Science.gov

Sample records for observed decadal variability

  1. Sub-decadal North Atlantic Oscillation variability in observations and the Kiel Climate Model

    NASA Astrophysics Data System (ADS)

    Reintges, Annika; Latif, Mojib; Park, Wonsun

    2016-07-01

    The North Atlantic Oscillation (NAO) is the dominant mode of winter climate variability in the North Atlantic sector. The corresponding index varies on a wide range of timescales, from days and months to decades and beyond. Sub-decadal NAO variability has been well documented, but the underlying mechanism is still under discussion. Other indices of North Atlantic sector climate variability such as indices of sea surface and surface air temperature or Arctic sea ice extent also exhibit pronounced sub-decadal variability. Here, we use sea surface temperature and sea level pressure observations, and the Kiel Climate Model to investigate the dynamics of the sub-decadal NAO variability. The sub-decadal NAO variability is suggested to originate from dynamical large-scale air-sea interactions. The adjustment of the Atlantic Meridional Overturning Circulation to previous surface heat flux variability provides the memory of the coupled mode. The results stress the role of coupled feedbacks in generating sub-decadal North Atlantic sector climate variability, which is important to multiyear climate predictability in that region.

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

    NASA Astrophysics Data System (ADS)

    Hüttl-Kabus, Sabine; Klein, Birgit

    2010-05-01

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

  3. Observed decadal variability of southern African rainfall, their teleconnections, and uncertainties

    NASA Astrophysics Data System (ADS)

    Dieppois, Bastien; Pohl, Benjamin; Rouault, Mathieu; New, Mark; Lawler, Damian; Keenlyside, Noel

    2016-04-01

    This study examines for the first time the changing characteristics of summer and winter southern African rainfall, and their teleconnections with large-scale climate through the dominant timescales of variability. The summer and winter rainfall indices exhibit three significant timescales of variability over the 20th century: interdecadal (15-28 year), quasi-decadal (8-13 year) and interannual (2-8 year). Teleconnections with global sea-surface temperature and atmospheric circulation anomalies, which have been established here using different data sets, are different for each timescale. Uncertainty related to the choice of observed-based SST and reanalysis data sets appears stronger over the winter rainfall region and at the interdecadal timescale. However, only SST and atmospheric anomalies which show an agreement greater than 90% between data sets, or between the members of the reanalysis, have been described. Tropical/subtropical teleconnections emerge as the main driver of summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño Southern Oscillation (ENSO) and, at decadal timescales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper-zonal circulation interact with asymmetric ocean-atmospheric modifications between the South Atlantic and South Indian Oceans; together these lead to shift in the South Indian Convergence Zone, and a modulation of the development of convective rain bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the Mascarene High, which dominate southerly moisture fluxes from the St Helena High. Winter rainfall variability is more influenced by mid-latitude atmospheric variability, in particular the Southern Annular Mode, but interactions with ENSO remain, especially in the subtropics. Asymmetrical

  4. 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."

  5. Coupled Decadal Variability in the North Pacific: An Observationally-Constrained Idealized Model

    NASA Astrophysics Data System (ADS)

    Qiu, B.; Schneider, N.; Chen, S.

    2006-12-01

    Air-sea coupled variability is investigated in this study by focusing on the observed sea surface temperature signals in the Kuroshio Extension (KE) region of 32°--38°N and 142°E--180°. This region corresponds to where both the oceanic circulation variability and the heat exchange variability across the air-sea interface are the largest in the midlatitude North Pacific. SST variability in the KE region has a dominant timescale of ~ 10 yr and this decadal variation is caused largely by the regional, wind-induced sea surface height changes that represent the lateral migration and strengthening/weakening of the KE jet. The importance of the air-sea coupling in influencing KE jet is explored by dividing the large-scale wind forcing into those associated with the intrinsic atmospheric variability and those induced by the SST changes in the KE region. The latter signals are extracted from the NCEP-NCAR reanalysis data using the lagged correlation analysis. In the absence of the SST feedback, the intrinsic atmospheric forcing enhances the decadal and longer timescale SST variance through oceanic advection, but fails to capture the observed decadal spectral peak. When the SST feedback is present, a warm (cold) KE SST anomaly works to generate a positive (negative) wind stress curl in the eastern North Pacific basin, resulting in negative (positive) local SSH anomalies through Ekman divergence (convergence). As these wind-forced SSH anomalies propagate into the KE region in the west, they shift the KE jet and alter the sign of the pre-existing SST anomalies. Given the spatial pattern of the SST-induced wind stress curl forcing, the optimal coupling in the midlatitude North Pacific occurs at the period of ~ 10 yr, slightly longer than the basin crossing time of the baroclinic Rossby waves along the KE latitude.

  6. 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

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  9. 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.

  10. On the variability of Pacific Ocean tides at seasonal to decadal time scales: Observed vs modelled

    NASA Astrophysics Data System (ADS)

    Devlin, Adam Thomas

    forward in time to the predicted sea level in 2100. Results suggest that stations with large positive combined A-TATs produce total water levels that are greater than those predicted by an increase in MSL alone, increasing the chances of high-water events. Part II examines the mechanisms behind the yearly (TAT) variability in the Western Tropical Pacific Ocean. Significant amplitude TATs are found at more than half of 26 gauges for each of the two strongest tidal constituents, K1 (diurnal) and M2 (semidiurnal). For the lesser constituents analyzed (O1 and S2), significant trends are observed at ten gauges. Part III analyzes the seasonal behavior of tides (STATs) at twenty tide gauges in the Southeast Asian waters, which exhibit variation by 10 -- 30% of mean tidal amplitudes. A barotropic ocean tide model that considers the seasonal effects of MSL, stratification, and geostrophic and Ekman velocity is used to explain the observed seasonal variability in tides due to variations in monsoon-influenced climate forcing, with successful results at about half of all gauges. The observed changes in tides are best explained by the influence of non-tidal velocities (geostrophic and Ekman), though the effect of changing stratification is also an important secondary causative mechanism. From the results of these surveys and investigations, it is concluded that short-term fluctuations in MSL and tidal properties at multiple time scales may be as important in determining the state of future water levels as the long-term trends. Global explanations for the observed tidal behavior have not been found in this study; however, significant regional explanations are found at the yearly time scale in the Solomon Sea, and at the seasonal time scale in Southeast Asia. It is likely that tidal sensitivity to annual and seasonal variations in MSL at other locations also are driven by locally specific processes, rather than factors with basin-wide coherence. (Abstract shortened by ProQuest.).

  11. Interannual to decadal temperature variability in the north-west Atlantic: Observations from the MV Oleander XBT line

    NASA Astrophysics Data System (ADS)

    Forsyth, J. S. T.; Andres, M.; Gawarkiwicz, G.

    2014-12-01

    Despite convincing evidence of deep ocean warming, temperature changes over the shelves have proven difficult to quantify as most long-term records lack the spatial and temporal resolution needed to resolve shelf variability. XBT data have been collected for 37 years along a repeat track from New Jersey to Bermuda from the MV Oleander providing the resolution necessary for shelf analysis. The XBT temperature data on the shelf (onshore of the 80 m isobath) were binned with 10 km horizontal and 5 m vertical resolution to produce monthly and annually averaged temperature sections. A climatology produced from the binned data identifies key seasonal temperature features consistent with previous climatologies, showing the utility of the XBT data. Annual spatially-averaged shelf temperatures have trended upwards since the beginning of the record in 1977 (0.025 C/yr), with recent trends (i.e., since 2002, 0.10 C/yr) substantially larger than the overall 37- year trend. Comparison of composite sections for the most anomalous years suggests that the interannual variability in the spatially-averaged temperatures is most heavily influenced by temperature anomalies near the shelf break. The spatially-averaged temperature anomalies are not correlated with annually-averaged coastal sea level anomalies from tide gauges at zero lag, which suggest that interannual variability in coastal sea level is not due to thermo steric effects. However, a strong positive correlation is found between 2-year lagged temperature anomalies and coastal sea level anomalies. This relationship is most pronounced for the shelf break temperature anomalies, with the strongest 2-year lag correlations found in winter and spring. Connections between the observed interannual to decadal temperature variability on the shelf and variability in the AMOC are being investigated in an ongoing effort to better understand open-ocean/shelf interactions in the Northwest Atlantic.

  12. 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

  13. Interannual variability of the earth's climate during the last decade as observed by the Nimbus-7 spacecraft

    NASA Technical Reports Server (NTRS)

    Kyle, H. Lee; Han, Daesoo; Ardanuy, Philip E.; Hoyt, Douglas V.

    1989-01-01

    A set of earth radiation budget observations spanning the time period 1979 to 1987 is considered. A diurnally averaged eight year top-of-the-atmosphere net radiation field is analyzed along with a zonally averaged radiation budget. Variability in the net radiation due to changes in the clear sky shortwave and longwave radiation fields or changes in the total cloudiness distribution and the cloud properties is assessed, along with those radiation-budget parameters key to the earth's heat balance.

  14. 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.

    2012-05-01

    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. Canopy-level ozone flux measurements were analysed for deposition characteristics and partitioning into stomatal and non-stomatal fractions, focusing on growing season day-time data. Ten years of measurements enabled the analysis of ozone deposition variation at different time- scales, including daily to inter-annual variation as well as the dependence on environmental variables and concentration of biogenic volatile organic compounds (BVOC-s). Stomatal deposition was estimated by using multi-layer canopy dispersion and optimal stomatal control modelling from simultaneous carbon dioxide and water vapour flux measurements, non-stomatal was inferred as residual. Also, utilising big-leaf assumption stomatal conductance was inferred from water vapour fluxes for dry canopy conditions. The total ozone deposition was highest during the peak growing season (4 mm s-1) and lowest during winter dormancy (1 mm s-1). During the course of the growing season the fraction of the non-stomatal deposition of ozone was determined to vary from 26 to 44% during day time, increasing from the start of the season until the end of the growing season. By using multi-variate analysis it was determined that day-time total ozone deposition was mainly driven by photosynthetic capacity of the canopy, vapour pressure deficit (VPD), photosynthetically active radiation and monoterpene concentration. The multi-variate linear model explained high portion of ozone deposition variance on daily average level (R2 = 0.79). The explanatory power of the multi-variate model for ozone non-stomatal deposition was much lower (R2 = 0.38). Model calculation was performed to evaluate the potential sink strength of the chemical reactions of ozone with sesquiterpenes in the canopy air space, which revealed that sesquiterpenes in typical

  15. 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.

  16. Atlantic forcing of Pacific decadal variability

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    This paper investigates the Atlantic Ocean influence on equatorial Pacific decadal variability. 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 Multidecadal Oscillation (AMO) has had a substantial influence on the equatorial Pacific decadal variability. According to AMO phases we have identified three periods with strong Atlantic forcing of equatorial Pacific changes, namely (1) 1931-1950 minus 1910-1929, (2) 1970-1989 minus 1931-1950 and (3) 1994-2013 minus 1970-1989. Both observations and the model show easterly surface wind anomalies in the central Pacific, cooling in the central-eastern Pacific and warming in the western Pacific/Indian Ocean region in events (1) and (3) and the opposite signals in event (2). The physical mechanism for these responses is related to a modification of the Walker circulation because a positive (negative) AMO leads to an overall warmer (cooler) tropical Atlantic. The warmer (cooler) tropical Atlantic modifies the Walker circulation, leading to rising (sinking) and upper-level divergence (convergence) motion in the Atlantic region and sinking (rising) motion and upper-level convergence (divergence) in the central Pacific region.

  17. Decadal Variability of Clouds and Comparison with Climate Model Simulations

    NASA Astrophysics Data System (ADS)

    Su, H.; Shen, T. J.; Jiang, J. H.; Yung, Y. L.

    2014-12-01

    An apparent climate regime shift occurred around 1998/1999, when the steady increase of global-mean surface temperature appeared to hit a hiatus. Coherent decadal variations are found in atmospheric circulation and hydrological cycles. Using 30-year cloud observations from the International Satellite Cloud Climatology Project, we examine the decadal variability of clouds and associated cloud radiative effects on surface warming. Empirical Orthogonal Function analysis is performed. After removing the seasonal cycle and ENSO signal in the 30-year data, we find that the leading EOF modes clearly represent a decadal variability in cloud fraction, well correlated with the indices of Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). The cloud radiative effects associated with decadal variations of clouds suggest a positive cloud feedback, which would reinforce the global warming hiatus by a net cloud cooling after 1998/1999. Climate model simulations driven by observed sea surface temperature are compared with satellite observed cloud decadal variability. Copyright:

  18. Processes Understanding of Decadal Climate Variability

    NASA Astrophysics Data System (ADS)

    Prömmel, Kerstin; Cubasch, Ulrich

    2016-04-01

    The realistic representation of decadal climate variability in the models is essential for the quality of decadal climate predictions. Therefore, the understanding of those processes leading to decadal climate variability needs to be improved. Several of these processes are already included in climate models but their importance has not yet completely been clarified. The simulation of other processes requires sometimes a higher resolution of the model or an extension by additional subsystems. This is addressed within one module of the German research program "MiKlip II - Decadal Climate Predictions" (http://www.fona-miklip.de/en/) with a focus on the following processes. Stratospheric processes and their impact on the troposphere are analysed regarding the climate response to aerosol perturbations caused by volcanic eruptions and the stratospheric decadal variability due to solar forcing, climate change and ozone recovery. To account for the interaction between changing ozone concentrations and climate a computationally efficient ozone chemistry module is developed and implemented in the MiKlip prediction system. The ocean variability and air-sea interaction are analysed with a special focus on the reduction of the North Atlantic cold bias. In addition, the predictability of the oceanic carbon uptake with a special emphasis on the underlying mechanism is investigated. This addresses a combination of physical, biological and chemical processes.

  19. Pacific Decadal Climate Variability and Predictability

    NASA Astrophysics Data System (ADS)

    Kirtman, B.

    2006-12-01

    The current understanding of decadal variability in both the tropical and extra-tropical Pacific is presented. Modeling studies into causes of mid-latitude ocean variability often focus on to what extent the variability involves coupled ocean-atmosphere feedbacks versus the uncoupled response to atmospheric stochastic white noise forcing. The coupled feedbacks are either viewed as a generalization of the Hasselman (1976) theory to include local air-sea interactions, which could amplify the low frequency response without any preferred time scale or as involving a "delayed oscillator" due to ocean memory whereby the variability has some preferred time scale. Generally, the coupled air-sea feedbacks are stable requiring atmospheric stochastic forcing, and the inclusion of ocean dynamics is thought to enhance the variability. The uncoupled stochastic forcing of the ocean includes a number of proposed physical mechanisms for the preferred low frequency. These mechanisms include oceanic advection processes associated with the mid-latitude gyre, an atmospheric pattern of forcing with a preferred length scale or position, the dynamical adjustment of the extra-tropical ocean circulation via long baroclinic Rossby waves, and Ekman pumping. Another possibility is that tropical forcing via some atmospheric "bridge" acts as a source of North Pacific decadal variations, which may or may not be amplified by coupled feedbacks. The amplitude and frequency of ENSO exhibits variations on decadal timescales. Whether these variations are driven by low frequency variability in the tropical Pacific mean state or are just sampling issues associated with some sort of random walk process has been the subject of some debate. Accordingly, the current literature includes a number of studies proposing mechanisms for the decadal variability of the tropical Pacific, and, as a counter argument, studies examining the null hypothesis that the amplitude and frequency variations are simply related to

  20. Decadal variability in Floods and Extreme Rainfall

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  1. Decadal variability in the Eastern North Atlantic

    NASA Astrophysics Data System (ADS)

    Köllner, Manuela; Klein, Birgit; Kieke, Dagmar; Klein, Holger; Rhein, Monika; Roessler, Achim; Denker, Claudia

    2016-04-01

    The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the subpolar gyre and stronger inflow of waters from the subtropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses. We examine the decadal variability in the eastern North Atlantic based on Argo data from 2000-2015 and have constructed time series for four water masses (Subpolar Mode Water (SPMW), Intermediate Water (IW), upper Labrador Sea Water (uLSW) and deep Labrador Sea Water (dLSW)) at selected locations along the Northwest European shelf. Data from the Rockall Trough and the Iceland Basin are chosen to represent advective pathways in the subpolar gyre at two major branches of the North Atlantic Current towards the Nordic Seas and the Arctic Ocean. Temporal variability of subtropical waters transported northward along the eastern boundary is studied at Goban Spur around 48°N. The Argo data are extended in time with long-term hydrographic observations such as the Extended Ellet Line data and other climatological sources in the region. For the study of transport fluctuations time series from the RACE (Regional circulation and Global change) program (2012-2015) and predecessor programs have been used. These programs have monitored the subpolar gyre in the western basin and provide time series of transports and hydrographic anomalies from moored instruments at the western flank of the Mid Atlantic Ridge (MAR). First results show that the temperatures and salinities remained at high levels for the upper waters (SPMW and IW) until 2010 and have been decreasing since

  2. 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.

  3. Decadal climate variability in the eastern Caribbean

    NASA Astrophysics Data System (ADS)

    Jury, Mark R.; Gouirand, Isabelle

    2011-11-01

    Rainfall variability in the eastern Caribbean during the 20th century is analyzed using principal component analysis and singular value decomposition. In contrast to earlier studies that used seasonal data, here we employ continuous signal processing. The leading mode is a decadal oscillation related to third and fourth modes of sea level pressure (SLP) and sea surface temperatures (SST) which together identify three zones of action in the Atlantic: 35°N-20°N, 20°N-5°N, and 5°N-20°S. The ability of the ECHAM4.5 model to simulate this signal is investigated. Its decadal variability is also represented through lower-order SLP and SST modes that comprise an Atlantic tripole pattern with lower pressure east of the Caribbean. Composite analysis of high and low phases of the decadal mode reflects a cool east Pacific and a more active Atlantic Intertropical Convergence Zone during boreal summer, conditions that favor the intensification of African easterly waves. The decadal signal has strengthened since 1970, yet the three centers of action in Atlantic SST are relatively unsynchronized.

  4. Multi-decadal climate variability, New South Wales, Australia.

    PubMed

    Franks, S W

    2004-01-01

    Traditional hydrological risk estimation has treated the observations of hydro-climatological extremes as being independent and identically distributed, implying a static climate risk. However, recent research has highlighted the persistence of multi-decadal epochs of distinct climate states across New South Wales (NSW), Australia. Climatological studies have also revealed multi-decadal variability in the magnitude and frequency of El Niño/Southern Oscillation (ENSO) impacts. In this paper, examples of multi-decadal variability are presented with regard to flood and drought risk. The causal mechanisms for the observed variability are then explored. Finally, it is argued that the insights into climate variability provide (a) useful lead time for forecasting seasonal hydrological risk, (b) a strong rationale for a new framework for hydrological design and (c) a strong example of natural climate variability for use in the testing of General Circulation Models of climate change. PMID:15195429

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    We are investigating the controls that climate and local oceanography exert on sedimentation patterns in 4 salt marsh-estuary complexes around Long Island, New York, USA. These systems encompass a variety of physical settings, including a range of tidal conditions, wave fetches, and human influences, but are all located within one climatic regime. Within these settings, we hypothesize that sedimentation patterns in limited-fetch, mesotidal salt marshes are influenced most strongly by sea-level changes, as the system is largely steady-state under high-energy conditions and sedimentation should track the longer-term sea-level transgression. Conversely, sedimentation in microtidal systems with large fetch should better track atmospheric forcings, because marsh-surface accretion largely occurs during episodic wind and storm events. To test this hypothesis, accretion rates (cm/yr) were determined by applying a constant-flux model to profiles of excess 210Pb, which reveals temporal variation in sedimentation. Additionally, we examined the rate of mineral sediment deposition (g/cm2/yr) and rate of organic matter accumulation (g/cm2/yr). These measures yielded a chronology of sedimentation patterns ~100 years long with a temporal resolution of 2-5 years, sufficient for resolving decadal-scale oscillations. Our proxies for sea-level change come from a variety of tide gauges; including the gauge at Battery Park, NYC which covers much of the past century, as well as local tide gauges with records spanning several decades. Proxies used for atmospheric forcings include mean annual winds for the past 50 years, storm histories and Hurrel's index of the North Atlantic Oscillation, which extends for over a century. Initial results reveal clear decadal-scale variability in marsh accretion, with variations ranging 2-3 fold about the long-term mean. These oscillations are very similar in timing and magnitude to those observed for the climate proxies and sea-level records. However

  6. Decadal variability in the oxygen inventory of North Atlantic subtropical underwater captured by sustained, long-term oceanographic time series observations

    NASA Astrophysics Data System (ADS)

    Montes, Enrique; Muller-Karger, Frank E.; Cianca, Andrés.; Lomas, Michael W.; Lorenzoni, Laura; Habtes, Sennai

    2016-03-01

    Historical observations of potential temperature (θ), salinity (S), and dissolved oxygen concentrations (O2) in the tropical and subtropical North Atlantic (0-500 m; 0-40°N, 10-90°W) were examined to understand decadal-scale changes in O2 in subtropical underwater (STUW). STUW is observed at four of the longest, sustained ocean biogeochemical and ecological time series stations, namely, the CArbon Retention In A Colored Ocean (CARIACO) Ocean Time Series Program (10.5°N, 64.7°W), the Bermuda Atlantic Time-series Study (BATS; 31.7°N, 64.2°W), Hydrostation "S" (32.1°N, 64.4°W), and the European Station for Time-series in the Ocean, Canary Islands (ESTOC; 29.2°N, 15.5°W). Observations over similar time periods at CARIACO (1996-2013), BATS (1988-2011), and Hydrostation S (1980-2013) show that STUW O2 has decreased approximately 0.71, 0.28, and 0.37 µmol kg-1 yr-1, respectively. No apparent change in STUW O2 was observed at ESTOC over the course of the time series (1994-2013). Ship observation data for the tropical and subtropical North Atlantic archived at NOAA National Oceanographic Data Center show that between 1980 and 2013, STUW O2 (upper ~300 m) declined 0.58 µmol kg-1 yr-1 in the southeastern Caribbean Sea (10-15°N, 60-70°W) and 0.68 µmol kg-1 yr-1 in the western subtropical North Atlantic (30-35°N, 60-65°W). A declining O2 trend was not observed in the eastern subtropical North Atlantic (25-30°N, 15-20°W) over the same period. Most of the observed O2 loss seems to result from shifts in ventilation associated with decreased wind-driven mixing and a slowing down of STUW formation rates, rather than changes in diffusive air-sea O2 gas exchange or changes in the biological oceanography of the North Atlantic. Variability of STUW O2 showed a significant relationship with the wintertime (January-March) Atlantic Multidecadal Oscillation index (AMO, R2 = 0.32). During negative wintertime AMO years trade winds are typically stronger between 10°N and 30

  7. 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.

  8. Food Price Volatility and Decadal Climate Variability

    NASA Astrophysics Data System (ADS)

    Brown, M. E.

    2013-12-01

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

  9. Advances in Understanding Decadal Climate Variability

    NASA Technical Reports Server (NTRS)

    Busalacchi, Antonio J.

    1999-01-01

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

  10. Advances in Understanding Decadal Climate Variability

    NASA Technical Reports Server (NTRS)

    Busalaacchi, Antonio J.

    1998-01-01

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

  11. Westerly Wind Bursts, ENSO Asymmetry, and Tropical Pacific Decadal Variability

    NASA Astrophysics Data System (ADS)

    Levine, A. F. Z.; McPhaden, M. J.

    2014-12-01

    Over the past half century, epochs of enhanced and suppressed ENSO activity have coincided with changes in mean trade wind strength (tropical Pacific mean state) and westerly wind burst variability. Previous research has considered this westerly wind burst variability as state-dependent noise forcing for ENSO. In agreement with the observations, we find that in the current generation of coupled climate models, the westerly wind burst variability is highly correlated with decadal and multi-decadal scale Pacific mean state variability as well as ENSO variability. However, precisely how concurrent changes to ENSO, the tropical Pacific mean state, and westerly wind burst variability is still an open question. Our previous research has shown that there is a relationship between the magnitude of the state-dependence of the noise forcing and ENSO amplitude asymmetry (i.e. that the El Nino events have a larger temperature anomaly than the La Nina events) . In turn, ENSO amplitude asymmetry can produce a signal on the tropical Pacific mean state on multi-decadal timescales. Here, we develop a systematic method to investigate the hypothesis that the inherent randomness of the state-dependent noise forcing of ENSO can explain the coincident changes in ENSO variability and the tropical Pacific mean state, using a hierarchy of coupled models, from conceptual to intermediate to coupled GCMs.

  12. 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

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

    SciTech Connect

    Graham, N.E.

    1994-08-01

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

  14. Solar forcing synchronizes decadal North Atlantic climate variability.

    PubMed

    Thiéblemont, Rémi; Matthes, Katja; Omrani, Nour-Eddine; Kodera, Kunihiko; Hansen, Felicitas

    2015-01-01

    Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth's regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1-2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface. PMID:26369503

  15. Solar forcing synchronizes decadal North Atlantic climate variability

    PubMed Central

    Thiéblemont, Rémi; Matthes, Katja; Omrani, Nour-Eddine; Kodera, Kunihiko; Hansen, Felicitas

    2015-01-01

    Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth's regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1–2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface. PMID:26369503

  16. 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.

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

    PubMed Central

    Wang, Kaicun; Dickinson, Robert E.

    2013-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Wang, Kaicun; Dickinson, Robert

    2014-05-01

    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.

  19. 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.

  20. Chandra's First Decade Observing AR Lac

    NASA Astrophysics Data System (ADS)

    Ratzlaff, Peter; Drake, Jeremy J.; Durham, R. Nicholas; Kashyap, Vinay; Posson-Brown, Jennifer; Wargelin, Bradford J.

    2009-09-01

    X-ray observations of the eclipsing RS CVn-type binary AR Lacertae have been obtained every year from 1999 to 2008 with the Chandra High Resolution Camera imaging and spectroscopic detectors (HRC-I, HRC-S) as part of their gain and point spread function calibration. These represent the best quality data yet obtained on the long term variability of the X-ray emission of an RS CVn star, and are rendered especially valuable for the multi-epoch coverage of the AR Lac eclipses. The data are characterised by stochastic variability by factors of ˜2 on timescales of one to several ks, and by minor flaring events in which count rates are observed to be elevated by slightly larger factors. During primary eclipse, the X-ray count rate is generally observed at approximately 60% of its value outside of eclipse and during periods of relative quiescence. Little evidence for secondary eclipses is present in the data, reminiscent of earlier X-ray and EUV observations. The X-ray count rate modulation through the eclipses allow us to place an upper limit on the extent of a spherically symmetric coronae of about two stellar radii, the exact limit depending on the details of the coronal models and partition of emission between the component stars. We compare the observed Chandra count rates to earlier EUVE, EINSTEIN, EXOSAT and ROSAT observations and comment on the apparent lack of cyclic coronal activity on RS CVn-type binaries.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    A detailed analysis of the polar ozone loss processes during 10 recent Antarctic winters is presented with high-resolution MIMOSA-CHIM (Modèle Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection avec CHIMie) model simulations and high-frequency polar vortex observations from the Aura microwave limb sounder (MLS) instrument. The high-frequency measurements and simulations help to characterize the winters and assist the interpretation of interannual variability better than either data or simulations alone. Our model results for the Antarctic winters of 2004-2013 show that chemical ozone loss starts in the edge region of the vortex at equivalent latitudes (EqLs) of 65-67° S in mid-June-July. The loss progresses with time at higher EqLs and intensifies during August-September over the range 400-600 K. The loss peaks in late September-early October, when all EqLs (65-83° S) show a similar loss and the maximum loss (> 2 ppmv - parts per million by volume) is found over a broad vertical range of 475-550 K. In the lower stratosphere, most winters show similar ozone loss and production rates. In general, at 500 K, the loss rates are about 2-3 ppbv sh-1 (parts per billion by volume per sunlit hour) in July and 4-5 ppbv sh-1 in August-mid-September, while they drop rapidly to 0 by mid-October. In the middle stratosphere, the loss rates are about 3-5 ppbv sh-1 in July-August and October at 675 K. On average, the MIMOSA-CHIM simulations show that the very cold winters of 2005 and 2006 exhibit a maximum loss of ~ 3.5 ppmv around 550 K or about 149-173 DU over 350-850 K, and the warmer winters of 2004, 2010, and 2012 show a loss of ~ 2.6 ppmv around 475-500 K or 131-154 DU over 350-850 K. The winters of 2007, 2008, and 2011 were moderately cold, and thus both ozone loss and peak loss altitudes are between these two ranges (3 ppmv around 500 K or 150 ± 10 DU). The modeled ozone loss values are in reasonably good agreement with those estimated from

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

    NASA Astrophysics Data System (ADS)

    Yu, Jia-Yuh; Chang, Cheng-Wei

    2014-05-01

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

  3. Role of Planetary waves in Winter Stratospheric Warming: Decadal variability

    NASA Astrophysics Data System (ADS)

    Bhagavathiammal, G. J.

    2016-07-01

    Winter Stratospheric dynamics is quiet variable and fascinating in nature, because of the energetic planetary waves, propagates upward from troposphere. Using ECMWF ERA Interim Reanalysis datasets, this paper presents the decadal behaviour of winter stratosphere. Traditional diagnostic tool, Eliassen Palm (E-P) flux provides a realistic understanding of the middle atmospheric processes. Horizontal and vertical component of E-P flux is used to characterize the intensity of upward propagating tropospheric planetary waves. Inter annual variability reveals that the intensification planetary wave energy in the extratropical stratosphere was observed in the month of December; revert the stratospheric circulation, by creating the preconditioning state for the occurrence of stratospheric warming in January (mid-winter). After SSW, No evidence of heat flux energy is observed. This work will provide a better understanding in planetary wave - stratospheric warming mechanism.

  4. Decadal variability of surface solar radiation over China

    NASA Astrophysics Data System (ADS)

    Wang, K.

    2015-12-01

    Observations show that national average surface solar radiation (Rs) decreased by -8.0 W m-2 per decade from 1960 to 1990 and sharply increased from 1990 to 1993. However, none of the state-of-the-art climate models can reproduce such decrease/increase of Rs. This study shows that Rs observations over China have significant inhomogeneity. Before 1989, Rs was calculated as a sum of direct (Rsdir) and diffuse (Rsdif) solar radiation observations measured by pyrheliometers and shaded pyranometers separately. Due to technical limitations and irregular calibration, pyranometers before 1990 had a strong sensitivity drift problem, which introduced crucial spurious decreasing trends into Rsdif and Rs data. From 1990 to 1993, instruments and measurement methods were replaced and measuring stations were restructured in China, which resulted in an abrupt increase in the observed Rs. Rs calculated from Sunshine duration (SunDu) provide a reliable reference in assessing decadal variability of Rs. SunDu derived Rs have no sensitivity drift problem because of its daily changed recording material. SunDu-derived Rs averaged over China decreased by -2.9 W m-2 per decade from 1961 to 1990, and had a negligible trend afterward. During the period of 1994-2012 when Rs observations were free of inhomogeneity mentioned above, the observed and SunDu-derived Rs consistently show a negligible trend, being less than 0.1 W m-2 per decade. These trends can be reproduced by high-quality CMIP5 Earth System Models (ESM). This level of agreement is due to the incorporation of a near real emission inventory of atmospheric aerosols by CMIP5 ESMs. Rs from ERA-Interim has a good agreement with SunDu-derived Rs. However, ERA-interim does not allow aerosol loading to change annually. ERA-Interim Rs shows an unreliable increasing trend of 1.9 W m-2 per decade from 1990 to 2013 because it does not include the impact of recent increased atmospheric aerosols over China. GEWEX Rs calculated from ISCCP cloud

  5. A Decade of Satellite Ocean Color Observations

    NASA Technical Reports Server (NTRS)

    McClain, Charles R.

    2009-01-01

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

  6. 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 2σ 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.

  7. Interannual and Decadal Variability of Summer Rainfall over South America

    NASA Technical Reports Server (NTRS)

    Zhou, Jiayu; Lau, K.-M.

    1999-01-01

    Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific

  8. An oceanic mechanism for decadal variability in the North Pacific

    NASA Astrophysics Data System (ADS)

    Dawson, Andrew; Stevens, David; Matthews, Adrian

    2013-04-01

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

  9. The role of meltwater variability in modulating diurnal to inter-annual ice-sheet flow: New insights from a ~decade of high-temporal resolution GPS observations on the western Greenland margin

    NASA Astrophysics Data System (ADS)

    Stevens, L. A.; Behn, M. D.; Das, S. B.; Joughin, I.; van den Broeke, M.; Herring, T.; McGuire, J. J.

    2015-12-01

    Meltwater-driven processes across the ablation zone of the Greenland Ice Sheet are controlled by seasonal fluxes as well as shorter-term variability in surface melt. Few high-temporal resolution GPS observations of ice-sheet flow extend for longer than a couple years, limiting multiyear analyses of seasonal variability in ice-sheet flow. Using a small GPS network installed at ~1000-m above sea level (m a.s.l.) operating from 2006-2014, and supplemented with a larger array of 20 GPS stations installed from 2011­-2014, we observe nine years of ice-sheet surface motion on the western margin of the Greenland Ice Sheet. The GPS array spans a horizontal distance of 30 km across an elevation range of 700-1250 m a.s.l., and captures the ice-sheet's velocity response to the seasonal melt cycle. By combining the GPS array measurements with temperature, precipitation, and runoff estimates from the Regional Atmospheric Climate Model (RACMO), we examine the relationship between ice-sheet flow and surface melt variability both at the seasonal scale (i.e., during melt onset, summer melt season and melt cessation) as well as during transient high melt periods such as precipitation events, anomalously high melt episodes, and supraglacial lake drainages. We observe varying surface motion following early versus late summer extended melt events, with early-season extended melt events inducing longer sustained speed-up than late summer events. We also examine differences in the timing of melt onset and magnitude, comparing the anomalously high runoff observed across the ice sheet in 2010 and 2012 against the average to low runoff observed in the years comprising the remainder of the record. This nearly decadal record improves our understanding of the role of meltwater variability in modulating ice-sheet flow on diurnal to inter-annual timescales.

  10. Decadal variability in historical simulations by coupled climate models in CMIP5

    NASA Astrophysics Data System (ADS)

    Yoon, J.; Rasch, P. J.

    2013-12-01

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

  11. Decadal variability of Arctic sea ice in the Canada Basin

    NASA Astrophysics Data System (ADS)

    Connor, L. N.

    2015-12-01

    A series of spring Arctic flight campaigns surveying a region over the Canada Basin, from 2006 to 2015, has resulted in unique observations that reveal new details of sea ice leads and freeboard evolution, during a decade of significant interannual variability in the Arctic ice cover. The series began in 2006 with a joint NASA/NOAA airborne altimetry campaign over a 1300 km survey line northwest of the Canadian Archipelago extending into the northern Beaufort Sea. Operation IceBridge (OIB) took up this flight line again in 2009 and repeated it annually through 2012. Additional observations have been collected along a 1000+ km flight line, in the southern Canada Basin and eastern Beaufort Sea, between 2009 and 2015. Here we examine laser altimetry, snow radar data, and high-resolution visible imagery to better understand the frequency and distribution of leads and ice floes, the characteristics of first- and multi-year ice types in the survey region, and their impact on the derivation and accuracy of sea ice freeboard. We demonstrate a novel lead detection methodology that depends only upon laser altimeter measurements, and we quantify the impact of low lead frequencies on estimates of instantaneous sea surface height. The analysis reveals a variable springtime freeboard north of 78° N, significantly reduced after 2006, and a notable lead outbreak over the Canada Basin during 2010.

  12. A simple coupled model of tropical Atlantic decadal climate variability

    NASA Astrophysics Data System (ADS)

    Kushnir, Yochanan; Seager, Richard; Miller, Jennifer; Chiang, John C. H.

    2002-12-01

    A linear, zonally averaged model of the interaction between the tropical Atlantic (TA) atmosphere and ocean is presented. A balance between evaporation and meridional heat advection in the mixed layer determines the sea surface temperature tendency. The atmosphere is a fixed-depth, sub-cloud layer in which the specific humidity anomaly is determined by a steady-state balance between evaporation, meridional advection, and a parameterized humidity exchange with the free atmosphere. When the model is integrated, forced with observed surface wind anomalies from 1965 to the present, its simulation of the observed sea surface temperature (SST) is realistic and comparable to a simulation with a full ocean GCM. A statistical representation of surface winds and their relationship to the SST gradient across the equator is used to formulate and test a coupled model of their regional variability. Forced on both sides of the equator, in the trade-wind regions, with ``white-noise'' windspeed perturbations, the SST-wind relationship in the near-equatorial region feeds back positively on existing SST anomalies and gives rise to decadal variability.

  13. Decadal variability of precipitation over Western North America

    USGS Publications Warehouse

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

    1998-01-01

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

  14. Simulated decadal modes of the NH atmospheric circulation arising from intra-decadal variability, external forcing and slow-decadal climate processes

    NASA Astrophysics Data System (ADS)

    Lou, Jiale; Zheng, Xiaogu; Frederiksen, Carsten S.; Liu, Haibo; Grainger, Simon; Ying, Kairan

    2016-06-01

    A decadal variance decomposition method is applied to the Northern Hemisphere (NH) 500-hPa geopotential height (GPH) and the sea level pressure (SLP) taken from the last millennium (850-1850 AD) experiment with the coupled climate model CCSM4, to estimate the contribution of the intra-decadal variability to the inter-decadal variability. By removing the intra-decadal variability from the total inter-decadal variability, the residual variability is more likely to be associated with slowly varying external forcings and slow-decadal climate processes, and therefore is referred to as slow-decadal variability. The results show that the (multi-)decadal changes of the NH 500-hPa GPH are primarily dominated by slow-decadal variability, whereas the NH SLP field is primarily dominated by the intra-decadal variability. At both pressure levels, the leading intra-decadal modes each have features related to the El Niño-southern oscillation, the intra-decadal variability of the Pacific decadal oscillation (PDO) and the Arctic oscillation (AO); while the leading slow-decadal modes are associated with external radiative forcing (mostly with volcanic aerosol loadings), the Atlantic multi-decadal oscillation and the slow-decadal variability of AO and PDO. Moreover, the radiative forcing has much weaker effect to the SLP than that to the 500-hPa GPH.

  15. Comparison of Decadal AMOC Variability Among Climate Models

    NASA Astrophysics Data System (ADS)

    Klinger, B. A.; Garuba, O. A.

    2012-12-01

    Atmosphere-ocean general circulation models (AOGCM's) often exhibit decadal variability of the Atlantic Meridional Overturning Circulation (AMOC), but the nature of this variability shows great quantitative and qualitative differences among different experiments. Here uniform metrics compare AMOC variability among several AOGCM's in preindustrial control runs for the Climate Model Intercomparison Project (CMIP). All the models show decadal variability in meridional overturning. The 3-61 year band is examined to isolate this frequency range. The meridional stream function shows maximum variability in the North Atlantic ranging from about .5 to 1.8 Sv (about 3% to 10% of the time-mean overturning strength), with period (based on the lagged autocorrelation) ranging from about 10 to 25 years for most of the models (50 years for one model). In all models, overturning variability is strongest between 40N and 60N, with a weaker overturning signal propagating across the equator within a few years. Most of the models show a somewhat complex high-latitude density field associated with the meridional overturning, but with a tendency for high density to precede high overturning, as Dong and Sutton (2005) found in a single model. In summary, O(1) Sv North Atlantic decadal overturning variability associated with high latitude density variations is a robust feature of different climate models.

  16. Decadal ENSO variability as reflected by Local Lyapunov Exponents

    NASA Astrophysics Data System (ADS)

    Karamperidou, C.; Cane, M. A.; Wittenberg, A. T.; Lall, U.; Di Nezio, P. N.

    2011-12-01

    Decadal variability of ENSO is present in historical and paleo records, and has been simulated by a hierarchy of dynamical and statistical models. The ENSO variability in the IPCC AR4 Coupled GCMs ranges from constant periodicity or amplitude to significant inter-decadal variability in both period and amplitude. While long runs of intermediate dynamical models that exhibit inter-decadal and inter-centennial variability, such as the ZC model, have been a subject of numerous studies, only recently have long runs of coupled GCMs, such as the GFDL CM2.1 2000-yr control run, become available. The presence of such rich variability in the absence of external forcing that could induce persistent regimes, along with the length of the simulation, provides new ground for investigation of the causes of long-term modulation of ENSO behavior and the implications for predictability at multiple time-scales from the short-range to the decadal. In this work, we investigate ENSO predictability in long unforced runs of a fully coupled GCM (GFDL's CM2.1) and the intermediate ZC model in a dynamical systems theory context. We compute the Local Lyapunov Exponents (LLEs) of the NINO3 time series, and use them as a means of classifying epochs of distinct ENSO behavior. The 'loss' or 'gain' of predictability across these epochs and their relation to the physical evolution of the ENSO events is examined. The correspondence of the LLE statistics with prediction error in 'perfect-model' reforecasts is also discussed.

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

    NASA Astrophysics Data System (ADS)

    Newman, M.

    2013-12-01

    Predictability of Pacific sea surface temperature (SST) climate variations and climate impacts on time scales of 1-10 years is discussed, using a global linear inverse model (LIM) as an empirical benchmark for decadal surface temperature forecast skill. Constructed from the observed simultaneous and 1-yr lag covariability statistics of annually averaged sea surface temperature (SST) and surface (2 m) land temperature global anomalies during 1901-2009, the LIM has hindcast skill for leads of 2-5 yr and 6-9 yr comparable to and sometimes even better than skill of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) model hindcasts initialized annually over the period 1960-2000 and has skill far better than damped persistence (e.g., a local univariate AR1 process). Pronounced similarity in geographical variations of skill between LIM and CMIP5 hindcasts suggests similarity in their sources of skill as well, supporting additional evaluation of LIM predictability. For forecast leads above 1-2 yr, LIM skill almost entirely results from three nonorthogonal patterns: one corresponding to the secular trend and two more, each with about 10-yr decorrelation time scales but no trend, that represent most of the predictable portions of the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) indices, respectively. In contrast, for forecasts greater than about two years, ENSO acts as noise and degrades forecast skill. These results suggest that current coupled model decadal forecasts may not yet have much skill beyond that captured by multivariate, predictably linear dynamics. A particular focus will be on the predictability of the PDO, which represents the dominant mode of Pacific decadal SST variability. The PDO is shown to represent a few different physical processes, including wind-driven changes of SSTs that can occur either due to daily weather variability or to tropical forcing, and variations in the North Pacific western boundary

  18. Exploring the impact of CMIP5 model biases on the simulation of North Atlantic decadal variability

    NASA Astrophysics Data System (ADS)

    Menary, Matthew B.; Hodson, Daniel L. R.; Robson, Jon I.; Sutton, Rowan T.; Wood, Richard A.; Hunt, Jonathan A.

    2015-07-01

    Instrumental observations, paleoproxies, and climate models suggest significant decadal variability within the North Atlantic subpolar gyre (NASPG). However, a poorly sampled observational record and a diversity of model behaviors mean that the precise nature and mechanisms of this variability are unclear. Here we analyze an exceptionally large multimodel ensemble of 42 present-generation climate models to test whether NASPG mean state biases systematically affect the representation of decadal variability. Temperature and salinity biases in the Labrador Sea covary and influence whether density variability is controlled by temperature or salinity variations. Ocean horizontal resolution is a good predictor of the biases and the location of the dominant dynamical feedbacks within the NASPG. However, we find no link to the spectral characteristics of the variability. Our results suggest that the mean state and mechanisms of variability within the NASPG are not independent. This represents an important caveat for decadal predictions using anomaly assimilation methods.

  19. Decadal-Interdecadal SST Variability and Regional Climate Teleconnections

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  20. Decadal variability of the Arctic Ocean in a changing climate

    NASA Astrophysics Data System (ADS)

    Ding, Y.

    2015-12-01

    Arctic climate is characterized by strong interannual to interannual/decadal variability involving interactions with the overlying atmosphere as well as exchanges with the Pacific and Atlantic Oceans. By increasing the geographic area of contact as well as by changing the mean stratification and overturning circulation future reductions of sea ice cover offers the potential to enhance and alter these interactions. This study begins with a comparison of simulated and historical interannual/decadal variability in the Arctic Ocean, and the relative importance of local atmospheric heating and ocean heat convergence, as they appear in a collection of CMIP5 model simulations. This analysis reveals that the models can be classified into two groups depending on their responses. Then we examine the changes in this variability over the coming centuries as simulated by the models, which reveal dramatic changes to the strength and frequency of the variability as the sea ice retreats. The connections to interannual/decadal variations of the overturning circulation and to atmospheric weather patterns will be discussed.

  1. Interannual to Decadal Variability of Ocean Evaporation as Viewed from Climate Reanalyses

    NASA Technical Reports Server (NTRS)

    Robertson, Franklin R.; Bosilovich, Michael G.; Roberts, Jason B.; Wang, Hailan

    2015-01-01

    Questions we'll address: Given the uncoupled framework of "AMIP" (Atmosphere Model Inter-comparison Project) experiments, what can they tell us regarding evaporation variability? Do Reduced Observations Reanalyses (RedObs) using Surface Fluxes and Clouds (SFC) pressure (and wind) provide a more realistic picture of evaporation variability? What signals of interannual variability (e.g. El Nino/Southern Oscillation (ENSO)) and decadal variability (Interdecadal Pacific Oscillation (IPO)) are detectable with this hierarchy of evaporation estimates?

  2. Decadal variability of tropical tropopause temperature and its relationship to the Pacific Decadal Oscillation

    NASA Astrophysics Data System (ADS)

    Wang, Wuke; Matthes, Katja; Omrani, Nour-Eddine; Latif, Mojib

    2016-07-01

    Tropopause temperatures (TPTs) control the amount of stratospheric water vapour, which influences chemistry, radiation and circulation in the stratosphere, and is also an important driver of surface climate. Decadal variability and long-term trends in tropical TPTs as well as stratospheric water vapour are largely unknown. Here, we present for the first time evidence, from reanalysis and state-of-the-art climate model simulations, of a link between decadal variability in tropical TPTs and the Pacific Decadal Oscillation (PDO). The negative phase of the PDO is associated with anomalously cold sea surface temperatures (SSTs) in the tropical east and central Pacific, which enhance the zonal SST gradient across the equatorial Pacific. The latter drives a stronger Walker Circulation and a weaker Hadley Circulation, which leads to less convection and subsequently a warmer tropopause over the central equatorial Pacific. Over the North Pacific, positive sea level pressure anomalies occur, which damp vertical wave propagation into the stratosphere. This in turn slows the Brewer-Dobson circulation, and hence warms the tropical tropopause, enabling more water vapour to enter the stratosphere. The reverse chain of events holds for the positive phase of the PDO. Such ocean-troposphere-stratosphere interactions may provide an important feedback on the Earth’s global surface temperature.

  3. Decadal variability of tropical tropopause temperature and its relationship to the Pacific Decadal Oscillation.

    PubMed

    Wang, Wuke; Matthes, Katja; Omrani, Nour-Eddine; Latif, Mojib

    2016-01-01

    Tropopause temperatures (TPTs) control the amount of stratospheric water vapour, which influences chemistry, radiation and circulation in the stratosphere, and is also an important driver of surface climate. Decadal variability and long-term trends in tropical TPTs as well as stratospheric water vapour are largely unknown. Here, we present for the first time evidence, from reanalysis and state-of-the-art climate model simulations, of a link between decadal variability in tropical TPTs and the Pacific Decadal Oscillation (PDO). The negative phase of the PDO is associated with anomalously cold sea surface temperatures (SSTs) in the tropical east and central Pacific, which enhance the zonal SST gradient across the equatorial Pacific. The latter drives a stronger Walker Circulation and a weaker Hadley Circulation, which leads to less convection and subsequently a warmer tropopause over the central equatorial Pacific. Over the North Pacific, positive sea level pressure anomalies occur, which damp vertical wave propagation into the stratosphere. This in turn slows the Brewer-Dobson circulation, and hence warms the tropical tropopause, enabling more water vapour to enter the stratosphere. The reverse chain of events holds for the positive phase of the PDO. Such ocean-troposphere-stratosphere interactions may provide an important feedback on the Earth's global surface temperature. PMID:27404090

  4. Decadal variability of tropical tropopause temperature and its relationship to the Pacific Decadal Oscillation

    PubMed Central

    Wang, Wuke; Matthes, Katja; Omrani, Nour-Eddine; Latif, Mojib

    2016-01-01

    Tropopause temperatures (TPTs) control the amount of stratospheric water vapour, which influences chemistry, radiation and circulation in the stratosphere, and is also an important driver of surface climate. Decadal variability and long-term trends in tropical TPTs as well as stratospheric water vapour are largely unknown. Here, we present for the first time evidence, from reanalysis and state-of-the-art climate model simulations, of a link between decadal variability in tropical TPTs and the Pacific Decadal Oscillation (PDO). The negative phase of the PDO is associated with anomalously cold sea surface temperatures (SSTs) in the tropical east and central Pacific, which enhance the zonal SST gradient across the equatorial Pacific. The latter drives a stronger Walker Circulation and a weaker Hadley Circulation, which leads to less convection and subsequently a warmer tropopause over the central equatorial Pacific. Over the North Pacific, positive sea level pressure anomalies occur, which damp vertical wave propagation into the stratosphere. This in turn slows the Brewer-Dobson circulation, and hence warms the tropical tropopause, enabling more water vapour to enter the stratosphere. The reverse chain of events holds for the positive phase of the PDO. Such ocean-troposphere-stratosphere interactions may provide an important feedback on the Earth’s global surface temperature. PMID:27404090

  5. 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

  6. 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.

  7. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  9. Multi-decadal Variability of Indian Summer Monsoon in CMIP5 Models

    NASA Astrophysics Data System (ADS)

    Sandeep, S.; Ravindran, A.

    2013-12-01

    The multi-decadal variability of Indian Summer Monsoon (ISM) Rainfall in the fifth phase Coupled Model Inter-comparison Project (CMIP5) climate model simulations is analyzed. Recent studies, suggest a slight weakening of the Indian precipitation as assessed from CMIP3 simulations. The ISM rainfall simulated by CMIP5 runs with all historical forcing (AF) also suggest a strong multi-decadal weakening trend in ISM precipitation during 1901 - 2005. Further, the decadal scale variability in ISM land precipitation in multi model ensemble of AF simulations is fairly comparable with the observed variability. However, these simulations show patterns of regional variability and trends within the monsoon domain. The CMIP5 ensembles with natural variability alone and those with only Green House Gas (GHG) forcing could not reproduce the observed variability in ISM precipitation. This suggests strong influence of anthropogenic aerosols on multi-decadal variability in ISM precipitation, which is consistent with previous findings. Further investigation revealed that the weakening of zonal winds in AF simulations, possibly due to aerosol induced weakening in land-ocean thermal contrast, resulted in reduced moisture transport from ocean to the land. The trends and variability of ISM in multi model ensemble of CMIP5 simulations will be discussed in detail.

  10. Surface Salinity Variability in the North Atlantic During Recent Decades

    NASA Technical Reports Server (NTRS)

    Haekkinen, Sirpa

    2001-01-01

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

  11. 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."

  12. Stochastically-forced Decadal Variability in Australian Rainfall

    NASA Astrophysics Data System (ADS)

    Taschetto, A.

    2015-12-01

    Iconic Australian dry and wet periods were driven by anomalous conditions in the tropical oceans, such as the worst short-term drought in the southeast in 1982 associated with the strong El Niño and the widespread "Big Wet" in 1974 linked with a La Niña event. The association with oceanic conditions makes droughts predictable to some extent. However, prediction can be difficult when there is no clear external forcing such as El Niños. Can dry spells be triggered and maintained with no ocean memory? In this study, we investigate the potential role of internal multi-century atmospheric variability in controlling the frequency, duration and intensity of long-term dry and wet spells over Australia. Two multi-century-scale simulations were performed with the NCAR CESM: (1) a fully-coupled simulation (CPLD) and (2) an atmospheric simulation forced by a seasonal SST climatology derived from the coupled experiment (ACGM). Results reveal that droughts and wet spells can indeed be generated by internal variability of the atmosphere. Those internally generated events are less severe than those forced by oceanic variability, however the duration of dry and wet spells longer than 3 years is comparable with and without the ocean memory. Large-scale ocean modes of variability seem to play an important role in producing continental-scale rainfall impacts over Australia. While the Pacific Decadal Oscillation plays an important role in generating droughts in the fully coupled model, perturbations of monsoonal winds seem to be the main trigger of dry spells in the AGCM case. Droughts in the mid-latitude regions such as Tasmania can be driven by perturbations in the Southern Annular Mode, not necessarily linked to oceanic conditions even in the fully-coupled model. The mechanisms behind internally-driven mega-droughts and mega-wets will be discussed.

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

    PubMed

    Latif, M; Barnett, T P

    1994-10-28

    The cause of decadal climate variability over the North Pacific Ocean and North America is investigated by the analysis of data from a multidecadal integration with a state-of-the-art coupled ocean-atmosphere model and observations. About one-third of the low-frequency climate variability in the region of interest can be attributed to a cycle involving unstable air-sea interactions between the subtropical gyre circulation in the North Pacific and the Aleutian low-pressure system. The existence of this cycle provides a basis for long-range climate forecasting over the western United States at decadal time scales. PMID:17793457

  14. Multi-decadal water resource variations in France : connexion with the Altantic Multidecadal Variability

    NASA Astrophysics Data System (ADS)

    Habets, F.; Boe, J.; Dayon, G.

    2015-12-01

    Hydrological cycles have strong temporal variations. Analysis of the long-term observations can help detect trends that may be consistent with theses projected in the context of climate change and thus help awareness of stakeholders. However, one must remain cautious on the analysis of these trends when they are estimated on the basis of a few decades, because the water cycle can have strong multi-decadal variations. Indeed, in France, long observed series shown that river flows generally exhibit large multidecadal variation since the late 19th century to the present, especially in spring. Differences of means between 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations. Such multi decadal variations were also found on glaciers, but are difficult to detect on the groundwater resource, which might be linked to the recharge processes. Multi-decadal spring river flow variations are associated with variations in spring precipitation and temperature. These multi-decadal variations in precipitation are themselves found to be driven by large-scale atmospheric circulation, more precisely by a multi-decadal oscillation in a sea level pressure dipole between western Europe and the eastern Atlantic. It is suggested that the Atlantic Multidecadal Variability (AMV), the main mode of multi-decadal variability in the North Atlantic-Europe sector, controls those variations in large-scale circulation and is therefore the main ultimate driver of multi-decadal variations in spring river flows.Impact of such teleconnection for the management of the water resource is important, since the threshold alert used by stakeholder vary also at multi decadal scale. Moreover, such natural variabilities are not well reproduced by climate model, especially because of weak teleconnection between the simulated AMV and the simulated precipitation over France. Statistical methods could help correct such bias, and are currently assessed on the 20th century.

  15. Greenhouse warming, decadal variability, or El Nino? An attempt to understand the anomalous 1990s

    SciTech Connect

    Latif, M.; Eckert, C.; Kleeman, R.

    1997-09-01

    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{degrees}S-60{degrees}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 that was forced by the same SSTs. The tropical SST variability can be characterized by three modes: an interannual mode [the El Nino-Southern Oscillation (ENSO)], a decadal mode, and a trend or unresolved ultra-low-frequency variability. 48 refs., 20 figs.

  16. 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.

  17. Role of the North Pacific sea surface temperature in the East Asian winter monsoon decadal variability

    NASA Astrophysics Data System (ADS)

    Sun, Jianqi; Wu, Sha; Ao, Juan

    2016-06-01

    In this study, a possible mechanism for the decadal variability in the East Asian winter monsoon (EAWM) is proposed. Specifically, the North Pacific sea surface temperature (SST) may play an important role. An analysis of the observations shows that the North Pacific SST has a remarkable decadal pattern whose phase shifted around the mid-1980s. This North Pacific SST decadal pattern can weaken the East Asian trough and enhance the North Pacific Oscillation through changing air-sea interactions over the North Pacific. The weak East Asian trough enhances the zonal circulation and weakens the meridional circulation over East Asia, consequently leading to a weaker southward cold surge and East Asia warming around the mid-1980s. The numerical experiment further confirms the pronounced physical processes. In addition, over the longer period of 1871-2012, the indices of the EAWM and North Pacific SST decadal pattern are also highly consistent on the decadal timescale, which further confirms the impact of the North Pacific SST decadal pattern on the EAWM decadal variability.

  18. 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.

  19. 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.

  20. Decadal variability of rift propagation on the Amery Ice Shelf

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  1. The Relative Contribution of Internal and Model Variabilities to the Uncertainty in Decadal Climate Predictions

    NASA Astrophysics Data System (ADS)

    Strobach, Ehud; Bel, Golan

    2016-04-01

    Decadal climate predictions, which are initialized with observed conditions, are characterized by two main sources of uncertainties--internal and model variabilities. The former is due to the sensitivity of the models to the initial conditions, and the latter is due to the different predictions of different models. There is not much that can be done to reduce the internal variability; however, there are several methods for reducing the model variability--for example, using an ensemble weighted according to the past performance of the models rather than an equally weighted ensemble. Quantifying the contribution of each of these sources can help in assessing the potential reduction of the total uncertainty of these climate predictions. We used an ensemble of climate model simulations, from the CMIP5 decadal experiments, that includes different climate models and several initializations for each of the models, to analyze the uncertainties on a decadal time scale. Time series of the monthly and annual means of the surface temperature and wind components were established for the variability analysis. The analysis focused on the contributions of the internal and model variabilities and the total uncertainty. We found that different definitions of the anomaly resulted in different conclusions regarding the variability of the ensemble. However, some features of the uncertainty were common to all the anomalies we considered. In particular, we found that (i) over decadal time scales, there is no considerable increase in the uncertainty with time; (ii) the model variability is more sensitive to the annual cycle than the internal variability (this, in turn, results in a maximal uncertainty during the winter in the northern hemisphere); (iii) the uncertainty of the surface temperature prediction is dominated by the model variability, whereas the uncertainty of the surface wind components is determined by both the model and the internal variabilities. Analysis of the spatial

  2. Long-term climate change in the Mediterranean region in the midst of decadal variability

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Long-term climate change and decadal variability in the Mediterranean region during 1860-2100 are investigated based on observational data and the newly available Coupled Model Intercomparison Project—Phase 5 (CMIP5) experiments. Observational records show that decadal variability and a general tendency for annual-mean conditions to be warmer and drier have characterized the Mediterranean during 1860-2005. Consistency with CMIP5 model simulations including greenhouse gases (GHG), as well as anthropogenic aerosols and natural forcings, suggest that forced changes have characterized aspects of Mediterranean climate during this period. Future GHG-forced change will take place in the midst of decadal variability, both internal and forced, as it has occurred in the past. However, future rates of forced warming and drying over the Mediterranean are projected to be higher than in the past century. The degree to which forced change and internal variability will matter depends on the climatic quantity being considered. For surface air temperature and Mediterranean Sea annual-mean evaporation and surface freshwater fluxes, variability and forced change have become comparable and the forced signal has already emerged from internal variability. For quantities with large internal variability and relatively small forced signal such as precipitation, forced change will emerge later on in the twenty-first century over selected regions and seasons. Regardless, the probability distribution of future precipitation anomalies is progressively shifting towards drier conditions. Overall, results highlight that both mean projected forced change and the variability that will accompany forced mean change should be considered in the development of future climate outlooks.

  3. Decadal-scale Holocene climate variability in the Nordic seas

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

    Sea-surface temperatures (SST) at decadal resolution have been reconstructed from core MD 95-2011, core MD 99-2269 and core BS88-6-5A based on diatom transfer functions. Core MD 95-2011 is located on the Vöring Plateau (66^o58.18N; 07^o38.36E, 1050 m water depth) along the main axis of the northward flowing warm Atlantic water. It is, therefore, in an ideal position to monitor changes in the northward heat flux to northwestern Europe. Core MD 99-2269 is located in the deep Hunafloi trough, off N Iceland (66^o37.53N; 20^o51.16W, 365 m water depth). Today the core lies under the influence of the Irminger current, but it also may be influenced by the cold East Greenland current (EGC) as the Polar front migrates eastward. Core BS88-6-5A is located on the East Greenland shelf (67^o07.54N; 30^o54.26W, 707 m water depth) and is influenced by the EGC. The cores has been dated by AMS C-14 and Pb 210 isotope profiles. SST variations are estimated by means of 3 different diatom transfer function methods. Results indicate a division of the Holocene into three periods and a climate development in step with the decreasing Northern Hemisphere insolation. However, regional differences between the surface currents occur regarding both timing and magnitude of changes. Superimposed on the general Holocene cooling trend there is a high frequency SST variability, which is in the order of 1--1.5 degrees C for the Vöring Plateau and the East Greenland shelf, and 2.5--3 degrees C for the North Iceland shelf. There is clear evidence for late Holocene climatic events such as the "Little Ice Age" and the "Medieval Warm Period". Timing of late Holocene climatic events at the eastern versus western Nordic Seas will be discussed.

  4. 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

  5. IRIS observations of moss variability

    NASA Astrophysics Data System (ADS)

    Testa, P.; Robinson, C.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen, V. H.; DeLuca, E. E.; Tarbell, T. D.; Lemen, J. R.; Title, A. M.; Wuelser, J.

    2013-12-01

    The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions, provides stringent constraints on the characteristics of heating events. Recent moss observations with the Hi-C (High resolution coronal imager) sounding rocket in a EUV narrow band around 193A at high spatial (~0.3 arcsec) and temporal (~5.5s) resolution, have revealed in some moss regions variability on timescales down to ~15 s, significantly shorter than the minute-scale variability typically found in previous observations of moss. The Hi-C and SDO observations of these events suggest that they are signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. The Hi-C rocket only produced few minutes of data, therefore preventing a detail study of the statistical properties of these events. The Interface Region Imaging Spectrograph (IRIS), launched in June 2013, provides imaging and spectral observations at high spatial (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV and NUV wavelengths. We present here an analysis of the temporal variability properties of moss regions as observed by IRIS, focusing on high cadence (<5s) slit-jaw images (SJI) in the 1400A band, centered around Si IV transition region emission. We compare the results with simultaneous analysis of AIA data, and with previous findings.

  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

    2016-03-01

    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

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

    NASA Astrophysics Data System (ADS)

    Ding, Ruiqiang; Li, Jianping

    2016-04-01

    Current coupled atmosphere-ocean general circulation models (CGCMs) 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 (NLLE) method is adopted to estimate the limit of decadal predictability based on 9-yr 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 (NAM and SAM) 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

  8. The first decade of RR Lyrae space photometric observations

    NASA Astrophysics Data System (ADS)

    Molnar, L.

    2016-05-01

    Space-based photometric telescopes stirred up stellar astrophysics in the last decade, and RR Lyrae stars have not been an exception from that either. The long, quasi-continuous, high-precision data from MOST, CoRoT and Kepler revealed a wealth of new insights about this well-known variable class. One of the most surprising mysteries turned out to be the apparent omnipresence of a common additional mode in all RRd and RRc stars. Moreover, fundamental- mode stars seem to populate two distinct classes, one of which is characterized by the presence of additional modes and/or modulation, and another limited to strict single-mode pulsation. The presence of additional modes and multiple modulations in RRab stars allowed us to construct Petersen diagrams for these parameters: while the pulsation modes show clear structures according to period ratios, there seems to be no relation between the modulation periods themselves.

  9. Evidence for multiple drivers of North Atlantic multi-decadal climate variability using CMIP5 models

    NASA Astrophysics Data System (ADS)

    Terray, L.

    2012-12-01

    Observed North Atlantic Ocean surface temperatures have changed in a non-monotonic and non-uniform fashion over the last century. While future North Atlantic decadal-to-multi-decadal climate change will be driven by a combination of internal variability and anthropogenic as well as natural forcings, the relative importance of these effects is still unclear for the 20th century [Ting et al., 2009; Knight 2009; Ottera et al. 2010; DelSole et al., 2011; Booth et al. 2012]. Here we assess the relative roles of greenhouses gases, anthropogenic aerosols, natural forcings and internal variability to the North Atlantic surface temperature decadal fluctuations using CMIP5 multi-model historical simulations driven by estimates of observed external forcings. While the latter are the main source of decadal variability in the tropics and subtropics, there is a large contribution from the unforced component to subpolar Atlantic variations. Reconstruction of forced response patterns suggests that anthropogenic forcings are the main causes of the accelerated warming of the last three decades while internal variability has a dominant contribution to the early 20th-century temperature multi-decadal swings and recent abrupt changes in the subpolar Atlantic. Significant inter-model spread with regard to the spatial response patterns to anthropogenic forcing leads to substantial uncertainty as to robust attribution statements for the mid-to-late 20th century North Atlantic warm and cold periods. Comparing internal variability from preindustrial simulations with that estimated from the observed residual after removing the best estimate of the total forced response leads to a consistency metric which allows to identify models with a biased forced response.; CMIP5 multi-model ratio (ρ_LF) of the externally forced -natural and anthropogenic- variance, σ_EF to the total variance, σ_T, of fluctuations with a period greater than 10 years. Stippling indicates regions where the null

  10. 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.

  11. Heat Recharge of the Equatorial Ocean: from ENSO to Decadal Climate Variability

    NASA Astrophysics Data System (ADS)

    Fedorov, A. V.; Muir, L.; Di Nezio, P. N.

    2012-12-01

    A key element of ENSO dynamics is heat recharge of the equatorial ocean that typically occurs prior to El Niño events. This recharge is evident in the observations and is included into conceptual models of ENSO, such as the recharge oscillator (Jin 1997, Meinen and McPhaden 2000). The focus of the present study is the phase lag between ocean heat recharge (measured as variations in upper ocean heat content along the equator) and variations in the Nino3 SST. First, from a theoretical perspective using the low-frequency approximation (Fedorov 2010), we derive a simple analytical expression for the phase lag that depends on the characteristic frequency of the oscillation, the meridional structure of wind stress anomalies, and oceanic damping. In a realistic parameter range, the phase lag given by the theory approaches 60° for an oscillation with a 4-year period, which on average agrees well with the observations. We next explore the dependence of this phase lag in CMIP5 models. We show that while some of those models do reproduce a reasonable phase lag in the interannual frequency band, many models simulate a lag significantly shorter or longer than observed (±60%). Further, the theory and observations predict a longer phase lag, ~90°, for decadal timescales. Only a few coupled models are able to capture this behavior, whereas other models produce a much shorter phase lag, and some produce a phase lag close to zero. These results suggest several types of dynamical behavior of tropical decadal variability in different models - from a dynamical mode similar to ENSO to purely damped mixed-layer variability. We conclude that differences in the simulated phase lag on timescales from interannual to decadal contribute to the broad diversity of simulated ENSO and decadal variability, as well as different prediction skills of the models.

  12. Inter-decadal variability of summer rainfall in Eastern China detected by the Lepage test

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Huang, Gang; Huang, Ronghui

    2011-12-01

    On the basis of the latest observational datasets, the inter-decadal changes of summer rainfall in East China in the past 50 years are analyzed using the Lepage test. The two traditional methods moving t-test and Mann-Kendall test are also performed on the rainfall data as a comparison. Results indicate four inter-decadal abrupt changes of summer rainfall that occurred near 1979, 1983, 1993, and 1999, and each of them is characterized by remarkable regional features. The abrupt change of summer rainfall around 1979 is accompanied by significant rainfall increase in Yangtze-Huai River Valley and a decrease in its flank. The one near 1983 shows similar structures of the rainfall changes to that near 1979, but with more significant changes in the South China and Northeast China (NEC). The inter-decadal change around 1993 brings a notable increase of summer rainfall to the South China; and the abrupt shift near 1999 exhibits significant decrease in summer rainfall over a large part of North China and NEC. The spatial-temporal features of the inter-decadal changes in summer rainfall are also investigated. Consistent results are observed. Moreover, results indicate that, on the inter-decadal scale, the rainfall variability mode changes from typical tripole to dipole structure since the early 1990s.

  13. The leading modes of decadal SST variability in the Southern Ocean in CMIP5 simulations

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2015-12-01

    The leading modes of Sea Surface Temperature variability in the Southern Ocean on decadal and even larger time scales are analysed using Coupled Model Intercomparison Project 5 (CMIP5) model simulations and observations. The analysis is based on Empirical Orthogonal Function modes of the CMIP5 model super ensemble. We compare the modes from the CMIP5 super ensemble against several simple null hypotheses, such as isotropic diffusion (red noise) and a Slab Ocean model, to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes. The results show three main modes in the Southern Ocean: the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the Pacific, which is strongly related to atmospheric forcing by the Southern Annular Mode and El Nino Southern Oscillation. The second mode is an almost basin wide monopole pattern, which has pronounced multi-decadal and longer time scales variability. It is firstly inducted by the Wave-3 patterns in the atmosphere and further developed via ocean dynamics. The third mode is a dipole pattern in the southern Pacific that has a pronounced peak in the power spectrum at multi-decadal time scales. All three leading modes found in the CMIP5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis, thus all three leading modes are ocean-atmosphere coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes.

  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

  15. The Leading Modes of Decadal SST Variability in the Southern Ocean in CMIP5 Simulations

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2016-04-01

    The leading modes of Sea Surface Temperature (SST) variability in the Southern Ocean on decadal and even larger time scales are analysed using Coupled Model Intercomparison Project 5 (CMIP5) model simulations and observations. We compare the modes from the CMIP5 super ensemble against several simple null hypotheses, such as isotropic diffusion (red noise) and a Slab Ocean model, to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes. The results show three main modes in the Southern Ocean: the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the Pacific, which is strongly related to atmospheric forcing by the Southern Annular Mode (SAM) and El Nino Southern Oscillation (ENSO). The second mode is an almost basin wide monopole pattern, which has pronounced multi-decadal and longer time scales variability. It is firstly inducted by the Wave-3 patterns in the atmosphere and further developed via ocean dynamics. The third mode is a dipole pattern in the southern Pacific that has a pronounced peak in the power spectrum at multi-decadal time scales. All three leading modes found in the CMIP5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis, thus all three leading modes are ocean-atmospheric coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes. The mechanism of the basin-wide mode is further analysed based on a series of idealized experiments. The results show that the monopole mode has a two-step power spectrum, with a first spectral increase on interannual time scale and a second higher up level on the multi-decadal to centennial time scales. Ocean dynamics, especially the ocean advection, transport the anomalous signals, connect the entire ocean and lead to the homogeneous-like spatial pattern even under stochastic

  16. Decadal Variability of Tropical Cyclone Annual Frequency in Different Ocean Basins

    NASA Astrophysics Data System (ADS)

    Zhao, Y.

    2015-12-01

    Yating Zhao1, Jing Jiang1 1 School of Atmospheric Sciences, Nanjing University Nanjing 210093 China Abstract: Tropical cyclone, one of the most severe global natural disasters, causes massive casualties and economic losses every year, greatly influences the rapid development of the modern society. Using hurricane best track data from JTWC and TPC we investigate the decadal variations of TC activities. Our research indicates that the variability of TC frequency of different ocean basins (North Indian Ocean (NIO), Northwest Pacific Ocean (WP), Northeast Pacific Ocean (NEP), North Atlantic Ocean (NA) and South Hemisphere (SH)) all have significant decadal periods, and these decadal signals have something connect with the Pacific Decadal Oscillation (PDO), which acting as the background, modulating and influencing the synoptic scale weather systems. Through diagnosing the oceanic and atmospheric circulation in different stages of PDO, we find that, as the PDO signal transmits through the Pacific Ocean, the atmospheric circulation changes accordingly all over the tropical ocean. And they influence the dynamic conditions in the troposphere and promote or restrain the tropical cyclone activities in these areas. In another word, in the positive phase of PDO, there are much more (less) TC activities observed over the NEP (NA, WP, NIO, SH), which very likely due to the favorable (unfavorable) environmental factors, such as higher (lower) SST, weaker (stronger) vertical wind shear, higher (lower) relative humidity in the middle level of troposphere, and low level positive (negative) vorticity in the local area. Meanwhile, what should be noted is that the primary environmental factor could be very different in different ocean basin. Keywords: tropical cyclone, decadal variability, PDO

  17. Decadal variability of chlorophyll a in the South China Sea: a possible mechanism

    NASA Astrophysics Data System (ADS)

    Liu, Fenfen; Chen, Chuqun; Zhan, Haigang

    2012-11-01

    Four climatologies on a monthly scale (January, April, May and November) of chlorophyll a within the South China Sea (SCS) were calculated using a Coastal Zone Color Scanner (CZCS) (1979-1983) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1998-2002). We analyzed decadal variability of chlorophyll a by comparing the products of the two observation periods. The relationships of variability in chlorophyll a with sea surface wind speed (SSW), sea surface temperature (SST), wind stress (WS), and mixed layer depth (MLD) were determined. The results indicate that there is obvious chlorophyll a decadal variability in the SCS. The decadal chlorophyll a presents distinct seasonal variability in characteristics, which may be as a result of various different dynamic processes. The negative chlorophyll a concentration anomaly in January was associated with the warming of SST and a shallower MLD. Generally, there were higher chlorophyll a concentrations in spring during the SeaWiFS period compared with the CZCS period. However, the chlorophyll a concentration exhibits some regional differences during this season, leading to an explanation being diffi cult. The deepened MLD may have contributed to the positive chlorophyll a concentration anomalies from the northwestern Luzon Island to the northeastern region of Vietnam during April and May. The increases of chlorophyll a concentration in northwestern Borneo during May may be because the stronger SSW and higher WS produce a deeper mixed layer and convective mixing, leading to high levels of nutrient concentrations. The higher chlorophyll a off southeastern Vietnam may be associated with the advective transport of the colder water extending from the Karimata Strait to southeastern Vietnam.

  18. 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

  19. Decadal variability in coupled sea-ice-thermohaline circulation systems

    SciTech Connect

    Yang, J.; Neelin, J.D.

    1997-12-01

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

  20. Variability of oceanic carbon cycle in the North Pacific from seasonal to decadal scales

    NASA Astrophysics Data System (ADS)

    Xiu, Peng; Chai, Fei

    2014-08-01

    Variability of upper-ocean carbon cycle in the North Pacific during 1958-2010 period is investigated using a physical-biogeochemical model. Comparisons with in situ data from five different oceanographic environments in the South China Sea, Monterey Bay, North Pacific gyre, northwestern Pacific, and Gulf of Alaska indicate that the model usually captures observed seasonal and interannual variability in both sea surface pCO2 and sea-air CO2 flux. Seasonal variability of pCO2 and CO2 flux in the North Pacific follows the change in sea surface temperature (SST) closely with high and low values in summer and winter, respectively. Total CO2 modifies pCO2 seasonal pattern in an opposite manner with respect to SST, and surface wind speed modifies the magnitude of CO2 flux variations. On interannual and decadal time scales, sea surface pCO2 is primarily controlled by anthropogenic CO2, followed by modulations by the El Niño-Southern Oscillation and the Pacific Decadal Oscillation (PDO), while sea-air CO2 flux is significantly regulated by the PDO and the North Pacific Gyre Oscillation (NPGO). We show that anthropogenic CO2 tends to amplify the influence on CO2 flux from the PDO but to damp the influence from the NPGO.

  1. Polar lightning and decadal-scale cloud variability on Jupiter.

    PubMed

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

    2007-10-12

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

  2. HERSCHEL OBSERVATIONS OF CATACLYSMIC VARIABLES

    SciTech Connect

    Harrison, Thomas E.; Hamilton, Ryan T.; Tappert, Claus; Hoffman, Douglas I.; Campbell, Ryan K. E-mail: rthamilt@nmsu.edu E-mail: dhoffman@ipac.caltech.edu

    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.

  3. IUE observations of cataclysmic variable

    NASA Astrophysics Data System (ADS)

    Szkody, Paula

    1993-06-01

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

  4. IUE observations of cataclysmic variable

    NASA Technical Reports Server (NTRS)

    Szkody, Paula

    1993-01-01

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

  5. Decadal variability in the occurrence of wintertime haze in central eastern China tied to the Pacific Decadal Oscillation

    NASA Astrophysics Data System (ADS)

    Zhao, Sen; Li, Jianping; Sun, Cheng

    2016-06-01

    Haze is a serious issue in China with increasing concerns, and understanding the factors driving decadal-scale variations in haze occurrence is relevant for government policymaking. Using a comprehensive observational haze dataset, we demonstrate notable decadal fluctuations in the number of haze days (HD) during winter in central eastern China, showing a decline since the mid-1980s. The leading mode of the wintertime HD features an increasing trend for 1959–2012 in eastern China, highly correlated with China’s gross domestic product (GDP) that represents increasing trend of pollutant emissions, and to a lesser extent meteorological factors. The second mode shows decadal variations in central eastern China associated with Pacific Decadal Oscillation (PDO). Observations and numerical simulations suggest that Mongolia High and corresponding descending motion tend to be enhanced (weakened) in central eastern China during the positive (negative) phase of PDO. With PDO shifting towards a negative phase, the weakened Mongolia High and ascending anomalies make the air unstable and conduce to the spread of pollutants, leading to the decline in the wintertime HD over central eastern China since the mid-1980s. Based on above physical mechanisms, a linear model based on PDO and GDP metrics provided a good fit to the observed HD.

  6. Decadal variability in the occurrence of wintertime haze in central eastern China tied to the Pacific Decadal Oscillation

    PubMed Central

    Zhao, Sen; Li, Jianping; Sun, Cheng

    2016-01-01

    Haze is a serious issue in China with increasing concerns, and understanding the factors driving decadal-scale variations in haze occurrence is relevant for government policymaking. Using a comprehensive observational haze dataset, we demonstrate notable decadal fluctuations in the number of haze days (HD) during winter in central eastern China, showing a decline since the mid-1980s. The leading mode of the wintertime HD features an increasing trend for 1959–2012 in eastern China, highly correlated with China’s gross domestic product (GDP) that represents increasing trend of pollutant emissions, and to a lesser extent meteorological factors. The second mode shows decadal variations in central eastern China associated with Pacific Decadal Oscillation (PDO). Observations and numerical simulations suggest that Mongolia High and corresponding descending motion tend to be enhanced (weakened) in central eastern China during the positive (negative) phase of PDO. With PDO shifting towards a negative phase, the weakened Mongolia High and ascending anomalies make the air unstable and conduce to the spread of pollutants, leading to the decline in the wintertime HD over central eastern China since the mid-1980s. Based on above physical mechanisms, a linear model based on PDO and GDP metrics provided a good fit to the observed HD. PMID:27282140

  7. Decadal variability in the occurrence of wintertime haze in central eastern China tied to the Pacific Decadal Oscillation.

    PubMed

    Zhao, Sen; Li, Jianping; Sun, Cheng

    2016-01-01

    Haze is a serious issue in China with increasing concerns, and understanding the factors driving decadal-scale variations in haze occurrence is relevant for government policymaking. Using a comprehensive observational haze dataset, we demonstrate notable decadal fluctuations in the number of haze days (HD) during winter in central eastern China, showing a decline since the mid-1980s. The leading mode of the wintertime HD features an increasing trend for 1959-2012 in eastern China, highly correlated with China's gross domestic product (GDP) that represents increasing trend of pollutant emissions, and to a lesser extent meteorological factors. The second mode shows decadal variations in central eastern China associated with Pacific Decadal Oscillation (PDO). Observations and numerical simulations suggest that Mongolia High and corresponding descending motion tend to be enhanced (weakened) in central eastern China during the positive (negative) phase of PDO. With PDO shifting towards a negative phase, the weakened Mongolia High and ascending anomalies make the air unstable and conduce to the spread of pollutants, leading to the decline in the wintertime HD over central eastern China since the mid-1980s. Based on above physical mechanisms, a linear model based on PDO and GDP metrics provided a good fit to the observed HD. PMID:27282140

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  9. Interannual-to-decadal variability and trends of sea level in the South China Sea

    NASA Astrophysics Data System (ADS)

    Cheng, Xuhua; Xie, Shang-Ping; Du, Yan; Wang, Jing; Chen, Xiao; Wang, Juan

    2016-05-01

    Interannual-to-decadal variability and trends of sea level in the South China Sea (SCS) are studied using altimetric data during 1993-2012 and reconstructed sea level data from 1950-2009. The interannual variability shows a strong seasonality. Surface wind anomalies associated with El Niño-Southern Oscillation explain the sea-level anomaly pattern in the interior SCS, while Rossby waves radiated from the eastern boundary dominate the sea-level variability in the eastern SCS. Decadal variability of sea level in the SCS follows that in the western tropical Pacific, with large variance found west of Luzon Island. Local atmospheric forcing makes a negative contribution to decadal variability in the central SCS, and Rossby waves radiated from the eastern boundary appear to be important. During 1993-2012, decadal sea level averaged in the SCS is significantly correlated with the Pacific Decadal Oscillation (PDO) ( r = -0.96). The decadal variability associated with the PDO accounts for most part of sea-level trends in the SCS in the last two decades.

  10. North Pacific decadal variability in the CMIP5 last millennium simulations

    NASA Astrophysics Data System (ADS)

    Fleming, Laura E.; Anchukaitis, Kevin J.

    2016-02-01

    The Pacific ocean-atmosphere system exerts an important influence on the climate of Asia and North America, but the limited length of the observational record prevents a complete understanding of its bidecadal and multidecadal time scales. Paleoclimate reconstructions provide one source of information on longer time scales, although they differ in their estimation of the behavior of the Pacific decadal oscillation (PDO) prior to the instrumental period. Forced general circulation model simulations offer complementary long-term perspectives on both the history and dynamics of this important mode of variability. Here, we analyze the PDO in the ensemble of CMIP5/PMIP3 last millennium (past1000 + historical) simulations. We evaluate the modeled spatial, temporal, and spectral characteristics of this mode, as well as teleconnections between North Pacific variability and global climate. All models produce a mode of North Pacific variability over the last millennium with spatial patterns and spectral power density similar to observations. CCSM, FGOALS, and IPSL best reproduce observed spatial patterns, spectral characteristics, and teleconnections to terrestrial regions used in paleoclimate proxy reconstructions. In these simulations, the PDO shows no consistent response to solar or volcanic forcing.

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

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, Lakshmi

    This study has investigated the influence of the decadal variability associated with global oceans on South Asian monsoon and El Nino-Southern Oscillation (ENSO)-monsoon relation. The results are based on observational analysis using long records of monsoon rainfall and circulation and coupled general circulation model experiments using the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) version 4 model. The multi-channel singular spectrum analysis (MSSA) of the observed rainfall over India yields three decadal modes. The first mode (52 year period) is associated with the Atlantic Multidecadal Oscillation (AMO), the second one (21 year) with the Pacific Decadal Oscillation (PDO) and the third mode (13 year) with the Atlantic tripole. The existence of these decadal modes in the monsoon was also found in the control simulation of NCAR CCSM4. The regionally de-coupled model experiments performed to isolate the influence of North Pacific and North Atlantic also substantiate the above results. The relation between the decadal modes in the monsoon rainfall with the known decadal modes in global SST is examined. The PDO has significant negative correlation with the Indian Monsoon Rainfall (IMR). The mechanism for PDO-monsoon relation is hypothesized through the seasonal footprinting mechanism and further through Walker and Hadley circulations. The model results also confirm the negative correlation between PDO and IMR and the mechanism through which PDO influences monsoon. Both observational and model analysis show that droughts (floods) are more likely over India than floods (droughts) when ENSO and PDO are in their warm (cold) phase. This study emphasizes the importance of carefully distinguishing the different decadal modes in the SST in the North Atlantic Ocean as they have different impacts on the monsoon. The AMO exhibits significant positive correlation with the IMR while the Atlantic tripole has significant negative

  12. Investigating the role of the Sun, the quasi-biennial oscillation, and the pacific decadal oscillation on decadal climate variability of the stratosphere

    NASA Astrophysics Data System (ADS)

    Kren, Andrew Charles

    Assessing and distinguishing between natural climate variability and anthropogenic forcing, and quantifying their relative contributions to climate change is a formidable challenge. Understanding how variations in the Sun and natural modes of variability affect the climate system will aid future climate projections. The Sun is Earth's primary source of energy, providing a global average irradiance that is four orders of magnitude greater than the largest secondary energy source, Earth's interior heat flux. Variations in the Sun occur both in the total solar irradiance and solar spectral irradiance (SSI), impacting the ocean, troposphere, and stratosphere via atmospheric winds, temperature, and planetary waves. Yet one of the difficulties in assessing the solar response is the fact that several internal modes of variability are present which can prevent accurate detection. The response of the stratosphere to the combined interaction of the Quasi-Biennial Oscillation (QBO) and the solar cycle was investigated using the Whole Atmosphere Community Climate Model (WACCM). Transient and fully coupled simulations that included observed greenhouse gases, varying SSI, and an internally generated QBO, were analyzed. A persistent wintertime solar response in the polar vortex when stratifying by QBO phase was not found. Results contradict conclusions drawn from observational data over the period 1953-2012. The Pacific Decadal Oscillation (PDO) is defined as the leading mode of sea surface temperature variability in the North Pacific, oscillating on decadal timescales. Changes in the PDO are linked to changes in precipitation, temperature, sea-level pressure, and sea-level height changes. Here we show in WACCM that the PDO also influences the stratosphere, with a weaker polar vortex in the positive PDO phase, which has implications for decadal prediction. Some evidence also points to possible modulation of the PDO by the solar cycle, which may provide an additional pathway for

  13. 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

  14. Reconciling two alternative mechanisms behind bi-decadal variability in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Ortega, Pablo; Mignot, Juliette; Swingedouw, Didier; Sévellec, Florian; Guilyardi, Eric

    2015-09-01

    Understanding the preferential timescales of variability in the North Atlantic, usually associated with the Atlantic meridional overturning circulation (AMOC), is essential for the prospects for decadal prediction. However, the wide variety of mechanisms proposed from the analysis of climate simulations, potentially dependent on the models themselves, has stimulated the debate of which processes take place in reality. One mechanism receiving increasing attention, identified both in idealized models and observations, is a westward propagation of subsurface buoyancy anomalies that impact the AMOC through a basin-scale intensification of the zonal density gradient, enhancing the northward transport via thermal wind balance. In this study, we revisit a control simulation from the Institut Pierre-Simon Laplace Coupled Model 5A (IPSL-CM5A), characterized by a strong AMOC periodicity at 20 years, previously explained by an upper ocean-atmosphere-sea ice coupled mode driving convection activity south of Iceland. Our study shows that this mechanism interacts constructively with the basin-wide propagation in the subsurface. This constructive feedback may explain why bi-decadal variability is so intense in this coupled model as compared to others.

  15. Aerosols impact on the multi-decadal SST variability simulation over the North Pacific

    NASA Astrophysics Data System (ADS)

    Boo, Kyung-On; Booth, Ben; Byun, Young-Hwa; Cho, ChunHo; Lee, Johan; Park, Soo-Hyun; Shim, Sung-Bo; Park, Sung-Bin

    2013-04-01

    Aerosol emission by the anthropogenic source has increased in the 20th century and the effects on climate have received much attention for understanding of historical climate change and variability. Aerosols contribute to change solar radiation at the surface directly and indirectly enhance radiative effect through cloud properties changes, altering surface climate and large-scale atmospheric circulation as well. Recently Oldenborgh et al. [2012] , Chikamoto et al. [2012] and Wang et al.[2012] showed the Pacific decadal scale variability is able to be affected by the aerosols. Since climate response in global warming is modulated by decadal variability and the Asian monsoon circulation changes are known to be affected by anthropogenic aerosols [Lau et al., 2006; Ramana et al., 2010], aerosol impact over the Pacific needs to be studied. Both effects by natural and anthropogenic emissions are important. To simulate the North Atlantic climate variability, aerosol forcing is important [Mann and Emanuel, 2006; Oldenborgh et al., 2012]. In particular, it is known to be better represented when indirect effect by anthropogenic emitted aerosols is considered [Booth et al, 2011]. Therefore, considering previous studies, this study investigates aerosol effect with indirect effect by anthropogenic aerosol emission over the Pacific. In this study, comparison between historical run and fixed aerosol experiments using HadGEM2-AO shows that multidecadal variability in historical run is closer to the observed ERSST variability over the North Pacific. In detrended SST anomalies, warming and cooling in the period of 1925-1960 and 1965-1990 are reproduced in aerosol forced historical simulation. The climate variability is partly related by the shortwave changes in response to aerosols emission. There is cooling effect, directly. Here, we are interested in indirect cloud property changes and the Pacific SST variability is investigated using previous results [Williams et al., 2001

  16. 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.

  17. 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

  18. Pacific Decadal Variability and Central Pacific Warming El Niño in a Changing Climate

    SciTech Connect

    Di Lorenzo, Emanuele

    2015-02-27

    This research aimed at understanding the dynamics controlling decadal variability in the Pacific Ocean and its interactions with global-scale climate change. The first goal was to assess how the dynamics and statistics of the El Niño Southern Oscillation and the modes of Pacific decadal variability are represented in global climate models used in the IPCC. The second goal was to quantify how decadal dynamics are projected to change under continued greenhouse forcing, and determine their significance in the context of paleo-proxy reconstruction of long-term climate.

  19. Estimating decadal variability in sea level from tide gauge records: An application to the North Sea

    NASA Astrophysics Data System (ADS)

    Frederikse, Thomas; Riva, Riccardo; Slobbe, Cornelis; Broerse, Taco; Verlaan, Martin

    2016-03-01

    One of the primary observational data sets of sea level is represented by the tide gauge record. We propose a new method to estimate variability on decadal time scales from tide gauge data by using a state space formulation, which couples the direct observations to a predefined state space model by using a Kalman filter. The model consists of a time-varying trend and seasonal cycle, and variability induced by several physical processes, such as wind, atmospheric pressure changes and teleconnection patterns. This model has two advantages over the classical least-squares method that uses regression to explain variations due to known processes: a seasonal cycle with time-varying phase and amplitude can be estimated, and the trend is allowed to vary over time. This time-varying trend consists of a secular trend and low-frequency variability that is not explained by any other term in the model. As a test case, we have used tide gauge data from stations around the North Sea over the period 1980-2013. We compare a model that only estimates a trend with two models that also remove intra-annual variability: one by means of time series of wind stress and sea level pressure, and one by using a two-dimensional hydrodynamic model. The last two models explain a large part of the variability, which significantly improves the accuracy of the estimated time-varying trend. The best results are obtained with the hydrodynamic model. We find a consistent low-frequency sea level signal in the North Sea, which can be linked to a steric signal over the northeastern part of the Atlantic.

  20. 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

  1. Prioritizing Global Observations Along Essential Climate Variables

    NASA Astrophysics Data System (ADS)

    Bojinski, Stephan; Richter, Carolin

    2010-12-01

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

  2. Sahel decadal rainfall variability and the role of model horizontal resolution

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Substantial low-frequency rainfall fluctuations occurred in the Sahel throughout the twentieth century, causing devastating drought. Modeling these low-frequency rainfall fluctuations has remained problematic for climate models for many years. Here we show using a combination of state-of-the-art rainfall observations and high-resolution global climate models that changes in organized heavy rainfall events carry most of the rainfall variability in the Sahel at multiannual to decadal time scales. Ability to produce intense, organized convection allows climate models to correctly simulate the magnitude of late-twentieth century rainfall change, underlining the importance of model resolution. Increasing model resolution allows a better coupling between large-scale circulation changes and regional rainfall processes over the Sahel. These results provide a strong basis for developing more reliable and skilful long-term predictions of rainfall (seasons to years) which could benefit many sectors in the region by allowing early adaptation to impending extremes.

  3. Multi-decadal variability of the eastern North Atlantic subpolar gyre

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  5. 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.

  6. A decade of progress in observing and modelling Antarctic subglacial water systems.

    PubMed

    Fricker, Helen A; Siegfried, Matthew R; Carter, Sasha P; Scambos, Ted A

    2016-01-28

    In the decade since the discovery of active Antarctic subglacial water systems by detection of subtle surface displacements, much progress has been made in our understanding of these dynamic systems. Here, we present some of the key results of observations derived from ICESat laser altimetry, CryoSat-2 radar altimetry, Operation IceBridge airborne laser altimetry, satellite image differencing and ground-based continuous Global Positioning System (GPS) experiments deployed in hydrologically active regions. These observations provide us with an increased understanding of various lake systems in Antarctica: Whillans/Mercer Ice Streams, Crane Glacier, Recovery Ice Stream, Byrd Glacier and eastern Wilkes Land. In several cases, subglacial water systems are shown to control ice flux through the glacier system. For some lake systems, we have been able to construct more than a decade of continuous lake activity, revealing internal variability on time scales ranging from days to years. This variability indicates that continuous, accurate time series of altimetry data are critical to understanding these systems. On Whillans Ice Stream, our results from a 5-year continuous GPS record demonstrate that subglacial lake flood events significantly change the regional ice dynamics. We also show how models for subglacial water flow have evolved since the availability of observations of lake volume change, from regional-scale models of water routeing to process models of channels carved into the subglacial sediment instead of the overlying ice. We show that progress in understanding the processes governing lake drainage now allows us to create simulated lake volume time series that reproduce time series from satellite observations. This transformational decade in Antarctic subglacial water research has moved us significantly closer to understanding the processes of water transfer sufficiently for inclusion in continental-scale ice-sheet models. PMID:26667904

  7. Global Ocean Evaporation: How Well Can We Estimate Interannual to Decadal Variability?

    NASA Technical Reports Server (NTRS)

    Robertson, Franklin R.; Bosilovich, Michael G.; Roberts, Jason B.; Wang, Hailan

    2015-01-01

    Evaporation from the world's oceans constitutes the largest component of the global water balance. It is important not only as the ultimate source of moisture that is tied to the radiative processes determining Earth's energy balance but also to freshwater availability over land, governing habitability of the planet. Here we focus on variability of ocean evaporation on scales from interannual to decadal by appealing to three sources of data: the new MERRA-2 (Modern-Era Retrospective analysis for Research and Applications -2); climate models run with historical sea-surface temperatures, ice and atmospheric constituents (so-called AMIP experiments); and state-of-the-art satellite retrievals from the Seaflux and HOAPS (Hamburg Ocean-Atmosphere Parameters and Fluxes from Satellite) projects. Each of these sources has distinct advantages as well as drawbacks. MERRA-2, like other reanalyses, synthesizes evaporation estimates consistent with observationally constrained physical and dynamical models-but data stream discontinuities are a major problem for interpreting multi-decadal records. The climate models used in data assimilation can also be run with lesser constraints such as with SSTs and sea-ice (i.e. AMIPs) or with additional, minimal observations of surface pressure and marine observations that have longer and less fragmentary observational records. We use the new ERA-20C reanalysis produced by ECMWF embodying the latter methodology. Still, the model physics biases in climate models and the lack of a predicted surface energy balance are of concern. Satellite retrievals and comparisons to ship-based measurements offer the most observationally-based estimates, but sensor inter-calibration, algorithm retrieval assumptions, and short records are dominant issues. Our strategy depends on maximizing the advantages of these combined records. The primary diagnostic tool used here is an analysis of bulk aerodynamic computations produced by these sources and uses a first

  8. Analysis and modeling of decadal and long-term variability of coastal California summer temperature changes

    NASA Astrophysics Data System (ADS)

    Sequera, Pedro

    Summer average daily maximum temperature (Tmax) trends for 1950-2010 were calculated for 241 locations along all of California by use of daily max temperatures from NWS Coop sites to understand the spatial and temporal variabilities of the previously reported summer coastal-cooling. Results show that coastal-cooling appears almost continuously throughout the California coast in locations open to marine air penetrations for the period of 1970-2010. Correlations with the Pacific Decadal Oscillation (PDO) Index show that coastal-cooling disappears during the increasing PDO period (1950-1985). The most influential factor(s) on California summer coastal temperatures, i.e., Greenhouse Gas (GHG) warming, PDO and changes in Land Cover/Land Use (LCLU), were determined through numerical atmospheric modeling using the Weather Research & Forecasting (WRF) model. Combined results from observations, reanalysis and modeling lead to the conclusion that PDO is the main mechanism of decadal variability of California summer temperatures, dominating over global GHG-warming effects. PDO affects both coastal and inland temperatures by controlling the position and intensity of the two dominating global circulation patterns on California summer: the semi-permanent Pacific High Pressure System and the continental Thermal-Low. Coastal cooling will rise on decreasing PDO periods, where the warming of inland regions and cooling of nearshore Sea Surface Temperatures (SSTs) results in an increase in sea-breeze activity. Coastal-warming results in increasing periods of the PDO. Global warming induced by GHG and hyper-urbanization were found to be major sources of coastal warming over complete PDO cycles (1950-2010).

  9. Decadal-scale thermohaline variability in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Hutchinson, K.; Swart, S.; Meijers, A.; Ansorge, I.; Speich, S.

    2016-05-01

    An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 ± 0.11°C decade-1 and 0.006 ± 0.014 decade-1, and diabatic differences of -0.044 ± 0.13°C decade-1 and -0.01 ± 0.017 decade-1 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000 dbar of the ACC with a mean warming of 0.12 ± 0.087°C decade-1. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (-0.17°C decade-1) and freshening (-0.032 decade-1) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.31°C decade-1) and salinification (0.014 decade-1) of AAIW.

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

    NASA Astrophysics Data System (ADS)

    Karnauskas, Kristopher B.

    2014-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  14. Decadal variability of the Turner Angle in the Mediterranean Sea and its implications for double diffusion

    NASA Astrophysics Data System (ADS)

    Meccia, Virna L.; Simoncelli, Simona; Sparnocchia, Stefania

    2016-08-01

    The physical reanalysis component of the Mediterranean Forecasting System is used to construct a high-resolution three-dimensional atlas of the Turner Angle. An assessment of the model quality shows a maximum degree of agreement with observations in the water column between 150 and 1000 m depth. The mean state of the favourable conditions for double diffusion processes is evaluated and the recent decadal variability is studied in terms of changes in the water mass properties. The results show that approximately 50% of the Mediterranean Sea is favourable to double diffusion processes, from which around 47% is associated with salt fingering. The Tyrrhenian, Ionian and southwestern Mediterranean are the most vulnerable basins to salt fingering, and the strongest processes can occur in the Tyrrhenian deep waters. Diffusive convection is most likely to occur in the Ionian, Aegean and eastern Mediterranean at vertical levels deeper than 1000 m. The observed gradual warming and salinification of the Mediterranean after 1997 decreased and increased the possibilities of the occurrence of salt fingers and double diffusive convections, respectively. The climatological atlas that is presented in this paper provides a three-dimensional picture of the regions that are either doubly stable or favourable to double diffusion instability and allows for the characterization of the diffusive properties of the water masses.

  15. Variability and evolution of global land surface phenology over the past three decades (1982-2012).

    PubMed

    Garonna, Irene; de Jong, Rogier; Schaepman, Michael E

    2016-04-01

    Monitoring land surface phenology (LSP) is important for understanding both the responses and feedbacks of ecosystems to the climate system, and for representing these accurately in terrestrial biosphere models. Moreover, by shedding light on phenological trends at a variety of scales, LSP provides the potential to fill the gap between traditional phenological (field) observations and the large-scale view of global models. In this study, we review and evaluate the variability and evolution of satellite-derived growing season length (GSL) globally and over the past three decades. We used the longest continuous record of Normalized Difference Vegetation Index data available to date at global scale to derive LSP metrics consistently over all vegetated land areas and for the period 1982-2012. We tested GSL, start- and end-of-season metrics (SOS and EOS, respectively) for linear trends as well as for significant trend shifts over the study period. We evaluated trends using global environmental stratification information in place of commonly used land cover maps to avoid circular findings. Our results confirmed an average lengthening of the growing season globally during 1982-2012 - averaging 0.22-0.34 days yr(-1), but with spatially heterogeneous trends. About 13-19% of global land areas displayed significant GSL change, and over 30% of trends occurred in the boreal/alpine biome of the Northern Hemisphere, which showed diverging GSL evolution over the past three decades. Within this biome, the 'Cold and Mesic' environmental zone appeared as an LSP change hotspot. We also examined the relative contribution of SOS and EOS to the overall changes, finding that EOS trends were generally stronger and more prevalent than SOS trends. These findings constitute a step towards the identification of large-scale phenological drivers of vegetated land surfaces, necessary for improving phenological representation in terrestrial biosphere models. PMID:26924776

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    Earth's climate exhibits internal modes of variability on various timescales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions. We report an inter-annual GMT variability of about ±0.1° C originating solely from natural variability in the model ensemble. By decomposing the GMT variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade-1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC-deep-ocean system, our results are inconclusive about the role of this feedback in the model ensemble.

  17. The role of Atlantic Multi-decadal Oscillation in the global mean temperature variability

    NASA Astrophysics Data System (ADS)

    Chylek, Petr; Klett, James D.; Dubey, Manvendra K.; Hengartner, Nicolas

    2016-02-01

    The global mean 1900-2015 warming simulated by 42 Coupled Models Inter-comparison Project, phase 5 (CMIP5) climate models varies between 0.58 and 1.70 °C. The observed warming according to the NASA GISS temperature analysis is 0.95 °C with a 1200 km smoothing radius, or 0.86 °C with a 250 km smoothing radius. The projection of the future 2015-2100 global warming under a moderate increase of anthropogenic radiative forcing (RCP4.5 scenario) by individual models is between 0.7 and 2.3 °C. The CMIP5 climate models agree that the future climate will be warmer; however, there is little consensus as to how large the warming will be (reflected by an uncertainty of over a factor of three). A parsimonious statistical regression model with just three explanatory variables [anthropogenic radiative forcing due to greenhouse gases and aerosols (GHGA), solar variability, and the Atlantic Multi-decadal Oscillation (AMO) index] accounts for over 95 % of the observed 1900-2015 temperature variance. This statistical regression model reproduces very accurately the past warming (0.96 °C compared to the observed 0.95 °C) and projects the future 2015-2100 warming to be around 0.95 °C (with the IPCC 2013 suggested RCP4.5 radiative forcing and an assumed cyclic AMO behavior). The AMO contribution to the 1970-2005 warming was between 0.13 and 0.20 °C (depending on which AMO index is used) compared to the GHGA contribution of 0.49-0.58 °C. During the twenty-first century AMO cycle the AMO contribution is projected to remain the same (0.13-0.20 °C), while the GHGA contribution is expected to decrease to 0.21-0.25 °C due to the levelling off of the GHGA radiative forcing that is assumed according to the RCP4.5 scenario. Thus the anthropogenic contribution and natural variability are expected to contribute about equally to the anticipated global warming during the second half of the twenty-first century for the RCP4.5 trajectory.

  18. The role of Atlantic Multi-decadal Oscillation in the global mean temperature variability

    DOE PAGESBeta

    Chylek, Petr; Klett, James D.; Dubey, Manvendra K.; Hengartner, Nicolas

    2016-02-20

    We simulated the global mean 1900–2015 warming by 42 Coupled Models Inter-comparison Project, phase 5 (CMIP5) climate models varies between 0.58 and 1.70 °C. The observed warming according to the NASA GISS temperature analysis is 0.95 °C with a 1200 km smoothing radius, or 0.86 °C with a 250 km smoothing radius. The projection of the future 2015–2100 global warming under a moderate increase of anthropogenic radiative forcing (RCP4.5 scenario) by individual models is between 0.7 and 2.3 °C. The CMIP5 climate models agree that the future climate will be warmer; however, there is little consensus as to how largemore » the warming will be (reflected by an uncertainty of over a factor of three). Moreover, a parsimonious statistical regression model with just three explanatory variables [anthropogenic radiative forcing due to greenhouse gases and aerosols (GHGA), solar variability, and the Atlantic Multi-decadal Oscillation (AMO) index] accounts for over 95 % of the observed 1900–2015 temperature variance. This statistical regression model reproduces very accurately the past warming (0.96 °C compared to the observed 0.95 °C) and projects the future 2015–2100 warming to be around 0.95 °C (with the IPCC 2013 suggested RCP4.5 radiative forcing and an assumed cyclic AMO behavior). The AMO contribution to the 1970–2005 warming was between 0.13 and 0.20 °C (depending on which AMO index is used) compared to the GHGA contribution of 0.49–0.58 °C. During the twenty-first century AMO cycle the AMO contribution is projected to remain the same (0.13–0.20 °C), while the GHGA contribution is expected to decrease to 0.21–0.25 °C due to the levelling off of the GHGA radiative forcing that is assumed according to the RCP4.5 scenario. Therefore, the anthropogenic contribution and natural variability are expected to contribute about equally to the anticipated global warming during the second half of the twenty-first century for the RCP4.5 trajectory.« less

  19. 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

  20. Variability of Ocean Heat Uptake: Reconciling Observations and Models

    SciTech Connect

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

    2005-05-05

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

  1. The Hydroclimate of East Africa: Seasonal cycle, Decadal Variability, and Human-induced Climate Change

    NASA Astrophysics Data System (ADS)

    Yang, Wenchang

    The hydroclimate of East Africa shows distinctive variabilities on seasonal to decadal time scales and poses a great challenge to climatologists attempting to project its response to anthropogenic emissions of greenhouse gases (GHGs). Increased frequency and intensity of droughts over East Africa in recent decades raise the question of whether the drying trend will continue into the future. To address this question, we first examine the decadal variability of the East African rainfall during March--May (MAM, the major rainy season in East Africa) and assess how well a series of models simulate the observed features. Observational results show that the drying trend during MAM is associated with decadal natural variability of sea surface temperature (SST) variations over the Pacific Ocean. The multimodel mean of the SST-forced, Coupled Model Intercomparison Project Phase 5 (CMIP5) AMIP experiment models reproduces both the climatological annual cycle and the drying trend in recent decades. The fully coupled models from the CMIP5 historical experiment, however, have systematic errors in simulating the East African rainfall annual cycle by underestimating the MAM rainfall while overestimating the October--December (OND, the second rainy season in East Africa) rainfall. The multimodel mean of the historical coupled runs of the MAM rainfall anomalies, which is the best estimate of the radiatively-forced change, shows a weak wetting trend associated with anthropogenic forcing. However, the SST anomaly pattern associated with the MAM rainfall has large discrepancies with the observations. The errors in simulating the East African hydroclimate with coupled models raise questions about how reliable model projections of future East African climate are. This motivates a fundamental study of why East African climate is the way it is and why coupled models get it wrong. East African hydroclimate is characterized by a dry annual mean climatology compared to other deep tropical

  2. Decadal and Lower Frequency South Pacific Climate Variability Since 1619 AD from Replicated Coral Records

    NASA Astrophysics Data System (ADS)

    Linsley, B. K.; Wellington, G. M.; Kaplan, A.; Demenocal, P. B.

    2004-12-01

    both influenced to varying degrees by the South Pacific Convergence Zone (SPCZ) one explanation for the \\delta18O trend is that the SPCZ has been intensifying over the last 200 years with increasing cloud cover and rainfall as the surface ocean warmed. On decadal-interdecadal time-scales, comparison of the Fiji and Rarotonga coral \\delta18O series to other coral \\delta18O records from New Caledonia and the Great Barrier Reef indicates that some interdecadal climate shifts apparently were related to changes in the SPCZ and others apparently were unrelated to the SPCZ. This observation suggests the possibility that decadal-interdecadal climate variability in the South Pacific has multiple sources, and may at times be related to higher latitude South Pacific processes.

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

    USGS Publications Warehouse

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    HäKkinen, Sirpa

    2002-12-01

    The sea surface salinity (SSS) variability in the North Atlantic is investigated using numerical model simulations for the last 50 years based on atmospheric forcing variability from the Comprehensive Atmosphere Ocean Data Set (COADS) and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The focus here is the SSS variability in the subpolar region. The seasonality of the subpolar surface salinity variability is prominent with the maximum standard deviation (SD) occurring in the summer/fall period so that the amplitude of the summer SSS anomalies far exceed those of the wintertime. The interannual SSS variability in the subpolar gyre can be attributed mainly to excess ice melt, while the longer-term (decadal) variability is associated with meridional overturning variability. In these two hindcasts, the deep mixing (which drives overturning changes) is forced by heat flux variability so that weak subpolar heat loss and subsequent weak overturning are usually manifested in fresh surface conditions in the subpolar gyre within 2 years. This is because the role of deep convection is to mix down the net fresh water input received by the high latitudes. Hence, at the lack of widespread deep mixing, a signal of slowing down overturning, the fresh water input that would be expected based on climatology would accumulate at the surface.

  5. What has driven the interannual variability of atmospheric methane concentrations over the last three decades?

    NASA Astrophysics Data System (ADS)

    Coulon, A.; Stenke, A.; Peter, T.

    2015-12-01

    Atmospheric methane (CH4) is the second most anthropogenic greenhouse gas (IPCC, 2013). Observations of methane concentrations at the surface from the last three decades show puzzling fluctuations; from the early 1980s they indicate a nearly constant increase of 8.7 ppbv/year until 2000, including a slowdown after 1990. After a period of about eight years with near zero growh rates, methane concentrations have again been rising since 2007 (Sussmann et al., 2012). Simulations forced with prescribed meteorological fields have been performed for the 1980-2010 period using the chemistry-climate model (CCM) SOCOL. 48 methane tracers have been included in SOCOL and used together with flux boundary conditions for CH4 to allow the tracking of methane emissions from different source categories, such as wetlands, rice paddies, ruminants, industry…, as well as geographical regions. These new simulations provide an innovative way to better understand methane variability, both in terms of emission changes and changes in tropospheric OH, which is investigated with a tracer based on methyl chloroform emissions. An analysis of the tracers elucidates the impact of different emission source categories for different time periods. For 1980-1990, positive gobal methane growth rates result from increasing anthropogenic emissions over Europe, India, and China. A decrease of anthropogenic emissions over Europe after 1990 is consistent with the slow down in the global methane growth rate for 1990-2000. During this period short-lived events such as the eruption of Mount Pinatubo and the strong 1997-1998 El-Niño also affect global methane concentrations, largely by a decrease in wetlands emissions during 1992 and high levels of biomass burning in tropical Asia, respectively. The near-zero trend is maintained after 2000 because of reduced natural emissions, again from wetlands. After 2005, our simulations show a positive global methane growth rate, in agreement with the observations, due

  6. PDO and ENSO modulations intensified decadal sea level variability in the tropical Pacific

    NASA Astrophysics Data System (ADS)

    Moon, Jae-Hong; Song, Y. Tony; Lee, HuiKyo

    2015-12-01

    According to long-term sea level reconstruction and steric sea level data, regional sea levels in the tropical Pacific have oscillated between east and west on a decadal time scale over the past 60 years, but the oscillation has been intensified significantly in the last three decades. Using conditional composite analysis, we show that the recent intensification in sea level variability is caused by modulation between the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO), i.e., an El Niño in a positive PDO or a La Niña in a negative PDO phase. Our analysis of meteorological fields indicates that atmospheric circulation associated with the changes in ENSO-PDO phase relationship plays a positive role in enhancing the decadal sea level oscillation. The intensified sea level oscillation, when superimposed on the global trend of sea level rise, will have profound implications for coastal communities, therefore, the combined effect of PDO and ENSO should be taken into account in the decadal sea level prediction in the tropical Pacific.

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    New evidence emerged from satellite data analyses and modeling study indicate that patterns of vegetation spatial distribution and vegetation structure are important in the soil-vegetation-atmosphere system (SVAS) and including a fully coupled dynamic vegetation/climate process is of imminent important in increasing our understanding and predictive capabilities of the SVAS. We apply the Simplified Simple Biosphere Model version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID) to investigate the interactions between vegetation dynamics and climate variability for West Africa. The TRIFFID is a dynamic vegetation model, in which the relevant vegetation spatial distribution and structure are modeled based on the surface carbon balance. SSiB4 is a biophysical model based on surface water and energy balance and produces carbon assimilation rate for TRIFFID. The offline SSiB2, which uses specified vegetation spatial distribution and vegetation structure with no inter-annual and decadal variability, and SSiB4/TRIFFID are integrated using the observed precipitation and reanalysis-based meteorological forcing from 1948 to 2006 with 1 degree horizontal resolution over West Africa. West Africa is a diverse climatic and ecosystem region and suffered the most severe and longest drought in the world during the Twentieth Century since the later 1960s. The simulation results indicate that the SSiB4/TRIFFID model was able to produce reasonable vegetation spatial distributions, generally consistent with the products derived from satellites and with the Sahel drought in the 1970s and the 1980s and the partial recovery in the 1990s and the 2000s. The SSiB4/TRIFFID and SSIB2 results show quite different spatial patterns and vegetation structure, which lead to differences in surface net radiation, latent and sensible heat flux partitioning, soil moisture and runoff distribution, and carbon cycles at seasonal and inter-decadal time scales

  9. 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.

  10. 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 ΔT(z), the change in this profile in response to external forcing. T(z) has a strong latitudinal dependence, as does ΔT(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

  11. Southern ocean SST variability and its relationship with ENSO on inter-decadal time scales

    NASA Astrophysics Data System (ADS)

    Yan, Li; Du, Yan; Zhang, Lan

    2013-06-01

    Empirical orthogonal function (EOF) analysis reveals a co-variability of Sea surface temperatures (SSTs) in the Southern Hemisphere (0°-60°S). In the South Indian and Atlantic Oceans, there is a subtropical dipole pattern slanted in the southwest-northeast direction. In the South Pacific Ocean, a meridional tripole structure emerges, whose middle pole co-varies with the dipoles in the South Indian and Atlantic Oceans and is used in this study to track subtropical Pacific variability. The South Indian and Atlantic Ocean dipoles and the subtropical Pacific variability are phase-locked in austral summer. On the inter-decadal time scales, the dipoles in the South Indian and Atlantic Oceans weaken in amplitude after 1979/1980. No such weakening is found in the subtropical South Pacific Ocean. Interestingly, despite the reduced amplitude, the correlation of the Indian Ocean and Atlantic dipoles with El Niño and Southern Oscillation (ENSO) are enhanced after 1979/1980. The same increase in correlation is found for subtropical South Pacific variability after 1979/1980. These inter-decadal modulations imply that the Southern Hemisphere participates in part of the climate shift in the late 1970s. The correlation between Southern Hemisphere SST and ENSO reduces after 2000.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  13. Multi-Decadal Modulations in the Variability of the East Asian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Nakamura, H.; Machimura, T.; Ogawa, S.; Kosaka, Y.; Nishii, K.; Miyasaka, T.

    2015-12-01

    The East Asian summer monsoon fluctuates from its climatological activity on monthly and interannual time scales, and the most dominant pattern of the variability is known as the Pacific-Japan (PJ) pattern. Characterized by a meridional teleconnection in anomalous activity of the Meiyu/Baiu rainband, tropical storms and a surface subtropical anticyclone (the Bonin High) in between, the PJ pattern exerts substantial influence on summertime climatic conditions over East Asia and the western North Pacific. Despite the recent warming trend observed in its background state, no assessment thus far has been made on how substantially the PJ has undergone, if any, multi-decadal modulations in its structure and/or dominance. Through an EOF analysis applied to a new dataset of global atmospheric reanalysis (JRA-55), the predominance of the PJ pattern is confirmed as being extracted in the leading EOF of lower-tropospheric monthly vorticity anomalies over 55 recent years. Both efficient barotropic/baroclinic energy conversion from the climatological-mean state and efficient generation of available potential energy through anomalous convective activity over the tropical western Pacific are shown to be essential for the maintenance of the monthly atmospheric anomalies of the PJ pattern over the entire 55-year period. At the same time, however, the same EOF analysis as above but applied separately to each of the sub-periods reveals a distinct signature of long-term modulations in amplitude and thus the dominance of the PJ pattern. While being extracted in the first EOF up to the 1980s, the PJ pattern is extracted in the second EOF in the period since the 1990s with marked reductions in both the variance fraction explained and the efficiency of energy conversion/generation. The resultant modulations of the summertime meridional teleconnection are also discussed with implications for future changes.

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

    USGS Publications Warehouse

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

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

  15. EUVE Observations of Nonmagnetic Cataclysmic Variables

    SciTech Connect

    Mauche, C W

    2001-09-05

    The authors summarize EUVE's contribution to the study of the boundary layer emission of high accretion-rate nonmagnetic cataclysmic variables, especially the dwarf novae SS Cyg, U Gem, VW Hyi, and OY Car in outburst. They discuss the optical and EUV light curves of dwarf nova outbursts, the quasi-coherent oscillations of the EUV flux of SS Cyg, the EUV spectra of dwarf novae, and the future of EUV observations of cataclysmic variables.

  16. Tropical Atlantic Impacts on the Decadal Climate Variability of the Tropical Ocean and Atmosphere.

    NASA Astrophysics Data System (ADS)

    Li, X.; Xie, S. P.; Gille, S. T.; Yoo, C.

    2015-12-01

    Previous studies revealed atmospheric bridges between the tropical Pacific, Atlantic, and Indian Ocean. In particular, several recent works indicate that the Atlantic sea surface temperature (SST) may contribute to the climate variability over the equatorial Pacific. Inspired by these studies, our work aims at investigating the impact of the tropical Atlantic on the entire tropical climate system, and uncovering the physical dynamics under these tropical teleconnections. We first performed a 'pacemaker' simulation by restoring the satellite era tropical Atlantic SST changes in a fully coupled model - the CESM1. Results reveal that the Atlantic warming heats the Indo-Western Pacific and cools the Eastern Pacific, enhances the Walker circulation and drives the subsurface Pacific to a La Niña mode, contributing to 60-70% of the above tropical changes in the past 30 years. The same pan-tropical teleconnections have been validated by the statistics of observations and 106 CMIP5 control simulations. We then used a hierarchy of atmospheric and oceanic models with different complexities, to single out the roles of atmospheric dynamics, atmosphere-ocean fluxes, and oceanic dynamics in these teleconnections. With these simulations we established a two-step mechanism as shown in the schematic figure: 1) Atlantic warming generates an atmospheric deep convection and induces easterly wind anomalies over the Indo-Western Pacific in the form of Kelvin waves, and westerly wind anomalies over the eastern equatorial Pacific as Rossby waves, in line with Gill's solution. This circulation changes warms the Indo-Western Pacific and cools the Eastern Pacific with the wind-evaporation-SST effect, forming a temperature gradient over the Indo-Pacific basins. 2) The temperature gradient further generates a secondary atmospheric deep convection, which reinforces the easterly wind anomalies over the equatorial Pacific and enhances the Walker circulation, triggering the Pacific to a La Ni

  17. Hydrologic Sensitivities of Upper Indus Basin (North Pakistan) Rivers to Multi-Decadal Climatic Variability

    NASA Astrophysics Data System (ADS)

    Farhan, S. B.; Zhang, Y.; Ma, Y.; Haifeng, G.; Jilani, R.; Hashmi, D.; Rasul, G.

    2014-12-01

    Thermal inputs play a vital role in the management and seasonal distribution of stream-flows particularly in snow and glacier fed basins, therefore the signatures of the recent climate trends can also be observed in various hydrological variables in those basins. Upper Indus Basin (UIB) is located in the western part of Tibetan Plateau, and most of its flows are dependent on snow- and glacier-melt produced water, thus the analyses of historical stream-flows and climatic indicators in the snow-melt dominated rivers of UIB was carried out, which points towards an advance in the spring flow onset time over the past few decades. Trend results reveal that warm temperature spells in spring have occurred much earlier in recent years, which explains in part the trend in the timing of spring peak stream-flows owing to earlier occurrence of snow melt onset. The observed increase in spring stream-flows and decrease in summer stream-flows suggests a broad shift of snow-melt yield and spring peak flows. These trends are found to be strongest at lower elevations basins where winter temperatures are closer to the melting point, even modest variation in temperatures are capable to enforce large shifts in the basin hydrologic feedback. In addition, it appears that in recent years due to winter and spring warming, more of the precipitation is falling as rain rather than snow particularly in late winter and early spring seasons, consequently it is speculated that this shift in precipitation ratio (snow vs rain) and early warming spells might also affect local (basin-scale) Albedo via early recession and systematic decrease of snow cover area, which tends in lowering Albedo from an increased fraction of snow-free area, which instigate positive feedback on radiative balance that can perhaps causes local-scale heat redistribution, which collectively in turn augmented winter and early spring stream-flows in those basins. These observed hydro-climatological trends over UIB can have

  18. Decadal-scale variability in climate proxy records: a search for tidal and solar forcing

    NASA Astrophysics Data System (ADS)

    Berger, W.; Paetzold, J.; Wefer, G.

    2003-04-01

    Decadal-scale climate- and ocean variability is an unsolved problem. The geologic record holds a number of clues as to possible forcing functions; useful proxy series are in ice cores, corals, biogenic deposits in anaerobic basins, marine varves and small turbidites, in the sea and in lakes. Certain decadal-scale cycles seem to occur more commonly than others, and in a number of records with an entirely different pedigree, suggesting effects from outside forcing. If we assume that both solar forcing and tidal forcing play some role (as supported by spectra from corals and varves), we should expect interference between the respective forcing functions. From such interference, we can calculate the most likely periods to be found. Analysis of an 800-y coral record from Bermuda suggests that such interference periods are expressed in this proxy record.

  19. Swithin St. Cleeve: Variable Star Observer

    NASA Astrophysics Data System (ADS)

    Weitzenhoffer, K.

    1986-12-01

    THomas Hardy's romance "Two on a Tower" is the first novel to use an astronomical background as its unifying theme and the first to cast an astronomer in the role of protagonist. One subplot of the novel concerns Swithin St. Cleeve's quest for fame through his observations of variable stars. Despite a number of observational and instrumental setbacks, he makes an amazing discovery about variable stars, one he is certain will excite the astronomical world. But before he can get the news into print, another astronomer announces that very discover and takes from St. Cleeve the fame he thought would be his.

  20. Ocean surface temperature variability: Large model–data differences at decadal and longer periods

    PubMed Central

    Laepple, Thomas; Huybers, Peter

    2014-01-01

    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

  1. Interannual and decadal variability and trends in upper ocean temperatures in the North Pacific Ocean

    SciTech Connect

    White, W.B.; Cayan, D.R.

    1994-12-31

    Temperature profiles from the surface to 400 m deployed over the North Pacific Ocean for the 45 years from 1950--1994 are mapped onto a coarse grid each month, allowing trends in the upper ocean temperature to be estimated. Only temperature profiles distributed from 20{degree}N-60{degree}N are used, these subjected to rigorous scientific quality control. Two parameters are chosen to be representative of the upper ocean thermal structure; i.e., sea surface temperature (SST) and heat storage over the upper 400 m (HS400). Mapping of SST and HS400 is conducted monthly, with optimal interpolation utilizing a priori estimates of the covariance structure of the anomalous fields determined by White. This yields a time sequence of 540 monthly maps for each parameter over this 45-year period. Examining these time sequences for decadal variability and trends finds their magnitude and sign to change substantially as a function of geographical location over the North Pacific Ocean. For example, all along the west coast of North America, both SST and HS400 warmed during the past 45 years. But, in the middle of the North Pacific Ocean, both parameters cooled over this period. The average SST and HS400 over the entire domain from 20{degree}-60{degree}N did not show a trend. Rather, decadal variability dominated the time sequence, with the 1950`s colder than normal, the 1960`s near normal, the 1970`s warmer than normal, the 1980`s colder than normal, and the 1990`s warmer than normal. This natural decadal variability obscures any possible anthropogenic warming due to increased greenhouse gas concentrations in the atmosphere over this period.

  2. 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

    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.

  3. 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

    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.

  4. Kuroshio variability at 24 degrees N on mesoscale, seasonal, and decadal time scales

    NASA Astrophysics Data System (ADS)

    Zhang, Dongxiao

    1999-10-01

    The 24°N section crosses the North Pacific Subtropical Gyre, with the intensified Kuroshio on the western boundary confined by the East Taiwan Channel (ETC). As part of the World Ocean Circulation Experiment (WOCE), the PCM-1 moored current meter array was deployed in the ETC to monitor the Kuroshio transport and structure from September 1994 to May 1996. In this study, the moored measurement of the Kuroshio is combined with historical data, both long-term sea level records and basinwide hydrographic surveys, in addition to modern satellite observations and numerical model results, to investigate the Kuroshio variability and its role in the North Pacific climate system. Approximately 60% of the subinertial velocity and temperature variance in the Kuroshio east of Taiwan is associated with two modes revealed from empirical orthogonal function (EOF) analysis. The `transport' mode is dominated by a 100-day peak, while the most coherent energetic `meandering' signals are found in four limited frequency bands centered near periods of 100 days, 40 days, 18 days, and 10 days. On the 100-day time scale, the Kuroshio transport entering the East China Sea is strongly related to meandering of the current caused by westward-propagating anticyclonic eddies from the interior ocean. During low transport events, the Kuroshio meanders off-shore and partially bypasses the East Taiwan Channel to flow east of the Ryukyu islands. The improved estimate of Kuroshio transport and its seasonal variation from continuous measurements by the PCM-1 array and sea level difference (SLD) are used to determine the trans-Pacific heat flux and its seasonal cycle across 24°N. With 0.55 PW annual mean and an uncertainty of 0.2 PW, the heat flux has a minimum value of -0.07 PW in January and February but becomes stronger in the second half of the year with a maximum of 1.01 PW in July and a secondary maximum of 0.9 PW in November. The PCM-1 records, hydrographic sections, and SLD across the Kuroshio

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

    NASA Astrophysics Data System (ADS)

    Orsolini, Yvan J.; Kvamstø, Nils G.

    2009-10-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  8. 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

  9. Variability Statistics for Galaxies Observed by Kepler

    NASA Astrophysics Data System (ADS)

    Fanelli, Michael N.; Marcum, Pamela M.; Van Cleve, Jeffrey E.

    2016-01-01

    The Kepler / K2 telescope combines high photometric precision with near-continuous observing cadence, permitting a unique perspective on the optical / near-IR variability of galactic systems. In particular, Kepler / K2 data can be exploited to quantify the amplitude of AGN signals in galaxy cores, to directly address this question - What fraction of galactic nuclei are active at any given time ? Alternatively stated, this question becomes - What is the duty cycle for supermassive black hole accretion of sufficient strength to produce a detectable optical signal ? Additionally, the quasi-continuous cadence provides the capability to detect low-level episodic variations from the central AGN, highly luminous stars and other compact objects.Previously we reported on analysis of a subset of the complete galaxy dataset observed during the Kepler prime mission: ~1200 individual light curves of ~150 targeted galaxies observed during Quarters 3-10 and ~1000 light curves of galaxies observed serendipitously by the exoplanet program from Q2 through Q16. Based on an average of 8 quarters of data for ~300 systems and excluding systems specifically targeted as AGNs, we found that the observed occurrence rate of nuclear variability in galaxies with amplitude > 1 millimag is ~2-3%, a value which is ~ 2-3 times smaller than previous estimates from ground-based monitoring.Here we provide an update on galactic nuclear variability statistics using an expanded dataset from the Kepler Prime mission. We combine the previous data with 1200 light curves for ~200 targeted systems from Q11-16 and ~800 additional light curves found in the exoplanet program. These data are the longest continuous time series for galaxies ever obtained - some systems were observed for the entire mission (Q2-16). Our previous result is confirmed using this expanded dataset; only a few percent of galaxies show variability above 0.5 millimag. Several systems exhibiting activity in other bands, or via their optical

  10. 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

  11. Dynamics and mechanisms of decadal variability of the Pacific-South America mode over the 20th century

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Ma, Hao; Wu, Lixin

    2015-08-01

    In this paper, decadal variability of the Pacific-South America (PSA) mode is examined from year 1871 to 2008 based on the newly developed ocean and atmosphere reanalysis products. The PSA mode, mirroring the Pacific-North America mode in the Northern Hemisphere, emerges as the second EOF mode of 500 mb geopotential height anomalies. The mode displays substantial interannual-decadal variability with distinct timescales between 3-8 and 10-18 years, respectively. The decadal variability of the PSA mode is found to be associated with the coupled ocean-atmosphere interaction over the subtropical South and tropical Pacific. The subduction of the subtropical temperature anomalies in the South Pacific in conjunction with the tropical-subtropical atmospheric teleconnection plays important role in the decadal variability of the PSA mode.

  12. Dynamics and mechanisms of decadal variability of the Pacific-South America mode over the 20th century

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Ma, Hao; Wu, Lixin

    2016-06-01

    In this paper, decadal variability of the Pacific-South America (PSA) mode is examined from year 1871 to 2008 based on the newly developed ocean and atmosphere reanalysis products. The PSA mode, mirroring the Pacific-North America mode in the Northern Hemisphere, emerges as the second EOF mode of 500 mb geopotential height anomalies. The mode displays substantial interannual-decadal variability with distinct timescales between 3-8 and 10-18 years, respectively. The decadal variability of the PSA mode is found to be associated with the coupled ocean-atmosphere interaction over the subtropical South and tropical Pacific. The subduction of the subtropical temperature anomalies in the South Pacific in conjunction with the tropical-subtropical atmospheric teleconnection plays important role in the decadal variability of the PSA mode.

  13. 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

  14. Decadal variability in seawater pH in the West Pacific: Evidence from coral δ11B records

    NASA Astrophysics Data System (ADS)

    Wei, Gangjian; Wang, Zhibing; Ke, Ting; Liu, Ying; Deng, Wenfeng; Chen, Xuefei; Xu, Jifeng; Zeng, Ti; Xie, Luhua

    2015-11-01

    Long-term seawater pH records are essential for evaluating the rates of ocean acidification (OA) driven by anthropogenic emissions. Widespread, natural decadal variability in seawater pH superimposes on the long-term anthropogenic variations, likely influencing the OA rates estimated from the pH records. Here, we report a record of annual seawater pH estimated using the δ11B proxy over the past 159 years reconstructed from a Porites coral collected to the east of Hainan Island in the northern South China Sea (SCS). By coupling this time series with previously reported long-term seawater pH records in the West Pacific, the decadal variability in seawater pH records and its possible driving mechanisms were investigated. The results indicate that large decadal variability in seawater pH has occurred off eastern Hainan Island over the past 159 years, in agreement with previous records. The Qiongdong upwelling system, which controls nutrient supplies, regulates surface water productivity, and is driven by the East Asian summer monsoon, is the primary control of this decadal variability, while terrestrial inputs appear not influence significantly. Meanwhile the impacts of the Pacific Decadal Oscillation (PDO) and the El Nino and Southern Oscillation (ENSO) systems on seawater pH off eastern Hainan Island is likely limited. In contrast, the PDO is the main factor to influence the decadal seawater pH variability offshore the East Australia, while the mechanism controlling the decadal seawater pH variability in Guam is not clear yet. Meanwhile, The rate of decrease in seawater pH estimated from coral records are significantly different in different regions and over different time spans, which may reflect a combination of natural decadal variability in seawater pH and long-term variations. Therefore, understanding the mechanisms driving natural variability in seawater pH is important for improving estimates of ocean acidification rates driven by anthropogenic emissions.

  15. Impact of the Atlantic meridional overturning circulation on the decadal variability of the Gulf Stream path and regional chlorophyll and nutrient concentrations

    NASA Astrophysics Data System (ADS)

    Sanchez-Franks, A.; Zhang, R.

    2015-11-01

    In this study, we show that the underlying physical driver for the decadal variability in the Gulf Stream (GS) path and the regional biogeochemical cycling is linked to the low frequency variability in the Atlantic meridional overturning circulation (AMOC). There is a significant anticorrelation between AMOC variations and the meridional shifts of the GS path at decadal time scale in both observations and two Earth system models (ESMs). The chlorophyll and nutrient concentrations in the GS region are found significantly correlated with the AMOC fingerprint and anticorrelated with the GS path at decadal time scale through coherent isopycnal changes in the GS front in the ESMs. Our results illustrate how changes in the large-scale ocean circulation, such as AMOC, are teleconnected with regional decadal physical and biogeochemical variations near the North American east coast. Such linkages are useful for predicting future physical and biogeochemical variations in this region.

  16. X-ray observations of cataclysmic variables

    NASA Technical Reports Server (NTRS)

    Becker, R. H.

    1981-01-01

    Cataclysmic variables (CVs) as a class are defined by their optical properties, in particular the amplitudes and frequency of their outbursts. The availability of the Imaging Proportional Counter (IPC) on the Einstein Laboratory has increased significantly the number of CVs which can be studied on the basis of X-ray observations. In this connection, Becker and Marshall (1981) and Cordova et al. (1980) have surveyed 20 CVs and detected 70% of them. A description is presented of observations of an additional 12 CVs, and the properties of the combined set of 32 CVs are discussed. It is found that the CVs do not have any distinguishing X-ray characteristics. The IPC data alone cannot be used to determine to which category of CVs a particular source belongs, or even to identify an object as a CV. On the other hand, the optical observations are essential for estimating the X-ray luminosity from the IPC data.

  17. Deep ocean mass fluxes in the coastal upwelling off Mauritania from 1988 to 2012: variability on seasonal to decadal timescales

    NASA Astrophysics Data System (ADS)

    Fischer, Gerhard; Romero, Oscar; Merkel, Ute; Donner, Barbara; Iversen, Morten; Nowald, Nico; Ratmeyer, Volker; Ruhland, Götz; Klann, Marco; Wefer, Gerold

    2016-05-01

    A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analysed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales. High winter fluxes of biogenic silica (BSi), used as a measure of marine production (mostly by diatoms) largely correspond to a positive North Atlantic Oscillation (NAO) index (December-March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004-2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter and occasionally in summer/autumn enhanced particle sedimentation and carbon export on short timescales via the ballasting effect. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) might have weakened the relationships between fluxes and large-scale climatic oscillations. As phytoplankton biomass is high throughout the year, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by incorporating dust into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all bulk fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997-1999 where low fluxes were obtained for almost 1 year during the warm El Niño and high fluxes in the following cold La Niña phase. For decadal timescales, Bakun (1990) suggested an intensification of coastal upwelling

  18. Coordinated Multifrequency Observations of Variable Agns

    NASA Astrophysics Data System (ADS)

    Worrall, Diana M.

    1984-07-01

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

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

    PubMed

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

    2001-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Swetnam, Thomas W.; Betancourt, Julio L.

    1998-12-01

    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

  1. Annual and decadal variability in the western subtropical North Atlantic: signal characteristics and sampling methodologies

    NASA Astrophysics Data System (ADS)

    Molinari, Robert L.

    2004-07-01

    Upper ocean (above 750 m) temperature structure of the northwestern subtropical Atlantic, including the Gulf Stream and a recirculation gyre south of the Stream, is characterized using primarily bathythermograph (BT) data collected between 1950 and 2003. Geostrophic calculations, using mean temperature-salinity relationships to compute dynamic height, are used to estimate velocities and transports. The mean annual Gulf Stream transport at 72° W relative to 750 m, 36.1 Sv, is approximately equal to the sum of the transport of the Florida Current, 32.0 Sv, and a shallow recirculation gyre described by Wang and Koblinsky [Journal of Physical Oceanography 26 (1996) 2462-2479], 5.5 Sv. The annual cycle of geostrophic transport relative to 750 m at 72° W is in phase with both an earlier published annual cycle of transport relative to 2000 m derived from hydrographic observations and the annual cycle of Florida Current transport measured indirectly by a submarine cable (i.e., maximum transports are observed in the summer and minimum in the fall, early winter). However, simple Sverdrup dynamics are inadequate to explain these cycles as maximum Sverdrup transports extend from winter to summer, while observed transports are minimum (maximum) in fall/winter (summer). The annual cycles derived from the BT data of the size of the shallow southern recirculation gyre, Gulf Stream position and upper layer transport (relative to 300 m) are in phase (maximum size, northern position and transport in fall) and consistent with the WK results derived from altimetry. However, the shallower annual cycles are out of phase with the deeper signals (i.e., maximum for the former (latter) are observed in fall (summer)). Decadal signals after 1965 in Gulf Stream position, geostrophic transport relative to 450 m, and the size of a recirculation gyre south of the Stream are approximately in phase as observed for the annual signal. This gyre and the shallow WK gyre exhibit the same horizontal

  2. Satellite observations of global atmospheric energy budgets: annual means and decadal records

    NASA Astrophysics Data System (ADS)

    Lin, B.; Stackhouse, P.; Minnis, P.; Wielicki, B.; Schlosser, C. A.; Rodell, M.; Hu, Y.; Sun, W.; Fan, T. A.; Hinkelman, L.

    2008-05-01

    The global atmospheric energy budget can tell us a lot about the earth's climate system, and is critical for general circulations of the atmosphere. This study uses satellite data sets of the radiation at the top of atmosphere (TOA) and surface from ERBE, CERES and ISCCP and the latent and sensible heat over oceans from SSM/I to assess the global energy budgets. Over land, surface radiation estimates are used to constrain GLDAS model assimilated results and to force the radiation, turbulent heat, and land surface heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Because of satellite data availability of broadband observations for radiation and microwave measurements for turbulent fluxes, this study considers the atmospheric energy budgets during 1988 and 2005. Global annual means of the TOA net radiation are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 W/m2, respectively. The estimated atmospheric and surface heat imbalances are about ­ 8 ~ 9 W/m2, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget: the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. For long term energy budgets, TOA radiation measurements show a clear relationship with the changes in the ocean heat storage. Although most oceanic latent and sensible heat data sets have significant unrealistic long-term variations, some satellite global observations of marine latent heat fluxes from evaporation and precipitation measurements exhibit potential correlations with sea surface

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  4. External forcing as a source for the observed multi-decadal relation between AMV and the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Svendsen, Lea; Luo, Feifei; Sankar, Syam; Gao, Yongqi; Keenlyside, Noel; Vareed Joseph, Porathur; Johannessen, Ola

    2016-04-01

    The instrumental records show a significant positive correlation between the Atlantic multi-decadal variability (AMV) and the Indian summer monsoon (ISM) rainfall, where a positive (negative) AMV is associated with more (less) ISM rainfall. We have used both proxy reconstruction and twelve models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to investigate if the observed AMV-ISM relation is a persistent internal climate signal or externally forced. A comparison of several annual resolution proxy records both from the Atlantic and for the ISM show that the multi-decadal variability in both indices is persistent, but the link between them is not. The correlation between the two regions is weak, and even negative in some periods, before the instrumental time period. The analysis of CMIP5 simualtions is consistent with these results. While none of the CMIP5 models investigated simulate the significant AMV-ISM connection in the pre-industrial control simulations with fixed external forcing, three of the models reproduce the relation in the 20th century historical simulations with transient forcing. In these models external forcing is linked to the mid-to-upper tropospheric temperature pattern with a strengthened land-ocean contrast over South Asia, consistent with an enhanced ISM, as well as the evolution of AMV. We conclude that the significant AMV-ISM relation found in the observations after the industrial revolution may be associated with external forcing, rather than being internal climate variability.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  7. Decadal variability of the Pacific Subtropical Cells and its relevance to the sea surface height in the western tropical Pacific during recent decades

    NASA Astrophysics Data System (ADS)

    Yamanaka, Goro; Tsujino, Hiroyuki; Nakano, Hideyuki; Hirabara, Mikitoshi

    2015-01-01

    variability of the Pacific Subtropical Cells (STCs) and associated sea surface height (SSH) in the western tropical Pacific during recent decades are examined by using an historical OGCM simulation. The model represents decadal variations of the STCs concurrent with tropical Pacific thermal anomalies: the eastern tropical Pacific is warmer when the STCs are weaker and cooler when they are stronger. The spatial patterns of the SSH in the western tropical Pacific show different features, depending on events associated with decadal variability. During the warm phase (1977-1987), the SSH anomalies exhibit deviations from a meridionally symmetric distribution, with weakly positive (strongly negative) anomalies in the western tropical North (South) Pacific. Analysis of the heat budget in the upper tropical Pacific indicates that the termination of the warm phase around 1985 results from a poleward heat transport anomaly that is induced by a horizontal gyre associated with the SSH anomalies. During the cold phase (1996-2006), in contrast, the SSH anomalies are nearly meridionally symmetric, with positive anomalies in both hemispheres. Enhanced easterly wind anomalies contribute to the development of the cold phase after the late 1990s.

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

    NASA Technical Reports Server (NTRS)

    Dunkerton, Timothy J.

    2000-01-01

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

  9. Deep ocean mass fluxes in the coastal upwelling off Mauritania from 1988 to 2012: variability on seasonal to decadal timescales

    NASA Astrophysics Data System (ADS)

    Fischer, G.; Romero, O.; Merkel, U.; Donner, B.; Iversen, M.; Nowald, N.; Ratmeyer, V.; Ruhland, G.; Klann, M.; Wefer, G.

    2015-11-01

    A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analyzed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales possibly linked to the Atlantic Multidedadal Oscillation (AMO). High winter fluxes of biogenic silica (BSi), used as a measure of marine production mostly by diatoms largely correspond to a positive North Atlantic Oscillation (NAO) index during boreal winter (December-March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004-2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter but also in summer/fall enhanced particle sedimentation and carbon export on rather short timescales via the ballasting effect, thus leading to these episodic sedimentation events. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) weakened the relationships between fluxes and larger scale climatic oscillations. As phytoplankton biomass is high throughout the year in our study area, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by being incorporated into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997-1999 where low fluxes were obtained for almost one year during the warm El Niño and

  10. 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

  11. Wave power variability and trends across the North Atlantic influenced by decadal climate patterns

    NASA Astrophysics Data System (ADS)

    Bromirski, Peter D.; Cayan, Daniel R.

    2015-05-01

    Climate variations influence North Atlantic winter storm intensity and resultant variations in wave energy levels. A 60 year hindcast allows investigation of the influence of decadal climate variability on long-term trends of North Atlantic wave power, PW, spanning the 1948-2008 epoch. PW variations over much of the eastern North Atlantic are strongly influenced by the fluctuating North Atlantic Oscillation (NAO) atmospheric circulation pattern, consistent with previous studies of significant wave height, Hs. Wave activity in the western Atlantic also responds to fluctuations in Pacific climate modes, including the Pacific North American (PNA) pattern and the El Niño/Southern Oscillation. The magnitude of upward long-term trends during winter over the northeast Atlantic is strongly influenced by heightened storm activity under the extreme positive phase of winter NAO in the early 1990s. In contrast, PW along the United States East Coast shows no increasing trend, with wave activity there most closely associated with the PNA. Strong wave power "events" exhibit significant upward trends along the Atlantic coasts of Iceland and Europe during winter months. Importantly, in opposition to the long-term increase of PW, a recent general decrease in PW across the North Atlantic from 2000 to 2008 occurred. The 2000-2008 decrease was associated with a general shift of winter NAO to its negative phase, underscoring the control exerted by fluctuating North Atlantic atmospheric circulation on PW trends.

  12. Linear Ground-Motions in the Wabash Valley, Central United States: Two Decades of Unconventional Observations

    NASA Astrophysics Data System (ADS)

    Woolery, E. W.

    2012-12-01

    Since the mid-1980's small and moderate-sized earthquakes in the Ohio and Wabash River valleys of the central United States have been digitally recorded by seismographs, called blast monitors, deployed to monitor vibrations from chemical explosions associated with regional mining and quarrying. Because there were relatively few conventional networked strong-motion and broad-band instruments for this area between 1980 and the early 2000's, the more than 200 observations have provided a relatively widespread source of digital earthquake ground motions. Additional deployment of networked instrumentation during the last decade and their numerous recordings of the April 2008, Mt. Carmel, Illinois earthquake sequence have provided the first effective means for comparing free-field blast monitor and conventional network ground-motion observations. The peak ground-motion characteristics for both data sets relative to a common predictive relationship are similar, suggesting that blast monitor observations in the central U.S. compliment conventional network data for moderate-sized (< M5.5) events. Much of the ground motion prediction effort in the central United States has been focused on deep (>> 30 m) alluvial sites, such as those found in the Mississippi embayment. The free-field digital velocity records at blast-monitor sites in the Wabash Valley are more typical of the areas outside the embayment. The ground-motion database is composed of small to moderate size regional earthquakes with a magnitude range between M3 and M5.2; however, the bulk of the observations are associated with the 1987 M4.96 and 2008 M5.2 southeastern Illinois earthquakes, and the 2002 M4.5 southwestern Indiana earthquake. The velocity recordings and ancillary site investigations for the 2008 southeastern Illinois earthquake sequence put the findings into context with the previous observations, and quantify the reduction in ground-motion variability that can be achieved with conventional site

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the pre-instrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~160° E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ18O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (~1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite δ18O record coincides with previously identified decadal shifts in PDV-related Pacific ocean-atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal climate variability. The 600 yr Solomon Islands stalagmite δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.

  14. Decadal Supbolar Gyre Variability Linked to MWA-LIA Climate Regime Shift in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Moreno-Chamarro, E.; Zanchettin, D.; Lohmann, K.; Jungclaus, J. H.

    2015-12-01

    Recent paleoceanographic reconstructions of subpolar North Atlantic variability during the last millennium describe oceanic conditions associated with a stronger subpolar gyre (SPG) during the Medieval Climate Anomaly (950-1250 CE) followed by a weak phase during the Little Ice Age (1450-1850 CE). Yet the mechanism behind this relatively abrupt SPG shift remains unclear. Here, we investigate the SPG dynamics during the last millennium in an ensemble of three transient climate simulations performed with the Max Planck Institute-Earth system model. In particular, we focus on the dynamics underlying a decadal-scale SPG transition from an initial strong to a later weak state, which is found in one of the simulations and whose features are similar to the reconstructed event. Our results indicate that the simulated shift is triggered by a rapid increase in the freshwater transport from the Arctic toward the subpolar North Atlantic, which causes a broad freshening of the upper Labrador Sea. As a result, upper ocean densities largely decrease in the area, leading to a shut-down of oceanic deep mixing and, eventually, to a substantial weakening of the SPG. This event triggers a series of long-lasting feedbacks relating anomalous oceanic and atmospheric circulations, sea-ice extent, deep water formation in the Labrador Sea, and upper-ocean east-west density gradient within the SPG, all contributing to maintain the North Atlantic in an anomalous state for at least 200 years. A reorganization of the North Atlantic/Arctic ocean-atmosphere coupled system sustained by internal feedbacks acting on multicentennial time scales can therefore be initiated by changes in the SPG. Such reorganization, by contrast, does not depend on a long-lasting weakening of the Atlantic Meridional overturning circulation or a shift in large-scale modes of atmospheric variability, such as the North Atlantic Oscillation. The simulated SPG shift occurs right after a cluster of relatively small volcanic

  15. Variability of the directly observed, middepth subpolar North Atlantic circulation

    NASA Astrophysics Data System (ADS)

    Palter, Jaime B.; Caron, Charles-André; Law, Kara Lavender; Willis, Joshua K.; Trossman, David S.; Yashayaev, Igor M.; Gilbert, Denis

    2016-03-01

    Satellite views of the ocean have suggested a decline of the subpolar North Atlantic surface circulation during the 1990s and 2000s. This was a period of unprecedented observational capacity in the basin, thanks to the presence of many hundreds of profiling floats. We use more than 40,000 subsurface displacements of these floats to characterize the circulation at 1000 m depth, and its evolution from 1997-2013. We show a statistically significant slowdown in the Labrador Sea boundary currents of -0.8 cm s-1 per decade (95% confidence interval of -1.4 to -0.15 cm s—1 per decade, a conservative estimate of the uncertainty). Otherwise, the middepth circulation field was largely stable. Our analysis of the location where the North Atlantic Current crosses the Mid-Atlantic Ridge shows that profiling floats can reveal steering by bathymetric features, but do not reveal of decadal variability in the position where the current crosses the ridge.

  16. Observational constraints on interannual variability projections in CMIP5

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  17. Observations of Atlantic overturning variability and latitudinal coherence with GRACE time-variable gravity

    NASA Astrophysics Data System (ADS)

    Landerer, Felix; Wiese, David; Bentel, Katrin; Watkins, Michael; Boening, Carmen

    2016-04-01

    The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of pole-ward planetary heat transport. Concerns about AMOC changes imply the need for a continuous, large-scale observation capability to detect and monitor changes on interannual to decadal time scales. Here we present measurements of AMOC component transport changes directly obtained from time-variable gravity observations of the Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 until now. Recent improvements at JPL of monthly gravity field retrievals allow the detection of AMOC-related interannual bottom pressure anomalies and in turn LNADW transport estimates. In the Atlantic at 26N, these GRACE AMOC estimates are in good agreement with those from the Rapid Climate Change-Meridional Overturning Circulation and Heatflux Array (RAPID/MOCHA) . We extend the GRACE-based estimates of AMOC variability from the Southern Ocean to the Northern sinking branch to assess meridional coherence and discuss challenges of the GRACE observing system. Our results highlight the efficacy and utility of space-gravimetry for observing AMOC variations to evaluate latitudinal coherency and long-term variability.

  18. Observed and simulated inter-decadal changes in the structure of Southern Hemisphere large-scale circulation

    NASA Astrophysics Data System (ADS)

    Freitas, Ana C. V.; Frederiksen, Jorgen S.; Whelan, Jennifer; O'Kane, Terence J.; Ambrizzi, Tércio

    2015-12-01

    Several studies have identified that, in the mid-1970s to early 1980s, a major shift occurred in the structure of the large-scale circulation in both hemispheres. This work employs the CSIRO Mk3L general circulation model in ensemble simulations with observed sea surface temperatures (SSTs) and historical time-evolving carbon dioxide (CO2) concentrations to investigate the inter-decadal changes found observationally in the jet streams, temperature, Hadley circulation, mean sea level pressure and precipitation. First, the performance of the model in simulating these changes for the mean July climate fields of 1949-1968 and 1975-1994, in comparison with the corresponding observations (NCEP/NCAR Reanalysis I and the Twentieth Century Reanalysis V2), is investigated. We find that the model is quite skilful in reproducing the broad features of the important inter-decadal changes that occurred in the mid-1970s. The model simulations and the NCEP/NCAR and twentieth century reanalyses agree in the eastern hemisphere; whereas in the western hemisphere the reanalyses show differences, and the simulations combine aspects of these two datasets. The role of the direct radiative forcing due to CO2 in driving the inter-decadal changes is also examined. Results indicate that, in comparison with the indirect effect of CO2 carried by the changing SSTs, there is little additional impact of the direct radiative forcing due to CO2 on the changes in the latter period. However, our simulations with fixed CO2 concentration have shown clearly that the atmospheric simulations with historical time-evolving CO2 concentrations are more skilful in reproducing the inter-decadal changes. The sensitivity of the ensemble results to employing the same or different time evolving sea ice boundary conditions in the ensemble members is also studied. The contributions of internal and external variability are discussed.

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

    NASA Technical Reports Server (NTRS)

    Mehta, Vikram M.; Delworth, Thomas

    1995-01-01

    Sea surface temperature (SST) variability was investigated in a 200-yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The second 100 yr of SST in the coupled model's tropical Atlantic region were analyzed with a variety of techniques. Analyses of SST time series, averaged over approximately the same subregions as the Global Ocean Surface Temperature Atlas (GOSTA) time series, showed that the GFDL SST anomalies also undergo pronounced quasi-oscillatory decadal and multidecadal variability but at somewhat shorter timescales than the GOSTA SST anomalies. Further analyses of the horizontal structures of the decadal timescale variability in the GFDL coupled model showed the existence of two types of variability in general agreement with results of the GOSTA SST time series analyses. One type, characterized by timescales between 8 and 11 yr, has high spatial coherence within each hemisphere but not between the two hemispheres of the tropical Atlantic. A second type, characterized by timescales between 12 and 20 yr, has high spatial coherence between the two hemispheres. The second type of variability is considerably weaker than the first. As in the GOSTA time series, the multidecadal variability in the GFDL SST time series has approximately opposite phases between the tropical North and South Atlantic Oceans. Empirical orthogonal function analyses of the tropical Atlantic SST anomalies revealed a north-south bipolar pattern as the dominant pattern of decadal variability. It is suggested that the bipolar pattern can be interpreted as decadal variability of the interhemispheric gradient of SST anomalies. The decadal and multidecadal timescale variability of the tropical Atlantic SST, both in the actual and in the GFDL model, stands out significantly above the background 'red noise' and is coherent within each of the time series, suggesting that specific sets of

  20. Decadal variability in core surface flows deduced from geomagnetic observatory monthly means

    NASA Astrophysics Data System (ADS)

    Whaler, K. A.; Olsen, N.; Finlay, C. C.

    2016-07-01

    Monthly means of the magnetic field measurements at ground observatories are a key data source for studying temporal changes of the core magnetic field. However, when they are calculated in the usual way, contributions of external (magnetospheric and ionospheric) origin may remain, which make them less favourable for studying the field generated by dynamo action in the core. We remove external field predictions, including a new way of characterising the magnetospheric ring current, from the data and then calculate revised monthly means using robust methods. The geomagnetic secular variation (SV) is calculated as the first annual differences of these monthly means, which also removes the static crustal field. SV time series based on revised monthly means are much less scattered than those calculated from ordinary monthly means, and their variances and correlations between components are smaller. On the annual to decadal timescale, the SV is generated primarily by advection in the fluid outer core. We demonstrate the utility of the revised monthly means by calculating models of the core surface advective flow between 1997 and 2013 directly from the SV data. One set of models assumes flow that is constant over three months; such models exhibit large and rapid temporal variations. For models of this type, less complex flows achieve the same fit to the SV derived from revised monthly means than those from ordinary monthly means. However, those obtained from ordinary monthly means are able to follow excursions in SV that are likely to be external field contamination rather than core signals. Having established that we can find models that fit the data adequately, we then assess how much temporal variability is required. Previous studies have suggested that the flow is consistent with torsional oscillations (TO), solid body-like oscillations of fluid on concentric cylinders with axes aligned along the Earth's rotation axis. TO have been proposed to explain decadal

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  2. A dynamical fingerprint of tropical Pacific sea surface temperatures on the decadal-scale variability of cool-season Arctic precipitation

    NASA Astrophysics Data System (ADS)

    Hegyi, Bradley M.; Deng, Yi

    2011-10-01

    The temporal and spatial characteristics of decadal-scale variability in the Northern Hemisphere (NH) cool-season (October-March) Arctic precipitation are identified from both the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the Global Precipitation Climatology Project (GPCP) precipitation data sets. This decadal variability is shown to be partly connected to the decadal-scale variations in tropical central Pacific sea surface temperatures (SSTs) that are primarily associated with a decadal modulation of the El Niño-Southern Oscillation (ENSO), i.e., transitions between periods favoring typical eastern Pacific warming (EPW) events and periods favoring central Pacific warming (CPW) events. Regression and composite analyses reveal that increases of central Pacific SSTs drive a stationary Rossby wave train that destructively interferes with the wave number-1 component of the extratropical planetary wave. This destructive interference is opposite to the mean effect of typical EPW on the extratropical planetary wave. It leads to suppressed upward propagation of wave energy into the polar stratosphere, a stronger stratospheric polar vortex, and a tendency toward a positive phase of the Arctic Oscillation (AO). The positive AO tendency is synchronized on the decadal scale with a poleward shift of the NH storm tracks, particularly in the North Atlantic. Storm track variations further induce changes in the amount of moisture transported into the Arctic by synoptic eddies. The fluctuations in the eddy moisture transport ultimately contribute to the observed decadal-scale variations in the total Arctic precipitation in the NH cool season.

  3. Santa Ana Winds of Southern California: Their Climatology and Variability Spanning 6.5 Decades from Regional Dynamical Modelling

    NASA Astrophysics Data System (ADS)

    Guzman-Morales, J.; Gershunov, A.

    2015-12-01

    Santa Ana Winds (SAWs) are an integral feature of the regional climate of Southern California/Northern Baja California region. In spite of their tremendous episodic impacts on the health, economy and mood of the region, climate-scale behavior of SAW is poorly understood. In the present work, we identify SAWs in mesoscale dynamical downscaling of a global reanalysis product and construct an hourly SAW catalogue spanning 65 years. We describe the long-term SAW climatology at relevant time-space resolutions, i.e, we developed local and regional SAW indices and analyse their variability on hourly, daily, annual, and multi-decadal timescales. Local and regional SAW indices are validated with available anemometer observations. Characteristic behaviors are revealed, e.g. the SAW intensity-duration relationship. At interdecadal time scales, we find that seasonal SAW activity is sensitive to prominent large-scale low-frequency modes of climate variability rooted in the tropical and north Pacific ocean-atmosphere system that are also known to affect the hydroclimate of this region. Lastly, we do not find any long-term trend in SAW frequency and intensity as previously reported. Instead, we identify a significant long-term trend in SAW behavior whereby contribution of extreme SAW events to total seasonal SAW activity has been increasing at the expense of moderate events. These findings motivate further investigation on SAW evolution in future climate and its impact on wildfires.

  4. History of Amateur Variable Star Observations in Japan

    NASA Astrophysics Data System (ADS)

    Kiyota, S.

    2012-06-01

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

  5. A Generalized Stability Analysis of the AMOC in Earth System Models: Implication for Decadal Variability and Abrupt Climate Change

    SciTech Connect

    Fedorov, Alexey V.; Fedorov, Alexey

    2015-01-14

    The central goal of this research project was to understand the mechanisms of decadal and multi-decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) as related to climate variability and abrupt climate change within a hierarchy of climate models ranging from realistic ocean models to comprehensive Earth system models. Generalized Stability Analysis, a method that quantifies the transient and asymptotic growth of perturbations in the system, is one of the main approaches used throughout this project. The topics we have explored range from physical mechanisms that control AMOC variability to the factors that determine AMOC predictability in the Earth system models, to the stability and variability of the AMOC in past climates.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  7. Space-time variability of Indonesian rainfall at inter-annual and multi-decadal time scales

    NASA Astrophysics Data System (ADS)

    Yanto; Rajagopalan, Balaji; Zagona, Edith

    2016-01-01

    We investigated the space-time variability of wet (Nov-Apr) and dry (May-Oct) season rainfall over Indonesia, using monthly gridded rainfall data from the University of East Angela Climatic Research Unit covering the period 1901-2012. Three complimentary techniques were employed—(1) principal component analysis to identify the dominant modes of variability, (2) wavelet spectral analysis to identify the spectral characteristics of the leading modes and their coherence with large scale climate variables and (3) Bayesian Dynamical Linear Model (BDLM) to quantify the temporal variability of the association between rainfall modes and climate variables. In the dry season when the Inter Tropical Convergence Zone (ITCZ) is to the north of the equator the leading two principal components (PCs) explain close to 50 % of the rainfall. In the wet season the ITCZ moves to the south and the leading PCs explain close to 30 % of the variance. El Niño Southern Oscillation (ENSO) is the driver of the leading modes of rainfall variability during both seasons. We find asymmetry in the teleconnections of ENSO to high and low rainfall years in the dry season. Furthermore, ENSO and the leading PCs of rainfall have spectral coherence in the inter-annual band (2-8 years) over the entire period of record and in the multi-decadal (8-16 years) band in post-1980 years. In addition, during the 1950-1980 period the second mode of variability in both seasons has a strong relationship with Pacific Decadal Oscillation. The association between ENSO and the leading mode of Indonesian rainfall has strengthened in recent decades, more so during dry season. These inter-annual and multi-decadal variability of Indonesian rainfall modulated by Pacific climate drivers has implications for rainfall and hydrologic predictability important for water resources management.

  8. Decadal trend of precipitation and temperature patterns and impacts on snow-related variables in a semiarid region, Sierra Nevada, Spain.

    NASA Astrophysics Data System (ADS)

    José Pérez-Palazón, María; Pimentel, Rafael; Herrero, Javier; José Polo, María

    2016-04-01

    , with the exception of the average annual mean and maximum daily temperature. In the case of the snow-related variables, no significant trends are observed at this time scale; nonetheless, a global decreasing rate is predominant in most of the variables. The torrential events are more frequent in the last decades of the study period, with an apparently increasing associated dispersion. This study constitutes a first sound analysis of the long-term observed trends of the snow regime in this area under the context of increasing temperature and decreasing precipitation regimes. The results highlight the complexity of non-linearity in environmental processes in Mediterranean regions, and point out to a significant shift in the precipitation and temperature regime, and thus on the snow-affected hydrological variables in the study area.

  9. Two decades of ice melt reconstruction in Greenland and Antarctica from time-variable gravity

    NASA Astrophysics Data System (ADS)

    Talpe, M.; Nerem, R. S.; Lemoine, F. G.

    2014-12-01

    In this study, we present a record of ice-sheet melt derived from space-borne gravity that spans over two decades—beyond the time-frame of the GRACE mission. GRACE fields are merged with conventional tracking data (SLR/DORIS) spanning 1992 to the present. They are provided as weekly global fields of degree and order five without C50 and S50 but with C61 and S61. Their multi-decade timespan complements the monthly fields of GRACE of degree and order 60 that start in 2003 and will end when the GRACE mission terminates. The two datasets are combined via an empirical orthogonal function analysis, whereby the conventional tracking data temporal modes are obtained by fitting the SLR/DORIS coefficients to the GRACE spatial modes via linear least squares. Combining those temporal modes with GRACE spatial modes yields the reconstructed global gravity fields. The error budget of the reconstructions is composed of three components: the SLR/DORIS covariances, the errors estimated from the assumption that GRACE spatial modes can be mapped over the SLR/DORIS timeframe, and the covariances from the least squares fit applied to obtain the SLR/DORIS temporal modes. The reconstructed surface mass changes in Greenland and Antarctica, predominantly captured in the first mode, show a rate of mass loss that is increasing since 1992. The trend of mass changes in Greenland over various epochs match with an overarching study assembling altimetry, gravimetry, and interferometry estimates of ice-sheet balance over a 1992-2011 time-frame [Shepherd et al., 2012]. Antarctica shows a trend that is different because of updated GIA models [A et al., 2013] compared to the other studies. We will also show regional mass changes over various other basins, as well as the influence of each SLR/DORIS coefficient on the reconstructions. The consistency of these results underscores the possibility of using low-resolution SLR/DORIS time-variable gravity solutions as a way to continuously monitor the

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-06-01

    In the South Pacific, interdecadal-decadal oceanic and atmospheric variability, referred to as the Interdecadal Pacific Oscillation (IPO), is most pronounced in the South Pacific Convergence Zone (SPCZ) salinity front region. Here we have used annual average oxygen isotope (δ18O) time series from five coral cores collected from Fiji and Tonga in this region to construct a Fiji-Tonga Interdecadal-Decadal Pacific Oscillation (F-T IDPO) index of low-frequency (>9 and <55 years) climate variability back to 1650 A.D. We first demonstrate the consistency between this F-T IDPO index and a mean sea level (MSL) pressure-based SPCZ position index (SPI) (1891-2000), thus verifying the ability of coral δ18O to record past interdecadal-decadal climatic variations in this region back to 1891. The F-T IDPO index is then shown to be synchronous with the IPO index (1856-2000), suggesting that this coral-based index effectively represents the interdecadal-decadal scale climate variance back to 1650. The regularity of the F-T IDPO index indicates that interdecadal-decadal variability in the SPCZ region has been relatively constant over the past 350 years with a mean frequency of ˜20 years (variance peaks near 11 and 35 years). There is a consistent antiphase correlation of the F-T IDPO index and the interdecadal-decadal components in equatorial Pacific coral δ18O series from Maiana and Palmyra. This observation indicates that the eastward expansion (westward contraction) of the eastern salinity front of the Western Pacific Warm Pool (WPWP) occurs simultaneously (±<1 year) with the westward (eastward) shift of the SPCZ salinity front during positive IPO (negative IPO) phases. This is the same relationship observed during the phases of the El Niño Southern Oscillation.

  13. 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.

  14. 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.

  15. Spatio-temporal Variability of Arctic Sea Ice from Days to Decades.

    NASA Astrophysics Data System (ADS)

    Wettlaufer, J. S.; Agarwal, S.

    2014-12-01

    We examine the daily satellite retrievals of Arctic sea-ice extent over three decades. The Arctic basin is divided into 14 different regions and we study how the Arctic wide observations emerge from these regional trends. In order to capture all possible time scales, the temporal dynamics within each spatial region, and in the basin as a whole, are treated as a multifractal. Our approach is Multi-Fractal Temporally Weighted Detrended Fluctuation Analysis (MF-TWDFA), which captures long time scales that are not accessible by standard DFA or MF-DFA and are by definition not part of a procedure that assumes the dynamics are described by an order one auto-regressive process. We examine how the eastern, western, central and the marginal seas control the longest time scales and what processes are responsible for the responses found in the data. Of particular interest is how regions with substantial seasonality contribute to the basin-wide dynamics of the system. The importance of this is intertwined with the general problem of how and when the Arctic may pass on to a state in which the ice cover is seasonal. The transition from a perennial state to a seasonal ice cover is the persistent state of affairs in the marginal regions of the ice cover, which constitute 10 of the 14 subregions, whereas the remaining 4 are in various stages of partial ice cover at various times of the year. In this manner, we use sub-basins as laboratories for the entire basin.

  16. 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.

  17. Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability

    NASA Astrophysics Data System (ADS)

    Meehl, Gerald A.; Arblaster, Julie M.; Bitz, Cecilia M.; Chung, Christine T. Y.; Teng, Haiyan

    2016-08-01

    Antarctic sea-ice extent has been slowly increasing in the satellite record that began in 1979. Since the late 1990s, the increase has accelerated, but the average of all climate models shows a decline. Meanwhile, the Interdecadal Pacific Oscillation, an internally generated mode of climate variability, transitioned from positive to negative, with an average cooling of tropical Pacific sea surface temperatures, a slowdown of the global warming trend and a deepening of the Amundsen Sea Low near Antarctica that has contributed to regional circulation changes in the Ross Sea region and expansion of sea ice. Here we show that the negative phase of the Interdecadal Pacific Oscillation in global coupled climate models is characterized by anomalies similar to the observed sea-level pressure and near-surface 850 hPa wind changes near Antarctica since 2000 that are conducive to expanding Antarctic sea-ice extent, particularly in the Ross Sea region in all seasons, involving a deepening of the Amundsen Sea Low. These atmospheric circulation changes are shown to be mainly driven by precipitation and convective heating anomalies related to the Interdecadal Pacific Oscillation in the equatorial eastern Pacific, with additional contributions from convective heating anomalies in the South Pacific convergence zone and tropical Atlantic regions.

  18. 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.

  19. Decadal covariability of Atlantic SSTs and western Amazon dry-season hydroclimate in observations and CMIP5 simulations

    NASA Astrophysics Data System (ADS)

    Fernandes, Katia; Giannini, Alessandra; Verchot, Louis; Baethgen, Walter; Pinedo-Vasquez, Miguel

    2015-08-01

    The unusual severity and return time of the 2005 and 2010 dry-season droughts in western Amazon is attributed partly to decadal climate fluctuations and a modest drying trend. Decadal variability of western Amazon hydroclimate is highly correlated to the Atlantic sea surface temperature (SST) north-south gradient (NSG). Shifts of dry and wet events frequencies are also related to the NSG phase, with a 66% chance of 3+ years of dry events per decade when NSG > 0 and 19% when NSG < 0. The western Amazon and NSG decadal covariability is well reproduced in general circulation models (GCMs) historical (HIST) and preindustrial control (PIC) experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The HIST and PIC also reproduce the shifts in dry and wet events probabilities, indicating potential for decadal predictability based on GCMs. Persistence of the current NSG positive phase favors above normal frequency of western Amazon dry events in coming decades.

  20. 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...

  1. 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

  2. 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.

  3. 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.

  4. A Decade of Volcanic Observations from Aura and the A-Train

    NASA Technical Reports Server (NTRS)

    Carn, Simon A.; Krotkov, Nickolay Anatoly; Yang, Kai; Krueger, Arlin J.; Hughes, Eric J.; Wang, Jun; Flower, Verity; Telling, Jennifer

    2014-01-01

    Aura observations have made many seminal contributions to volcanology. Prior to the Aura launch, satellite observations of volcanic degassing (e.g., from TOMS) were mostly restricted to large eruptions. However, the vast majority of volcanic gases are released during quiescent 'passive' degassing between eruptions. The improved sensitivity of Aura OMI permitted the first daily, space-borne measurements of passive volcanic SO2 degassing, providing improved constraints on the source locations and magnitude of global SO2 emissions for input to atmospheric chemistry and climate models. As a result of this unique sensitivity to volcanic activity, OMI data were also the first satellite SO2 measurements to be routinely used for volcano monitoring at several volcano observatories worldwide. Furthermore, the Aura OMI SO2 data also offer unprecedented sensitivity to volcanic clouds in the UTLS, elucidating the transport, fate and lifetime of volcanic SO2 and providing critical input to aviation hazard mitigation efforts. Another major advance has been the improved vertical resolution of volcanic clouds made possible by synergy between Aura and other A-Train instruments (e.g., AIRS, CALIPSO, CloudSat), advanced UV SO2 altitude retrievals, and inverse trajectory modeling of detailed SO2 cloud maps. This altitude information is crucial for climate models and aviation hazards. We will review some of the highlights of a decade of Aura observations of volcanic activity and look ahead to the future of volcanic observations from space.

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

    SciTech Connect

    DelSole, Timothy

    2015-08-31

    The purpose of the proposed research was 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. The question of whether anthropogenic forcing changes decadal predictability, or gives rise to new forms of decadal predictability, also will be

  6. 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

  7. Mapping of decadal middle Adriatic oceanographic variability and its relation to the BiOS regime

    NASA Astrophysics Data System (ADS)

    Mihanović, Hrvoje; Vilibić, Ivica; Dunić, Natalija; Å epić, Jadranka

    2015-08-01

    We analyzed long-term time series of temperature, salinity, and dissolved oxygen (DO) concentrations collected along the Palagruža Sill transect (middle Adriatic) between 1952 and 2010. The data have been mostly collected on seasonal basis, allowing for extraction of seasonal signal from the series. By applying Self-Organizing Maps (SOM) method, a kind of unsupervised neural network method, the processes on a decadal time scale emerged as the most relevant for changes of oceanographic properties in the middle Adriatic area. Sensitivity studies revealed that oceanographic patterns obtained by SOM were not sensitive to shortening of time series, to removal of data from one station or to removal of DO from the analysis. Simultaneous SOM-based mapping of sea surface heights in the northern Ionian Sea, with these heights serving as a proxy for the Adriatic-Ionian Bimodal Oscillating System (BiOS), revealed asymmetry between anticyclonic and cyclonic BiOS patterns and correlated the decadal oscillations in the middle Adriatic with the reversals in the BiOS circulation regimes. These reversals are found to either rapidly change oceanographic properties in the middle Adriatic (e.g., during the Eastern Mediterranean Transient) or to change them with a time lag of 2-3 years. The mapped connections may be used for a short-time (a few years) forecasting of the Adriatic oceanographic properties or for mapping future climate decadal oscillations as seen by ocean climate models.

  8. An updated set of nutations derived from the reanalysis of 3.5 decades VLBI observations

    NASA Astrophysics Data System (ADS)

    Zhu, Ping; Koot, Laurence; Rivoldini, Attilio; Dehant, Veronique

    2016-04-01

    The global VLBI observation started in the 1979. After that the qualities of the measurements are continuously improving by taking into account various instrumental and environmental effects. The MHB2000 models was introduced in 2002 (Mathews, et.al. 2002, [1]) and it has a good agreement (5 μas) on the short period nutation series (<400 days) with the values derived from 2 decades (1979-2000) VLBI data while a higher uncertainties up to 56 μas for those longer periods (>400 days) nutation series (Herring et.al. 2002). In MHB2000, the forcing frequencies of the nutation series are solved by least-squares fitting to the VLBI data in frequency domain. Koot et al. (2008), have processed another similar set of nutation series by inversing the time series of VLBI data (1984-2005) using a Bayesian approach. In the present work, we will repeat both approaches using the up-to-date 3.5 decades VLBI observations (1980-2014) meanwhile paying more attention on the results of longer period (>400 days). Finally some features of Earth's interior structure will be discussed based on the determined nutation series. [1] Mathews, P.M., Herring, T.A. & Buffett, B.A., 2002. Modeling of nutation and precession: new nutation series for nonrigid Earth and insights into the Earth's interior, J. Geophys. Res., 107, 2068, doi: 10.1029/2001JB000390. [2] Herring, T. A., P. M. Mathews, and B. A. Buffett, Modeling of nutation and precession: Very long baseline interferometry results, J. Geophys. Res., 107, B4, 2069, doi: 10.1029/2001JB000165, 2002 [3] Koot, L., Rivoldini, A., de Viron, O. & Dehant, V., 2008. Estimation of Earth interior parameters from a Bayesian inversion of very long baseline interferometry nutation time series, J. Geophys. Res., 113, 8414, doi: 10.1029/2007JB005409.

  9. Interesting Cataclysmic Variables Observed with K2

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    The K2 long continuous coverage (75 days) of various fields around the ecliptic has provided novel light curves of a variety of cataclysmic variables, many of which are too faint for previous detailed studies. The data through K2-6 has produced light curves for 38 systems, many of which have multiple dwarf nova outbursts. The coverage allows visibility of pre-cursors, inter-outburst behavior as well as orbital features such as eclipses and hot spots. Some of the most intriguing features are presented.

  10. Mean SST bias and variability at inter-annual and decadal time-scales in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Polo, Irene; Villamayor, Julian; Rodriguez-Fonseca, Belen; Mohino, Elsa; Losada, Teresa

    2016-04-01

    Analysis of model systematic errors in Sea Surface Temperature (SST) has generally focused on local processes and particular basins. Mean warm bias over the south subtropical upwelling systems in coupled models are largely studied and local cloud cover, alongshore winds and ocean stratification are pointed out as the responsible processes. Mean errors have impacts on the variability but this is less understood. In this study we try to understand the relation between mean global SST biases and how models perform the variability at different time-scales. To this end, we calculate the SST variability modes for 18 models in the preindustrial control CMIP5 experiment. We first analyse the seasonality of those modes and the inter-model differences. Associated parameters are confronted with the mean SST bias variability among models, thus we conclude how realistic models simulate the variability depending on the mean SST bias. Preliminary results suggest that models with cooler (warmer) that average SST mean bias over the southern hemisphere reproduce better (worse) the Inter-Decadal Pacific variability. Similar mean bias pattern has an effect on the skill for reproducing Pacific El Nino and Atlantic Nino modes. Finally an inter-model SST bias variability mode is found relating errors over the southern upwelling systems with cloud cover around 60S and equatorial precipitation shift. This mode is able to summarize some features in relation with inter-decadal to inter-annual variability in CMIP5 models and thus represents a potential tool to understand the wider picture in relation to SST biases and future projections.

  11. A new centennial index to study the Western North Pacific Monsoon decadal variability

    NASA Astrophysics Data System (ADS)

    Vega, Inmaculada; Gómez-Delgado, F. de Paula; Gallego, David; Ribera, Pedro; Peña-Ortiz, Cristina; García-Herrera, Ricardo

    2016-04-01

    The concept of the Western North Pacific Summer Monsoon (WNPSM) appeared for the first time in 1987. It is, unlike the Indian Summer Monsoon (ISM) and the East Asian summer monsoon (EASM), an oceanic monsoon mostly driven by the meridional gradient of sea surface temperature. Its circulation is characterized by a northwest-southeast oriented monsoon trough with intense precipitation and low-level southwesterlies and upper-tropospheric easterlies in the region [100°-130° E, 5°-15°N]. Up to now, the primary index to characterize the WNPSM has been the Western North Pacific Monsoon Index (WNPMI) which covers the 1949-2013 period. The original WNPMI was defined as the difference of 850-hPa westerlies between two regions: D1 [5°-15°N, 100°-130°E] and D2 [20°-30°N, 110°-140°E]. Both domains are included in the main historical ship routes circumnavigating Asia for hundreds of years. Many of the logbooks of these ships have been preserved in historical archives and they usually contain daily observations of wind force and direction. Therefore, it has been possible to compute a new index of instrumental character, which reconstructs the WNPSM back to the middle of the 19th Century, by using solely historical wind direction records preserved in logbooks. We define the monthly Western North Pacific Directional Index (WNPDI) as the sum of the persistence of the low-level westerly winds in D1 and easterly winds in D2. The advantages of this new index are its nature (instrumental) and its length (1849-2013), which is 100 years longer than the WNPMI (which was based on reanalysis data). Our WNPDI shows a high correlation (r=+0.87, p<0.01) with the previous WNPMI in summer for the 1949-2009 period, thus allowing to study the multidecadal variability of the WNPSM in a more robust way. Our results show that the WNPDI has a strong impact on the precipitation in densely populated areas in South-East Asia, such as the Philippines or the west coast of Myanmar where the

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

    NASA Astrophysics Data System (ADS)

    Hayashi, Masaki; Farrow, Christopher R.

    2014-12-01

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

  13. On the mechanisms of decadal variability of the North Pacific Gyre Oscillation over the 20th century

    NASA Astrophysics Data System (ADS)

    Yi, Daling Li; Zhang, Liping; Wu, Lixin

    2015-09-01

    The decadal variability of the North Pacific gyre oscillation (NPGO) over the 20th century is examined from a long-term integration of the Simple Ocean Data Assimilation (SODA) reanalysis. The NPGO is reflected by the second dominant pattern of sea surface height (SSH) variability in SODA, with a north-south dipole structure over the northeast Pacific. SSH anomalies in this region exhibit distinct decadal variability with a significant spectrum peak at approximately 18 years. The upper-ocean heat budget reveals that this dipole structure associated with the NPGO is predominantly due to the anomalous Ekman pumping and Ekman advection induced by the surface wind. The NPGO mode in SODA reanalysis originates from atmosphere stochastic noise (North Pacific Oscillation) which has a meridional dipole pattern but no preferred time scale. The oceanic planetary wave, particularly the advective baroclinic mode, integration of atmospheric stochastic noise leads to a spatial resonance with preferred decadal time scale. The limitation of current study is also discussed.

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

    PubMed

    Kivinen, Sonja; Rasmus, Sirpa

    2015-04-01

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

  15. 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

  16. Chandra Watches Over A Decade Of Variability In M31 Globular Clusters

    NASA Astrophysics Data System (ADS)

    Barnard, Robin; Li, Z.; Garcia, M.; Murray, S.

    2011-05-01

    The central region of M31 has been monitored with Chandra > 120 times over the last 11 years. In this region we find X-ray sources corresponding to 35 out of 420 globular clusters; these are highly likely to be X-ray binaries. We have created long-term, calibrated lightcurves for all 35 sources, and will present highlights of our variability survey. We have detected significant variability in all the sources with 0.3-10 keV luminosity > 2x10E+36 erg/s. Since the emission spectra of background active galaxies often resemble those of X-ray binaries, the long term variability will be a valuable tool for identifying X-ray binaries in the remaining 400 sources in our field. This work is funded by Chandra grant GO9-0100X and HST grant GO-1101.

  17. Atmospheric Variability of CO2 impact on space observation Requirements

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  18. Does mesoscale matters in decadal changes observed in the northern Canary upwelling system?

    NASA Astrophysics Data System (ADS)

    Relvas, P.; Luís, J.; Santos, A. M. P.

    2009-04-01

    The Western Iberia constitutes the northern limb of the Canary Current Upwelling System, one of the four Eastern Boundary Upwelling Systems of the world ocean. The strong dynamic link between the atmosphere and the ocean makes these systems highly sensitive to global change, ideal to monitor and investigate its effects. In order to investigate decadal changes of the mesoscale patterns in the Northern Canary upwelling system (off Western Iberia), the field of the satellite-derived sea surface temperature (SST) trends was built at the pixel scale (4x4 km) for the period 1985-2007, based on the monthly mean data from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA series satellites, provided by the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory. The time series were limited to the nighttime passes to avoid the solar heating effect and a suite of procedures were followed to guarantee that the temperature trends were not biased towards the seasonally more abundant summer data, when the sky is considerably clear. A robust linear fit was applied to each individual pixel, crossing along the time the same pixel in all the processed monthly mean AVHRR SST images from 1985 until 2007. The field of the SST trends was created upon the slopes of the linear fits applied to each pixel. Monthly mean SST time series from the one degree enhanced International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and from near-shore measurements collected on a daily basis by the Portuguese Meteorological Office (IM) are also used to compare the results and extend the analysis back until 1960. A generalized warming trend is detected in the coastal waters off Western Iberia during the last decades, no matter which data set we analyse. However, significant spatial differences in the warming rates are observed in the satellite-derived SST trends. Remarkably, off the southern part of the Western Iberia the known

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Bruhwiler, L. M.; Matthews, E.

    2007-12-01

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

  1. From seasonal to decadal inter-annual variability of mesozooplankton biomass in the Northern Adriatic Sea (Gulf of Trieste)

    NASA Astrophysics Data System (ADS)

    Kamburska, Lyudmila; Fonda-Umani, Serena

    2009-11-01

    This paper reports the rate of change of mesozooplankton biomass on seasonal, inter-annual and decadal time scale in the Gulf of Trieste (NE Mediterranean, Northern Adriatic). We measured variability in mesozooplankton dry weight (mg DW m - 3 ), organic carbon and nitrogen contents of the DW in relation to mesozooplankton taxonomic structure and some environmental parameters. The study is based on data obtained from mesozooplankton samples collected monthly by a vertical WP2 net (200 µm) from January 1986 to September 2005 at one monitoring station, a coastal site in the Gulf of Trieste. We considered mesozooplankton DW in relation to copepods, phytoplankton taxonomic structure, water temperature and North Atlantic Oscillation. For further analyses we counted also on data for DW for the period 1972-1980, monthly data for organic carbon (mg C m - 3 ) and nitrogen contents (mg N m - 3 ) of the DW for the period 1991-2005, determined by a CHN Elemental Analyzer. We explored statistically our high temporal resolution time series data picking out the main features: seasonal components and trends. Mesozooplankton DW ranged from only 1 mg m - 3 (January 1977) to 95 mg m - 3 (March 1990) in the coastal ecosystem of the Northern Adriatic during the period 1972-2005. The annual cycle of the DW was found to be bimodal with maximum in late winter-spring and a weaker one in late summer. Maximum DW were regularly recorded when Copepods prevailed the mesozooplankton community structure. Similarly, high organic carbon and nitrogen contents were detected when copepods dominated, although wide-ranging on a seasonal scale. Irregular intra- and inter-annual fluctuations were typical mostly during the 1990s. Mesozooplankton DW sharply shifted since 2001-2002 to the level exceeding the observed one during the regime of the 1980s. Our results indicate substantial changes in the seasonal timing of mesozooplankton DW, which together with decadal inter-annual fluctuations match

  2. FUSE observations of Luminous Blue Variables

    NASA Astrophysics Data System (ADS)

    Iping, Rosina C.; Sonneborn, George; Massa, Derck L.

    P Cyg, AG Car, HD 5980 and η Car were observed with the Far Ultraviolet Spectroscopic Explorer ( FUSE) satellite. FUSE covers the spectral range from 980 Å to 1187 Å at a resolution of 0.05 Å. In this paper we discuss the far-UV properties of these LBVs and explore their similarities and differences. The FUSE observations of P Cyg and AG Car, both spectral type B2pe, are very similar. The atmospheres of both η Car and HD 5980 appear to be somewhat hotter and have much higher ionization stages (Si IV, S IV, and P V) in the FUSE spectrum than P Cyg and AG Car. There is a very good agreement between the FUSE spectrum of P Cygni and the model atmosphere computed by John Hillier with his code CMFGEN. The FUSE spectrum of η Car, however, does not agree very well with existing model spectra.

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

    SciTech Connect

    Tippett, Michael K.

    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.

  4. Decadal variability in abundances of the dominant euphausiid species in southern sectors of the California Current

    NASA Astrophysics Data System (ADS)

    Brinton, Edward; Townsend, Annie

    2003-08-01

    Euphausiid abundance data from broadly based California Cooperative Oceanic Fisheries Investigation surveys in California and Baja California sectors of the California Current provided a time series distinguishing periodic, rhythmic and irregular species patterns. Comparisons with environmental indexes indicate significant correlations with warm-water species, most notably in coastal Nyctiphanes simplex. Oceanic warm-water species were similarly, but less extremely, allied with an index. Coastal warm-water N. simplex was uncommon off southern California before the atmospheric regime shift of the 1970s. It assumed a post-1978 pattern of rhythmic biannual abundance increases and decreases during 1981-2000. The near-tropical oceanic Euphausia eximia and Pacific Central subtropicals patterned similarly, but was more periodic than rhythmic. Euphausia pacifica, the most dominant and broadly ranging Euphausia species, peaked at irregular but distinct bi-decadal abundances during 6 strong La Niña episodes. The peaks uniformly collapsed by 90%, becoming El Niño-associated minima. The cold-water coastal northern species Thysanoessa spinifera frequently ranged far south off Baja California before 1960 but became limited to Central California in the 1980s. The importance of T. spinifera off the Californias is small compared with northern regions, but it extends to southern upwelling centers contributing to dominance, here, by cold-water euphausiids. Decadal periodicity of species abundances decreased in the 1990s, when trends became more common. Differences among sectors were minimal between the two Californias, but were often distinct between southern California and Central Baja California. Species abundances, comparing pre- and post-climate shift species averages, differed insignificantly for all species when logarithmic values were used. With arithmetic values, most 1977-1998 average values were the greater, but with large standard deviations.

  5. Decadal wave power variability in the North-East Atlantic and North Sea

    NASA Astrophysics Data System (ADS)

    Santo, H.; Taylor, P. H.; Woollings, T.; Poulson, S.

    2015-06-01

    Estimation of the long-term behavior of wave climate is crucial for harnessing wave energy in a cost-effective way. Previous studies have linked wave heights to the north-south atmospheric pressure anomalies in the North Atlantic, suggesting that the wave climate fluctuates as a response to changes in zonal circulation in the atmosphere. We identify changes in wave power in the North-East Atlantic that are strongly correlated to the dominant pressure anomalies, the North Atlantic Oscillation (NAO), and other modes. We present a reconstructed wave power climate for 1665-2005, using a combination of known and proxy indices for the NAO and other modes. Our reconstruction shows high interannual and multidecadal variability, which makes wave energy prediction challenging. This variability should be considered in any long-term reliability analysis for wave energy devices and in power scheme economics.

  6. A Decade of Combination Antiretroviral Treatment in Asia: The TREAT Asia HIV Observational Database Cohort.

    PubMed

    2016-08-01

    Asian countries have seen the expansion of combination antiretroviral therapy (cART) over the past decade. The TREAT Asia HIV Observational Database (TAHOD) was established in 2003 comprising 23 urban referral sites in 13 countries across the region. We examined trends in treatment outcomes in patients who initiated cART between 2003 and 2013. Time of cART initiation was grouped into three periods: 2003-2005, 2006-2009, and 2010-2013. We analyzed trends in undetectable viral load (VL; defined as VL <400 copies/ml), CD4 changes from pre-cART levels, and overall survival. Of 6,521 patients included, the overall median CD4 count at cART initiation was 120 cells/μl (interquartile range: 38-218). Despite an increase over time, pre-cART CD4 counts remained <200 cells/μl. Adjusted analyses showed undetectable VL was more likely when starting cART in later years [2006-2009: odds ratio (OR) = 1.76, 95% confidence interval (CI) (1.45, 2.15); and 2010-2013: OR = 3.04, 95% CI (2.33, 3.97), all p < .001, compared to 2003-2005], and survival was improved [2006-2009: subdistribution hazard ratio (SHR) = 0.41, 95% CI (0.27, 0.61), 2010-2013: SHR = 0.29, 95% CI (0.17, 0.49), all p < .001, compared to 2003-2005]. No differences in CD4 response was observed over time. Age and CD4 levels prior to cART initiation were associated with all three treatment outcomes, with older age and higher CD4 counts being associated with undetectable VL. Survival and VL response on cART have improved over the past decade in TAHOD, although CD4 count at cART initiation remained low. Greater effort should be made to facilitate earlier HIV diagnosis and linkage to care and treatment, to achieve greater improvements in treatment outcomes. PMID:27030657

  7. Mechanisms of internally generated decadal-to-multidecadal variability of SST in the Atlantic Ocean in a coupled GCM

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Schneider, Edwin K.; Wu, Zhiwei

    2016-03-01

    Mechanisms of the internally generated decadal-to-multidecadal variability of SST in the Atlantic Ocean are investigated in a long control simulation of the Community Climate System Model version 3 with constant external forcing. The interactive ensemble (IE) coupling strategy, with an ensemble of atmospheric GCMs (AGCM) coupled to an ocean model, a sea-ice model and a land model, is used to diagnose the roles of various processes in the coupled GCM (CGCM). The noise components of heat flux, wind stress and fresh water flux of the control simulation, determined from the CGCM surface fluxes by subtracting the SST-forced surface fluxes, estimated as the ensemble mean of AGCM simulations, are applied at the ocean surface of the IE in different regions and in different combinations. The IE simulations demonstrate that the climate variability in the control simulation is predominantly forced by noise. The local noise forcing is found to be responsible for the SST variability in the Atlantic Ocean, with noise heat flux and noise wind stress playing a critical role. The control run Atlantic multidecadal variability (AMV) index is decomposed into interannual, decadal and multidecadal modes based on the ensemble empirical mode decomposition. The AMV multidecadal mode, a combination of 50- and 100-year modes, is examined in detail. The North Atlantic Oscillation (NAO) pattern in the atmosphere, dominated by the noise component, forces the multidecadal mode through noise heat flux and noise wind stress. The noise wind stress forcing on the multidecadal mode is associated with ocean dynamics, including gyre adjustment and the Atlantic Meridional Overturning Circulation (AMOC). The AMV decadal mode is also found to be related to noise NAO forcing. The associated ocean dynamics are connected with both noise heat flux and noise wind stress, but the AMOC related to the decadal mode is more likely to be forced by noise heat flux. For both multidecadal and decadal modes, the

  8. Solar variability observed with GMS/SEM

    NASA Astrophysics Data System (ADS)

    Nagai, Tsugunobu

    1987-06-01

    Daily averaged data on energetic protons, alpha particles, and electrons obtained between 1978-1986 with different channels of SEM aboard the Geostationary Meteorological Satellite 'Himawari' are presented and discussed. Most solar particle events (SPEs), observed in the P2-P6 and A1-A5 channels, show a gradual rise and a further gradual decay of the particle fluxes, although some SREs displayed a sharp rise and a gradual decay. SPEs, which occurred frequently in the 1978-1979 and 1981-1982 periods, were less frequent after 1983; however, there occurred several large and energetic SREs between 1983 and 1986. Therefore, the long-term trend in the high-energy particle ejection from the sun is quite different from that in the sunspot number. The fluxes from the EL and P1 channel response, largely due to energetic particles trapped in the earth's magnetic field, show substorm-induced variations, the characteristics of which depend highly on local time.

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  11. Evolving into a remnant: optical observations of SN 1978K at three decades

    NASA Astrophysics Data System (ADS)

    Kuncarayakti, H.; Maeda, K.; Anderson, J. P.; Hamuy, M.; Nomoto, K.; Galbany, L.; Doi, M.

    2016-05-01

    We present new optical observations of the supernova SN 1978K, obtained in 2007 and 2014 with the Very Large Telescope. We discover that the supernova has not faded significantly, even more than three decades after its explosion. The spectrum exhibits numerous narrow (FWHM ≲600 km s-1) emission lines, indicating that the supernova blastwave is persistently interacting with dense circumstellar material (CSM). Evolution of emission lines indicates that the supernova ejecta is slowly progressing through the reverse shock, and has not expanded past the outer edge of the circumstellar envelope. We demonstrate that the CSM is not likely to be spherically distributed, with mass of ≲1 M⊙. The progenitor mass loss rate is estimated as ≳0.01 M⊙ yr-1. The slowly fading late-time light curve and spectra show striking similarity with SN 1987A, indicating that a rate at which the CSM is being swept-up by the blastwave is gradually decaying and SN 1978K is undergoing similar evolution to become a remnant. Due to its proximity (4 Mpc), SN 1978K serves as the next best example of late-time supernova evolution after SN 1987A.

  12. 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.

  13. Decadal to Millennial Scale Climate Variability in the Gulf of Maine

    NASA Astrophysics Data System (ADS)

    Steponaitis, E. A.; Keigwin, L. D.

    2009-12-01

    We analyze a 288 centimeter giant gravity core (CH1204 GGC-5) and a 53 centimeter multicore (OCE400 MC-44) from the Jordan Basin in the Gulf of Maine to construct an approximately 10,000 year record of past sea surface temperature. δ18O values and assemblages of planktonic foraminifera species, primarily the left and right coiling varieties of Neogloboquadrina pachyderma, serve as proxies for sea surface temperature. The 10,000 year, low-resolution δ18O record from CH1204 GGC-5 suggests long-term cooling with significant millennial-scale fluctuations; the approximately 200 year, high-resolution δ18O record from OCE400 MC-44 shows a decadal-scale signal with no apparent trend. Comparison of the high-resolution record of OCE400 MC-44 with the low-resolution record of CH1204 GGC-5 is relevant to our understanding of Holocene modes of the North Atlantic Oscillation, the Atlantic Multidecadal Oscillation, and the strength of the Labrador Current.

  14. A Decade of Cassini Radio Science Observations of the Saturn System

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  15. 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

    -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.

  16. Rainfall variability in southern Spain on decadal to centennial time scales

    NASA Astrophysics Data System (ADS)

    Rodrigo, F. S.; Esteban-Parra, M. J.; Pozo-Vázquez, D.; Castro-Díez, Y.

    2000-06-01

    In this work a long rainfall series in Andalusia (southern Spain) is analysed. Methods of historical climatology were used to reconstruct a 500-year series from historical sources. Different statistical tools were used to detect and characterize significant changes in this series. Results indicate rainfall fluctuations, without abrupt changes, in the following alternating dry and wet phases: 1501-1589 dry, 1590-1649 wet, 1650-1775 dry, 1776-1937 wet and 1938-1997 dry. Possible causal mechanisms are discussed, emphasizing the important contribution of the North Atlantic Oscillation (NAO) to rainfall variability in the region. Solar activity is discussed in relation to the Maunder Minimum period, and finally the past and present are compared. Results indicate that the magnitude of fluctuations is similar in the past and present.

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

    NASA Astrophysics Data System (ADS)

    Willems, Patrick

    2014-05-01

    Recent studies have shown that rainfall and hydrological extremes do not randomly occur in time, but are subject to multidecadal oscillations. In addition to these oscillations, there are temporal trends due to climate change. Design statistics, such as intensity-duration-frequency (IDF) for extreme rainfall or flow-duration-frequency (QDF) relationships, are affected by both types of temporal changes (short term and long term). This presentation discusses these changes, how they influence water engineering design and decision making, and how this influence can be assessed and taken into account in practice. The multidecadal oscillations in rainfall and hydrological extremes were studied based on a technique for the identification and analysis of changes in extreme quantiles. The statistical significance of the oscillations was evaluated by means of a non-parametric bootstrapping method. Oscillations in large scale atmospheric circulation were identified as the main drivers for the temporal oscillations in rainfall and hydrological extremes. They also explain why spatial phase shifts (e.g. north-south variations in Europe) exist between the oscillation highs and lows. Next to the multidecadal climate oscillations, several stations show trends during the most recent decades, which may be attributed to climate change as a result of anthropogenic global warming. Such attribution to anthropogenic global warming is, however, uncertain. It can be done based on simulation results with climate models, but it is shown that the climate model results are too uncertain to enable a clear attribution. Water engineering design statistics, such as extreme rainfall IDF or peak or low flow QDF statistics, obviously are influenced by these temporal variations (oscillations, trends). It is shown in the paper, based on the Brussels 10-minutes rainfall data, that rainfall design values may be about 20% biased or different when based on short rainfall series of 10 to 15 years length, and

  18. 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

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

    NASA Astrophysics Data System (ADS)

    Wei, Z.; Kuang, W.; Jiang, W.

    2006-12-01

    In this presentation we discuss the application of EOF and Complex EOF approaches to examine possible correlation between temporal-spatial distributions of the time variable gravity (TVG) and magnetic secular variations (SV) on decadal time scales and longer. The advantage of such approaches is to enable us identifying approximately 3 to 4 EOF/CEOF modes that account for the most of the signals. We apply these approaches to examine the gravity and magnetic field data generated by the MoSST numerical core dynamics model and the PREM model. Our results show that the first 3 EOF modes reproduce the most significant features of the spatial distributions, thus sufficient for understanding the correlation between the two potential fields. We are currently working on applying this analysis to the 20-year time variable gravity from SLR and satellite measurements, and the surface geomagnetic field from GUFM1.

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

    NASA Astrophysics Data System (ADS)

    Jimenez-Amat, Patricia; Zahn, Rainer

    2013-04-01

    High-resolution records of natural interglacial climate variability can provide knowledge if the currently ongoing climate change and variability are part of or are already beyond the natural state. Warmer-than-present climatic conditions, a reduced Greenland Ice Sheet and higher sea level are some of the features the Last Interglacial (LIG, MIS5e; 129-115 kyr) climate has in common with numerous model projections of our future climate (Otto-Bliesner et al., 2006; Koop et al., 2009). Establishing multi-decadal resolution records of past North Atlantic climate variability hence contributes to a better understanding of the ocean and climate sensitivity of the wider North Atlantic region. We present palaeoceanographic time series of surface ocean climatology from Ocean Drilling Program (ODP) Site 976 in the Alboran Sea, westernmost Mediterranean that span the LIG and Present Interglacial (PIG, Holocene, 11-0 kyr). The site receives North Atlantic climate signals through the atmosphere and with the advection of Atlantic inflow waters which in connection with the high rate of sediment deposition underscores the exceptional quality of the site to monitor North Atlantic climate variability at multi-decadal resolution (60-90 yrs). Sea surface temperature (SST) time series derived from Mg/Ca ratios and stable isotope records (δ18O, δ13C) of the planktonic foraminifera Globigerina bulloides are presented. Mg/Ca data display similar SST for the climatic optima PIG and LIG. The records compare well with speleothem and ice core palaeoclimatic profiles, confirming that Site 976 palaeo-profiles reflect climate of the North Atlantic region. The close link between SSTMg-Caand the LIG δ18O record from the Antro del Corchia speleothem in northern Italy highlights the strong connection between marine and terrestrial climatology during that time indicating a farfield contribution of atmospheric signals. Comparison with SST and benthic δ13C records at North Atlantic sites instructs

  1. Multi-decadal variability of ice extent in the Barents Sea

    NASA Astrophysics Data System (ADS)

    Vinje, T.; Colony, R.

    2003-04-01

    The European Arctic has been explored and commercially exploited for more than 400 years. In 1596, Willem Barentsz sailed the northern Barents Sea reporting on sea-ice extent and on the large number of whales found along the ice edge. By the early 17th century, an extensive and sophisticated whaling industry had developed in northern Spitzbergen. The whale hunters systematically observed and logged sea-ice conditions and ice edge location. These shipboard observations provide sea-ice extent information throughout the Nordic Seas and the western Barents for much of the 17th and 18th centuries. In 1850, Norway began extensive whale/seal hunting along the ice edge, stretching from Iceland to Novaya Zemlya. The records of sea-ice conditions and extent were archived by the Norwegian Polar Research Institute and are now placed in the ACSYS Historical Ice Chart Database. The annual April and August latitude of sea-ice extent in the western Barents is constructed for the period 1730-2000. The early part of the record (1730-1790) suggests April and August ice conditions similar to the modern era. However, just at the end of the 18th century, the sea-ice moved 300 km southward of its previous mean position. For the next 200 years (1800-2000), sea ice cover in the western Barents has steadily receded to its present state. Covariance studies offer insight into the processes controlling sea-ice extent and serve to bound the observational errors. The instrumental temperature record is mostly limited to the past 150-years. During this period, we estimate the correlation between Northern Hemisphere mean temperature and August sea-ice extent at r = 0.80 (using 7-year running means). Temperature records from central England are available from 1700, as are proxy temperature based data boreholes from the Greenland Ice Sheet Project. Again, significant covariance is found. The most provocative data come from sun spot observations and the associated time series of solar total irradiance

  2. The Decadal Variability of Cosmic Ray Flux Outside of a Grand Solar Maximum

    NASA Astrophysics Data System (ADS)

    Thomas, Simon; Owens, Mathew; Lockwood, Mike

    2016-04-01

    Galactic cosmic ray (GCR) flux is modulated by changes in the Sun's magnetic field. In the long-term, GCRs flux at Earth varies in a 22-year cycle. Observing time-series of GCR flux we see a pattern of 'flat topped' and 'spiked topped' peaks. It is thought that differing drift patterns for when the northern solar pole is predominantly positive (qA>0) to when the northern pole is negative (qA<0) cause this difference in modulation. We demonstrate a link between GCR modulation and long-term changes in the intensity and structure of the large-scale heliospheric magnetic field, particularly during the declining phase of consecutive solar cycles. Using reconstructions of the heliospheric field from geomagnetic data, we demonstrate that this cause of GCR modulation is only present in cycles during the recent Grand Solar Maximum and not during the weaker period of activity prior to it. We therefore suggest that the current decline in solar activity will result in different long-term patterns in GCR data to those observed during the space-age which would be important for the planning of space-based missions. Finally, we compare our results to ice-core data (found to display the 22-year variation) to further explore how the 22-year cycle varies between different solar activity periods.

  3. 30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  4. Temperature Responses to Spectral Solar Variability on Decadal and Centennial Time Scales

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    We apply two scenarios of 11-year solar spectral forcing, namely SIM-based out-of-phase variations and proxy-based in-phase variations, as input to a time-dependent radiative-convective model (RCM), and also to the GISS modelE GCM. For both scenarios, and both models, we find that the maximum temperature response occurs in the upper stratosphere, and temperature responses decrease downward to the surface. The upper stratospheric temperature peak-to-peak responses to out-of-phase solar forcing are ~0.6 K in RCM and ~0.9 K over the tropical region in GCM simulations, a factor of ~5 times as large as responses to in-phase solar forcing. Stratospheric responses are in-phase with TSI (Total Solar Irradiance) variations. The modeled upper stratospheric temperature response to the SORCE SIM observed SSI (Spectral Solar Irradiance) forcing resembles 11-year temperature variations observed with HALOE (Halogen Occultation Experiment). Surface responses to the two SSI scenarios are small for both RCM and GCM studies, as compared to stratospheric responses. Though solar irradiance variations on centennial time scale are not well known, the two scenarios of reconstructed TSI time series (i.e., one based on 11-year cycles with background [Lean 2000] and the second from flux transport that has much less background change [Wang, Lean, and Sheeley, 2005]) provide a range of variations of TSI on centennial time scales. We apply phase relations among different spectral irradiance bands both from SIM observation and proxy reconstructions to the two scenarios of historical TSI. The spectral solar forcing is used to drive the RCM. The updated atmosphere and ocean mixed coupled RCM including diffusion to deep-ocean provides a first-order estimate of climate response. We report the different responses of stratosphere, troposphere, and ocean surface to these 4 scenarios of centennial spectral solar forcing. We further discuss the mechanisms for atmosphere-ocean and stratosphere

  5. Observed decadal ocean warming (2005-2014) and its contribution to the top of atmosphere energy budget

    NASA Astrophysics Data System (ADS)

    Llovel, W.; Terray, L.

    2015-12-01

    Quantifying ocean heat content and its change is essential for understanding the response of the climate system to radiative forcing because the oceans are the dominant reservoir of heat on Earth. Here we investigate the 2005-2014 ocean heat content change inferred by Argo gridded products provided by three different groups. Overall, we demonstrate a good agreement among the different products despite a few discrepancies at global and regional scales. We found a decadal increase of ocean heat content of 8.19 +/- 0.68 J/yr. This corresponds to an ocean heat uptake of 0.74 +/- 0.06 W/m2, in good agreement with the IPCC-AR5 estimate report of 0.71W/m2 for 1993-2010. As the Argo coverage is not perfect (coastal regions, marginal seas and semi-enclosed seas are not well sampled by the floats), we compare the global ocean heat content (0-2000m) with and without the aforementioned regions using the ORAS4 ocean reanalysis and find no significant differences between the two estimates. We then show that the Southern hemisphere explains about 90% of the net global ocean heat content increase during 2005-2014 while the Northern hemisphere shows large interannual variability and explains only 10% of the net increase. We also find that the maximum warming is centered at 40°S with two main structures located in the Indian and Pacific oceans, suggesting a possible heat penetration due to the wind-driven mean ocean circulation. We finally compare the annually averaged ocean heating rates with the net TOA flux inferred by CERES and the atmospheric reanalysis ERA-Interim. We find that ocean heating rates show large interannual variability associated with a large spread around the mean estimate (based on the three gridded T/S products). We confirm that the mean ocean heating rate is comparable to the net TOA flux for the last decade within observational uncertainties. However, we find a discrepancy for 2013 that could be due to unsampled regions and/or the significant contribution to

  6. 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.

  7. Interannual and decadal variability in zooplankton communities of the southeast Bering Sea shelf

    NASA Astrophysics Data System (ADS)

    Napp, Jeffrey M.; Baier, Christine T.; Brodeur, Richard D.; Coyle, Kenneth O.; Shiga, Naonobu; Mier, Kathy

    2002-12-01

    The southeastern Bering Sea shelf ecosystem is an important fishing ground for fin- and shellfish, and is the summer foraging grounds for many planktivorous seabirds and marine mammals. In 1997 and 1998, Northern Hemisphere climate anomalies affected the physical and biological environment of the southeastern Bering Sea shelf. The resulting anomalous conditions provided a valuable opportunity to examine how longer-term climate change might affect this productive ecosystem. We compared historical and recent zooplankton biomass and species composition data for the southeastern Bering Sea shelf to examine whether or not there was a response to the atmosphere-ocean-ice anomalies of 1997 and 1998. Summer zooplankton biomass (1954-1994) over the southeastern shelf did not exhibit a decline as previously reported for oceanic stations. In addition, zooplankton biomass in 1997 and 1998 was not appreciably different from other years in the time series. Spring concentrations of numerically abundant copepods ( Acartia spp., Calanus marshallae, and Pseudocalanus spp.), however, were significantly higher during 1994-1998 than 1980-1981; spring concentrations of Metridia pacifica and Neocalanus spp. were not consistently different between the two time periods. Neocalanus spp. was the only taxon to have consistent differences in stage composition between the two time periods—CV copepodites were much more prevalent in May of the 1990s than early 1980s. Since relatively high zooplankton concentrations were observed prior to 1997, we do not attribute the high concentrations observed in the summers of 1997 and 1998 directly to the acute climate anomalies. With the present data it is not possible to distinguish between increased production (control from below) and decreased predation (control from above) to explain the recent increase in concentrations of the species examined.

  8. FRESIP project observations of cataclysmic variables: A unique opportunity

    NASA Technical Reports Server (NTRS)

    Howell, Steve B.

    1994-01-01

    FRESIP Project observations of cataclysmic variables would provide unique data sets. In the study of known cataclysmic variables they would provide extended, well sampled temporal photometric information and in addition, they would provide a large area deep survey; obtaining a complete magnitude limited sample of the galaxy in the volume cone defined by the FRESIP field of view.

  9. 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…

  10. Observations and simulations of the ionospheric lunar tide: Seasonal variability

    NASA Astrophysics Data System (ADS)

    Pedatella, N. M.

    2014-07-01

    The seasonal variability of the ionospheric lunar tide is investigated using a combination of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations and thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) simulations. The present study focuses on the seasonal variability of the lunar tide in the ionosphere and its potential connection to the occurrence of stratosphere sudden warmings (SSWs). COSMIC maximum F region electron density (NmF2) and total electron content observations reveal a primarily annual variation of the ionospheric lunar tide, with maximum amplitudes occurring at low latitudes during December-February. Simulations of the lunar tide climatology in TIME-GCM display a similar annual variability as the COSMIC observations. This leads to the conclusion that the annual variability of the lunar tide in the ionosphere is not solely due to the occurrence of SSWs. Rather, the annual variability of the lunar tide in the ionosphere is generated by the seasonal variability of the lunar tide at E region altitudes. However, compared to the observations, the ionospheric lunar tide annual variability is weaker in the climatological simulations which is attributed to the occurrence of SSWs during the majority of the years included in the observations. Introducing a SSW into the TIME-GCM simulation leads to an additional enhancement of the lunar tide during Northern Hemisphere winter, increasing the lunar tide annual variability and resulting in an annual variability that is more consistent with the observations. The occurrence of SSWs can therefore potentially bias lunar tide climatologies, and it is important to consider these effects in studies of the lunar tide in the atmosphere and ionosphere.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  12. GALEX observations of quasar variability in the ultraviolet

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    Aims: Using archival observations recorded over a 5+ year timeframe with the NASA GALaxy Evolution eXplorer (GALEX) satellite, we present a study of the ultraviolet (UV) variability of 4360 quasars of redshifts up to z = 2.5 that have optical counterparts in the Sloan Digital Sky Survey DR5 spectroscopic catalog of Schneider et al. (2007, AJ, 134, 102). The observed changes in both the far UV (FUV: 1350-1785 Å) and near UV (NUV: 1770-2830 Å) AB magnitudes as a function of time may help differentiate between models of the emission mechanisms thought to operate in these active galaxies. Methods: A list of NUV and FUV variable quasars was derived from the UV light-curves of sources with 5 or more observational visits by GALEX that spanned a time-frame > 3 months. By measuring the error in the derived mean UV magnitude from the series of GALEX observations for each source, quasars whose UV variability was greater than the 3-σ variance from the mean observed value were deemed to be (intrinsically) UV variable. This conservative selection criterion (which was applied to both FUV and NUV observations) resulted in identifying 550 NUV and 371 FUV quasars as being statistically significant UV variable objects. Results: Following the work of Vanden Berk et al. (2004, ApJ, 601, 692), we have performed a structure function (SF) analysis of these data to search for possible correlations between UV variability and parameters such as rest frame time-lag, redshift, luminosity and radio loudness. Firstly, we observe that the amplitudes of variability as a function of time-lag for both the NUV and FUV data are far larger than those observed at visible wavelengths. Secondly, the levels of FUV variability are greater than those observed in the NUV for a given value of time-lag. Also, the amplitudes of both the NUV and FUV variability of quasars increase as a function of rest frame time-lag, irrespective of the value of quasar redshift, for time-lags <200 days. For time-lags >300

  13. Constraining Model Climate Sensitivity by Observations of the Decadal Solar Cycle

    NASA Astrophysics Data System (ADS)

    Camp, C. D.; Tung, K. K.; Zhou, J.

    2010-12-01

    Recent analyses have revealed the global response of the Earth's surface temperature to the decadal solar cycle. The strength of this response can be used as a constraint on model climate sensitivity. We shall review evidence supporting the argument that the real climate sensitivity is probably towards the high end in the range of values reported by the coupled atmosphere-ocean general circulation models assessed by the most recent Intergovernmental Panel on Climate Change.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  16. 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

    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 μM 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.

  17. 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.

  18. 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

  19. 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

  20. Comparisons of observed and modelled lake δ18O variability

    NASA Astrophysics Data System (ADS)

    Jones, Matthew D.; Cuthbert, Mark O.; Leng, Melanie J.; McGowan, Suzanne; Mariethoz, Gregoire; Arrowsmith, Carol; Sloane, Hilary J.; Humphrey, Kerenza K.; Cross, Iain

    2016-01-01

    With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

  1. Surface Mass Balance of the Greenland Ice Sheet: Connections to Mechanisms of Climate Variability on Decadal to Centennial Time Scales

    NASA Astrophysics Data System (ADS)

    Andres, H.; Peltier, W. R.

    2011-12-01

    The role of natural forcing in generating variability in the surface mass balance of the Greenland ice sheet (GrIS) remains unclear. Furthermore, mass variations in the GrIS over the past several centuries are poorly constrained. Until the impact of natural climate variations is better understood, it will be difficult to isolate the role anthropogenic greenhouse gases have had on GrIS-induced sea level rise, and to make predictions of GrIS changes in the future. To begin to address these issues, we have performed a suite of global, atmosphere-ocean general circulation model simulations of the past millennium. These runs are long enough to establish the connection between Arctic climate conditions and surface mass balance changes over the Greenland ice sheet over a wide range of timescales. We have created five historical simulations from years 850 to 2000 using the Community Climate System Model 3 and boundary conditions consistent with the Paleoclimate Modelling Intercomparison Project Phase 3. Over this preindustrial period, we have examined how average temperatures and total precipitation over regions of the GrIS varied with Arctic sea ice extent, NAO/NAM, Atlantic Meridional Overturning Circulation, Atlantic Multi-decadal Oscillation, ENSO, volcanic aerosol loading, and total solar irradiance changes. Overall, we find that variations on timescales longer than 30 years correlate well with several of these sources of climate variability, and that variations on shorter timescales are less well-connected. We also find that there are clear regional differences in the temperature and precipitation responses. Thus, in this presentation we focus on the sources of climate variability that we find to be most important to Greenland regional temperatures and precipitation in our suite of millennium simulations. Finally, we extended these simulations into the future using representative concentration pathways from the Coupled Model Intercomparison Project Phase 5. We

  2. 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/).

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  6. Potential impacts of a future Grand Solar Minimum on decadal regional climate change and interannual hemispherical climate variability

    NASA Astrophysics Data System (ADS)

    Spiegl, Tobias; Langematz, Ulrike

    2016-04-01

    The political, technical and socio-economic developments of the next decades will determine the magnitude of 21st century climate change, since they are inextricably linked to future anthropogenic greenhouse gas emissions. To assess the range of uncertainty that is related to these developments, it is common to assume different emission scenarios for 21st climate projections. While the uncertainties associated with the anthropogenic greenhouse gas forcing have been studied intensely, the contribution of natural climate drivers (particularly solar variability) to recent and future climate change are subject of intense debate. The past 1,000 years featured at least 5 excursions (lasting 60-100 years) of exceptionally low solar activity, induced by a weak magnetic field of the Sun, so called Grand Solar Minima. While the global temperature response to such a decrease in solar activity is assumed to be rather small, nonlinear mechanisms in the climate system might amplify the regional temperature signal. This hypothesis is supported by the last Grand Solar Minimum (the Maunder Minimum, 1645-1715) which coincides with the Little Ice Age, an epoch which is characterized by severe cold and hardship over Europe, North America and Asia. The long-lasting minimum of Solar Cycle 23 as well as the overall weak maximum of Cycle 24 reveal the possibility for a return to Grand Solar Minimum conditions within the next decades. The quantification of the implications of such a projected decrease in solar forcing is of ultimate importance, given the on-going public discussion of the role of carbon dioxide emissions for global warming, and the possible role a cooling due to decreasing solar activity could be ascribed to. Since there is still no clear consensus about the actual strength of the Maunder Minimum, we used 3 acknowledged solar reconstruction datasets that show significant differences in both, total solar irradiance (TSI) and spectral irradiance (SSI) to simulate a future

  7. 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).

  8. Variations in water storage in China over recent decades from GRACE observations and GLDAS

    NASA Astrophysics Data System (ADS)

    Mo, X.; Wu, J. J.; Wang, Q.; Zhou, H.

    2016-02-01

    We applied Gravity Recovery and Climate Experiment (GRACE) Tellus products in combination with Global Land Data Assimilation System (GLDAS) simulations and data from reports, to analyze variations in terrestrial water storage (TWS) in China as a whole and eight of its basins from 2003 to 2013. Amplitudes of TWS were well restored after scaling, and showed good correlations with those estimated from models at the basin scale. TWS generally followed variations in annual precipitation; it decreased linearly in the Huai River basin (-0.56 cm yr-1) and increased with fluctuations in the Changjiang River basin (0.35 cm yr-1), Zhujiang basin (0.55 cm yr-1) and southeast rivers basin (0.70 cm yr-1). In the Hai River basin and Yellow River basin, groundwater exploitation may have altered TWS's response to climate, and TWS kept decreasing until 2012. Changes in soil moisture storage contributed over 50 % of variance in TWS in most basins. Precipitation and runoff showed a large impact on TWS, with more explained TWS in the south than in the north. North China and southwest rivers region exhibited long-term TWS depletions. TWS has increased significantly over recent decades in the middle and lower reaches of Changjiang River, southeastern coastal areas, as well as the Hoh Xil, and the headstream region of the Yellow River in the Tibetan Plateau. The findings in this study could be helpful to climate change impact research and disaster mitigation planning.

  9. How well can interannual to decadal-scale variability in stratospheric ozone and water vapor be quantified using limb-based satellite measurements?

    NASA Astrophysics Data System (ADS)

    Davis, S. M.; Rosenlof, K. H.; Hurst, D. F.; Hassler, B.; Read, W. G.

    2015-12-01

    Vertical profiles of ozone and humidity from the upper troposphere to stratosphere have been retrieved from a number of limb sounding and solar occultation satellite instruments since the 1980's. In particular, measurements from the SAGE instruments, UARS MLS, UARS HALOE, and most recently Aura MLS, have provided overlapping data since 1984. In order to quantify interannual- to decadal-scale variability in water vapor and ozone, it is necessary to have a uniform and homogenous record over the period of interest. With this in mind, we merged the aforementioned satellite measurements to create the Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) data set, which contains vertically resolved zonal-mean (2.5°) monthly-mean water vapor and ozone concentration at levels covering the stratosphere. In this presentation, we describe the process of merging the satellite data sets, which involves adjusting the data to a reference measurement using offsets calculated from coincident observations taken during instrument overlap periods. Uncertainties associated with individual measurement precision, geophysical variability, and the merging process are quantified and compared to one another. We show that while the SWOOSH data can be used to quantify interannual variability, quantifying long-term trends in SWOOSH is complicated by the various sources of uncertainty, as well as by potential drifts of individual instruments. The issue of satellite-derived trends is discussed in relation to the long-term record of balloon-borne frostpoint hygrometer measurements from Boulder, CO.

  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. Influence of internal decadal variability on the summer rainfall in Eastern China as simulated by CCSM4

    NASA Astrophysics Data System (ADS)

    Zhu, Yali; Wang, Tao; Ma, Jiehua

    2016-06-01

    The combined impact of the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) on the summer rainfall in eastern China was investigated using CCSM4. The strongest signals occur with the combination of a positive PDO and a negative AMO (+PDO-AMO), as well as a negative PDO and a positive AMO (-PDO+AMO). For the +PDO-AMO set, significant positive rainfall anomalies occur over the lower reaches of the Yangtze River valley (YR), when the East Asian summer monsoon becomes weaker, while the East Asian westerly jet stream becomes stronger, and ascending motion over the YR becomes enhanced due to the jet-related secondary circulation. Contrary anomalies occur over East Asia for the -PDO+AMO set. The influence of these two combinations of PDO and AMO on the summer rainfall in eastern China can also be observed in the two interdecadal rainfall changes in eastern China in the late 1970s and late 1990s.

  12. The American Association of Variable Star Observers (AAVSO)

    NASA Astrophysics Data System (ADS)

    Searle, Travis; Templeton, M.; Price, A.; Henden, A.

    2006-12-01

    Founded in 1911 and headquartered in Cambridge, Massachusetts, the American Association of Variable Star Observers (AAVSO) is a non-profit worldwide scientific and educational organization of professional and amateur astronomers dedicated to the observing and research of variable stars. The AAVSO International Database has over 13 million observations contributed by over 2,500 observers from around the world. The AAVSO receives thousands of data requests per year from the astronomical community. AAVSO observers also contribute to active research programs and community support activities like target-of-opportunity monitoring and coordinated observing campaigns, as well as providing early notification of rare events like novae and supernovae. In 2006, the AAVSO received over 700,000 new observations. Approximately 2/3rds were photometric (UBVRIJH) and about 3/5ths of AAVSO active observers reside outside the United States. The AAVSO is also active in training amateurs in observing techniques, data mining, and data analysis and also runs an active education and public outreach (E/PO) program including the NSF-funded Hands-On Astrophysics Curriculum. AAVSO data is available for download in near real-time at www.aavso.org.

  13. 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.

  14. 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.

    2014-06-01

    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.

  15. A decade of Rossi X-ray Timing Explorer Seyfert observations: An RXTE Seyfert spectral database

    NASA Astrophysics Data System (ADS)

    Mattson, Barbara Jo

    2008-10-01

    With over forty years of X-ray observations, we should have a grasp on the X- ray nature of active galactic nuclei (AGN). The unification model of Antonucci and Miller (1985) offered a context for understanding observations by defining a "typical" AGN geometry, with observed spectral differences explained by line- of-sight effects. However, the emerging picture is that the central AGN is more complex than unification alone can describe. We explore the unified model with a systematic X-ray spectral study of bright Seyfert galaxies observed by the Rossi X-Ray Timing Explorer (RXTE) over its first 10 years. We develop a spectral-fit database of 821 time-resolved spectra from 39 Seyfert galaxies fitted to a model describing the effects of an X-ray power-law spectrum reprocessed and absorbed by material in the central AGN region. We observe a relationship between radio and X-ray properties for Seyfert 1s, with the spectral parameters differing between radio-loud and radio-quiet Seyfert 1s. We also find a complex relationship between the Fe K equivalent width ( EW ) and the power-law photon index (Gamma) for the Seyfert 1s, with a correlation for the radio-loud sources and an anti-correlation for the radio- quiet sources. These results can be explained if X-rays from the relativistic jet in radio-loud sources contribute significantly to the observed spectrum. We observe scatter in the EW-Gamma relationship for the Seyfert 2s, suggesting complex environments that unification alone cannot explain. We see a strong correlation between Gamma and the reflection fraction ( R ) in the Seyfert 1 and 2 samples, but modeling degeneracies are present, so this relationship cannot be trusted as instructive of the AGN physics. For the Seyfert 1 sample, we find an anticorrelation between EW and the 2 to 10 keV luminosity ( L x ), also known as the X-ray Baldwin effect. This may suggest that higher luminosity sources contain less material or may be due to a time-lag effect. We do not

  16. Variability of Arctic Sea Ice as Determined from Satellite Observations

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1999-01-01

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

  17. Characteristics of IR variable stars as observed from orbit

    NASA Technical Reports Server (NTRS)

    Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Chapman, R. D.; Hobbs, R. W.; Michalitsanos, A. G.

    1976-01-01

    A selection of infrared variable stars was studied at wavelength 2.7 microns during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. The correlation of 2.7 micron and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 microns.

  18. 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

    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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    It has been widely recognized that soil moisture is one of the main drivers of the water, energy and carbon cycles. It is a crucial variable for Numerical Weather Prediction (NWP) and climate projections because it plays a key role in hydro-meteorological processes. A good representation of soil moisture conditions can help improving the forecasting of precipitation, temperature, droughts and floods. For many applications global or continental scale soil moisture maps are needed. As a consequence, a signi?cant amount of studies have been conducted to obtain such information. For that purpose, land surface modeling, remote sensing techniques or a combination of both through Land Data Assimilation Systems are used. Assessing the quality of these products is required and for instance, the release of a new -long term- harmonized soil moisture product (SM-MW hereafter) from remote sensing within the framework of the European Space Agency's Water Cycle Multi-mission Observation Strategy (WACMOS) and Climate Change Initiative (CCI) projects in 2012 (more information at http://www.esa-soilmoisture-cci.org/) triggered several evaluation activities. The typical validation approach for model and satellite based data products is to compare them to in situ observations. However the evaluation of soil moisture products using ground measurements is not trivial. Even if in the recent years huge efforts were made to make such observations available in contrasting biomes and climate conditions, long term and large scale ground measurements networks are still sparse. Additionally, different networks will present different characteristics (e.g. measurement methods, installation depths and modes, calibration techniques, measurement interval, and temporal and spatial coverage). Finally using in situ measurements, the quality of retrieved soil moisture can be accurately assessed for the locations of the stations. That is why it is of interest to conceive new validation methods

  1. Simultaneous observation of monochromatic and variable period geomagnetic pulsations

    SciTech Connect

    McDiarmid, D.R.; Nielsen, E. )

    1987-05-01

    On February 4, 1983, following a storm sudden commencement, a monochromatic and a variable period pulsation were simultaneously observed by the Scandinavian Twin Auroral Radar Experiment (STARE) and Sweden and Britain Radar Experiment (SABRE) radar systems. Both pulsations differed from previously analyzed examples of their class. The phase of the monochromatic pulsation increased linearly with latitude rather than decreased. Its amplitude remained relatively constant over the latitude interval of linear phase change. The variable period pulsation experienced a change of orientation of its essentially linear polarization diagram in association with a discontinuity of its period. The variable period pulsation was thus manifest in both the toroidal and poloidal components. The results are discussed in terms of recent developments in theoretical pulsation modeling.

  2. The IRIS Data Management Center: Enabling Access to Observational Time Series Spanning Decades

    NASA Astrophysics Data System (ADS)

    Ahern, T.; Benson, R.; Trabant, C.

    2009-04-01

    The Incorporated Research Institutions for Seismology (IRIS) is funded by the National Science Foundation (NSF) to operate the facilities to generate, archive, and distribute seismological data to research communities in the United States and internationally. The IRIS Data Management System (DMS) is responsible for the ingestion, archiving, curation and distribution of these data. The IRIS Data Management Center (DMC) manages data from more than 100 permanent seismic networks, hundreds of temporary seismic deployments as well as data from other geophysical observing networks such as magnetotelluric sensors, ocean bottom sensors, superconducting gravimeters, strainmeters, surface meteorological measurements, and in-situ atmospheric pressure measurements. The IRIS DMC has data from more than 20 different types of sensors. The IRIS DMC manages approximately 100 terabytes of primary observational data. These data are archived in multiple distributed storage systems that insure data availability independent of any single catastrophic failure. Storage systems include both RAID systems of greater than 100 terabytes as well as robotic tape robots of petabyte capacity. IRIS performs routine transcription of the data to new media and storage systems to insure the long-term viability of the scientific data. IRIS adheres to the OAIS Data Preservation Model in most cases. The IRIS data model requires the availability of metadata describing the characteristics and geographic location of sensors before data can be fully archived. IRIS works with the International Federation of Digital Seismographic Networks (FDSN) in the definition and evolution of the metadata. The metadata insures that the data remain useful to both current and future generations of earth scientists. Curation of the metadata and time series is one of the most important activities at the IRIS DMC. Data analysts and an automated quality assurance system monitor the quality of the incoming data. This insures data

  3. 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

  4. A large increase in U.S. methane emissions over the past decade inferred from satellite data and surface observations

    NASA Astrophysics Data System (ADS)

    Turner, A. J.; Jacob, D. J.; Benmergui, J.; Wofsy, S. C.; Maasakkers, J. D.; Butz, A.; Hasekamp, O.; Biraud, S. C.

    2016-03-01

    The global burden of atmospheric methane has been increasing over the past decade, but the causes are not well understood. National inventory estimates from the U.S. Environmental Protection Agency indicate no significant trend in U.S. anthropogenic methane emissions from 2002 to present. Here we use satellite retrievals and surface observations of atmospheric methane to suggest that U.S. methane emissions have increased by more than 30% over the 2002-2014 period. The trend is largest in the central part of the country, but we cannot readily attribute it to any specific source type. This large increase in U.S. methane emissions could account for 30-60% of the global growth of atmospheric methane seen in the past decade.

  5. Dynamics and variability of the plasmasphere observed from synchronous orbit

    SciTech Connect

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

    1996-07-01

    The behavior of the cold ions in the outer plasmasphere is studied using data obtained with the magnetospheric plasma analyzers from multiple geosynchronous satellites. Dense (10{endash}100 cm{sup {minus}3}), cold ({approx_equal}1 eV) regions of plasma are often observed at geosynchronous orbit; in this study we refer to these as plasmaspheric intervals. The duration, local time of observation, density variability, and temperature behavior within these regions often depend in a systematic way on geomagnetic and substorm activity. With increasing geomagnetic activity (as indicated by {ital Kp}) the plasmaspheric regions are generally observed over shorter durations and at earlier local times. With increasing substorm activity (as indicated by geosynchronous energetic electron injections) the density becomes increasingly variable in these regions. Occasionally, up to order-of-magnitude density variations are observed over several minute timescales corresponding to regions with physical dimensions on the order of 1000 km or less. The appearance of these short-duration, cold-plasma intervals is strongly correlated with energetic ion and electron signatures both at the spacecraft making the plasmaspheric observations and at other spacecraft observing simultaneously in the midnight region. Such energetic particle signatures are indicative of the growth and expansive phase of geomagnetic substorms. We conclude that the appearance of these short-duration, plasmaspheric intervals is due to a reconfiguration of the duskside magnetosphere during geomagnetic substorms. {copyright} {ital 1996 American Institute of Physics.}

  6. Cataclysmic variables to be monitored for HST observations

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.

    2012-09-01

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

  7. Religious education and midlife observance are associated with dementia three decades later in Israeli men

    PubMed Central

    Beeri, Michal Schnaider; Davidson, Michael; Silverman, Jeremy M.; Schmeidler, James; Springer, Ramit Ravona; Noy, Shlomo; Goldbourt, Uri

    2010-01-01

    Objective The aim of the study was to examine the association of religious education and observance with dementia among participants in the Israeli Ischemic Heart Disease study. Study Design and Setting We assessed dementia in 1,890 participants among 2,604 survivors of 10,059 participants in the Israeli Ischemic Heart Disease study, a longitudinal investigation of the incidence and risk factors for cardiovascular disease among Jewish male civil servants in Israel. Face-to-face interviews were conducted with 651 subjects identified as possibly demented by the Modified Telephone Interview for Cognitive Status. Results Of 1,628 subjects included in this analysis (mean age 82 at assessment), 308 (18.9%) had dementia. The prevalence rates of dementia (and odds ratios (ORs) relative to those with exclusively religious education, adjusted for age, area of birth, and socioeconomic status) were 27.1% for those with exclusively religious education, 12.6% (OR=0.49) for those with mixed education, and 16.1% (OR=0.76) for those with secular education. For religious self-definition and practice, the prevalence rates were 9.7%, 17.7%, 14.1%, 19.3%, and 28.8% for categories from least to most religious (ORs relative to the most religious: 0.43, 0.67, 0.48, 0.55). Conclusions Examining lifestyles associated with religiosity might shed light onto environmental risks for dementia. Mechanisms underlying these associations remain elusive. PMID:18538995

  8. MISR Decadal Observations of Mineral Dust: Property Characterization and Climate Applications

    NASA Technical Reports Server (NTRS)

    Kalashnikova, Olga V.; Garay, Michael J.; Sokolik, Irina; Kahn, Ralph A.; Lyapustin, A.; Diner, David J.; Lee, Jae N.; Torres, Omar; Leptoukh, Gregory G.; Sabbah, Ismail

    2012-01-01

    The Multi-angle Imaging SpectroRadiometer (MISR) provides a unique, independent source of data for studying dust emission and transport. MISR's multiple view angles allow the retrieval of aerosol properties over bright surfaces, and such retrievals have been shown to be sensitive to the non-sphericity of dust aerosols over both land and water. MISR stereographic views of thick aerosol plumes allow height and instantaneous wind derivations at spatial resolutions of better than 1.1 km horizontally and 200m vertically. We will discuss the radiometric and stereo-retrieval capabilities of MISR specifically for dust, and demonstrate the use of MISR data in conjunction with other available satellite observations for dust property characterization and climate studies.First, we will discuss MISR non-spherical (dust) fraction product over the global oceans. We will show that over the Atlantic Ocean, changes in the MISR-derived non-spherical AOD fraction illustrate the evolution of dust during transport. Next, we will present a MISR satellite perspective on dust climatology in major dust source regions with a particular emphasis on the West Africa and Middle East and discuss MISR's unique strengths as well as current product biases. Finally, we will discuss MISR dust plume product and climatological applications.

  9. Decadal changes in carbon Emissions and sinks optimized using a Bayesian fusion of multiple observations.

    NASA Astrophysics Data System (ADS)

    Ciais, P.

    2015-12-01

    A better understanding of current human perturbation global carbon cycle is fundamental to support the projection of future climate change and designing better informed climate policy. making. Here, we develop a Bayesian approach that fuses different data-streams to optimize fossil fuel emission (F), land use change emission (L), land sink (B) and ocean sink (O) at a 5-year time step from 1980 to 2014. Here we show that the optimization decreases uncertainties compared with those of the carbon budget established by Global Carbon Project (GCP) and the IPCC where single datasets are used and the land sink deduced as a residual from other terms. Uncertainties of F, L, B and O are reduced by 11%, 26, 36% and 40% compared to those of the GCP budget. Fossil fuel and land use change emissions show a significantly increasing and decreasing trend, respectively, while no significant trend is detected for land and ocean uptakes. We infer with a 93% confidence that the net biosphere uptake with land use change (BL) has increased since 1980. After a further decomposition of the net land flux, sum of L and B, into gross terrestrial fluxes of primary productivity (GPP) and ecosystem respiration (TER), we attribute the increase of B+L to a faster growth of GPP than TER from 1980~1984 to 1990~1994 and a lower decreasing rate of GPP than TER in the 2000s. This approach can be potentially implemented on a yearly basis in future with growing observation-based datasets.

  10. Anne S. Young: Professor and Variable Star Observer Extraordinaire

    NASA Astrophysics Data System (ADS)

    Bracher, K.

    2012-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

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

    SciTech Connect

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

    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.

  13. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    NASA Astrophysics Data System (ADS)

    Anderson, Lesleigh; Berkelhammer, Max; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-02-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean-atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north-south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean-atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean-atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north-south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean-atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive

  14. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    USGS Publications Warehouse

    Anderson, Lesleigh; Max Berkelhammer; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-01-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the

  15. Using Observations and Climate Models to Investigate Recent Variability in Upper Ocean Warming

    NASA Astrophysics Data System (ADS)

    Durack, P. J.; Gleckler, P. J.; Guilyardi, E.; Landerer, F. W.

    2015-12-01

    The global ocean is responsible for storing more than 90% of the heat associated with observed greenhouse-gas-attributed warming. Our previous work used multiple in-situ estimates as well as altimetry in conjunction with a large suite of climate models to quantify how estimates of global upper-ocean warming since 1970 are likely biased low. This apparent underestimation, consistent with earlier studies, was attributed to poor observational coverage of the Southern Hemisphere. Recent 2006-2013 Argo ocean heat content (OHC) change estimates have placed 67-98% of increased heat in the Southern Hemisphere. The new estimates contrast markedly to long-term evaluations that place only 35-49% of the warming since 1970 in the Southern Hemisphere - even though the Southern Hemisphere contains more than 60% of the upper ocean volume. Although unforced variability is likely to play a larger role on resolved trends over this shorter time period, results from climate models provide one mechanism for investigating the role of variability across time scales. Extending our previous work, we investigate the hemispheric distribution of OHC using a number of observed change estimates along with a large suite of CMIP5 model simulations. We consider changes over decadal (Argo) to multi-decadal (multi-platform) time scales and contrast the observation-based hemispheric partitioning of OHC changes to a distribution of results from individual model simulations.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Hesperian to Amazonian-aged valleys (HAVs) are predominantly found in the southern equatorial and mid-latitudes of Mars and form parallel to dendritic networks. These features record a significant warming of the regional/global climate which may have been associated with outflow channel formation and/or a period of alluvial fan deposition in Margaritifer Terra [1]. HAVs are distinct from older valley networks in both their age and morphology and they provide a window into the past climate conditions and potential water sources which formed them. Using quantitative geomorphic analysis we calculate the expected range of timescales, water volumes, precipitation rates and atmospheric conditions which contributed to HAV formation. In Newton crater (40oS, -159oE) we measured valley widths, depths, slopes and alluvial fan volumes. These observations, when combined with a set of terrestrial sediment transport prediction functions [2,3,4,5], allow us to calculate an expected duration of fluvial activity ranging from 0.1 to 10 years for water-filled channel depths ranging between 20 and 130 cm, and median sediment grain size ranging from 1 mm to 10 cm. The water volume required to form a single HAV in Newton crater ranges between 1.8 and 5.7~km3 based on the Darcy-Weisbach equation [6] in combination with the aforementioned range in channel depths, grain sizes and formation timescales. These results imply water runoff rates of between 1 to 10~cm/day over a typical, 300~km2, drainage area. Such a high runoff rate and short formation time suggest a brief, dramatic regional to global climate excursion. The source of water which formed these features remains unclear, but it must have been released at the aforementioned rates, and was widely distributed within each drainage catchment, and regionally over Newton crater and the southern highlands. HAV formation was likely a two-step process involving, first, the deposition of a 10s of meters thick regional snowpack along

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    Understanding the natural climate variations in the eastern tropical Pacific is crucial for predicting the evolution of the El Niño-Southern Oscillation (ENSO) system and for anticipating the ways in which increases in atmospheric CO2 will affect climate. Here we present the first continuous, high-resolution (11-12 yr) climate record across the mid-Holocene transition (10ka-1.4ka) from the Peru-Chile Margin near the epicenter of the modern ENSO system. Although the high productivity of the Peru margin should promote high deposition rates, and the anaerobic bottom water conditions should inhibit sediment mixing by benthic organisms, nearly all sediment cores recovered from this region suffer from major gaps in Holocene sedimentation. Our data comes from a ~5 meter piston core collected from the mid-Peruvian shelf (15° 15"S, 75° 58"W, ~250mwd) in the heart of the oxygen minimum/denitrification zone that provides the first uninterrupted archive of conditions along the Peru-Chile margin. A suite of geochemical proxies allow us to reconstruct sea surface temperature (SST- Uk'37), phytoplankton productivity (C37total and %BSi), and thermocline ventilation (δ15N), variables that are tightly correlated to ENSO events today. Despite the observation that the mean late Holocene state of all three variables did not change over the last 10,000 years, our data reveal a dramatic increase in climate variability after the mid Holocene (~5ka); represented by prolonged periods (50-200yrs) of climate extremes, which are absent in the early Holocene. To further investigate these climate extremes we examine benthic foraminiferal assemblages and oxygen isotopes in combination with our other proxy records in selected late Holocene sections. The roughly centennial-scale oscillations do not show typical El Niño-La Niña correlations between proxies. We therefore posit that a significant fraction of super-ENSO variance during the course of the Holocene may originate outside the tropics

  18. Long-term Solar Irradiance Variability: 1984-1989 Observations

    NASA Technical Reports Server (NTRS)

    Lee, Robert B., III

    1990-01-01

    Long-term variability in the total solar irradiance has been observed in the Earth Radiation Budget Experiment (ERBE) solar monitor measurements. The monitors have been used to measure the irradiance from the Earth Radiation Budget Satellite (ERBS) and the National Oceanic and Atmospheric Administration NOAA-9 and NOAA-10 spacecraft platforms since October 25, 1984, January 23, 1985, and October 22, 1986, respectively. Before September 1986, the ERBS irradiance values were found to be decreasing -0.03 percent per year. This period was marked by decreasing solar magnetic activity. Between September 1986 and mid-1989, the irradiance values increased approximately 0.1 percent. The latter period was marked by increasing solar activity which was associated with the initiations of the sunspot cycle number 22 and of a new 22-year Hale solar magnetic cycle. Therefore, long-term solar-irradiance variability appears to be correlated directly with solar activity. The maximum smoothed sunspot number occurred during September 1989, according to the Sunspot Index Data Center. Therefore, the recent irradiance increasing trend should disappear during early 1990 and change into a decreasing trend if the observed irradiance variability is correlated more so with the 11-year sunspot cycle than the 22-year Hale cycle. The ERBE irradiance values are presented and compared with sunspot activity for the 1984 to 1989 period. The ERBE values are compared with those available from the Nimbus-7 and Solar Maximum Mission spacecraft experiments.

  19. Analysis of Marine Stratocumulus Drizzle Variability Using In Situ Observations

    NASA Astrophysics Data System (ADS)

    Witte, M.; Chuang, P. Y.; Rossiter, D.

    2013-12-01

    Precipitation is an important factor in the dynamics and large-scale organization of marine stratocumulus, yet it remains poorly understood. We aim to elucidate the factors driving the amount and variability of marine stratocumulus drizzle using in situ observations. We use aircraft measurements from two regions: a) in the near-coastal region of Monterey, CA during the Physics of Stratocumulus Top (POST) project from July and August 2008 and b) in the near-coastal region of Iquique, Chile during the VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS) from October 2008. Using these two different projects, we examine whether or not changes in conditions such as boundary layer depth, cloud top liquid water content, aerosol or drop concentrations, turbulence strength and inversion strength affect drizzle amount and variability. Interpreting which of these factors tend to associate most closely with various measures of drizzle intensity and variability will give insight into processes relevant to both precipitation formation and maintenance, and hopefully help explain how stratocumulus organize into the large-scale cellular patterns observed.

  20. 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

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

    PubMed

    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

  2. Decadal-to-centennial-scale climate variability: Insights into the rise and fall of the Great Salt Lake

    NASA Technical Reports Server (NTRS)

    Mann, Michael E.; Lall, Upmanu; Saltzman, Barry

    1995-01-01

    We demonstrate connections between decadal and secular global climatic variations, and historical variations in the volume of the Great Salt Lake. The decadal variations correspond to a low-frequency shifting of storm tracks which influence winter precipitation and explain nearly 18% of the interannual and longer-term variance in the record of monthly volume change. The secular trend accounts for a more modest approximately 1.5% of the variance.

  3. Atmospheric CO2 Variability Observed From ASCENDS Flight Campaigns

    NASA Technical Reports Server (NTRS)

    Lin, Bing; Browell, Edward; Campbell, Joel; Choi, Yonghoon; Dobler, Jeremy; Fan, Tai-Fang; Harrison, F. Wallace; Kooi, Susan; Liu, Zhaoyan; Meadows, Byron; Nehrir, Amin; Obland, Michael; Plant, James; Yang, Melissa

    2015-01-01

    Significant atmospheric CO2 variations on various spatiotemporal scales were observed during ASCENDS flight campaigns. For example, around 10-ppm CO2 changes were found within free troposphere in a region of about 200x300 sq km over Iowa during a summer 2014 flight. Even over extended forests, about 2-ppm CO2 column variability was measured within about 500-km distance. For winter times, especially over snow covered ground, relatively less horizontal CO2 variability was observed, likely owing to minimal interactions between the atmosphere and land surface. Inter-annual variations of CO2 drawdown over cornfields in the Mid-West were found to be larger than 5 ppm due to slight differences in the corn growing phase and meteorological conditions even in the same time period of a year. Furthermore, considerable differences in atmospheric CO2 profiles were found during winter and summer campaigns. In the winter CO2 was found to decrease from about 400 ppm in the atmospheric boundary layer (ABL) to about 392 ppm above 10 km, while in the summer CO2 increased from 386 ppm in the ABL to about 396 ppm in free troposphere. These and other CO2 observations are discussed in this presentation.

  4. Existence and inter-decadal changes of the Antarctic Circumpolar Wave during the last 142 years and its relationship to large scale modes of variability

    NASA Astrophysics Data System (ADS)

    Cerrone, Dario; Fusco, Giannetta; Cotroneo, Yuri; Simmonds, Ian; Budillon, Giorgio

    2016-04-01

    The Southern Ocean is the region of the world ocean bordering on Antarctica over which important exchanges between the atmosphere, the ocean and the sea ice take place. Here, the strong and nearly unhindered eastward flow of the Antarctic Circumpolar Current (ACC) plays an important control on mean global climate as it transmits climate anomalies around the globe. Features of interannual variability have been often observed to propagate eastward around the Southern Ocean with the circumpolar flow in form of a system of coupled anomalies, known as the Antarctic Circumpolar Wave (ACW). In the present study, using a 142-year series of a composite dataset (850hPa geopotential height, sea level pressure, sea surface temperature, surface meridional wind, surface air temperature) spanning from 1871-2012, the presence of ACWs was investigated. Results show the presence of the ACW before the mid-1950s and interdecadal changes in its variability. Modifications in strength and speed of circumpolar wave have also been observed in connection with large-scale climate changes. CEOF analyses on the same period confirmed that the ACW becomes apparent when there is a constructive combination between the Pacific-South America pattern and the subantarctic zonal wavenumber-3 (ZW3). The analyses also quantify the role played by El-Niño Southern Oscillation (ENSO) teleconnections for the appearance of the ACW. The composite dataset and various climate indices have been also used to diagnose interactions among the Southern Annular Mode (SAM), ENSO and ZW3 circulation patterns on interannual and sub-decadal scales. Results show that SAM and ENSO patterns interact with each other modulating ACW anomalies in the western and central south Pacific Ocean on interannual scale.

  5. Climate variability as observed by the Nimbus-7 ERB

    NASA Technical Reports Server (NTRS)

    Ardanuy, P. E.; Kyle, H. L.

    1986-01-01

    Limits to the accuracy of the Earth Radiation Budget (ERB) data being obtained by the Nimbus-7 satellite are discussed with emphasis on the implications for the measured variabilities in the global climate. Error analyses are performed for both wide and narrow field of view instruments and the success of in-flight calibration efforts is noted. Alterations in the ERB due to the eruptions of El Chichon in 1982 and the 1982-1983 ENSO event are summarized, particularly the teleconnections which were observed during ENSO.

  6. Trends and Variability in Observed Runoff from Land Terminating Glaciers in Greenland

    NASA Astrophysics Data System (ADS)

    Petersen, D.; Ahlstrom, A. P.

    2015-12-01

    The Greenland ice sheet is losing mass at an accelerated rate with both surface melting and iceberg discharge increasing notably over the last decade. The impact of Greenland ice sheet mass loss on the ongoing global sea level rise has raised concern and a better understanding of the reaction of the ice sheet to a future warmer climate is needed. Yet, observational records of surface melting have so far only been in the form of stake readings or short-term discharge measurements. Here we present continuous, long-term observations of discharge from pro-glacial lake Tasersiaq in West Greenland (66.3°N, 50.4°W) whose drainage basin extends over around 8500 km2 of which around 80% is ice covered (by Greenland Ice Sheet and local glaciers). The discharge time series covers the period from 1975 to 2014 and gives insight into the hydrological system's reaction to climatic forcing, e.g. a clear impact from major volcanic eruptions is observed. Over the entire data period a significant positive trend of 0.06 km3/yr in annual discharge is seen, where the median annual discharge is 2.50 km3. In addition to the trend in annual discharge a large and increasing year-to-year variability is observed. We examine both discharge trend and variability in the context of atmospheric circulation patterns and indicators of climate variability.

  7. 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.

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    Prior studies on Holocene marine sediments from the Antarctic Peninsula, including ODP Site 1098 and USAP N. B. Palmer jumbo piston cores have revealed pronounced multi-century scale variations within a number of paleoenvironmental proxies. In order to fully understand the exact timing of this signal an ultra-high resolution jumbo piston core from the Schollaert Drift was correlated with the well-known Palmer Deep record. A precise and accurate radiocarbon chronology is now available from the former site that utilizes in-situ mollusks, rather than bulk organic matter. The resulting time series spans the last 5000 years over the 20 m length of core NBP99-03 JPC28 and the surface stratigraphy of kasten core NBP01-07 KC8. The corrected and calibrated ages (with an applied reservoir correction of 1170 years) of 10 mollusks dated by the National Ocean Sciences Accelerator Mass Spectrometry Facility and the University of Arizona TAMS facility were used to construct an age-depth profile for JPC28 and KC8. A linear trend (R2 value of 0.993) of the age-depth profile was used to extrapolate the constant time interval between magnetic susceptibility measurements, which were analyzed every 1 cm. Dominant periods in the upper 10 m of the time series were identified using the Arand Spectral Analysis Package (Howell, 2001). This analysis revealed a single pronounced maxima at 160 years, which is inconsistent with the dominant periods found in time series of climate proxies from other sites on the western side of the Antarctic Peninsula. In particular, periods of 200 and 400 years, which are dominant in the Palmer Deep site (Warner and Domack, 2002), are not present in the Schollaert Drift. The spectral peaks derived from the two records are significantly different at the 95% confidence level. The cycles in the Palmer Deep record have been associated with solar variability, where as the 160 year cycle in the Schollaert Drift is close to a 180 year cycle in tidal forces (Keeling

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  11. Interannual and (multi-)decadal variability in the sedimentary BIT index of Lake Challa, East Africa, over the past 2200 years: assessment of the precipitation proxy

    NASA Astrophysics Data System (ADS)

    Buckles, Laura K.; Verschuren, Dirk; Weijers, Johan W. H.; Cocquyt, Christine; Blaauw, Maarten; Sinninghe Damsté, Jaap S.

    2016-05-01

    The branched vs. isoprenoid tetraether (BIT) index is based on the relative abundance of branched tetraether lipids (brGDGTs) and the isoprenoidal GDGT crenarchaeol. In Lake Challa sediments the BIT index has been applied as a proxy for local monsoon precipitation on the assumption that the primary source of brGDGTs is soil washed in from the lake's catchment. Since then, microbial production within the water column has been identified as the primary source of brGDGTs in Lake Challa sediments, meaning that either an alternative mechanism links BIT index variation with rainfall or that the proxy's application must be reconsidered. We investigated GDGT concentrations and BIT index variation in Lake Challa sediments at a decadal resolution over the past 2200 years, in combination with GDGT time-series data from 45 monthly sediment-trap samples and a chronosequence of profundal surface sediments.Our 2200-year geochemical record reveals high-frequency variability in GDGT concentrations, and therefore in the BIT index, superimposed on distinct lower-frequency fluctuations at multi-decadal to century timescales. These changes in BIT index are correlated with changes in the concentration of crenarchaeol but not with those of the brGDGTs. A clue for understanding the indirect link between rainfall and crenarchaeol concentration (and thus thaumarchaeotal abundance) was provided by the observation that surface sediments collected in January 2010 show a distinct shift in GDGT composition relative to sediments collected in August 2007. This shift is associated with increased bulk flux of settling mineral particles with high Ti / Al ratios during March-April 2008, reflecting an event of unusually high detrital input to Lake Challa concurrent with intense precipitation at the onset of the principal rain season that year. Although brGDGT distributions in the settling material are initially unaffected, this soil-erosion event is succeeded by a massive dry-season diatom bloom in

  12. Analysis of Kepler Observations of ASAS Variable Stars

    NASA Astrophysics Data System (ADS)

    Pezzato, Jacklyn M.; Mighell, Kenneth J.

    2016-01-01

    We present preliminary results of a study that compares the performance of period-finding algorithms when using data gathered by ground-based telescopes to their performance when using data gathered by space-based telescopes. In order to make this comparison, the periods reported by the All Sky Automated Survey (ASAS) Catalog for Variable Stars in the Kepler Field of View, a study that identified targets for the Kepler Mission before its launch, were compared to periods determined by this study. Only targets that were identified in the ASAS Catalog and later observed by the Kepler Mission were selected for analysis, for a total of 599 targets. The observations gathered by the Kepler Mission were analyzed using three period-finding algorithms: the Lafler-Kinman algorithm, the Analysis of Variance algorithm, and the Conditional Entropy algorithm. These three algorithms analyzed the light curves of each target, and one of the periods produced was selected to be compared to the period found by the ASAS Catalog. The analysis of the two data sets highlights issues with the performance of period finding algorithms with ground-based data, leading to crude period estimates for all targets with periods longer than 10 days. Since the Large Synoptic Scanning Telescope (LSST), due for first light in 2020, will have a similar observation schedule to that of the ASAS survey, similar issues can be expected with the analysis of LSST data for some types of long period variables, like semiregulars), that have periods longer than 10 days. Pezzato was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program (AST-1262829).

  13. 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

  14. 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.

  15. OBSERVATIONS OF THERMAL FLARE PLASMA WITH THE EUV VARIABILITY EXPERIMENT

    SciTech Connect

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

    2013-06-20

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

  16. Climate and polar motion during the GRACE observing period: 2002-2015: Implications for decadal scale oscillations during the 20th Century

    NASA Astrophysics Data System (ADS)

    Ivins, Erik; Adhikari, Surendra; Larour, Eric

    2016-04-01

    The motion of the Earth's pole in space has been observed with great accuracy for the last 115 years. The angular variations of the pole position away from its mean are a well explained at annual and 434-day periods. Variations at annual periods are caused by changes in the mass and angular momentum forced by all Earth surface changes that have near seasonality. The 434-day period is explained as a resonance between the cumulative driving forces having periods near the Chandler wobble free eigenmode of the Earth and is well understood theoretically. The Earth also has a longer-term drift that is explained primarily as a response to the ice age changes in the moments of inertial of the Earth. However, there has been a long-standing search for the origins of pole variations that have a period near 10 years. Using GRACE space gravimetry we show that ice mass losses from Greenland and Antarctica, and when combined with changes in continental hydrology, explain almost all the main features of interannual time scale polar wander. The discovery has broad interdisciplinary implications, as we show that decadal scale pole variations are directly linked to global changes continental water. The energy sources for these pole position changes are, therefore, likely to be associated with decadal scale ocean and atmospheric oscillations that also drive 20th Century on-land wet-dry oscillations at decadal-scale across the globe. Variability in pole position, therefore, offers a tool for assessing past stability of our climate, and for the future, now faced with an increased intensity in the water cycle and more vulnerable to ice sheet instability.

  17. Climate variability and atmospheric teleconnection from satellite observed cloud fluctuations

    NASA Technical Reports Server (NTRS)

    Lau, K. M.; Chan, P. H.

    1983-01-01

    To investigate the low-frequency variability of the large-scale circulation over the tropics and its relationship with different regions of the globe, statistics of cloud fluctuations, as inferred from outgoing longwave radiation (OLR) are used. The data consists of seven years of global OLR in a 2.5 x 2.5-deg grid derived from NOAA polar orbiting satellite observations. The time series of area-averaged monthly deviation from the seven-year mean of OLR over an equatorial Central Pacific region is presented. It is shown that positive and negative deviations reflect local drier and wetter than normal conditions, respectively. Consideration is given to teleconnection based on the Central Pacific variations and to southern oscillation contributions.

  18. On the causes of plasmaspheric rotation variability: IMAGE EUV observations

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

  19. Field Observations of Soil Moisture Variability across Scales

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Williams, Thomas R.; Saladyga, Michael

    2011-05-01

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

  1. 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

  2. Decadal variability of soil CO2, NO, N2O,and CH4 fluxes at the Hoeglwald Forest, Germany

    NASA Astrophysics Data System (ADS)

    Luo, G. J.; Brüggemann, N.; Wolf, B.; Gasche, R.; Butterbach-Bahl, K.

    2012-04-01

    Besides agricultural soils, temperate forest soils have been identified as significant sources of or sinks for important atmospheric trace gases (N2O, NO, CH4, and CO2). Although the number of studies for this ecosystem type increased more than tenfold during the last decade, studies covering an entire year and spanning more than 1-2 yr remained scarce. This study reports the results of continuous measurements of soil atmosphere C- and N-gas exchange with high temporal resolution carried out since 1994 at the Höglwald Forest spruce site, an experimental field station in Southern Germany. Annual soil N2O emission, NO emission, CH4 uptake, and CO2 emission (1994-2010) varied in a range of 0.2-3.2 kg N2O-N ha-1 yr-1, 6.4-11.4 kg NO-N ha-1 yr-1,0.9-3.5 kg CH4-C ha-1 yr-1, and 7.0-9.2 t CO2-C ha-1 yr-1, respectively. The observed high fluxes of N-trace gases are most likely a consequence of high rates of atmospheric nitrogen deposition (> 20 kg N ha-1 yr-1) of NH3 and NOx to our site. For N2O cumulative annual emissions were > 0.8kg N2O-N ha-1 yr-1 high in years with freeze-thaw events (5 out 14 yr). This shows that long-term, multi-year measurements are needed to obtain reliable estimates of N2O fluxes for a given ecosystem. Cumulative values of soil respiratory CO2 fluxes were highest in years with prolonged freezing periods e.g. the years 1996 and 2006, i.e. years with below average annual mean soil temperatures and high N2O emissions. The results indicate that long freezing periods may even drive increased CO2 fluxes not only during soil thawing but also throughout the following growing season. Furthermore, based on our unique database on GHGs we analyzed if soil temperature, soil moisture, or precipitation measurements can be used to approximate GHGs at weekly, monthly, or annual scale. Our analysis shows that simple-to-measure environmental drivers such as soil temperature or soil moisture are suitable to approximate fluxes of NO and CO2 in weekly and monthly

  3. Interannual to decadal climate variability of sea salt aerosols in the coupled climate model CESM1.0

    NASA Astrophysics Data System (ADS)

    Xu, Li; Pierce, David W.; Russell, Lynn M.; Miller, Arthur J.; Somerville, Richard C. J.; Twohy, Cynthia H.; Ghan, Steven J.; Singh, Balwinder; Yoon, Jin-Ho; Rasch, Philip J.

    2015-02-01

    This study examines multiyear climate variability associated with sea salt aerosols and their contribution to the variability of shortwave cloud forcing (SWCF) using a 150 year simulation for preindustrial conditions of the Community Earth System Model version 1.0. The results suggest that changes in sea salt and related cloud and radiative properties on interannual timescales are dominated by the El Niño-Southern Oscillation cycle. Sea salt variability on longer (interdecadal) timescales is associated with low-frequency variability in the Pacific Ocean similar to the Interdecadal Pacific Oscillation but does not show a statistically significant spectral peak. A multivariate regression suggests that sea salt aerosol variability may contribute to SWCF variability in the tropical Pacific, explaining up to 20-30% of the variance in that region. Elsewhere, there is only a small sea salt aerosol influence on SWCF through modifying cloud droplet number and liquid water path that contributes to the change of cloud effective radius and cloud optical depth (and hence cloud albedo), producing a multiyear aerosol-cloud-wind interaction.

  4. Observed and simulated variability of the Atlantic meridional overturning circulation and the deep western boundary current

    NASA Astrophysics Data System (ADS)

    Mielke, Charlotte; Frajka-Williams, Eleanor; Gary, Stefan; Shimizu, Kenji; Toole, John; Baehr, Johanna

    2014-05-01

    Despite the importance of Atlantic meridional overturnig circulation (AMOC) for the climate of Africa, America and Europe, continuous AMOC observations are at present restricted to two latitudes, and are available for less than ten years. We therefore investigate whether the AMOC's variability can be inferred from measurements of the deep western boundary current (DWBC), which are already available at several locations. To that end, we jointly analyze the available 26°N RAPID and the 41°N Argo-based AMOC estimates with RAPID and line W (40°N) DWBC estimates. We also compare them to a 60-year simulation with a high-resolution NCEP-forced ocean model. The DWBC and its layers are defined dynamically in the model based on a comparison of temperature-versus-salinity data in model and observations and the time-dependent velocity field. On the timescales where observations are available, the model is able to reproduce the variability of the DWBC and its individual layers at both locations. Our preliminary analysis of the observational data and model results suggests that different mechanisms dominate the DWBC's variability at different timescales. On sub-seasonal to seasonal timescales, the DWBC is mostly barotropic, and its variability is linked to local processes. Thus, the DWBC has a well-defined seasonal cycle which is opposite to the seasonal cycle of the non-Ekman component of the AMOC seasonal cycle. On interannual timescales, there is no obvious relation between AMOC and DWBC. However, on decadal timescales, our analysis indicates covariability between AMOC and DWBC. We conclude that although caution should be exercised on interannual timescales, the DWBC might be used as a proxy for long-term AMOC trends and possibly modulations of the AMOC's seasonal cycle.

  5. Observed Variability of the Solar Mg II h Spectral Line

    NASA Astrophysics Data System (ADS)

    Schmit, D.; Bryans, P.; De Pontieu, B.; McIntosh, S.; Leenaarts, J.; Carlsson, M.

    2015-10-01

    The Mg ii h&k doublet are two of the primary spectral lines observed by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are tracers of the magnetic and thermal environment that spans from the photosphere to the upper chromosphere. We use a double-Gaussian model to fit the Mg ii h profile for a full-Sun mosaic data set taken on 2014 August 24. We use the ensemble of high-quality profile fits to conduct a statistical study on the variability of the line profile as it relates the magnetic structure, dynamics, and center-to-limb viewing angle. The average internetwork profile contains a deeply reversed core and is weakly asymmetric at h2. In the internetwork, we find a strong correlation between h3 wavelength and profile asymmetry as well as h1 width and h2 width. The average reversal depth of the h3 core is inversely related to the magnetic field. Plage and sunspots exhibit many profiles that do not contain a reversal. These profiles also occur infrequently in the internetwork. We see indications of magnetically aligned structures in plage and network in statistics associated with the line core, but these structures are not clear or extended in the internetwork. The center-to-limb variations are compared to predictions of semi-empirical model atmospheres. We measure a pronounced limb darkening in the line core that is not predicted by the model. The aim of this work is to provide a comprehensive measurement baseline and preliminary analysis on the observed structure and formation of the Mg ii profiles observed by IRIS.

  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

  7. West African monsoon decadal variability and surface-related forcings: second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

    NASA Astrophysics Data System (ADS)

    Xue, Yongkang; De Sales, Fernando; Lau, William K.-M.; Boone, Aaron; Kim, Kyu-Myong; Mechoso, Carlos R.; Wang, Guiling; Kucharski, Fred; Schiro, Kathleen; Hosaka, Masahiro; Li, Suosuo; Druyan, Leonard M.; Sanda, Ibrah Seidou; Thiaw, Wassila; Zeng, Ning; Comer, Ruth E.; Lim, Young-Kwon; Mahanama, Sarith; Song, Guoqiong; Gu, Yu; Hagos, Samson M.; Chin, Mian; Schubert, Siegfried; Dirmeyer, Paul; Ruby Leung, L.; Kalnay, Eugenia; Kitoh, Akio; Lu, Cheng-Hsuan; Mahowald, Natalie M.; Zhang, Zhengqiu

    2016-06-01

    The second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II) is designed to improve understanding of the possible roles and feedbacks of sea surface temperature (SST), land use land cover change (LULCC), and aerosols forcings in the Sahel climate system at seasonal to decadal scales. The project's strategy is to apply prescribed observationally based anomaly forcing, i.e., "idealized but realistic" forcing, in simulations by climate models. The goal is to assess these forcings' effects in producing/amplifying seasonal and decadal climate variability in the Sahel between the 1950s and the 1980s, which is selected to characterize the great drought period of the last century. This is the first multi-model experiment specifically designed to simultaneously evaluate such relative contributions. The WAMME II models have consistently demonstrated that SST forcing is a major contributor to the twentieth century Sahel drought. Under the influence of the maximum possible SST forcing, the ensemble mean of WAMME II models can produce up to 60 % of the precipitation difference during the period. The present paper also addresses the role of SSTs in triggering and maintaining the Sahel drought. In this regard, the consensus of WAMME II models is that both Indian and Pacific Ocean SSTs greatly contributed to the drought, with the former producing an anomalous displacement of the Intertropical Convergence Zone before the WAM onset, and the latter mainly contributes to the summer WAM drought. The WAMME II models also show that the impact of LULCC forcing on the Sahel climate system is weaker than that of SST forcing, but still of first order magnitude. According to the results, under LULCC forcing the ensemble mean of WAMME II models can produces about 40 % of the precipitation difference between the 1980s and the 1950s. The role of land surface processes in responding to and amplifying the drought is also identified. The results suggest that catastrophic

  8. Cataclysmic Variables Observed During K2 Campaigns 0 and 1

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    There are 15 cataclysmic variables (CVs) observed in the first two campaigns of the K2 mission. In this paper, the eight CVs showing distinct features are analyzed in detail. Among these eight, modulations during quiescence are evident at the known orbital periods in the SU UMa stars QZ Vir and RZ Leo, and at our newly determined orbital periods for 1RXS J0632+2536 and WD 1144+011. The periodogram analysis for the quiescent light curve of QZ Vir reveals multi-period modulations and the coexistence of orbital and superhump periods. The phased orbital light curves for the other three CVs in quiescence display wide (about half cycle) and shallow (<0.5 mag) eclipse features. Besides these modulations, their quiescent light curves reveal several transient events: a sudden decrease of system light in 1RXS J0632+2536, a low-level flare-like event in QZ Vir, a short brightening event in RZ Leo, and a temporary disappearance of the orbital modulation in WD 1144+011. The two known dwarf novae UV Gem and TW Vir and the CVs USNO-B1.01144-00115322 and CSS 130516:111236:111236.7+002807 show outbursts, including one complete and three incomplete normal outbursts and two complete superoutbursts. An incomplete but typical normal outburst confirms the dwarf nova identification of the USNO-B1.01144-00115322. The one complete normal outburst in UV Gem may provide the orbital period, since its modulations are shorter than the previously observed superhump period. The superoutburst of CSS 130516:111236.7+002807, along with the corresponding superhump period, indicates that this object is an SU UMa star. The derived superhump period of CSS 130516:111236:111236.7+002807 is 1.44 hr, implying that this new SU UMa star is close to the period minimum.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    the observed GPS velocities. Bright, mid-crustal horizontal reflections observed in COCORP reflection seismic data west of 114°W have been postulated to represent a detachment that could accommodate shearing along the base of the crust in Nevada [Hauser et al., 1987], a hypothesis broadly consistent with the observed GPS velocities, with the crust shearing relatively east over the subcrustal lithosphere. A deep observatory in the Sevier Desert region, transecting the Sevier Desert detachment, would complement existing paleoseismic and neotectonic studies, and the decade of BARGEN continuous GPS observations, as well as new GPS data from 8 Earthscope Plate Boundary Observatory sites installed along this transect in the past few years. Key questions that could be assessed with a deep observatory are how slip, and strain, at depth on an inclined fault are reflected in geodetic observations of strain at the surface; whether the state of stress and strain rate on the Sevier Desert detachment change through time, as suggested by long-term periodicity in strain release as recorded in the geologic record, and what effect long-lived velocity excursions, such as observed from 2000-2003, have on the regional stress state, perhaps leading to a clearer understanding of the source of these anomalies, and the aseismic tectonic behavior of the lithosphere.

  10. Multi-Decadal Aerosol Variations from 1980 to 2009: A Perspective from Observations and a Global Model

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    Aerosol variations and trends over different land and ocean regions during 1980-2009 are analyzed with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and observations from multiple satellite sensors and ground-based networks. Excluding time periods with large volcanic influences, the tendency of aerosol optical depth (AOD) and surface concentration over polluted land regions is consistent with the anthropogenic emission changes.The largest reduction occurs over Europe, and regions in North America and Russia also exhibit reductions. On the other hand, East Asia and South Asia show AOD increases, although relatively large amount of natural aerosols in Asia makes the total changes less directly connected to the pollutant emission trends. Over major dust source regions, model analysis indicates that the dust emissions over the Sahara and Sahel respond mainly to the near-surface wind speed, but over Central Asia they are largely influenced by ground wetness. The decreasing dust trend in the tropical North Atlantic is most closely associated with the decrease of Sahel dust emission and increase of precipitation over the tropical North Atlantic, likely driven by the sea surface temperature increase. Despite significant regional trends, the model-calculated global annual average AOD shows little changes over land and ocean in the past three decades, because opposite trends in different regions cancel each other in the global average. This highlights the need for regional-scale aerosol assessment, as the global average value conceals regional changes, and thus is not sufficient for assessing changes in aerosol loading.

  11. Long-term Variability in Pacific Decadal Oscillation Teleconnections to Climate in Alaska: From "In a Relationship" to "It's Complicated"

    NASA Astrophysics Data System (ADS)

    Heckler, S.; McAfee, S. A.

    2015-12-01

    Since the Pacific Decadal Oscillation's (PDO) identification in 1997, it has been widely used as a seasonal-forecasting and decision-making tool in Alaska. Gulf of Alaska sea surface temperatures have oscillated every few decades between warmer (positive PDO) and colder (negative PDO). In the historical record, there are two negative phases and two positive phases, but since 2000, the PDO has vacillated between warm and cold states annually. Recent inconsistencies in the phase of the PDO as well as its influence on climate have warranted further study of this climate phenomenon. Previous work found that strength and importance of the PDO teleconnections to temperature and precipitation varied widely over time in the Twentieth Century Reanalysis (v2) data and in CRU TS3.2.1. In light of the inherent problems with reanalyses and with gridded products in data-poor areas, it is necessary to examine individual station data to further understand the relationship of the PDO with climate in Alaska. This study examines temperature and precipitation data for individual stations across Alaska to determine the stability of PDO teleconnections. Individual station data were downloaded from the NOAA National Centers for Environmental Information GHCN-D database. For the months of January, February and March, stations with at least 90% complete data for all three months were selected. Using stations grouped according to the recently developed Alaska climate divisions, the stability of PDO teleconnections was analyzed in terms of station anomalies from the PRISM climatology. In many parts of the state, the relationship between the PDO and local climate was not as stable as expected. Even at individual stations, the strength and influence of the PDO was often inconsistent over time.

  12. Effects of variable climate, land use, and hydrogeochemical setting on decadal surface water quality trends, Iowa, USA

    NASA Astrophysics Data System (ADS)

    Green, C. T.; Bekins, B. A.; Kalkhoff, S.; Hirsch, R. M.; Liao, L.; Barnes, K.

    2013-12-01

    Nitrogen fluxes from agricultural lands are a major concern for ecological health and water quality. Understanding how these fluxes respond to changes in agricultural practices and climatic variations is important for improving water quality in agricultural settings. In the midwestern USA, intensification of corn cropping as a result of ethanol production led to increases in N application rates in the 2000s during a period including both extreme dry and wet conditions. To examine the effect of these recent changes, a study was conducted on surface water quality in 10 major Iowa Rivers. Long term (~20 to 30 years) water quality and flow data were analyzed with Weighted Regression on Time, Discharge and Season (WRTDS), a statistical method that provides internally consistent estimates of the concentration history and reveals decadal trends that are independent of random variations of stream flow from seasonal averages. Trends of surface water quality showed constant or decreasing flow-normalized concentrations of nitrate+nitrite-N 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 annual concentrations. The recent declining concentration trends can be attributed to both very high and very low discharge in the 2000's and to the long (e.g. 8-year) subsurface residence times in some basins. Dilution of surface water nitrate and depletion of stored nitrate may occur in years with very high discharge. Limited transport of N to surface water and accumulation of stored N may occur in years with very low discharge. Central Iowa basins showed the greatest reduction in concentrations, likely because extensive tile drainage results in smaller storage volumes and shorter residence times, and the glacial sediments are naturally reducing. Effects of agricultural intensification from ethanol production and other factors will likely be delayed for years or decades in

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  14. Clinical Research Quo Vadis? Trends in Reporting of Clinical Trials and Observational Study Designs Over Two Decades

    PubMed Central

    Wyler von Ballmoos, Moritz C.; Ware, James H.; Haring, Bernhard

    2015-01-01

    Background Multiple classifications have been developed that classify the medical literature into different levels of evidence to facilitate the evaluation of study results and practice of evidence-based medicine. The suggested hierarchies of evidence are generally based on the type of study design; randomized, controlled clinical trials constitute the top level of evidence while case reports rank the lowest among epidemiologic study designs. However, little is known about the frequency with which different study designs appear in the medical literature overall. The purpose of this study was to describe trends in the frequency of reports of randomized control trials (RCTs) as compared to other study designs in the medical literature over two decades. Methods Data about the prevalence of various types of study designs in the medical literature over the last two decades (years 1990 - 2009) were abstracted from PubMed, validated and subjected to cross-sectional and longitudinal analysis. Results In the last 20 years, the annual rate of publication of journal articles has more than doubled. During this period, the percentage of observational studies increased from 29.9% to 40.5%, the percentage of reports of RCTs increased minimally, and there was a striking decline in the percentage of case reports (from 49.8% to 33.6%) in the medical literature overall. In contrast, in three selected, highly cited medical journals, the percentage of reports of RCTs increased by almost 10%. Surprisingly, the percentage of articles classified as case reports also increased (from 36.3% to 43.8%) in these three journals, while the percentage of reports of cohort and case-control studies decreased. Conclusion Though the relative frequency of reports from RCTs has not changed substantially in the last 20 years, cohort studies and case-control studies have largely supplanted simple case reports. In contrast, in high impact journals, the representation of RCTs and case reports has increased

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  16. Observed Variables Are Indeed More Mysterious than Commonly Supposed

    ERIC Educational Resources Information Center

    Howell, Roy D.

    2008-01-01

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

  17. 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

  18. 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.

  19. GLIMPSE Proper: Mid-Infrared Observations of Proper Motion and Variability Towards Galactic Center

    NASA Astrophysics Data System (ADS)

    Benjamin, Robert; Babler, Brian; Churchwell, Ed; Clarkson, Will; Kirkpatrick, Davy; Meade, Marilyn; Whitney, Barbara

    2015-10-01

    We propose to re-image 43.4 square degrees of the Galactic center to measure the proper motions of over fifteen million sources within 5 degrees of Galactic center over the last decade. This stellar sample will be over 20 times larger than the previous optical ground-based measurements and will allow us to constrain the anisotropic stellar velocity dispersion as a function of direction and distance as well as test previous claims of streaming motions associated with the near/far side of the Galactic bar, the X-shaped bar, and the vertically thin extended Long Bar. Not only will this be the largest Galactic bulge proper motion survey to date, it will also be the most uniform as mid-infrared observations are minimally affected by extinction over most of the region. We also expect to find at least 150 high proper motion stars (>100 mas/yr) which could be substellar objects and possible microlensing candidates against the crowded Galactic bulge. We will put constraints on the current production rate of hyper-velocity stars thought to be formed in binary interactions with the supermassive black hole of the Galaxy. Finally, we will be able to identify many new variable stars, particularly in the central 2x1.5 degree region of the Galaxy which has only been observed in a single epoch with Spitzer; we expect to find 1000 new sources with variability amplitudes greater than 0.2 mag.

  20. Systematic attribution of observed Southern Hemisphere 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.

    2015-09-01

    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 midlatitude blocking is most active and stratospheric ozone should not 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.

  1. 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.

  2. 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.

  3. 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

  4. 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)

  5. Mythological Evidence for Ancient Observations of Variable Stars

    NASA Astrophysics Data System (ADS)

    Wilk, Stephen R.

    I suggest that the variability of Algol was known in pre-classical Greece, and that knowledge of its period is reflected in the myth of Perseus. Moreover, knowledge of the variability of Algol, Mira, delta Cephei, and gamma Cassiopeiae accounts for all their parent constellations being associated in the same myth as antagonists of Perseus. Finally, I propose alternative interpretations of the same constellations which show their influence upon classical myth.

  6. Variability of Madden Julian Oscillations (MJO) observed over southern India using radiosonde observations

    NASA Astrophysics Data System (ADS)

    Leena, P. P.; Ratnam, M. Venkat; Krishna Murthy, B. V.; Bhaskara Rao, S. Vijaya

    2016-05-01

    In the present work, characteristics of 30-50 day oscillations (referred to as the MJO) in tropospheric and lower stratospheric wind and temperature have been studied using long-term high resolution radiosonde observations at a tropical station, Gadanki (13.5°N, 79.2°E) for the period 2006-2012. Wind and temperature perturbations showed clear features of the MJO with higher amplitudes between 10 and 18 km altitude. Interestingly, the MJO signal is confined vertically to different altitudes in different seasons. Variability in the perturbations of wind and temperature similar to that of outgoing long-wave radiation (OLR) with a few cases showing an out of phase relation. The amplitudes of these oscillations are larger in the winter and pre-monsoon seasons than in the monsoon season where the largest amplitudes are confined below the Tropical Easterly Jet (~16 km). There also exists a large inter-annual variability in the MJO. Spatio-temporal variability of OLR not only showed the features of the MJO but also northward and eastward propagation in the monsoons and winter seasons, respectively, in a few cases. It is found that convection leads the MJO in the zonal wind by 8-12 days in all the seasons except in winter. One intriguing result observed is the vitiation of the MJO pattern by the presence of strong wind shears during monsoon season. We expect this study would be helpful in representing the MJO features in the vertical in the general circulation models (GCMs) which is still a major challenge.

  7. Multi-decadal Variability of Flood Risk in Southwestern Canadian Prairie Rivers as Characterized by the PDO and ENSO

    NASA Astrophysics Data System (ADS)

    Gurrapu, S.; St Jacques, J. M.; Sauchyn, D.; Hodder, K. R.

    2014-12-01

    The 2013 floods across southern Alberta, Canada, are considered to be one of the worst natural disasters in recent Canadian history. This region is highly vulnerable to flooding during spring as the frozen ground restricts infiltration and the melting snow directly contributes to streamflow. Studies have concluded that the 2013 floods in Alberta were a result of heavier snowpack from winter precipitation and higher amounts of spring precipitation as rain over the eastern slopes of the Rockies. Although this flood is considered to be less than the 100-year flood of the region, the effects were economically devastating. The return periods of floods are generally determined under the assumption that the annual peak flow series are independent and identically distributed (i.i.d.). However, researchers have demonstrated that this assumption is not valid in Australia and that the i.i.d. assumption can lead to under- or over-estimation of the true long-term flood risk. The Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO) have a strong impact on western Canadian hydroclimate via teleconnections. The negative phase of the PDO and La Niña typically produce heavier snowpack across the prairies compared to that during the positive phase of PDO and El Niño. In this study, we explore the connections between the PDO, ENSO and the peak annual streamflow in southwestern Canadian prairie rivers. Daily averaged annual peak flow records from 22 rivers were stratified according to the PDO phases and ENSO states and fit to the Log-Pearson III (LP3) distribution. We determined that the flood risk is significantly higher in the negative phase of the PDO and is enhanced during La Niña episodes within the negative PDO phase. To ensure these results were not due to sampling error or unequal record lengths, a regional index approach was also employed, which confirmed these results. Our results are important for the optimal planning and design of flood control

  8. 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; Rosenhagen, Gudrun; Schenk, Frederik; van der Schrier, Gerard; Woollings, Tim

    2016-04-01

    In the upcoming North Sea Region Climate Change Assessment (NOSCCA), we present a synthesis of current knowledge about past, present and possible future climate change in the North Sea region. A climate change assessment from published scientific work has been conducted as a kind of regional IPCC report, and a book has been produced that will be published by Springer in 2016. In the framework of the NOSCCA project, we examine past and present studies of variability and changes in atmospheric variables within the North Sea region over the instrumental period, roughly the past 200 years, based on observations and reanalyses. The variables addressed in this presentation are large-scale circulation, pressure and wind, surface air temperature, precipitation and radiative properties (clouds, solar radiation, and sunshine duration). While air temperature over land, not unexpectedly, has increased everywhere in the North Sea region, with strongest trends in spring and in the north of the region, a precipitation increase has been observed in the north and a decrease in the south of the region. This pattern goes along with a north-eastward shift of storm tracks and is in agreement with climate model projections under enhanced greenhouse gas concentrations. For other variables, it is not obvious which part of the observed changes may be due to anthropogenic activities and which is internally forced. It remains also unclear to what extent atmospheric circulation over the North Sea region is influenced by distant factors, in particular Arctic sea-ice decline in recent decades. There are indications of an increase in the number of deep cyclones (but not in the total number of cyclones), while storminess since the late 19th century shows no robust trends. The persistence of circulation types appears to have increased over the last century, and consequently, there is an indication for 'more extreme' extreme events. However, changes in extreme weather events are difficult to assess

  9. Southern Ocean deep convection in global climate models: A driver for variability of subpolar gyres and Drake Passage transport on decadal timescales

    NASA Astrophysics Data System (ADS)

    Behrens, Erik; Rickard, Graham; Morgenstern, Olaf; Martin, Torge; Osprey, Annette; Joshi, Manoj

    2016-06-01

    We investigate the individual and joint decadal variability of Southern Ocean state quantities, such as the strength of the Ross and Weddell Gyres, Drake Passage transport, and sea ice area, using the National Institute of Water and Atmospheric Research UK Chemistry and Aerosols (NIWA-UKCA) model and CMIP5 models. Variability in these quantities is stimulated by strong deep reaching convective events in the Southern Ocean, which produce an Antarctic Bottom Water-like water mass and affect the large-scale meridional density structure in the Southern Ocean. An increase in the (near) surface stratification, due to freshwater forcing, can be a precondition for subsequent strong convection activity. The combination of enhanced-gyre driven sea ice and freshwater export, as well as ongoing subsurface heat accumulation, lead to a time lag between changes in oceanic freshwater and heat content. This causes an ongoing weakening of the stratification until sudden strong mixing events emerge and the heat is released to the atmosphere. We find that strong convection reduces sea ice cover, weakens the subpolar gyres, increases the meridional density gradient and subsequently results in a positive Drake Passage transport anomaly. Results of available CMIP5 models confirm that variability in sea ice, Drake Passage transport, and the Weddell Gyre strength is enhanced if models show strong open ocean convective events. Consistent relationships between convection, sea ice, Drake Passage transport, and Ross Gyre strength variability are evident in most models, whether or not they host open ocean convection.

  10. Variability of Attention Processes in ADHD: Observations from the Classroom

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  11. 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. ...

  12. Spatiotemporal variability of methane over the Amazon from satellite observations

    NASA Astrophysics Data System (ADS)

    Ribeiro, Igor Oliveira; de Souza, Rodrigo Augusto Ferreira; Andreoli, Rita Valéria; Kayano, Mary Toshie; Costa, Patrícia dos Santos

    2016-07-01

    The spatiotemporal variability of the greenhouse gas methane (CH4) in the atmosphere over the Amazon is studied using data from the space-borne measurements of the Atmospheric Infrared Sounder on board NASA's AQUA satellite for the period 2003-12. The results show a pronounced variability of this gas over the Amazon Basin lowlands region, where wetland areas occur. CH4 has a well-defined seasonal behavior, with a progressive increase of its concentration during the dry season, followed by a decrease during the wet season. Concerning this variability, the present study indicates the important role of ENSO in modulating the variability of CH4 emissions over the northern Amazon, where this association seems to be mostly linked to changes in flooded areas in response to ENSO-related precipitation changes. In this region, a CH4 decrease (increase) is due to the El Niño-related (La Niña-related) dryness (wetness). On the other hand, an increase (decrease) in the biomass burning over the southeastern Amazon during very dry (wet) years explains the increase (decrease) in CH4 emissions in this region. The present analysis identifies the two main areas of the Amazon, its northern and southeastern sectors, with remarkable interannual variations of CH4. This result might be useful for future monitoring of the variations in the concentration of CH4, the second-most important greenhouse gas, in this area.

  13. 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.

  14. Rainfall variability and trends of the past six decades (1950-2014) in the subtropical NW Argentine Andes

    NASA Astrophysics Data System (ADS)

    Castino, F.; Bookhagen, B.; Strecker, M. R.

    2016-04-01

    The eastern flanks of the Central Andes are characterized by deep convection, exposing them to hydrometeorological extreme events, often resulting in floods and a variety of mass movements. We assessed the spatiotemporal pattern of rainfall trends and the changes in the magnitude and frequency of extreme events (≥95th percentile) along an E-W traverse across the southern Central Andes using rain-gauge and high-resolution gridded datasets (CPC-uni and TRMM 3B42 V7). We generated different climate indices and made three key observations: (1) an increase of the annual rainfall has occurred at the transition between low (<0.5 km) and intermediate (0.5-3 km) elevations between 1950 and 2014. Also, rainfall increases during the wet season and, to a lesser degree, decreases during the dry season. Increasing trends in annual total amounts characterize the period 1979-2014 in the arid, high-elevation southern Andean Plateau, whereas trend reversals with decreasing annual total amounts were found at low elevations. (2) For all analyzed periods, we observed small or no changes in the median values of the rainfall-frequency distribution, but significant trends with intensification or attenuation in the 95th percentile. (3) In the southern Andean Plateau, extreme rainfall events exhibit trends towards increasing magnitude and, to a lesser degree, frequency during the wet season, at least since 1979. Our analysis revealed that low (<0.5 km), intermediate (0.5-3 km), and high-elevation (>3 km) areas respond differently to changing climate conditions, and the transition zone between low and intermediate elevations is characterized by the most significant changes.

  15. Sea state variability observed by high resolution satellite radar images

    NASA Astrophysics Data System (ADS)

    Pleskachevsky, A.; Lehner, S.

    2012-04-01

    The spatial variability of the wave parameters is measured and investigated using new TerraSAR-X (TS-X) satellite SAR (Synthetic Aperture Radar) images. Wave groupiness, refraction and breaking of individual wave are studied. Space borne SAR is a unique sensor providing two dimensional information of the ocean surface. Due to its daylight, weather independency and global coverage, the TS-X radar is particularly suitable for many ocean and coastal observations and it acquires images of the sea surface with up to 1m resolution; individual ocean waves with wavelength below 30m are detectable. Two-dimensional information of the ocean surface, retrieved using TS-X data, is validated for different oceanographic applications: derivation of the fine resolved wind field (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). The algorithms are capable to take into account fine-scale effects in the coastal areas. This two-dimensional information can be successfully applied to validate numerical models. For this, wind field and sea state information retrieved from SAR images are given as input for a spectral numerical wave model (wind forcing and boundary condition). The model runs and sensitivity studies are carried out at a fine spatial horizontal resolution of 100m. The model results are compared to buoy time series at one location and with spatially distributed wave parameters obtained from SAR. The comparison shows the sensitivity of waves to local wind variations and the importance of local effects on wave behavior in coastal areas. Examples for the German Bight, North Sea and Rottenest Island, Australia are shown. The wave refraction, rendered by high resolution SAR images, is also studied. The wave ray tracking technique is applied. The wave rays show the propagation of the peak waves in the SAR-scenes and are estimated using image spectral analysis by deriving peak wavelength and direction. The changing of wavelength and direction in the rays allows

  16. Direct observation of homoclinic orbits in human heart rate variability

    NASA Astrophysics Data System (ADS)

    Żebrowski, J. J.; Baranowski, R.

    2003-05-01

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

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

    USGS Publications Warehouse

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

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  19. 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

  20. Amplitude Spectrum Variability in gamma Dor and delta Sct Pulsating Variable Stars Observed by the NASA Kepler Spacecraft

    NASA Astrophysics Data System (ADS)

    Guzik, Joyce Ann; Kosak, Katie; Bradley, Paul A.; Jackiewicz, Jason

    2015-08-01

    The NASA Kepler spacecraft data has revealed a large number of new multimode nonradially pulsating gamma Dor and delta Sct variable stars. The Kepler high precision long time-series photometry makes it possible to study amplitude variations of the frequencies. We summarize recent literature on amplitude and frequency variations in nonradially pulsating variables. We apply several methods, including those we have developed, and the wavelet technique of the VStar software (http://www.aavso.org/vstar-overview), to study amplitude variability in about a dozen gamma Doradus or delta Scuti candidate variable stars observed for several quarters as part of the Kepler Guest Observer program. We discuss the magnitude and timescale of the amplitude variations, and the presence or absence of correlations between amplitude variations for different frequencies of a given star. We discuss proposed causes of amplitude spectrum variability that will require further investigation.

  1. Inter-annual to inter-decadal streamflow variability in Quebec and Ontario in relation to dominant large-scale climate indices

    NASA Astrophysics Data System (ADS)

    Nalley, D.; Adamowski, J.; Khalil, B.; Biswas, A.

    2016-05-01

    The impacts of large-scale climate oscillations on hydrological systems and their variability have been documented in different parts of the world. Since hydroclimatic data are known to exhibit non-stationary characteristics, spectral analyses such as wavelet transforms are very useful in extracting time-frequency information from such data. As Canadian studies, particularly those of regions east of the Prairies, using wavelet transform-based methods to draw links between relevant climate indices [e.g., the El Niño Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Pacific Decadal Oscillation (PDO)] and streamflow variability are not common, this study aims to analyze such relationships for the southern regions of Quebec and Ontario. Monthly and annual streamflow data with a record length of 55 years were used to capture streamflow variability at intra-annual, inter-annual and inter-decadal scales. The continuous wavelet transform spectra of monthly streamflow data revealed consistent significant 6- and 12-month periodicities, which are likely associated with strong seasonality factors. Its annual counterparts showed four different significant periodicities: up to 4 years, 4-6 years, 6-8 years, and greater than 8 years - all of which occurred after the late 1960s/early 1970s. Wavelet coherence analyses show that the influence of ENSO and NAO at the inter-annual scale occurs at 2-6 year periodicities, and the influence of PDO occur at periodicities up to 8 years and exceeding 16 years. Correlations between these climate indices and streamflow were computed to determine the time delay of streamflow response to the influence of ENSO, NAO, and PDO. The lag times ranged from 6-48 months (for monthly data) and 1-4 years (for annual data). This research contributes to our understanding of streamflow variability over the southern parts of Quebec and Ontario, and the role of ENSO, NAO, and PDO phenomena on this variability. These relationships can

  2. Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  3. Observations of the sun, an ultraviolet variable star

    NASA Technical Reports Server (NTRS)

    Heath, D. F.

    1972-01-01

    The uncertainty as to whether or not the sun is a variable star in that region of the ultraviolet which is absorbed in the mesosphere and stratosphere led to an experiment with acronym MUSE, Monitor of Ultraviolet Solar Energy. The experiment was first flown on an Aerobee rocket in August 1966 and subsequently on Nimbus 3 and 4 in April 1969 and April 1970 respectively. The basic philosophy behind the design of the experiment was to provide an instrument which would not require a solar pointing mechanism and at the same time would be capable of high radiometric accuracy for long periods in space.

  4. Optimization of the transmission of observable expectation values and observable statistics in continuous-variable teleportation

    SciTech Connect

    Albano Farias, L.; Stephany, J.

    2010-12-15

    We analyze the statistics of observables in continuous-variable (CV) quantum teleportation in the formalism of the characteristic function. We derive expressions for average values of output-state observables, in particular, cumulants which are additive in terms of the input state and the resource of teleportation. Working with a general class of teleportation resources, the squeezed-bell-like states, which may be optimized in a free parameter for better teleportation performance, we discuss the relation between resources optimal for fidelity and those optimal for different observable averages. We obtain the values of the free parameter of the squeezed-bell-like states which optimize the central momenta and cumulants up to fourth order. For the cumulants the distortion between in and out states due to teleportation depends only on the resource. We obtain optimal parameters {Delta}{sub (2)}{sup opt} and {Delta}{sub (4)}{sup opt} for the second- and fourth-order cumulants, which do not depend on the squeezing of the resource. The second-order central momenta, which are equal to the second-order cumulants, and the photon number average are also optimized by the resource with {Delta}{sub (2)}{sup opt}. We show that the optimal fidelity resource, which has been found previously to depend on the characteristics of input, approaches for high squeezing to the resource that optimizes the second-order momenta. A similar behavior is obtained for the resource that optimizes the photon statistics, which is treated here using the sum of the squared differences in photon probabilities of input versus output states as the distortion measure. This is interpreted naturally to mean that the distortions associated with second-order momenta dominate the behavior of the output state for large squeezing of the resource. Optimal fidelity resources and optimal photon statistics resources are compared, and it is shown that for mixtures of Fock states both resources are equivalent.

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  6. Decadal changes in all and clear-sky shortwave radiation from high spatial resolution satellite-derived and ground-based observations over Europe

    NASA Astrophysics Data System (ADS)

    Sanchez-Lorenzo, A.; Enriquez-Alonso, A.; Wild, M.; Trentmann, J.; Sanchez-Romero, A.; Posselt, R.; Hakuba, M. Z.; Bartok, B.; Vicente-Serrano, S. M.; Calbo Angrill, J.

    2015-12-01

    Trends of all-sky downward surface shortwave radiation (SSR) from high-spatial resolution satellite-derived data over Europe from 1983 to 2010 are first presented. The results show a widespread (i.e., non-local dimension) brightening in the major part of Europe, especially since the mid-1990s and in springtime. There is a mean increase of SSR of around 2 Wm-2 per decade over the whole Europe, which, taking into account that the satellite-derived product lacks of aerosol variations, can be related to a decrease in the cloud radiative effects over Europe. The reported increase in SSR is slightly lower than the obtained using high-quality ground-based series over Europe. Secondly, clear-sky SSR estimates have been derived as the result of the difference between ground-based and satellite-derived all-sky SSR data (i.e., this latter lacking direct aerosol effects). The results highlight that these residual series can be useful to estimate clear-sky SSR trends, pointing to a significant increase during the period 1983-2010, with higher rates of around 2 Wm-2 per decade over central and eastern Europe. This increase in clear-sky SSR is mainly due to a strong increase from the mid-1980s to the late 1990s, possibly linked to a decrease in anthropogenic emissions and a recovery from the El Chichón and Pinatubo volcanic eruptions. These results are in line with observations and other estimates of clear-sky SSR (e.g., by making use of sunshine duration records), as well as reported anthropogenic aerosol emissions and concentrations in Europe. Overall, from the results of this study it can be concluded that around one third of the brightening trend in Europe from 1983 to 2010 can be explained by direct aerosol effects, whereas the other two third is related to clouds, i.e. via changes in natural cloud variability and/or aerosol indirect effect on clouds.

  7. Observed Inter-decadal weakening of the Asian summer monsoon and different response of South and East Asian monsoons during a warming climate scenario

    NASA Astrophysics Data System (ADS)

    Ding, Y.

    2012-12-01

    Based on the observed analysis by using 123-yr observed data, we have shown the inter-decadal weakening of summer monsoon precipitation in East Asia and China, with two major features identified: (1)the rainfall pattern has undergone an obvious southward shift from North China to South China in the mid -and late 1970s. This shift of the precipitation pattern is in good coincidence with a significant abrupt climate change for other variables; and (2) occurrence of prolonged droughts in North China and , at the same time, marked flooding in the Yangtze River Valley and South China in the period from the end 1970s to the beginning of the 21st century. On the other hand , it has been found that after the end of the 1970s the Indian summer monsoon has also underwent a weakening processes which is in good agreement with that in East Asia. So, the Asian summer monsoon has holistically become weaker during past 30 years. One key issue is how long this unusual change in the Asian summer monsoon and associated precipitation patterns will continue to occur. By using outputs from climate models of IPCC AR4 we have projected the responses of the South Asian summer monsoon (SASM) and the East Asian summer monsoon (EASM) circulations and precipitation to different warming over land and ocean under a medium warming scenario, SRES A1B. Our results suggest that, at inter-decadal and longer time scales, the change in the SASM circulation is consistent with the change in the TP(Tibetan Plateau) -TIO (tropical Indian Ocean) upper-troposphere thermal contrast (i.e. meridional temperature gradient) that is believed to be the main driver for SASM. Conversely, the change in the EASM circulation is consistent with the change in the TP-TPO (tropical Pacific Ocean) lower-troposphere thermal contrast, which will be enhanced due to the decreasing winter snow over TP and SSTA over the tropical Pacific. Further analyses suggest that increases in moisture and change in cloud cover induced by

  8. KEPLER OBSERVATIONS OF RAPID OPTICAL VARIABILITY IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

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

    2011-12-10

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

  9. Component noise variables of a light observation helicopter

    NASA Technical Reports Server (NTRS)

    Robinson, F.

    1973-01-01

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

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

    SciTech Connect

    Lai, Chung-Chieng A.

    1997-10-01

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

  11. EUVE Io Plasma Torus Observations: Galileo Support and Variability Studies

    NASA Astrophysics Data System (ADS)

    Gladstone, G. Randall

    We propose a Large Observing Program (1000 ksec) to monitor and investigate EUV emissions from the Io plasma torus and Jupiter during the last four Galileo Europa Mission encounters. These encounters all occur in the last half of 1999 (on Aug. 12, Sept. 14, Oct. 11, and Nov. 26), and will provide a perhaps never-to-be-repeated opportunity for acquiring ground truth (i.e., in situ) measurements with which to calibrate remote sensing observations of the torus. With these new data, we will 1) monitor the global properties of the torus during the Galileo observation epoch, 2) resolve two important but closely spaced torus periodicities, 3) determine the torus stability time constants, 4) search for very faint localized emissions from the Galilean satellites, and 5) continue monitoring the Jovian dayglow. We feel that such a program will make excellent use of EUVEs capabilities, and will allow for a much deeper understanding of the physics of the Jovian system.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

    We present a monthly resolved, 213-year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (δ18Ocoral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The δ18Ocoral anomaly reflects sea surface temperature (SST) anomaly and sea surface salinity (SSS) anomaly with significant r values of -0.69 and 0.49, respectively, which are strongly linked to oceanographic changes that occur during El Niño-Southern Oscillation (ENSO) warm and cool phases. We identified 46 ENSO warm (El Niño) and 53 cool phases (La Niña) in the coral record, which are consistent with those phases reconstructed by Niño 3.4 SST anomaly. Spectral analyses of the δ18Ocoral anomaly record for the years 1790-1999 identified significant peaks around ˜3 to ˜7 years. These results indicate that the Guam coral has recorded ENSO periodicity. The δ18Ocoral anomaly shows decadal variability of ˜15- to ˜45-year periodicity with significant shifts (<0.2‰) from warmer to cooler condition and vice versa. An accumulative decrease in δ18Ocoral time series may imply ˜0.75°C warming of SST and ˜0.23‰ freshening of seawater δ18O, corresponding to a decrease of SSS by ˜0.85, in the northwestern tropical Pacific over the last 2 centuries.

  13. Spatiotemporal Variability and Propagation of Equatorial Noise Observed by Cluster

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  14. Anne S. Young: Professor and Variable Star Observer Extraordinaire

    NASA Astrophysics Data System (ADS)

    Bracher, Katherine

    2011-05-01

    Anne Sewell Young (1871-1961) was one of the eight original members of the AAVSO, to which she contributed more than 6500 observations over 33 years. She also taught astronomy for 37 years at Mount Holyoke College; among her students was Helen Sawyer Hogg. This paper will look at her life and career both at Mount Holyoke and with the AAVSO.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  16. Two Decades of Global and Regional Sea Level Observations from the ESA Climate Change Initiative Sea Level Project

    NASA Astrophysics Data System (ADS)

    Legeais, JeanFrancois; Larnicol, Gilles; Cazenave, Anny; Ablain, Michael; Benveniste, Jérôme; Lucas, BrunoManuel; Timms, Gary; Johannessen, Johnny; Knudsen, Per; Cipollini, Paolo; Roca, Monica; Rudenko, Sergei; Fernandes, Joana; Balmaseda, Magdalena; Quartly, Graham; Fenoglio-Marc, Luciana; Scharfennberg, Martin; Meyssignac, Benoit; Guinle, Thierry; Andersen, Ole

    2015-04-01

    Sea level is a very sensitive index of climate change and variability. Sea level integrates the ocean warming, mountain glaciers and ice sheet melting. Understanding the sea level variability and changes implies an accurate monitoring of the sea level variable at climate scales, in addition to understanding the ocean variability and the exchanges between ocean, land, cryosphere, and atmosphere. That is why Sea Level is one of the Essential Climate Variables (ECV) selected in the frame of the ESA Climate Change Initiative (CCI) program. It aims at providing long-term monitoring of the sea level ECV with regular updates, as required for climate studies. After a first phase (2011-2013), the program has started in 2014 a second phase of 3 years. The objectives of this second phase are to involve the climate research community, to refine their needs and collect their feedbacks on product quality, to develop, test and select the best algorithms and standards to generate an updated climate time series and to produce and validate the Sea Level ECV product. This will better answer the climate user needs by improving the quality of the Sea Level products and maintain a sustain service for an up-to-date production. To this extent, the ECV time series has been extended and it now covers the period 1993-2013. We will firstly present the main achievements of the ESA CCI Sea Level Project. On the one hand, the major steps required to produce the 21 years climate time series are briefly described: collect and refine the user requirements, development of adapted algorithms for climate applications and specification of the production system. On the other hand, the product characteristics are described as well as the results from product validation, performed by several groups of the ocean and climate modeling community. At last, the work plan and key challenges of the second phase of the project are described.

  17. Two decades of global and regional sea level observations from the ESA climate change initiative sea sevel project

    NASA Astrophysics Data System (ADS)

    Cazenave, Anny; Benveniste, Jérôme; Legeais, JeanFrancois

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

  18. A Review of Direct Observation Research within the Past Decade in the Field of Emotional and Behavioral Disorders

    ERIC Educational Resources Information Center

    Adamson, Reesha M.; Wachsmuth, Sean T.

    2014-01-01

    This study reviewed prominent journals within the field of emotional and behavioral disorders to identify direct observation approaches, reported reliability statistics, and key features of direct observation. Selected journals were systematically reviewed for the past 10 years identifying and quantifying specific direct observation systems and…

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

    SciTech Connect

    Szkody, Paula; Vasquez-Soltero, Stephanie; Everett, Mark E.; Silva, David R.; Howell, Steve B.; Landolt, Arlo U.; Bond, Howard E. E-mail: dsilva@noao.edu E-mail: landolt@rouge.phys.lsu.edu

    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.

  20. Pacific Decadal Variability in the Southern Indian Ocean: A 1 ky Interdecadal Pacific Oscillation and Australian Megadrought Reconstruction from Law Dome, East Antarctica.

    NASA Astrophysics Data System (ADS)

    Vance, T.; Roberts, J. L.; Plummer, C. T.; Kiem, A.; van Ommen, T. D.

    2014-12-01

    The Interdecadal Pacific Oscillation (IPO) is a multidecadal mode of Pacific basin SST anomalies, and is the basin-wide, bi-hemispheric expression of the Pacific Decadal Oscillation (PDO). The two indices are highly correlated, but the extent to which they are merely low frequency ENSO is debated. Nonetheless, the IPO/PDO significantly influences interannual rainfall variability and drought risk across and beyond the Pacific region on multi-decadal timescales, thus an understanding of long-term IPO/PDO variability will help with assessing past and future drought risk. A new and highly accurate 1 ky IPO reconstruction has been produced from the Law Dome ice core (East Antarctica). Law Dome is a high accumulation site on the coast of Antarctica in the Indian Ocean sector of the Southern Ocean, and the Law Dome record is directly related to atmospheric anomalies across a broad mid-latitude swathe of this region. The reconstruction utilizes both the accumulation (snowfall) and sea salt (wind proxy) records to produce a reconstruction that is highly calibrated to the instrumental IPO record from 1870-2009 and shows excellent skill (reduction of error value of 0.86). We then super-imposed the 1 ky IPO on a Law Dome proxy for rainfall in eastern subtropical Australia (previously shown to represent rainfall with high significance during IPO positive phases (r =0.406-0.677, p <0.0001-0.01) to identify eight Australian 'mega-droughts' (dry periods >5 y duration) over the last millennium. Six mega-droughts occur 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 instrumental record and lack of rainfall proxies. A recent drought (the 'Big Dry' ~1995-2009) brought both agricultural and urban water supplies to critically low levels, while the Murray-Darling Basin river system, which provides 65% of the water used for

  1. The influence of PMCs on water vapor and drivers behind PMC variability from SOFIE observations

    NASA Astrophysics Data System (ADS)

    Hervig, Mark E.; Siskind, David E.; Bailey, Scott M.; Russell, James M.

    2015-09-01

    Observations from the Solar Occultation For Ice Experiment (SOFIE) are used to quantify relationships between polar mesospheric clouds (PMC) and their environment. Dehydration due to ice growth is found to be greatest ∼1.8 km above the height of peak ice mass density on average, and H2O enhancement due to sublimation is greatest near the bottom of the PMC layer. The dehydration and hydration layers contain a similar amount of H2O, although less than is found in ice layers, a difference that may be due to meridional transport. Because PMCs modify the surrounding water vapor, PMC-H2O relationships can be misleading and recommendations are made for dealing with this issue. The dependence of PMCs on water vapor and temperature was quantified, accounting for the effects of ice on water vapor. The approach examined inter-annual variations and considered the subset of PMCs detected by the Solar Backscatter Ultraviolet (SBUV) instruments, which are less sensitive than SOFIE. Results in the Northern Hemisphere indicate that PMC variations are dominated by temperature, but that a combination of temperature and water vapor provides the best explanation of the observations. In the Southern Hemisphere PMC variability is attributed primarily to temperature, with water vapor playing a minor role. The subset of SBUV PMCs are found to be one third as sensitive to changing temperature as the entire PMC population observed by SOFIE. Finally, an approach is presented which allows temperature and water vapor anomalies to be estimated from various PMC data sets such as SBUV. Using recently reported SBUV PMC trends at 64-74°N latitude with the results of this study indicates a cooling trend of -0.27±0.14 K decade-1 and a water vapor increase of +0.66±0.34% decade-1 (both at 80-84 km). This cooling trend agrees with reports based on observations in the middle atmosphere at similar latitudes. The water vapor increase is lower than expected due to increasing methane, although this

  2. Observations of SST diurnal variability in the South China Sea

    NASA Astrophysics Data System (ADS)

    Tu, Qianguang; Pan, Delu; Hao, Zengzhou; Chen, Jianyu

    2015-10-01

    In this study, a 3-hourly time resolution gap free sea surface temperature (SST) analysis is generated to resolve the diurnal cycle in the South China Sea (SCS, 0°-25°N, 100°-125°E).It takes advantage of hourly geostationary satellite MTSAT observations and combines three infrared and two microwave polar satellite observations at different local times. First, all the data are classified into eight SST datasets at 3 hour intervals and then remapped to 0.05°resolution grids. A series of critical quality control is done to remove the outliers.Then bias adjustment is applied to the polar satellite observations with reference to the MTSAT data. Finally, the six satellites SST data are blended by using the optimal interpolated algorithm. The 3-hourly blended SST is compared against buoy measurements. It shows a good agreement that the biases do not exceed 0.2 °C and root mean square errors range from 0.5 to 0.65 °C. A typical diurnal cycle similar to sine wave is observed. The minimum SST occurs at around 0600h and warming peak occurring between 1300h and 1500h local solar time and then decrease in the late afternoon, tapering off at night on March 13, 2008 for example. The frequency of diurnal warming events derived from four years of the blended SST provides solid statistics to investigate the seasonal and spatial distributions of the diurnal warming in the SCS. The sea surface diurnal warming tends to appear more easily in spring, especially in the coastal regions than other seasons and the central regions.

  3. Combined optical and X-ray observations of variable stars

    NASA Technical Reports Server (NTRS)

    Bowyer, C. S.

    1975-01-01

    Questions concerning the optical identification of X-ray sources are considered. There are now a total of eight optically identified galactic X-ray sources. Of these eight, five are definitely established as binaries. The nature of the other three sources remains unknown. Studies of U Geminorum conducted on the basis of optical and X-ray observations are also discussed. From the upper limit to the accretion rate for U Gem obtained with the aid of soft X-ray data, it is seen that most of the mass flow in U Gem is lost from the system.

  4. Gait Variability in Older Adults: Observational Rating Validated by Comparison With a Computerized Walkway Gold Standard

    PubMed Central

    Huang, Wen-Ni Wennie; VanSwearingen, Jessie M; Brach, Jennifer S

    2008-01-01

    Background and Purpose: Gait variability has been measured with computerized technology–intensive techniques, which are not practical in clinical settings. The purpose of this study was to validate an observational rating of gait variability for routine clinical practice. Subjects: Community-dwelling older adults aged 65 years and older (n=46; mean age=81.2 years, SD=6.8 years, range=66–91 years) participated in this study. Methods: The standard deviation of stance time (stance time variability) derived from gait characteristics recorded by use of a computerized walkway was used as the gold standard for gait variability. The validity of the diagnostic test evaluated in this study (an observational rating of gait variability) was determined by comparison with the quantitative measure of stance time variability. Results: Six validity indexes were defined for the observational rating of gait variability: sensitivity=81%; specificity=53%; positive predictive value=65%; negative predictive value=71%; positive likelihood ratio=1.72; and negative likelihood ratio=0.36. Discussion and Conclusion: An observational rating of gait variability was validated by comparison with stance time variability derived from a computerized walkway. The concurrent validity of the 2 methods of determining gait variability provides support for the use of the observational rating as an alternative measure of gait variability for the purpose of identifying older adults at risk for mobility disability in clinical settings. PMID:18719005

  5. Demographic Variables for Wild Asian Elephants Using Longitudinal Observations

    PubMed Central

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

    2013-01-01

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

  6. Interannual Variability of OLR as Observed by AIRS and CERES

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  7. Observational constraints on a variable dark energy model

    SciTech Connect

    Movahed, M. Sadegh; Rahvar, Sohrab

    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.

  8. Two Decades of Global and Regional Sea Level Observations from the ESA Climate Change Initiative Sea Level Project

    NASA Astrophysics Data System (ADS)

    Benveniste, J.; Gilles, G.; Cazenave, A. A.; Ablain, M.; Legeais, J. F.; Faugère, Y.; Lucas, B.; Dinardo, S.; Johannessen, J. A.; Stammer, D.; Timms, G.; Knudsen, P.; Cipollini, P.; Roca, M.; Rudenko, S.; Fernandes, J.; Balmaseda, M.; Quartly, G.; Fenoglio-Marc, L.; Guinle, T.

    2014-12-01

    Sea level is a very sensitive index of climate change and variability. Sea level integrates the ocean warming, mountain glaciers and ice sheet melting. Understanding the sea level variability and changes implies an accurate monitoring of the sea level variable at climate scales, in addition to understanding the ocean variability and the exchanges between ocean, land, cryosphere, and atmosphere. That is why Sea Level is one of the Essential Climate Variables (ECV) selected in the frame of the ESA Climate Change Initiative (CCI) program. It aims at providing long-term monitoring of the sea level ECV with regular updates, as required for climate studies. The program has just completed its first phase (Oct. 2010 to Dec. 2013) and has started in February 2014 the second phase of 3 years. The objectives of the second phase are to involve the climate research community, to refine their needs and collect their feedbacks on product quality, to develop, test and select the best algorithms and standards to generate an updated climate time series and to produce and validate the Sea Level ECV product. This will better answer the climate user needs by improving the quality of the Sea Level products and maintain a sustain service for an up-to-date production. To this extent, a temporal extension of the ECV will be delivered at the end of 2014 so that the covered period becomes 1993-2013. We will firstly present the main achievements of the ESA CCI Sea Level Project. On the one hand, the major steps required to produce the 18 years climate time series (delivered in Sept. 2012) are briefly described: collect and refine the user requirements, development of adapted algorithms for climate applications and specification of the production system. On the other hand, the product characteristics are described as well as the results from product validation, performed by several groups of the ocean and climate modeling community. At last, the work plan and key challenges of the second phase

  9. Interannual Variability of OLR as Observed by AIRS and CERES

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  10. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    SciTech Connect

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

    1989-11-01

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

  13. Intra-annual to inter-decadal variability in the upper Colorado hydroclimatology: Diagnosis, forecasting and implications for water resources management

    NASA Astrophysics Data System (ADS)

    Regonda, Satish Kumar

    stressed. Last, but not least, a methodology is proposed to generate realistic streamflow scenarios using paleo reconstructions (tree ring based reconstructions of past streamflows) in conjunction with the limited observational record. This approach provides the ability to generate a richer variety of drought and flood scenarios than those observed in recent history. It, thus, provides useful insight into streamflow variability, which is crucial for water resources management and planning in the basin.

  14. Seasonal variability in global sea level observed with Geosat altimetry

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  15. Observations of Millisecond Variability from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    1997-04-01

    Observations carried out over the past year by the Rossi X-ray Timing Explorer (RXTE) have revealed both quasiperiodic and nearly coherent oscillations with frequencies from 300 - 1200 Hz in at least 10 low mass X-ray binary (LMXB) systems. The X-ray luminosity from these systems is the result of accretion of matter into the deep gravitational potential well of a neutron star. Four of these sources show nearly coherent oscillations during some thermonuclear X-ray bursts which very likely reveal the long sought millisecond spin periods of neutron stars in at least some LMXB. The millisecond timescales of the quasiperiodic oscillations (QPO) are characteristic of processes occuring in the immediate vicinity of the neutron star and provide a new means to investigate the physics of neutron stars and their environs. I will review the discovery and current understanding of these kHz QPO, as they have come to be known, and briefly discuss what their study can teach us about neutron stars.

  16. Observations of mesoscale variability in the Rockall Trough

    NASA Astrophysics Data System (ADS)

    Ullgren, J. E.; White, M.

    2012-06-01

    The Rockall Trough west of Ireland displays a high level of mesoscale activity for an eastern ocean boundary region. Eddies off the continental slope at 50-56°N have been studied using a combination of in situ observations of current velocity and hydrography from two deep-sea moorings at the southern entrance to the Trough, and data from satellite altimetry and Argo floats. South of Rockall-Hatton Plateau, where a branch of the NAC enters the region from the west, more cyclonic eddies are found, while anticyclonic eddies dominate along the path of the Slope Current in the east. Temperature-salinity profiles from the perimeters of a cyclone and an anticyclone, respectively, show large differences on isopycnals both at the level of the subsurface salinity maximum and at intermediate depths. Anticyclonic eddies likely formed by instabilities of the Slope Current can include a parcel of salty Mediterranean Water (MW) at the intermediate level, contributing to the patchy distribution of MW in the region.

  17. Variability in solar irradiance observed at two contrasting Antarctic sites

    NASA Astrophysics Data System (ADS)

    Petkov, Boyan H.; Láska, Kamil; Vitale, Vito; Lanconelli, Christian; Lupi, Angelo; Mazzola, Mauro; Budíková, Marie

    2016-05-01

    The features of erythemally weighted (EW) and short-wave downwelling (SWD) solar irradiances, observed during the spring-summer months of 2007-2011 at Johann Gregor Mendel (63°48‧S, 57°53‧W, 7 m a.s.l.) and Dome Concordia (75°06‧S, 123°21‧E, 3233 m a.s.l.) stations, placed at the Antarctic coastal region and on the interior plateau respectively, have been analysed and compared to each other. The EW and SWD spectral components have been presented by the corresponding daily integrated values and were examined taking into account the different geographic positions and different environmental conditions at both sites. The results indicate that at Mendel station the surface solar irradiance is strongly affected by the changes in the cloud cover, aerosols and albedo that cause a decrease in EW between 20% and 35%, and from 0% to 50% in SWD component, which contributions are slightly lower than the seasonal SWD variations evaluated to be about 71%. On the contrary, the changes in the cloud cover features at Concordia station produce only a 5% reduction of the solar irradiance, whilst the seasonal oscillations of 94% turn out to be the predominant mode. The present analysis leads to the conclusion that the variations in the ozone column cause an average decrease of about 46% in EW irradiance with respect to the value found in the case of minimum ozone content at each of the stations. In addition, the ratio between EW and SWD spectral components can be used to achieve a realistic assessment of the radiation amplification factor that quantifies the relationship between the atmospheric ozone and the surface UV irradiance.

  18. Spatial Variability of Trace Gases During DISCOVER-AQ: Planning for Geostationary Observations of Atmospheric Composition

    NASA Technical Reports Server (NTRS)

    Follette-Cook, Melanie B.; Pickering, K.; Crawford, J.; Appel, W.; Diskin, G.; Fried, A.; Loughner, C.; Pfister, G.; Weinheimer, A.

    2015-01-01

    Results from an in-depth analysis of trace gas variability in MD indicated that the variability in this region was large enough to be observable by a TEMPO-like instrument. The variability observed in MD is relatively similar to the other three campaigns with a few exceptions: CO variability in CA was much higher than in the other regions; HCHO variability in CA and CO was much lower; MD showed the lowest variability in NO2All model simulations do a reasonable job simulating O3 variability. For CO, the CACO simulations largely under over estimate the variability in the observations. The variability in HCHO is underestimated for every campaign. NO2 variability is slightly overestimated in MD, more so in CO. The TX simulation underestimates the variability in each trace gas. This is most likely due to missing emissions sources (C. Loughner, manuscript in preparation).Future Work: Where reasonable, we will use these model outputs to further explore the resolvability from space of these key trace gases using analyses of tropospheric column amounts relative to satellite precision requirements, similar to Follette-Cook et al. (2015).

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  20. Evidence For Decadal and Century Scale Climate and Oceanic Variability in the Guaymas Basin, Gulf of California, Over the Last Millenium

    NASA Astrophysics Data System (ADS)

    Pineda, L.; Ravelo, A. C.; Aiello, I. W.; Stewart, Z.; Sauthoff, W.

    2015-12-01

    Linda Pineda1Ana Christina Ravelo2Ivano Aiello3Zach Stewart2Wilson Sauthoff2 Earth and Planetary Sciences Department, UCSC Ocean Sciences Department, UCSC Moss Landing Marine Lab Natural climate change affects coastal water resources, human land use, and marine biological productivity. In particular, the seasonal migration of the Intertropical Convergence Zone (ITCZ) is influenced by changes in global-scale temperature and pressure gradients and is responsible for spatial changes in summertime rainfall in Mesoamerica impacting regional water resources and the strength of upwelling. In October 2014, aboard the Research Vessel El Puma, a 3.9 meter long core (G14-P12) was recovered from the Northeast flank of the Guaymas Basin in the Gulf of California within the oxygen minimum zone (27˚52.11'N, 111˚41.51'W, water depth of 677m) to investigate changes in seasonal upwelling and Central Mexico rainfall over the last ~1000 years. The age model was developed using Pb210, C14 and lamination counting. The time interval includes the Little Ice Age and the Medieval Warm Period. Biological productivity and precipitation proxy records were produced using an X-Ray Fluorescence (XRF) core-scanner and a color line scanner to generate a record of bulk chemistry and color reflectance. The records indicate marked decadal and centennial scale variability in the lithologic composition of the sediment superimposed on millimeter-scale variability that reflects the presence of seasonally laminated sediments. Nitrogen isotopic and nitrogen weight % measurements were used, in combination with the scanned data, to interpret changes in nitrate utilization and biological productivity. These new records will have broad implications on the link between regional coastal environmental conditions in the Gulf of California and global climate change.

  1. Impact of synoptic weather patterns and inter-decadal climate variability on air quality in the North China Plain during 1980-2013

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Ding, Aijun; Mao, Huiting; Nie, Wei; Zhou, Derong; Liu, Lixia; Huang, Xin; Fu, Congbin

    2016-01-01

    Potential relationships between air quality, synoptic weather patterns, and the East Asian Monsoon (EAM) over the North China Plain (NCP) were examined during the time period of 1980-2013 using a weather typing technique and ground-based air pollution index (API) data from three cities: Beijing, Tianjin and Shijiazhuang. Using the Kirchhofer method, circulation patterns during the 34-yr study period were classified into 5 categories, which were further used to understand the quantitative relationship between weather and air quality in NCP. The highest API values were associated with a stagnant weather condition when wide-spread stable conditions controlled most part of NCP, while westerly and southerly wind flowed over the northern and eastern part of this region, resulting in both the regional transport and local build-up of air pollutants. Under the continuous control of this weather pattern, API values were found to increase at a rate of 8.5 per day on average. Based on the qualitative and quantitative analysis, a significant correlation was found between the strength of EAM and inter-annual variability of frequencies of the weather patterns. The strengthening of summer/winter monsoon could increase the frequency of occurrence of cyclone/anticyclone related weather patterns. Time series of climate-induced variability in API over the 34 years were reconstructed based on the quantitative relationship between API and predominant weather patterns during 2001-2010. Significant connections between EAM and reconstructed API were found on both the inter-annual and inter-decadal scales. In winter and summer, strengthening/weakening of EAM, which was generally associated with the change of the representative circulation patterns, could improve/worsen air quality in this region.

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

    SciTech Connect

    Fox-Rabinovitz, M; Cote, J

    2009-06-05

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  4. 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.

  5. Two decades of historical phenology observations of African tropical tree species: exploring the past to predict the futur

    NASA Astrophysics Data System (ADS)

    Hufkens, K.; Kosmala, M.; Ewango, C.; Richardson, A. D.; Beeckman, H.

    2015-12-01

    African tropical forests cover ~630 million ha, store up to 66 Pg of carbon and represent a significant carbon sink (0.34Pg C yr-1 ). As such African tropical forests provide an important negative feedback to the global carbon cycle. Unlike temperate forests, tropical forests lack sharp temperature and photoperiod cues to constrain phenology and growth. Therefore, events such as seasonal leaf abscission and reproductive life cycles are often driven by changes in water availability. With future climate predictions expecting a warmer, and especially drier tropical Africa, it is likely we will see concomitant changes in tree growth and phenology.As tropical trees show a high degree of phenological plasticity depending on the severity of the dry season, intermittent water stress or the location of an individual in the canopy structure. As such, frequent and long term observations are key to characterize tropical tree phenology. Here I use two long term historical phenology records of weekly observations, some digitized within the context of a citizen science project (http://junglerhythms.org/), to explore differences in tree phenology between two sites (Luki and Yangambi, DR Congo) with contrasting climate regimes within the Congo basin. I describe variation in leaf, flower and fruit phenology across similar species at both locations in relation to complementary historical climatological observations. I further discuss the potential implications of changing phenology under future climate conditions as phenological changes could alter both ecosystem demography and growing season length providing important feedbacks to the climate system.

  6. 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

  7. 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

  8. The American Association of Variable Star Observers as a Professional-Amateur Astronomical Community of practice

    NASA Astrophysics Data System (ADS)

    Kafka, Stella; 6173540484

    2016-06-01

    The AAVSO was formed in 1911 as a group of US-based amateur observers obtaining data in support of professional astronomy projects. Now, it has evolved into an International Organization with members and observers in all continents, contributing photometry to a public database of about 22,000 variable objects. I will present main aspects of the association and how it has evolved with time to a premium resource for variable star research. I will also discuss current projects and opportunities for Professional-Amateur collaborations within the AAVSO, building a stronger international community of variable star observers!

  9. Improvements in observed and relative survival in follicular grade 1-2 lymphoma during 4 decades: the Stanford University experience

    PubMed Central

    Tan, Daryl; Horning, Sandra J.; Hoppe, Richard T.; Levy, Ronald; Rosenberg, Saul A.; Sigal, Bronislava M.; Warnke, Roger A.; Natkunam, Yasodha; Han, Summer S.; Yuen, Alan; Plevritis, Sylvia K.

    2013-01-01

    Recent studies report an improvement in overall survival (OS) of patients with follicular lymphoma (FL). Previously untreated patients with grade 1 to 2 FL treated at Stanford University from 1960-2003 were identified. Four eras were considered: era 1, pre-anthracycline (1960-1975, n = 180); era 2, anthracycline (1976-1986, n = 426); era 3, aggressive chemotherapy/purine analogs (1987-1996, n = 471); and era 4, rituximab (1997-2003, n = 257). Clinical characteristics, patterns of care, and survival were assessed. Observed OS was compared with the expected OS calculated from Berkeley Mortality Database life tables derived from population matched by gender and age at the time of diagnosis. The median OS was 13.6 years. Age, gender, and stage did not differ across the eras. Although primary treatment varied, event-free survival after the first treatment did not differ between eras (P = .17). Median OS improved from 11 years in eras 1 and 2 to 18.4 years in era 3 and has not yet been reached for era 4 (P < .001), with no suggestion of a plateau in any era. These improvements in OS exceeded improvements in survival in the general population during the same period. Several factors, including better supportive care and effective therapies for relapsed disease, are likely responsible for this improvement. PMID:23777769

  10. Observed Multi-Decade DD and DT Z-Pinch Fusion Rate Scaling in 5 Dense Plasma Focus Fusion Machines

    SciTech Connect

    Hagen, E. C.; Lowe, D. R.; O'Brien, R.; Meehan, B. T.

    2013-06-18

    Dense Plasma Focus (DPF) machines are in use worldwide or a wide variety of applications; one of these is to produce intense, short bursts of fusion via r-Z pinch heating and compression of a working gas. We have designed and constructed a series of these, ranging from portable to a maximum energy storage capacity of 2 MJ. Fusion rates from 5 DPF pulsed fusion generators have been measured in a single laboratory using calibrated activation detectors. Measured rates range from ~ 1015 to more than 1019 fusions per second have been measured. Fusion rates from the intense short (20 – 50 ns) periods of production were inferred from measurement of neutron production using both calibrated activation detectors and scintillator-PMT neutron time of flight (NTOF) detectors. The NTOF detectors are arranged to measure neutrons versus time over flight paths of 30 Meters. Fusion rate scaling versus energy and current will be discussed. Data showing observed fusion cutoff at D-D fusion yield levels of approximately 1*1012, and corresponding tube currents of ~ 3 MA will be shown. Energy asymmetry of product neutrons will also be discussed. Data from the NTOF lines of sight have been used to measure energy asymmetries of the fusion neutrons. From this, center of mass energies for the D(d,n)3He reaction are inferred. A novel re-entrant chamber that allows extremely high single pulse neutron doses (> 109 neutrons/cm2 in 50 ns) to be supplied to samples will be described. Machine characteristics and detector types will be discussed.

  11. Nearly a Decade of CALIPSO Observations of Asian and Saharan Dust Properties Near Source and Transport Regions

    NASA Technical Reports Server (NTRS)

    Omar, Ali H.; Liu, Z.; Tackett, J.; Vaughan, M.; Trepte, C.; Winker, D.; H. Yu,

    2015-01-01

    The lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission, makes robust measurements of dust and has generated a length of record that is significant both seasonally and inter-annually. We exploit this record to determine a multi-year climatology of the properties of Asian and Saharan dust, in particular seasonal optical depths, layer frequencies, and layer heights of dust gridded in accordance with the Level 3 data products protocol, between 2006-2015. The data are screened using standard CALIPSO quality assurance flags, cloud aerosol discrimination (CAD) scores, overlying features and layer properties. To evaluate the effects of transport on the morphology, vertical extent and size of the dust layers, we compare probability distribution functions of the layer integrated volume depolarization ratios, geometric depths and integrated attenuated color ratios near the source to the same distributions in the far field or transport region. CALIPSO is collaboration between NASA and Centre National D'études Spatiales (CNES), was launched in April 2006 to provide vertically resolved measurements of cloud and aerosol distributions. The primary instrument on the CALIPSO satellite is the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), a near-nadir viewing two-wavelength polarization-sensitive instrument. The unique nature of CALIOP measurements make it quite challenging to validate backscatter profiles, aerosol type, and cloud phase, all of which are used to retrieve extinction and optical depth. To evaluate the uncertainty in the lidar ratios, we compare the values computed from dust layers overlying opaque water clouds, considered nominal, with the constant lidar ratio value used in the CALIOP algorithms for dust. We also explore the effects of noise on the CALIOP retrievals at daytime by comparing the distributions of the properties at daytime to the nighttime distributions.

  12. Nearly a Decade of CALIPSO Observations of Asian and Saharan Dust Properties near Source and Transp