre. Results Considerable overall variability was observed among estimates. There were statistically significant differences between participants' measurements and between fluorescence emission and absorption spectroscopy. Conclusion Anecdotal evidence of variability in DNA concentration estimation has been substantiated. Reduction in variability between participants will require the identification of major sources of variation, specification of effective remedies and their implementation.

Brown, Jay; Donev, Alexander N; Aslanidis, Charalampos; Bracegirdle, Pippa; Dixon, Katherine P; Foedinger, Manuela; Gwilliam, Rhian; Hardy, Matthew; Illig, Thomas; Ke, Xiayi; Krinka, Dagni; Lagerberg, Camilla; Laiho, Paivi; Lewis, David H; McArdle, Wendy; Patton, Simon; Ring, Susan M; Schmitz, Gerd; Stevens, Helen; Tybring, Gunnel; Wichmann, H Erich; Ollier, William ER; Yuille, Martin A

2009-01-01

347

Observational constraints on the sub-grid variability of cloud and rain: Implications for microphysical parameterization  

NASA Astrophysics Data System (ADS)

The transition of cloud water to rain water through the autoconversion and accretion processes are highly non-linear. Furthermore, accretion is sensitive to the covariance of cloud and rain water. Accurately representing these process in global models therefore requires assumptions regarding the sub-grid variability and co-variability of cloud and rain hydrometeors. In addition, recent results suggest that model estimates of the aerosol indirect effect are largely determined by the balance between accretion and autoconversion. We present a multi-sensor analysis of the covariance parameters that govern these processes derived from Aqua-MODIS and CloudSat observations for marine boundary layer clouds. These observational results provide critical constraints on the sub-grid variability and co-variability that are assumed in microphysical parameterizations. These results reiterate a substantial dependence of the sub-grid cloud water on cloud regime, which scales well with cloud fraction and cloud water path. A power-law dependence of the rain water content on the cloud water content is found that permits straightforward integration into existing cloud microphysics parameterizations. The power-law covariance scaling between cloud and rain shows only minor variation with cloud regime. However, the interaction of this covariance with the sub-grid cloud variability results in significant regime dependence in the derived accretion rates. In particular, a significant enhancement of accretion rates can be inferred in shallow convection regimes relative to stratocumulus cloud regimes. This result is particularly relevant to modelling efforts that seek to unify microphysical representation across cloud regimes that have traditionally been treated by independent parameterization schemes. Initial implementation of the observational constraints in the Community Atmosphere Model (CAM) suggest that obtaining the correct balance between autoconversion and accretion requires careful attention to both sub-grid varibility of cloud water and the covariance of cloud and rain water.

Lebsock, M. D.; Morrison, H.; Gettelman, A.

2012-12-01

348

Observations of alongshore variability of swash motions on an intermediate beach  

NASA Astrophysics Data System (ADS)

Alongshore variability in swash motions - shoreline oscillations about the mean water level on the beach face - were investigated using video images and a high-resolution morphology survey on an intermediate beach. Under mild, swell-dominated offshore wave conditions, alongshore variation of up to 78% in significant runup height Rs (defined as 4 times the standard deviation of the swash time series) was observed. This variation was predominantly driven by energy at the incident (>0.05 Hz) frequencies (where most of the swash energy was observed), and, consistent with previous observations, was mainly controlled by changes in the slope of the beach face (measured at the mean swash location). However, alongshore patterning in wave breaking over the sandbar caused variation in the degree of wave dissipation along the beach and also resulted in alongshore changes to swash motions. Although alongshore changes in beach slope and wave breaking patterning over the bar were observed to be typically correlated, both were needed in a regression model to provide the best explaination of alongshore changes in Rs. At infragravity frequencies (<0.05 Hz), alongshore variability was not well associated either with changes in beach slope or wave breaking patterning. Low-mode edge waves were observed in the swash measurements and their contribution to the total energy spectrum was greatest near the location where a shoal was observed, suggesting this shoal may play a role in forcing. The edge waves may have contributed to the swash variability observed at infragravity frequencies. However, in these reflective conditions, the infragravity band plays a secondary role in controlling alongshore variations to swash motions.

Guedes, Rafael M. C.; Bryan, Karin R.; Coco, Giovanni

2012-10-01