Sample records for observed decadal variability

  1. Global scale decadal climate variability

    Microsoft Academic Search

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

    1998-01-01

    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

  2. Tides and Decadal Variability

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.

    2003-01-01

    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."

  3. Measurement biases explain discrepancies between the observed and simulated decadal variability of surface incident solar radiation.

    PubMed

    Wang, Kaicun

    2014-01-01

    Observations have reported a widespread dimming of surface incident solar radiation (Rs) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. We find that the decadal variability of observed Rs may have important errors due to instrument sensitivity drifting and instrument replacement. While sunshine duration (SunDu), which is a robust measurement related to Rs, is nearly free from these problems. We estimate Rs from SunDu with a method calibrated by the observed Rs at each station. SunDu-derived Rs declined over China by -2.8 (with a 95% confidence interval of -1.9 to -3.7) W m(-2) per decade from 1960 to 1989, while the observed Rs declined by -8.5 (with a 95% confidence interval of -7.3 to -9.8) W m(-2) per decade. The former trend was duplicated by some high-quality CMIP5 models, but none reproduced the latter trend. PMID:25142756

  4. Measurement Biases Explain Discrepancies between the Observed and Simulated Decadal Variability of Surface Incident Solar Radiation

    PubMed Central

    Wang, Kaicun

    2014-01-01

    Observations have reported a widespread dimming of surface incident solar radiation (Rs) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. We find that the decadal variability of observed Rs may have important errors due to instrument sensitivity drifting and instrument replacement. While sunshine duration (SunDu), which is a robust measurement related to Rs, is nearly free from these problems. We estimate Rs from SunDu with a method calibrated by the observed Rs at each station. SunDu-derived Rs declined over China by ?2.8 (with a 95% confidence interval of ?1.9 to ?3.7) W m?2 per decade from 1960 to 1989, while the observed Rs declined by ?8.5 (with a 95% confidence interval of ?7.3 to ?9.8) W m?2 per decade. The former trend was duplicated by some high-quality CMIP5 models, but none reproduced the latter trend. PMID:25142756

  5. Measurement Biases Explain Discrepancies between the Observed and Simulated Decadal Variability of Surface Incident Solar Radiation

    NASA Astrophysics Data System (ADS)

    Wang, Kaicun

    2014-08-01

    Observations have reported a widespread dimming of surface incident solar radiation (Rs) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. We find that the decadal variability of observed Rs may have important errors due to instrument sensitivity drifting and instrument replacement. While sunshine duration (SunDu), which is a robust measurement related to Rs, is nearly free from these problems. We estimate Rs from SunDu with a method calibrated by the observed Rs at each station. SunDu-derived Rs declined over China by -2.8 (with a 95% confidence interval of -1.9 to -3.7) W m-2 per decade from 1960 to 1989, while the observed Rs declined by -8.5 (with a 95% confidence interval of -7.3 to -9.8) W m-2 per decade. The former trend was duplicated by some high-quality CMIP5 models, but none reproduced the latter trend.

  6. Ocean impact on decadal Atlantic climate variability revealed by sea-level observations.

    PubMed

    McCarthy, Gerard D; Haigh, Ivan D; Hirschi, Joël J-M; Grist, Jeremy P; Smeed, David A

    2015-05-28

    Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall, European summer precipitation, Atlantic hurricanes and variations in global temperatures. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres--the intergyre region. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States. PMID:26017453

  7. Global scale decadal climate variability

    NASA Astrophysics Data System (ADS)

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

    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.

  8. An observational analysis of the oceanic and atmospheric structure of global-scale multi-decadal variability

    NASA Astrophysics Data System (ADS)

    Liu, Peng; Sui, Chung-Hsiung

    2014-03-01

    The aim of the present study was to identify multi-decadal variability (MDV) relative to the current centennial global warming trend in available observation data. The centennial global warming trend was first identified in the global mean surface temperature (STgm) data. The MDV was identified based on three sets of climate variables, including sea surface temperature (SST), ocean temperature from the surface to 700 m, and the NCEP and ERA40 reanalysis datasets, respectively. All variables were detrended and low-pass filtered. Through three independent EOF analyses of the filtered variables, all results consistently showed two dominant modes, with their respective temporal variability resembling the Pacific Decadal Oscillation/Inter-decadal Pacific Oscillation (PDO/IPO) and the Atlantic Multi-decadal Oscillation (AMO). The spatial structure of the PDO-like oscillation is characterized by an ENSO-like structure and hemispheric symmetric features. The structure associated with the AMO-like oscillation exhibits hemispheric asymmetric features with anomalous warm air over Eurasia and warm SST in the Atlantic and Pacific basin north of 10°S, and cold SST over the southern oceans. The Pacific and Atlantic MDV in upper-ocean temperature suggest that they are mutually linked. We also found that the PDO-like and AMO-like oscillations are almost equally important in global-scale MDV by EOF analyses. In the period 1975-2005, the evolution of the two oscillations has given rise to strong temperature trends and has contributed almost half of the STgm warming. Hereon, in the next decade, the two oscillations are expected to slow down the global warming trends.

  9. Decadal-Scale Variability of The Mesosphere And Lower Thermosphere As Observed by SABER/TIMED From 2002 to 2014

    NASA Astrophysics Data System (ADS)

    Yee, J. H.

    2014-12-01

    In this paper, we will analyze over a decade of SABER/TIMED observations to quantify and interpret the decadal-scale variability of temperature, composition, and airglow intensity, including those associated with the 11-year solar cycle (SC) and long-term anthropogenic change (AC), 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 activity and long-term changes will be extracted using the multiple regression technique from12+ years of SABER/TIMED observations (2002 to 2014). Accuracies of the extracted SC and AC sensitivities will be assessed and discussed in terms of our analysis technique, the proxies we used, and the noise, drift and length of the data we used in the study.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  11. Decadal variability of prediction skill of ENSO

    NASA Astrophysics Data System (ADS)

    Yasuda, T.

    2014-12-01

    The variability of SST in the tropical Pacific associated with ENSO is well predicted in time scales from 6 months to 1 year advance. However, the prediction skills of ENSO in many ENSO prediction systems are lower in the 2000s than those in the 1980s and 1990s. Since late 1990s sea surface height and SST have increased in the western equatorial Pacific and easterly surface wind has increased in the decadal time scale. It has not been fully understood whether the decadal variability in the tropical Pacific could cause the lower prediction skill of ENSO during the recent decade. In this study, decadal variability of prediction skill of ENSO using ocean-atmosphere coupled general circulation model and its relationship with decadal variability of tropical Pacific are examined. It is found that prediction skill of ENSO fluctuates in the decadal time scale. Anomaly correlation coefficient of NINO3 SST for the 1979-2006 period is 0.76 at 6-month lead time, but 0.40 for the 2003-2011 period. NINO3 SST error at 6-month lead time changes in the decadal time scale and has increased since late 1990s. The period of large SST error corresponds to that of large decadal anomalies of observed NINO3 SST. It is shown that decadal variability of NINO3 SST error is consistent with that of magnitude of initial SST anomalies in the prediction. Decadal anomalies of zonal gradient of observed thermocline depth in the equatorial Pacific are large in the early 1990s and late 2000s. However, those anomalies decrease rapidly in the prediction. Positive temperature errors at the depth of thermocline at the beginning of the prediction develop with propagating eastward accompanied by westerly surface wind anomalies. It is important for successful ENSO prediction to reduce errors of thermocline depth at the beginning of prediction and to understand how decadal anomalies in the equatorial Pacific are maintained in the observation and prediction.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  14. Changes in the mesoscale variability and in extreme sea levels over two decades as observed by satellite altimetry

    NASA Astrophysics Data System (ADS)

    Woodworth, Philip L.; Menéndez, Melisa

    2015-01-01

    data set of precise radar altimeter sea surface heights obtained from the same 10 day repeat ground track has been analyzed to determine the magnitude of change in the ocean "mesoscale" variability over two decades. Trends in the standard deviation of sea surface height variability each year are found to be small (typically ˜0.5 percent/yr) throughout the global ocean. Trends in positive and negative extreme sea level in each region are in general found to be similar to those of mean sea level, with some small regional exceptions. Generalized Extreme Value Distribution (GEVD) analysis also demonstrates that spatial variations in the statistics of extreme positive sea levels are determined largely by the corresponding spatial variations in mean sea level changes, and are related to regional modes of the climate system such as the El Niño-Southern Oscillation. Trends in the standard deviation of along-track sea level gradient variability are found to be close to zero on a global basis, with regional exceptions. Altogether our findings suggest an ocean mesoscale variability that displays little change when considered over an extended period of two decades, but that is superimposed on a spatially and temporally varying signal of mean sea level change.

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

    NASA Astrophysics Data System (ADS)

    Lique, Camille; Steele, Michael

    2013-04-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    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.

  17. Elements of tropical Pacific decadal variability 

    E-print Network

    Fuckar, Neven-Stjepan

    2003-01-01

    The evolution of decadal variability in the tropical Pacific is investigated using a global assimilation reanalysis. At the nexus of this study are monthly means of an ocean general circulation model coupled with a data assimilation routine...

  18. Anatomy of North Pacific Decadal Variability

    Microsoft Academic Search

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

    A systematic analysis of North Pacific decadal variability in a full-physics coupled ocean-atmosphere model is executed. The model is an updated and improved version of the coupled model studied by Latif and Barnett. Evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20-30-yr timescales. The possible mechanisms include a midlatitude

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  20. A decade of SETI observations

    NASA Technical Reports Server (NTRS)

    Dixon, R. S.

    1986-01-01

    A full time dedicated search for extraterrestrial radio signals of intelligent origin has been in progress at the Ohio State University Radio Observatory since 1973. The radio telescope has a collecting area of 2200 square meters, which is equivalent to a circular dish 175 feet in diameter. The search concentrates on a 500 kHz bandwidth centered on the 1420 MHz hydrogen line, Doppler corrected to the galactic standard of rest. A large portion of the sky visible from Ohio was searched, with particulat emphasis on the galactic center region and the M31 Andromeda galaxy. The survey is largely computer automated, and all data reduction is done in real time. Two distinct populations of signals were detected. The first is a relatively small number of signals which persist for over a minute and which are clearly extraterrestrial in origin. The second is the large number of signals which persist less than 10 seconds whose locations are anticorrelated with the galactic plane but show clumps along the galactic axis. None of these signals were observed to recur, despite repeated observations. The cause of these signals were not determined.

  1. Model Assessment of Decadal Variability and Trends in the Tropical Pacific Ocean

    Microsoft Academic Search

    Thomas R. Knutson; Syukuro Manabe

    1998-01-01

    In this report, global coupled ocean-atmosphere models are used to explore possible mechanisms for observed decadal variability and trends in Pacific Ocean SSTs over the past century. The leading mode of internally generated decadal (>7 yr) variability in the model resembles the observed decadal variability in terms of pattern and amplitude. In the model, the pattern and time evolution of

  2. Decadal to multidecadal variability and the climate change background

    Microsoft Academic Search

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

    2007-01-01

    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

  3. Origin of Quasi-decadal North Atlantic Oscillation Variability

    NASA Astrophysics Data System (ADS)

    Reintges, Annika; Latif, Mojib; Park, Wonsun

    2015-04-01

    The North Atlantic Oscillation (NAO) is the leading mode of internal atmospheric variability in the North Atlantic sector. It depicts significant quasi-decadal variability that is well documented, but the underlying mechanism is still under discussion. Other quantities in the North Atlantic sector such as sea surface temperature (SST) exhibit variability on a similar timescale. Here we present results from a global climate model which simulates the quasi-decadal NAO and North Atlantic SST variability consistent with observations. The quasi-decadal NAO variability is suggested to originate from large-scale air-sea interactions, where the Atlantic Meridional Overturning Circulation (AMOC) basically sets the timescale. Wind-driven ocean circulation changes provide a fast positive feedback on North Atlantic SST through anomalous Ekman currents and the establishment of an "intergyre" gyre. A delayed negative feedback on SST is accomplished through surface heat flux-driven changes of the AMOC and associated heat transport. The results stress the importance of both wind-induced and thermohaline-induced changes in the ocean circulation for quasi-decadal climate variability in the North Atlantic sector.

  4. Decadal Variability of Surface Incident Solar Radiation over China

    NASA Astrophysics Data System (ADS)

    Wang, Kaicun

    2015-04-01

    Observations have reported a widespread dimming of surface incident solar radiation (Rs) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. This study provides metadata and reference data to investigate the observed variability of Rs in China. From 1958 to 1990, diffuse solar radiation (Rsdif) and direct solar radiation (Rsdir) was measured separately in China, from which Rs was calculated a sum. However, pyranometers used to measure Rsdif had a strong sensitivity drift problem, which introduced a spurious decreasing trend to Rsdif and Rs measurements. The observed Rsdir did not suffer from such sensitivity drift problem. From 1990 to 1993, the old instruments were replaced and measuring stations were relocated in China, which introduced an abrupt increase in the observed Rs. After 1993, Rs was measured by solid black thermopile pyranometers. Comprehensive comparisons between observation-based and model-based Rs performed in this research have shown that sunshine duration (SunDu)-derived Rs is of high quality and provide accurate estimate of decadal variability of Rs over China. SunDu-derived Rs averaged over 105 stations in China decreased at -2.9 W m-2 per decade from 1961 to 1990 and remained stable afterward. This decadal variability has been confirmed by the observed Rsdir, independent studies on aerosols and diurnal temperature range, and can be reproduced by certain high-quality earth system models. However, neither satellite retrievals (the Global Energy and Water Exchanges Project Surface Radiation Budget (GEWEX SRB)) nor reanalyses (ERA-Interim and Modern-Era Retrospective analysis for Research and Applications (MERRA)) can accurately reproduce such decadal variability of Rs over China for their exclusion of annual variability of tropospheric aerosols.

  5. Decadal Modulation of Global Surface Temperature By Internal Climate Variability

    NASA Astrophysics Data System (ADS)

    Dai, A.; Fyfe, J. C.; Xie, S. P.; Dai, X.

    2014-12-01

    Despite a steady increase in atmospheric greenhouse gases (GHGs), global-mean surface temperature (T) has shown no discernable warming since about 2000, in sharp contrast to model simulations which on average project strong warming. The recent slowdown in observed surface warming has been attributed to decadal cooling in the tropical Pacific, intensifying trade winds, changes in El Niño activity, increasing volcanic activity and decreasing solar irradiance. Earlier periods of arrested warming have been observed but received much less attention than the recent period, and their causes are poorly understood. Here we analyze observed and model-simulated global T fields to quantify the contributions of internal climate variability (ICV) to decadal changes in global-mean T since 1920. We show that the Inter-decadal Pacific Oscillation (IPO) has been associated with large T anomalies over both ocean and land since 1920. Combined with another leading mode of ICV, the IPO explains most of the difference between observed and model-simulated rates of decadal change in global-mean T since 1920, and particularly over the so-called "hiatus" period since about 2000. We conclude that ICV, mainly through the IPO, was largely responsible for the recent slowdown, as well as for earlier slowdowns and accelerations in global-mean T since 1920, with preferred spatial patterns different from GHG-induced warming. Recent history suggests that the IPO could reverse course and lead to accelerated global warming in the coming decades.

  6. Contribution of solar radiation to decadal temperature variability over land.

    PubMed

    Wang, Kaicun; Dickinson, Robert E

    2013-09-10

    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

  7. Decadal modulation of global surface temperature by internal climate variability

    NASA Astrophysics Data System (ADS)

    Dai, Aiguo; Fyfe, John C.; Xie, Shang-Ping; Dai, Xingang

    2015-06-01

    Despite a steady increase in atmospheric greenhouse gases (GHGs), global-mean surface temperature (T) has shown no discernible warming since about 2000, in sharp contrast to model simulations, which on average project strong warming. The recent slowdown in observed surface warming has been attributed to decadal cooling in the tropical Pacific, intensifying trade winds, changes in El Niño activity, increasing volcanic activity and decreasing solar irradiance. Earlier periods of arrested warming have been observed but received much less attention than the recent period, and their causes are poorly understood. Here we analyse observed and model-simulated global T fields to quantify the contributions of internal climate variability (ICV) to decadal changes in global-mean T since 1920. We show that the Interdecadal Pacific Oscillation (IPO) has been associated with large T anomalies over both ocean and land. Combined with another leading mode of ICV, the IPO explains most of the difference between observed and model-simulated rates of decadal change in global-mean T since 1920, and particularly over the so-called `hiatus' period since about 2000. We conclude that ICV, mainly through the IPO, was largely responsible for the recent slowdown, as well as for earlier slowdowns and accelerations in global-mean T since 1920, with preferred spatial patterns different from those associated with GHG-induced warming or aerosol-induced cooling. Recent history suggests that the IPO could reverse course and lead to accelerated global warming in the coming decades.

  8. Sahel rainfall and decadal to multi-decadal sea surface temperature variability

    NASA Astrophysics Data System (ADS)

    Mohino, Elsa; Janicot, Serge; Bader, Juergen

    2010-05-01

    Sahel rainfall variability at decadal time-scales has been mainly driven by Sea Surface Temperatures (SSTs) in the 20th century. During that period, SSTs have shown a marked long-term trend of global warming (GW) that was externally forced by natural and anthropogenic sources. Superimposed on this long-term trend, patterns of decadal variability have been observed. Centred in the North Atlantic, the Atlantic Multidecadal Oscillation (AMO) is a pattern of variation related to the oceanic thermohaline circulation. The Pacific basin also hosts a pattern of oscillation at decadal time-scales called the Interdecadal Pacific Oscillation (IPO). In this work we investigated the relative contribution of each component to Sahel precipitation variability at decadal time-scales. For the sake of completeness, we also analysed the contribution of Indian decadal variability (IDV). For this aim we used simulations forced by idealized patterns of world-wide SST anomalies representative of these components. The simulations show that all four SST signals have a significant impact over West African Monsoon: the positive phases of GW, IPO and IDV lead to drought over the Sahel, while a positive AMO enhances Sahel rainfall. Our simulations also show that tropical warming of SST is the main cause for the GW impact on Sahel. Regarding AMO, the pattern of anomalous precipitation is established by the SSTs in the Atlantic and Mediterranean basins. Conversely, the Pacific basin alone can not account for the IPO effect over WAM. In turn, the tropical SSTs control the IDV impact on WAM. Though GW, AMO and IPO signals are highly unrelated among them, IDV is found to be mostly explained by AMO and IPO global signals. Our results suggest that decadal evolution of Sahel rainfall can be interpreted as the competition of three factors: the effect of GW, AMO and IPO. Following this interpretation, our results show that 40 to 50% of Sahel drought in the 1980s is explained by the change to a negative phase of the AMO, and that GW contributed between 10 and 30%. In addition, the partial recovery of Sahel rainfall in recent years was mainly driven by the AMO.

  9. Sahel rainfall and decadal to multi-decadal sea surface temperature variability

    NASA Astrophysics Data System (ADS)

    Mohino, Elsa; Janicot, Serge; Bader, Juergen

    2011-08-01

    Decadal Sahelian rainfall variability was mainly driven by sea surface temperatures (SSTs) during the twentieth century. At the same time SSTs showed a marked long-term global warming (GW) trend. Superimposed on this long-term trend decadal and multi-decadal variability patterns are observed like the Atlantic Multidecadal Oscillation (AMO) and the inter-decadal Pacific Oscillation (IPO). Using an atmospheric general circulation model we investigate the relative contribution of each component to the Sahelian precipitation variability. To take into account the uncertainty related to the use of different SST data sets, we perform the experiments using HadISST1 and ERSSTv3 reconstructed sets. The simulations show that all three SST signals have a significant impact over West Africa: the positive phases of the GW and the IPO lead to drought over the Sahel, while a positive AMO enhances Sahel rainfall. The tropical SST warming is the main cause for the GW impact on Sahel rainfall. Regarding the AMO, the pattern of anomalous precipitation is established by the SSTs in the Atlantic and Mediterranean basins. In turn, the tropical SST anomalies control the impact of the IPO component on West Africa. Our results suggest that the low-frequency evolution of Sahel rainfall can be interpreted as the competition of three factors: the effect of the GW, the AMO and the IPO. Following this interpretation, our results show that 50% of the SST-driven Sahel drought in the 1980s is explained by the change to a negative phase of the AMO, and that the GW contribution was 10%. In addition, the partial recovery of Sahel rainfall in recent years was mainly driven by the AMO.

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

    Microsoft Academic Search

    M. Latif; T. P. Barnett

    1996-01-01

    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

  11. Decadal Record of Satellite Carbon Monoxide Observations

    NASA Astrophysics Data System (ADS)

    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

    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.

  12. Stochastic modeling of decadal variability in ocean gyres

    NASA Astrophysics Data System (ADS)

    Kondrashov, D.; Berloff, P.

    2015-03-01

    Decadal large-scale low-frequency variability of the ocean circulation due to its nonlinear dynamics remains a big challenge for theoretical understanding and practical ocean modeling. This paper presents a novel fully data driven approach that addresses this challenge. Proposed is non-Markovian low-order methodology with stochastic closure and use of mode decomposition by multichannel Singular Spectrum Analysis. The multilayer stochastic linear model is obtained from the coarse-grained eddy-resolving ocean model solution, and with high accuracy it reproduces the main statistical properties of the decadal variability. The proposed methodology does not depend on the governing fluid dynamics equations and geometry of the problem, and it can be extended to other ocean models and ultimately to the real data.

  13. Stochastic Modeling of Decadal Variability in Ocean Gyres

    NASA Astrophysics Data System (ADS)

    Kondrashov, Dmitri; Berloff, Pavel

    2015-04-01

    Decadal large-scale low-frequency variability of the ocean circulation due to its nonlinear dynamics remains a big challenge for theoretical understanding and practical ocean modeling. This paper presents a novel fully data-driven approach that addresses this challenge. We propose non-Markovian low-order methodology with stochastic closure and data-adaptive mode decomposition. The multilayer stochastic linear model is obtained from the coarse-grained eddy-resolving ocean model solution, and it reproduces with high accuracy the main statistical properties of the decadal variability. The proposed methodology does not depend on the governing fluid dynamics equations and geometry of the problem, and it can be extended to other ocean models and ultimately to the real data.

  14. Multi-decadal Variability of the Wind Power Output

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  15. Seasonal to multi-decadal oxygen variability in the eastern tropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Brandt, Peter; Hahn, Johannes; Krahmann, Gerd; Schmidtko, Sunke

    2015-04-01

    Ocean observations taken in the oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA) are analysed to study seasonal variability to long-term changes in the oxygen distribution and its causes. The dataset includes repeat shipboard hydrographic and velocity measurements along 23°W and multi-year moored observations at several locations between 4°N and 11.5°N. Below the mixed layer, the water column in the ETNA OMZ can be devided into two regimes. A well-ventilated upper layer (above 300 m depth) is separated by a sharp oxycline from the core of the OMZ below. The observations show that the upper layer is dominantly ventilated by zonal advection, while the ventilation of the OMZ core is due to lateral eddy fluxes, vertical mixing, and advection. Both regimes differ in their oxygen variability on seasonal to decadal time-scales. Amplitudes of the annual oxygen cycle are enhanced at the locations of main eastward current bands at approximately 5°N and 8°-9°N. Seasonal variability is out of phase between the upper and deeper layers as well as between the two current bands. Oxygen changes during the last decade are characterized by a strong deoxygenation of the upper layer, while oxygen levels in the OMZ core increased. These differing decadal trends are superimposed on the multi-decadal oxygen decline observed since the 1960s. Spatial patterns of seasonal to decadal oxygen variability suggest a dominant role of the advective oxygen supply for the observed changes.

  16. Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  17. Evaluating SODA for Indo-Pacific Ocean decadal climate variability studies

    NASA Astrophysics Data System (ADS)

    Vargas-Hernandez, J. Mauro; Wijffels, Susan; Meyers, Gary; Holbrook, Neil J.

    2014-11-01

    Estimates of changes in upper ocean temperature, heat content, and sea level are dependent on the coverage of subsurface observations in space and time. Historically, these data are sparse, which has limited our understanding of ocean climate variability and change mechanisms. Ocean state estimates, which effectively represent a model synthesis and integration of the available observations, including internal observations in the ocean and surface forcing, help to address the inhomogeneity of sparse observations in space and time. Here we evaluate the representativeness of ocean state estimates from the Simple Ocean Data Assimilation Version 2.2.4 (SODA) data for studying Indo-Pacific Ocean decadal temperature and sea level variability over the period 1950-2007. The SODA data are evaluated against independent sea level anomalies from long-record tide gauges at Midway Island and Fremantle, reconstructed sea surface height anomalies, and sea surface height anomalies from TOPEX/Poseidon satellite altimeter observations at the decadal time scale. This study demonstrates that SODA captures the characteristic Interdecadal Pacific Oscillation (IPO) over the upper 200 m, and accurately represents these decadal changes against the independent observations. The SODA-product shows a meridional asymmetry of patterns that connect the western tropical Pacific and the Indian Ocean, apparently in relation to IPO changes. Regional sea level at the Midway Island and Fremantle tide gauges confirm this decadal connection and the relationship with the IPO. We concluded that SODA is potentially a useful tool to examine ocean decadal climate variability across the Indo-Pacific Ocean.

  18. Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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).

  19. Drivers of decadal variability in the Tasman Sea

    NASA Astrophysics Data System (ADS)

    Sloyan, Bernadette M.; O'Kane, Terence J.

    2015-05-01

    In this study, we compare optimally interpolated monthly time series Tasman Sea XBT data and a comprehensive set of ocean data assimilation models forced by atmospheric reanalysis to investigate the stability of the Tasman Sea thermocline and the transport variability of the East Australian Current (EAC), the Tasman Front, and EAC-extension. We find that anomalously weaker EAC transport at 25°S corresponds to an anomalously weaker Tasman Front and anomalously stronger EAC-extension. We further show that, post about 1980 and relative to the previous 30 years, the anomalously weaker EAC transport at 25°S is associated with large-scale changes in the Tasman Sea; specifically stronger stratification above the thermocline, larger thermocline temperature gradients, and enhanced energy conversion. Significant correlations are found between the Maria Island station Sea Surface Temperature (SST) variability and stratification, thermocline temperature gradient, and baroclinic energy conversion suggesting that nonlinear dynamical responses to variability in the basin-scale wind stress curl are important drivers of decadal variability in the Tasman Sea. We further show that the stability of the EAC is linked, via the South Caledonian Jet, to the stability of the pan-basin subtropical South Pacific Ocean "storm track."

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

    NASA Astrophysics Data System (ADS)

    Chen, H.; Schneider, E. K.

    2011-12-01

    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.

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

    SciTech Connect

    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

    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.

  2. Tropospheric ozone trends at Mauna Loa Observatory tied to decadal climate variability

    NASA Astrophysics Data System (ADS)

    Lin, Meiyun; Horowitz, Larry W.; Oltmans, Samuel J.; Fiore, Arlene M.; Fan, Songmiao

    2014-02-01

    A potent greenhouse gas and biological irritant, tropospheric ozone is also the primary source of atmospheric hydroxyl radicals, which remove numerous hazardous trace gases from the atmosphere. Tropospheric ozone levels have increased in spring at remote sites in the mid-latitudes of the Northern Hemisphere over the past few decades; this increase has been attributed to a growth in Asian precursor emissions. In contrast, 40 years of continuous measurements at Mauna Loa Observatory in Hawaii reveal little change in tropospheric ozone levels during spring (March-April), but a rise in autumn (September-October). Here we examine the contribution of decadal shifts in atmospheric circulation patterns to decadal variability in tropospheric ozone levels at Mauna Loa using a suite of chemistry-climate model simulations. We show that the flow of ozone-rich air from Eurasia towards Hawaii during spring weakened in the 2000s as a result of La-Niña-like decadal cooling in the eastern equatorial Pacific Ocean. During autumn, in contrast, the flow of ozone-rich air from Eurasia to Hawaii strengthened in the mid-1990s onwards, coincident with the positive phase of the Pacific-North American pattern. We suggest that these shifts in atmospheric circulation patterns can reconcile observed trends in tropospheric ozone levels at Mauna Loa and the northern mid-latitudes in recent decades. We conclude that decadal variability in atmospheric circulation patterns needs to be considered when attributing observed changes in tropospheric ozone levels to human-induced trends in precursor emissions.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  4. Decadal scale variability of sea surface temperature in the Mediterranean Sea in relation to atmospheric variability

    Microsoft Academic Search

    Nikolaos Skliris; Sarantis Sofianos; Athanasios Gkanasos; Anneta Mantziafou; Vasilis Vervatis; Panagiotis Axaopoulos; Alex Lascaratos

    2011-01-01

    Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985-2008) and 35 years of NOCS (V.2) in situ-based SST data (1973-2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in relation to local air-sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate a strong eastward increasing sea surface warming trend

  5. Icarus Revisted: Three Decades of Radar Observations of Asteroids

    NASA Technical Reports Server (NTRS)

    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

    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.

  6. Estimating the limit of decadal-scale climate predictability using observational data

    NASA Astrophysics Data System (ADS)

    Ding, Ruiqiang; Li, Jianping; Zheng, Fei; Feng, Jie; Liu, Deqiang

    2015-05-01

    Current coupled atmosphere-ocean general circulation models can not simulate decadal variability well, and model errors would have a significant impact on the estimation of decadal predictability. In this study, the nonlinear local Lyapunov exponent method is adopted to estimate the limit of decadal predictability based on 9-year low-pass filtered sea surface temperature (SST) and sea level pressure (SLP) observations. The results show that the limit of decadal predictability of the SST field is relatively large in the North Atlantic, North Pacific, Southern Ocean, tropical Indian Ocean, and western North Pacific, exceeding 7 years at most locations in these regions. In contrast, the limit of the SST field is relatively small in the tropical central-eastern Pacific (4-6 years). Similar to the SST field, the SLP field has a relatively large limit of decadal predictability over the Antarctic, North Pacific, and tropical Indian Ocean (>6 years). In addition, a relatively large limit of decadal predictability of the SLP field also occurs over the land regions of Africa, India, and South America. Distributions of the limit of decadal predictability of both the SST and SLP fields are almost consistent with those of their intensity and persistence on decadal timescales. By examining the limit of decadal predictability of several major climate modes, we found that the limit of decadal predictability of the Pacific decadal oscillation (PDO) is about 9 years, slightly lower than that of the Atlantic multidecadal oscillation (AMO) (about 11 years). In contrast, the northern and southern annular modes have limits of decadal predictability of about 4 and 9 years, respectively. However, the above limits estimated using time-filtered data may overestimate the predictability of decadal variability due to the use of time filtering. Filtered noise with the same spectral characteristics as the PDO and AMO, has a predictability of about 3 years. Future work is required with a longer period of observations or using a more realistic model of decadal variability to assess the real-time decadal predictability.

  7. Pacific decadal variability in the view of linear equatorial wave theory

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    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.

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

    Microsoft Academic Search

    Vikram M. Mehta; Thomas Delworth

    1995-01-01

    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

  10. Climatological Mean Features and Interannual to Decadal Variability of Ring Formations in the Kuroshio Extension Region

    NASA Astrophysics Data System (ADS)

    Sasaki, Y. N.; Minobe, S.

    2014-12-01

    We examine the climatological mean features of oceanic rings shed from the Kuroshio Extension jet and their interannual to decadal variability using satellite altimeter observations from October 1992 to December 2010. To objectively capture a ring shedding from the Kuroshio Extension jet, a new method that consists of the detection of the jet length changes and the tracking of a ring is proposed. A spatial distribution of the ring formations in the Kuroshio Extension region indicates that cyclonic (cold-core) rings were most frequently formed in the upstream region between 143°-147°E around the steady meander of the Kuroshio Extension jet. In contrast, most of anticyclonic (warm-core) rings formed in the downstream region west of the Shatsky Rise. These pinched-off rings in both the upstream and downstream regions generally propagate westward, but about two-third of the rings is reabsorbed by the jet. Nevertheless, about one-fourth of the meridional eddy heat transport at the latitude of the Kuroshio Extension results from the rings that are not reabsorbed by the jet. The number of ring formations shows substantial interannual to decadal variability. In the upstream and downstream Kuroshio Extension region, decadal and interannual variability is dominant, respectively. These fluctuations of the ring formations are negatively correlated with the strength of the Kuroshio Extension jet. It is also revealed that the ring formation variations play an important role in sea surface temperature changes north of the Kuroshio Extension jet.

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

    E-print Network

    Wisconsin at Madison, University of

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

  12. Intercomparison of North Atlantic decadal variability in the CMIP3 coupled model database

    Microsoft Academic Search

    F. Alvarez-Garcia; M. J. Ortizbeviá; W. Cabosnarvaez; G. Gomez-Prada

    2009-01-01

    Several mechanisms have been pointed out as possible sources of decadal variability in the North Atlantic ocean. This work attempts to gain further insight into the characteristics of these mechanisms by examining the properties of the North Atlantic decadal variability found in the control simulations available at the CMIP3 coupled model database. Multi-channel Singular Spectrum Analysis of the annual anomalies

  13. Decadal variability of hydrography in the upper northern North Atlantic in 1948-1990

    Microsoft Academic Search

    G. Reverdin; D. Cayan; Y. Kushnir

    1997-01-01

    We investigate the variability of the North Atlantic subarctic gyre in recent decades from time series of station temperature and salinity. Decadal variability stronger at the surface is identified, which exhibits vertical coherence over a layer deeper than the late winter mixed layer. In the northwestern Atlantic, it corresponds to the layer with a component of water from the Arctic

  14. Regional circulation around New Caledonia from two decades of observations

    NASA Astrophysics Data System (ADS)

    Cravatte, Sophie; Kestenare, Elodie; Eldin, Gérard; Ganachaud, Alexandre; Lefèvre, Jérôme; Marin, Frédéric; Menkes, Christophe; Aucan, Jérôme

    2015-08-01

    The regional and near-coastal circulation around New Caledonia is investigated using a compilation of more than 20 years of observations. Velocity profiles acquired by Shipboard Acoustic Doppler Current Profiler (SADCP) during 109 research cruises and ship transits since 1991 are analyzed and compared with absolute geostrophic currents inferred from hydrographic profiles and Argo floats drifts. In addition, altimetric surface currents are used to explore the variability of the circulation at various timescales. By making the best use of the strength of these various observations, this study provides an unprecedented detailed picture of the mean circulation around New Caledonia and of its variability in the upper layers. New Caledonia, together with the Vanuatu Archipelago and the Fiji Islands, acts as a 750-km long obstacle to the westward South Equatorial Current (SEC) entering the Coral Sea. On average, the SEC bifurcates against New Caledonia's east coast into a northwestward boundary current, the East Caledonian Current, beginning east of the Loyalty Islands and extending to at least 1000 m depth, and into a weak southeastward current. The latter, the Vauban Current, flows into the Loyalty channel against the mean trade winds where it extends to at least 500 m depth. It is highly variable at intraseasonal timescales; it often reverses and its variability is mainly driven by incoming mesoscale eddies east and south of New Caledonia. West of the Island, the southeastward Alis Current of New Caledonia (ACNC) flows along the reef slope in the 0-150 m layer. It overlays a weaker northwestward current, creating an unusual coastal circulation reminiscent of the current system along the Australian west coast. The ACNC is a persistent feature of the observations, even if its transport is also strongly modulated by the presence of offshore eddies. This study highlights the fact, if needed, that a snapshot view of the currents provided by a single transect can be strongly impacted by mesoscale eddies, and should be put into context, e.g. by using simultaneous altimetric data.

  15. Satellite observations of cataclysmic variables

    NASA Astrophysics Data System (ADS)

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

    1982-07-01

    The nature of cataclysmic variables (CVs) is discussed and the results of various satellite observations of CVs are assessed. In the early 1970, the dwarf nova EX Hydrae was discovered by Uhuru, and Ariel 5 and HEAO 1 confirmed U Geminorum and SS Cygni as hard X-ray sources. The Einstein satellite in the late 1970s found large numbers of CVs, enabling the study of their energy output in a wide range of spectral bands. The IUE confirmed the thermonuclear nature of classical novae and studied high-velocity winds in dwarf novae. X-ray observations also resulted in the discovery of magnetic variables, whose nature is discussed.

  16. Decadal scale variability of sea surface temperature in the Mediterranean Sea in relation to atmospheric variability

    NASA Astrophysics Data System (ADS)

    Skliris, Nikolaos; Sofianos, Sarantis; Gkanasos, Athanasios; Mantziafou, Anneta; Vervatis, Vasilis; Axaopoulos, Panagiotis; Lascaratos, Alex

    2012-01-01

    Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985-2008) and 35 years of NOCS (V.2) in situ-based SST data (1973-2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in relation to local air-sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate a strong eastward increasing sea surface warming trend from the early 1990s onwards. The satellite-derived mean annual warming rate is about 0.037°C year-1 for the whole basin, about 0.026°C year-1 for the western sub-basin and about 0.042°C year-1 for the eastern sub-basin over 1985-2008. NOCS-derived data indicate similar variability but with lower warming trends for both sub-basins over the same period. The long-term Mediterranean SST spatiotemporal variability is mainly associated with horizontal heat advection variations and an increasing warming of the Atlantic inflow. Analysis of SST and net heat flux inter-annual variations indicates a negative correlation, with the long-term SST increase, driving a net air-sea heat flux decrease in the Mediterranean Sea through a large increase in the latent heat loss. Empirical orthogonal function (EOF) analysis of the monthly average anomaly satellite-derived time series showed that the first EOF mode is associated with a long-term warming trend throughout the whole Mediterranean surface and it is highly correlated with both the Eastern Atlantic (EA) pattern and the Atlantic Multidecadal Oscillation (AMO) index. On the other hand, SST basin-average yearly anomaly and NAO variations show low and not statistically significant correlations of opposite sign for the eastern (negative correlation) and western (positive correlation) sub-basins. However, there seems to be a link between NAO and SST decadal-scale variations that is particularly evidenced in the second EOF mode of SST anomalies. NOCS SST time series show a significant SST rise in the western basin from 1973 to the late 1980s following a large warming of the inflowing surface Atlantic waters and a long-term increase of the NAO index, whereas SST slowly increased in the eastern basin. In the early 1990s, there is an abrupt change from a very high positive to a low NAO phase which coincides with a large change in the SST spatiotemporal variability pattern. This pronounced variability shift is followed by an acceleration of the warming rate in the Mediterranean Sea and a change in the direction (from westward to eastward) of its spatial increasing tendency.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Latif, M.; Barnett, T. P.

    1996-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  20. Decadal to seasonal variability of Arctic sea ice albedo

    E-print Network

    Agarwal, S; Wettlaufer, J S

    2011-01-01

    A controlling factor in the seasonal and climatological evolution of the sea ice cover is its albedo $\\alpha$. Here we analyze Arctic data from the Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder and assess the seasonality and variability of broadband albedo from a 23 year daily record. We produce a histogram of daily albedo over ice covered regions in which the principal albedo transitions are seen; high albedo in late winter and spring, the onset of snow melt and melt pond formation in the summer, and fall freeze up. The bimodal late summer distribution demonstrates the combination of the poleward progression of the onset of melt with the coexistence of perennial bare ice with melt ponds and open water, which then merge to a broad peak at $\\alpha \\gtrsim $ 0.5. We find the interannual variability to be dominated by the low end of the $\\alpha$ distribution, highlighting the controlling influence of the ice thickness distribution and large-scale ice edge dynamics. The statistics obtained pro...

  1. Decadal-Scale Temperature Variability in the Southern Ocean

    E-print Network

    Gille, Sarah T.

    neighbor comparisons ship observation 110 km radius 220 km radius float hydrography: SODB (Olbers et al;Nearest Neighbor Comparisons for Profiling Floats · Hydrography: World Ocean Database 2001 data quality pairs at each depth #12;Stratification changes (from PALACE vs Hydrography) #12;Temperature trend

  2. Variability of western Amazon dry-season precipitation extremes: importance of decadal fluctuations and implications for predictability

    NASA Astrophysics Data System (ADS)

    Fernandes, K.; Baethgen, W.; Verchot, L. V.; Giannini, A.; Pinedo-Vasquez, M.

    2014-12-01

    A complete assessment of climate change projections requires understanding the combined effects of decadal variability and long-term trends and evaluating the ability of models to simulate them. The western Amazon severe droughts of the 2000s were the result of a modest drying trend enhanced by reduced moisture transport from the tropical Atlantic. Most of the WA dry-season precipitation decadal variability is attributable to decadal fluctuations of the north-south gradient (NSG) in Atlantic sea surface temperature (SST). The observed WA and NSG decadal co-variability is well reproduced in Global Climate Models (GCMs) pre-industrial control (PIC) and historical (HIST) experiments that were part of the Intergovernmental Panel on Climate Change fifth assessment report (IPCC-AR5). This suggests that unforced or natural climate variability, characteristic of the PIC simulations, determines the nature of this coupling, as the results from HIST simulations (forced with greenhouse gases (GHG) and natural and anthropogenic aerosols) are comparable in magnitude and spatial distribution. Decadal fluctuation in the NSG also determines shifts in the probability of repeated droughts and pluvials in WA, as there is a 65% chance of 3 or more years of droughts per decade when NSG>0 compared to 18% when NSG<0. The HIST and PIC model simulations also reproduce the observed shifts in probability distribution of droughts and pluvials as a function of the NSG decadal phase, suggesting there is great potential for decadal predictability based on GCMs. Persistence of the current NSG positive phase may lead to continuing above normal frequencies of western Amazon dry-season droughts.

  3. Interannual to Multi-Decadal Variability of Indo-Pacific SST

    NASA Astrophysics Data System (ADS)

    Slawinska, J.; Giannakis, D.

    2014-12-01

    Low-frequency (decadal to centennial) modes of ocean are important components of climate variability. With the rise of supercomputers, these modes are inferred often from long-term climate simulations after being preprocessed by low-pass filtering. Notably, the few modes that are consistently found in many climate models differ significantly, even in frequency, as every model has biases and model errors. At the same time, validation of the extracted signals against observations is limited by the time span of the observational record (e.g., sea surface temperature and sea ice extent observed during the satellite era), which is oftentimes shorter than the timescales of interest and also significantly altered by anthropogenic factors. More importantly, due to preprocessing as well as the subsequent data analysis techniques (such as EOFs), the results have frequently ambiguous physical interpretation. Here, we investigate Indo-Pacific Ocean variability from 1300 control run of CCSM4. For that, we apply recently introduced technique called Nonlinear Laplacian Spectral Analysis (NLSA, Giannakis and Majda 2012). Through this technique, drawbacks associated with ad-hoc filtering are avoided as the extracted signals span many temporal scales without preprocessing the input data, enabling detection of low-frequency and intermittent modes not previously accessible with classical EOF-based approaches. Here, we identify spatiotemporal modes covering multiple scales of interest, including several intraseasonal modes such as ENSO, the Indian Ocean Dipole, and Tropical Biennial Oscillation, revealing refined linkages between these patterns. Additionally, the amplitudes of these patterns are modulated by low-frequency envelopes whose character can in certain cases be related to patterns of decadal or longer variability which are also identified. As such, our study unambiguously clarifies interdependencies between intraseasonal modes which are sometimes treated in the climate science community as independent, but also lead to the identification of previously-unknown decadal to centennial modes. Giannakis, G. and A. J. Majda, 2012: Nonlinear Laplacian spectral analysis for time series with intermittency and low-frequency variability. Proc. Natl. Acad. Sci., 109(7), 2222

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

    Microsoft Academic Search

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

    2000-01-01

    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

  5. OCEAN CIRCULATION. Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises.

    PubMed

    Srokosz, M A; Bryden, H L

    2015-06-19

    The importance of the Atlantic Meridional Overturning Circulation (AMOC) heat transport for climate is well acknowledged. Climate models predict that the AMOC will slow down under global warming, with substantial impacts, but measurements of ocean circulation have been inadequate to evaluate these predictions. Observations over the past decade have changed that situation, providing a detailed picture of variations in the AMOC. These observations reveal a surprising degree of AMOC variability in terms of the intraannual range, the amplitude and phase of the seasonal cycle, the interannual changes in strength affecting the ocean heat content, and the decline of the AMOC over the decade, both of the latter two exceeding the variations seen in climate models. PMID:26089521

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  7. Surface salinity variability in the northern North Atlantic during recent decades

    E-print Network

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

  8. Mesoscale disturbance and ecological response to decadal - scale climate variability in the American Southwest

    Microsoft Academic Search

    Tw Swetnam; Jl Betancourt

    1998-01-01

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

  9. Aerosol Variability Observed with Rpas

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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.

  10. Decadal Variability in the South Atlantic Convergence Zone and Changes in Precipitation over Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Zilli, M. T.; Carvalho, L. V.

    2014-12-01

    The present study examines the role of the South Atlantic Convergence Zone (SACZ) in the observed extreme precipitation changes along the southeast coast of Brazil (-18°S to -25°S). This area is under the influence of the South American Monsoon System (SAMS) and its main feature, the SACZ, which together are related to extreme precipitation events during the wet season (Oct-Mar). Previous studies suggest that one possible change in convergence zones behavior due to climate change is an increase in precipitation intensity at their central portion at the expense of moisture advected from their margin. By analyzing extremes in daily precipitation during the wet season based on more than 70 years of rain gauge data, we identified a positive trend in the intensity of precipitation and a reduction in the number of rainy days over the north portion of southeast coast. Further south, the tendency was for an overall increase in total precipitation. This spatial pattern in extreme precipitation trends along the coast is likely linked to changes in the characteristics of the SACZ. In this study we investigate decadal variations in the SACZ intensity, location and persistence using a multivariate daily index obtained with combined EOF analysis. The variables considered are zonal and meridional winds, temperature and specific humidity at low levels, derived from two different reanalysis datasets: NCEP/NCAR Reanalysis 1 and CFSR. The extent and spatial variability of the SACZ is investigated with daily Outgoing Longwave Radiation (OLR). The focus of this analysis is on intense SACZ events according to the SACZ index. Mechanisms associated with the decadal variability of the SACZ are also explored and include changes in sea surface temperature, the low-level Jet east of the Andes, and changes in circulation and moisture transport over South America and the South Atlantic Ocean.

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

    NASA Technical Reports Server (NTRS)

    Hakkinen, Sirpa

    1998-01-01

    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.

  12. Added-value from initialization in predictions of Atlantic multi-decadal variability

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Identifying regions sensitive to external radiative changes, including anthropogenic (sulphate aerosols and greenhouse gases) and natural (volcanoes and solar variations) forcings, is important to formulate actionable information at multi-year time-scales. Internally-generated climate variability can overcome this radiative forcing, especially at regional level, so that detecting the areas for this potential dominance is likewise critical for decadal prediction. This work aims to clarify where each contribution has the largest effect on North Atlantic sea surface temperature (SST) predictions in relation to the Atlantic multi-decadal variability (AMV). Initialized decadal hindcasts and radiatively-forced historical simulations from the fifth phase of the Climate Model Intercomparison Project are analysed to assess multi-year skill of the AMV. The initialized hindcasts reproduce better the phase of the AMV index fluctuations. The radiatively-forced component consists of a residual positive trend, although its identification is ambiguous. Initialization reduces the inter-model spread when estimating the level of AMV skill, thus reducing its uncertainty. Our results show a skilful performance of the initialized hindcasts in capturing the AMV-related SST anomalies over the subpolar gyre and Labrador Sea regions, as well as in the eastern subtropical basin, and the inability of the radiatively-forced historical runs to simulate the horseshoe-like AMV signature over the North Atlantic. Initialization outperforms empirical predictions based on persistence beyond 1-4 years ahead, suggesting that ocean dynamics play a role in the AMV predictability beyond the thermal inertia. The initialized hindcasts are also more skilful at reproducing the observed AMV teleconnection to the West African monsoon. The impact of the start date frequency is also described, showing that the standard of 5-year interval between start dates yields the main features of the AMV skill that are robustly detected in hindcasts with yearly start date sampling. This work updates previous studies, complementing them, and concludes that skilful initialized multi-model forecasts of the AMV-related climate variability can be formulated, improving uninitialized projections, until 3-6 years ahead.

  13. HERSCHEL OBSERVATIONS OF CATACLYSMIC VARIABLES

    SciTech Connect

    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

    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.

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

    SciTech Connect

    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

    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.

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

    USGS Publications Warehouse

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

    2007-01-01

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

  16. Observed decadal variations in surface solar radiation and their causes

    Microsoft Academic Search

    Atsumu Ohmura

    2009-01-01

    Long-term variations of global solar irradiance at the Earth's surface from the beginning of the observations to 2005 are analyzed for more than 400 sites. Further, likely causes for the variations, an estimation of the magnitudes of aerosol direct and indirect effects, and the temperature sensitivity of the climate system due to radiation changes are evaluated. The record of observed

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

    Microsoft Academic Search

    Thomas W. Swetnam; Julio L. Betancourt

    1998-01-01

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

  18. Herschel Observations of Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    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.

  19. Atlantic forcing of Pacific decadal variability: Forcing of long-term trend and Pacific Climate Shifts

    NASA Astrophysics Data System (ADS)

    Kucharski, Fred; Ikram, Farah; Molteni, Franco; Farneti, Riccardo; No, Hyun-Ho; King, Martin P.; Giuliani, Graziano; Mogensen, Kristian; Kang, In-Sik

    2015-04-01

    This paper investigates the Atlantic Ocean influence on equatorial Pacific long-term changes and three Climate Shift events that occurred in the 20th Century. The latest of these Climate Shift events has been linked previously to the hiatus in global warming. Using an ensemble of simulations, where the ICTPAGCM (``speedy'') is coupled to the NEMO/OPA ocean model in the Indo- Pacific region and forced by observed sea surface temperatures in the Atlantic region, it is shown that the Atlantic warming has had a substantial impact on the long-term tendency for the Pacific Walker circulation to strengthen. The model reproduces the overall tendency for the equatorial eastern (western) Pacific ocean to cool (warm) in the 20th century. From decadal central equatorial Pacific zonal surface wind variability, three major Pacific Climate Shift events are identified that can be characterized by the differences: (i) 1936 to 1950 minus 1910 to 1924, (ii) 1980 to 1994 minus 1958 to1972, (iii) 1998 to 2012 minus 1980 to 1994. From these events, the early 20th century event (i) is reproduced by the model with increased amplitude, the late 20th Century event (iii) is reproduced with reduced amplitude and the mid 70s Climate Shift (ii) is not reproduced in the model. This shows that although the Atlantic has had some role in two individual Climate Shift events, other mechanisms, such as Pacific internal variability are perhaps as important as the Atlantic forcing. The physical mechanism for the Atlantic influence on the Pacific low-frequency variability is consistent with the previously suggested alteration of the Walker circulation, and the resulting low-level wind changes in the central Pacific.

  20. Diagnosing the causes of decadal-scale precipitation variability in northeastern sub-Saharan Africa

    NASA Astrophysics Data System (ADS)

    Williams, P.

    2010-12-01

    The northeastern part of sub-Saharan Africa receives maximum rainfall during summer (June-September), as precipitation tracks the migration of the inter-tropical convergence zone (ITCZ) throughout tropical eastern Africa. Importantly, Ethiopia, Sudan, Eritrea, and northern Uganda experienced substantial precipitation declines during the past 50-60 years. These declines have not been spatially uniform. In the southern portion of this region, the decline has been steady and is ongoing with ~15-20% less summer rainfall in recent years than in the 1950s and 1960s. In the northwest, rainfall is much more variable inter-annually and a partial recovery has occurred after declines of ~30% from 1950-1985. In the northeast, declines from 1950-1985 were less extreme and have since completely recovered. What is the reasoning behind the rainfall declines in these regions, and why have they reversed in the north but continued in the south? I use a variety of observational, reanalysis, and modeled climate data to address these questions. The ongoing intensification of drought in the south is mainly attributable to declining moisture transports from the tropical Indian Ocean as a result of increasing subsidence over the eastern Horn of Africa. The increasing subsidence appears to be associated with warming of the tropical warm pool and increasing convection above the warm pool. In northern Sudan and Ethiopia, the drought from 1950-1985 and subsequent recovery appear to be associated with decadal-scale variability in the position and intensity of the ITCZ. This variability may be due to variations in the contrasting temperatures of the northern and southern hemisphere. I will refer to modeled and reconstructed past climate data to address whether increasing global temperatures have impacted these large-scale climate processes impacting summer rainfall in northeastern sub-Saharan Africa.

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

    Microsoft Academic Search

    Bruce A. Wielicki; Takmeng Wong; Richard P. Allan; Anthony Slingo; Jeffrey T. Kiehl; Brian J. Soden; C. T. Gordon; Alvin J. Miller; Shi-Keng Yang; Franklin Robertson; Joel Susskind; Herbert Jacobowitz

    2002-01-01

    It is widely assumed that variations in Earth's radiative energy budget at large time and space scales are 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. Results indicate that the radiation budget changes are caused

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

    Microsoft Academic Search

    Dmitri Nechaev; Max Yaremchuk; Motoyoshi Ikeda

    2004-01-01

    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

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

    E-print Network

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

  4. The Nature of the Decadal Variability of Surface Climate Over the North Atlantic Ocean --- --- Coupled Ocean-Atmosphere-Sea Ice Interaction Organized by Damped Ocean Mode

    Microsoft Academic Search

    F. He; Z. Liu

    2008-01-01

    The nature of the observed 11-14 year decadal variability of the surface climate over the North Atlantic Ocean is investigated using the Fast Ocean Atmosphere Model (FOAM) and its data-atmosphere configuration. A 14-16 year damped ocean mode, characterized by the decadal variability of Atlantic Meridional Overturning Circulation (AMOC), is found to be able to organize coupled ocean--atmosphere-- sea ice interaction

  5. Decadal climate variability and prediction: Understanding the mid-1970s climate shift and the early-2000s hiatus (Invited)

    NASA Astrophysics Data System (ADS)

    Hu, A.; Meehl, G. A.; Teng, H.; Arblaster, J.; Branstator, G.; Fasullo, J.; Trenberth, K. E.

    2013-12-01

    The interplay between external forcing and internally generated decadal timescale variability is explored through analysis of case studies of multi-decadal climate shifts, focusing particularly on the Pacific. The Interdecadal Pacific Oscillation (IPO) in its positive phase adds to warming from external forcing to contribute to accelerated warming decades like the mid-1970s shift. The IPO in its negative phase counteracts warming from external forcing to contribute to decades with little warming such as the early-2000s hiatus. In the CCSM4 in future climate simulations, hiatus periods with zero global warming trend can last for 15 years due to this internal variability. Initialization with observations produces improvement over uninitialized free-running 20th century simulations for the mid-1970s shift and early-2000s hiatus. A CMIP5 multi-model data set of 30 year predictions shows about 16% less global warming for the period 2016-2035 partly due to initialization with observations during the cooler hiatus, and partly due to a reduced trend from bias adjustment. Initialization also improves predictions of area-averaged Pacific-region precipitation compared to the uninitialized projections for the mid-1970s shift and early-2000s hiatus.

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

    NASA Astrophysics Data System (ADS)

    Henley, Benjamin J.; Thyer, Mark A.; Kuczera, George; Franks, Stewart W.

    2011-11-01

    A hierarchical framework for incorporating modes of climate variability into stochastic simulations of hydrological data is developed, termed the climate-informed multi-time scale stochastic (CIMSS) framework. A case study on two catchments in eastern Australia illustrates this framework. To develop an identifiable model characterizing long-term variability for the first level of the hierarchy, paleoclimate proxies, and instrumental indices describing the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO) are analyzed. A new paleo IPO-PDO time series dating back 440 yr is produced, combining seven IPO-PDO paleo sources using an objective smoothing procedure to fit low-pass filters to individual records. The paleo data analysis indicates that wet/dry IPO-PDO states have a broad range of run lengths, with 90% between 3 and 33 yr and a mean of 15 yr. The Markov chain model, previously used to simulate oscillating wet/dry climate states, is found to underestimate the probability of wet/dry periods >5 yr, and is rejected in favor of a gamma distribution for simulating the run lengths of the wet/dry IPO-PDO states. For the second level of the hierarchy, a seasonal rainfall model is conditioned on the simulated IPO-PDO state. The model is able to replicate observed statistics such as seasonal and multiyear accumulated rainfall distributions and interannual autocorrelations. Mean seasonal rainfall in the IPO-PDO dry states is found to be 15%-28% lower than the wet state at the case study sites. In comparison, an annual lag-one autoregressive model is unable to adequately capture the observed rainfall distribution within separate IPO-PDO states.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  9. A multi-century perspective of variability in the Pacific Decadal Oscillation: new insights from tree rings and coral

    E-print Network

    Gedalof, Ze'ev

    correlated with the Pacific Decadal Oscillation (PDO) index, and provides a better record of PDO variabilityA multi-century perspective of variability in the Pacific Decadal Oscillation: new insights from and consequent surface climate patterns of variability over the Americas. INDEX TERMS: 3344 Meteorology

  10. South Pacific Decadal Variability Since the 1790s and Changes in Earth Surface Temperature

    NASA Astrophysics Data System (ADS)

    Linsley, B. K.; Wu, H. C.; Dassie, E. P.; Schrag, D. P.

    2014-12-01

    Changes in oceanic heat storage may be partly responsible for the most recent stall (or hiatus) in rising Earth surface temperatures since ~2000 C.E. Instrumental data indicates that this most recent stall is coincident with a phase reversal of the North Pacific Decadal Oscillation (PDO). The main locations for this heat exchange with the atmosphere appear to be the tropical and mid-latitude regions of the surface ocean, primarily in the Pacific. We have been investigating poorly understood decadal surface ocean variability in the South Pacific Convergence Zone (SPCZ) region. Despite very sparse instrumental water temperature data in the South Pacific to define the decadal changes at the sea surface and in the upper water column, the available data suggests a disproportionately large role of the Southwest Pacific in decadal-scale changes in heat sequestration. We have generated coral Sr/Ca-derived sea surface temperature (SST) time-series extending back to 1791 C.E. from Fiji, Tonga and Rarotonga (FTR) in the SPCZ region of the subtropical Southwest Pacific and show that decadal-scale SST fluctuations in this broad region are concurrent with the PDO at least since ~1930 C.E. Beginning in the mid-20th century, when more reliable instrumental temperature and ocean heat content data exist, decades of warmer South Pacific subtropical SST co-occur with elevated South Pacific upper ocean (0-700m) heat content. These decadal-scale South Pacific warming events coincide with decadal-scale stalls or plateaus in rising global temperatures. Cross wavelet coherence analysis reveals an increase in the frequency of decadal SST variability from a period near 30 years throughout the 1800s to ~20 years in the later half of the 20th century. Our results provide strong supporting evidence that decadal-scale changes in global surface temperatures are in-part, related to heat storage in the upper water column in the subtropical Pacific. Our results also suggest that decadal-scale stalls in rising global surface temperature are to be expected in the near-future and may be predictable.

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

    E-print Network

    Riser, Stephen C.

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    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.

  13. D/H Ratios From Sierra Nevada Varved Lake Sediments Record Decadal Hydroclimate Variability During The Medieval Period

    NASA Astrophysics Data System (ADS)

    Roach, L. D.; Cayan, D. R.; Sessions, A. L.; Charles, C. D.; Anderson, R. S.

    2009-12-01

    Assessment of the risks of persistent drought requires multiple realizations of decadal and centennial scale hydroclimate variability that extend beyond the relatively short period of instrumental record. Much remains to be learned about the so called “mega droughts” in the Sierra Nevada Mountains, where various lines of evidence point toward the occurrence of severe, decades-long droughts during Medieval times, approximately 900-1400 AD. Here we present a continuous, decadal scale record of hydroclimate variability in the Sierra Nevada Mountains that extends through the heart of the purported Medieval mega droughts. Previous work on the stable hydrogen isotope (D/H) ratios of refractory plant lipid compounds stored in lake sediments demonstrated that these compounds reflect the D/H values of lake water and/or shallow ground water--reservoirs both fed by local precipitation. Lake sediment D/H can therefore reflect the processes that determine D/H of precipitation, including temperature, humidity and moisture source. We have measured D/H of aquatic and terrestrial plant fatty acids extracted from a suite of sediment cores collected at Swamp Lake (elevation: 1554m), in Yosemite National Park, along the Sierra Nevada crest. Measurements with biennial resolution were made for two time periods: the 20th century and the 13th-15th centuries. D/H fluctuations in 20th century sediment contain relatively strong decadal structure. Comparison with instrumentally recorded climate variability reveals that lower D/H concentrations are associated with years of higher than normal annual precipitation, cooler than normal wintertime temperatures, and positive April 1 Snow Water Equivalent (SWE) anomalies throughout the Sierra Nevada, (and conversely for elevated D/H concentrations). The range of variability is approximately 50‰. These associations may be driven by the variable mass-balance impact of evaporation on the isotopic composition of lake water and shallow groundwater in the Swamp Lake watershed, depending on the extent to which these reservoirs are replenished seasonally by wintertime precipitation. Throughout the Medieval period, we observe significant (>30‰), reproducible D/H variability that also fluctuates on multi-year to decadal time scales, with mean values falling within the same range as those recorded over the 20th century. Strong covariance among the aquatic and terrestrial plant fatty acids analyzed, along with the mean values, lends confidence that primary isotopic signatures have been retained. These results can therefore be compared directly to other measures of hydroclimate variability throughout the last millennium, offering a unique new perspective on the mega-drought intervals.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  15. Indian Ocean heat content changes masked by multi-decadal variability: Is the Indian Ocean warming or not?

    NASA Astrophysics Data System (ADS)

    Ummenhofer, Caroline; Biastoch, Arne; Böning, Claus

    2015-04-01

    The Indian Ocean has sustained robust surface warming in recent decades, with warming rates exceeding those of other tropical ocean basins. Significant, non-uniform trends in Indian Ocean sea surface temperatures - both in observations and projections for the 21st Century - have the potential to impact regional climate, through variations in the monsoon circulation, characteristics of Indian Ocean Dipole events, and the associated hydroclimate across the wider Indo-Pacific. However, it remains unclear what role decadal to multi-decadal variability in upper-ocean Indian Ocean thermal characteristics play in these trends. Using high-resolution ocean model hindcasts building on the ocean/sea-ice numerical Nucleus for European Modelling of the Ocean (NEMO) framework forced with atmospheric forcing fields of the Coordinated Ocean Reference Experiments (CORE), the characteristics of Indian Ocean temperature changes are explored. Sensitivity experiments, where interannual atmospheric forcing variability is restricted to thermal or wind-stress forcing only, support the interpretation of forcing mechanisms for the evolution of temperature characteristics across the Indian Ocean, focusing on the top 700m. Simulated temperature changes across the Indian Ocean in the hindcasts are consistent with those recorded in observational products, as well as ocean reanalyses. Assessment of Indian Ocean heat content since the 1950s suggests extensive (subsurface) cooling for much of the tropical Indian Ocean. The presence of substantial multi-decadal variability in its heat content further implies caution in interpreting linear trends in thermal properties, as long-term trends can be masked. The sensitivity experiments reveal that cooling trends in Indian Ocean heat content since the mid-1960s to the late 1990s are largely driven by wind-stress forcing, likely due to remote Pacific wind forcing associated with the Pacific Decadal Oscillation (PDO). As such, multi-decadal wind-forcing has masked increases in Indian Ocean heat content due to thermal forcing since the 1960s. However, wind and thermal forcing both contribute positively to Indian Ocean heat content since 1999 and thus drastic increases in Indian Ocean heat content in coming decades are likely, with implications for regional climate and vulnerable societies in Indian Ocean rim-countries.

  16. Initialized Decadal Climate Predictions of the Observed Early-2000s Hiatus of Global Warming

    NASA Astrophysics Data System (ADS)

    Meehl, G. A.; Teng, H.; Arblaster, J.

    2014-12-01

    The slow-down in the rate of global warming in the early-2000s is not evident in the multi-model ensemble average of traditional climate change projection simulations. However, a number of individual ensemble members from that set of models successfully simulate the early-2000s hiatus when naturally-occurring climate variability involving the Interdecadal Pacific Oscillation (IPO) coincided, by chance, with the observed negative phase of the IPO that contributed to the early-2000s hiatus. If the recent methodology of initialized decadal climate prediction could have been applied in the mid-1990s using the CMIP5 multi-models, both the negative phase of the IPO in the early 2000s as well as the hiatus could have been simulated, with the multi-model average performing better than most of the individual models. The loss of predictive skill for six initial years prior to the mid-1990s points to the need for consistent hindcast skill to establish reliability of an operational decadal climate prediction system.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  18. Climate-informed stochastic hydrological modeling: Incorporating decadal-scale variability using paleoclimate data

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  19. Missing pieces of the puzzle: understanding decadal variability of Sahel Rainfall

    NASA Astrophysics Data System (ADS)

    Vellinga, Michael; Roberts, Malcolm; Vidale, Pier-Luigi; Mizielinski, Matthew; Demory, Marie-Estelle; Schiemann, Reinhard; Strachan, Jane; Bain, Caroline

    2015-04-01

    The instrumental record shows that substantial decadal fluctuations affected Sahel rainfall from the West African monsoon throughout the 20th century. Climate models generally underestimate the magnitude of decadal Sahel rainfall changes compared to observations. This shows that the processes that control low-frequency Sahel rainfall change are misrepresented in most CMIP5-era climate models. Reliable climate information of future low-frequency rainfall changes thus remains elusive. Here we identify key processes that control the magnitude of the decadal rainfall recovery in the Sahel since the mid-1980s. We show its sensitivity to model resolution and physics in a suite of experiments with global HadGEM3 model configurations at resolutions between 130-25 km. The decadal rainfall trend increases with resolution and at 60-25 km falls within the observed range. Higher resolution models have stronger increases of moisture supply and of African Easterly wave activity. Easterly waves control the occurrence of strong organised rainfall events which carry most of the decadal trend. Weak rainfall events occur too frequently at all resolutions and at low resolution contribute substantially to the decadal trend. All of this behaviour is seen across CMIP5, including future scenarios. Additional simulations with a global 12km version of HadGEM3 show that treating convection explicitly dramatically improves the properties of Sahel rainfall systems. We conclude that interaction between convective scale and global scale processes is key to decadal rainfall changes in the Sahel. This work is distributed under the Creative Commons Attribution 3.0 Unported License together with an author copyright. This license does not conflict with the regulations of the Crown Copyright.Crown Copyright

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

    E-print Network

    de Weck, Olivier L.

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

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

    NASA Astrophysics Data System (ADS)

    Dong, Lu; Zhou, Tianjun; Chen, Xiaolong

    2014-12-01

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

  2. Rule-Based System Architecting of Earth Observing Systems: Earth Science Decadal Survey

    E-print Network

    Selva, Daniel

    This paper presents a methodology to explore the architectural trade space of Earth observing satellite systems, and applies it to the Earth Science Decadal Survey. The architecting problem is formulated as a combinatorial ...

  3. Decadal variability and trends of the Benguela upwelling system as simulated in a high-resolution ocean simulation

    NASA Astrophysics Data System (ADS)

    Tim, N.; Zorita, E.; Hünicke, B.

    2015-06-01

    Detecting the atmospheric drivers of the Benguela upwelling systems is essential to understand its present variability and its past and future changes. We present a statistical analysis of a high-resolution (0.1°) ocean-only simulation driven by observed atmospheric fields over the last 60 years with the aim of identifying the large-scale atmospheric drivers of upwelling variability and trends. The simulation is found to reproduce well the seasonal cycle of upwelling intensity, with a maximum in the June-August season in North Benguela and in the December-February season in South Benguela. The statistical analysis of the interannual variability of upwelling focuses on its relationship to atmospheric variables (sea level pressure, 10 m wind, wind stress). The relationship between upwelling and the atmospheric variables differ somewhat in the two regions, but generally the correlation patterns reflect the common atmospheric pattern favouring upwelling: southerly wind/wind stress, strong subtropical anticyclone, and an ocean-land sea level pressure gradient. In addition, the statistical link between upwelling and large-scale climate variability modes was analysed. The El Niño-Southern Oscillation and the Antarctic Oscillation exert some influence on austral summer upwelling velocities in South Benguela. The decadal evolution and the long-term trends of simulated upwelling and of ocean-minus-land air pressure gradient do not agree with Bakun's hypothesis that anthropogenic climate change should generally intensify coastal upwelling.

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

    PubMed

    Laepple, Thomas; Huybers, Peter

    2014-11-25

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

  5. Footprints of decadal climate variability in ozone at Mauna Loa Observatory

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  6. State observers for variable-reluctance motors

    Microsoft Academic Search

    A. Lumsdaine; J. H. Lang

    1990-01-01

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

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

    Microsoft Academic Search

    M. Latif; R. Kleeman; C. Eckert

    1997-01-01

    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

  8. Hiatuses in global warming: the role of volcanic eruptions and Pacific decadal variability

    NASA Astrophysics Data System (ADS)

    Maher, Nicola; England, Matthew; Gupta, Alexander Sen; McGregor, Shayne

    2015-04-01

    The latest generation of climate model simulations is used to investigate hiatuses in global warming. Large tropical volcanic eruptions are found to cause decade long hiatus periods consistently across the models. These eruptions not only cool the globe to cause hiatus decades, but are also found to influence modes of Indo-Pacific variability. Specifically we find an increased probability of an initial positive Indian Ocean Dipole / El Niño-like response followed by a La Niña-like cooling in the third Southern Hemisphere summer after the eruption, which may increase the persistence of the post-volcanic global cooling anomaly. We further demonstrate that most non-volcanic hiatuses across CMIP5 models are associated with enhanced cooling in the equatorial eastern Pacific, linked to a transition to the negative phase of the Interdecadal Pacific Oscillation. Finally, two future scenarios are investigated to determine the likelihood of hiatus periods occurring under different rates of greenhouse gas emissions. Under high rates of greenhouse gas emissions there is little chance of a hiatus decade occurring beyond 2030, even in the event of a large volcanic eruption.

  9. Decadal climatic variability and regional weather simulation: stochastic nature of forest fuel moisture and climatic forcing

    NASA Astrophysics Data System (ADS)

    Tsinko, Y.; Johnson, E. A.; Martin, Y. E.

    2014-12-01

    Natural range of variability of forest fire frequency is of great interest due to the current changing climate and seeming increase in the number of fires. The variability of the annual area burned in Canada has not been stable in the 20th century. Recently, these changes have been linked to large scale climate cycles, such as Pacific Decadal Oscillation (PDO) phases and El Nino Southern Oscillation (ENSO). The positive phase of the PDO was associated with the increased probability of hot dry spells leading to drier fuels and increased area burned. However, so far only one historical timeline was used to assess correlations between the natural climate oscillations and forest fire frequency. To counteract similar problems, weather generators are extensively used in hydrological and agricultural modeling to extend short instrumental record and to synthesize long sequences of daily weather parameters that are different from but statistically similar to historical weather. In the current study synthetic weather models were used to assess effects of alternative weather timelines on fuel moisture in Canada by using Canadian Forest Fire Weather Index moisture codes and potential fire frequency. The variability of fuel moisture codes was found to increase with the increased length of simulated series, thus indicating that the natural range of variability of forest fire frequency may be larger than that calculated from available short records. It may be viewed as a manifestation of a Hurst effect. Since PDO phases are thought to be caused by diverse mechanisms including overturning oceanic circulation, some of the lower frequency signals may be attributed to the long term memory of the oceanic system. Thus, care must be taken when assessing natural variability of climate dependent processes without accounting for potential long-term mechanisms.

  10. Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest

    USGS Publications Warehouse

    Swetnam, T.W.; Betancourt, J.L.

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    Microsoft Academic Search

    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

    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

  13. Naturally driven variability in the global secondary organic aerosol over a decade

    NASA Astrophysics Data System (ADS)

    Tsigaridis, K.; Lathière, J.; Kanakidou, M.; Hauglustaine, D. A.

    2005-07-01

    In order to investigate the variability of the secondary organic aerosol (SOA) distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA to temperature and moisture changes as well as to biogenic emission changes over a decade (1984-1993) has been evaluated. The considered emissions of biogenic non-methane volatile organic compounds (VOC) are driven by temperature, light and vegetation. They vary between 756 and 810 Tg Cy-1 and are therefore about 5.5 times higher than the anthropogenic VOC emissions. All secondary aerosols (sulphuric, nitrates and organics) are computed on-line together with the aerosol associated water. Over the studied decade, the computed natural variations (8%) in the chemical SOA production from biogenic VOC oxidation equal the chemical SOA production from anthropogenic VOC oxidation. Maximum values are calculated for 1990 (warmer and drier) and minimum values for 1986 (colder and wetter). The SOA computed variability results from a 7% increase in biogenic VOC emissions from 1986 to 1990 combined with 8.5% and 6% increases in the wet and dry deposition of SOA and leads to about 11.5% increase in the SOA burden of biogenic origin. The present study also demonstrates the importance of the hydrological cycle in determining the built up and fate of SOA in the atmosphere. It also reveals the existence of significant positive and negative feedback mechanisms in the atmosphere responsible for the non linear relationship between emissions of biogenic VOC and SOA burden.

  14. Naturally driven variability in the global secondary organic aerosol over a decade

    NASA Astrophysics Data System (ADS)

    Tsigaridis, K.; Lathière, J.; Kanakidou, M.; Hauglustaine, D. A.

    2005-03-01

    In order to investigate the variability of the secondary organic aerosol (SOA) distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA to temperature and moisture changes as well as to biogenic emission changes over a decade (1984-1993) has been evaluated. The considered emissions of biogenic non-methane volatile organic compounds (VOC) are driven by temperature, light and vegetation. They vary between 756 and 810 TgC y-1 and are therefore about 5.5 times higher than the anthropogenic VOC emissions. All secondary aerosols (sulphuric, nitrates and organics) are computed on-line together with the aerosol associated water. Over the studied decade, the computed natural variations (8%) in the chemical SOA production from biogenic VOC oxidation equal the chemical SOA production from anthropogenic VOC oxidation. This computed variability results from a 7% increase in biogenic VOC emissions combined with 8.5% and 6% increases in the wet and dry deposition of SOA and leads to about 11.5% increase in the SOA burden of biogenic origin. The present study also demonstrates the importance of the hydrological cycle in determining the built up and fate of SOA in the atmosphere. It also reveals the existence of significant positive and negative feedback mechanisms in the atmosphere responsible for the non linear relationship between emissions of biogenic VOC and SOA burden.

  15. Temporal Variability of Observed and Simulated Hyperspectral Earth Reflectance

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  16. Temporal Variability of Observed and Simulated Hyperspectral Earth Reflectance

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    PubMed

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

    2012-06-01

    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

  18. Internal variability, external forcing and climate trends in multi-decadal AGCM ensembles

    NASA Astrophysics Data System (ADS)

    Bracco, Annalisa; Kucharski, Fred; Kallummal, Rameshan; Molteni, Franco

    2004-11-01

    An atmospheric general circulation model of intermediate complexity is used to investigate the origin and structure of the climate change in the second half of the twentieth century. The variability of the atmospheric flow is considered as a superposition of an internal part, due to intrinsic dynamical variability, and an external part, due to the variations of the sea surface temperature (SST) forcing. The two components are identified by performing a 50-member ensemble of atmospheric simulations with prescribed, observed SSTs in the period 1949 2002. The large number of realizations allows the estimation of statistics of the atmospheric variability with a high confidence level. The analysis performed focuses on interdecadal and interannual variability of 500 hPa geopotential height in the Northern Hemisphere (NH) during winter. The model reproduces well the structure of the observed trend (defined as the difference in the two 25-year intervals 1977 2001 and 1952 1976), particularly in the Pacific region, and about half of the amplitude of the signal. The trend in 500 hPa height projects mainly onto the second empirical orthogonal function (EOF), both in the observations and in the model ensemble. However, differences between the modelled and the observed variability are found in the pattern of the second EOF in the Atlantic sector. SST changes associated with the El Niño southern oscillation (ENSO) are responsible for about 50% of the signal of the 500 hPa height trend in the Pacific. A second 50-member ensemble is used to evaluate the sensitivity of interdecadal variability to an increase in CO2 optical depth compatible with observed concentration changes. In this second experiment, the simulated trend includes a statistically significant contribution from the positive phase of the Arctic oscillation (AO). Such a contribution is also found in observations. Furthermore, the additional CO2 forcing accounts for part of the NH trend in near-surface temperature, and brings the zonal-mean temperature changes in the stratosphere and upper-troposphere closer to observations.

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

    NASA Astrophysics Data System (ADS)

    Committee On Earth Science; Applications From Space

    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.

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

    USGS Publications Warehouse

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

    2014-01-01

    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.

  1. Decadal variation of surface solar radiation in the Tibetan Plateau from observations, reanalysis and model simulations

    NASA Astrophysics Data System (ADS)

    You, Qinglong; Sanchez-Lorenzo, Arturo; Wild, Martin; Folini, Doris; Fraedrich, Klaus; Ren, Guoyu; Kang, Shichang

    2013-04-01

    In this study, the annual and seasonal variations of all-sky and clear-sky surface solar radiation (SSR) in the eastern and central Tibetan Plateau (TP) during the period 1960-2009 are investigated, based on surface observational data, reanalyses and ensemble simulations with the global climate model ECHAM5-HAM. The mean annual all-sky SSR series shows a decreasing trend with a rate of -1.00 Wm-2 decade-1, which is mainly seen in autumn and secondly in summer and winter. A stronger decrease of -2.80 Wm-2 decade-1 is found in the mean annual clear-sky SSR series, especially during winter and autumn. Overall, these results confirm a tendency towards a decrease of SSR in the TP during the last five decades. The comparisons with reanalysis show that both NCEP/NCAR and ERA-40 reanalyses do not capture the decadal variations of the all-sky and clear-sky SSR. This is probably due to a missing consideration of aerosols in the reanalysis assimilation model. The SSR simulated with the ECHAM5-HAM global climate model under both all-sky and clear-sky conditions reproduce the decrease seen in the surface observations, especially after 1980. The steadily increasing aerosol optical depth (AOD) at 550 nm over the TP in the ECHAM5-HAM results suggests transient aerosol emissions as a plausible cause.

  2. Decadal variability in growth of the Caribbean spiny lobster Panulirus argus (Decapoda: Paniluridae) in Cuban waters.

    PubMed

    de León, Maria Estela; Martínez, Juana López; Cota, Daniel Lluch; Vázquez, Sergio Hernández; Rafael, Puga

    2005-01-01

    Annual von Bertalanffy growth parameters of the Caribbean spiny lobster (Panulirus argus) in Cuban waters were estimated from a long term study (40 years) by length-based methods ELEFAN and the new version of SLCA. Data of around 800 000 lobsters (with carapace length ranging 14 to 199mm) were randomly sampled in artificial shelters (a non selective fishing gear very common in the lobster fishery), through the field monitory program established for this species since 1963 in 14 localities of southwestern Cuban shelf. The software ELEFAN showed problems to converge in an optimal combination of the instantaneous growth coefficient (K) and the asymptotic length (Linfinity) of the von Bertalanffy equation, whereas the new SLCA software produced value estimates of K between 0.20 and 0.27 year(-1) and values of Linfinity between 177 and 190 mm carapace length, all within the range reported in the literature. The standardized anomalies of both parameters showed the presence of cycles along the analyzed time series. Decadal variability in growth parameters was revealed through the spectral analysis indicating cycles of 16 and 20 years for K and of 16 years for Linfinity. The incidence of some factors such as biomass and temperature that modulate growth in this crustacean was explored, using a nonlinear multiple regression model. These combined factors explained 33% and 69% of the variability of K and Linfinity respectively. The growth coefficient appeared to be maximum with annual mean sea surface temperature of 28. 1 degrees C and the largest Linfinity is reached at a annual men biomass level of 23,000 t. These results should be the basis to understand the Cuban lobster population dynamics. PMID:17354457

  3. An observational evidence of decrease in Indian summer monsoon rainfall in the recent three decades of global warming era

    NASA Astrophysics Data System (ADS)

    Naidu, C. V.; Dharma Raju, A.; Satyanarayana, G. Ch.; Vinay Kumar, P.; Chiranjeevi, G.; Suchitra, P.

    2015-04-01

    The variability of summer monsoon over India has been studied using the subdivisional rainfall amounts for the period 1871-2012, upper air temperatures, Sea Surface Temperatures [SSTs] and zonal wind components for the period 1953-2012. It is observed that the rainfall activity over India during the last three decades has decreased. CRU [Climate Research Unit] and GPCP [Global Precipitation Climatology Project] rainfall data sets also exhibit a declined rainfall activity over a major part of India. This decrease in rainfall is associated with the decrease in the north-south SST gradient over the North Indian Ocean as well as monsoon circulation over India and neighborhood. Further, a decrease in the soil moisture over a major part of India is observed in the warming environment.

  4. Have Aerosols Caused the Observed Atlantic Multidecadal Variability?

    E-print Network

    Zhang, Rong

    Identifying the prime drivers of the twentieth-century multidecadal variability in the Atlantic Ocean is crucial for predicting how the Atlantic will evolve in the coming decades and the resulting broad impacts on weather ...

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

    NASA Astrophysics Data System (ADS)

    Kooi, Henk

    2008-06-01

    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.

  6. Impact of the river nutrient load variability on the North Aegean ecosystem functioning over the last decades

    NASA Astrophysics Data System (ADS)

    Tsiaras, K. P.; Petihakis, G.; Kourafalou, V. H.; Triantafyllou, G.

    2014-02-01

    The impact of river load variability on the North Aegean ecosystem functioning over the last decades (1980-2000) was investigated by means of a coupled hydrodynamic/biogeochemical model simulation. Model results were validated against available SeaWiFS Chl-a and in situ data. The simulated food web was found dominated by small cells, in agreement with observations, with most of the carbon channelled through the microbial loop. Diatoms and dinoflagellates presented a higher relative abundance in the more productive coastal areas. The increased phosphate river loads in the early 80s resulted in nitrogen and silicate deficiency in coastal, river-influenced regions. Primary production presented a decreasing trend for most areas. During periods of increased phosphate/nitrate inputs, silicate deficiency resulted in a relative decrease of diatoms, triggering an increase of dinoflagellates. Such an increase was simulated in the late 90s in the Thermaikos Gulf, in agreement with the observed increased occurrence of Harmful Algal Blooms. Microzooplankton was found to closely follow the relative increase of dinoflagellates under higher nutrient availability, showing a faster response than mesozooplankton. Sensitivity simulations with varying nutrient river inputs revealed a linear response of net primary production and plankton biomass. A stronger effect of river inputs was simulated in the enclosed Thermaikos Gulf, in terms of productivity and plankton composition, showing a significant increase of dinoflagellates relative abundance under increased nutrient loads.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  8. Multi-decadal variability and trends in the El Niño-Southern Oscillation and tropical Pacific fisheries implications

    NASA Astrophysics Data System (ADS)

    Harrison, D. E.; Chiodi, Andrew M.

    2015-03-01

    Extremes of the El Niño-Southern Oscillation (ENSO) are known to have various socio-economic impacts, including effects on several Pacific fisheries. The 137-year-long record of Darwin sea-level pressure offers a uniquely long-term perspective on ENSO and provides important insight into various aspects of interannual to century-scale variability that affects these fisheries. One particular issue of interest is whether there is a centennial-scale (or longer) trend that can be expected to alter the future distributions of these fisheries. Since most tropical Pacific fishery records are no longer than a few decades, another issue is the extent to which trends over these recent decades are a good basis for detecting the presence of long-term (e.g., centennial-scale) deterministic changes, and perhaps thereby projecting future conditions. We find that the full 137-yr trend cannot be distinguished from zero with 95% confidence, and also that the ENSO variance in recent decades is very similar to that of the early decades of the record, suggesting that ENSO has not fundamentally changed over the period of large increase in atmospheric CO2. However, the strong multi-decadal variability in ENSO is reflected in decades with quite different levels of ENSO effects on the ecosystem. Many multi-decadal subsets of the full record have statistically significant trends, using standard analysis techniques. These multi-decadal trends are not; however, representative of the record-length trend, nor are they a useful basis for projecting conditions in subsequent decades. Trend statistical significance is not a robust foundation for speculation about the future. We illustrate how the difficulties involved in determining whether a trend is statistically significant or not mean that, even after careful consideration, an unexpectedly large number of trends may reach standard statistical significance levels over the time spans for which many newer records are available, but still not continue into future decades or be indicative of deterministic changes to the system. Analysis of the Southern Oscillation Index, another common ENSO index, but one that has been directly measured for fewer years than has Darwin, yields similar results.

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

    NASA Astrophysics Data System (ADS)

    Chu, P. C.; Li, H.

    2011-12-01

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

  10. 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)

    Sandford, Stephen P.

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

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

    SciTech Connect

    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

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  14. Formation and variability of the South Pacific Sea Surface Salinity maximum in recent decades

    NASA Astrophysics Data System (ADS)

    Hasson, Audrey; Delcroix, Thierry; Boutin, Jacqueline

    2013-10-01

    This study investigates causes for the formation and variability of the Sea Surface Salinity maximum (SSS > 36) centered near 18°S-124°W in the South Pacific Ocean over the 1990-2011 period at the seasonal time scale and above. We use two monthly gridded products of SSS based on in situ measurements, high-resolution along-track Voluntary Observing Ships thermo-salinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a seasonal cycle of the location of the 36-isohaline barycenter of about ±400 km in longitude in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show a low frequency westward shift of the barycenter of 1400 km from the mid 1990s to the early 2010s 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 (˜+0.73 pss/yr), the horizontal salinity advection (˜-0.37 pss/yr), and processes occurring at the mixed layer base (˜-0.35 pss/yr).

  15. Formation and variability of the south Pacific sea surface salinity maximum in recent decades

    NASA Astrophysics Data System (ADS)

    Hasson, Audrey; Delcroix, Thierry; Boutin, Jacqueline

    2014-05-01

    This presentation investigates causes for the formation and the variability of the Sea Surface Salinity (SSS) maximum of the South Pacific Ocean over the 1990-2011 period at the seasonal timescale and above. We use a monthly 1ºx1º gridded product of SSS based on in-situ measurements, high-resolution along-track Voluntary Observing Ships thermosalinograph data, 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 an interannual westward shift of the barycentre of 1400 km. The possible origins of this shift, that could not be linked to the El Nino Southern Oscillation phenomena, are discussed. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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).

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  19. Anthropogenic Forcing and Decadal Climate Variability in Sensitivity Experiments of Twentieth and Twenty-First-Century Climate

    Microsoft Academic Search

    Gerald A. Meehl; Warren M. Washington; Julie M. Arblaster; Thomas W. Bettge; Warren G. Strand Jr.

    2000-01-01

    A methodology is formulated to evaluate the possible changes in decadal-timescale (10-20-yr period) surface temperature variability and associated low-frequency fluctuations of anthropogenic forcing and changes in climate base state due to the forcing in simulations of twentieth- and twenty-first-century climate in a global coupled climate model without flux adjustment. The two climate change experiments both start in the year 1900.

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

    Microsoft Academic Search

    David W. Peterson; David L. Peterson

    2001-01-01

    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

  1. Influence of Mean State on Climate Variability at Interannual and Decadal Time Scales 

    E-print Network

    Zhu, Xiaojie

    2013-05-17

    for many phenomena associated with variables that are nonlinear by definition, such as the vertical wind shear and surface wind speed. In the first part of this dissertation, the influence of mean flow and anomalous flow on vertical wind shear variability...

  2. Observing Variable Stars, Novae and Supernovae

    NASA Astrophysics Data System (ADS)

    North, Gerald; James, Nick

    2014-08-01

    1. Foundations, federations and finder-charts; 2. Variables in vision; 3. Astrovariables reckoned; 4. Photometry; 5. Stars great and small; 6. Variable beginnings; 7. Clockwork pulsators; 8. Less regular single-star variables; 9. Eclipsing binary stars and novae; 10. Cataclysmic and symbiotic systems; 11. The extra-galactic realm; Appendices.

  3. Validation of the German Mid-Range Climate Prediction (MiKlip) decadal ensemble prediction system using radiosonde observations.

    NASA Astrophysics Data System (ADS)

    Pattantyús-Ábrahám, Margit; Steinbrecht, Wolfgang

    2015-04-01

    We report validation results for three simulations by the Max-Planck-Institute's Earth System Model (MPI-ESM) ensemble prediction system (EPS), which is used for hindcasts and predictions of global-scale decadal climate variability in the framework of the German MiKlip project. Three experiments were analyzed: Baseline0 simulations with ocean anomaly field initialization, Baseline1 simulations with additional atmospheric full field initialization, and Prototype simulations with full field initialization for both ocean and atmosphere. Our validation compares homogenized radiosonde observations to the decadal ensemble hindcast projections. So far, we focused on the European region. Comparison of observed and simulated European temperature profiles showed noticeable model cold bias, about 1 K near the surface, increasing to about 3 K near the tropopause. This has implications for atmospheric stability, which is underestimated in the simulations compared to the radiosonde profiles. The simulations also tend to overestimate humidity throughout the troposphere. Both biases combine to give, e.g., much larger simulated values for standard severe weather indices, which might be interpreted as higher severe weather probability in the simulations. While Baseline 0 and Baseline 1 simulations showed no dependence of temperature bias on simulation lead years, the temperature bias of Prototype simulations increased systematically with increasing lead years. Apart from bias and probability density functions, the predictive skills of the Ensemble Prediction System were also analyzed with respect to the radiosonde observations. Here the Mean Square Error Skill Score (MSESS) and Continuously Ranked Probability Skill Scores (CRPSS) were used. For tropospheric temperatures, the full-field initialized Prototype experiments showed the best skills (MSESS and CRPSS), compared to the Baseline 0 and 1 experiments. In the stratosphere predictive skills were comparable for all experiments.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Bearden, David A.

    2002-01-01

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

  6. Climate-Informed Multi-Scale Stochastic (CIMSS) Hydrological Modeling: Incorporating Decadal-Scale Variability Using Paleo Data

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Incorporating the influence of climate change and long-term climate variability in the estimation of drought risk is a priority for water resource planners. Australia's highly variable rainfall regime is influenced by ocean-atmosphere climate mechanisms which induce decadal-scale variability in hydrological data. This talk will summarize research on the identification of appropriate models for incorporating decadal scale variability into stochastic hydrological models. These will include autoregressive, hidden Markov models and a Bayesian hierarchical approach which combines paleo information on climate indices and hydrological data into a climate informed multi-time scale stochastic (CIMSS) framework. To characterize long-term variability for the first level of the hierarchy, paleoclimate and instrumental data describing the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO) are analyzed. A new paleo IPO-PDO time series dating back 440 yr is produced, combining seven IPO-PDO paleo sources using an objective smoothing procedure to fit low-pass filters to individual records. The paleo data analysis indicates that wet/dry IPO-PDO states have a broad range of run lengths, with 90% between 3 and 33 yr and a mean of 15 yr. Model selection techniques were used to determine a suitable stochastic model to simulate these run lengths. For the second level of the hierarchy, a seasonal rainfall model is conditioned on the simulated IPO-PDO state. Application to two high quality rainfall sites close to water supply reservoirs found that mean seasonal rainfall in the IPO-PDO dry state was 15%-28% lower than the wet state. Furthermore, analysis of the impact of the CIMSS framework on drought risk analysis found that short-term drought risks conditional on IPO/PDO state were far higher than the traditional AR(1) model.

  7. Observation of methane in this decade by ground-based FTIR Spectrometer over Poker Flat, ALASKA

    NASA Astrophysics Data System (ADS)

    Kasai, Y.; Kagawa, A.; Jones, N. B.; Murayama, Y.

    2010-12-01

    Tropospheric CH4 is an important greenhouse gas as second largest radiative forcing in the troposphere with a long lifetime of ~10 years (Rinsland et. al., 2005). Poker Flat is a suitable location to detect CH4 abnormally due to Siberian/Alaskan biomass burning (Kasai et. al., 2005), volcano, and an anthropogenical emissions such as gas leakage from pipe-lines. We have been observed troposheric CH4 over 10 years between 2000-2010 by using ground-based spectroscopic infrared solar absorption remote sensing measurement over Poker Flat, ALASKA (65.11N, 147.42W, 0.61km). CH4 vertical profiles were obtained by using SFIT2 ver.3.9 which incorporates Rodgers’ formulation of the Optimal Estimation Method (OEM) with an iterative Newton scheme (Rodgers, 2000). Frequency region of the CH4 is used 2600-2900 cm-1 region with the resolution 0.036cm-1. Seasonal and annual variation of the tropospheric CH4 in this decades was obtained. Increasing trend of tropospheric CH4 was observed. Several enhancement and depletion events were also observed.

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

    NASA Astrophysics Data System (ADS)

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

    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.

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

    SciTech Connect

    Tippett, Michael K. [Columbia University

    2014-04-09

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  11. Shoreline variability from days to decades: Results of long-term video imaging

    NASA Astrophysics Data System (ADS)

    Pianca, C.; Holman, R.; Siegle, E.

    2015-03-01

    The present work characterizes the time-space scales of variability and forcing dependencies of a unique 26 year record of daily to hourly shoreline data from a steep beach at Duck, North Carolina. Shoreline positions over a 1500 m alongshore span were estimated using a new algorithm called ASLIM based on fitting the band of high light intensity in time exposure images to a local Gaussian fit, with a subsequent Kalman filter to reduce noise and uncertainty. Our findings revealed that the shoreline change at long times scales dominates seasonal variability, despite that wave forcing had only 2% variance at interannual frequencies. The shoreline response presented 66% of the variance at interannual scales. These results were not expected since from wave forcing it would have been expected that the shoreline response should similarly lack interannual variability, but we found it to be dominated by this scale. The alongshore-mean shoreline time series revealed no significant annual cycle. However, there are annual oscillations in the shoreline response that are coherent with wave forcing and deserves further explanations. The pier was found to have a significant influence on shoreline behavior since restricts the seasonal longshore transport between the sides, resulting in a seasonally reversing sediment accumulation. Thus, there is a significant annual peak in shoreline variability that is coherent with the annual forcing but becomes insignificant in the longshore-average.

  12. Temporal variability of Centropages typicus in the Mediterranean Sea over seasonal-to-decadal scales

    Microsoft Academic Search

    Maria Grazia Mazzocchi; Epaminondas D. Christou; Iole Di Capua; M Fernández de Puelles; Serena Fonda-Umani; Juan Carlos Molinero; Paul Nival; Ioanna Siokou-Frangou

    2007-01-01

    Centropages typicus is one of the most common, abundant and best studied calanoid copepods in neritic waters of the Mediterranean Sea, which means it can provide useful information about the long-term dynamics of the Mediterranean epipelagic ecosystem. This paper presents the first comparative overview of the seasonal and long-term variability of C. typicus in different Mediterranean regions. This review is

  13. 30-Year satellite record reveals contrasting Arctic and Antarctic decadal sea ice variability

    E-print Network

    Vinnikov, Konstantin

    processes (0689); 4227 Oceanography: General: Diurnal, seasonal, and annual cycles. Citation: Cavalieri, D], with a noted asymmetry between Arctic and Antarctic variabilities and trends [Cavalieri et al., 1997­1998 [Zwally et al., 2002]. This hemispheric asymmetry is not inconsistent with some GCM simulations in which

  14. Naturally driven variability in the global secondary organic aerosol over a decade

    Microsoft Academic Search

    K. Tsigaridis; J. Lathière; M. Kanakidou; D. A. Hauglustaine

    2005-01-01

    In order to investigate the variability of the secondary organic aerosol (SOA) distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA

  15. Naturally driven variability in the global secondary organic aerosol over a decade

    Microsoft Academic Search

    K. Tsigaridis; M. Kanakidou; D. A. Hauglustaine

    2005-01-01

    In order to investigate the variability of the sec- ondary organic aerosol (SOA) distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been ap- plied. The response of the global budget

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  17. North Sea sea level rise and the role of inter-annual to multi-decadal variability since the late 19th century

    NASA Astrophysics Data System (ADS)

    Dangendorf, S.; Wahl, T.; Arns, A.; Jensen, J.

    2013-12-01

    The recent interest in potential climate change impacts has encouraged sea level scientists to focus mainly on long-term trends and acceleration patterns in mean sea level (MSL) on both global and regional scales. However, these long-term changes are superimposed by large inter-annual to multi-decadal variability exacerbating reliable estimates of longer-term changes and the distinction of internal-climatic and anthropogenic signals. The present study aims at identifying major influences on sea level rise and variability from 31 tide gauge records in the entire North Sea basin since the late 19th century. It is analyzed which forcing factors were responsible for the observed sea level variations on different timescales and whether they are important for the detection of longer-term trend and acceleration patterns. It is found that atmospheric forcing plays the most important role; depending on the region up to 80% of the observed variability can be explained by local atmospheric forcing (wind stress, inverse barometric effect (IBE)) when focussing on timescales up to a decade. In the northern part of the North Sea the IBE dominates MSL variability, whereas the southern parts are mainly influenced by wind stress, driving a counter-clockwise circulation within the basin and piling up the water at the coastlines. On multi-decadal scales, remote forcing over the North Atlantic (long-shore winds and wave propagation) is mainly responsible for the observed changes in the entire basin. We combine the different forcing factors as predictors in a multiple linear regression model (LRM) and examine their common effects on trend and acceleration patterns of MSL. The results are twofold: First, the uncertainties of trend estimations can be considerably reduced when removing these atmospheric influences. In this region standard errors (SEs) < 0.5 mm/yr are obtained when at least 60 years of tide gauge data are available. After the removal only ~30 years of data are required. Second, a comparison of trend rates from observations and the LRM indicates that major parts of highs and lows in the rates of rise can be explained by changes in local and large scale wind fields. The results clearly demonstrate the large amount of natural variability in MSL time series that has to be considered when analyzing long-term changes. When determining acceleration patterns such short-term fluctuations may have a significant impact on the results, especially if only short time series such as from satellite altimetry are available.

  18. Decadal Climate Variability: Economic Implications in Agriculture and Water in the Missouri River Basin 

    E-print Network

    Fernandez Cadena, Mario

    2013-07-23

    and energy supply and demand balances, yields from fisheries, and modulate higher frequency events such as floods and droughts. Moreover, their low frequency natural variability may obscure human influences on hydrologic variations and climate change...). The appearance of longer periodicities combined with a greater number of large PDO?ENSO climate swings reveal anomalous conditions in the 1900s. This has significant implications for climate change research because anthropogenic greenhouse warming may...

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

    Microsoft Academic Search

    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

    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

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

    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.

  1. Modelling the response of cyanobacteria to pH-variability on seasonal to decadal time scales

    NASA Astrophysics Data System (ADS)

    Hofmeister, Richard; Hinners, Jana; Hense, Inga

    2015-04-01

    Cyanobacteria blooms regularly occurred in the Baltic Sea during the last decades. The possible effects of increasing temperatures and eutrophication on cyanobacteria have been already investigated. This model study concentrates on the combined effect of expected temperature increase and ocean acidification on cyanobacteria blooms in the Baltic Sea. We make use of an established model system that comprises the life cycle model of cyanobacteria (CLC) and a biogeochemical model (ERGOM), a carbon chemistry model, and the water column model GOTM. These models are modularly coupled through the framework for aquatic biogeochemical models (FABM). In the CLC model, the cyanobacteria growth is dependent on the sea water pH following the results of experimental studies. The numerical experiments are forced by the output of a regional climate model (RCAO) for the period 1960-2100. A number of simulations are performed for different configurations of the coupled ecosystem, in order to estimate the effect of acidification and the effect of seasonally varying pH on the cyanobacteria bloom. Our simulation experiments show that cyanobacteria growth is stimulated by the increase of temperature in the future, while the blooms' strength decreases in the second half of the 21th century due to ocean acidification. The magnitude and trend of cyanobacteria concentrations are also affected by the seasonal variations of pH. Overall, the results show that the combined effect of the climate stressors, warming and acidification, on the cyanobacteria bloom is weak.

  2. Variations of the Arabian Sea nitrogen cycle: trend or decadal variability?

    NASA Astrophysics Data System (ADS)

    Gaye, Birgit; Tim, Rixen; Böll, Anna; Wiggert, Jerry

    2015-04-01

    Warmer periods of the Holocene have been characterized by a northward shift of the intertropical convergence zone (ITCZ), especially in the South Asian Monsoon sector, thereby increasing the strength and northward extension of monsoon rains. Marine sediments record increased monsoonal upwelling in the Arabian Sea during such warming periods associated with increased denitrification in the oxygen minimum zone. A similar increase can be expected due to anthropogenic warming as it may have a strong impact on Central Asia where feed-back mechanisms of stronger summer warming such as melting of glaciers and reduced albedo may increase summer monsoon strength and thus upwelling and productivity in the Arabian Sea. Models have so far had difficulties to simulate the ITCZ fluctuation in the monsoon area and to make reasonable predictions of its response to global warming. Recent data analyses showed a decrease of oxygen and an increase of nitrite concentrations in the northern part of the Arabian Sea during the last 50 years which could be related to a strengthening of the summer monsoon. To identify whether recent changes in productivity, sea surface temperatures and denitrification are related to decadal fluctuations or global warming trends, we take a comprehensive, multi-disciplinary approach that makes use of the available remote sensing records, nutrient data, and sediment trap as well as high resolution sedimentary records.

  3. Estimating seasonal and interannual variability in ice mass loss using a stochastic filter and decade-long GRACE time series

    NASA Astrophysics Data System (ADS)

    Wang, L.; Davis, J. L.; Hill, E.; Tamisiea, M. E.

    2013-12-01

    Monthly gravity estimates produced by the Gravity Recovery and Climate Experiment (GRACE) satellite mission have been used to investigate the mass loss of glaciers and ice sheets. The mass loss signals have significant temporal (seasonal and interannual) as well as spatial variability. To obtain accurate estimates of present-day melting from decade-long GRACE measurements, a model that allows for variabilities in both mass loss rates and seasonal signals would seem appropriate. A stochastic filter approach enables us to estimate variable melting rates and seasonal amplitudes. However, it requires the statistical information on various signals and errors in the monthly GRACE estimates. Unfortunately, monthly GRACE gravity fields are contaminated by order-dependent correlated errors in the short-wavelength components, manifesting themselves as north-south elongated linear stripes in the map of surface mass changes. The widely used 'ad-hoc' destriping method is not able to preserve statistical information, and is thus inappropriate for the stochastic filter approach. In this study, we present decade-long mass variations estimated using a Kalman filter approach, which is designed to separate geophysical signals and correlated 'stripe' contamination in a series of GRACE monthly spherical-harmonic coefficient (SHC) estimates. This technique preserves statistical information, and thus enables us to estimate the impact on the SHC uncertainties associated with the destriping. The calculations are statistically rigorous and enable estimation of space-dependent robust uncertainties for ice melting rates. The Kalman-filter approach also provides smooth estimates of the gravity field that are devoid of stripes and that do not require smoothing. We use the newly produced gravity fields to revisit mass loss signals in the cryosphere, with an emphasis on investigating seasonal and interannual variabilities.

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

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  6. The decadal variability of the tropical Indian Ocean SST-the South Asian High relation: CMIP5 model study

    NASA Astrophysics Data System (ADS)

    Qu, X.; Huang, G.

    2015-07-01

    Based on Coupled Model Intercomparison Project phase 5 (CMIP5) models, present study investigates the decadal variability of the tropical Indian Ocean (TIO) sea surface temperature (SST)-the South Asian High (SAH) relation (hereafter TSR) as well as its responses to the global warming. Out of the 17 CMIP5 models, only one (GFDL-CM3) reproduces reasonably the influence of the TIO SST on the SAH. In the historical simulations of GFDL-CM3, the TSR features fluctuations modulated by the western Pacific SST and the Indian subcontinent precipitation. When the TIO warming is accompanied by warm western Pacific, the western Pacific SST-induced tropospheric warming propagates westwards, warms the troposphere surrounding the Indian Ocean, enhances SAH and leads to higher TSR; when accompanied by not so warmed western Pacific, the TSR is lower. While, if the TIO warming is accompanied by negative rainfall anomalies over the Indian subcontinent, the rainfall-induced upper-troposphere cyclone over the subtropical Asia weakens the response of the SAH and leads to lower TSR; if not accompanied by negative rainfall anomalies, the TSR is higher. The decadal variability of the TSR is not subject to the global warming. In RCP45 and RCP85 scenarios, the TSR is also not directly affected by global warming. The rainfall over the Indian subcontinent is still a factor modulating the TSR. While, the western Pacific SST is invalid in the influences of the TIO SST on the SAH.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. Investigating decadal variability of El Nino-Southern Oscillation asymmetry by conditional nonlinear optimal perturbation

    Microsoft Academic Search

    Wansuo Duan; Mu Mu

    2006-01-01

    The observed El Nino events are generally stronger than the La Nina events. This property of El Nino-Southern Oscillation (ENSO) is termed as ENSO asymmetry. Evidence is presented to show that this asymmetry has changed since the famous 1976 climate shift. Along the thinking of how the tropical background field modulates ENSO cycle, we explore the effect of the climatological

  9. Decadal slowdown in global air temperature rise triggered by variability in the Atlantic Meridional Overturning Circulation

    NASA Astrophysics Data System (ADS)

    England, Matthew H.

    2015-04-01

    Various explanations have been proposed for the recent slowdown in global surface air temperature (SAT) rise, either involving enhanced ocean heat uptake or reduced radiation reaching Earth's surface. Among the mechanisms postulated involving enhanced ocean heat uptake, past work has argued for both a Pacific and Atlantic origin, with additional contributions from the Southern Ocean. Here we examine the mechanisms driving 'hiatus' periods originating out of the Atlantic Ocean. We show that while Atlantic-driven hiatuses are entirely plausible and consistent with known climate feedbacks associated with variability in the Atlantic Meridional Overturning Circulation (AMOC), the present climate state is configured to enhance global-average SAT, not reduce it. We show that Atlantic hiatuses are instead characterised by anomalously cool fresh oceanic conditions in the North Atlantic, with the atmosphere advecting the cool temperature signature zonally. Compared to the 1980s and 1990s, however, the mean climate since 2001 has been characterised by a warm saline North Atlantic, suggesting the AMOC cannot be implicated as a direct driver of the current hiatus. We further discuss the impacts of a warm tropical Atlantic on the unprecedented trade wind acceleration in the Pacific Ocean, and propose that this is the main way that the Atlantic has contributed to the present "false pause" in global warming.

  10. New Observations of Three Lyra Variables

    Microsoft Academic Search

    Jerry D. Horne

    2009-01-01

    New V, B, Ic, and R band photometry is obtained for V480 Lyr, V575 Lyr and GSC 2118-0402. These new observations, when combined with other published observational data, allowed the determination of multiple period values for each star. From its multi-period behavior and from an examination of other intrinsic parameters, V480 Lyr was determined to be that of an RV

  11. One decade of thermohaline variability in the deep western Mediterranean Sea (2004-2014)

    NASA Astrophysics Data System (ADS)

    Schroeder, Katrin; Ismail, S. Ben; Bryden, Harry; Borghini, Mireno; Sparnocchia, Stefania; Chiggiato, Jacopo; Ribotti, Alberto

    2015-04-01

    Recent intense deep water formation events in the western Mediterranean have produced a huge amount of a new deep water. Significantly warmer and saltier than previously, it substituted the resident deep water. The deep structure and properties began to change after winter 2004/2005 and the water rapidly spread towards the interior of the basin, in the direction of the Strait of Gibraltar and within the Tyrrhenian Sea. The changes observed over the past 10 years are substantial: since 2004 we witnessed increases in deep water temperature and salinity 3-4 times faster than during 1961-2004. The possible impacts these changes could have on a global scale are still an open issue.

  12. Climate Predictions and Projections in the Coming Decades: Uncertainty due to Natural Variability

    NASA Astrophysics Data System (ADS)

    Hurrell, J. W.; Deser, C.; Phillips, A.

    2013-12-01

    Future climate change at local and regional scales will result from a combination of human and natural factors. In this talk we show that unpredictable, internally-generated climate fluctuations make a substantial contribution to climate trends projected for the next 50 years over North America and Europe. Results are based on large ensembles of climate change integrations with the Community Earth System Model (CESM). We also will show that the large-scale atmospheric circulation is responsible for much of the diversity in climate change projections across the individual ensemble members. We conclude by discussing some implications of the results for model validation, inter-model comparisons, and interpretation of observed climate trends.

  13. 6) Midlatitude stratospheric variability and sudden stratospheric a) Observations

    E-print Network

    Lott, Francois

    1 6) Midlatitude stratospheric variability and sudden stratospheric warmings a) Observations b of vertically propagating Rossby waves a) Observations: the daily variability in the stratosphere #12 penetrate in the stratosphere The planetary waves only penetrate in winter The wave s=1 dominates a

  14. Observed variability of aircraft noise footprint measurements

    NASA Technical Reports Server (NTRS)

    Maglieri, D. J.; Henderson, H. R.; Hilton, D. A.

    1977-01-01

    A description is presented of some measurements which illustrate the variability of the experimentally developed ground noise footprints for a series of landing approach operations of a turbojet aircraft and a turbine powered helicopter. Measurements on the recently developed NASA Remotely Operated Multiple Array Acoustic Range are considered. The information presented is related to a turbojet fighter aircraft and a turbine powered helicopter performing landing approach operations along a 3 deg approach path. Each vehicle was acquired on radar tracking approximately 10 kilometers from the touchdown point and entered the test area at an altitude of about 470 m. The measured variations in meteorological quantities for the two time periods during which these tests were conducted are presented in graphs. Other graphs show the ground noise contour for the turbojet aircraft and the turbine helicopter.

  15. 8) Stratospheric equatorial variability a) Observations

    E-print Network

    Lott, Francois

    oscillation #12;3 Kelvin wave Index for entrance in the low stratosphere based on T at 21km filtred) a) Observations: Equatorial waves and quasi biennal oscillation #12;6 Index de l'OQB Moyenne du vent oscillation b) Quasi-Biennal Oscillation explained in terms of gravity waves mean flow interactions c

  16. An Assessment of the Potential Predictability of Interannual and Decadal Variability Based on Climate Model Simulations with Specified SST

    NASA Technical Reports Server (NTRS)

    Schubert, Siegfried; Wang, Hailan; Suarez, Max; Koster, Randal

    2009-01-01

    The USCLIVAR working group on drought recently initiated a series of global climate model simulations forced with idealized SST anomaly patterns, designed to address a number of uncertainties regarding the impact of SST forcing and the role of land-atmosphere feedbacks on regional drought. The runs were done with several global atmospheric models including NASA/NSIPP-1, NCEP/GFS, GFDL/AM2, and NCAR CCM3 and CAM3.5. Here we focus on the potential predictability associated with the leading patterns of inter-annual and decadal Pacific SST variability. Specific issues addressed include the nature of the seasonality and regionality of the signal, the noise, and the signal-to-noise ratios, as well as the dependence of the results on the models.

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

    PubMed Central

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  19. Variability of the Tropical Atlantic and Pacific SSS Minimum Zones in the Last Three Decades and Their Relations to the ITCZ and NECC

    NASA Astrophysics Data System (ADS)

    Delcroix, T. C.; Tchilibou, M. L.; Alory, G.; Reverdin, G. P.; Arnault, S.

    2014-12-01

    This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters located from the West to the East within about 2°N-12°N in the Atlantic and Pacific oceans. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats and (few) CTD profiles. We show that the mean position of the Atlantic and Pacific low SSS waters is tightly related to the local minimum in Evaporation minus Precipitation (E-P) budget linked to the Inter Tropical Convergence Zones (ITCZ) and to salt transport by the eastward flowing North Equatorial Counter Current (NECC). We also show via EOF analyses that the meridional position of this SSS minimum varies both at seasonal time scale, with a northernmost position in boreal summer, and at interannual time scale in relation with ENSO and the Atlantic meridional mode, with however subtle differences in timing between the western, central and eastern basins. The role of the ITCZ-related E-P budget and NECC-related salt advection in these seasonal and interannual changes is examined. We further document the long-term meridional migration of these low SSS waters in the last three decades and discuss whether or not it is consistent with the expected global change effects.

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

    USGS Publications Warehouse

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

    2011-01-01

    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.

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

    PubMed Central

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

    2013-01-01

    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. PMID:24948849

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  3. Observed Global Precipitation Variability During the 20th Century

    E-print Network

    Anisimov, Mikhail

    models WHY? (Do we observe weather/climate?) #12;n Global Averages - do observations and models agreeObserved Global Precipitation Variability During the 20th Century Phil Arkin and John Janowiak on global (or regional) means? n Annual Cycle ­ global, hemispheric, land/ocean n Long-term Change ­ models

  4. Bayesian Network Models for Local Dependence among Observable Outcome Variables

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  5. Einstein x-ray observations of cataclysmic variables

    SciTech Connect

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

    1982-01-01

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

  6. Improving flood prediction by assimilation of the distributed streamflow observations with variable uncertainty and intermittent behavior

    NASA Astrophysics Data System (ADS)

    Mazzoleni, Maurizio; Alfonso, Leonardo; Solomatine, Dimitri

    2015-04-01

    Data assimilation techniques have been used in the last decades to integrate water measurements for physical sensors in mathematical model in order to improve flood prediction. Parallel to this, the continued technological improvement has stimulated the spread of low-cost sensors used to infer hydrological variables in a more distributed way but less accurately. The main goal of this study is to demonstrate how assimilation of streamflow observations having variable uncertainty and intermittent characteristics can improve flood prediction using hydrological model. The methodology is applied in the Brue catchment, South West of England. The catchment is divided in small sub-basins, about 2km2 resolution, in order to represent the spatial variability of the streamflow observations by means of a semi-distributed Kalinin-Milyukov-Nash Cascade model. The measured precipitation values are used as perfect forecast input in the hydrological model. Then, an Ensemble Kalman filter is implemented and adapted to account for streamflow observations having random uncertainty and coming at irregular time steps. Due to the fact that distributed observations are not available within the Brue basin, synthetic streamflow values are generated. The results show how streamflow observations having variable uncertainty can improve the flood prediction according to the location from which these observations are coming. Overall, streamflow observations coming from low cost sensors can be integrated with physical sensors observation to improve flood prediction. This study is part of the FP7 European Project WeSenseIt Citizen Water Observatory (www.http://wesenseit.eu/).

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

    Microsoft Academic Search

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

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

  9. A Decade of Global CO2 Observations from the Satellite Instrument SCIAMACHY

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Technical Reports Server (NTRS)

    Markevitch, Maxim

    2012-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  12. North Atlantic atmospheric and ocean inter-annual variability over the past fifty years - Dominant patterns and decadal shifts

    NASA Astrophysics Data System (ADS)

    Hauser, Tristan; Demirov, Entcho; Zhu, Jieshun; Yashayaev, Igor

    2015-03-01

    The atmosphere and ocean of the North Atlantic have undergone significant changes in the past century. To understand these changes, their mechanisms, and their regional implications requires a quantitative understanding of processes in the coupled ocean and atmosphere system. Central to this understanding is the role played by the dominant patterns of ocean and atmospheric variability which define coherent variations in physical characteristics over large areas. Cluster analysis is used in this article to identify the patterns of the North Atlantic atmospheric variability in the subseasonal and interannual spectral intervals. Four dominant subseasonal weather regimes are defined using Bayesian Gaussian mixture models. All correlation patterns of the Sea Level Pressure (SLP) anomalies with the membership probability time series for the weather regimes show similarities with the dipole structure typical for the North Atlantic Oscillation (NAO). The SLP patterns of two of the regimes represent the opposite phases NAO+ and NAO-. The two other weather regimes, the Atlantic Ridge (AR) and Scandinavian-Greenland dipole (SG), have dipole spatial structures with the northern and southern centers of action shifted with respect to the NAO pattern. These two patterns define blocking structures over Scandinavia and near the southern tip of Greenland, respectively. The storm tracks typical for the four regimes resemble the well known paths for positive/negative phases of NAO for the NAO+/NAO- weather regimes, and paths influenced by blocking off the south Greenland tip for AR and over Scandinavia for SG. The correlation patterns of momentum and heat fluxes to the ocean for the four regimes have tripole structures with positive (warm) downward heat flux anomalies over the Subpolar North Atlantic (SPNA) for the NAO- and the AR and negative heat flux anomalies over the SPNA for the NAO+. The downward heat flux anomalies associated with the SG are negative over the Labrador Sea and positive over the eastern SPNA. The long term impact of the weather regimes on the regional climate is characterized by their distribution; i.e. the frequency of occurrence and persistence in time of each of them. Four typical distributions of the weather regimes are identified in this study which are associated with four dominant spatial interannual patterns representing the phases of two asymmetrical "modes". The first two patterns have the spatial structures of positive and negative phases of the North Atlantic Oscillation (NAO). The third and fourth patterns, here referred to as G+ and G-, define the opposite phases of a mode, that has a spatial structure defined by three centers found over Florida, south of Greenland and over Scandinavia. The NAO+ interannual patterns are associated with negative anomalies of the surface downward heat flux and ocean heat content over the SPNA. The NAO- and G+ are associated with positive anomalies of heat flux and ocean heat content. In the 1960s the dominant NAO- and G+ interannual patterns favored warmer than normal atmospheric and ocean temperatures over the SPNA. The winters in the late 1980s and early 1990s over the SPNA were colder than normal. This decadal shift in the atmospheric state between 1970s and 1980s was associated with a change in the dominant interannual patterns towards NAO+ and G- in the late 1980s and early 1990s. The recent warming of the SPNA since the mid-1990s was related to dominance of the G+/G- interannual patterns in the distribution of interannual patterns probability membership. Our analysis suggests that this decadal variability was associated with long term shifts in atmospheric behavior over the SPNA that can be described by a change in the 1980s of the distribution of membership probabilities for the interannual patterns. Within the interannual pattern phase space, this change is characterized with a shift from the NAO-/G+/G- subspace in the 1950 and 1960s, towards NAO+/G+/G- since the mid 1980s.

  13. Analysis of observer variability in the assessment of FLIR performance

    NASA Astrophysics Data System (ADS)

    Mazz, John P.

    1996-06-01

    One of the larger sources of variation in human performance predictions is observer-to-observer variability. Whether because of differences in experience, training, motivation, innate ability, or perceived risk, observer performance varies. This paper explores observer variability in the task of detecting military targets in a FLIR image. Data for the analysis were obtained from a recent perception experiment conducted by NVESD utilizing 36 observers examining thermal imagery. Using the aggregate performance of the group as a measure of target difficulty, this paper compared the individual observer performance to that of the group. It was obvious that individual observers did not have identical performance characteristics. FOr example, targets detected by 50 percent of the group were detected by 20 percent of the observers over 70 percent of the time while another 20 percent of the observers detected then less than 20 percent of the time. Thus, the distribution of observer performance is fairly broad. This analysis of observer variability has implications for the modeling of target acquisition in combat simulations such as CASTFOREM and JANUS. These simulations currently use a uniformly-distributed, randomly-assigned threshold approach.

  14. Two centuries of observed atmospheric variability and change over the North Sea region

    NASA Astrophysics Data System (ADS)

    Stendel, Martin; van den Besselaar, Else; Hannachi, Abdel; Kent, Elizabeth; Lefebvre, Christiana; van Oldenborgh, Geert Jan; Rosenhagen, Gudrun; Schenk, Frederik; van der Schrier, Gerard

    2015-04-01

    Situated in northwestern Europe, the North Sea region is under influence of air masses from subtropical to arctic origin, and thus exhibits significant natural climate variability. As the land areas surrounding the North Sea are densely populated, climate change is an important issue in terms of e.g. coastal protection, fishery and trade. This study is part of the NOSCCA initiative (North Sea Region Climate Change Assessment) and presents observed variability and changes in atmospheric parameters during the last roughly 200 years. Circulation patterns show considerable decadal variability. In recent decades, a northward shift of storm tracks and increased cyclonic activity has been observed. There is also an indication of increased persistence of weather types. The wind climate is dominated by large multidecadal variability, and no robust long-term trends can be identified in the available datasets. There is a clear positive trend in near-surface temperatures, in particular during spring and winter. Over the region as a whole, no clear long-term precipitation trends are visible, although regional indications exist for an increased risk of extreme precipitation events.

  15. Validation of Mpi-Esm Decadal Hindcast Experiments with Terrestrial Water Storage Variations As Observed By the Grace Satellite Mission

    NASA Astrophysics Data System (ADS)

    Dobslaw, H.; Zhang, L.

    2014-12-01

    Time-variations in the gravity field as observed by the GRACE mission launched in 2002 provide for the first time quantitative estimates of the terrestrially stored water masses at monthly resolution over more than one decade. TWS from GRACE is applied here to validate different sets of ensemble hindcasts performed with the coupled climate model MPI-ESM that have been prepared within the German Research Initiative on Decadal Climate Prediction (MiKlip) during recent years. Moderately positive skill scores of the initialized hindcasts are obtained both with respect to the zero anomaly forecast and the uninitialized projections in particular for leadyear 1 in particular in moderate to high latitudes of the Northern Hemisphere. Skill scores gradually increase when moving in more recent experiments and also for experiments performed at higher spatial resolution, thereby documenting improvements of the MPI-ESM decadal prediction system during course of the Miklip project. Analyses indicate that the skill changes obtained here reflect in particular changes in the large-scale precipitaiton pattern between the individual experiments, which itself is an important target quantity of the climate prediction. We will explain in this talk how GRACE-based TWS might contribute to the validation of precipitation changes in particular in regions of the world where reliable in-situ observations are sparse.

  16. 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)

    Cardin, Vanessa; Bensi, Manuel; Pacciaroni, Massimo

    2011-06-01

    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.

  17. Contribution of Thermal Expansion to Observed Sea Level Rise During the Past Decade

    Microsoft Academic Search

    A. Lombard; A. Cazenave; P. Letraon

    2003-01-01

    Recent studies by Cabanes et al. (2001) and Cabanes (2003) have suggested that thermal expansion of the oceans is likely to be the main cause of observed sea level rise during the recent years. These results were based on a single ocean temperature data set (Levitus et al., 2000) and the comparison with the Topex\\/Poseidon global mean sea level rise

  18. Frequency Dependence of Short Period Seismic Noise from Two Decades of Observations at Warramunga Seismic Array (WRA), Australia

    NASA Astrophysics Data System (ADS)

    Gal, M.; Reading, A. M.; Ellingsen, S. P.; Koper, K. D.; Tkalcic, H.; Hemer, M. A.

    2014-12-01

    The analysis of the seismic ambient noise field has recently received increased attention owing to its success in mapping the Earth's shallow and deep structures. The origin of the passive seismic wavefield is associated with deep ocean and coastal regions where ocean waves, under certain conditions, can excite seismic waves (microseisms) that propagate as surface and body waves. Previous seismological studies mainly focused on the observation of the strongest microseisms that are associated with the frequency range 0.1-0.3Hz. In our study, we focus on short period microseisms (0.325-0.725Hz) and examine the frequency dependant wave field and temporal variations over two decades. We use data recorded over two decades (1991-2012) from the Warramunga array (WRA) in central Australia. The analysis is carried out using IAS Capon beamforming that shows robust estimates of slowness and backazimuth, and is able to resolve multiple wave arrivals. Continuous data records are divided into one hour long recordings and evaluated for multiple arrivals in 8 separate frequency bands. We find multiple surface and body wave sources, which display seasonality and frequency dependence and remain stationary for two decades. We observe, for surface waves, that Rayleigh waves dominate for low frequencies while higher frequencies show a transition to leaky Rayleigh waves. The strong stationarity of the signal over multiple years, supports the suggestion that bathymetry and other site effects, such as coast line geometry, create favourable conditions for the generation of ocean induced surface waves. For body waves, source locations are identified in deep ocean regions for low frequencies and in shallow waters for higher frequencies. We further discuss correlation between arrivals and a WAVEWATCH III ocean wave hindcast for strong events. Fig 1: a) Shows the slowness of strongest incoming arrivals for 1 hour of WRA data over two decades. b) Displays the surface waves paths of incoming Rayleigh (red) and leaky Rayleigh (blue) waves. c) Shows source locations from back projected body wave arrivals.

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

    NASA Astrophysics Data System (ADS)

    Schreier, Gunter; Dech, Stefan

    2005-07-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Moudden, Y.; Forbes, J. M.

    2014-03-01

    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.

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

    PubMed Central

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

    2014-01-01

    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

  3. Changes in SO2 and NO2 Pollution over the Past Decade Observed by Aura OMI

    NASA Astrophysics Data System (ADS)

    Krotkov, N. A.; Li, C.; Lamsal, L. N.; Celarier, E. A.; Marchenko, S. V.; Swartz, W.; Bucsela, E. J.; Fioletov, V.; McLinden, C. A.; Joiner, J.; Bhartia, P. K.; Duncan, B. N.; Dickerson, R. R.

    2014-12-01

    The Ozone Monitoring Instrument (OMI), a NASA partnership with the Netherlands and Finland, flies on the EOS Aura satellite and uses reflected sunlight to measure two critical atmospheric trace gases, nitrogen dioxide (NO2) and sulfur dioxide (SO2), characterizing daily air quality. Both gases and the secondary pollutants they produce (particulate matter, PM2.5, and tropospheric ozone) are among USEPA designated criteria pollutants, posing serious threats to human health and the environment (e.g., acid rain, plant damage, and reduced visibility). A new generation of the OMI standard SO2 and NO2 products (based on critically improved DOAS spectral fitting for NO2 and innovative Principal Component Analysis method for SO2) provides a valuable dataset for studying anthropogenic pollution on local to global scales. Here we highlight some of the OMI observed long-term changes in air quality over several regions. Over the US, average NO2 and SO2 pollution levels have decreased dramatically as a result of both technological improvements (e.g., catalytic converters on cars) and stricter regulations of emissions. We see continued decline in NO2 and SO2 pollution over Europe. Over China OMI observed a ~ 60% increase in NO2 pollution between 2005 and 2013, despite a temporary reversal of the growing trend due to both 2008 Olympic Games and the economic recession in 2009. Chinese SO2 pollution seems to have stabilized since peaking in 2007, probably due to government efforts to curb SO2 emissions from the power sector. We have also observed large increases in both SO2 and NO2 pollution particularly in Eastern India where a number of new large coal power plants have been built in recent years. We expect that further improvements in the OMI NO2 and SO2 products will allow more robust quantification of long-term trends in local to global air quality.

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

    PubMed Central

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

    2014-01-01

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

  5. Trends and variability in East African rainfall and temperature observations

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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).

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

    E-print Network

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

    2009-01-01

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

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

    SciTech Connect

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    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.

  9. Dominant spatial variability scales from observations around the Hawaiian Islands

    NASA Astrophysics Data System (ADS)

    Matthews, Dax; Powell, Brian; Milliff, Ralph

    2011-10-01

    We utilize a variety of available observations with a semivariogram technique to quantify the oceanic variability around the Hawaiian Islands. The Hawaiian Islands have a significant impact on the North Pacific circulation, and quantifying the characteristics of the variability is important for understanding the eddy energy, as well as required for statistical techniques to work with the data, such as optimal interpolation, data assimilation, etc. Both satellite sea surface height and temperature data are used to determine horizontal scales of variability, while Argo profiles, ship-borne profiles, and autonomous Seagliders provide estimates of the vertical scales. In the lee of the islands, satellite data reveal an increase in horizontal variability attributed to enhanced eddy activity that persists for over 1000 km westward; however, only within 400 km of the immediate lee the horizontal length scales are greatly reduced. Further west, length scales increase significantly indicating a change in the generation mechanism for eddy variability and where eddies merge and coalesce. The meridional length scale gradient is found to be larger than previous results and more representative of the gradient of the first baroclinic mode of the internal Rossby radius. Vertical length scales are shown to increase in the lee, with vertical temperature variability doubled from the windward side.

  10. Variability of the Mindanao Current: Mooring observation results

    NASA Astrophysics Data System (ADS)

    Kashino, Yuji; Ishida, Akio; Kuroda, Yoshifumi

    2005-09-01

    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.

  11. 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)

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

    2012-12-01

    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.

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

    PubMed

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

    2014-01-01

    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

  13. Seasonal to Decadal Variability in the Upper Ocean Scattering Layer in Drake Passage in Relation to Atmospheric and Oceanic Forcing

    NASA Astrophysics Data System (ADS)

    Chereskin, T. K.; Koenig, Z.

    2012-12-01

    The surface shoaling of nutrient-rich waters poleward across the Antarctic Circumpolar Current is responsible for the elevated productivity of the Southern Ocean. Over the last half century, the Southern Ocean has been warming at a faster rate than the global ocean as a whole. In particular, the Antarctic Peninsula region has undergone rapid atmospheric warming, significant glacial retreat and a decrease in seasonal sea ice extent, impacting krill and its predators. Improving knowledge of the Southern Ocean is a high priority for understanding the effects of climate change, but the harsh environment poses substantial observational challenges. The U.S. Antarctic Research and Supply Vessel Laurence M. Gould crosses Drake Passage 2-4 times per month in all seasons, collecting underway data on transits between Punta Arenas, Chile and Palmer Station, Antarctica. High-resolution measurements of upper ocean temperature, salinity, velocity and acoustic backscatter, along with concurrent meteorological, surface water CO2 and nutrient measurements have been routinely acquired since the late 1990s. This study makes use of 238 acoustic Doppler current profiler (ADCP) transects collected over a 12-year period to remotely sense the characteristics of the near-surface scattering layer, which at 153.6 kHz is dominated by macrozooplankton. Although the primary use of the shipboard ADCP is to measure ocean currents, the measured acoustic backscatter has provided valuable insights into the depth distributions, vertical migration behaviors and even life cycles of dominant biological scatterers. Diel vertical migration and a well defined annual cycle are observed, consistent with krill behavior. Significant geographic variations are present on both seasonal and interannual time scales. Interannual variability is linked to two main climate modes, the El Niño-Southern Oscillation and the Southern Annular Mode, as well as to variations in seasonal sea ice extent. Limitations of the present study and proposed sampling to address them will also be discussed.

  14. Observations of suspected variables. 2. NSV 1280 Tau = CSV 6048

    Microsoft Academic Search

    C. Lloyd; D. McAdam

    1995-01-01

    NSV 1280 (HD 23410, SAO 76156, BD +22°545, Melotte 22 801, ADS 2748 A) is a relatively well observed member of the Pleiades. According to the NSV (Kholopov et al. 1982) it is possibly a rapid, irregular variable with a range, mpg = 6.5 - 7.3, and a spectral type of A0 V. The SAO catalogue gives mpg = 7.7,

  15. 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)

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

    2001-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  17. 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)

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

    2014-05-01

    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.

  18. INTEGRAL observations of the variability of OAO 1657-415

    E-print Network

    J. Barnstedt; R. Staubert; A. Santangelo; C. Ferrigno; D. Horns; D. Klochkov; P. Kretschmar; I. Kreykenbohm; A. Segreto; J. Wilms

    2008-05-13

    The Galactic Plane Scan (GPS) was one of the core observation programmes of the INTEGRAL satellite. The highly variable accreting pulsar OAO 1657-415 was frequently observed within the GPS. We investigate the spectral and timing properties of OAO 1657-415 and their variability on short and long time scales in the energy range 6-160 keV. During the time covered by the INTEGRAL observations, the pulse period evolution shows an initial spin-down, which is followed by an equally strong spin-up. In combining our results with historical pulse period measurements (correcting them for orbital variation) and with stretches of continuous observations by BATSE, we find that the long-term period evolution is characterised by a long-term spin-up overlayed by sets of relative spin-down/spin-up episodes, which appear to repeat quasi-periodically on a 4.8 yr time scale. We measure an updated local ephemeris and confirm the previously determined orbital period with an improved accuracy. The spectra clearly change with pulse phase. The spectrum measured during the main peak of the pulse profile is particularly hard. We do not find any evidence of a cyclotron line, wether in the phase-averaged spectrum or in phase-resolved spectra.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

  20. Observations of ultraviolet variability in RV Tauri stars

    NASA Technical Reports Server (NTRS)

    Brugel, Edward W.; Cardelli, Jason A.

    1988-01-01

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

  1. Decadal hindcasts with MPI-ESM initialized from coupled assimilation of oceanic observations and atmospheric re-analysis data

    NASA Astrophysics Data System (ADS)

    Brune, Sebastian; Pohlmann, Holger; Nerger, Lars; Müller, Wolfgang; Baehr, Johanna

    2015-04-01

    We present a set of decadal hindcast simulations initialized from a coupled assimilation of oceanic sub-surface observations and atmospheric re-analysis data within the same model. In the global coupled Max Planck Institute for Meteorology Earth System Model (MPI-ESM), we assimilate ocean observations using the singular evolutive ensemble Kalman filter (SEIK) and atmospheric re-analysis data using simple nudging. Our set of hindcast simulations consists of yearly initializations between 1960 to 2014, with 8 ensemble members each. This set of hindcast simulations from the SEIK-nudged assimilation is compared against a set of hindcasts simulations where both ocean an atmosphere are nudged to re-analysis data. In the assimilation experiments, we find for surface temperature, the nudged assimilation experiment in closer agreement with observations than the SEIK-nudged assimilation experiment. In contrast, the hindcasts initialized from the SEIK-nudged assimilation experiment improve over the hindcasts initialized from the nudged assimilation experiment for global mean surface temperature, and in particular for the Northeast Atlantic and for the lead years 1 to 3. In terms of the Atlantic meridional overturning circulation (AMOC), which has not been assimilated directly, we find that the SEIK-nudged assimilation experiment is closer to observations (26°N, 2004 to 2013) than the nudged assimilation experiment. We also investigate the hindcast skill for the AMOC in both experiments. Our initial results suggest that the subtle changes from the SEIK assimilation compared to the nudged assimilation in the ocean component of the coupled MPI-ESM do not necessarily degrade but even regionally improve hindcast skill.

  2. Inter-decadal transition of the leading mode of inter-annual variability of summer rainfall in East China and its associated atmospheric water vapor transport

    NASA Astrophysics Data System (ADS)

    Sun, Bo; Wang, Huijun

    2015-05-01

    This study investigated the inter-decadal variations of the leading empirical orthogonal function mode of the inter-annual variability of summer precipitation in East China from 1951 to 2012. From the 1950s to the 1980s, the main rain belt in the positive-phase years was centered along the middle and lower Yangtze River Valleys, with negative rainfall anomalies in South China and North China. Since the 1990s, the main rain belt of the positive-phase years has been shifted northward. During the period 2001-2012, the center of the main rain belt in the positive-phase years has shifted to the regions between the Yangtze and Yellow Rivers. This shift could be attributed to the inter-decadal variations of the anomalous atmospheric water vapor transport (AWVT) associated with the leading mode, which changed from a previously "anticyclone-cyclone" dipole structure to an anticyclonic monopole structure. The underlying physical mechanisms concerning the exertions from sea surface temperatures (SSTs) have also been preliminarily explored. The results indicate that the significant inter-decadal transition in the leading mode of summer precipitation in East China and the causative anomalous AWVT from 2001 to 2012 may be related to an inter-decadal change of inter-annual variability of the tropical SSTs in both the Indian and Pacific Oceans, which has been below normal from 2001 to 2012. Therefore, the influence of the tropical SSTs on the inter-annual variability of the East Asian climate may be diminished from 2001 to 2012, whereby a strongly coupled "anticyclone-cyclone" dipole-structured anomalous AWVT cannot be induced.

  3. Decadal Variability of the Biosphere, the Climate, and the Carbon Cycle in a Coupled Atmosphere-Biosphere Model, CCM3-IBIS.

    NASA Astrophysics Data System (ADS)

    Delire, C.; Foley, J.; Coe, M. T.

    2002-12-01

    We analyze a 500-year run of the coupled atmosphere, dynamic vegetation and soil model CCM3-IBIS that presents different slow modes of variability in the climate, vegetation and carbon cycle. IBIS (Foley et al., 1996; Kucharik et al., 2000) is a dynamic vegetation model that describes the physical, physiological and ecological processes occurring in vegetation and soils in a coherent and mechanistic way. The model includes land-surface physics, canopy physiology, plant phenology, vegetation dynamics and competition, and carbon cycling. We coupled IBIS to the NCAR CCM3 at a T31 resolution (~3.75o x 3.75o). We ran a 500-year equilibrium simulation of the 'present day' climate imposing a constant atmospheric CO2 concentration of 350 ppm and fixed sea-surface temperatures. A spectral analysis shows that the precipitation, the leaf area index of the vegetation, the net primary productivity and the heterotrophic respiration present slow modes of variation at decadal timescales. Because we ran CCM3-IBIS with fixed sea-surface temperatures, this detected variability can only be attributed to changes in vegetation structure and functioning. A comparison with a similar run with fixed vegetation confirm this hypothesis. Transition zones between vegetation types like the Sahel contribute the most to the slow variability. This study shows that feedbacks between vegetation dynamics, the carbon cycle and the atmosphere alone can produce internal variability at decadal scale.

  4. Decadal variability of the biosphere, the climate, and the carbon cycle in a coupled atmosphere-biosphere model, CCM3-IBIS.

    NASA Astrophysics Data System (ADS)

    Delire, C.; Foley, J.; Coe, M.

    2003-04-01

    We analyze a 500-year run of the coupled atmosphere, dynamic vegetation and soil model CCM3-IBIS that presents different slow modes of variability in the climate, vegetation and carbon cycle. IBIS (Foley et al., 1996; Kucharik et al., 2000) is a dynamic vegetation model that describes the physical, physiological and ecological processes occurring in vegetation and soils in a coherent and mechanistic way. The model includes land-surface physics, canopy physiology, plant phenology, vegetation dynamics and competition, and carbon cycling. We coupled IBIS to the NCAR CCM3 at a T31 resolution (~3.75o x 3.75o). We ran a 500-year equilibrium simulation of the 'present day' climate imposing a constant atmospheric CO2 concentration of 350 ppm and fixed sea-surface temperatures. A spectral analysis shows that the precipitation, the leaf area index of the vegetation, the net primary productivity and the heterotrophic respiration present slow modes of variation at decadal timescales. Because we ran CCM3-IBIS with fixed sea-surface temperatures, this detected variability can only be attributed to changes in vegetation structure and functioning. A comparison with a similar run with fixed vegetation confirm this hypothesis. Transition zones between vegetation types like the Sahel contribute the most to the slow variability. This study shows that feedbacks between vegetation dynamics, the carbon cycle and the atmosphere alone can produce internal variability at decadal scale.

  5. Variability in the Initial Costs of Care and One-Year Outcomes of Observation Services

    PubMed Central

    Abbass, Ibrahim

    2015-01-01

    Introduction The use of observation units (OUs) following emergency departments (ED) visits as a model of care has increased exponentially in the last decade. About one-third of U.S. hospitals now have OUs within their facilities. While their use is associated with lower costs and comparable level of care compared to inpatient units, there is a wide variation in OUs characteristics and operational procedures. The objective of this research was to explore the variability in the initial costs of care of placing patients with non-specific chest pain in observation units (OUs) and the one-year outcomes. Methods The author retrospectively investigated medical insurance claims of 22,962 privately insured patients (2009–2011) admitted to 41 OUs. Outcomes included the one-year chest pain/cardiovascular related costs and primary and secondary outcomes. Primary outcomes included myocardial infarction, congestive heart failure, stroke or cardiac arrest, while secondary outcomes included revascularization procedures, ED revisits for angina pectoris or chest pain and hospitalization due to cardiovascular diseases. The author aggregated the adjusted costs and prevalence rates of outcomes for patients over OUs, and computed the weighted coefficients of variation (WCV) to compare variations across OUs. Results There was minimal variability in the initial costs of care (WCV=2.2%), while the author noticed greater variability in the outcomes. Greater variability were associated with the adjusted cardiovascular-related costs of medical services (WCV=17.6%) followed by the adjusted prevalence odds ratio of patients experiencing primary outcomes (WCV=16.3%) and secondary outcomes (WCV=10%). Conclusion Higher variability in the outcomes suggests the need for more standardization of the observation services for chest pain patients. PMID:25987913

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

    NASA Astrophysics Data System (ADS)

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

    1999-11-01

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

  7. Multiannual to decadal circulation variability in the deep subpolar North Atlantic - A modal decomposition of Deep Water export from the Labrador Sea, sea level pressure and atmospheric forcing fields.

    NASA Astrophysics Data System (ADS)

    Fischer, Jürgen; Karstensen, Johannes; Visbeck, Martin; Zantopp, Rainer; Kopte, Robert

    2015-04-01

    The exit of the Labrador Sea is the location where different elements of the deep MOC limb merge in the Deep Western Boundary Current. Multiannual to decadal variability dominates the longer time scales with strong dissimilarities across the North Atlantic Deep water layers. While the overflow transport contributions (DSOW and NEADW) exhibit nearly decadal oscillations, the overlying LSW layer is much more constant over the observational time period -- 1997 to 2012. The observations are obtained from a combination of moored current meter records and shipboard observations by direct current profiles from CTD/LADCP casts. Although our records are long enough to apply spectral analysis methods on short time scales including seasonal, they are not long enough to perform a spectral analysis of multiannual to decadal variations. We therefore use Singular Spectral Analysis (SSA) techniques to separate the transport records into trends, non-harmonic oscillations, and noise. Temporal modes of transports are compared with sea level pressure, NAO and other climate relevant indices.

  8. Simultaneous Fuse/rxte Observations of Magnetic Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Mukai, Koji

    In magnetic cataclysmic variables (mCVs), the accretion stream near the white dwarf is irradiated by the X-rays to produce strong emission lines in the far ultraviolet. These UV emission lines contain information on the kinematics, the abundances, and the physical conditions of the stream. We have therefore started a multi-year FUSE campaign to observe selected mCVs which highlight different aspects and/or show unique characterstics. In this context, we have submitted FUSE AO-2 proposals on PQ Gem and AE Aqr; to take full advantage of the FUV data, we need the knowledge about the photoionizing continuum, i.e., X-rays. We therefore propose simultaneous RXTE observations of these proposed FUSE targets.

  9. Subtropical Gyre Variability Observed by Ocean Color Satellites

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    Microsoft Academic Search

    Vincent Moron

    1997-01-01

    Annual rainfall anomalies over subequatorial and northern tropical Africa are analysed for interannual and interdecadal variability over the time interval 1900-1994. Then, the main modes of variation in the annual rainfall field are related to the same frequencies of variation in several SST indexes chosen in key-areas. First, empirical orthogonal function (EOF) analysis is performed on the annual rainfall anomalies

  11. Ground based observations of Io plasma torus variability

    NASA Astrophysics Data System (ADS)

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

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

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

    Microsoft Academic Search

    A. Grötzner; M. Latif; T. P. Barnett

    1998-01-01

    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

  13. Cycles and shifts: 1,300 years of multi-decadal temperature variability in the Gulf of Alaska

    Microsoft Academic Search

    Rob Wilson; Greg Wiles; Rosanne D'Arrigo; Chris Zweck

    2006-01-01

    The Gulf of Alaska (GOA) is highly sensi- tive to shifts in North Pacific climate variability. Here we present an extended tree-ring record of January- September GOA coastal surface air temperatures using tree-ring width data from coniferous trees growing in the mountain ranges along the GOA. The reconstruction (1514-1999), based on living trees, ex- plains 44% of the temperature variance,

  14. Observations of Total Solar Irradiance indicate a + 0.04 % per decade trend during solar cycles 21 - 23

    NASA Astrophysics Data System (ADS)

    Willson, R. C.

    2004-12-01

    Continuous Total solar irradiance (TSI) observations have been made by satellite experiments since late 1978. A precise, contiguous composite TSI can be derived for the past 26 years by relating these results through consecutive overlapping observations. A crucial issue for a composite is the relationship between ACRIM1 and ACRIM2 results across the two year gap between them. This can be established by using one of the two overlapping data sets, the Nimbus7/ERB or ERBS/ERBE. The choice is important because the effects on the composite are significantly different. The ACRIM composite uses unaltered published results and the Nimbus7/ERB overlapping comparisons to link ACRIM1 and ACRIM2. The most significant feature of the ACRIM composite for climate change is an upward trend of 0.04 (+/- 0.01) % per decade between activity minima during solar cycles 21-23. [Willson & Mordvinov] TSI composites using the ERBS/ERBE data to link ACRIM1&2 results, such as the well known PMOD of Frohlich & Lean, use the same TSI data sets in a different approach but do not find a significant trend between minima. The absence of a trend in such ERBS/ERBE-based composites can be shown to be an artifact of uncorrected ERBS/ERBE degradation during the ACRIM1-ACRIM2 `gap'.There are other differences between the ACRIM and PMOD composites, driven principally by the PMOD's use of TSI proxy models to justify modifying the published results of ACRIM1 and Nimbus7/ERB. TSI regression (proxy) models based on chromospheric spectral features are not competitive in accuracy, precision or traceability with satellite TSI observations and are therefore likely to cause spurious effects when used in the construction of TSI composites. The TSI record has been sustained by overlapping, redundant experiments using their level of measurement precision to sustain longer term traceability. This TSI monitoring strategy is essential for continuity in the future because the uncertainty of current satellite sensors (~ 0.1 %) is an order of magnitude too large to detect subtle long term TSI variations of potential climate change significance. [Willson, R.C., A. V. Mordvinov, JGRL 30, pp. 1199-1202, 2003, Frohlich C., J. Lean, JGRL 25, pp. 4377-4380, 1998

  15. SMC X-1 variability observed from HEAO 1

    NASA Technical Reports Server (NTRS)

    Gruber, D. E.; Rothschild, R. E.

    1984-01-01

    Studies are reported of the slow variability of SMC X-1 and its spectrum. An analysis of red-noise random variability is based on a method discussed by Deeter and Boynton (1982). The 0.7 s X-ray pulsar SMC X-1 is in a 3.89 day eclipsing binary system with a B0 I supergiant companion. Observations of the pulsar were conducted with the aid of the UCSD/MIT instrument on HEAO 1 from 1977 August through 1979 January. A light curve was constructed for the period 1977 September to 1978 December. The apparent tendency of SMC X-1 to be in one of two states, high or low, suggests the acquisition of average spectra separately for each state. The total (steady plus pulsed) emission from SMC X-1 displays a continuum spectrum with a dominant exponential form which implies a temperature of 17 keV for thin thermal bremsstrahlung emission or 5 keV if the other limit of a Wien spectrum is assumed.

  16. Observations of Thermal Flare Plasma with the EUV Variability Experiment

    E-print Network

    Warren, Harry P; Doschek, George A

    2012-01-01

    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 (SDO) 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 GOES soft X-ray fluxes indicate that the isothermal approximation is generally a poor representation of ...

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  19. 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)

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

    2010-05-01

    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.

  20. Systematic Attribution of Observed Southern Hemispheric Circulation Trends to External Forcing and Internal Variability

    NASA Astrophysics Data System (ADS)

    Franzke, Christian; O'Kane, Terence; Monselesan, Didier; Risbey, James; Horenko, Illia

    2015-04-01

    A critical question in the global warming debate concerns the causes of the observed trends of the Southern Hemisphere (SH) atmospheric circulation over recent decades. Secular trends have been identified in the frequency of occurrence of circulation regimes, namely the positive phase of the Southern Annular Mode (SAM) and the hemispheric wave 3 pattern which is associated with blocking. Previous studies into the causes of these secular trends have either been purely model based, have not included observational forcing data or have mixed external forcing with indices of internal climate variability impeding a systematic and unbiased attribution of the causes of the secular trends. Most model studies also focused mainly on the austral summer season. However, the changes to the storm tracks have occurred in all seasons and particularly in the winter and early spring when mid-latitude blocking is most active and stratospheric ozone plays no role. Here we systematically attribute the secular trends over the recent decades using a non-stationary clustering method applied to both reanalysis and observational forcing data from all seasons. While most previous studies emphasized the importance of stratospheric ozone depletion in causing summer SH circulation trends, we show observational evidence that anthropogenic greenhouse gas concentrations have been the major driver of these secular trends in the SAM and blocking when all seasons are considered. Our results suggest that the recovery of the ozone hole might delay the signal of global warming less strongly than previously thought and that seasonal effects are likely crucial in understanding the causes of the secular trends.

  1. Systematic attribution of observed southern hemispheric circulation trends to external forcing and internal variability

    NASA Astrophysics Data System (ADS)

    Franzke, C. L. E.; O'Kane, T. J.; Monselesan, D. P.; Risbey, J. S.; Horenko, I.

    2015-04-01

    A critical question in the global warming debate concerns the causes of the observed trends of the Southern Hemisphere (SH) atmospheric circulation over recent decades. Secular trends have been identified in the frequency of occurrence of circulation regimes, namely the positive phase of the Southern Annular Mode (SAM) and the hemispheric wave 3 pattern which is associated with blocking. Previous studies into the causes of these secular trends have either been purely model based, have not included observational forcing data or have mixed external forcing with indices of internal climate variability impeding a systematic and unbiased attribution of the causes of the secular trends. Most model studies also focused mainly on the austral summer season. However, the changes to the storm tracks have occurred in all seasons and particularly in the austral winter and early spring when mid-latitude blocking is most active and stratospheric ozone should not a play a role. Here we systematically attribute the secular trends over the recent decades using a non-stationary clustering method applied to both reanalysis and observational forcing data from all seasons. While most previous studies emphasized the importance of stratospheric ozone depletion in causing austral summer SH circulation trends, we show observational evidence that anthropogenic greenhouse gas concentrations have been the major driver of these secular trends in the SAM and blocking when all seasons are considered. Our results suggest that the recovery of the ozone hole might delay the signal of global warming less strongly than previously thought and that effects from all seasons are likely crucial in understanding the causes of the secular trends.

  2. Surface Wind Observational Database in North Eastern North America: Quality Control Procedure and Climatological Variability

    NASA Astrophysics Data System (ADS)

    Lucio-Eceiza, Etor E.; Fidel González-Rouco, J.; Navarro, Jorge; Hidalgo, Ángela; Conte, Jorge; Beltrami, Hugo

    2015-04-01

    This work summarizes the design and application of a Quality Control (QC) procedure for an observational surface wind database located in North Eastern North America. It also presents some insights of the long-term climatological variability over the region. The database consists of 527 sites (487 land stations and 40 buoys) with varying resolutions of hourly, 3 hourly and 6 hourly data, compiled from three different source institutions. The records span from 1940 to 2010 and cover an approximate spatial extension of 2.2 × 106 km2. The QC process is composed of different phases focused either on problems related with the providing source institutions or measurement errors. Due to the size of the data set, a great effort has been made on the automation of the procedures. A number of problems are associated with data management and data conventions: unification of measurement units and recording times due to the variety of institutional sources; detection of erroneous data sequence duplications within a station or among different ones; and detection of errors related with physically unrealistic data measurements. From the other hand there is a variety of treated instrumental errors: problems related with low variability, placing particular emphasis on the detection of unrealistic low wind speed records with the help of regional references; high variability related erroneous records; wind speed biases on week to monthly timescales and homogenization of wind direction records. As a result, around 1.7% of wind speed records and 0.4% of wind direction records have been deleted, making a combined total of 1.9% of removed records. Around 2.4% of wind direction data have been also corrected. The already quality controlled database allows for subsequent climatological analyses. The intra and inter decadal variability of the monthly surface wind field in such a vast and orographically complex region as the North Eastern North America is explored. Several decades of quality observations allow for the calibration of a statistical downscaling method based on Canonical Correlation Analysis. The method relates the main large-scale atmospheric circulation modes over the North Atlantic with the regional wind field. The relations are centered over the extended seasons of summer and winter. These seasons present interesting distinct dynamical features such as the frequent passage of tropical storms and hurricanes during summer and strong mid-latitude winter storms.

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

    Microsoft Academic Search

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

    1998-01-01

    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

  4. A new direction for Antarctic ice cores: reconstructing Pacific decadal variability and Australian drought history from the Law Dome ice core.

    NASA Astrophysics Data System (ADS)

    Vance, Tessa; Roberts, Jason; Plummer, Chris; Kiem, Anthony; van Ommen, Tas

    2015-04-01

    Decadal scale SST oscillations in the Pacific significantly influence rainfall variability and drought risk across and beyond the Pacific region. Understanding long-term decadal SST behavior in the Pacific is necessary to assess past and future climate, particularly drought risk. However, short instrumental records through much of the Pacific region, in particular the South Pacific, make such assessments difficult. A new reconstruction of Pacific decadal variability covering the last millennium has been produced from the Law Dome ice core, a high snow accumulation site in East Antarctica. The Law Dome ice core samples (at sub-annual resolution) a broad mid-latitude swathe of the Indian and South West Pacific region. This region exhibits wind speed and direction anomalies that are coherent with the phase of the Interdecadal Pacific Oscillation (IPO), an index measuring the decadal-scale Pacific SST state. This is the first millennial length IPO reconstruction and is based on the annual accumulation (snowfall) and sub-annual sea salt (wind proxy) records from Law Dome. To demonstrate the versatility of this new IPO reconstruction, we used it to explore drought history in eastern Australia, a region where drought risk is elevated during IPO positive phases. To do this, we super-imposed the 1000 year IPO reconstruction on a Law Dome proxy for eastern Australian rainfall (previously shown to represent rainfall with high significance during IPO positive phases (r =0.406-0.677, p <0.0001-0.01). Eight 'mega-droughts' (dry periods >5 years duration) were identified over the last millennium. Six mega-droughts occurred between AD 1000-1320 including one 39 y drought (AD 1174-1212). Water resources and infrastructure planning in Australia has been based on very limited statistical certainty around drought risk due to the short (~100 year) instrumental record and lack of rainfall proxies. This study shows that, similar to SW North America, Australia also experienced mega-droughts during the medieval period. Knowledge of the occurrence, duration and frequency of such mega-droughts will greatly improve drought risk assessment in Australia. Importantly, this new IPO reconstruction will help with assessing climate risk over the longer term in the wider Pacific Basin, particularly in the data-sparse Southern Hemisphere. In addition, the hydrological application of producing an annually dated drought record to calculate long-term drought risk represents a new use of Antarctic ice core records.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  6. Follow up Observations of SDSS and CRTS Candidate Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    We present photometry and spectroscopy of 11 and 35 potential cataclysmic variables, respectively, from the Sloan Digital Sky Survey, the Catalina Real-Time Transient Survey, and vsnet alerts. The photometry results include quasi-periodic oscillations during the decline of V1363 Cyg, nightly accretion changes in the likely Polar (AM Herculis binary) SDSS J1344+20, eclipses in SDSS J2141+05 with an orbital period of 76 ± 2 minutes, and possible eclipses in SDSS J2158+09 at an orbital period near 100 minutes. Time-resolved spectra reveal short orbital periods near 80 minutes for SDSS J0206+20, 85 minutes for SDSS J1502+33, and near 100 minutes for CSS J0015+26, RXS J0150+37, SDSS J1132+62, SDSS J2154+15, and SDSS J2158+09. The prominent He II line and velocity amplitude of SDSS J2154+15 are consistent with a Polar nature for this object, while the absence of this line and a low velocity amplitude argue against this classification for RXS J0150+37. Single spectra of 10 objects were obtained near outburst and the rest near quiescence, confirming the dwarf novae nature of these objects. Based on observations obtained with the Apache Point Observatory (APO) 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

  7. Observed and simulated multidecadal variability in the Northern Hemisphere

    Microsoft Academic Search

    T. L. Delworth; M. E. Mann

    2000-01-01

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

  8. Observing Simulated Cepheid Variable Stars in an Introductory Astronomy Lab.

    ERIC Educational Resources Information Center

    Flesch, Terry R.

    1979-01-01

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

  9. Ground-Based and ISO Observations of Semiregular and Mira Variables

    NASA Astrophysics Data System (ADS)

    Hron, J.

    2006-06-01

    We briefly compare various properties of Semiregular, Irregular, and Mira variables, and then discuss the importance of new observational and theoretical tools for understanding these groups of long period variables.

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

    PubMed

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

    2009-01-01

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

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

    PubMed Central

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

    2009-01-01

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

  12. Field observations of soil moisture variability across scales

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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. ...

  13. Subtropical gyre variability observed by ocean-color satellites

    Microsoft Academic Search

    Charles R McClain; Sergio R Signorini; James R Christian

    2004-01-01

    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

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

    Microsoft Academic Search

    P. Hajek

    2006-01-01

    Brno Regional Network of Observers (BRNO) is a group which prefers to observe eclipsing binary stars. A team called the Jelly-Fish has been formed within BRNO for the purpose of observing variable stars other than eclipsing binaries. The observations by Jelly-Fish members are predominantly visual; CCD observing has started only recently and such observations are not yet included in our

  15. Temperature Variability during Delirium in ICU Patients: An Observational Study

    PubMed Central

    van der Kooi, Arendina W.; Kappen, Teus H.; Raijmakers, Rosa J.; Zaal, Irene J.; Slooter, Arjen J. C.

    2013-01-01

    Introduction Delirium is an acute disturbance of consciousness and cognition. It is a common disorder in the intensive care unit (ICU) and associated with impaired long-term outcome. Despite its frequency and impact, delirium is poorly recognized by ICU-physicians and –nurses using delirium screening tools. A completely new approach to detect delirium is to use monitoring of physiological alterations. Temperature variability, a measure for temperature regulation, could be an interesting component to monitor delirium, but whether temperature regulation is different during ICU delirium has not yet been investigated. The aim of this study was to investigate whether ICU delirium is related to temperature variability. Furthermore, we investigated whether ICU delirium is related to absolute body temperature. Methods We included patients who experienced both delirium and delirium free days during ICU stay, based on the Confusion Assessment method for the ICU conducted by a research- physician or –nurse, in combination with inspection of medical records. We excluded patients with conditions affecting thermal regulation or therapies affecting body temperature. Daily temperature variability was determined by computing the mean absolute second derivative of the temperature signal. Temperature variability (primary outcome) and absolute body temperature (secondary outcome) were compared between delirium- and non-delirium days with a linear mixed model and adjusted for daily mean Richmond Agitation and Sedation Scale scores and daily maximum Sequential Organ Failure Assessment scores. Results Temperature variability was increased during delirium-days compared to days without delirium (?unadjusted=0.007, 95% confidence interval (CI)=0.004 to 0.011, p<0.001). Adjustment for confounders did not alter this result (?adjusted=0.005, 95% CI=0.002 to 0.008, p<0.001). Delirium was not associated with absolute body temperature (?unadjusted=-0.03, 95% CI=-0.17 to 0.10, p=0.61). This did not change after adjusting for confounders (?adjusted=-0.03, 95% CI=-0.17 to 0.10, p=0.63). Conclusions Our study suggests that temperature variability is increased during ICU delirium. PMID:24194955

  16. Observations of changes in the dissolved CO2 system in the North Sea, in four summers of the 2001-2011 decade

    NASA Astrophysics Data System (ADS)

    Clargo, Nicola; Salt, Lesley; Thomas, Helmuth; de Baar, Hein

    2015-04-01

    Since the industrial revolution, atmospheric concentrations of carbon dioxide (CO2) have risen dramatically, largely due to the combustion of fossil fuels, changes in land-use patterns and the production of cement. The oceans have absorbed a large amount of this CO2, with resulting impacts on ocean chemistry. Coastal seas play a significant role in the mitigation of anthropogenic atmospheric CO2 as they contribute approximately 10-30% of global primary productivity despite accounting for only 7% of the surface area. The North Sea is a perfect natural laboratory in which to study the CO2 system as it consists of two biogeochemically distinct regions displaying both oceanic and relatively coastal behaviour. It has also been identified as a continental shelf pump with respect to CO2, transporting it to the deeper waters of the North Atlantic. Large scale forcing has been shown to have a significant impact on the CO2 system over varying time scales, often masking the effects of anthropogenic influence. Here, we present data from the North Sea spanning the 2001-2011 decade. In order to investigate the dynamics of the dissolved CO2 system in this region in the face of climate change, four basin-wide cruises were conducted during the summers of 2001, 2005, 2008 and 2011. The acquired Dissolved Inorganic Carbon (DIC) and alkalinity data were then used to fully resolve the carbon system in order to assess trends over the 2001-2011 decade. We find significant interannual variability, but with a consistent, notable trend in decreasing pH. We found that surface alkalinity remained relatively constant over the decade, whereas DIC increased, indicating that the pH decline is DIC-driven. We also found that the partial pressure of CO2 (pCO2) increased faster than concurrent atmospheric CO2 concentrations, and that the CO2 buffering capacity of the North Sea decreased over the decade, with implications for future CO2 uptake.

  17. Analysis of the Evolution of the Chemical Composition of the Atmosphere over the Past Three Decades: Comparisons of Chemistry-Climate Model Simulations with In-situ and Remote Sensing Observations

    NASA Astrophysics Data System (ADS)

    Granier, C.; Doumbia, E. H. T.; Sindelarova, K.; Tilmes, S.; Hilboll, A.; Richter, A.; Colette, A.

    2014-12-01

    Global chemistry-climate models have been used to simulate the evolution of the atmospheric composition over the past decades. These simulations have been performed in free-running and specified dynamic modes, using the Community Atmosphere Model version 4 included in the the NCAR Community Earth System Model. We have analyzed the long-term changes as well as the interannual variability of several atmospheric compounds with a focus on ozone, carbon monoxide and nitrogen dioxide. We have investigated the behavior of these species by focusing on two regions, Europe and Asia. In Europe, surface emissions have decreased significantly since the 1980s, which have led to a decrease in the concentrations of several tropospheric compounds. On the contrary, emissions in Asia have dramatically increased, particularly during the past two decades, which has resulted in large increases in the atmospheric content of several species. We have used in-situ observations of O3, CO and NO2 from the Cooperative Air Sampling Network and from network of the European monitoring and evaluation programme (EMEP) to analyze the model results in different stations in the regions under consideration. We have also compared the model results with remote sensing observations from MOPITT, OMI, GOME, GOME-2 and SCIAMACHY instruments. Results show an underestimation of modeled CO concentrations, which has also been reported by previous studies. We will also analyse the simulated O3 and NO2 concentrations through comparisons with monitoring surface stations and satellite observations.

  18. Polarization observations of DQ HER stars and other cataclysmic variables

    NASA Astrophysics Data System (ADS)

    Cropper, M.

    1986-09-01

    Linear and circular polarizations are presented for the DQ Her stars FO Aqr, AE Aqr, EX Hya, AO Psc and V1223 Sgr and for 17 other cataclysmic variables. Upper limits (?0.1 per cent in circular) are set to any periodic variations in the polarization for the DQ Her stars. The source of the large periodic intensity variations in some of these stars is investigated in the light of the null results. Cyclotron radiation is ruled out. AE Aqr may be circularly polarized at the 0.05±0.01 per cent level. Previous claims for the detection of circular polarization in HL CMa and V603 Aql are not confirmed.

  19. Decadal- to biennial scale variability of planktic foraminifera in the northeastern Arabian Sea during the last two millennia: evidence for winter monsoon forcing mechanisms

    NASA Astrophysics Data System (ADS)

    Munz, Philipp; Lückge, Andreas; Siccha, Michael; Kucera, Michal; Schulz, Hartmut

    2015-04-01

    The Asian monsoon system is controlling the hydrologic cycle, and thus the agricultural and economic prosperity of the worlds most densely populated region. Strong and moisture-laden winds from the southwest induce upwelling and significant productivity in the western Arabian Sea during boreal summer. During boreal winter, weaker dry and cold surface winds from the northeast nourish ocean productivity mainly in the northeastern Arabian Sea. Instrumental records spanning the last century are too short to understand how the monsoon system reacts to external forcing mechanisms and to accurately determine its natural variability. Compared to the summer monsoon component, the dynamics of the winter monsoon are virtually unknown, due to the lack of adequate archives that are affected only by winter conditions. Here we present a decadal- to biennial-scale resolution record of past winter monsoon variability over the last two millennia, based on census counts of planktic foraminifera from two laminated sediment cores collected offshore Pakistan. One shorter box core (SO90-39KG) spans the last 250 years with an average ~2-year resolution, whereas the longer piston core (SO130-275KL) spans the last 2,100 years with a 10-year resolution. We use Globigerina falconensis as a faunal indicator for winter conditions, a species that is most abundant during winter in the NE Arabian Sea (Peeters and Brummer, 2002; Schulz et al., 2002). Our results show that during the past 2,100 years G. falconensis varied with significant periodicities centered on ˜ 60, ˜ 53, ˜ 40, ˜ 34 and ˜ 29 years per cycle. Some of these periods closely match cycles that are known from proxy records of solar irradiance, suggesting a solar forcing on winter monsoon variability. During the past 250 years G. falconensis varied in correlation with the (11-year) Schwabe and the (22-year) Hale solar cycles. Furthermore, a significant ˜ 7 year cyclicity could indicate a teleconnection to the El Niño Southern Oscillation, but is at the edge of the resolution of this record. A significant harmonic 46-year cycle, however, is coherent with the winter Pacific Decadal Oscillation (PDO) index, the leading mode of sea surface temperature (SST) anomalies in the North Pacific. Cold (warm) SST in the North Pacific are associated with higher (lower) abundances of G. falconensis. Wavelet coherency analysis revealed increasing coherence on higher frequency timescales since the 1960s, suggesting that global warming could lead to a stronger linkage between winter monsoon and PDO. References: Peeters, F., and Brummer, G.-J.A.: The seasonal and vertical distribution of living planktic foraminifera in the NW Arabian Sea. In: The Tectonic and Climatic Evolution of the Arabian Sea, Clift, P.D., et al. (Eds.), Geological Society Special Publication, 195, London, pp. 463--497, 2002. Schulz, H., von Rad, U., and Ittekkot, V.: Planktic foraminifera, particle flux and oceanic productivity off Pakistan, NE Arabian Sea: modern analogues and application to the palaeoclimatic record. In: The Tectonic and Climatic Evolution of the Arabian Sea, Clift, P.D., et al. (Eds.), Geological Society Special Publication, 195, London, pp. 499--516, 2002.

  20. Delay Identification in Time-Delay Systems using Variable Structure Observers

    E-print Network

    Paris-Sud XI, Université de

    Delay Identification in Time-Delay Systems using Variable Structure Observers S. V. Drakunov , W. Perruquetti, J.-P. Richard , L. Belkoura Abstract In this paper we discuss delay estimation in time-delay based on variable structure observers. 1 Introduction Numerous researches involve time-delay systems

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  2. Reconstruction of past oceanographic variability in Southeast Greenland from marine sedimentary records: The influence from the Atlantic Multi-decadal Oscillation

    NASA Astrophysics Data System (ADS)

    Hansen, M. J.; Andresen, C. S.; Seidenkrantz, M.-S.; Kuijpers, A.; Nørgaard-Pedersen, N.

    2012-04-01

    The Greenland ice sheet is one of the most significant water contributors to the rising global sea level, and therefore there are concerns about its long term stability. However, prediction of its contribution to global sea-level rise is complicated by lack of knowledge about mechanisms behind ice sheet change. In particular ice streams and their interaction with components of the atmospheric and oceanic climate system needs further investigation in order to make realistic models of future sea level rise. The SEDIMICE project ('Linking sediments with ice-sheet response and glacier retreat in Southeast Greenland') investigates past outlet glacier fluctuations in Southeast Greenland. The aim is to extend the knowledge from observational time series further back in time by analysing sediment cores retrieved from fjords by outlet glaciers and from the shelf. This presentation is based on results from a core retrieved near Sermilik Fjord by Helheim Glacier. The past 6000 years of Irminger water variability on the shelf has been reconstructed by analysing sediments from a side-bassin to the through connecting Sermilik fjord with the Irminger Sea. This reconstruction shows the Late-Holocene climate deterioration and is superimposed by a centennial-scale climate variability, which at times concurs with the climate records obtained for Northwest Europe. A wavelet analysis of the high-resolution K/Ti data (indicating grainsize variability) shows that the AMO (50-70 yr quasi-periodicity) recurrently controls Irminger water variability on the shelf. These results highlight the importance of adequate representation of regional climate modes in prognostic ice-sheet models.

  3. Regional Variability in Tropical Convection: Observations from TRMM

    Microsoft Academic Search

    Walter A. Petersen; Steven A. Rutledge

    2001-01-01

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

  4. Assessing the vulnerability of economic sectors to climate variability to improve the usability of seasonal to decadal climate forecasts in Europe - a preliminary concept

    NASA Astrophysics Data System (ADS)

    Funk, Daniel

    2015-04-01

    Climate variability poses major challenges for decision-makers in climate-sensitive sectors. Seasonal to decadal (S2D) forecasts provide potential value for management decisions especially in the context of climate change where information from present or past climatology loses significance. However, usable and decision-relevant tailored climate forecasts are still sparse for Europe and successful examples of application require elaborate and individual producer-user interaction. The assessment of sector-specific vulnerabilities to critical climate conditions at specific temporal scale will be a great step forward to increase the usability and efficiency of climate forecasts. A concept for a sector-specific vulnerability assessment (VA) to climate variability is presented. The focus of this VA is on the provision of usable vulnerability information which can be directly incorporated in decision-making processes. This is done by developing sector-specific climate-impact-decision-pathways and the identification of their specific time frames using data from both bottom-up and top-down approaches. The structure of common VA's for climate change related issues is adopted which envisages the determination of exposure, sensitivity and coping capacity. However, the application of the common vulnerability components within the context of climate service application poses some fundamental considerations: Exposure - the effect of climate events on the system of concern may be modified and delayed due to interconnected systems (e.g. catchment). The critical time-frame of a climate event or event sequence is dependent on system-internal thresholds and initial conditions. But also on decision-making processes which require specific lead times of climate information to initiate respective coping measures. Sensitivity - in organizational systems climate may pose only one of many factors relevant for decision making. The scope of "sensitivity" in this concept comprises both the potential physical response of the system of concern as well as the criticality of climate-related decision-making processes. Coping capacity - in an operational context coping capacity can only reduce vulnerability if it can be applied purposeful. With respect to climate vulnerabilities this refers to the availability of suitable, usable and skillful climate information. The focus for this concept is on existing S2D climate service products and their match with user needs. The outputs of the VA are climate-impact-decision-pathways which characterize critical climate conditions, estimate the role of climate in decision-making processes and evaluate the availability and potential usability of S2D climate forecast products. A classification scheme is developed for each component of the impact-pathway to assess its specific significance. The systemic character of these schemes enables a broad application of this VA across sectors where quantitative data is limited. This concept is developed and will be tested within the context of the EU-FP7 project "European Provision Of Regional Impacts Assessments on Seasonal and Decadal Timescales" EUPORIAS.

  5. Follow up observations of SDSS and CRTS candidate cataclysmic variables

    SciTech Connect

    Szkody, Paula; Vasquez-Soltero, Stephanie [Department of Astronomy, University of Washington, P.O. Box 351580, Seattle, WA 98195 (United States); Everett, Mark E.; Silva, David R. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Landolt, Arlo U. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Bond, Howard E., E-mail: szkody@astro.washington.edu, E-mail: dsilva@noao.edu, E-mail: steve.b.howell@nasa.gov, E-mail: landolt@rouge.phys.lsu.edu, E-mail: heb11@psu.edu [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

    2014-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    We quantify gravity changes after great earthquakes present within the 10 year long time series of monthly Gravity Recovery and Climate Experiment (GRACE) gravity fields. Using spherical harmonic normal-mode formulation, the respective source parameters of moment tensor and double-couple were estimated. For the 2004 Sumatra-Andaman earthquake, the gravity data indicate a composite moment of 1.2x10(exp 23)Nm with a dip of 10deg, in agreement with the estimate obtained at ultralong seismic periods. For the 2010 Maule earthquake, the GRACE solutions range from 2.0 to 2.7x10(exp 22)Nm for dips of 12deg-24deg and centroid depths within the lower crust. For the 2011 Tohoku-Oki earthquake, the estimated scalar moments range from 4.1 to 6.1x10(exp 22)Nm, with dips of 9deg-19deg and centroid depths within the lower crust. For the 2012 Indian Ocean strike-slip earthquakes, the gravity data delineate a composite moment of 1.9x10(exp 22)Nm regardless of the centroid depth, comparing favorably with the total moment of the main ruptures and aftershocks. The smallest event we successfully analyzed with GRACE was the 2007 Bengkulu earthquake with M(sub 0) approx. 5.0x10(exp 21)Nm. We found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events. Deeper sources (i.e., in the upper mantle) could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume, thus reducing the negative gravity component. Focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  9. Recent Advances in X-ray Observations of Cataclysmic Variables

    E-print Network

    K. Mukai

    2004-11-02

    A personal selection of noteworthy X-ray results on CVs are presented, with emphasis on XMM-Newton and Chandra observations. Progressing roughly from broad-band view to narrow-band, high spectral resolution studies, I summarize: the energy balance of polars; X-ray confirmation of IPs; eclipses in non-magnetic CVs; search for magnetism in "non-magnetic" CVs; multi-temperature plasma emission from the boundary layer; complex absorption in magnetic CVs; temperature and density diagnostics; and X-ray radial velocity studies.

  10. On the shock-induced variability of emission lines in M-type Mira variables. I. Observational data

    Microsoft Academic Search

    He. Richter; P. R. Wood

    2001-01-01

    We present time-resolved observations of metallic emission lines of Mg I, Mn I, Si I, Fe I and Fe II, including forbidden emission lines of [Fe II], for the six M-type Mira variables RR Sco, R Aql, R Car, R Leo, S Scl and R Hya, which range in period from 281 to 389 days. Data is also presented for

  11. Observational constraints on a variable dark energy model

    SciTech Connect

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

    2006-04-15

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

  12. XMM-Newton Observations of the Cataclysmic Variable GW Lib

    E-print Network

    Hilton, Eric J; Mukadam, Anjum; Mukai, Koji; Hellier, Coel; van Zyl, Liza; Homer, Lee

    2007-01-01

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

  13. XMM-Newton Observations of the Cataclysmic Variable GW Lib

    E-print Network

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

    2007-06-22

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

  14. Decadal Comparison of Plankton Levels

    NSDL National Science Digital Library

    Joycelyn Thomson

    2002-08-08

    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.

  15. Two Decades of Variability in Nutrient Budgets for Ice-Covered, Closed Basin Lakes in the McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Truhlar, A. M.; Gooseff, M. N.; McKnight, D. M.; Priscu, J. C.; Doran, P. T.

    2013-12-01

    The McMurdo Dry Valleys (MCM) of Antarctica represent one of the world's driest deserts. A collection of permanently ice-covered lakes in the MCM provide an important refuge for microorganisms. Thus, it is of interest to understand the nutrient dynamics of these lakes and how these dynamics have changed over time. One to two decade-long records of physical, chemical, and biological characteristics in the East Lobe of Lake Bonney (ELB), Lake Fryxell (FRX), and Lake Hoare (HOR) allowed for development of annual nutrient budgets and analysis of possible causes of variability. Annual nutrient budgets were built by accounting for total seasonal streamflow and average seasonal nutrient concentration in streamflow, as well as nutrient diffusion across the chemocline, which roughly coincides with the bottom of the photic zone. Unaccounted-for changes in nutrient content were assumed to be caused by processes internal to the lake. Changes to the proportion of lake volume in the photic zone, seasonal streamflow, and biological activity, represented by chlorophyll-a (CHL) concentration, were considered as potential explanations. For all three lakes, nutrient diffusion either into or out of the photic zone was minimal compared to nutrient inputs from streamflow. The sole exception to this was NH4 inputs to FRX; for eight of the nine years considered, diffusive inputs of NH4 to the photic zone were greater than streamflow inputs. In most cases, internal processes appeared to dominate over streamflow inputs; this is likely because seasonal streamflow represented less than 8% of the photic zone volume in all three lakes. Three exceptions to this trend were the phosphorus budget in ELB, and the NH4 and NO3 budgets in HOR; in these cases, streamflow inputs represented a notable portion of the annual nutrient budgets. The MCM lakes decreased in volume from the early 1990s to the early 2000s; they have since been increasing in volume. The volume of the photic zone was positively correlated to the mean concentrations of NH4 and NO3 in ELB, and to the mean NO2 concentration in FRX. Mean CHL concentration in the photic zone was positively correlated to mean NO2 concentration in ELB; mean CHL concentration in the photic zone was negatively correlated to mean NO2 concentration in HOR. These results suggest that internal nutrient cycling processes dominate the nutrient dynamics of the MCM lakes. To further explore inputs from biological processes, the potential for diffusion from benthic microbial mats in shallow waters could be considered.

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

    E-print Network

    Pringle, James "Jamie"

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

  17. PICTURE OF THE MONTH Observed Inner-Core Structural Variability in Hurricane Dolly (2008)*

    E-print Network

    Schubert, Wayne H.

    2008-01-01

    PICTURE OF THE MONTH Observed Inner-Core Structural Variability in Hurricane Dolly (2008)* ERIC A June 2012) ABSTRACT Hurricane Dolly (2008) exhibited dramatic inner-core structural variability during intensification and deepening event occurred while Dolly was in a favorable environment with weak deep

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

    Microsoft Academic Search

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

    1994-01-01

    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

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

    Microsoft Academic Search

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

    1994-01-01

    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

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

    Microsoft Academic Search

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

    1988-01-01

    Broadband photographic observations of 22 optically violent variable (OVV) active galactic nuclei are presented. Over 3100 observations made between 1968 and 1986 at Rosemary Hill Observatory are tabulated and displayed graphically. The majority of the observations were made in either the Johnson B system or the international photographic (PG) system. Multicolor data are presented for a few objects. Descriptions of

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Hajek, P.

    2006-06-01

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

  3. Observer-based variable structure control in microstepping for permanent magnet stepper motors

    Microsoft Academic Search

    Wonhee Kim; Donghoon Shin; Chung Choo Chung

    2010-01-01

    In this paper, we propose observer-based variable structure control (VSC) in microstepping for permanent magnet stepper motors (PMSMs) without position feedback. The back-emfs of the currents dynamics are defined as the disturbance terms. The observers for the back-emf estimation are designed. The proposed observers are in the form of the high pass filter. Observer-based VSC is developed to guarantee local

  4. On X-ray variability in ROSAT-PSPC observations of F7-K2 stars

    NASA Astrophysics Data System (ADS)

    Marino, A.; Micela, G.; Peres, G.; Sciortino, S.

    2002-01-01

    We have analyzed the X-ray variability of dF7-dK2 stars in the solar neighborhood detected with the pointed ROSAT-PSPC observations. Our data base is the sample of all stars listed in the CNS3 catalog (Gliese & Jahreibeta 1991) having a B-V color between 0.5 and 0.9; it includes 70 pointed observations of 40 distinct stars or multiple systems. We have applied the unbinned Kolmogorov-Smirnov test on all X-ray photon time series of our sample: only 10 observations relative to 8 distinct stars are variable at a confidence level greater than 99% and 4 of them belong to multiple systems. For the subsample of 9 stars observed both at the beginning and at the end of the mission, we can study the variability on time scale of years and compare amplitude variations at short and long time scales. Our analysis suggests that, for these stars, the X-ray variability is more likely on longer time scale. All the stars variable on long time scale, and not on short time scale, are relatively quiet and similar to the Sun, suggesting that the variations may be due to cycles. The comparison of our results with those previously obtained for dM stars shows that the amplitude of variability of X-ray emission from dF7-dK2 stars is smaller than that observed in dM stars.

  5. Seasonal and interannual variability in the Mozambique Channel from moored current observations

    NASA Astrophysics Data System (ADS)

    Ridderinkhof, H.; van der Werf, P. M.; Ullgren, J. E.; van Aken, H. M.; van Leeuwen, P. J.; de Ruijter, W. P. M.

    2010-06-01

    Direct observations from an array of current meter moorings across the Mozambique Channel in the south-west Indian Ocean are presented covering a period of more than 4 years. This allows an analysis of the volume transport through the channel, including the variability on interannual and seasonal time scales. The mean volume transport over the entire observational period is 16.7 Sv poleward. Seasonal variations have a magnitude of 4.1 Sv and can be explained from the variability in the wind field over the western part of the Indian Ocean. Interannual variability has a magnitude of 8.9 Sv and is large compared to the mean. This time scale of variability could be related to variability in the Indian Ocean Dipole (IOD), showing that it forms part of the variability in the ocean-climate system of the entire Indian Ocean. By modulating the strength of the South Equatorial Current, the weakening (strengthening) tropical gyre circulation during a period of positive (negative) IOD index leads to a weakened (strengthened) southward transport through the channel, with a time lag of about a year. The relatively strong interannual variability stresses the importance of long-term direct observations.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  7. 10-years of Atlantic Overturning observations: variability revealed on sub-annual, seasonal, annual and multi-annual timescales

    NASA Astrophysics Data System (ADS)

    McCarthy, Gerard; Johns, William; Meinen, Chris; Baringer, Molly; Rayner, Darren; Moat, Ben; Smeed, David

    2015-04-01

    The RAPID/MOCHA/WBTS project has been measuring the Atlantic Overturning circulation (AMOC) at 26.5 N in the North Atlantic since 2004. The joint UK-US project has recently reached the 10 year milestone. Here we present some of the key results from the first 10 years of the program. The first year's measurements revealed a sub-annual variability that encompassed all previous ship-based, hydrographic estimates of the AMOC, thus showing that a perceived decline could be encompassed in short-term variability. Seasonal variability in the AMOC was larger than expected with a 6 Sv range, with the largest single component derived from wind-stress curl induced density fluctuations at the eastern boundary. Interannual variability, far larger than that present in state of the art climate models, was seen in 2009/10. A 30% reduction lasted 18 months and cooled the subtropical North Atlantic significantly. The existence of continuous heat transport measurements enabled us to show that the main cause of the cooling was a reduction in ocean heat convergence rather than air-sea fluxes. The winter of 2010/11 revealed a second consecutive winter of low AMOC: a double dip. Whether ocean re-emergence or the change in AMOC circulation was the cause of the SST tripole pattern pattern that emerged in the winter of 2010/11 is a topic of ongoing research. Nonetheless, this SST pattern was shown to be sufficient to push the atmosphere into a second consecutive negative wintertime North Atlantic Oscillation (NAO) and increased predictability of this negative NAO. Most recently a multi-year decline in the AMOC has been observed. This 0.5 Sv/year decline is much larger than the long-term decline predicted due to anthropogenic climate change. The decline first reported on the 8.5-year timeseries has continued in the 10-year timeseries. The magnitude of the decline is so large as to suggest it may be decadal variability. A decline in the AMOC is consistent with a declining phase of the Atlantic Multi-decadal oscillation of sea-surface temperatures that is predicted by a number of authors.

  8. VARIABILITY IN RAINFALL DROP-SIZE DISTRIBUTIONS OBSERVED AT THE ARM DARWIN SITE

    E-print Network

    VARIABILITY IN RAINFALL DROP-SIZE DISTRIBUTIONS OBSERVED AT THE ARM DARWIN SITE Mary Jane Radiation Measurement (ARM) Climate Research Facility's site at Darwin, Australia. Drop-size distribution of complementary long-term observations from the ARM collocated surface instruments, including a millimeter cloud

  9. VARIABILITY IN RAINFALL DROP-SIZE DISTRIBUTIONS OBSERVED AT THE DARWIN ARM SITE

    E-print Network

    VARIABILITY IN RAINFALL DROP-SIZE DISTRIBUTIONS OBSERVED AT THE DARWIN ARM SITE Jensen, M/storm characteristics is investigated using observations from the Atmospheric Radiation Measurement (ARM) program from the ARM suite of instruments, including a millimeter cloud radar, micropulse lidar, ceilometers

  10. Comparing variability and trends in observed and modelled globalmean surface temperature

    E-print Network

    land surface temperature and sea surface temperature (SST) datasets [Brohan et al., 2006Comparing variability and trends in observed and modelled globalmean surface temperature John C; accepted 6 July 2010; published 19 August 2010. [1] The observed evolution of the globalmean surface

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

    NASA Astrophysics Data System (ADS)

    Liakos, A.; Niarchos, P.

    2009-03-01

    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.

  12. ROSAT all-sky survey observations of X-ray variability in cool giant stars

    NASA Technical Reports Server (NTRS)

    Haisch, Bernhard; Schmitt, J. H. M. M.

    1994-01-01

    We have identified 24 active late-type giant stars, including 11 RS CVn systems, with soft X-ray count rates high enough to allow the detection of statistically significant variability on a Roentgen Satellite (ROSAT) orbital timescale (96 minutes) as observed by the Position Sensitive Proportional Counter (PSPC) during the all-sky survey. Our sensitivity typically lies in the range of 10% - 25%, depending on the source count rate. Comparison is made to the daily, nonflare solar soft X-ray variability as observed by the Solrad satellites during solar minimum in 1969 and solar maximum in 1975. Seven of the 24 stars show significant variability; in two of these cases (HR 3922 and HR 8448) major flares were observed in which the peak count rate is enhanced by at least a factor of 3 above quiescent. While HR 3922 (G5 III) is not (yet) classified as an RS CVn star, its flare is more energetic (3 x 10(exp 31) ergs/s) than previously observed RS CVn flares. The apparently single giant HR 8167 (G8 III) also shows two flares. While one might expect to find an anticorrelation between saturated coronae and variability, we find no evidence of this: the two stars in our sample with the highest ratio of f(sub x)/f(sub v) both show variability. We also point out that Capella (G6 III + F9 III) is one of the stars manifesting variability.

  13. 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)

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

    2013-04-01

    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.

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

    E-print Network

    R. Smith; S. Vaughan

    2007-01-08

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  16. VLBA observations of SiO masers towards Mira variable stars

    Microsoft Academic Search

    W. D. Cotton; B. Mennesson; P. J. Diamond; G. Perrin; V. Coudé du Foresto; G. Chagnon; H. J. van Langevelde; S. Ridgway; R. Waters; W. H. T. Vlemmings; S. Morel; W. Traub; N. Carleton; M. Lacasse

    2004-01-01

    We present new total intensity and linear polarization VLBA observations of the nu=2 and nu=1 J=1-0 maser transitions of SiO at 42.8 and 43.1 GHz in a number of Mira variable stars over a substantial fraction of their pulsation periods. These observations were part of an observing program that also includes interferometric measurements at 2.2 and 3.6 micron \\\\citep{Mennesson2002}; comparison

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

    PubMed

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

    2012-10-01

    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

  18. Observations of IntraDay Variable sources with the Effelsberg and Urumqi Radio Telescopes

    E-print Network

    N. Marchili; T. P. Krichbaum; X. Liu; H. G. Song; K. É. Gabányi; L. Fuhrmann; P. Müller; A. Witzel; J. A. Zensus; J. L. Han

    2008-04-17

    A sample of classical IntraDay Variable (IDV) and IDV candidate sources has been monitored with the Urumqi 25m telescope and the Effelsberg 100m telescope. Aim of the project is to investigate the origin of IntraDay Variability, a phenomenon which has been observed in about 30% of flat spectrum radio quasars. Simultaneous Effelsberg-Urumqi observations demonstrated that the Urumqi antenna, although relatively small in diameter, is well suitable for IDV experiments. A few Urumqi datasets, however, turned out to be affected by a spurious $\\sim 24$ hours modulation, an effect which has been removed by means of a new procedure for data reduction. In about 14 months, 12 epochs of observation have been collected, for a total observing time of more than 45 days. The epochs are regularly distributed over the whole year, in order to check for the presence of systematic annual changes in the variability time scales - a crucial test for verifying the consistency of source-extrinsic models of the variability. Preliminary time-analysis of the monitored sources revealed some hint for a slowing down of the characteristic time scales of S5~0716+714, a result that, if confirmed, would be compatible with a source-extrinsic origin of the variability, in contrast to previous IDV studies. No significant modulation of the time scales has been detected for S4~0954+658.

  19. Improved estimates of upper-ocean warming and multi-decadal sea-level rise

    Microsoft Academic Search

    Catia M. Domingues; John A. Church; Neil J. White; Peter J. Gleckler; Susan E. Wijffels; Paul M. Barker; Jeff R. Dunn

    2008-01-01

    Changes in the climate system's energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database, even when volcanic and other variable climate forcings are included. The sum of the observed contributions

  20. X-ray observation of 3U 1700-37. [showing three categories of flux variability

    NASA Technical Reports Server (NTRS)

    Mason, K. O.; Branduardi, G.; Sanford, P. W.

    1976-01-01

    X-ray observations with Copernicus reveal three categories of flux variability in 3U 1700-37. High amplitude hourly variations are energy independent in the 3-11 keV range while a change in the low energy absorbing column causes variations in flux level on an orbital time scale. This absorption is most severe prior to eclipse ingress, suggesting that the distribution of absorbing material around the X-ray source is asymmetrical with respect to the line of centers of the binary system. The absorbing material may be identical with a high density region inferred from optical observations of HD 153919. In the third category, the maximum source intensity per binary cycle is variable by at least a factor of two between observations. Measurement of the eclipse duration on three occasions indicate that it is significantly less than when observed by Uhuru.

  1. Narrow absorption line variability in repeat quasar observations from the Sloan Digital Sky Survey

    E-print Network

    Hacker, Troy L; Lundgren, Britt F; York, Donald G

    2013-01-01

    We present the results from a time domain study of absorption lines detected in quasar spectra with repeat observations from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). Beginning with over 4500 unique time separation baselines of various absorption line species identified in the SDSS DR7 quasar spectra, we create a catalogue of 2522 quasar absorption line systems with two to eight repeat observations, representing the largest collection of unbiased and homogeneous multi-epoch absorption systems ever published. To investigate these systems for time variability of narrow absorption lines, we refine this sample based on the reliability of the system detection, the proximity of pixels with bright sky contamination to individual absorption lines, and the quality of the continuum fit. Variability measurements of this sub-sample based on the absorption line equivalent widths yield a total of 33 systems with indications of significantly variable absorption strengths on time-scales ranging from one day to ...

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

    E-print Network

    Miami, University of

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

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

    Microsoft Academic Search

    N. H. Saji; T. Yamagata

    2003-01-01

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

  4. Estimating Latent Variable Interactions with Nonnormal Observed Data: A Comparison of Four Approaches

    ERIC Educational Resources Information Center

    Cham, Heining; West, Stephen G.; Ma, Yue; Aiken, Leona S.

    2012-01-01

    A Monte Carlo simulation was conducted to investigate the robustness of 4 latent variable interaction modeling approaches (Constrained Product Indicator [CPI], Generalized Appended Product Indicator [GAPI], Unconstrained Product Indicator [UPI], and Latent Moderated Structural Equations [LMS]) under high degrees of nonnormality of the observed

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

    E-print Network

    Mendillo, Michael

    Review A review of observed variability in the dayside ionosphere of Mars Paul Withers Center dayside ionosphere available for study. Together with earlier measurements from the Viking era ionosphere and to discover new ionospheric features. The dayside ion- osphere includes the main peak, called

  6. Depth of Field Adaptation for Observation of Microscopic Objects by Using Variable Annular Aperture System

    Microsoft Academic Search

    Deokhwa Hong; Hyungsuck Cho

    2010-01-01

    High magnification optical systems such as microscopes usually suffer from limited depth-of-field (DOF) problem. This hinders efficient observation of microscopic objects and prevents vision based approaches from being applied to automatic micromanipulation tasks. A DOF extension method using variable annular pupil was proposed by the authors' previous publication, and a tradeoff between the depth extension range and image quality was

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  8. The Trend in the Observation of Legacy Long Period Variable Stars (Poster abstract)

    NASA Astrophysics Data System (ADS)

    Dudley, R.

    2015-06-01

    (Abstract only) A decrease in the number of observers of the Legacy Long Period Variable Stars has been noted by the AAVSO. Amongst the observing community there is the perception that observers collecting digital data is making up for this gap. Data from the annual President's report (2002–2013) and the AAVSO International Data Base for the years 1993, 2003, and 2013 were analyzed. For the period of 2002 to 2013 the total number of observers remained fairly constant (816 ± 97) with a large bump in 2011. The number of observations has slowly declined since 2007 though there has recently been an increase in the number of observations. From the AID data the number of observations reached a maximum in 2003 and has slowly declined afterwards. These trends as well as other information gleamed from the data will be present and discussed.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  10. Decadal variability of aerosol optical depth in Europe and its relationship to the global dimming and brightening and the temporal shift of the NAO

    Microsoft Academic Search

    Marc Chiacchio; Tracy Ewen; Martin Wild; Mian Chin; Thomas Diehl

    2010-01-01

    Long-term aerosol optical depth (AOD) for Europe were analysed using the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model for the period 1979-2007. In particular, we study the long-term sulfate AOD variability because their emission was at a maximum in 1988-1989 in Europe and they contain the largest fraction of anthropogenic components. A statistically significant decline of 68% was found

  11. 5, 16791731, 2005 Two decades of OH

    E-print Network

    ACPD 5, 1679­1731, 2005 Two decades of OH variability P. Bousquet et al. Title Page Abstract decades of OH variability as inferred by an inversion of atmospheric transport and chemistry of methyl continentaux, UMR INRA-CNRS-PARIS 6, INRA-INAPG, Thiverval-Grignon, France Received: 23 December 2004

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  13. X-ray observations of selected cataclysmic variable stars using the Einstein Observatory

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    X-ray observations of 12 cataclysmic variable stars using the Einstein Observatory are reported. Nine of these stars, representing all subclasses of cataclysmic variables, were detected. Their fluxes range from 2 x 10 to the -13th to 1 x 10 to the -11th ergs/sq cm-s in the energy interval 0.16-4.5 keV. The spectra of all the sources detected are relatively hard (kT not less than 5 keV). There is no evidence for an ultrasoft emission component (kT of about 50 eV) such as has been observed from the dwarf novae SS Cyg and U Gem during optical outburst. The X-ray and optical fluxes of the objects observed can be understood in terms of differences in mass accretion rate if the accreting stars in these close binary systems possess a weak magnetic field.

  14. New Variable Stars Discovered by the APACHE Survey. II. Results After the Second Observing Season

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Routinely operating since July 2012, the APACHE survey has celebrated its second birthday. While the main goal of the project is the detection of transiting planets around a large sample of bright, nearby M dwarfs in the northern hemisphere, the APACHE large photometric database, consisting of hundreds of different fields, represents a relevant resource to search for and provide a first characterization of new variable stars. We celebrate here the conclusion of the second year of observations by reporting the discovery of 14 new variables.

  15. New Variable Stars Discovered by the APACHE Survey. II. Results After the Second Observing Season

    E-print Network

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

    2015-01-01

    Routinely operating since July 2012, the APACHE survey has celebrated its second birthday. While the main goal of the Project is the detection of transiting planets around a large sample of bright, nearby M dwarfs in the northern hemisphere, the APACHE large photometric database for hundreds of different fields represents a relevant resource to search for and provide a first characterization of new variable stars. We celebrate here the conclusion of the second year of observations by reporting the discovery of 14 new variables.

  16. IUE observations of HL CMa and the winds of cataclysmic variables

    NASA Technical Reports Server (NTRS)

    Mauche, C. W.; Raymond, J. C.

    1987-01-01

    As evidenced by the P Cygni profiles of their ultraviolet resonance lines, cataclysmic variables - like early-type stars - are known to have extensive, high velocity winds. Assisted by AAVSO visual data and IUE ultraviolet spectra, an observational and theoretical study of the P Cygni profiles of the dwarf nova HL CMa is presented. As these profiles are dependent upon the ionization structure of the wind, a model of a radiatively-driven shocked wind for cataclysmic variables is described, and results for the temperature and ionization structure of the outflowing gas are presented.

  17. High Angular Resolution Observations of Episodic Dust Emission from Long Period Variable Stars Twenty Years of Observations with the Berkeley Infrared Spatial Interferometer

    NASA Technical Reports Server (NTRS)

    Danchi, William

    2010-01-01

    Over the past twenty years the U. C. Berkeley Infrared Spatial Interferometer has observed a number of Long Period Variable stars in the mid-infrared, obtaining information on the spatial distribution of dust around these stars with resolutions of the order of a few tens of milliarcseconds. The ISI is a heterodyne interferometer operating mostly at 11.15 microns, initially with two telescopes. In the last decade, it has been taking data regularly with three telescopes, thus obtaining visibility data on three baselines and also a closure phase. Over the course of the years, the ISI has been able to measure the physical properties of the dust shells surrounding these stars, in particular the inner radii of the dust shells, as well as the temperature and density distribution. For some stars, the ISI has also made precision measurements of their diameters in the mid-infrared. Closure phase measurements have revealed asymmetries in the dust distributions around many stars. Most surprisingly the ISI data has shown evidence for substantial changes in the amount of dust on time scales of 5-10 years, rather than being directly correlated with the stellar pulsation periods, which are of the order of one year. We discuss past results and new results from the ISI that highlight the dynamic environment around these stars.

  18. Observed Prosocial and Antisocial Behaviors in Male Soccer Teams: Age Differences across Adolescence and the Role of Motivational Variables

    Microsoft Academic Search

    Maria Kavussanu; Alistair R. Seal; Daniel R. Phillips

    2006-01-01

    This study examined the frequency of observed prosocial and antisocial behaviors in soccer teams, age differences in observed behaviors and motivational variables, and whether motivational variables account for age differences in observed behaviors. Participants were 313 adolescent soccer players, recruited from three age groups: under 13, under 15, and under 17. Each age group was represented by eight teams. Players

  19. A new method for observing the running states of a single-variable nonlinear system.

    PubMed

    Meng, Yu; Chen, Hong; Chen, Cheng

    2015-03-01

    In order to timely grasp a single variable nonlinear system running states, a new method called Scatter Point method is put forward in this paper. It can be used to observe or monitor the running states of a single variable nonlinear system in real-time. In this paper, the definition of the method is given at first, and then its working principle is expounded theoretically, after this, some physical experiments based on Chua's nonlinear system are conducted. At the same time, many scatter point graphs are measured by a general analog oscilloscope. The motion, number, and distribution of these scatter points shown on the oscilloscope screen can directly reflect the current states of the tested system. The experimental results further confirm that the method is effective and practical, in which the system running states are not easily lost. In addition, this method is not only suitable for single variable systems but also for multivariable systems. PMID:25833428

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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.

  1. Features of the Observed Annual Ocean-Atmosphere Flux Variability on the West Florida Shelf.

    NASA Astrophysics Data System (ADS)

    Virmani, Jyotika I.; Weisberg, Robert H.

    2003-02-01

    The annual cycle of sea surface temperature and ocean-atmosphere fluxes on the west Florida shelf is described using in situ measurements and climatology. Seasonal reversals in water temperature tendency occur when the net surface heat flux changes sign in boreal spring and fall. Synoptic-scale variability is also important. Momentum and heat flux variations result in successive water column stratification and destratification events, particularly at shallower depths during spring. Fall is characterized by destratification of the water column and a series of steplike decreases in the temperature. These are in response to both tropical storms and extratropical fronts. Tropical storms are responsible for the largest momentum fluxes, but not necessarily for the largest surface heat fluxes. A one-dimensional analysis of the temperature equation suggests that surface heat flux is primarily responsible for the spring and fall seasonal ocean temperature changes, but that synoptic-scale variability is also controlled by the ocean circulation dynamics. During summer, the situation is reversed and the major influence on water temperature is ocean dynamics, with the heat flux contributing to the synoptic-scale variability. There is also evidence of interannual variability: the wintertime temperatures get increasingly colder from 1998 to 2000, and the greatest stratification and coldest subsurface temperatures occur in 1998. NCEP-NCAR reanalysis fields do not reproduce the high spatial flux variability observed in situ or with satellite measurements. Reconciling these differences and their impacts on the climate variability of this region provides challenges to coupled ocean-atmosphere models and their supporting observing systems.

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

    E-print Network

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

    2005-10-07

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

  3. Examining Soil Moisture Variability and Field Mean Estimation Methods using Nested Observations

    NASA Astrophysics Data System (ADS)

    Peterson, A.; Helgason, W.; Ireson, A. M.

    2014-12-01

    Information about soil moisture is typically required at the field scale. Direct measurements of soil moisture at this scale are not possible, though there are a number of promising indirect methods (e.g. remote sensing methods and cosmic-ray neutrons). Methods for obtaining point scale measurements of soil moisture are well established. However, variability of soil moisture, in both space and time, makes accurately determining field scale soil moisture from point measurements difficult. Understanding sub-field scale variability is a key step in determining how to upscale point measurements, and in particular to identify the minimum number of point measurements necessary to represent field scale mean soil moisture. Objectives of this study are to: (1) examine the spatial variability of soil moisture with time, and (2) compare field scale soil moisture estimation methods. Nested soil moisture measurements provided observations covering a 5002m2 area within a semi-arid prairie pasture site in southern Saskatchewan, Canada. Complementary measurements of the water balance were measured using meteorological and flux instrumentation. Spatial variability of surface and root zone soil moisture were examined using data from gridded dielectric water content probe surveys and a neutron probe array. Field scale surface soil moisture was measured at the site using a cosmic-ray neutron probe. The field scale estimation methods compared are: (1) water balance, (2) upscaling by averaging point scale measurements, (3) upscaling by identification of average representative time stable sites, and (4) extrapolation of shallow soil moisture measured by cosmic-ray neutron probe. Variability of surface soil moisture was found to be smallest under extreme dry and wet conditions, and largest during intermediate moisture conditions. Large spatial variability was found in the root zone, with soil moisture being most temporally variable closer to the surface.

  4. Narrow absorption line variability in repeat quasar observations from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Hacker, Troy L.; Brunner, Robert J.; Lundgren, Britt F.; York, Donald G.

    2013-09-01

    We present the results from a time domain study of absorption lines detected in quasar spectra with repeat observations from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). Beginning with over 4500 unique time separation baselines of various absorption line species identified in the SDSS DR7 quasar spectra, we create a catalogue of 2522 quasar absorption line systems with two to eight repeat observations, representing the largest collection of unbiased and homogeneous multi-epoch absorption systems ever published. To investigate these systems for time variability of narrow absorption lines, we refine this sample based on the reliability of the system detection, the proximity of pixels with bright sky contamination to individual absorption lines and the quality of the continuum fit. Variability measurements of this sub-sample based on the absorption line equivalent widths yield a total of 33 systems with indications of significantly variable absorption strengths on time-scales ranging from one day to several years in the rest frame of the absorption system. Of these, at least 10 are from a class known as intervening absorption systems caused by foreground galaxies along the line of sight to the background quasar. This is the first evidence of possible absorption line variability detected in intervening systems, and their short time-scale variations suggest that small-scale structures (˜10-100 au) are likely to exist in their host foreground galaxies.

  5. All quantum observables in a hidden-variables model must commute simultaneously

    E-print Network

    James D. Malley

    2004-02-18

    Under a standard set of assumptions for a hidden-variables model for quantum events, we show that all observables must commute simultaneously. And, despite Bell's complaint that a key condition of von Neumann's was quite unrealistic, we show these these conditions are entirely equivalent to those later introduced by Bell, Kochen and Specker. As is it known that these conditions are also equivalent to those under which the Bell-Clauser-Horne inequalities are derived, we see that any experimental violations of the inequalities demonstrate only that quantum observables do not commute.The same conclusion applies to the collection of elegant inequality-free no-go proofs of Greenberger-Horne-Zeilinger, Mermin and Peres. Otherwise expressed, the usual hidden-variable models have assumptions that are collectively too strong to be interesting, and hence need modification or deletion.

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

    Microsoft Academic Search

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

    2009-01-01

    We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016\\/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo

  7. Ultraviolet photometry with the Astronomical Netherlands Satellite /ANS/ Observations of Beta Canis Majoris variables

    NASA Technical Reports Server (NTRS)

    Lesh, J. R.; Wesselius, P. R.

    1979-01-01

    The paper deals with detailed ANS observations of three Beta Canis Majoris variables: Xi-1 CMa, HD 61068 (whose discovery is reported here) and 15 CMa. Light curves at five ultraviolet wavelengths are presented, and the periods and amplitudes are discussed. The ultraviolet colors are used to derive temperatures and temperature variations, which are compared with the MK spectral types. The anomalously high luminosity found for Xi-1 CMa on the basis of certain line strengths is also discussed.

  8. Observations of the Cataclysmic Variable 1 RXPJ113123+4322.5

    NASA Astrophysics Data System (ADS)

    Holtgrewe, Kirk S.; Durig, Douglas T.

    We observed the cataclysmic variable star l RXPJ113123+4322.5 while it was undergoing its recent outburst. We collected data using R and V filters, alternating the filters every two minutes. We obtained two to three hour-long data sets on two different nights. The light curve was analyzed using Mathematica. The period determined was near 95 minutes and there was also some indication of a lower amplitude, higher frequency variation.

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

    NASA Astrophysics Data System (ADS)

    Templeton, Matthew R.

    2009-10-01

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

  10. Spectral signatures of Earth's climate variability as observed from space and diagnosed from reanalyses

    NASA Astrophysics Data System (ADS)

    Brindley, Helen; Bantges, Richard; Russell, Jacqueline; Murray, Jonathan; Harries, John

    2015-04-01

    Measurements of the Earth's spectrally resolved outgoing longwave radiation have the intrinsic information content and link to the overall energy budget that implies that they are ideal candidates to monitor the climate and detect and attribute change. Theoretical studies have shown how distinct longwave spectral signals from different climate forcing and feedback mechanisms may be derived and appear to combine with a high degree of linearity. However, an open, important question which has not yet been fully addressed concerns the exact level of short-term variability seen in observed longwave spectra. We investigate this here by exploiting the emerging radiance record available from the Infrared Atmospheric Sounding Interferometer (IASI) on the Metop-A satellite. We use five years of IASI data to assess the level of interannual variability seen in all-sky spectra at different spatial scales. Maximum variability is seen at the smallest scales investigated (10° zonal means) at northern and southern high latitudes across the centre of the 15 ?m CO2 band. As spatial scale increases, the overall magnitude of interannual variability reduces across the spectrum and the spectral shape of the variability changes. We show that the interannual variability manifested across the IASI spectra is less than 0.17 K in brightness temperature in the all-sky global annual mean, collapsing to a value of less than 0.05 K in the atmospheric window, a spectral region whose variability is dominated by fluctuations in surface and cloud properties. Spectrally integrating the IASI measurements to create pseudo broadband and window channels indicates a variation about the mean that is higher for the broadband than the window channel at the global and quasi-global scale and over the Southern Hemisphere. These findings are in agreement with observations from CERES Terra over the same period and imply that at the largest spatial scales, over the period considered here, fluctuations in mid-upper tropospheric temperatures and water vapour, and not cloud or surface temperature, play the dominant role in determining the level of interannual variability in all-sky outgoing longwave radiation. This pattern of behavior is not seen in spectra simulated using reanalysis fields that have been sub-sampled to match the Metop-A satellite track. Possible reasons for this discrepancy will be discussed in this paper.

  11. Summertime tropospheric ozone variability over the Mediterranean basin observed with IASI

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  12. Identification of RR Lyrae Variables in SDSS from Single-Epoch Photometric and Spectroscopic Observations

    E-print Network

    Ronald Wilhelm; W. Lee Powell Jr.; Timothy C. Beers; Branimir Sesar; Carlos Alende Prieto; Kenneth W. Carrell; Young Sun Lee; Brian Yanny; Constance M. Rockosi; Nathan De Lee; Gwen Hansford Armstrong; Stephen J. Torrence

    2007-12-05

    We describe a new RR Lyrae identification technique based on out-of-phase single-epoch photometric and spectroscopic observations contained in SDSS Data Release 6 (DR-6). This technique detects variability by exploiting the large disparity between the g-r color and the strength of the hydrogen Balmer lines when the two observations are made at random phases. Comparison with a large sample of known variables in the SDSS equatorial stripe (Stripe 82) shows that the discovery efficiency for our technique is ~85%. Analysis of stars with multiple spectroscopic observations suggests a similar efficiency throughout the entire DR-6 sample. We also develop a technique to estimate the average g apparent magnitude (over the pulsation cycle) for individual RR Lyrae stars, using the for the entire sample and measured colors for each star. The resulting distances are found to have precisions of ~14%. Finally, we explore the properties of our DR-6 sample of N = 1087 variables, and recover portions of the Sagittarius Northern and Southern Stream. Analysis of the distance and velocity for the Southern Stream are consistent with previously published data for blue horizontal-branch stars. In a sample near the North Galactic Polar Cap, we find evidence for the descending leading Northern arm, and a possible detection of the trailing arm.

  13. Identification of RR Lyrae Variables in SDSS from Single-Epoch Photometric and Spectroscopic Observations

    E-print Network

    Wilhelm, Ronald; Beers, Timothy C; Sesar, Branimir; Prieto, Carlos Alende; Carrell, Kenneth W; Lee, Young Sun; Yanny, Brian; Rockosi, Constance M; De Lee, Nathan; Armstrong, Gwen Hansford; Torrence, Stephen J

    2007-01-01

    We describe a new RR Lyrae identification technique based on out-of-phase single-epoch photometric and spectroscopic observations contained in SDSS Data Release 6 (DR-6). This technique detects variability by exploiting the large disparity between the g-r color and the strength of the hydrogen Balmer lines when the two observations are made at random phases. Comparison with a large sample of known variables in the SDSS equatorial stripe (Stripe 82) shows that the discovery efficiency for our technique is ~85%. Analysis of stars with multiple spectroscopic observations suggests a similar efficiency throughout the entire DR-6 sample. We also develop a technique to estimate the average g apparent magnitude (over the pulsation cycle) for individual RR Lyrae stars, using the for the entire sample and measured colors for each star. The resulting distances are found to have precisions of ~14%. Finally, we explore the properties of our DR-6 sample of N = 1087 variables, and recover portions of the Sagittarius Northe...

  14. IUE observations of the dwarf nova HL Canis Majoris and the winds of cataclysmic variables

    NASA Technical Reports Server (NTRS)

    Mauche, Christopher W.; Raymond, John C.

    1987-01-01

    An observational and theoretical study is conducted of the P Cygni profiles of cataclysmic variables, with attention to the profiles of the dwarf nova HL CMa, in light of the ionization structure of the wind for a given geometry. It is found that a spherically symmetric wind is capable of generating the observed profile shapes when the accretion disk is limb-darkened, provided that the acceleration of the wind is very low and that the wind represents a mass-loss rate of about 10 to the -11th/C IV ionization fraction of the solar mass per year; a wind of this magnitude, however, cannot be driven by radiation pressure.

  15. THE VARIABLE OPTICAL POLARIZATION AND FERMI OBSERVATIONS OF PMN J0948+0022

    SciTech Connect

    Eggen, Joseph R.; Miller, H. Richard; Maune, Jeremy D., E-mail: eggen@chara.gsu.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303-3083 (United States)

    2013-08-20

    We report on observations of the {gamma}-ray and optical photopolarimetric behavior of the radio-loud, narrow-line type-1 Seyfert galaxy PMN J0948+0022 over a 27 month period. As this object has recently been suggested to represent a prototype of an emerging class of blazar-like objects, the observed properties are compared to those of blazars. We extract doubling timescales of roughly 4 hr for the optical and {gamma}-ray bands. The rapid microvariability in the optical/near-IR, significant and variable optical polarization, and strong yet rapidly variable {gamma}-ray emission we observe for PMN J0948+0022 are all classical observational characteristics associated with blazars. However, since these observations do not show a clear correlation between the {gamma}-ray and optical behavior, they do not offer conclusive proof that the emissive behavior of PMN J0948+0022 is due to a relativistic jet oriented close to our line of sight.

  16. Seasonal variability of upper tropospheric acetone using ACE-FTS observations and LMDz-INCA model simulations

    NASA Astrophysics Data System (ADS)

    Dufour, Gaëlle; Harrison, Jeremy; Szopa, Sophie; Bernath, Peter

    2014-05-01

    The vertically-resolved distributions of oxygenated organic compounds (oVOCs) are mainly inferred from surface and airborne measurements with limited spatial and temporal coverage. This results in a limited understanding of the atmospheric budget of these compounds and of their impact on the upper tropospheric chemistry. In the last decade, satellite observations which complement in-situ measurements have become available, providing global distributions of several oVOCs. For example, Scisat-1, also known as the Atmospheric Chemistry Experiment (ACE) has measured several oVOCs including methanol and formaldehyde. ACE is a Canadian-led satellite mission for remote sensing of the Earth's atmosphere that has been in operation since 2004. The primary instrument on board is a Fourier transform spectrometer (FTS) featuring broad spectral coverage in the infrared (750-4400 cm-1) with high spectral resolution (0.02 cm-1). The FTS instrument can measure down to 5 km altitude with a high signal-to-noise ratio using solar occultation. The ACE-FTS has the ability to measure seasonal and height-resolved distributions of minor tropospheric constituents on a near-global scale and provides the opportunity to evaluate our understanding of important atmospheric oxygenated organic species. ACE-FTS acetone retrievals will be presented. The spatial distribution and seasonal variability of acetone will be described and compared to LMDz-INCA model simulations.

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

    PubMed Central

    2014-01-01

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

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

    PubMed Central

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  20. Summertime tropospheric ozone variability over the Mediterranean basin observed with IASI

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  1. Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability

    E-print Network

    I. A. Smith; E. P. Liang

    1998-12-08

    As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present the rapid X-ray variability observed July 26 using the RXTE when the source was in a hard state (= soft X-ray low state). We found that the source was extremely variable, with many bright flares. The flares have relatively symmetric time profiles. There are a few time intervals where the flux rises steadily and then drops suddenly, sometimes to a level lower than the average before the increase. Hardness ratios showed that the source was slightly softer when the flux was brighter. The power density spectra (PDS) were also complicated and we found that broken power laws do not provide adequate fits to any of them. Instead a pair of zero-centered Lorentzians gives a good general description of the shape of the PDS. We found several quasi-periodic oscillations (QPO), including some that are harmonically spaced with the most stable frequency at 0.35 Hz. While the overall rms variability of the source was close to being constant throughout the observation (29% integrating between 0.01 and 50 Hz), there is a small but significant change in the PDS shape with time. More importantly, we show that the soft 2-5 keV band is more variable than the harder 5-10 and 10-40 keV bands, which is unusual for this source and for other black hole candidates. Cross correlation functions (CCF) between these bands show that the light curve for the 10-40 keV band lags that of the 2-5 keV band by 5 msec.

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

    USGS Publications Warehouse

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

    2005-01-01

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

  3. Variability of indication criteria in knee and hip replacement: an observational study

    PubMed Central

    2010-01-01

    Background Total knee (TKR) and hip (THR) replacement (arthroplasty) are effective surgical procedures that relieve pain, improve patients' quality of life and increase functional capacity. Studies on variations in medical practice usually place the indications for performing these procedures to be highly variable, because surgeons appear to follow different criteria when recommending surgery in patients with different severity levels. We therefore proposed a study to evaluate inter-hospital variability in arthroplasty indication. Methods The pre-surgical condition of 1603 patients included was compared by their personal characteristics, clinical situation and self-perceived health status. Patients were asked to complete two health-related quality of life questionnaires: the generic SF-12 (Short Form) and the specific WOMAC (Western Ontario and Mcmaster Universities) scale. The type of patient undergoing primary arthroplasty was similar in the 15 different hospitals evaluated. The variability in baseline WOMAC score between hospitals in THR and TKR indication was described by range, mean and standard deviation (SD), mean and standard deviation weighted by the number of procedures at each hospital, high/low ratio or extremal quotient (EQ5-95), variation coefficient (CV5-95) and weighted variation coefficient (WCV5-95) for 5-95 percentile range. The variability in subjective and objective signs was evaluated using median, range and WCV5-95. The appropriateness of the procedures performed was calculated using a specific threshold proposed by Quintana et al for assessing pain and functional capacity. Results The variability expressed as WCV5-95 was very low, between 0.05 and 0.11 for all three dimensions on WOMAC scale for both types of procedure in all participating hospitals. The variability in the physical and mental SF-12 components was very low for both types of procedure (0.08 and 0.07 for hip and 0.03 and 0.07 for knee surgery patients). However, a moderate-high variability was detected in subjective-objective signs. Among all the surgeries performed, approximately a quarter of them could be considered to be inappropriate. Conclusions A greater inter-hospital variability was observed for objective than for subjective signs for both procedures, suggesting that the differences in clinical criteria followed by surgeons when indicating arthroplasty are the main responsible factors for the variation in surgery rates. PMID:20977745

  4. Radar observations of the diurnal tide in the tropical mesosphere-lower thermosphere region: Longitudinal variabilities

    NASA Astrophysics Data System (ADS)

    Gurubaran, S.; Rajaram, R.; Nakamura, T.; Tsuda, T.; Riggin, D.; Vincent, R. A.

    2009-04-01

    Significant attention is being paid in recent times by several observational and modeling studies to quantify the spatial and temporal variabilities of diurnal tide in the mesosphere and lower thermosphere (MLT) region. These variabilities are ascribed to spatial and temporal variations in the tidal forcing or interactions between the propagating tides and background wind, planetary waves or gravity waves. The present work makes use of simultaneous ground-based radar wind observations of different durations from five equatorial/low latitude sites in the Indian, Indonesian and Pacific sectors: Tirunelveli (8.7°N, 77.8°E), Jakarta (6.4°S, 106.7°E), Pontianak (0.03°N, 109°E), Kauai (22°N, 160°W) and Christmas Island (2°N, 157°W). This study delineates the longitudinal differences in the tidal characteristics in (i) interannual time scales over Tirunelveli and Kauai during 1993-2002, (ii) seasonal time scales over Christmas Island, Jakarta and Tirunelveli for the years 1993-1997 and (iii) shorter than seasonal time scales over Christmas Island, Pontianak and Tirunelveli during 1996-1997. An important observational feature noticed in this work is the differing behavior of the long-term tidal fields over Tirunelveli and Kauai. The monthly tidal amplitudes over Tirunelveli reveal a strong QBO signature whereas a similar, strong QBO signal could not be traced in the long-term observations from Kauai.

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

    NASA Technical Reports Server (NTRS)

    Chao, Benjamin F.

    2003-01-01

    Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth's dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease -- until around 1998, when it switched quite suddenly to an increase trend which has continued to date. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this J2 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution (i.e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. In addition, although less precise than GRACE, the GPS/Meteorology constellation mission COSMIC, with 6 mini-satellites to be launched in late 2005, is expected to provide continued and complementary time-variable gravity observations. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

  6. Extreme Ultraviolet Explorer observations of the magnetic cataclysmic variable RE 1938-461

    NASA Technical Reports Server (NTRS)

    Warren, John K.; Vallerga, John V.; Mauche, Christopher W.; Mukai, Koji; Siegmund, Oswald H. W.

    1993-01-01

    The magnetic cataclysmic variable RE 1938-461 was observed by the Extreme Ultraviolet Explorer (EUVE) Deep Survey instrument on 1992 July 8-9 during in-orbit calibration. It was detected in the Lexan/ boron (65-190 A) band, with a quiescent count rate of 0.0062 +/- 0.0017/s, and was not detected in the aluminum/carbon (160-360 A) band. The Lexan/boron count rate is lower than the corresponding ROSAT wide-field camera Lexan/boron count rate. This is consistent with the fact that the source was in a low state during an optical observation performed just after the EUVE observation, whereas it was in an optical high state during the ROSAT observation. The quiescent count rates are consistent with a virtual cessation of accretion. Two transient events lasting about 1 hr occurred during the Lexan/boron pointing, the second at a count rate of 0.050 +/- 0.006/s. This appears to be the first detection of an EUV transient during the low state of a magnetic cataclysmic variable. We propose two possible explanations for the transient events.

  7. The influence of resolution in simulating interannual and interdecadal variability in a coupled

    E-print Network

    Dufresne, Jean-Louis

    The influence of resolution in simulating inter­annual and inter­decadal variability in a coupled frequency climate variability at inter­annual or inter­decadal time scale is the key to any kind temperature anomaly variations at decadal time scales have been observed. Bjerknes (1964) found that low

  8. Non-tidal aliasing in seasonal sea-level variability and annual Rossby waves as observed by satellite altimetry

    E-print Network

    Paris-Sud XI, Université de

    Non-tidal aliasing in seasonal sea-level variability and annual Rossby waves as observed with altimeter observations of seasonal sea- level variability and annual Rossby waves. Our results indicate-mode inertia-gravity waves in the Paci®c Ocean is evidenced by three energy peaks centred at 3.0, 4.0 and 5

  9. Observable Effects of Dust Formation in Dynamic Atmospheres of M-type Mira Variables

    E-print Network

    M. J. Ireland; M. Scholz

    2006-01-18

    The formation of dust with temperature-dependent non-grey opacity is considered in a series of self-consistent model atmospheres at different phases of an O-rich Mira variable of mass 1.2 $M_\\odot$. Photometric and interferometric properties of these models are predicted under different physical assumptions regarding the dust formation. The iron content of the initial silicate that forms and the availability of grain nuclei are found to be critical parameters that affect the observable properties. In particular, parameters were found where dust would form at 2-3 times the average continuum photospheric radius. This work provides a consistent physical explanation for the larger apparent size of Mira variables at wavelengths shorter than 1 $\\mu$m than that predicted by dust free fundamental-mode pulsation models.

  10. The IPCC (1995) scientific assessment of climate change: Observed climate variability and change

    SciTech Connect

    Karl, T.R. [National Climatic Data Center, Asheville, NC (United States)

    1996-12-31

    The IPCC (1995) scientific assessment of climate change shows that human activities have increased the concentrations and changed the distributions of greenhouse gases and aerosols during the 19th and 20th Centuries. Questions arise regarding the magnitude and significance of observed changes and variations of temperature, precipitation (and related hydrologic variables), and other important weather events as the atmospheric composition has changed. This assessment addresses the following broad questions: (1) has the climate warmed? (2) has the climate become wetter? (3) has the atmospheric/oceanic circulation changed? (4) has the climate become more variable or extreme? and (5) is the 20th Century warming unusual? Research addressing those questions is briefly summarized. 16 refs., 1 fig.

  11. Tropospheric ozone and aerosol variability observed at high latitudes with an airborne lidar

    NASA Technical Reports Server (NTRS)

    Browell, Edward V.; Butler, Carolyn F.; Fenn, Marta A.; Kooi, Susan A.; Grant, William B.

    1994-01-01

    Large-scale summertime (July-August) distributions of O3 and aerosols were observed in a broad range of atmosphere conditions over the tundra, ice, and ocean regions near Alaska in 1988 and over the lowlands and boreal forests of Canada in 1990. The tropospheric O3 budget in the high-latitude regions was found to be strongly influenced by stratospheric intrusions, and deposition at the surface was found to be the main sink for O3 in the troposphere. Enhanced levels of O3 were observed in plumes from fires in Alaska and Canada. This paper discusses the large-scale variability of O3 and aerosols observed in the high-latitude regions during these field experiments.

  12. Photometry of Variable Stars from Dome A, Antarctica: Results from the 2010 Observing Season

    E-print Network

    Wang, Lingzhi; Wang, Lifan; Ashley, Michael C B; Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Lawrence, Jon S; Liu, Qiang; Luong-Van, Daniel; Pennypacker, Carl R; Shang, Zhaohui; Storey, John W V; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; York, Donald G; Zhou, Xu; Zhu, Zhenxi; Zhu, Zonghong

    2013-01-01

    We present results from a season of observations with the Chinese Small Telescope ARray (CSTAR), obtained over 183 days of the 2010 Antarctic winter. We carried out high-cadence time-series aperture photometry of 20,000 stars with i<15.3 mag located in a 23 square-degree region centered on the south celestial pole. We identified 188 variable stars, including 67 new objects relative to our 2008 observations, thanks to broader synoptic coverage, a deeper magnitude limit and a larger field of view. We used the photometric data set to derive site statistics from Dome A. Based on two years of observations, we find that extinction due to clouds at this site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time, respectively.

  13. Mechanisms for Diurnal Variability of Global Tropical Rainfall Observed from TRMM

    NASA Technical Reports Server (NTRS)

    Yang, Song; Smith, Eric a.

    2006-01-01

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

  14. Sea Ice and Ice Temperature Variability as Observed by Microwave and Infrared Satellite Data

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Recent reports of a retreating and thinning sea ice cover in the Arctic have pointed to a strong suggestion of significant warming in the polar regions. It is especially important to understand what these reports mean in light of the observed global warning and because the polar regions are expected to be most sensitive to changes in climate. To gain insight into this phenomenon, co-registered ice concentrations and surface temperatures derived from two decades of satellite microwave and infrared data have been processed and analyzed. While observations from meteorological stations indicate consistent surface warming in both regions during the last fifty years, the last 20 years of the same data set show warming in the Arctic but a slight cooling in the Antarctic. These results are consistent with the retreat in the Arctic ice cover and the advance in the Antarctic ice cover as revealed by historical satellite passive microwave data. Surface temperatures derived from satellite infrared data are shown to be consistent within 3 K with surface temperature data from the limited number of stations. While not as accurate, the former provides spatially detailed changes over the twenty year period. In the Arctic, for example, much of the warming occurred in the Beaufort Sea and the North American region in 1998 while slight cooling actually happened in parts of the Laptev Sea and Northern Siberia during the same time period. Big warming anomalies are also observed during the last five years but a periodic cycle of about ten years is apparent suggesting a possible influence of the North Atlantic Oscillation. In the Antarctic, large interannual and seasonal changes are also observed in the circumpolar ice cover with regional changes showing good coherence with surface temperature anomalies. However, a mode 3 is observed to be more dominant than the mode 2 wave reported in the literature. Some of these spatial and temporal changes appear to be influenced by the Antarctic Circumpolar Wave (ACW) and changes in coastal polynya activities.

  15. Spitzer Space Telescope Observations of the Magnetic Cataclysmic Variable AE Aqr

    E-print Network

    G. Dubus; R. E. Taam; C. Hull; D. M. Watson; J. C. Mauerhan

    2007-03-19

    The magnetic cataclysmic variable AE Aquarii hosts a rapidly rotating white dwarf which is thought to expel most of the material streaming onto it. Observations of AE Aqr have been obtained in the wavelength range of 5 - 70 microns with the IRS, IRAC, and MIPS instruments on board the Spitzer Space Telescope. The spectral energy distribution reveals a significant excess above the K4V spectrum of the donor star with the flux increasing with wavelength above 12.5 microns. Superposed on the energy distribution are several hydrogen emission lines, identified as Pf alpha and Hu alpha, beta, gamma. The infrared spectrum above 12.5 microns can be interpreted as synchrotron emission from electrons accelerated to a power-law distribution dN=E^{-2.4}dE in expanding clouds with an initial evolution timescale in seconds. However, too many components must then be superposed to explain satisfactorily both the mid-infrared continuum and the observed radio variability. Thermal emission from cold circumbinary material can contribute, but it requires a disk temperature profile intermediate between that produced by local viscous dissipation in the disk and that characteristic of a passively irradiated disk. Future high-time resolution observations spanning the optical to radio regime could shed light on the acceleration process and the subsequent particle evolution.

  16. Intraannual variability of tides in the thermosphere from model simulations and in situ satellite observations

    NASA Astrophysics Data System (ADS)

    Häusler, K.; Hagan, M. E.; Forbes, J. M.; Zhang, X.; Doornbos, E.; Bruinsma, S.; Lu, G.

    2015-01-01

    In this paper, we provide insights into limitations imposed by current satellite-based strategies to delineate tidal variability in the thermosphere, as well as the ability of a state-of-the-art model to replicate thermospheric tidal determinations. Toward this end, we conducted a year-long thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) simulation for 2009, which is characterized by low solar and geomagnetic activity. In order to account for tropospheric waves and tides propagating upward into the ˜30-400 km model domain, we used 3-hourly MERRA (Modern-Era Retrospective Analysis for Research and Application) reanalysis data. We focus on exospheric tidal temperatures, which are also compared with 72 day mean determinations from combined Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellite observations to assess the model's capability to capture the observed tidal signatures and to quantify the uncertainties associated with the satellite exospheric temperature determination technique. We found strong day-to-day tidal variability in TIME-GCM that is smoothed out when averaged over as few as ten days. TIME-GCM notably overestimates the 72 day mean eastward propagating tides observed by CHAMP/GRACE, while capturing many of the salient features of other tidal components. However, the CHAMP/GRACE tidal determination technique only provides a gross climatological representation, underestimates the majority of the tidal components in the climatological spectrum, and moreover fails to characterize the extreme variability that drives the dynamics and electrodynamics of the ionosphere-thermosphere system. A multisatellite mission that samples at least six local times simultaneously is needed to provide this quantification.

  17. Quantitative Comparison of the Variability in Observed and Simulated Shortwave Reflectance

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  18. A Decade of Growth

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  19. Microwave radiometer observations of interannual water vapor variability and vertical structure over a tropical station

    NASA Astrophysics Data System (ADS)

    Renju, R.; Suresh Raju, C.; Mathew, Nizy; Antony, Tinu; Krishna Moorthy, K.

    2015-05-01

    The intraseasonal and interannual characteristics and the vertical distribution of atmospheric water vapor from the tropical coastal station Thiruvananthapuram (TVM) located in the southwestern region of the Indian Peninsula are examined from continuous multiyear, multifrequency microwave radiometer profiler (MRP) measurements. The accuracy of MRP for precipitable water vapor (PWV) estimation, particularly during a prolonged monsoon period, has been demonstrated by comparing with the PWV derived from collocated GPS measurements based on regression model between PWV and GPS wet delay component which has been developed for TVM station. Large diurnal and intraseasonal variations of PWV are observed during winter and premonsoon seasons. There is large interannual PWV variability during premonsoon, owing to frequent local convection and summer thunderstorms. During monsoon period, low interannual PWV variability is attributed to the persistent wind from the ocean which brings moisture to this coastal station. However, significant interannual humidity variability is seen at 2 to 6 km altitude, which is linked to the monsoon strength over the station. Prior to monsoon onset over the station, the specific humidity increases up to 5-10 g/kg in the altitude region above 5 km and remains consistently so throughout the active spells.

  20. Space Technology 5 Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, G.; Wang, Y.; Slavin, J. A.; Strangeway, R. L.

    2009-01-01

    Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field-aligned currents using the ST5 data. We examine the field-aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large-scale current sheets, are very dynamic with highly variable current density and/or polarity in approx.10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are approx.1 min for mesoscale currents and approx.10 min for large-scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  1. Ocean variability east of Mindanao: Mooring observations at 7°N, revisited

    NASA Astrophysics Data System (ADS)

    Kashino, Yuji; Ueki, Iwao; Sasaki, Hedeharu

    2015-04-01

    Two subsurface moorings were deployed east of Mindanao Island, the Philippines, at 7°01'N, 126°55'E and 7°01'N, 127°46'E, at the location of the inshore and offshore cores of the Mindanao Undercurrent (MUC) suggested by past studies, from September 2011 to October 2012 and March 2013. A steady northward undercurrent, the MUC, was not confirmed by these observations, not only at the location of its inshore core but also of the offshore core. The observed mean flow at the mooring sites seems to be part of an anticyclonic eddy rather than the MUC. A particle-tracking experiment using a high-resolution general circulation model output showed that the northward mean flow, called the MUC by past studies, was too weak to advect water to the north. The Mindanao Current during 2011-2012 was weaker than during 1999-2002 because the sea surface height in the Philippine Sea during 2011-2012 was lower than that during 1999-2002. Intraseasonal variability with periods of 50-100 days was observed at the mooring sites, comparable to the previous observations during 1999-2002. Westward signal propagations were observed with periods and speeds of 50 days and 0.20 m s-1 at 300 m depth and of 60-72 days and 0.11-0.14 m s-1 at 960 m depth.

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

    E-print Network

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

    2006-05-02

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

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

    NASA Astrophysics Data System (ADS)

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

    1991-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Slingo, A.; Bharmal, N. A.; Robinson, G. J.; Settle, J. J.; Allan, R. P.; White, H. E.; Lamb, P. J.; LéLé, M. Issa; Turner, D. D.; McFarlane, S.; Kassianov, E.; Barnard, J.; Flynn, C.; Miller, M.

    2008-07-01

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

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

    SciTech Connect

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

    2008-10-17

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

  6. Observed MOC Variability at 26.5°N and 34.5°S: Structure and Time Scale Similarities and Differences in the North and South Atlantic

    NASA Astrophysics Data System (ADS)

    Meinen, C. S.; Johns, W. E.; Speich, S.; Smeed, D.; Perez, R. C.; McCarthy, G.; Dong, S.; Piola, A. R.; Garzoli, S. L.; Frajka-Williams, E.; Baringer, M. O.; Campos, E. J.

    2014-12-01

    Variations in the Meridional Overturning Circulation (MOC) have been connected in numerical models and paleo-climate records with changes in surface air temperature, precipitation patterns, and changes in hurricane intensification, but observations and models also suggest that the MOC is not an in-phase monolithic system driving simultaneous (or even identical lagged) variations at all latitudes and in all ocean basins. Prediction and understanding of MOC variability will require better comprehension of the latitudinal and temporal scales associated with MOC changes across the Atlantic. Continuous basin-wide MOC volume transport time series observations are available at 26.5°N from the RAPID-MOC/MOCHA/WBTS array for nearly a decade, and a 20-month continuous basin-wide MOC time series is available at 34.5°S based on the pilot arrays of the developing SAMBA array. At 26.5°N the longer record indicates that the bulk (nearly 50%) of the time variability in the record is at sub-annual periods - this energetic 'high frequency noise' illustrates the need for continuous-in-time (daily) measurements. The MOC at 34.5°S is similarly 'noisy' at sub-annual periods, and based on this short record there is no indication of coherence between the MOC time series at the two latitudes. Structure and variability comparisons between the two latitudes will be presented and discussed in the context of recent numerical model results, illustrating not only the veracity but also the limitations of the model results.

  7. Quantifying the diurnal variability of deep convection in the Congo basin using satellite observations, global and regional models.

    NASA Astrophysics Data System (ADS)

    White, Bethan; Kipling, Zak; Taylor, Sarah; Stier, Philip

    2015-04-01

    Convection transports moisture, momentum, heat and aerosols through the troposphere, and so the temporal variability of convection is a major driver of global weather and climate. The diurnal cycle of convection is associated with large variations in solar forcing and the ability of models to represent this cycle shows how well they represent radiative transfer and surface heat exchanges, as well as boundary layer, convective and cloud processes. Global models and some numerical weather prediction (NWP) models fail to capture the observed diurnal cycle of convection (Yang and Slingo, 2001; Stratton and Stirling, 2012), while the ability of cloud-resolving models (CRMs) to represent the diurnal cycle is strongly dependent on horizontal resolution. The Congo basin is home to some of the most intense convective activity on the planet, yet has been the focus of very few previous studies, especially when compared to the neighbouring, relatively well-understood West African climate system. Ground-based observations of convection and precipitation in the Congo region are sparse, and there has been a sharp decline in the number of rain gauges in the region over the past few decades (Washington, 2013). In this study we use a variety of tools to quantify the diurnal cycle of deep convection over the Congo including satellite observations, a global model both with and without a new convective parameterisation, and a regional convection-permitting model. This approach allows us to evaluate our simulations despite the lack of in-situ observational data. In contrast to the static picture provided by polar-orbiting satellites, the geostationary SEVIRI instrument provides continuous, high time resolution observations of cloud properties over a large area. It has the additional advantage of providing coverage of the Congo Basin, at a spatial resolution of between 3 and 5km. The CLAAS (Cloud Property Dataset Using SEVIRI) product is used to quantify the diurnal cycle of convective cloud top temperatures across the region. In global models, the mass-flux convection parameterisations commonly used limit our ability to represent the microphysics of convective clouds. We use ECHAM both with and without a new parameterisation (CCFM, the Convective Cloud Field Model), which represents a spectrum of convective updraughts in each grid box, allowing the microphysics to take account of the explicitly-simulated distributions of cloud area, cloud height and vertical velocity. High-resolution convection-permitting simulations are performed with the WRF model using a 2-moment bulk microphysics scheme. We quantify the diurnal cycle of convection and precipitation in the region on timescales much longer than those usually studied with high-resolution models. In addition, the use of CCFM in the global model allows us to compare the frequency distribution of convective precipitation rates in ECHAM with those from WRF. Comparing data from satellite observations, global and high-resolution models enables us to quantify the diurnal variability of deep convection in the Congo basin and evaluate our results against observations, providing a more comprehensive analysis of the diurnal cycle than has previously been shown, and also giving new insight into a region that has previously seen little investigation.

  8. Observed interannual variability of near-surface salinity in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Pant, Vimlesh; Girishkumar, M. S.; Udaya Bhaskar, T. V. S.; Ravichandran, M.; Papa, Fabrice; Thangaprakash, V. P.

    2015-05-01

    An in situ gridded data of salinity, comprising Argo and CTD profiles, has been used to study the interannual variability of near-surface salinity (within 30 m from sea surface) in the Bay of Bengal (BoB) during the years 2005-2013. In addition to the broad agreement with earlier studies on the north-to-south gradient of surface salinity and general features of seasonal variability of salinity, the data also revealed few episodes of enhanced freshening in the BoB. The observations showed distinct anomalous low salinity (< 2 psu) waters in the northern BoB during June-February of the years 2006-2007 (Y67), 2011-2012 (Y12), and 2012-2013 (Y23). The anomalous freshening during these years showed similar life cycle, such as, it starts in the northern BoB during July-September of current summer and extends up to February-March of next winter with a southward propagation. Analysis showed that the oceanic and atmospheric conditions associated with positive Indian Ocean Dipole (pIOD) lead to these freshening events, and IOD rather than El Niño/Southern Oscillation (ENSO) controls the interannual variability of salinity in the BoB. The mixed layer salt budget analysis indicated the dominant role of local fresh water flux (horizontal advection) on the observed salinity tendency during summer (winter) monsoon season. Enhanced precipitation associated with pIOD lead to enhanced freshening in northern BoB during June-September, which remained to this region with prevailing summer monsoon circulation. The weakening or absence of southward east India coastal current (EICC) during October-December of these freshening years trapped anomalous freshwater in the northern BoB.

  9. SABER Observations of the OH Meinel Airglow Variability Near the Mesopause

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  10. X-ray observations of a large sample of cataclysmic variable stars using the Einstein Observatory

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    This paper presents the results of an X-ray survey of 31 known or suspected cataclysmic variables. Eighteen of these close binary systems are detected with inferred luminosities in the 0.1-4.0 keV band of between 10 to the 30th and 10 to the 32nd erg/sec. The majority have relatively hard X-ray spectra (kT greater than 2 keV) irrespective of luminosity state. Of seven dwarf novae observed during optical outbursts only U Gem exhibited enhanced ultrasoft X-ray emission (kT of about 10 eV) in addition to weak, hard X-ray emission. Variability of the X-ray flux is observed in many of these stars, on time-scales ranging from tens of seconds to hours. The contribution to the flux from extended X-ray emission is investigated for SU UMa and GK Per. Several possibilities for the origin of the hard X-rays are considered.

  11. Observational Sensitivity to Climate Variability using AIRS/Aqua and MERRA

    NASA Astrophysics Data System (ADS)

    Hearty, T. J.; Fetzer, E.; Tian, B.; Yung, Y. L.; Vollmer, B.; Savtchenko, A. K.; Smith, P. M.; Theobald, M.; Ostrenga, D.

    2011-12-01

    The El Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) are two of the largest climate variabilities seen in AIRS observations of temperature, water vapor, and clouds. Numerous climate feedbacks are involved in these oscillations. We examine these oscillations using observations from the Atmospheric Infrared Sounder (AIRS) and the Modern Era Retrospective-Analysis for Research and Applications (MERRA). Since sampling can be an issue for infrared satellites in low earth orbit, we examine the MERRA data sampled at the AIRS space-time locations both with and without the AIRS quality control. We estimate the sampling bias of an AIRS climatology and the atmospheric conditions where AIRS has a lower sampling rate and examine the apparent differences in the ENSO and NAO based on the different sampling. While the AIRS temperature and water vapor sampling biases are small at low latitudes, they can be more than a few degrees in temperature and 10 percent in water vapor at higher latitudes. While these numbers are small they can be important for understanding climate variability.

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

    SciTech Connect

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

    2012-01-01

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

  13. Decadal changes in the equatorial Pacific circulation 

    E-print Network

    Urizar, S. Cristina

    2002-01-01

    An ocean general circulation model with data assimilation is used to analyze the decadal changes in the tropical Pacific Ocean circulation. Results indicate that the variability in the Equatorial Undercurrent (EUC) and subtropical cells (STC) have...

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  15. UVES radial velocity accuracy from asteroid observations. Implications for the fine structure constant variability

    E-print Network

    P. Molaro; S. A. Levshakov; S. Monai; M. Centurion; P. Bonifacio; S. D'Odorico; L. Monaco

    2007-12-20

    High resolution observations of the asteroids Iris and Juno have been performed by means of the UVES spectrograph at the ESO VLT to obtain the effective accurac y of the spectrograph's radial velocity. The knowledge of this quantity has impo rtant bearings on studies searching for a variability of the fine structure cons tant carried on with this instrument. Asteroids provide a precise radial velocit y reference at the level of 1 m/s which allows instrumental calibration and the recognition of small instrumental drifts and calibration systematics. In particu lar, radial velocity drifts due to non uniform slit illumination and slit optica l misalignment in the two UVES spectrograph arms can be investigated. The positi on of the solar spectrum reflected by the asteroids are compared with the solar wavelength positions or with that of asteroid observations at other epochs or wi th the twilight to asses UVES instrumental accuracy . Radial velocities offsets in the range 10--50 m/s are generally observed likely due to a non uniform slit illumination. However, no radial velocity patterns with wavelength are detected and the two UVES arms provide consistent radial velocities. These results suggest that the detected alpha variability by Levshakov et al. (2007) deduced from a drift of -180 (+/- 85) m/s at z =1.84, between two sets of FeII lines falling in the two UVES arms may be real or induced by other kinds of systematics than those investigated here. The proposed technique allows real time quality check of the spectrograph and should be followed for very accurate measurements.

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

    PubMed Central

    Kiiveri, Harri T

    2008-01-01

    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 a number of response types have been developed a general approach has been lacking. Results The major contribution of this paper is to present a unified methodology which allows many common (statistical) response models to be fitted to such data sets. The class of models includes virtually any model with a linear predictor in it, for example (but not limited to), multiclass logistic regression (classification), generalised linear models (regression) and survival models. A fast algorithm for finding sparse well fitting models is presented. The ideas are illustrated on real data sets with numbers of variables ranging from thousands to millions. R code implementing the ideas is available for download. Conclusion The method described in this paper enables existing work on response models when there are less variables than observations to be leveraged to the situation when there are many more variables than observations. It is a powerful approach to finding parsimonious models for such datasets. The method is capable of handling problems with millions of variables and a large variety of response types within the one framework. The method compares favourably to existing methods such as support vector machines and random forests, but has the advantage of not requiring separate variable selection steps. It is also works for data types which these methods were not designed to handle. The method usually produces very sparse models which make biological interpretation simpler and more focused. PMID:18410693

  17. Nature of the Mesoscale Boundary Layer Height and Water Vapor Variability Observed 14 June 2002 during the IHOP_2002 Campaign

    E-print Network

    Guichard, Francoise

    Nature of the Mesoscale Boundary Layer Height and Water Vapor Variability Observed 14 June 2002, Boulder, Colorado (Manuscript received 4 September 2007, in final form 23 June 2008) ABSTRACT Mesoscale at the mesoscale, with the spatial pattern and the magnitude of the variability changing from day to day. On 14

  18. An AUV survey in the littoral zone: small-scale subsurface variability accompanying synoptic observations of surface currents

    Microsoft Academic Search

    Manhar R. Dhanak; P. Edgar An; Ken Holappa

    2001-01-01

    A survey of small-scale subsurface variability within the synoptic observational field of an ocean surface current radar (OSCR) using an autonomous underwater vehicle (AUV) is described. The survey involved observation of a developing upper mixed layer in a littoral zone off southeast Florida, on the edge of a strong Florida current during the summer of 1999. Complimentary in situ observations

  19. Observation of periodic variable stars towards the Galactic spiral arms by EROS II

    NASA Astrophysics Data System (ADS)

    Derue, F.; Marquette, J.-B.; Lupone, S.; Afonso, C.; Alard, C.; Albert, J.-N.; Amadon, A.; Andersen, J.; Ansari, R.; Aubourg, É.; Bareyre, P.; Bauer, F.; Beaulieu, J.-P.; Blanc, G.; Bouquet, A.; Char, S.; Charlot, X.; Couchot, F.; Coutures, C.; Ferlet, R.; Fouqué, P.; Glicenstein, J.-F.; Goldman, B.; Gould, A.; Graff, D.; Gros, M.; Ha?ssinski, J.; Hamilton, J.-C.; Hardin, D.; de Kat, J.; Kim, A.; Lasserre, T.; Le Guillou, L.; Lesquoy, É.; Loup, C.; Magneville, C.; Mansoux, B.; Maurice, É.; Milsztajn, A.; Moniez, M.; Palanque-Delabrouille, N.; Perdereau, O.; Prévot, L.; Regnault, N.; Rich, J.; Spiro, M.; Vidal-Madjar, A.; Vigroux, L.; Zylberajch, S.; EROS Collaboration

    2002-07-01

    We present the results of a massive variability search based on a photometric survey of a six square degree region along the Galactic plane at (l = 305o, b = -0.8o) and (l = 330o, b = -2.5o). This survey was performed in the framework of the EROS II (Expérience de Recherche d'Objets Sombres) microlensing program. The variable stars were found among 1 913 576 stars that were monitored between April and June 1998 in two passbands, with an average of 60 measurements. A new period-search technique is proposed which makes use of a statistical variable that characterizes the overall regularity of the flux versus phase diagram. This method is well suited when the photometric data are unevenly distributed in time, as is our case. 1362 objects whose luminosity varies were selected. Among them we identified 9 Cepheids, 19 RR Lyræ, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular stars. Most of them are newly identified objects. The cross-identification with known catalogues has been performed. The mean distance of the RR Lyræ is estimated to be ~ 4.9 +/- 0.3 kpc undergoing an average absorption of ~ 3.4 +/- 0.2 mag. This distance is in good agreement with that of disc stars that contribute to the microlensing source star population. Our catalogue and light curves are available electronically from the CDS, Strasbourg and from our Web site http://eros.in2p3.fr. Full Tables 4 and 5 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/149 This work is based on observations made with the MARLY telescope of the EROS collaboration at the European Southern Observatory, La Silla, Chile.

  20. Implication of observed cloud variability for parameterizations of microphysical and radiative transfer processes in climate models

    NASA Astrophysics Data System (ADS)

    Huang, D.; Liu, Y.

    2014-12-01

    The effects of subgrid cloud variability on grid-average microphysical rates and radiative fluxes are examined by use of long-term retrieval products at the Tropical West Pacific (TWP), Southern Great Plains (SGP), and North Slope of Alaska (NSA) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) Program. Four commonly used distribution functions, the truncated Gaussian, Gamma, lognormal, and Weibull distributions, are constrained to have the same mean and standard deviation as observed cloud liquid water content. The PDFs are then used to upscale relevant physical processes to obtain grid-average process rates. It is found that the truncated Gaussian representation results in up to 30% mean bias in autoconversion rate whereas the mean bias for the lognormal representation is about 10%. The Gamma and Weibull distribution function performs the best for the grid-average autoconversion rate with the mean relative bias less than 5%. For radiative fluxes, the lognormal and truncated Gaussian representations perform better than the Gamma and Weibull representations. The results show that the optimal choice of subgrid cloud distribution function depends on the nonlinearity of the process of interest and thus there is no single distribution function that works best for all parameterizations. Examination of the scale (window size) dependence of the mean bias indicates that the bias in grid-average process rates monotonically increases with increasing window sizes, suggesting the increasing importance of subgrid variability with increasing grid sizes.

  1. Hydroxyl emission altitude variability during the last solar cycle retrieved from SCIAMACHY nightglow observations

    NASA Astrophysics Data System (ADS)

    Teiser, Georg; von Savigny, Christian; Winkler, Holger

    2015-04-01

    Night-sky hydroxyl (OH*) emission observations are an important tool to study the mesosphere. They are especially t used to derive OH temperatures. For the interpretation of ground-based OH temperature measurements the knowledge of the spatial and temporal variability of the OH* nightglow emission altitude is of importance. In this context the OH* nightglow data set from SCIAMACHY (Scanning Imaging Absorption spectrometer for Atmospheric CHartographY) on Envisat (from August 2002 to April 2012) is analyzed for the 11-year solar cycle signatures and short-term variability, e.g. solar-driven 27-day cycle and QBO (Quasi-Biennial Oscillation) signatures in vertical volume emission rate profiles and mean emission altitude of the OH(3 -- 1) Meinel emission near the mesopause. The data set is also used to investigate the effect of SPEs (solar proton events) on the OH Meinel emission altitude and volume emission rate. On that point first results and the comparison with simulations using the UBIC (University of Bremen Ion Chemistry) model are presented.

  2. Observed variability in coastal atmospheric CO2 and its impact on air-sea flux investigations

    NASA Astrophysics Data System (ADS)

    Vandemark, D.; Varner, R.; Salisbury, J.; McGillis, W. R.; Sabine, C. L.; Maenner, S.

    2006-12-01

    This study uses a network of autonomous atmospheric carbon dioxide measurements on the eastern seaboard of the U.S. to assess variability of gas concentrations in the coastal marine boundary layer. Our time series observation sites are located within the Western Gulf of Maine region and include an inland, offshore island, and offshore buoy as well as monthly cruise data. Results show that near-surface airside pCO2 levels often differ by as much as 80 uAtm from higher-level tropospheric flask measurements. Observed dynamics are shown to be strongly tied to the New England's forested terrestrial cycle in the summer months with a clear diurnal signal coinciding with daily photosynthesis and respiration cycles. Another timescale for observed dynamics is associated with multi-day continental airmass outflows. These CO2 events are traceable using the island site carbon monoxide measurements. The implication of these dynamics to monitoring, modeling, and rate determinations for air-sea carbon dioxide exchange is discussed in the context of the estimating the air-sea concentration difference without such dedicated atmospheric scalar measurements.

  3. Interannual variability of the regional CO2 and CH4 fluxes estimated with GOSAT observations

    NASA Astrophysics Data System (ADS)

    Maksyutov, Shamil; Takagi, Hiroshi; Kim, Heon-Sook; Saito, Makoto; Mabuchi, Kazuo; Matsunaga, Tsuneo; Ito, Akihiko; Belikov, Dmitry; Oda, Tomohiro; Valsala, Vinu; Morino, Isamu; Yoshida, Yukio; Yokota, Tatsuya

    2014-05-01

    GOSAT Level 4 products - monthly regional surface flux estimates by inverse modeling from CO2 and CH4 GOSAT column-averaged mixing ratios and ground-based observational data using a global atmospheric transport model - have been updated recently to cover the 2-year period starting June 2009. This temporal extension provides look at the interannual flux variability including events of CO2 and CH4 emissions from a large-scale climate anomaly and resultant forest fires in Russia in 2010. Higher emissions of CO2 and CH4 in western Russia in the summer of 2010 are estimated when GOSAT observations are also included in the inverse modeling compared to just using ground-based data. The estimated summer emissions in 2010 are also higher than in the same season of the adjacent years. GOSAT compliments the ground-based networks by observing the concentration response to emissions closer to fire locations, resulting in the inverse models identifying emission regions more accurately. Elsewhere, GOSAT-aided flux estimates point to higher CH4 emissions (compared to ground-based only estimates) in the remote sub-tropical regions of the South America, Africa and South-East Asia. Higher emissions over South America can be attributed to biomass burning and anthropogenic sources, while in South-East Asia those are likely to be caused by agriculture and natural ecosystems.

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

    NASA Technical Reports Server (NTRS)

    Chao, Benjamin F.

    2003-01-01

    Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth s dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease - until around 1998, when it switched quite suddenly to an increase trend which has continued to date. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this 52 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution @e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

  5. Quiescent climate models or noisy proxies: comparing observed and simulated Holocene temperature variability

    NASA Astrophysics Data System (ADS)

    Laepple, Thomas; Huybers, Peter

    2015-04-01

    Determining magnitudes of climate variability is important for attributing past and predicting future changes in climate. Multidecadal and longer temperature variability is poorly constrained, however, primarily because instrumental records are short and proxy records are noisy. Using a global compilation of Holocene marine temperature proxy records and correcting for non-climate variability, we derive an estimate for regional temperature variability between annual and millennial time-scales. Our estimate of temperature variability is consistent between different proxy types and with instrumental records. In comparison, general circulation model simulations have systematically less temperature variability than instrumental and proxy-based estimates. Discrepancies in variability are largest at low latitudes and increase with timescale, reaching two orders of magnitude for tropical variability at millennial timescales. This poster will summarize our recent efforts to estimate Holocene temperature variability and to understand the sources of the discrepancy between simulated and proxy-based Holocene variability estimates.

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

    SciTech Connect

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

    2009-03-15

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

  7. Photometric variability in FU Ori and Z CMa as observed by MOST

    E-print Network

    Siwak, Michal; Matthews, Jaymie M; Kuschnig, Rainer; Guenther, David B; Moffat, Anthony F J; Rowe, Jason F; Sasselov, Dimitar; Weiss, Werner W

    2013-01-01

    Photometric observations obtained by the MOST satellite were used to characterize optical small scale variability of the young stars FU Ori and Z CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2-9 d quasi-periodic features occurring nearly simultaneously; they may be interpreted as plasma parcels or other localized disc heterogeneities revolving at different Keplerian radii in the accretion disc. Their periods may shorten slowly which may be due to spiralling in of individual parcels toward the inner disc radius, estimated at 4.8+/-0.2 R_sun. Analysis of additional multicolour data confirms the previously obtained relation between variations in the B-V colour index and the V magnitude. In contrast to the FU Ori results, the oscillation spectrum of Z CMa does not reveal any periodicities with the wavelet spectrum possibly dominated by outburst of the Herbig Be component.

  8. Statistical Variability of Dispersion in the Convective Boundary Layer: Ensembles of Simulations and Observations

    NASA Astrophysics Data System (ADS)

    Weil, Jeffrey C.; Sullivan, Peter P.; Patton, Edward G.; Moeng, Chin-Hoh

    2012-10-01

    A Lagrangian particle dispersion model (LPDM) driven by velocity fields from large-eddy simulations (LESs) is used to determine the mean and variability of plume dispersion in a highly convective planetary boundary layer (PBL). The total velocity of a "particle" is divided into resolved and unresolved or random (subfilter scale, SFS) velocities with the resolved component obtained from the LES and the SFS velocity from a Lagrangian stochastic model. This LPDM-LES model is used to obtain an ensemble of dispersion realizations for calculating the mean, root-mean-square (r.m.s.) deviation, and fluctuating fields of dispersion quantities. An ensemble of 30 realizations is generated for each of three source heights: surface, near-surface, and elevated. We compare the LPDM calculations with convection tank experiments and field observations to assess the realism of the results. The overall conclusion is that the LPDM-LES model produces a realistic range of dispersion realizations and statistical variability (i.e., r.m.s. deviations) that match observations in this highly convective PBL, while also matching the ensemble-mean properties. This is true for the plume height or trajectory, vertical dispersion, and the surface values of the crosswind-integrated concentration (CWIC), and their dependence on downstream distance. One exception is the crosswind dispersion for an elevated source, which is underestimated by the model. Other analyses that highlight important LPDM results include: (1) the plume meander and CWIC fluctuation intensity at the surface, (2) the applicability of a similarity theory for plume height from a surface source to only the very strong updraft plumes—not the mean height, and (3) the appropriate variation with distance of the mean surface CWIC and the lower bound of the CWIC realizations for a surface source.

  9. Interannual variability of the Mediterranean outflow observed in Espartel sill, western Strait of Gibraltar

    NASA Astrophysics Data System (ADS)

    GarcíA-Lafuente, J.; Delgado, J.; SáNchez RomáN, A.; Soto, J.; Carracedo, L.; DíAz Del RíO, G.

    2009-10-01

    Four-year time series of observations in Espartel sill at the western part of the Strait of Gibraltar have been analyzed in order to investigate the variability of the Mediterranean outflow. It is assumed that the observed variability comes from the changing properties of the dense waters that are located at the maximum depth from where they can be uplifted in the upstream basin (Alborán Sea, inside the Mediterranean Sea) and evacuated through the strait. From this perspective, the following three mechanisms are investigated: (1) the replenishment of the deep basin by newly formed Western Mediterranean Deep Water that, depending on its density, can either uplift old resident waters or lay above them leaving in any case a cold signature in the temperature series; (2) the presence/absence of the energetic anticyclonic gyres in the Alborán Sea, particularly the western one, which can transfer momentum to the underlying Mediterranean vein and provide it with additional energy to ascend over the sills of the strait; and (3) the meteorologically enhanced flows that follow the rapid changes of atmospheric pressure over the western Mediterranean basin, which would be able to aspire deeper waters residing in the upstream basin. The three mechanisms act on different timescales, from annual in case (1) to monthly in case (2) to weekly in case (3) although these two latter are modulated annually by the seasonal prevalence of the western Alborán gyre in summer and of the strong meteorologically driven fluctuations in winter. The mechanisms overlap at annual timescales making it difficult to separate out the different contributions.

  10. Trend and variability in observed hydrometeorological extremes in the Lake Victoria basin

    NASA Astrophysics Data System (ADS)

    Nyeko-Ogiramoi, P.; Willems, P.; Ngirane-Katashaya, G.

    2013-05-01

    SummaryIn the Lake Victoria basin hydrology, trend analysis has mainly been limited to the mean of the hydrological variable without explicit consideration of extremes, which are very crucial in understanding the behaviour of disastrous hydrometeorological events. Since the effects of climate change are unleashed, more through the occurrence of extremes, analysis of both monotonic and cyclic trends in hydrological extremes is very crucial. The presence of a significant linear trend, in a long-term hydrometeorological record of extremes, may provide evidence of a shift from the natural trend to that which is enhanced by, for example, anthropogenic forcing. In addition, cyclic trends analysis of hydrological extremes provides information on the cyclic behaviour of the extreme anomalies that have occurred over and above the natural climate variability and may link them to past consequences and their drivers. Analysis of long term records of extremes for rainfall, temperature and streamflows for selected stations in the Lake Victoria basin, were carried out based on a linear trend test, to detect significant monotonic trends, and quantile perturbation analysis, to detect significant temporal extreme anomalies. In addition, correlations between change in rainfall extremes and that for the other extremes, as well as sunspot maxima, were investigated. The findings indicated that extremes in the Lake Victoria basin are, generally, experiencing positive linear trends. Albeit positive trend was generally demonstrated, the presence of significant linear trend was manifested in the extremes of the data obtained from the stations located in the northern and eastern parts of the Lake Victoria basin. This may suggest that the monotony in the positive trend is a result of an ever increasing and consistent external enhancement of the natural climate agitation. The latter has implications for flood risks if the trend persists in the near future. The cyclic analysis of the behaviour of extremes indicated that the 1940s and the 1970s experienced significantly low extremes. Furthermore, the higher significant anomalies for the 1990s, compared to that for the 1960s, may suggest a more intense enhancement of the change in the natural variability in the recent climate. Correlation between change in the extremes for rainfall and that of the minimum daily temperature was demonstrated to be stronger (c.f. maximum temperature and sunspot maxima) implying that if such correlation persists in the future then change in the extremes of daily minimum temperature can be used as an indicator for the change in rainfall extremes. The investigation of the correlations between climate indices/solar activity and hydrometeorological extremes suggests that oceanic and solar influences are part of the explanation of the variability observed in rainfall and temperatures extremes in the Lake Victoria basin.

  11. Low-Level Cloud Variability over the Equatorial Cold Tongue in Observations and Models

    NASA Technical Reports Server (NTRS)

    Mansbach, David K.; Norris, Joel R.

    2007-01-01

    A fourth paper now in press is, Low-level cloud variability over the equatorial cold tongue in observations and models, by D. K. Mansbach and J. R. Norris (2007, J. Climate). This study examined cloud and meteorological observations from satellite, surface, and reanalysis datasets and fount that monthly anomalies in low-level cloud amount and near-surface temperature advection are strongly negatively correlated on the southern side of the equatorial Pacific cold tongue. This inverse correlation occurs independently of relationships between cloud amount and sea surface temperature (SST) or lower tropospheric static stability (LTS) and the combination of advection plus SST or LTS explains significantly more interannual cloud variability in a multilinear regression than does SST or LTS alone. Warm anomalous advection occurs when the equatorial cold tongue is well defined and the southeastern Pacific trade winds bring relatively warm air over colder water. Ship meteorological reports and soundings show that the atmospheric surface layer becomes stratified under these conditions, thus inhibiting the upward mixing of moisture needed to sustain cloudiness against subsidence and entrainment drying. Cold anomalous advection primarily occurs when the equatorial cold tongue is weak or absent and the air-sea temperature difference is substantially negative. These conditions favor a more convective atmospheric boundary layer, greater cloud amount, and less frequent occurrence of clear sky. Examination of output from global climate models developed by the Geophysical Fluid Dynamics Laboratory (GFDL) and the National Center for Atmospheric Research (NCAR) indicates that both models generally fail to simulate the cloud-advection relationships observed on the northern and southern sides of the equatorial cold tongue. Although the GFDL atmosphere model does reproduce the expected signs of cloud-advection correlations when forced with prescribed historical SST variations, it does not consistently do so when coupled to an ocean model. The NCAR model has difficulty reproducing the observed correlations in both atmosphere-only and coupled versions. This suggests that boundary layer cloud parameterizations could be improved through better representation of the effects of advection over varying SST.

  12. Solar variability observed through changes in solar limb-darkening function and mean diameter

    NASA Astrophysics Data System (ADS)

    Hill, H. A.

    1995-05-01

    The advantages of a dedicated, ground-based observatory over measurements from spacecraft are its relative adaptability, ease of maintenance, and low cost. However, groundbased observations must contend with problems introduced by observing through the Earth's atmosphere and by changes in the long-term stability of the observing instrument. Both of these problems have been addressed at SCLERA and currently pose no limitation of solar diameter measurements at the parts-per-million level. The atmospheric problems of seeing and differential refraction are managed by separate procedures. For the former, a technique is used for the definition of the edge of a solar limb which exhibits a greatly reduced sensitivity to atmospheric seeing (Hill, Stebbins, and Oleson 1975). For the latter, diameters measured at several solar latitudes are used to yield a solar oblateness and diameter with reduced sensitivity to differential refraction. Differential radius measurements are used to detect changes in the solar limb-darkening function with a reduced sensitivity to differential refraction. The long-term stability of the telescope is monitored with an interferometric technique which is itself stable over long periods of time. Exploration of information contained in the global oscillations of the Sun is the basis of solar seismology programs. Such exploration permits the examination of the internal structure of a star at an unprecedented level of detail and accuracy. Changes in the internal structure of the Sun relevant to changes in energy output can be detected through observing changes in the mode frequency of oscillation. This approach is also used at SCLERA in its study of long-term variability in solar irradiance.

  13. Variability of global sea-level quantiles from satellite altimetry observations

    NASA Astrophysics Data System (ADS)

    Barbosa, Susana; Matos, Jose

    Satellite altimetry allows the study of global sea-level change with unprecedented accuracy. Altimetry observations acquired over the global ocean at each satellite revolution can be sum-marised by the corresponding (weighted) mean, yielding an estimate of global mean sea-level. A complementary approach is to take instead of the spatial mean the spatial quantiles of the altimetry observations, in order to obtain a comprehensive description of the variability of the global sea-level distribution. In this work, satellite altimetry observations from the Topex/Poseidon and Jason-1 missions from 1993 to 2008 are analysed. The data are obtained from the RADS databvase, and all standard instrumental and geophysical corrections are ap-plied, including the inverse barometer correction. For each cycle, the along-track data are summarised by computing the spatial mean, weighted by the cosine of the latitude, and the weighted quantiles 0.05, 0.25, 0.50, 075 and 0.95, corresponding to 5%, 25%, 50%, 75% and 95% respectively, of the sorted sea level anomalies. Trends are then computed on the resulting sea-level curves. The results show that the temporal evolution of global median and mean sea-level are very similar. The trend of median sea-level is only marginally lower (by 0.2 mm/year) than the global mean sea-level trend. The estimate of global mean sea-level from satellite altimetry is therefore robust, as a consequence of the high number of observations involved. However, the trend of the lower quantile curve is higher (by more than 0.5 mm/year) than the mean global sea-level trend, indicating that lower sea-levels have increased more than the mean.

  14. Registration of ‘Decade’ wheat

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  15. A distance to the galaxy NGC4258 from observations of Cepheid variable stars.

    PubMed

    Maoz, E; Newman, J A; Ferrarese, L; Stetson, P B; Zepf, S E; Davis, M; Freedman, W L; Madore, B F

    1999-09-23

    Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as 'standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distance scale and hence the value of the Hubble constant. Here we report observations of Cepheids in the nearby galaxy NGC4258; the distance calculated from the Cepheids is 8.1 +/- 0.4 Mpc, where the uncertainty does not include possible systematic errors. There is an independently determined geometric distance to this galaxy of 7.2 +/- 0.5 Mpc, based on the observed proper motions of water masers orbiting the central black hole; the distances differ by 1.3sigma. If the maser-based distance is adopted and the Cepheid distance scale revised accordingly, the derived value of the Hubble constant would increase by 12 +/- 9%, while the expansion age of the Universe would decrease by the same amount. PMID:16862105

  16. TES ammonia retrieval strategy and global observations of the spatial and seasonal variability of ammonia

    NASA Astrophysics Data System (ADS)

    Shephard, M. W.; Cady-Pereira, K. E.; Luo, M.; Henze, D. K.; Pinder, R. W.; Walker, J. T.; Rinsland, C. P.; Bash, J. O.; Zhu, L.; Payne, V. H.; Clarisse, L.

    2011-05-01

    Presently only limited sets of tropospheric ammonia (NH3) measurements in the Earth's atmosphere have been reported from satellite and surface station measurements, despite the well-documented negative impact of NH3 on the environment and human health. Presented here is a detailed description of the satellite retrieval strategy and analysis for the Tropospheric Emission Spectrometer (TES) using simulations and measurements. These results show that: (i) the level of detectability for a representative boundary layer TES NH3 mixing ratio value is ~0.3 ppbv, which typically corresponds to a profile that contains a maximum level value of ~1 ppbv; (ii) TES NH3 retrievals provide at most one degree of freedom for signal (DOFS), with peak sensitivity between 700 and 900 mbar; (iii) TES NH3 retrievals show significant spatial and seasonal variability of NH3 globally; (iv) Initial comparisons of TES observations with GEOS-CHEM estimates show TES values being higher overall. Important differences and similarities between modeled and observed seasonal and spatial trends are noted, with discrepancies indicating areas where the timing and magnitude of modeled NH3 emissions from agricultural sources, and to lesser extent biomass burning sources, need further study.

  17. TES ammonia retrieval strategy and global observations of the spatial and seasonal variability of ammonia

    NASA Astrophysics Data System (ADS)

    Shephard, M. W.; Cady-Pereira, K. E.; Luo, M.; Henze, D. K.; Pinder, R. W.; Walker, J. T.; Rinsland, C. P.; Bash, J. O.; Zhu, L.; Payne, V. H.; Clarisse, L.

    2011-10-01

    Presently only limited sets of tropospheric ammonia (NH3) measurements in the Earth's atmosphere have been reported from satellite and surface station measurements, despite the well-documented negative impact of NH3 on the environment and human health. Presented here is a detailed description of the satellite retrieval strategy and analysis for the Tropospheric Emission Spectrometer (TES) using simulations and measurements. These results show that: (i) the level of detectability for a representative boundary layer TES NH3 mixing ratio value is ~0.4 ppbv, which typically corresponds to a profile that contains a maximum level value of ~1 ppbv; (ii) TES NH3 retrievals generally provide at most one degree of freedom for signal (DOFS), with peak sensitivity between 700 and 900 mbar; (iii) TES NH3 retrievals show significant spatial and seasonal variability of NH3 globally; (iv) initial comparisons of TES observations with GEOS-CHEM estimates show TES values being higher overall. Important differences and similarities between modeled and observed seasonal and spatial trends are noted, with discrepancies indicating areas where the timing and magnitude of modeled NH3 emissions from agricultural sources, and to lesser extent biomass burning sources, need further study.

  18. Tidal Variability in a Whole Atmosphere Model (WAM): Comparison With SABER Observations on TIMED

    NASA Astrophysics Data System (ADS)

    Akmaev, R. A.; Fuller-Rowell, T. J.; Forbes, J. M.; Wu, F.; Anghel, A. F.; Iredell, M. D.; Moorthi, S.

    2007-12-01

    The upper atmosphere and ionosphere exhibit spatial and temporal variability characteristic of planetary waves and tides originating in the lower atmosphere. To study the origin, vertical propagation, and possible effects of these planetary-scale perturbations on the coupled thermosphere-ionosphere-electrodynamics system, a new model of Integrated Dynamics through Earth's Atmosphere (IDEA) is being developed under a NASA sponsored collaborative project between the University of Colorado and National Weather Service's (NWS) Environmental Modeling and Space Environment Centers. The neutral-atmosphere component of the coupled system, WAM, is a 150-layer general circulation model based on NWS's operational weather prediction Global Forecast System (GFS), extended from its nominal top altitude of about 60 km to over 600 km. WAM incorporates relevant physical processes in the extended domain, ranging from the hydrological cycle, cloud physics, and atmosphere-surface exchanges in the troposphere, to solar and Joule heating, ion drag, and mutual diffusion of major species in the thermosphere. First extended simulations reveal the presence of various tidal waves modulated at planetary wave periods in the mesosphere and lower thermosphere (MLT). Substantial contribution from non-migrating tidal modes, recently implicated in the observed spatial morphology of the ionosphere, is also evident. Comparisons with a recent analysis of multi-year MLT observations by the SABER instrument on TIMED will be presented.

  19. Multi-parameter continuous observations to detect ground deformation and to study environmental variability impacts

    NASA Astrophysics Data System (ADS)

    Zerbini, S.; Negusini, M.; Romagnoli, C.; Domenichini, F.; Richter, B.; Simon, D.

    2002-09-01

    In the framework of the European Union SELF II project, a study was developed in order to assess the accuracy with which vertical crustal movements could be determined by means of continuous GPS and gravity observations in a relatively short timespan of a few years. The reliable knowledge of vertical rates at tide gauge stations is necessary to properly interpret sea level variations. For height determinations, continuous GPS and gravity measurements started in mid-1996 at Medicina, in the southern Po Plain. Additionally, continuous GPS observations have also been performed at Porto Corsini, on the Adriatic coast, where a tide gauge station is located which belongs to the Italian tide gauge network, and at a station in Bologna. Negative linear trends, of different magnitude, have been identified at the three stations. The time variability of gravity and GPS heights in relation to variations of several environmental parameters was investigated. A marked seasonal signal has been identified in both data series. It has been interpreted as the sum of different loading and Newtonian attraction effects modeled on the basis of the relevant environmental data series. At Medicina, the comparison between height and gravity series has shown that the seasonal variations are quite comparable both in amplitude and phase. The only remarkable difference between the two data sets is a sudden increase in gravity, in the order of 3 ?gal, observed in mid-1997. This has been attributed to mass/density increase associated with uprising of deep-seated salty (connate) waters, likely triggered by local stress field changes. A simple model is proposed to check the feasibility of the suggested mechanism and the magnitude of the relevant gravity anomaly. This study demonstrated, among other aspects, the importance of collecting continuous, high accuracy, multi-parameter data series for an appropriate interpretation of signals related to environmental variability. For sea level fluctuation studies, the need for determining reliable long-term linear trends in station heights has been demonstrated for the Porto Corsini station. The sea level trend estimated by means of the tide gauge data and the GPS vertical crustal rate has been compared with the absolute sea level trend for the Northern Adriatic provided by the Topex-Poseidon satellite altimetry mission. Over the time frame of the satellite altimetry data set, the results provided by the two different measuring approaches agree within the errors of the estimated sea level trends.

  20. Canonical ADM Tetrad Gravity: from Metrological Inertial Gauge Variables to Dynamical Tidal Dirac observables

    E-print Network

    Luca Lusanna

    2014-11-26

    Dirac constraint theory allows to identify the York canonical basis (diagonalizing the York-Lichnerowicz approach) in ADM tetrad gravity for asymptotically Minkowskian space-times without super-translations. This allows to identify the inertial (gauge) and tidal (physical) degrees of freedom of the gravitational field and to interpret Ashtekar variables in these space-times. The use of radar 4-coordinates centered on a time-like observer allows to connect the 3+1 splittings of space-time with the relativistic metrology used in atomic physics and astronomy. The asymptotic ADM Poincar\\'e group replaces the Poincar\\'e group of particle physics. The general relativistic remnant of the gauge freedom in clock synchronization is described by the inertial gauge variable ${}^3K$, the trace of the extrinsic curvature of the non-Euclidean 3-spaces. The theory can be linearized in a Post-Minkowskian way by using the asymptotic Minkowski metric as an asymptotic background at spatial infinity and the family of non-harmonic 3-orthogonal Schwinger time gauges allows to reproduce the known results on gravitational waves in harmonic gauges. It is shown that the main signatures for the existence of dark matter can be reinterpreted as an relativistic inertial effect induced by ${}^3K$: while in the space-time inertial and gravitational masses coincide (equivalence principle), this is not true in the non-Euclidean 3-spaces (breaking of Newton equivalence principle), where the inertial mass has extra ${}^3K$-dependent terms simulating dark matter. Therefore a Post-Minkowskian extension of the existing Post-Newtonian celestial reference frame is needed.

  1. Comparison between the variability in the resolved infrared spectrum from observations and model simulations using reanalysis data

    NASA Astrophysics Data System (ADS)

    Bantges, R.; Belotti, C.; Brindley, H. E.

    2011-12-01

    Measurements of the spectrally resolved longwave energy emitted to space enable changes in the composition and structure of Earth's atmosphere to be detected. Detection and attribution of these changes and their variability are key to enabling a better understanding of how the climate is evolving, which in turn may lead to a better prediction of future climate. Here, we consider 3 years (2008 to 2010) of measurements from the Infrared Atmospheric Sounding Interferometer (IASI) instrument, and quantify the level of variability observed over a range of temporal and spatial scales, for both cloud-free and all-sky conditions. Regions of the outgoing longwave radiation (OLR) which exhibit the highest level of variability over seasonal and annual time scales are highlighted, and the level of variability observed in wavelength regions associated with key atmospheric parameters reported. These results are then compared to model simulations of the spectrally resolved outgoing longwave radiation. The model simulated spectra were calculated using the Reference Forward Model (RFM) and MODTRAN radiative transfer codes with surface temperature and atmospheric profile information prescribed from the European Centre for Medium Range Weather Forecast (ECMWF) Reanalysis Interim data set. The ability of the simulated spectra to represent the variability observed in the IASI measurements is then assessed. Finally, the impact of spectral, spatial and temporal sampling resolution on the ability to represent the variability observed is assessed, with the aim to inform and advise the requirements for future satellite missions focused on measuring changes in the Earth's spectrally resolved OLR.

  2. NuSTAR and XMM-Newton Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk

    E-print Network

    Walton, D J; Harrison, F A; Fabian, A C; Miller, J M; Arevalo, P; Ballantyne, D R; Boggs, S E; Brenneman, L W; Christensen, F E; Craig, W W; Elvis, M; Fuerst, F; Gandhi, P; Grefenstette, B W; Hailey, C J; Kara, E; Luo, B; Madsen, K K; Marinucci, A; Matt, G; Parker, M L; Reynolds, C S; Rivers, E; Ross, R R; Stern, D; Zhang, W W

    2014-01-01

    We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations of the Seyfert galaxy NGC 1365. These exhibit an extreme level of spectral variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for the first time. Despite the diverse range of absorption states, each of the observations displays the same characteristic signatures of relativistic reflection from the inner accretion disk. Through time-resolved spectroscopy we find that the strength of the relativistic iron line and the Compton reflection hump relative to the intrinsic continuum are well correlated, as expected if they are two aspects of the same broadband reflection spectrum. We apply self-consistent disk reflection models to these time-resolved spectra in order to constrain the inner disk parameters, allowing for variable, partially covering absorption to account for the vastly different absorption states observed. Each of the four observations is treated...

  3. The University of New South Wales Extrasolar Planet Search: a catalogue of variable stars from fields observed 2004--2007

    E-print Network

    J. L. Christiansen; A. Derekas; L. L. Kiss; M. C. B. Ashley; S. J. Curran; D. W. Hamacher; M. G. Hidas; M. R. Thompson; J. K. Webb; T. B. Young

    2008-02-01

    We present a new catalogue of variable stars compiled from data taken for the University of New South Wales Extrasolar Planet Search. From 2004 October to 2007 May, 25 target fields were each observed for 1-4 months, resulting in ~87000 high precision light curves with 1600-4400 data points. We have extracted a total of 850 variable light curves, 659 of which do not have a counterpart in either the General Catalog of Variable Stars, the New Suspected Variables catalogue or the All Sky Automated Survey southern variable star catalogue. The catalogue is detailed here, and includes 142 Algol-type eclipsing binaries, 23 beta Lyrae-type eclipsing binaries, 218 contact eclipsing binaries, 53 RR Lyrae stars, 26 Cepheid stars, 13 rotationally variable active stars, 153 uncategorised pulsating stars with periods stars, and 222 long period variableswith variability on timescales of >10 d. As a general application of variable stars discovered by extrasolar planet transit search projects, we discuss several astrophysical problems which could benefit from carefully selected samples of bright variables. These include: (i) the quest for contact binaries with the smallest mass ratio, which could be used to test theories of binary mergers; (ii) detached eclipsing binaries with pre-main-sequence components, which are important test objects for calibrating stellar evolutionary models; and (iii) RR Lyrae-type pulsating stars exhibiting the Blazhko-effect, which is one of the last great mysteries of pulsating star research.

  4. Inter-annual Variability of Mars Polar Processes as Observed by OMEGA/Mars Express

    NASA Astrophysics Data System (ADS)

    Langevin, Y.; Bibring, J.-P.; Plaut, J.; Vincendon, M.; Gondet, B.; Poulet, F.; Schmidt, F.

    2010-05-01

    Mars Express has now been operated successfully more than 6 earth years after orbit insertion in late 2003. Thanks to a much longer than expected lifetime of the cryocoolers, which still perform nominally, the coverage of polar regions by OMEGA now spans more than three full Mars years, from Ls 338°, M-year 26 to Ls 85°, M-year 30. Therefore, the South perennial cap (Ls 310° to Ls 0°), the South seasonal cap (Ls 0° to Ls 310°) and the North seasonal cap (Ls 170° to Ls 90°) have been observed over four successive Mars year while the North perennial cap (Ls 90° to Ls 170°) has been observed over three successive martian years. Due to the precession of the pericenter and of the orbit plane of the elliptical orbit of the satellite, the OMEGA imaging spectrometer on board this mission obtained data on polar regions at resolutions ranging from 300 m to 10 km over a wide range of Ls and local times [1, 2, 3, 4, 5]. This provides an excellent data set for comparing the evolution of seasonal caps and the spectral characteristics of the perennial caps over different Martian years. For both the perennial cap and the seasonal cap, the CO2 ice signatures dominate in the South while H2O ice signatures dominate in the North. The lag by a few weeks of the retreat of the seasonal caps observed by OMEGA between different Martian years is consistent with that of the "Crocus lines" derived from TES temperature data in 1999 - 2001 [6], with a possible link with dust storm activity in 2007. The spectral component which is not dominant (H2O in the South, CO2 in the North) shows overall consistency but significant year to year variability. CRISM/MRO observations at a much higher spatial resolution support these conclusions. In late 2009, OMEGA observations of the South cap at the time of minimum extent (Ls 340°) showed a much larger extent of H2O ice signatures compared to what had been observed in early 2004 [1]. As these regions show only weak albedo contrast, the observed variegation is likely linked with subsurface characteristics such as the high thermal inertia of underlying water ice rich layers at very shallow depths. This will be investigated by linking OMEGA observations with radar sounding of the subsurface by MARSIS/Mex [6] and SHARAD depending on the availability of data on regions of interest. [1] J-P. Bibring et al., Nature 428, p. 627 (2004) [2] Y. Langevin et al., Science 307, p. 1581 (2005) [3] Y. Langevin et al., Nature 442, p. 790 (2006) [4] Y. Langevin et al., J. Geophys. Res. 112, E08S12 (2007) [5] F. Schmidt et al., Icarus 200, p. 374 (2008) [5] T. Titus, H. H. Kieffer, abstract #2071, Lunar Planet. Science 33 (2002) [6] R. Jordan et al., Planet. Space Science 57, p. 1975 (2009)

  5. Assessment of atmospheric acidified pollutants trends observed by EANET in North-East Asia in the first decade of XXI century

    NASA Astrophysics Data System (ADS)

    Gromov, Sergey A.; Trifonova-Yakovleva, Alisa; Gromov, Sergey S.

    2015-04-01

    Owing to rapid development and subsequent enormous increase in energy consumption/fossil fuel use, anthropogenic emissions of sulphur and nitrogen oxides in China and other Asian countries surpass those in North America and Europe since mid-1990s. Consequently, regional air pollution has become an issue for the most of developing countries in North-East Asia. Since 1998, the Acid Deposition Monitoring Network in East Asia (EANET, http://www.eanet.asia/) provides constant monitoring of the air quality and precipitation (including gaseous and particulate phase chemistry) in 13 countries of the region. The measurements are conducted at 45 rural and remote stations using both filter pack sampling techniques and automatic monitoring equipment. In this study we present a comprehensive trend analysis of the long-term (last 15 years) air pollution monitoring data from selected EANET monitoring sites. Using several statistical approaches, we estimate the quality of the data and perform distribution tests, single out special events (detect outliers) and calculate an ensemble of trends (monthly, seasonal, long-term and quartile) and their statistical significance for a suite of observed compounds. Based on this analysis, we further estimate the statistics and overall significance of the observed temporal dynamics for each pollutant. Ultimately we derive more than 20 trend estimates for a total of up to 12 gas-phase and particulate compounds for each station. Our calculations ascertain that about half of the trends (either negative or positive) observed at the EANET stations in Russia, Korea and Japan are significant. Whilst an increase in SO2, HCl, Cl-, NO3 (except for the stations in Russia) concentrations is distinct, small or insignificant trends are reckoned for HNO3-. A marked decrease in K+ content is seen at all regarded stations. We commonly find station-wise correlation for the trends of the remaining compounds, and for several species we conclude a general spatial pattern, viz. an eastward increase in trend magnitudes in the north-south direction. We further identify special cases of statistically significant seasonal trends for the series that otherwise do not exhibit apparent long-term dynamics, i.e. show an insignificant overall trend. A case in point is the NH3 observational record at Mondy station (Russia), for which the spring-summer negative trends are comparable to the winter positive trends, and both significant. Finally, we discuss and compare these first results with an evaluation of changes in acid deposition over region from 2000 provided by WMO PC-SAG in its global wet deposition assessment (Vet et al., 2014). References: Vet, R., Artz, R. S., Carou, S., Shaw, M., Ro, C. U., Aas, W., Baker, A., Bowersox, V. C., Dentener, F., Galy Lacaux, C., Hou, A., Pienaar, J. J., Gillett, R., Forti, M. C., Gromov, S., Hara, H., Khodzher, T., Mahowald, N. M., Nickovic, S., Rao, P. S. P., and Reid, N. W.: A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus. Atmos. Environ., 93, 3-100, 2014.

  6. Observations of the bright novalike variable IX Velorum with the Hopkins Ultraviolet Telescope

    NASA Technical Reports Server (NTRS)

    Long, Knox S.; Wade, Richard A.; Blair, William P.; Davidsen, Arthur F.; Hubeny, Ivan

    1994-01-01

    The Hopkins Ultraviolet Telescope, an experiment flown on the Space Shuttle as part of the Astro-1 mission, was used to obtain a spectrum of the novalike variable IX Vel (= CPD -48 deg 1577) in the wavelength range 830-1860 A. The observation revealed a rich absorption-line and continuum spectrum that peaks near 1050 A at a flux of 1.6 x 10(exp -11) ergs/sq cm/s/A. In the sub-Lyman-alpha region, some of the more prominent absorption lines are S VI lambda lambda-933, 945, C III lambda-977, Lyman-beta, O VI lambda lambda-1032, 1038, P V lambda lambda-1118, 1128, and C III lambda-1176. No emission was detected below the Lyman limit. The overall continuum shape of IX Vel in the FUV can be approximated using models of an optically thick accretion disk in which the integrated spectrum has been constructed by summing model stellar atmospheres or proper disk model spectra. However, if the distance to IX Vel is approximately 95 pc, standard disk models without reddening cannot simultaneously reproduce the color and flux in the UV. While interstellar reddening can reconcile this difference, the amount of reddening appears inconsistent with the absence of a 2200 A bump in the spectrum and the very low H I column density measured along the line of sight. Improved fits to the data can be obtained by modifying the accretion disk stucture within three white dwarf radii. None of the models reproduces the profiles of the Li- and Na-like ions, which are observed as strong but relatively narrow absorption lines, and which are almost surely due to a wind above the disk.

  7. Ionospheric climatology and variability from long-term and multiple incoherent scatter radar observations: Climatology in eastern American sector

    Microsoft Academic Search

    Shun-Rong Zhang; John M. Holt

    2007-01-01

    Ionospheric climatology and variability studies are conducted using long-term incoherent scatter radar (ISR) observations from seven sites around the world. These studies result in an empirical model system, the ISR Ionospheric Model (ISRIM), which represents local and regional ionospheric climatology and variability of the ionosphere. This paper addresses some new climatological features revealed by the model for latitudes spanning 18–70°N

  8. Observer variability assessing US scans of the preterm brain: the ELGAN study

    PubMed Central

    Kuban, Karl; Adler, Ira; Allred, Elizabeth N.; Batton, Daniel; Bezinque, Steven; Betz, Bradford W.; Cavenagh, Ellen; Durfee, Sara; Ecklund, Kirsten; Feinstein, Kate; Fordham, Lynn Ansley; Hampf, Frederick; Junewick, Joseph; Lorenzo, Robert; McCauley, Roy; Miller, Cindy; Seibert, Joanna; Specter, Barbara; Wellman, Jacqueline; Westra, Sjirk

    2009-01-01

    Background Neurosonography can assist clinicians and can provide researchers with documentation of brain lesions. Unfortunately, we know little about the reliability of sonographically derived diagnoses. Objective We sought to evaluate observer variability among experienced neurosonologists. Materials and methods We collected all protocol US scans of 1,450 infants born before the 28th postmenstrual week. Each set of scans was read by two independent sonologists for the presence of intraventricular hemorrhage (IVH) and moderate/severe ventriculomegaly, as well as hyperechoic and hypoechoic lesions in the cerebral white matter. Scans read discordantly for any of these four characteristics were sent to a tie-breaking third sonologist. Results Ventriculomegaly, hypoechoic lesions and IVH had similar rates of positive agreement (68–76%), negative agreement (92–97%), and kappa values (0.62 to 0.68). Hyperechoic lesions, however, had considerably lower values of positive agreement (48%), negative agreement (84%), and kappa (0.32). No sonologist identified all abnormalities more or less often than his/her peers. Approximately 40% of the time, the tie-breaking reader agreed with the reader who identified IVH, ventriculomegaly, or a hypoechoic lesion in the white matter. Only about 25% of the time did the third party agree with the reader who reported a white matter hyperechoic lesion. Conclusion Obtaining concordance seems to be an acceptable way to assure reasonably high-quality of images needed for clinical research. PMID:17901950

  9. Costa Rica Variable Star Observation Program: Continuation of the research started in the Second Astronomical Observation Regional Campaign TAD/IAU Tegucigalpa Honduras, 1998.

    NASA Astrophysics Data System (ADS)

    Araya Rodriguez, E.

    1998-11-01

    In the last months of January and February, it was the Second Astronomical Observation Regional Campaign TAD/IAU in the Suyapa Astronomical Observatory, Tegucigalpa, Honduras; sponsored by the International Astronomical Union, Honduras Government and the Universidad Nacional Autonoma de Honduras. In that opportunity, during the campaign, it began a variable star observation program, according to international regulation of the American Association of Variable Stars Observers (AAVSO). The activities were about the use of general experimental techniques that allow people to do studies naked eye, with telescopes or photometers depending on the observed star magnitude. The continuation in Costa Rica of that research added to some gotten results will be presented in this work.

  10. Variability of Arctic Ocean heat content: A model-based analysis and implications for autonomous observing systems

    NASA Astrophysics Data System (ADS)

    Steele, M.; Lique, C.

    2012-12-01

    The modes of variability of the Arctic Ocean heat content are investigated for the 1968-2007 period using the DRAKKAR high resolution global ocean/sea-ice model. 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 the advection of Atlantic Water through Fram Strait drives a large part of the heat content variability (31% in total). Fram Strait heat transport variability is due to both changes of temperature and circulation. 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 yields heat content variations in the Eurasian Basin. The effect of the Bering Strait heat flux variations remains limited to the Chukchi Sea. Finally, we examine the capability of the current autonomous observing system to capture the Arctic heat content variability. Sea surface temperature satellite observations combined with temperature profiles of the top 800m in the deep Arctic covered by sea ice are sufficient to capture most of the heat content variability. The results emphasize the crucial need for measurements in the Eurasian Basin.

  11. Connecting Satellite Observations with Water Cycle Variables Through Land Data Assimilation: Examples Using the NASA GEOS-5 LDAS

    NASA Technical Reports Server (NTRS)

    Reichle, Rolf H.; De Lannoy, Gabrielle J. M.; Forman, Barton A.; Draper, Clara S.; Liu, Qing

    2013-01-01

    A land data assimilation system (LDAS) can merge satellite observations (or retrievals) of land surface hydrological conditions, including soil moisture, snow, and terrestrial water storage (TWS), into a numerical model of land surface processes. In theory, the output from such a system is superior to estimates based on the observations or the model alone, thereby enhancing our ability to understand, monitor, and predict key elements of the terrestrial water cycle. In practice, however, satellite observations do not correspond directly to the water cycle variables of interest. The present paper addresses various aspects of this seeming mismatch using examples drawn from recent research with the ensemble-based NASA GEOS-5 LDAS. These aspects include (1) the assimilation of coarse-scale observations into higher-resolution land surface models, (2) the partitioning of satellite observations (such as TWS retrievals) into their constituent water cycle components, (3) the forward modeling of microwave brightness temperatures over land for radiance-based soil moisture and snow assimilation, and (4) the selection of the most relevant types of observations for the analysis of a specific water cycle variable that is not observed (such as root zone soil moisture). The solution to these challenges involves the careful construction of an observation operator that maps from the land surface model variables of interest to the space of the assimilated observations.

  12. Solar apparent radius variability: a new statistical approach to astrolabe multisite observations

    NASA Astrophysics Data System (ADS)

    Badache-Damiani, C.; Rozelot, J. P.

    2006-06-01

    The results of the analysis of solar diameter measurements obtained by means of the astrolabe have been inconclusive so far. Temporal variations are found, but they differ in amplitude and phase. This paper presents the results of a new statistical approach to compare and analyse the astrolabe data obtained during the period 1998-2003 in Brazil, Chile, France and Turkey. We show that different time series can be considered as extracted from the same statistical population following the Gaussian law. As following on a variographic analysis, the series do not seem to be autocorrelated at small scale (40 d) and present the characteristics of a highly disorganized phenomenon. At medium scale (6 yr), a 1-yr periodicity can be seen. It could be the residual trace of a temporal latitudinal variability. At large scale (up to 30 yr, using only French and Chilean data available, respectively, from 1975 and 1990), a faint 11-yr component in the signal can be pointed out. As an 11-yr periodicity has been found in the stratospheric data, we have explored the possibility of a relationship between the measured radii and stratospheric phenomena. This would explain the discrepancy in amplitudes, the sign of the crossed correlation coefficients, and the apparent disorganized behaviour of the data. Therefore, a complementary non-determinist analysis has been done in order to distinguish a chaotic signal from a random noise. The Hurst exponent establishes the persistence of the series. It can be concluded that the solar measurements from astrolabes are not purely randomly distributed, but show the character of a deterministic series for which (i) the observations need to be far more accurate, as it is only possible if obtained from space or in real-time together with a seeing monitor; (ii) supposing that it is indeed possible to extract a solar component, data must be studied considering their heliographic latitude and (iii) data show the variability of the upper atmospheric conditions (maybe Quasi-Biennial Oscillations) and the stratospheric 11-yr periodicity, for which the modulation is caused by the solar irradiance.

  13. Final Progress Report submitted via the DOE Energy Link (E-Link) in June 2009 [Collaborative Research: Decadal-to-Centennial Climate & Climate Change Studies with Enhanced Variable and Uniform Resolution GCMs Using Advanced Numerical Techniques

    SciTech Connect

    Fox-Rabinovitz, M; Cote, J

    2009-10-09

    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. The results of the successful SGMIP multi-model ensemble simulations of the U.S. climate are available at the SGMIP web site (http://essic.umd.edu/~foxrab/sgmip.html) and through the link to the WMO/WCRP/WGNE web site: http://collaboration.cmc.ec.gc.ca/science/wgne. 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.

  14. Salinity in the Sicily Channel corroborates the role of the Adriatic-Ionian Bimodal Oscillating System (BiOS) in shaping the decadal variability of the Mediterranean overturning circulation

    NASA Astrophysics Data System (ADS)

    Ga?i?, M.; Schroeder, K.; Civitarese, G.; Cosoli, S.; Vetrano, A.; Eusebi Borzelli, G. L.

    2013-01-01

    Previous studies have demonstrated that the salinity in the Levantine basin depends on the intensity of the Atlantic water (AW) inflow. Moreover, its spreading eastward (to the Levantine basin) or northward (to the Ionian Sea) is determined by the Ionian circulation pattern, i.e. by the Adriatic-Ionian Bimodal Oscillating System (BiOS) mechanism. The aim of this paper is to relate salinity variations in the Levantine basin to the salt content variability in the core of the Levantine Intermediate Water (LIW) passing through the Sicily Channel (SC) and its possible impact on the Western Mediterranean Transition - WMT (i.e. the sudden salinity and temperature increase in the deep layer of the Algero-Provençal subbasin occurring since 2004). From the historical data set MEDAR/MEDATLAS in the Levantine and northern Ionian, we present evidence of decadal occurrences of extreme salinities associated with the varying influx of AW over the last 60 yr. Furthermore, we show that the salinity variations in the two subbasins are out of phase. High-salinity episodes in the Levantine are a pre-conditioning for the potential occurrence of the events like the Eastern Mediterranean Transient (EMT). Cross-correlation between the salinity time series in the Levantine basin and in the SC suggests that the travel time of the LIW is between 10 and 13 yr. Comparing the timing of the salinity increase associated with the WMT and the salinity in the LIW core in the SC, we estimate that the total time interval needed for the signal propagating from the Levantine to reach the deep mixed layers of the Algero-Provençal subbasin is about 25 yr. We also showed that the extra salt input from the eastern Mediterranean contribute up to about 60% to the salt content increase in the bottom layer of the western Mediterranean.

  15. Observed Relationships Between Large-Scale Atmospheric Variability and the Carbon Cycle

    Microsoft Academic Search

    A. K. Hawes; D. W. Thompson

    2005-01-01

    The impact of increasing atmospheric carbon dioxide on global climate change has been studied extensively, but the effect of large-scale patterns of atmospheric variability on biogeochemical cycling has received substantially less attention. In this study, we examine the impact of two such patterns of atmospheric variability, the so-called Northern and Southern Annular Modes, on monthly and daily mean concentrations of

  16. Observations of the Variability of Floc Sizes on the Louisiana Shelf

    NASA Astrophysics Data System (ADS)

    Sahin, Cihan; Sheremet, Alexandru

    2014-05-01

    The general principles of floc formation under variable turbulent stresses and sediment availability are well known, but the details of the dynamics are still unclear. Flocculation of primary particles occurs when these particles get close enough to collide, and a significant number of these collisions result in adhesion. Particle concentration, the intensity and number of collisions (turbulent shear) control the size of the flocs. However, aggregation transitions into fragmentation if the intensity of collisions or turbulent shear exceeds a certain threshold. In this case, a limiting maximum size might exist (Berhane et al., 1997; Dyer and Manning, 1999; Uncles et al., 2010). This study investigates the relation between SSC (suspended sediment concentration), turbulent stresses, and floc size using the high-resolution observations of suspended sediment concentration, flow and acoustic backscatter made for 2 weeks in Spring 2008 on the muddy Atchafalaya Shelf. During the experiment, pressure, near-bed current velocities, and acoustic backscatter profiles were sampled using a downward-pointing 1500-kHz PC-ADP (Pulse-Coherent Acoustic Doppler Profiler, Sontek/YSI). In addition, a downward-pointing single frequency ABS (Acoustic Backscatter Sensor, 700-kHz, Marine Electronics, Isle of Guernsey) measured the intensity of acoustic return in the first meter above bed. Thus, acoustic backscatter profiles were observed by two different frequencies (700 kHz for the ABS and 1500 kHz for the PC-ADP). Direct SSC observations were provided by two OBS-3s at 15 and 40-cm above the bed, which sampled synchronously with the PC-ADP. Simultaneous profiles of SSC and the mean floc size at cm-scale vertical resolution were obtained using acoustic backscatter intensity at the different acoustic frequencies. For the calibration of the instruments, which involves estimation of the instruments system constants, the algorithm described in Sahin et al. (2013) was followed. The mean floc size profiles were obtained at each range bin and propagated along the backscattered profile using the implicit iterative approach, which is based on calculation of SSC and mean size iteratively until the values in the last two iterations converge (Sahin, under review). Estimated SSC profiles are in agreement with OBS point measurements with a correlation coefficient of 0.88 and 0.12 kg/m3 RMS error. The range of floc size estimates is consistent with the floc-size measurements in 2006 at the same site. Turbulent shear profiles were estimated using the current velocity profiles measured by the PC-ADP. As a first step, the friction velocities are estimated following Lacy et. al. (2005) by fitting the logarithmic profiles in a least-square sense to the current velocity profiles outside the wave boundary layer (Safak et al., 2013), which can then be used to approximate the dissipation of turbulent kinetic energy and the turbulent shear for each bin. The detailed investigation of the resulting SSC, floc-size and the turbulent shear rate profiles showed that low-to-mid values of shear rate promotes flocculation by increasing cohesive sediment particle collision. However, higher turbulent shear strongly affects large flocs, which have weaker internal bonds than those of the primary particles. These field observations support the findings observed in several previous experimental and numerical studies (Parker et al., 1972; Dyer, 1989). Acknowledgements This research was supported by the Office of Naval Research funding of contracts N00014-10-1-0363 and N00014-11-1-0269. References Berhane, I., Sternberg R.W., Kineke G.C., Milligan T.G., Kranck, K., 1997. The variability of suspended aggregates on the Amazon Continental Shelf. Continental Shelf Research 17, 267-285. Dyer, K. R., 1989. Sediment processes in estuaries: future research requirements. Journal of Geophysical Research 97, 14327-14339. Dyer, K. R., Manning A.J., 1999. Observation of size, settling velocity and effective density of flocs, and their fractal dimensions. J. Sea. Res., 41, 87-95. Hay, A.E. and Sheng J.

  17. The Seyfert 2 galaxy NGC 2110: hard X-ray emission observed by NuSTAR and variability of the iron K$\\alpha$ line

    E-print Network

    Marinucci, A; Bianchi, S; Lu, T N; Arevalo, P; Balokovi?, M; Ballantyne, D; Bauer, F E; Boggs, S E; Christensen, F E; Craig, W W; Gandhi, P; Hailey, C J; Harrison, F; Puccetti, S; Rivers, E; Walton, D J; Stern, D; Zhang, W

    2014-01-01

    We present NuSTAR observations of the bright Seyfert 2 galaxy NGC 2110 obtained in 2012, when the source was at the highest flux level ever observed, and in 2013, when the source was at a more typical flux level. We include archival observations from other X-ray satellites, namely XMM-Newton, Suzaku, BeppoSAX, Chandra and Swift. Simultaneous NuSTAR and Swift broad band spectra (in the 3-80 keV range) indicate a cutoff energy $E_{\\rm c}>210$ keV, with no detectable contribution from Compton reflection. NGC 2110 is one of the very few sources where no evidence for distant Compton thick scattering is found and, by using temporal information collected over more than a decade, we investigate variations of the iron K$\\alpha$ line on time scales of years. The Fe K$\\alpha$ line is likely the sum of two components: one constant (originating from distant Compton-thick material) and the other one variable and linearly correlated with the source flux (possibly arising from Compton-thin material much closer to the black h...

  18. MULTI-EPOCH OBSERVATIONS OF HD 69830: HIGH-RESOLUTION SPECTROSCOPY AND LIMITS TO VARIABILITY

    SciTech Connect

    Beichman, C. A.; Tanner, A. M.; Bryden, G.; Akeson, R. L.; Ciardi, D. R. [NASA Exoplanet Science Institute, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91125 (United States); Lisse, C. M. [Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 (United States); Boden, A. F. [Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125 (United States); Dodson-Robinson, S. E.; Salyk, C. [University of Texas, Astronomy Department, Austin, TX 78712 (United States); Wyatt, M. C., E-mail: chas@pop.jpl.nasa.gov [Institute of Astronomy, University of Cambridge, Cambridge, CB3 0HA (United Kingdom)

    2011-12-10

    The main-sequence solar-type star HD 69830 has an unusually large amount of dusty debris orbiting close to three planets found via the radial velocity technique. In order to explore the dynamical interaction between the dust and planets, we have performed multi-epoch photometry and spectroscopy of the system over several orbits of the outer dust. We find no evidence for changes in either the dust amount or its composition, with upper limits of 5%-7% (1{sigma} per spectral element) on the variability of the dust spectrum over 1 year, 3.3% (1{sigma}) on the broadband disk emission over 4 years, and 33% (1{sigma}) on the broadband disk emission over 24 years. Detailed modeling of the spectrum of the emitting dust indicates that the dust is located outside of the orbits of the three planets and has a composition similar to main-belt, C-type asteroids in our solar system. Additionally, we find no evidence for a wide variety of gas species associated with the dust. Our new higher signal-to-noise spectra do not confirm our previously claimed detection of H{sub 2}O ice leading to a firm conclusion that the debris can be associated with the break-up of one or more C-type asteroids formed in the dry, inner regions of the protoplanetary disk of the HD 69830 system. The modeling of the spectral energy distribution and high spatial resolution observations in the mid-infrared are consistent with a {approx}1 AU location for the emitting material.

  19. Influence of internal variability on Arctic sea-ice trends

    NASA Astrophysics Data System (ADS)

    Swart, Neil C.; Fyfe, John C.; Hawkins, Ed; Kay, Jennifer E.; Jahn, Alexandra

    2015-02-01

    Internal climate variability can mask or enhance human-induced sea-ice loss on timescales ranging from years to decades. It must be properly accounted for when considering observations, understanding projections and evaluating models.

  20. Propagating decadal sea surface temperature signal identified in modern proxy records of the tropical Pacific

    Microsoft Academic Search

    Christina L. Holland; Robert B. Scott; Soon-Il An; Frederick W. Taylor

    2007-01-01

    Analysis of 86 years of multiple modern coral ?18O records in the tropical Pacific reveals a basin-scale decadal pattern of variability. Although coral ?18O records the effects of both temperature and seawater ?18O variability due to salinity effects, in practice, most of the records used here agree well with observations of sea surface\\u000a temperature on longer timescales. These coral proxy records

  1. Variability in the fraction of ambient fine particulate matter found indoors and observed heterogeneity in health effect estimates.

    PubMed

    Hodas, Natasha; Meng, Qingyu; Lunden, Melissa M; Rich, David Q; Ozkaynak, Halûk; Baxter, Lisa K; Zhang, Qi; Turpin, Barbara J

    2012-09-01

    Exposure to ambient (outdoor-generated) fine particulate matter (PM(2.5)) occurs predominantly indoors. The variable efficiency with which ambient PM(2.5) penetrates and persists indoors is a source of exposure error in air pollution epidemiology and could contribute to observed temporal and spatial heterogeneity in health effect estimates. We used a mass balance approach to model F for several scenarios across which heterogeneity in effect estimates has been observed: with geographic location of residence, residential roadway proximity, socioeconomic status, and central air-conditioning use. We found F is higher in close proximity to primary combustion sources (e.g. proximity to traffic) and for lower income homes. F is lower when PM(2.5) is enriched in nitrate and with central air-conditioning use. As a result, exposure error resulting from variability in F will be greatest when these factors have high temporal and/or spatial variability. The circumstances for which F is lower in our calculations correspond to circumstances for which lower effect estimates have been observed in epidemiological studies and higher F values correspond to higher effect estimates. Our results suggest that variability in exposure misclassification resulting from variability in F is a possible contributor to heterogeneity in PM-mediated health effect estimates. PMID:22617722

  2. Human- and model-observer performance in ramp-spectrum noise: effects of regularization and object variability.

    PubMed

    Abbey, C K; Barrett, H H

    2001-03-01

    We consider detection of a nodule signal profile in noisy images meant to roughly simulate the statistical properties of tomographic image reconstructions in nuclear medicine. The images have two sources of variability arising from quantum noise from the imaging process and anatomical variability in the ensemble of objects being imaged. Both of these sources of variability are simulated by a stationary Gaussian random process. Sample images from this process are generated by filtering white-noise images. Human-observer performance in several signal-known-exactly detection tasks is evaluated through psychophysical studies by using the two-alternative forced-choice method. The tasks considered investigate parameters of the images that influence both the signal profile and pixel-to-pixel correlations in the images. The effect of low-pass filtering is investigated as an approximation to regularization implemented by image-reconstruction algorithms. The relative magnitudes of the quantum and the anatomical variability are investigated as an approximation to the effects of exposure time. Finally, we study the effect of the anatomical correlations in the form of an anatomical slope as an approximation to the effects of different tissue types. Human-observer performance is compared with the performance of a number of model observers computed directly from the ensemble statistics of the images used in the experiments for the purpose of finding predictive models. The model observers investigated include a number of nonprewhitening observers, the Hotelling observer (which is equivalent to the ideal observer for these studies), and six implementations of channelized-Hotelling observers. The human observers demonstrate large effects across the experimental parameters investigated. In the regularization study, performance exhibits a mild peak at intermediate levels of regularization before degrading at higher levels. The exposure-time study shows that human observers are able to detect ever more subtle lesions at increased exposure times. The anatomical slope study shows that human-observer performance degrades as anatomical variability extends into higher spatial frequencies. Of the observers tested, the channelized-Hotelling observers best capture the features of the human data. PMID:11265678

  3. Can the solar system planetary motion be used to forecast the multidecadal variability of climate?

    Microsoft Academic Search

    N. Scafetta

    2008-01-01

    Global warming has been and will be significantly modified by natural decadal-scale climate variability. For example, the pacific decadal oscillation (PDO) has entered a cool phase that is expected to induce a global cooling in the following two decades. A cooling of the global climate, not predicted by the Intergovernmental Panel on Climate Change (IPCC) projections, has been observed since

  4. Atmospheric methane variability at the Peterhof station (Russia): ground-based observations and modeling

    NASA Astrophysics Data System (ADS)

    Makarova, Maria; Kirner, Oliver; Poberovskii, Anatoliy; Imhasin, Humud; Timofeyev, Yuriy; Virolainen, Yana; Makarov, Boris

    2014-05-01

    The Peterhof station (59.88 N, 29.83 E, 20 m asl) for atmospheric monitoring was founded by Saint - Petersburg State University, Russia. FTIR (Fourier transform IR) observations of methane total column are being carried out by Bruker IFS125 HR since 2009. The study presents a joint analysis of experimental data and EMAC (ECHAM/MESSy Atmospheric Chemistry model) model simulations for Peterhof over the period of 2009-2012. It was shown that CH4 total columns (TC) and column-averaged dry-air mole fractions (MF) obtained from observations are higher than model results with the difference of 1.3% and 0.3 % respectively. The correlation coefficients between FTIR and EMAC data are statistically significant (with 95% confidence) and equal to 0.82 ± 0.08 and 0.4 ± 0.1 for TC and MF of CH4 respectively. The high correlation for TCs shows that EMAC adequately reproduces CH4 variability due to meteorological processes in the atmosphere. On the other hand, the relatively low correlation coefficient for CH4 MF probably indicates an insufficiently precise knowledge of sources and sinks of the atmospheric methane. Amplitudes of the mean annual cycle of CH4 TC for experimental and model datasets (2009-2012) are of 2.1 % and 1.5 % respectively. The same amplitudes calculated for MF are less than for TC: 1.1% for FTIR and 0.6% for EMAC. Difference between FTIR and EMAC annual variations has pronounced seasonality with a maximum in September - November. It could be attributed to the underestimation of methane natural sources in the emission inventory used for EMAC simulations or by relatively coarse horizontal grid of the model (2.8°x2.8°). The analysis of modeling results allowed us to estimate the influence of the limited number of sunny days with FTIR measurement (i.e. specific meteorological conditions which usually take place during FTIR observations) on obtained FTIR estimates of the mean levels of TC and MF over 2009-2012. The systematic shifts of FTIR mean levels of TC and MF from the true ones were detected for the Peterhof station (0.4% for TC and -0.2% for MF). It should be also noted that the limited number of sunny days may distort the annual cycle estimated from FTIR data (comparing to true). This fact have to take into account when mean levels of CH4 TC and MF obtained from FTIR compare against climatological or averaged model data. Ground-based in situ (local) observations of CH4 mole fraction (LMF) are being performed by LGR GGA-24r-EP gas analyzer since 2013 (at the Peterhof station). The monthly averaged amplitude of LMF diurnal cycle shows variations which are similar to the temporal behavior of MF CH4 retrieved from FTIR for 2013. It is suggested that the value of the amplitude of CH4 LMF diurnal variation characterizes the intensity of methane sources for the North-western region of Russia and can be used to explain the observed features of the annual variation of FTIR MF CH4. However, to prove this statement further simultaneous FTIR and in situ measurements of CH4 should be continued. Both, FTIR observations and EMAC simulations, revealed the positive trend of CH4 over 2009-2012 of about 0.2% per year (statistically significant). FTIR data for 2013 that were taken into account led to a decrease in trend value from 0.2%/yr (2009-2012) to 0.13%/yr (2009-2013). It may indicate the end of the period of extremely high growth rates of methane in the atmosphere that have been registered by different observational systems since 2006. Acknowledgements: This study was funded by Saint-Petersburg State University (grant No.11.0.44.2010), Russian Foundation for Basic Research (grants No.12-05-00596, 14-05-897). Measurement facilities were provided by Geo Environmental Research Center "Geomodel" of Saint-Petersburg State University.

  5. Identification of errors-in-variables state space models with observation outliers based on minimum covariance determinant

    Microsoft Academic Search

    Jaafar AlMutawa

    2009-01-01

    In this paper, a subspace system identification algorithm for the errors-in-variables (EIV) state space models subject to observation noise with outliers has been developed. By using the minimum covariance determinant (MCD) estimator, the outliers have been identified and deleted. Then the classical EIV subspace system identification algorithms have been applied to estimate the parameters of the state space models. In

  6. XMM-Newton and VLA Observations of the Variable Wolf-Rayet Star EZ CMa: Evidence for a Close Companion?

    E-print Network

    Guedel, Manuel

    XMM-Newton and VLA Observations of the Variable Wolf-Rayet Star EZ CMa: Evidence for a Close of the Wolf-Rayet star EZ CMa (HD 50896) obtained with XMM-Newton and the VLA. This WN4 star exhibits optical but the existence of a companion has not been proven. The radio spectral energy distribution of EZ CMa determined

  7. Variability of polar stratospheric water vapor observed by ILAS L. L. Pan, W. J. Randel, and S. T. Massie

    E-print Network

    Pan, Laura

    Variability of polar stratospheric water vapor observed by ILAS L. L. Pan, W. J. Randel, and S. T an analysis of polar stratospheric water vapor from measurements of the Improved Limb Atmospheric Spectrometer is consistent with the known stratospheric circulation. Quantitatively, comparisons between ILAS and Halogen

  8. Mixture Factor Analysis for Approximating a Nonnormally Distributed Continuous Latent Factor with Continuous and Dichotomous Observed Variables

    ERIC Educational Resources Information Center

    Wall, Melanie M.; Guo, Jia; Amemiya, Yasuo

    2012-01-01

    Mixture factor analysis is examined as a means of flexibly estimating nonnormally distributed continuous latent factors in the presence of both continuous and dichotomous observed variables. A simulation study compares mixture factor analysis with normal maximum likelihood (ML) latent factor modeling. Different results emerge for continuous versus…

  9. Jelly-fish back to life. (Project of physical variable stars observing)

    Microsoft Academic Search

    P. Hájek

    1996-01-01

    B.R.N.O. - Brno Regional Network of Observers is group, which prefers observing of eclipsing binary stars. Now, inside the Brno Regional Network of Observers group, a team has been created that has got the name \\

  10. Effects of the variability of the nucleus of NGC1275 on X-ray observations of the surrounding intracluster medium

    E-print Network

    Fabian, A C; Pinto, C; Russell, H R; Edge, A C

    2015-01-01

    The active galaxy NGC1275 lies at the centre of the Perseus cluster of galaxies, which is the X-ray brightest cluster in the Sky. The nucleus shows large variability over the past few decades. We compile a lightcurve of its X-ray emission covering about 40 years and show that the bright phase around 1980 explains why the inner X-ray bubbles were not seen in the images taken with the Einstein Observatory. The flux had dropped considerably by 1992 when images with the ROSAT HRI led to their discovery. The nucleus is showing a slow X-ray rise since the first Chandra images in 2000. If it brightens back to the pre-1990 level, then X-ray absorption spectroscopy by ASTRO-H can reveal the velocity structure of the shocked gas surrounding the inner bubbles.

  11. Decades of Hurricanes

    NSDL National Science Digital Library

    2012-08-03

    On this worksheet, students are provided hurricane data by decade and are asked to calculate frequencies and averages. The resource is part of the teacher's guide accompanying the video, NASA SCI Files: The Case of the Phenomenal Weather. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

  12. Swift Observations of the highly X-ray variable Narrow Line Seyfert 1 galaxy RX J0148.3-2758

    E-print Network

    Dirk Grupe; Karen M. Leighly; Stefanie Komossa; Patricia Schady; Paul T. O'Brien; Davis N. Burrows; John A. Nousek

    2006-05-25

    We report on Swift observations of the Narrow-Line Seyfert 1 galaxy (NLS1) RX J0148.3--2758. It was observed for 41.6 ks in 2005 May and for 15.8 ks in 2005 December. On short as well as on long timescales RX J0148.3--2758 is a highly variable source. It doubles its X-ray flux within 18-25 ks. The observation of 2005 December 09, which had a flux 4 times lower than during the 2005 May observations, shows a significant hardening of the X-ray hardness ratio compared with the 2005-May and 2005-December 20/21 observations. A detailed analysis of the X-ray spectra shows that we actually observe two spectral changes in RX J0148.3-2758: First a decrease of the soft X-ray component between 2005 May and December 09, which is most likely due to an increase of the intrinsic absorber column, and second a decrease of the hard X-ray flux in the December 20/21 observations. The soft X-ray spectral slope $\\alpha_{\\rm X, soft}$=2.58$^{+0.15}_{-0.12}$ during the high state in 2005 May agrees well with that measured by ROSAT (\\axs=2.54\\plm0.82). In contrast to the strong X-ray variability, the analysis of the Swift UVOT photometry from December 2005 of RX J0148.3--2758 shows no significant variability in any of the 6 UVOT filters. From the simultaneous X-ray and UV observations in 2005 December we measured the X-ray loudness alpha-ox varies between alpha-ox=1.5 and 1.8. Our Swift observations of RX J0148.3-2758 demonstrate the great potential the multi-wavelength observatory Swift has for AGN science. (shortened)

  13. Interannual variability (1979-2013) of the North-Western Mediterranean deep water mass formation: past observation reanalysis and coupled ocean-atmosphere high-resolution modelling

    NASA Astrophysics Data System (ADS)

    Somot, Samuel; Houpert, Loic; Sevault, Florence; Testor, Pierre; Bosse, Anthony; Durrieu de Madron, Xavier; Dubois, Clotilde; Herrmann, Marine; Waldman, Robin; Bouin, Marie-Noëlle; Cassou, Christophe

    2015-04-01

    The North-Western Mediterranean Sea is known as one of the only place in the world where open-sea deep convection occurs (often up to more than 2000m) with the formation of the Western Mediterranean Deep Water (WMDW). This phenomena is mostly driven by local preconditioning of the water column and strong buoyancy losses during Winter. At the event scale, the WMDW formation is characterized by different phases (preconditioning, strong mixing, restratification and spreading), intense air-sea interaction and strong meso-scale activity but, on a longer time scale, it also shows a large interannual variability and may be strongly affected by climate change with impact on the regional biogeochemistry. Therefore observing, simulating and understanding the long-term temporal variability of the North-Western Mediterranean deep water formation is still today a very challenging task. We try here to tackle those issues thanks to (1) a thorough reanalysis of past in-situ observations (CTD, Argo, surface and deep moorings, gliders) and (2) an ERA-Interim driven simulation using a recently-developed fully coupled Regional Climate System Model (CNRM-RCSM4, Sevault et al. 2014). The multi-decadal simulation (1979-2013) is designed to be temporally and spatially homogeneous with a realistic chronology, a high resolution representation of both the regional ocean and atmosphere, specific initial conditions, a long-term spin-up and a full ocean-atmosphere coupling without constraint at the air-sea interface. The observation reanalysis allows to reconstruct interannual time series of deep water formation indicators (ocean surface variables, mixed layer depth, surface of the convective area, dense water volumes and characteristics of the deep water). Using the observation-based indicators and the model outputs, the 34 Winters of the period 1979-2013 are analysed in terms of weather regimes, related Winter air-sea fluxes, ocean preconditioning, mixed layer depth, surface of the convective area, deep water formation rate and long-term evolution of the deep water hydrology.

  14. Regional scale sandbar variability: Observations from the U.S. Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Di Leonardo, Diana; Ruggiero, Peter

    2015-03-01

    Understanding sandbar dynamics and variability is integral to developing a predictive capacity for nearshore flows, sediment transport, morphological change, and ultimately for determining coastline exposure to damaging storm waves. Here we report on a nearshore bathymetric data set from the U.S. Pacific Northwest (PNW) that stretches from Point Grenville, Washington to Cascade Head, Oregon, over approximately 260 km in the alongshore and includes 8 distinct littoral cells. We describe and quantify the morphological variability of sandbars on a regional scale, using 560 individual cross-shore transects, as well as attempt to explain the inter-littoral cell variability via relationships to various environmental parameters. The cross-shore extent of the bar zone extends over 1 km from the shoreline in the northern part of the study area, but only to about 600 m from the shoreline in the southern part. Maximum bar crest depths are typically 7 m below MLLW. Bar heights range from a step in the cross-shore profile to over 3 m from crest to trough. The northernmost littoral cells typically have two or more subtidal sandbars per cross-shore profile whereas the littoral cells in the southern part of our study area have only one bar. The mean depths of the bars, however, are much more consistent across littoral cells even while the upper shoreface slope significantly increases from north to south, requiring that the maximum bar distance from the shoreline decreases from north to south. Results from a limited study of the temporal variability suggest that while data collected over large spatial scales captures significant amounts of overall sandbar variability, it does not completely characterize the variability over the entirety of the net offshore migration cycle.

  15. On observer design for nonlinear Takagi-Sugeno systems with unmeasurable premise variable

    E-print Network

    Paris-Sud XI, Université de

    variables. The main result is established using the differential mean value theorem which provides a T-Sugeno systems, state estimation, dif- ferential mean value theorem, Lyapunov stability analysis, linear matrix-S representation of the differential equation generating the state estimation error. This allows to extend some

  16. On observer design for nonlinear Takagi-Sugeno systems with unmeasurable premise variable

    Microsoft Academic Search

    Dalil Ichalal; Benoit Marx; Jose Ragot; Didier Maquin

    2011-01-01

    In this paper, we propose a method for state estimation of nonlinear systems represented by Takagi- Sugeno (T-S) models with unmeasurable premise variables. The main result is established using the differential mean value theorem which provides a T-S representation of the differential equation generating the state estimation error. This allows to extend some results obtained in the case of measurable

  17. Observer design for two-wheeled vehicle: A Takagi-Sugeno approach with unmeasurable premise variables

    Microsoft Academic Search

    Dalil Ichalal; Hichem Arioui; Said Mammar

    2011-01-01

    This paper is dedicated to the problem of ob- server design for Takagi-Sugeno (T-S) nonlinear systems with unmeasurable premise variables (TSUPV) and application to autonomous bicycle system. The main idea is based on the use of differential mean value theorem combined to the sector nonlinearity transformation. The objective of this approach is to make the state estimation error dynamic on

  18. T. L. Delworth M. E. Mann Observed and simulated multidecadal variability

    E-print Network

    Mann, Michael E.

    for long-range climate forecasting and societal decision making, but it is precisely these time scales to that simulated in a coupled ocean-atmosphere model, making use of both existing instrumental analyses and newly for sea level pressure. Seasonal analyses of the variability demonstrate that for both the model

  19. Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N

    NASA Astrophysics Data System (ADS)

    McCarthy, G.; Frajka-Williams, E.; Johns, W. E.; Baringer, M. O.; Meinen, C. S.; Bryden, H. L.; Rayner, D.; Duchez, A.; Roberts, C.; Cunningham, S. A.

    2012-10-01

    The Atlantic meridional overturning circulation (MOC) plays a critical role in the climate system and is responsible for much of the heat transported by the ocean. A mooring array, nominally at 26°N between the Bahamas and the Canary Islands, deployed in Apr 2004 provides continuous measurements of the strength and variability of this circulation. With seven full years of measurements, we now examine the interannual variability of the MOC. While earlier results highlighted substantial seasonal and shorter timescale variability, there had not been significant interannual variability. The mean MOC from 1 Apr 2004 to the 31 March 2009 was 18.5 Sv with the annual means having a standard deviation of only 1.0 Sv. From 1 April 2009 to 31 March 2010, the annually averaged MOC strength was just 12.8 Sv, representing a 30% decline. This downturn persisted from early 2009 to mid-2010. We show that the cause of the decline was not only an anomalous wind-driven event from Dec 2009-Mar 2010 but also a strengthening of the geostrophic flow. In particular, the southward flow in the top 1100 m intensified, while the deep southward return transport—particularly in the deepest layer from 3000-5000 m—weakened. This rebalancing of the transport from the deep overturning to the upper gyre has implications for the heat transported by the Atlantic.

  20. An observational study of the variability of ocean wind stress and sea surface roughness

    Microsoft Academic Search

    Wei Chen

    1997-01-01

    The processes that are responsible for air-sea interaction in the planetary boundary layer are very complex, yet these processes shape the global weather and climate evolution. While appearing to be relatively well understood, the mean wind speed, wind stress and sea state over large averaging scales often show considerable scatter. Their variability over shorter averaging scales has received far less

  1. Glider observations of the biological response to Modified Circumpolar Deep Water Variability in the Ross Sea

    NASA Astrophysics Data System (ADS)

    O'Connell, D.; Kaufman, D.; Friedrichs, M. A.; Smith, W.

    2011-12-01

    The Ross Sea is the most productive area within the Southern Ocean, and is believed to play a significant role in the global marine carbon cycle. This region is also characterized by strong spatial and temporal variability in both physical and biogeochemical conditions; however this variability occurs on spatial and temporal scales that are difficult to resolve with traditional data sources. In order to better understand this variability, two gliders were deployed in the Ross Sea in late November 2010 during the early stages of the summer plankton bloom. Together, the two gliders made over 1500 dives and collected data (salinity, temperature, fluorescence and oxygen) throughout the water column for roughly two months. The data from these gliders were used to identify the presence of the relatively high-nutrient Modified Circumpolar Deep Water (MCDW), which has been hypothesized to be a significant factor affecting the spatial and temporal extent of the summer plankton blooms. Preliminary data analyses indicate a positive correlation between areas of MCDW and high chlorophyll concentrations. The glider data were also compared to contemporaneous cruise data and satellite data and were found to fit well with these other data, yet were better able to resolve the high temporal and spatial variability of this region. Specifically, the lower resolution of the cruise data, as compared to the glider data, made it difficult to resolve the correlation of MCDW to high chlorophyll from the cruise data alone.

  2. WindSat passive microwave polarimetric observations of soil moisture and land variables

    Technology Transfer Automated Retrieval System (TEKTRAN)

    WindSat is a spaceborne multi-frequency polarimetric microwave radiometer and has the potential of contributing to the retrieval of land variables and complementing efforts directed at the Aqua AMSR-E. In this study, a previously established algorithm was applied to WindSat data to estimate global s...

  3. Theoretical and Observational Studies of Mesospheric Responses to Short-term UV Variability

    Microsoft Academic Search

    E. R. Talaat; X. Zhu; J. Yee

    2001-01-01

    The majority of the solar UV flux is absorbed in the middle atmosphere and the more variable radiances of extreme ultraviolet and Lyman-alpha are absorbed in the mesosphere and lower thermosphere (MLT), inducing significant changes in MLT chemistry and dynamics. Analyses of satellite measurements have shown clear correlations between the solar UV irradiance variations and mesospheric ozone and temperature that

  4. Uranus' cloud structure and seasonal variability from Gemini-North and UKIRT observations

    Microsoft Academic Search

    P. G. J. Irwin; N. A. Teanby; G. R. Davis; L. N. Fletcher; G. S. Orton; D. Tice; A. Kyffin

    2011-01-01

    Observations of Uranus were made in September 2009 with the Gemini-North telescope in Hawaii, using both the NIFS and NIRI instruments. Observations were acquired in Adaptive Optics mode and have a spatial resolution of approximately 0.1\\

  5. Mechanisms for Diurnal Variability of Global Tropical Rainfall Observed from TRMM

    NASA Technical Reports Server (NTRS)

    Yang, Song; Smith, Eric A.

    2004-01-01

    The behavior and various controls of diurnal variability in tropical-subtropical rainfall are investigated using Tropical Rainfall Measuring Mission (TRMM) precipitation measurements retrieved from: (1) TRMM Microwave Imager (TMI), (2) Precipitation Radar (PR), and (3) TMI/PR Combined, standard level 2 algorithms for the 1998 annual cycle. Results show that the diurnal variability characteristics of precipitation are consistent for all three algorithms, providing assurance that TRMM retrievals are providing consistent estimates of rainfall variability. As anticipated, most ocean areas exhibit more rainfall at night, while over most land areas rainfall peaks during daytime ,however, various important exceptions are found. The dominant feature of the oceanic diurnal cycle is a rainfall maximum in late-evening/early-morning (LE-EM) hours, while over land the dominant maximum occurs in the mid- to late-afternoon (MLA). In conjunction with these maxima are pronounced seasonal variations of the diurnal amplitudes. Amplitude analysis shows that the diurnal pattern and its seasonal evolution are closely related to the rainfall accumulation pattern and its seasonal evolution. In addition, the horizontal distribution of diurnal variability indicates that for oceanic rainfall there is a secondary MLA maximum, co-existing with the LE-EM maximum, at latitudes dominated by large scale convergence and deep convection. Analogously, there is a preponderance for an LE-EM maximum over land, co-existing with the stronger MLA maximum, although it is not evident that this secondary continental feature is closely associated with the large scale circulation. The ocean results clearly indicate that rainfall diurnal variability associated with large scale convection is an integral part of the atmospheric general circulation.

  6. 4, 27272745, 2004 Decadal increase in

    E-print Network

    Boyer, Edmond

    /NCAR reanalysis, for the seventeen-year period 1984­2000. We constructed anomaly time-5 series of the OLR at TOA and 20 S. We compared the anomaly time-series of the model calculated OLR at TOA with that obtained from- sonal and inter-annual variability as the ERBS data, and indicate a decadal increase of10 OLR at TOA

  7. Observed variability of drought and aridity and its impact on the hydrological regime in the Barlad catchment (Romania)

    NASA Astrophysics Data System (ADS)

    Borcan, Mihaela; Cheval, Sorin; Chendes, Viorel

    2015-04-01

    The drought is a complex phenomenon with slow manifestation which engages, depending on its duration and intensity, a number of different components of the climatic, hydrologic, pedologic systems. This paper investigates the relationships between drought and aridity on one hand and hydrological regime, on the other hand, in Bârlad river basin, in the eastern part of Romania. Recent studies have revealed that both meteorological and hydrological drought events have a significant frequency and magnitude in the area, so that an important impact on the hydrological regime is likely to occur. For the next decades, climate change scenarios estimate increasing temperatures and relatively low decreasing of precipitation. Therefore, eventual changes in the aridity characteristics can be expected, and they might have a considerable impact on the water supply or agriculture in the Bârlad catchment. The analysis covers the period 1961-2013 and it is based on monthly data from meteorological and hydrological stations. Seasonal indices were calculated for characterising the drought (SPI, SFI, PDSI, PHDI) and aridity (UNEP, de Martonne, Pinna), while their temporal variability was further investigated in relations with specific hydrological parameters (monthly discharge time series). The spatial distribution of the selected indices was analysed in the same context using co-variables integrated in a GIS framework. The results show that the hydrological drought is influenced and determined mostly by the meteorological drought. The highest variability between the aridity indices has been identified for the summer season, where the time lag between the hydrological response to the meteorological impulse is up to 2 months. The work has been financed by the research project Changes in climate extremes and associated impact in hydrological events in Romania (CLIMHYDEX), Cod PN II-ID-2011-2-0073, sponsored by the National Authority for Scientific Research.

  8. Multifrequency observations of the optically active radio-quiet quasar GQ Comae. II - Ultraviolet, optical, and infrared continuum variability

    NASA Technical Reports Server (NTRS)

    Sitko, Michael L.; Sitko, Annamaria K.; Siemiginowska, Aneta; Szczerba, R.

    1993-01-01

    This paper summarizes the data and preliminary results of a 3 yr long project to monitor the continuum variability of GQ Comae (PG 1202 + 281) from 0.12 micron to 3.5 microns. Substantial variability in the optical/UV flux was observed. The variability is examined using a geometrically thin accretion disk model. The model is able to reproduce the variations, but contains problems with physical consistency. A comparison of the optical/UV data and the IR data indicates that the flux at 2.2 microns did not respond to the optical-UV continuum increase until nearly 250 days after the outburst and suggests that the variable flux at this wavelength is due to heated dust. We model the IR emission with a dust component which is heated by the radiation from the accretion disk. We show that a simple model using a disklike distribution of heated dust grains can explain most of the IR variability in a natural way.

  9. Evaluation of Interannual Variability of Cloud Liquid Water Path in Climate Models Using a Multidecadal Record of Passive Microwave Observations

    NASA Astrophysics Data System (ADS)

    Manaster, A.; Elsaesser, G.; O'Dell, C.

    2014-12-01

    Cloud Liquid Water Path (CLWP) is an important variable affected by changes in the climate system. The nature of its changes within a changing climate, and the connection of these changes to cloud-climate feedbacks, however, are not well-understood at present. The Multisensor Advanced Climatology of Liquid Water Path (MAC-LWP) climatology, an updated version of the University of Wisconsin (UWisc) CLWP dataset, seamlessly blends observations from many different passive microwave sensors over the past 26 years in order to create a robust, long-term record of CLWP. With this dataset, we are able to observe trends and interannual variability in CLWP with some degree of statistical significance. Present day climate models (those comprising the CMIP3 and CMIP5 collections) aim to accurately represent cloud feedbacks and, directly related to this, capture interannual variability in several different cloud variables including CLWP. In this work, we present the long-term evolution of CLWP in a few characteristic regions around the globe using the MAC-LWP dataset, and compare it to the simulated evolution of CLWP in the CMIP3 and CMIP5 models. The extent to which present-day GCM's accurately portray interannual and long-term CLWP changes will be discussed.

  10. Mesoscale variability in the Arabian Sea from HYCOM model results and observations: impact on the Persian Gulf Water path

    NASA Astrophysics Data System (ADS)

    L'Hégaret, P.; Duarte, R.; Carton, X.; Vic, C.; Ciani, D.; Baraille, R.; Corréard, S.

    2015-03-01

    The Arabian Sea and Sea of Oman circulation and water masses, subject to the monsoon forcing, reveal a strong seasonal variability and intense mesoscale features. We describe and analyse this variability and these features, using both meteorological data (from ECMWF reanalyses), in-situ observations (from the ARGO float program and the GDEM climatology), satellite altimetry (from AVISO) and a regional simulation with a primitive equation model (HYCOM). The EOFs of the seasonal variability of the water masses quantify their main changes in thermohaline characteristics and in position. The model and observations display comparable variability, and the model is then used to analyse the three-dimensional structure of eddies and water masses with a higher resolution. The mesoscale eddies have a deep dynamical influence and strongly drive the water masses at depth. In particular, in the Sea of Oman, the Persian Gulf Water presents several offshore ejection sites and a complex recirculation, depending on the mesoscale eddies. This water mass is also captured inside the eddies via several mechanisms, keeping high thermohaline characteristics in the Arabian Sea. These characteristics are validated on the GOGP99 cruise data.

  11. 1D accretion discs around eccentric planets: observable near-infrared variability

    E-print Network

    Dunhill, Alex

    2014-01-01

    I present the results of 1D models of circumplanetary discs around planets on eccentric orbits. I use a classical viscous heating model to calculate emission fluxes at the wavelengths targeted by the NIRCam instrument on JWST, and compare the variability of this signal with the published NIRCam sensitivity specifications. This variability is theoretically detectable by JWST for a sufficiently viscous disc ($\\alpha \\sim 10^{-2}$) around a sufficiently eccentric planet ($e \\sim 0.1-0.2$) and if the circumplanetary disc accretes material from its parent disc at a rate $\\dot{M} \\gtrsim 10^{-7}\\, \\mathrm{M}_{\\odot}\\,\\mathrm{yr}^{-1}$. I discuss the limitations of the models used, and the implications of the result for probing the effectiveness of disc interactions for growing a planet's orbital eccentricity.

  12. Application of a variable structure model in observation and control of an anaerobic digestor.

    PubMed

    Tartakovsky, B; Morel, E; Steyer, J P; Guiot, S R

    2002-01-01

    In this work, a variable structure model (VSM) of an anaerobic digestion process was developed. The anaerobic biodegradation process was described by four nonlinear submodels representing methanogenic, chemical oxygen demand overload, acidogenic, and hydrogen-inhibited states of the anaerobic process. At any instant, process dynamics was modeled only by one of the submodels, while the others were considered trailing. The choice of a leading submodel was handled by a knowledge-based system, which analyzed available process variables, such as off-gas composition and reactor pH. The feasibility of the proposed method was demonstrated both by using the VSM to predict the outputs of a comprehensive process model, and the experimental results obtained in a pilot scale anaerobic fixed-bed bioreactor. PMID:12153327

  13. Multifrequency observations of blazars. II - The variability of the 1 micron to 2 mm continuum

    NASA Technical Reports Server (NTRS)

    Gear, W. K.; Brown, L. M. J.; Robson, E. I.; Ade, P. A. R.; Griffin, M. J.; Smith, M. G.; Nolt, I. G.; Radostitz, J. V.; Veeder, G.

    1986-01-01

    The results of monitoring, over a period of two years, a sample of 12 blazars, in 11 wave bands between 1 micron and 2 mm are presented. All sources exhibit some variability, both in flux density and spectral shape. The infrared variability is consistent with repeated injections of reaccelerations of electrons, which subsequently suffer radiative losses. For OJ 287, 3C 279, and 3C 345, a decay and steepening of the infrared spectrum occurred as the submillimeter turnover evolved to lower frequencies, consistent with expansion of the emitting region. The peak flux, however, increased during this evolution. This behavior is inconsistent with most models for compact extragalactic sources, but it is naturally explained by shock waves traveling in an adiabatically expanding relativistic jet (Marscher and Gear, 1985).

  14. 1D accretion discs around eccentric planets: observable near-infrared variability

    NASA Astrophysics Data System (ADS)

    Dunhill, A. C.

    2015-03-01

    I present the results of 1D models of circumplanetary discs around planets on eccentric orbits. I use a classical viscous heating model to calculate emission fluxes at the wavelengths targeted by the NIRCam instrument on JWST, and compare the variability of this signal with the published NIRCam sensitivity specifications. This variability is theoretically detectable by JWST for a sufficiently viscous disc (? ˜ 10-2) around a sufficiently eccentric planet (e ˜ 0.1-0.2) and if the circumplanetary disc accretes material from its parent disc at a rate dot{M} ? 10^{-7} M_{?} yr-1. I discuss the limitations of the models used, and the implications of the result for probing the effectiveness of disc interactions for growing a planet's orbital eccentricity.

  15. Tidal variability in the lower thermosphere: Comparison of Whole Atmosphere Model (WAM) simulations with observations from TIMED

    NASA Astrophysics Data System (ADS)

    Akmaev, R. A.; Fuller-Rowell, T. J.; Wu, F.; Forbes, J. M.; Zhang, X.; Anghel, A. F.; Iredell, M. D.; Moorthi, S.; Juang, H.-M.

    2008-02-01

    The upper atmosphere and ionosphere exhibit variability on spatial and temporal scales characteristic of tides and planetary waves originating in the lower atmosphere. To study their generation, vertical propagation, possible nonlinear interactions and effects a new Whole Atmosphere Model (WAM) has been developed as part of the Integrated Dynamics through Earth's Atmosphere (IDEA) project. WAM is a 150-layer general circulation model based on the US National Weather Service's operational Global Forecast System (GFS) model extended upward to cover the atmosphere from the ground to about 600 km. First simulations reveal the presence of migrating and nonmigrating tides modulated at planetary wave periods in the upper atmosphere. Comparisons with observations from the TIMED satellite in the lower thermosphere show that WAM reproduces the seasonal variability of tides remarkably well, including the diurnal eastward harmonic with zonal wavenumber 3 (DE3) recently implicated in the observed spatial morphology of the ionosphere.

  16. Evidence for temporal variability of Enceladus' gas jets: Modeling of Cassini observations

    Microsoft Academic Search

    Joachim Saur; Nico Schilling; Fritz M. Neubauer; Darrell F. Strobel; Sven Simon; Michele K. Dougherty; Christopher T. Russell; Robert T. Pappalardo

    2008-01-01

    Time variability of Enceladus' gas plume is deduced from a joint investigation of Cassini spacecraft magnetic field data obtained during the first three flybys E0, E1 and E2 and neutral density measurements during the E2 flyby with a model that describes Enceladus' plasma interaction with individual jets. We infer a total plume content of ?7 × 1032 H2O molecules corresponding

  17. Eddy-driven low-frequency variability: physics and observability through altimetry

    NASA Astrophysics Data System (ADS)

    Penduff, Thierry; Sérazin, Guillaume; Arbic, Brian; Mueller, Malte; Richman, James G.; Shriver, Jay F.; Morten, Andrew J.; Scott, Robert B.

    2015-04-01

    Model studies have revealed the propensity of the eddying ocean circulation to generate strong low-frequency variability (LFV) intrinsically, i.e. without low-frequency atmospheric variability. In the present study, gridded satellite altimeter products, idealized quasi-geostrophic (QG) turbulent simulations, and realistic high-resolution global ocean simulations are used to study the spontaneous tendency of mesoscale (relatively high frequency and high wavenumber) kinetic energy to non-linearly cascade towards larger time and space scales. The QG model reveals that large-scale variability, arising from the well-known spatial inverse cascade, is associated with low frequencies. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing (by large-scale shear) and friction playing secondary roles. In realistic simulations, nonlinearities also generally drive kinetic energy to low frequencies and low wavenumbers. In some, but not all, regions of the gridded altimeter product, surface kinetic energy is also found to cascade toward low frequencies. Exercises conducted with the realistic model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies seen in some regions between the direction of frequency cascade in models versus gridded altimeter maps. Finally, the range of frequencies that are highly energized and engaged these cascades appears much greater than the range of highly energized and engaged wavenumbers. Global eddying simulations, performed in the context of the CHAOCEAN project in collaboration with the CAREER project, provide estimates of the range of timescales that these oceanic nonlinearities are likely to feed without external variability.

  18. FeLoBAL Outflow Variability Constraints from Multi-Year Observations

    NASA Astrophysics Data System (ADS)

    McGraw, Sean M.; Shields, Joseph C.; Hamann, Frederick W.; Capellupo, Daniel M.; Gallagher, Sarah C.; Brandt, William N.

    2014-07-01

    The physical properties and dynamical behavior of Broad Absorption Line (BAL) outflows are crucial themes in understanding the connections between galactic centers and their hosts. FeLoBALs (identified with the presence of low-ionization Fe II BALs) are a peculiar class of quasar outflows that constitute ~ 1% of the BAL population. With their large column densities and apparent outflow kinetic luminosities, FeLoBALs appear to be exceptionally powerful and are strong candidates for feedback in galaxy evolution. We conducted variability studies of 12 FeLoBAL quasars with emission redshifts 0.69 <= z <= 1.93, spanning both weekly and multi-year timescales in the quasar's rest frame. We detected absorption-line variabilit