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1

Tides and Decadal Variability  

NASA Technical Reports Server (NTRS)

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

Ray, Richard D.

2003-01-01

2

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

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

3

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

NASA Astrophysics Data System (ADS)

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.

Wang, Kaicun

2014-08-01

4

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

PubMed

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

Wang, Kaicun

2014-01-01

5

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

NASA Astrophysics Data System (ADS)

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.

Liu, Peng; Sui, Chung-Hsiung

2014-03-01

6

Coupled Decadal Variability in the North Pacific: An Observationally Constrained Idealized Model*  

E-print Network

circulation variability and the heat exchange variability across the air­sea interface are the largest. The first is the climate noise sce- nario (aka the null hypothesis) in which the low- frequency SST

Qiu, Bo

7

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

NASA Astrophysics Data System (ADS)

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

Xia, Xiangao

2011-10-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

11

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

Microsoft Academic Search

This paper gives an update on the observed decadal variability of the earth radiation budget (ERB) using the latest altitude-corrected Earth Radiation Budget Experiment (ERBE)\\/Earth Radiation Budget Satellite (ERBS) Nonscanner Wide Field of View (WFOV) instrument Edition3 dataset. The effects of the altitude correction are to modify the original reported decadal changes in tropical mean (20°N to 20°S) longwave (LW),

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

2006-01-01

12

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

NASA Astrophysics Data System (ADS)

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

Lique, Camille; Steele, Michael

2013-04-01

13

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

14

Decadal variability of the Indian Ocean dipole  

Microsoft Academic Search

Using the Simple Ocean Data Assimilation (SODA), NCEP\\/NCAR reanalysis and the GISST datasets from 1950–1999, and an atmosphere-ocean coupled general circulation model, we explored the possible existence of decadal Indian Ocean Dipole (IOD) variability for the first time. We find that there are strong decadal IOD events, and that the time series of the decadal IOD and decadal ENSO indices

Karumuri Ashok; Wing-Le Chan; Tatsuo Motoi; Toshio Yamagata

2004-01-01

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)

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

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

2005-01-01

16

Decadal variability of the Indian Ocean dipole  

NASA Astrophysics Data System (ADS)

Using the Simple Ocean Data Assimilation (SODA), NCEP/NCAR reanalysis and the GISST datasets from 1950-1999, and an atmosphere-ocean coupled general circulation model, we explored the possible existence of decadal Indian Ocean Dipole (IOD) variability for the first time. We find that there are strong decadal IOD events, and that the time series of the decadal IOD and decadal ENSO indices are not well correlated. The simulated decadal signal of the IOD index is highly correlated with the 20°C isotherm depth anomaly, indicating that ocean dynamics is involved in the decadal IOD. It is also associated with the zonal wind anomaly. We suggest that the decadal IOD in the tropics is interpreted as decadal modulation of the interannual IOD events.

Ashok, Karumuri; Chan, Wing-Le; Motoi, Tatsuo; Yamagata, Toshio

2004-12-01

17

Elements of tropical Pacific decadal variability  

E-print Network

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

Fuckar, Neven-Stjepan

2012-06-07

18

DECADAL VARIABILITY IN THE TROPICAL PACIFIC CLIMATE  

Microsoft Academic Search

decade long reanalysis of upper ocean temperature and surface meteorology. Indices are defined to reflect the decadal characteristics of the midlatitude and tropical ocean and much of the paper focuses on understanding the fluctuations of these indices. In midlatitudes the analysis reveals structures reminiscent of the Latif-Barnett advective mode. However, in the tropics the climate variability takes on a rather

James A. Carton; Kingtse Mo

19

Decadal variability in Floods and Extreme Rainfall  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

22

Decadal to multidecadal variability and the climate change background  

NASA Astrophysics Data System (ADS)

Three prominent quasi-global patterns of variability and change are observed using the Met Office's sea surface temperature (SST) analysis and almost independent night marine air temperature analysis. The first is a global warming signal that is very highly correlated with global mean SST. The second is a decadal to multidecadal fluctuation with some geographical similarity to the El Niño-Southern Oscillation (ENSO). It is associated with the Pacific Decadal Oscillation (PDO), and its Pacific-wide manifestation has been termed the Interdecadal Pacific Oscillation (IPO). We present model investigations of the relationship between the IPO and ENSO. The third mode is an interhemispheric variation on multidecadal timescales which, in view of climate model experiments, is likely to be at least partly due to natural variations in the thermohaline circulation. Observed climatic impacts of this mode also appear in model simulations. Smaller-scale, regional atmospheric phenomena also affect climate on decadal to interdecadal timescales. We concentrate on one such mode, the winter North Atlantic Oscillation (NAO). This shows strong decadal to interdecadal variability and a correspondingly strong influence on surface climate variability which is largely additional to the effects of recent regional anthropogenic climate change. The winter NAO is likely influenced by both SST forcing and stratospheric variability. A full understanding of decadal changes in the NAO and European winter climate may require a detailed representation of the stratosphere that is hitherto missing in the major climate models used to study climate change.

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

2007-09-01

23

On the observed relationship between the Pacific Decadal Oscillation and the Atlantic Multi-decadal Oscillation  

Microsoft Academic Search

We studied the relationship between the dominant patterns of sea surface temperature (SST) variability in the North Pacific\\u000a and the North Atlantic. The patterns are known as the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-decadal Oscillation\\u000a (AMO). In the analysis we used two different observational data sets for SST. Due to the high degree of serial correlation\\u000a in the

Shu WuZhengyu; Zhengyu Liu; Rong Zhang; Thomas L. Delworth

2011-01-01

24

Advances in Understanding Decadal Climate Variability  

NASA Technical Reports Server (NTRS)

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

Busalacchi, Antonio J.

1999-01-01

25

Advances in Understanding Decadal Climate Variability  

NASA Technical Reports Server (NTRS)

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

Busalaacchi, Antonio J.

1998-01-01

26

Decadal Climate Variability and the Thermohaline Circulation  

Microsoft Academic Search

a. to determine the predictability of climate - as stated in the COPES strategic framework, investigating the predictability of climate up to a decade ahead is one of the major immediate challenges faced by climate research. So far, climate predictions - in contrast to projections - have almost exclusively been performed for the seasonal-to-interannual timeframe, but the decadal scale is

Jochem Marotzke

2006-01-01

27

Contribution of solar radiation to decadal temperature variability over land.  

PubMed

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

Wang, Kaicun; Dickinson, Robert E

2013-09-10

28

Contribution of solar radiation to decadal temperature variability over land  

NASA Astrophysics Data System (ADS)

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

Wang, Kaicun; Dickinson, Robert

2014-05-01

29

Contribution of solar radiation to decadal temperature variability over land  

PubMed Central

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

Wang, Kaicun; Dickinson, Robert E.

2013-01-01

30

Multi-Decadal Variability of West African Rainfall in  

E-print Network

Multi-Decadal Variability of West African Rainfall in CMIP5 Simulations Elinor R. Martin and Chris-Decadal Variability of Sahel Rainfall L17712 ZHANG AND DELW Zhang and Delworth 2006 · Sahel rainfall large decadal · Summer peak is simulated · Most models underestimate summer peak and overestimate spring #12;0 5 10 15 20

Martin, Elinor R.

31

Multi-decadal variability of drought risk, eastern Australia  

Microsoft Academic Search

A number of previous studies have identified changes in the climate occurring on decadal to multi-decadal time-scales. Recent studies also have revealed multi-decadal variability in the modulation of the magnitude of El Niño-Southern Oscillation (ENSO) impacts on rainfall and stream flow in Australia and other areas. This study investigates multi-decadal variability of drought risk by analysing the performance of a

Anthony S. Kiem; Stewart W. Franks

2004-01-01

32

North Atlantic Decadal Variability: Air-Sea Coupling, Oceanic Memory, and Potential Northern Hemisphere Resonance  

Microsoft Academic Search

In this paper, the causes and mechanisms of North Atlantic decadal variability are explored in a series of coupled ocean-atmosphere simulations. The model captures the major features of the observed North Atlantic decadal variability. The North Atlantic SST anomalies in the model control simulation exhibit a prominent decadal cycle of 12-16 yr, and a coherent propagation from the western subtropical

Lixin Wu; Zhengyu Liu

2005-01-01

33

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

NASA Astrophysics Data System (ADS)

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

Mohino, Elsa; Janicot, Serge; Bader, Juergen

2010-05-01

34

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

NASA Astrophysics Data System (ADS)

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

Mohino, Elsa; Janicot, Serge; Bader, Juergen

2011-08-01

35

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

NASA Astrophysics Data System (ADS)

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

Yu, Jia-Yuh; Chang, Cheng-Wei

2014-05-01

36

A Decade of Satellite Ocean Color Observations  

NASA Technical Reports Server (NTRS)

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

McClain, Charles R.

2009-01-01

37

A decade of satellite ocean color observations.  

PubMed

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

McClain, Charles R

2009-01-01

38

Interannual and Decadal Variability of Summer Rainfall over South America  

NASA Technical Reports Server (NTRS)

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

Zhou, Jiayu; Lau, K.-M.

1999-01-01

39

Reconstructing the ocean subsurface decadal variability using surface nudging  

NASA Astrophysics Data System (ADS)

Initialising the ocean internal variability for decadal predictability studies is a new area of research and a variety of ad hoc methods are currently proposed. In this study, we explore how surface nudging can reconstruct the tri-dimensional variability of the ocean. We use a perfect model framework, as well a realistic set up with nudging towards observed anomalies. We illustrate that 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 2000 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-yr cycle of the model, the SST+SSS nudging is also able to reproduce most of the AMOC variations, a key source of decadal predictability. Reconstruction at depth does not significantly improve with amount of time spent nudging and the efficiency of the surface nudging rather depends on the period/events considered. Enhanced horizontal atmospheric resolution slightly improves performances in particular in the North Atlantic deep convection regions.

Mignot, Juliette; Ray, Sulagna; Servonnat, Jérôme; Swingedouw, Didier; Guilyardi, Eric

2014-05-01

40

An oceanic mechanism for decadal variability in the North Pacific  

NASA Astrophysics Data System (ADS)

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

Dawson, Andrew; Stevens, David; Matthews, Adrian

2013-04-01

41

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

Microsoft Academic Search

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

Dmitry Dukhovskoy; Mark Johnson; Andrey Proshutinsky

2006-01-01

42

Foraminiferal radiocarbon record of northeast Pacific decadal subsurface variability  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

43

Decadal Modulation of ENSO and Linkages to Pacific Decadal Variability: Analysis of a 1300-year CCSM4 Control Simulation  

NASA Astrophysics Data System (ADS)

Decadal modulation in the amplitude and other properties of El Nino-Southern Oscillation (ENSO) is analyzed in a 1300-year preindustrial control simulation of the Community Climate System Model version 4 (CCSM4). The CCSM4 displays notable improvements in simulating tropical Pacific mean climate and variability compared to its predecessor CCSM3. The amplitude of ENSO in CCSM4 exhibits pronounced decadal-interdecadal variability, in agreement with the analysis of observational data and paleoclimate proxy records. Decadal changes in the ENSO amplitude are closely linked to decadal changes in the background mean state, suggestive of their positive feedback. During the phase of strong ENSO, zonal gradients of sea surface temperature (SST) and thermocline weaken, the intertropical convergence zone is displaced southward, and the North Pacific subtropical high strengthens as part of the positive phase of the North Pacific Oscillation (NPO). These changes are associated with the second leading EOF mode of tropical Pacific decadal variability. The leading EOF mode, which resembles the so-called Pacific Decadal Oscillation, is not correlated with the ENSO amplitude but with the relative frequency of El Nino and La Nina. The two leading EOF modes of tropical Pacific decadal variability in CCSM4 are compared with those in a 500-year control simulation of the atmospheric component model coupled to a slab ocean model. It is suggested that the second mode in CCSM4 arises from a combination of stochastic NPO forcing and dynamical air-sea interactions in the equatorial Pacific. The first mode, on the other hand, appears to be linked to stochastic variability of the Pacific-South American pattern.

Okumura, Y.

2012-12-01

44

Observing Variable Stars  

NASA Astrophysics Data System (ADS)

Foreword; Opening thoughts; Acknowledgments; Part I. Getting To Know The Sky: 1. Beginning with the Big Dipper; 2. Magnitude, color, and distance; 3. A word on binoculars and telescopes; 4. Learning to see; Part II. Getting To Know The Variables: 5. Meeting the family; 6. Getting started with Cepheids; 7. Algol, the demon of autumn; 8. How to estimate a variable; 9. Names and records; 10. Observing hints; 11. Stately and wonderful; 12. Stars of challenge; 13. Bright, easy, and interesting; 14. Betelgeuse: easy and hard; 15. Not too regular; 16. Nova? What nova?; 17. Supernovae; 18. Three stars for all seasons; 19. A nova in reverse; 20. RU Lupi?; 21. Orion, the star factory; 22. Other variable things; 23. The Sun; Part III. Suggested Variables For Observation Throughout The Year: Introduction: January, February, March, April, May, June, July, August, September, October, November, December, Southern sky notes; Part IV. A Miscellany: 24. Stars and people; 25. The next generation; 26. Going further; Glossary and abbreviations; Index.

Levy, David H.; Mattei, Foreword by Janet A.

1998-04-01

45

Feedback strengths estimated from observations at seasonal and decadal timescales  

NASA Astrophysics Data System (ADS)

Quantifying the expected surface temperature response to radiative forcing, or climate sensitivity, from the observational record is complicated by the uncertain amount of ocean heat uptake, which delays equilibration. From a global mean perspective, rates of ocean heat uptake and surface warming multiplied by feedback strength are largely interchangeable when the system is transiently adjusting to increased radiative forcing. In our previous work, the spatial pattern of oceanic influence upon atmospheric temperature variability was assessed through a Lagrangian back trajectory analysis and applied to explain the phase and amplitude of the seasonal cycle, as well as patterns of temperature change. Here, we combine these previous results with an assumed uniform feedback strength in a simple, analytical model for local temperature variability for the observed seasonal cycle and recent inter-decadal temperature changes. The model predicts a pattern of temperature change between 1950 and 2012 that is significantly correlated with the observed change (r = 0.68, p-value < 0.01). The predictions capture more than simple land-sea contrast, also explaining a significant portion of the inter-decadal transient changes over only ocean (r = 0.36, p-value < 0.01) and only land (r = 0.44, p-value = 0.04). Significances are estimated using surrogate data generated via two-dimensional phase randomization. Importantly, the spatial component of the model permits for distinguishing between the influence of ocean heat uptake and the strength of the net feedback for both the seasonal cycle and inter-decadal temperature change. As expected, effective ocean heat capacity, which is indicative of the depth of the ocean interacting with the surface on each timescale in our simple formulation, is found to be smaller for the seasonal cycle than for longer timescales. More interestingly, the net feedback is found to be significantly more negative on seasonal timescales, suggesting stronger positive feedbacks at inter-decadal timescales. To better identify the physical mechanisms responsible for the timescale dependence in feedback strength, we apply the radiative kernel method to NCAR CCSM4 and explore the differences in atmospheric feedbacks for the seasonal cycle and inter-decadal forced changes.

McKinnon, K. A.; Huybers, P. J.; Bitz, C. M.

2013-12-01

46

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

NASA Astrophysics Data System (ADS)

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

Newman, M.

2013-12-01

47

Decadal Variability in the North Pacific: The Eastern North Pacific Mode  

Microsoft Academic Search

Decadal variability in the North Pacific is studied in a series of coupled global ocean-atmosphere simulations using coupled modeling surgery—a set of modeling approaches that can be used to identify the origins and causes of a specific variability mode in the coupled climate system. Both modeling and observational studies suggest two distinctive internal modes in the North Pacific: the North

LIXIN W UA; NDZHENGYU LIU

2003-01-01

48

Multi-decadal Variability of the Wind Power Output  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

49

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

50

Atmospheric Blocking and Atlantic Multi-Decadal Ocean Variability  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

51

Multi-decadal Variability of Indian Summer Monsoon in CMIP5 Models  

NASA Astrophysics Data System (ADS)

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.

Sandeep, S.; Ravindran, A.

2013-12-01

52

Decadal monitoring of variables by the AAVSO community  

NASA Astrophysics Data System (ADS)

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

Henden, Arne A.

2014-06-01

53

The Meridional Mode and Tropical Pacific Decadal Variability in the CMIP5 Models  

NASA Astrophysics Data System (ADS)

The Pacific Meridional Mode (MM), an intrinsic coupled ocean-atmosphere mode of variability in the tropical and subtropical Pacific Ocean, is tied to the precursor or excitation pattern of the El Niño-Southern Oscillation (ENSO). Like its Atlantic counterpart, however, the Pacific MM is likely also linked to interannual and decadal-scale variability of tropical Pacific sea surface temperatures (SSTs) and hence affects decadal-scale modulation of ENSO. Therefore, the representation of the Pacific MM in coupled climate models may impact the accuracy of simulated Pacific decadal climate variability and its associated global climate teleconnections. In this study, the fundamental dynamics of the Pacific MM are investigated in observations and the historical scenario of coupled climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Observations illustrate strong low-frequency (> 7 years) power in SSTs in the central tropical Pacific Ocean and in the subtropical North Pacific south of Hawaii, nearly co-located with the SST representation of the Pacific MM. Models that exhibit a clear signature of the Pacific MM and its relationship to ENSO are also characterized by more pronounced decadal variability in the tropical Pacific, reaffirming the hypothesis that the MM is an important mechanism driving low-frequency modulations of the tropical Pacific. Atmospheric variability associated with the Pacific MM is then studied. In the observations, the variance of the Pacific MM is dynamically tied to the North Pacific Oscillation (NPO), a dipole in sea level pressure in the North Pacific. This NPO teleconnection pattern, however, is not well reproduced in most CMIP5 models and thus leads to a decoupling between tropical and extratropical Pacific SST decadal variability in the models. Implications of these findings on future model evaluations and on the uncertainty in decadal climate forecasts are also discussed.

Furtado, J. C.; Di Lorenzo, E.

2012-12-01

54

Principal modes of interannual and decadal variability of summer rainfall over South America  

Microsoft Academic Search

Using the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) product together with the Goddard Earth Observing System (GEOS) reanalysis and the National Center for Environmental Prediction (NCEP) sea-surface temperature (SST) data, we have conducted a diagnostic study of the interannual and decadal scale variability of principal modes of summer rainfall over South America for the period 1979-1995. By

Jiayu Zhou; K.-M. Lau

2001-01-01

55

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

NASA Astrophysics Data System (ADS)

Observed North Atlantic Ocean surface temperatures have changed in a non-monotonic and non-uniform fashion over the last century. 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 (?_LF) of the externally forced -natural and anthropogenic- variance, ?_EF to the total variance, ?_T, of fluctuations with a period greater than 10 years. Stippling indicates regions where the null hypothesis H0: ?_LF = 0 cannot be rejected at the 5% level using an F-test.

Terray, L.

2012-12-01

56

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

NASA Astrophysics Data System (ADS)

Several recent observation-based studies suggest that ocean anthropogenic carbon uptake has slowed down due to the impact of anthropogenic forced climate change. However, it remains unclear if detected changes over the recent time period can really be attributed to anthropogenic climate change or to natural climate variability (internal plus naturally forced variability). One large uncertainty arises from the lack of knowledge on ocean carbon flux natural variability at the decadal time scales. To gain more insights into decadal time scales, we have examined the internal variability of ocean carbon fluxes in a 1000-yr long preindustrial simulation performed with the Earth System Model IPSL-CM5A-LR. Our analysis shows that ocean carbon fluxes exhibit low-frequency oscillations that emerge from their year-to-year variability in the North Atlantic, the North Pacific, and the Southern Ocean. In our model, a 20-yr mode of variability in the North Atlantic air-sea carbon flux is driven by sea surface temperature variability and accounts for ~40% of the interannual regional variance. The North Pacific and the Southern Ocean carbon fluxes are also characterized by decadal to multi-decadal modes of variability (10 to 50 yr) that account for 30-40% of the interannual regional variance. But these modes are driven by the vertical supply of dissolved inorganic carbon through the variability of Ekman-induced upwelling and deep-mixing events. Differences in drivers of regional modes of variability stem from the coupling between ocean dynamics variability and the ocean carbon distribution, which is set by large-scale secular ocean circulation.

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

2012-12-01

57

Icarus Revisted: Three Decades of Radar Observations of Asteroids  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

58

Decadal to bi-decadal rainfall variation in the western Pacific: A footprint of South Pacific decadal variability?  

NASA Astrophysics Data System (ADS)

Decadal to bi-decadal rainfall variation in the Western Pacific during July-October in the second half of the 20th century was identified in this study. This 10-20-year quasi-periodic oscillation was found associated with the leading sea surface temperature (SST) pattern in the South Pacific, which is called the 10-20-year South Pacific (inter) Decadal Oscillation (SPDO). It is suggested that the 10-20-year fluctuation of the SPDO resulted in significant decadal to bi-decadal rainfall variation along the western Pacific coast. The anomalous divergent circulations were likely driven by the SSTA (SST anomaly) and resulted in the anomalous rainfall in Eastern Australia and the Maritime Continent. It is conjectured that the SSTA in the Western South Pacific led to an anomalous Hadley-like circulation in the Western Pacific and indirectly affected the convection activity in the Philippine Sea, which in turn impacted the rainfall in the Philippines, Taiwan and Korea.

Hsu, Huang-Hsiung; Chen, Yun-Lan

2011-02-01

59

Decadal variability of wintertime North Atlantic and Pacific blockings: A possible cause  

Microsoft Academic Search

Decadal variability of the wintertime (DJFM) blocking occurring over the North Atlantic (NA) and North Pacific (NP) sectors is investigated by using the daily mean NCEP-NCAR reanalyses. It is found that the wintertime blocking activities over the NA and NP sectors exhibit a remarkable decadal variability, which is likely controlled by a decadal change in the basic-state (BS) baroclinicity associated

Dehai Luo; Han Wan

2005-01-01

60

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

Microsoft Academic Search

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

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

2002-01-01

61

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

62

Contribution of natural decadal variability to global warming acceleration and hiatus  

NASA Astrophysics Data System (ADS)

Reasons for the apparent pause in the rise of global-mean surface air temperature (SAT) after the turn of the century has been a mystery, undermining confidence in climate projections. Recent climate model simulations indicate this warming hiatus originated from eastern equatorial Pacific cooling associated with strengthening of trade winds. Using a climate model that overrides tropical wind stress anomalies with observations for 1958-2012, we show that decadal-mean anomalies of global SAT referenced to the period 1961-1990 are changed by 0.11, 0.13 and -0.11 °C in the 1980s, 1990s and 2000s, respectively, without variation in human-induced radiative forcing. They account for about 47%, 38% and 27% of the respective temperature change. The dominant wind stress variability consistent with this warming/cooling represents the deceleration/acceleration of the Pacific trade winds, which can be robustly reproduced by atmospheric model simulations forced by observed sea surface temperature excluding anthropogenic warming components. Results indicate that inherent decadal climate variability contributes considerably to the observed global-mean SAT time series, but that its influence on decadal-mean SAT has gradually decreased relative to the rising anthropogenic warming signal.

Watanabe, Masahiro; Shiogama, Hideo; Tatebe, Hiroaki; Hayashi, Michiya; Ishii, Masayoshi; Kimoto, Masahide

2014-10-01

63

Observations of solar irradiance variability  

Microsoft Academic Search

High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.001 percent. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near

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

1981-01-01

64

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

E-print Network

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

Wisconsin at Madison, University of

65

Nine decades of decreasing phenotypic variability in Atlantic cod  

E-print Network

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

Carlson, Stephanie

66

Interannual, decadal and multidecadal scale climatic variability and geomorphology  

Microsoft Academic Search

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

H. A. Viles; A. S. Goudie

2003-01-01

67

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

NASA Astrophysics Data System (ADS)

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.

Liu, Fenfen; Chen, Chuqun; Zhan, Haigang

2012-11-01

68

Decadal to seasonal variability of Arctic sea ice albedo  

E-print Network

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

Agarwal, S; Wettlaufer, J S

2011-01-01

69

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

70

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

71

A simple coupled model of tropical Atlantic decadal climate variability  

E-print Network

between evaporation and meridional heat advection in the mixed layer determines the sea surface exchange with the free atmosphere. When the model is integrated, forced with observed surface wind regions, with ``white-noise'' windspeed perturbations, the SST-wind relationship in the near

Columbia University

72

Role of ocean-atmosphere interaction in Atlantic Multi-decadal variability  

NASA Astrophysics Data System (ADS)

The mechanisms for Atlantic Multidecadal Variability (AMV) remain uncertain. In this presentation ocean, atmosphere, and coupled ocean-atmosphere models will be used to investigate one of the key uncertainties: ocean-atmosphere interaction. We first investigate the role of the ocean in setting the timescale. Ocean model experiments with historic and stochastically generated atmospheric forcing are performed; the NEMO ocean model with relatively high resolution (0.5 degree horizontal and 46 vertical levels) is used. Consistent with previous studies, our results show that ocean dynamics dominate decadal SST variations in the subpolar gyre, and decadal shifts in the North Atlantic Oscillation can explain most of the observed changes in this region. In addition, we find no evidence for an ocean-only oscillatory mode to explain AMV, rather a linear response of the ocean is found on multi-decadal and longer timescales and a weak response exists on shorter timescales. Second, we consider the role of active coupling in sustaining AMV. Recent studies suggest that resolving stratosphere troposphere interaction enhances the simulated response of the winter atmosphere to North Atlantic subpolar gyre SST. Here we extend on this work using to investigate the role of better resolving stratospheric processes in simulated AMV. Specifically, we compare twin coupled and uncoupled model experiments that only differ in their representation of the stratosphere. Consistent with our previous results, a warm North Atlantic causes a weakening of the polar vortex and in turn negative North Atlantic Oscillation. This mechanism is missing in the simulation that poorly resolves the stratosphere. How this alters simulated decadal variability, and implications for predictability are discussed.

Keenlyside, N. S.; Ba, J.; Mecking, J.; Omrani, N.; Shen, M.

2012-12-01

73

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

Microsoft Academic Search

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

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

2000-01-01

74

Decadal variability in coupled sea-ice-thermohaline circulation systems  

SciTech Connect

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

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

1997-12-01

75

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

NASA Astrophysics Data System (ADS)

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

Krishnamurthy, Lakshmi

76

Sea surface height: A versatile climate variable for investigations of decadal change  

Microsoft Academic Search

Decadal variations in climate are important, because the magnitude of sustained decadal change is often much larger than the often discussed background trends. Climate variability at interannual and longer periods is most often discussed in the context of climate modes defined by sea level pressure (SLP) and sea surface temperature (SST) patterns. However, SLP and SST are not capable descriptors

Philip Robert Thompson

2012-01-01

77

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

Microsoft Academic Search

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

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

2000-01-01

78

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

Microsoft Academic Search

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

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

2000-01-01

79

HERSCHEL OBSERVATIONS OF CATACLYSMIC VARIABLES  

SciTech Connect

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

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

2013-01-01

80

IUE observations of cataclysmic variable  

NASA Technical Reports Server (NTRS)

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

Szkody, Paula

1993-01-01

81

Seasonal to decadal variability of shallow tropical circulations and their role in poleward heat transport in the Atlantic Ocean  

NASA Astrophysics Data System (ADS)

In this oral presentation, we will present results of analyses of Atlantic Ocean observations assimilated in the Simple Ocean Data Assimilation (SODA) system for the 1950-2000 period. Specifically, we will address the following questions. bullet What are the dominant patterns of seasonal to decadal variability of Shallow Tropical Circulations (STCs) and poleward heat transport in the Atlantic Ocean? bullet How much mass and heat are transported by the STCs at seasonal to decadal timescales? bullet Are the STC and heat transport variabilities coherent among the Atlantic, Pacific, and Indian Oceans?

Mehta, V.; Fayos, C.; Schott, F.

2003-04-01

82

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

NASA Astrophysics Data System (ADS)

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.

Xiu, Peng; Chai, Fei

2014-08-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

84

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

E-print Network

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

85

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

Microsoft Academic Search

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

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

1999-01-01

86

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

NASA Technical Reports Server (NTRS)

The decadal, 12-14 year, cycle observed in the North Atlantic SST and tide gauge data was examined using the NCEP/NCAR reanalyses, COADS data and an ocean model simulation. Besides this decadal mode, a shorter, subdecadal period of about 8 years exists in tide gauge data north of 40N, in the subpolar SST and in the winter North Atlantic Oscillation (NAO) index and in subpolar winter heat flux values. The decadal cycle is a well separated mode in a singular spectrum analysis (SSA) for a time series of SST EOF mode 1 with a center over the Gulf Stream extension. Tide gauge and SST data are consistent in that both show a significant subdecadal periodicity exclusively in the subpolar gyre, but in subtropics the 12-14 year period is the prominent, but nonstationary, decadal signal. The main finding of this study is that this 12-14 year cycle can be constructed based on the leading mode of the surface heat flux. This connection to the surface heat flux implicates the participation of the thermohaline circulation in the decadal cycle. During the cycle starting from the positive index phase of NAO, SST and oceanic heat content anomalies are created in subtropics due to local heat flux and intensification of the thermohaline circulation. The anomalies advect to the subpolar gyre where they are amplified by local heat flux and are part of the negative feedback of thermohaline circulation on itself. Consequently the oceanic thermohaline circulation slows down and the opposite cycle starts. The oscillatory nature would not be possible without the active atmospheric participation in the cycle, because it provides the unstable interaction through heat flux, without it, the oceanic mode would be damped. This analysis suggests that the two principal modes of heat flux variability, corresponding to patterns similar to North Atlantic Oscillation (NAO) and Western Atlantic (WA), are part of the same decadal cycle and an indirect measure of the north-south movement of the storm tracks.

Hakkinen, Sirpa

1998-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

88

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

Microsoft Academic Search

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

Akihiko Ito

2011-01-01

89

Multi-decadal variability of the eastern North Atlantic subpolar gyre  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

90

Prioritizing Global Observations Along Essential Climate Variables  

NASA Astrophysics Data System (ADS)

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

Bojinski, Stephan; Richter, Carolin

2010-12-01

91

Beaufort Gyre freshwater reservoir: State and variability from observations  

Microsoft Academic Search

We investigate basin-scale mechanisms regulating anomalies in freshwater content (FWC) in the Beaufort Gyre (BG) of the Arctic Ocean using historical observations and data collected in 2003–2007. Specifically, the mean annual cycle and interannual and decadal FWC variability are explored. The major cause of the large FWC in the BG is the process of Ekman pumping (EP) due to the

Andrey Proshutinsky; Richard Krishfield; Mary-Louise Timmermans; John Toole; Eddy Carmack; Fiona McLaughlin; William J. Williams; Sarah Zimmermann; Motoyo Itoh; Koji Shimada

2009-01-01

92

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

NASA Astrophysics Data System (ADS)

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

Saatchi, S. S.; Asefi Najafabady, S.

2011-12-01

93

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

NASA Astrophysics Data System (ADS)

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

Saatchi, S.; Asefi, S.

2012-04-01

94

The Contribution of the Interannual ENSO Cycle to the Spatial Pattern of Decadal ENSO-Like Variability  

Microsoft Academic Search

A defining feature of Pacific decadal ENSO-like variability is the similarity between its spatial expression in sea surface temperature (SST) and the spatial structure of interannual ENSO variability. This similarity may indicate that the decadal variability is merely a long-term average over interannual ENSO variability. In contrast, subtle differences (namely the meridionally broadened tropical SST signature and emphasized midlatitude SST

Daniel J. Vimont

2005-01-01

95

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

SciTech Connect

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

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

1995-02-01

96

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

Microsoft Academic Search

Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th

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

2008-01-01

97

Multi-decadal thermohaline variability in an ocean–atmosphere general circulation model  

Microsoft Academic Search

A century scale integration of a near-global atmosphere–ocean model is used to study the multi-decadal variability of the thermohaline circulation (THC) in the Atlantic. The differences between the coupled and two supplementary ocean-only experiments suggest that a significant component of this variability is controlled by either a collective behavior of the ocean and the atmosphere, particularly in the form of

W. Cheng; R. Bleck; C. Rooth

2004-01-01

98

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

Microsoft Academic Search

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

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

1999-01-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

100

Southern Hemisphere PDO?: Interhemispheric symmetry suggests tropical forcing of Pacific decadal variability  

Microsoft Academic Search

There is considerable debate in the community over whether the Pacific Decadal Oscillation (PDO) is an independent mode of variability centered in the North Pacific or simply a reddened response to El Niño- Southern Oscillation (ENSO) forcing from the tropical Pacific. The PDO is defined as the leading Empirical Orthogonal Function of detrended monthly sea surface temperature (SST) anomalies in

J. D. Shakun; J. Shaman

2008-01-01

101

Connection between the decadal variability in the Southern Ocean circulation and the Southern Annular Mode  

E-print Network

of Antarctic Intermediate Water (AAIW). As AAIW is the upper branch of global thermohaline circulation, changesConnection between the decadal variability in the Southern Ocean circulation and the Southern with anthropogenic forcing. An oceanic reanalysis data set is used to investigate the response of the circulation

102

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

E-print Network

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

103

Importance of Clouds to the Decaying Trend and Decadal Variability in the Arctic Ice Cover  

Microsoft Academic Search

The areal extent of the sea ice cover in the Arctic. Ocean has declined in. the last 40 years with increased decadal variability. The trend is clearly influenced by the radiation balance over. all seasons. A cloudiness increase in the fall, winter and spring contributes to a reduction in the absolute amount of net longwave radiation at the sea surface.

M IKEDA; J WANG; A MAKSHTAS

2003-01-01

104

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

NASA Astrophysics Data System (ADS)

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

Williams, P.

2010-12-01

105

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

107

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

108

Decadal North Pacific sea surface temperature variability and the associated global climate anomalies in a coupled general circulation model  

Microsoft Academic Search

We explore the characteristics of decadal North Pacific sea surface temperature (SST) variability along with its relationship to global climate variations based on the analysis of a long-term coupled model simulation (300 years). Two key regions of North Pacific decadal variability, i.e., the western North Pacific (WNP) and central North Pacific (CNP) SST variability, are defined. While the global atmospheric

Sang-Wook Yeh; Ben P. Kirtman

2004-01-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2003-01-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

111

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

Microsoft Academic Search

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

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

2011-01-01

112

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

E-print Network

mean SST in the SOM run and (b) the RMSE for predicted global mean SST for each year. The first blue line beneath the observed SST (black line) is the 1st year prediction of annual global mean SST. It shows a warming of 0.1C between the first decade... mean SST in the SOM run and (b) the RMSE for predicted global mean SST for each year. The first blue line beneath the observed SST (black line) is the 1st year prediction of annual global mean SST. It shows a warming of 0.1C between the first decade...

Zhu, Xiaojie

2013-05-17

113

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

USGS Publications Warehouse

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

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

2008-01-01

114

Observations of Suspected RR Lyrae Variable Stars  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

115

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

Microsoft Academic Search

Satellite Observations to Benefit Science and Society: Recommended Missions for the Next Decade brings the next ten years into focus for the Earth and environmental science community with a prioritized agenda of space programs, missions, and supporting activities that will best serve scientists in the next decade. These missions will address a broad range of societal needs, such as more

2008-01-01

116

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

118

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

NASA Astrophysics Data System (ADS)

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

Han, Leqiong; Li, Shuanglin; Liu, Na

2014-03-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

120

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

Microsoft Academic Search

Variability and predictability of European summer drought conditions during observational period is investigated. The dominat patterns of European drought and their associated large-scale climatic anomalies are identified through canonical correlation analysis (CCA) of the field of self calibrating Palmer Drought Severity Index (PDSI) and global sea surface temperature (SST) anomalies. At interannual time scales we identified patterns of drought variability

Monica Ionita; Gerrit Lohmann; Norel Rimbu; Silvia Chelcea

2010-01-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

122

Holocene Decadal to Multidecadal Hydrologic Variability in the Everglades: Climate and Implications for Ecosystem Management  

NASA Astrophysics Data System (ADS)

The Florida Everglades are a complex, unique ecosystem. Adding to the complexity, a system of canals and gates control the flow of waters from central Florida southward into the Everglades, and ultimately Florida Bay and the Gulf of Mexico. With south Florida’s distinct wet and dry seasons, the hydrology has driven ecosystem evolution over the last 4-5 kya. However, since the 1920s the water content of the Everglades has largely been anthropogenically modulated, with the exception of the natural variability of evaporation and precipitation over the large area south of the Tamiami Trail. Because of the incredibly flat nature of the Everglades, small changes in the freshwater balance have substantial impacts on the diversity and distribution of organisms. Decadal and multidecadal variability in precipitation, hurricane incidence, and sea level rise all have important effects on the ecosystem. During the instrumental record, the natural precipitation across south Florida has been strongly influenced by combinations of the Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation, and ENSO. Here we discuss evidence of natural climate variability impacts on the ecosystem beyond the anthropogenic hydrological controls. Proxy environmental data from seeds, charcoal, and trees, plus the sparse, but available, instrumental records provide evidence of changes in the ecosystem over the Holocene, and suggest considerations for future management.

Moses, C. S.; Anderson, W. T.; Saunders, C.; Rebenack, C.

2009-12-01

123

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

Microsoft Academic Search

The southwest tropical Pacific is a region with temporally and spatially sparse sea surface temperature (SST) records that limit investigations of climate variability on interannual to centennial time scales for this region. We present a monthly resolved coral Sr\\/Ca record from 1648 to 1999 from Amédée Island, New Caledonia (22.48°S, 166.47°E), and reconstruct SST variability in the southwest Pacific for

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

2008-01-01

124

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

PubMed

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

Laepple, Thomas; Huybers, Peter

2014-11-25

125

Observing variable stars. A guide for beginners  

NASA Astrophysics Data System (ADS)

David Levy's entertaining, well-researched book is aimed at the amateur enthusiast who likes to learn enjoyably. Beginning with advice on binoculars and telescopes, and how to observe the night sky effectively, the author goes on to describe thoroughly the field of variable star observation, a field in which amateurs have made important contributions. He shows how to interpret variations in light output in terms of the life of a star, from birth through to sometimes violent death. All of the major variable stars are described and classified, as well as other variable objects such as active galaxies, asteroids, comets and the sun. The book also contains a guide to the seasonal night sky. Throughout, practical observations serve to complement the text, producing an exciting, very readable introduction to this fascinating subject.

Levy, David H.

126

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

NASA Astrophysics Data System (ADS)

Interannual to decadal variability of European summer drought and its relationship with global sea surface temperature (SST) is investigated using the newly developed self calibrated Palmer drought severity index (scPDSI) and global sea surface temperature (SST) field for the period 1901-2002. A European drought severity index defined as the average of scPDSI over entire Europe shows quasiperiodic variations in the 2.5-5 year band as well as at 12-13 years suggesting a possible potential predictability of averaged drought conditions over Europe. A Canonical Correlation Analysis between summer scPDSI anomalies over Europe and global SST anomalies reveals the existence of three modes of coupled summer drought scPDSI patterns and winter global SST anomalies. The first scPDSI-SST coupled mode represents the long-term trends in the data which manifest in SST as warming over all oceans. The associated long-term trend in scPDSI suggests increasing drought conditions over the central part of Europe. The second mode is related to the inter-annual ENSO and decadal PDO influence on the European climate and the third one captures mainly the drought pattern associated to Atlantic Multidecadal Oscillation. The lag relationships between winter SST and summer drought conditions established in this study can provide a valuable skill for the prediction of drought conditions over Europe on interannual to decadal time scales.

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

2012-01-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

129

Assigning environmental variables to observed biological changes.  

PubMed

A method for assigning environmental variables to observed biological changes in benthic communities is proposed. The approach requires biological and environmental sampling at the same sites. Additionally, a biological gradient or trend such as a change in observed species or a significant change in their relative abundances is necessary in order to connect the biological observations to the environmental measurements. Whether there is a statistical significant correspondence between the environmental measurements and the biological changes is tested after quantifying the biological changes by using the community disturbance index (CDI). Finally, the environmental variables that are most strongly associated with the biological changes are identified, and it is proposed that these are strong candidates as the pollutants responsible for the biological changes observed. However, this cannot be confirmed using the monitored data only. The approach is tested on data collected in monitoring surveys at the Ekofisk oil field in the North Sea. The results indicate the method is feasible for assigning environmental variables to observed biological changes. PMID:15340770

Flåten, Geir Rune; Botnen, Helge; Grung, Bjørn; Kvalheim, Olav M

2004-10-01

130

A Continental Shelf Sediment Transport Proxy Record of Decadal Atmospheric and Oceanographic Variability in Southern Alaska  

NASA Astrophysics Data System (ADS)

The Gulf of Alaska (GOA) margin is a prime location to study and quantitatively model glacial climate and continental margin sedimentation. Coupled oceanographic and atmospheric processes control sediment transport and sedimentation patterns on the GOA continental shelf, and consequently contain a proxy record for regional climate variability. However, the specifics of this coupled relationship between climate and sediment transport have not been studied. In collaboration with the GOA-NEP GLOBEC program, gravity cores were taken at three sites of high sedimentation rates along the GOA margin in 2001 and 2003 representing proximal and distal shelf depocenters. Chronologies were established using Pb-210 and Cs-137 and sedimentation rates vary from 0.3 to 3 cm/yr, providing near-annual to decadal-scale resolution. High-spatial resolution grain-size analyses and multi-sensor core logging of bulk density and magnetic susceptibility were measured to recognize relationships between these three proxies of sediment transport in each core and between sites. The time series of these properties have been compared to oceanographic and atmospheric instrumental records--generally beginning in the early to middle 20th century--such as sea level pressure, temperature, significant wave height, and wind speed. The three measured properties positively correlate within each core and between each core, indicating that these are likely controlled by similar sediment transport processes, such as wave resuspension and bottom-current transport, at all three sites. Strong correlation on a decadal scale was found between the physical properties of the cores and the instrumental records of temperature and significant wave height, as well as variability in regional precipitation. Also, there is a marked increase in bulk density, magnetic susceptibility, and grain size values from the late 1970's onward, which corresponds to the timing of a shift from a negative to a positive regime in the Pacific Decadal Oscillation. These results suggest that temporal variability in grain size, bulk density, and magnetic susceptibility on Alaska's continental shelf are, in part, controlled by changes in wind speed, wind direction, and wave height.

Vienne, W. F.; Jaeger, J.

2004-12-01

131

Northern Cascadia episodic tremor and slip: A decade of tremor observations from 1997 to 2007  

Microsoft Academic Search

We analyze continuous seismic and GPS records collected in the last decade (1997–2007) to establish the most comprehensive observational basis for northern Cascadia episodic tremor and slip (ETS) events. A simple “ETS scale” system, using a combination of a letter and a digit, is proposed to quantitatively characterize the spatial and temporal dimensions of ETS events. Clear correlation between GPS

Honn Kao; Shao-Ju Shan; Herb Dragert; Garry Rogers

2009-01-01

132

Information from low-density expendable bathythermograph transects: North Atlantic mean temperature structure and quasi-decadal variability  

NASA Astrophysics Data System (ADS)

The 1999 Ocean Observing System conference recommended that the Low density (LD) expendable bathythermograph (XBT) network be discontinued contingent on the completion of studies showing that the global Argo network and/or satellite altimetry can provide equivalent information. Herein, information content in North Atlantic LD lines relative to quasi-decadal variability in upper layer temperature structure is addressed as the first step in achieving this recommendation. Two LD lines are located in the subpolar gyre and support results from previous studies of shorter length that ocean advection and not only air-sea fluxes plays an important role, particularly in the eastern gyre, in determining the characteristics of the water masses transported to the source regions of North Atlantic Deep Water. Several sections cross the Gulf Stream and Labrador Current. They provide evidence to support the hypothesis that changes in the intensity of Labrador Current properties cause meridional motions of the Gulf Stream. Decadal variability in the subtropical gyre of the North Atlantic has been attributed to westward propagation of temperature anomalies by the mean currents and planetary waves. Modeling studies suggest that these signals are dominant in the thermocline at the northern latitudes (order 30°) of the subtropical gyre. Similar calculations from a line crossing the subtropical gyre at these same latitudes shows no indication of westward propagation. Quasi-decadal signals in upper layer temperature are coincident across the entire gyre with some suggestion of eastward motion of temperature anomalies. One line on the southern boundary of the subtropical gyre does include westward signal movement from the eastern boundary. Based on the information content of individual lines, recommendations are made relative to the continuation of specific transects until it has been demonstrated that Argo and satellite altimetry can provide equivalent results.

Molinari, Robert L.

2011-01-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

134

Simulated and observed variability in ocean temperature and heat content  

PubMed Central

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

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

2007-01-01

135

Moisture budget analysis of SST-driven decadal Sahel precipitation variability in the twentieth century  

NASA Astrophysics Data System (ADS)

It is well known that the Sahel region of Africa is impacted by decadal scale variability in precipitation, driven by global sea surface temperatures. This work demonstrates that the National Center for Atmospheric Research's Community Atmosphere Model, version 4 is capable of reproducing relationships between Sahelian precipitation variability and Indian and Atlantic Ocean sea surface temperature variations on such timescales. Further analysis then constructs a moisture budget breakdown using model output and shows that the change in precipitation minus evaporation in the region is dominated by column integrated moisture convergence due to the mean flow, with the convergence of mass in the atmospheric column mainly responsible. It is concluded that the oceanic forcing of atmospheric mass convergence and divergence to a first order explains the moisture balance patterns in the region. In particular, the anomalous circulation patterns, including net moisture divergence by the mean and transient flows combined with negative moisture advection, together explain the drying of the Sahel during the second half of the twentieth century. Diagnosis of moisture budget and circulation components within the main rainbelt and along the monsoon margins show that changes to the mass convergence are related to the magnitude of precipitation that falls in the region, while the advection of dry air is associated with the maximum latitudinal extent of precipitation.

Pomposi, Catherine; Kushnir, Yochanan; Giannini, Alessandra

2014-11-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

137

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

NASA Astrophysics Data System (ADS)

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

Swetnam, Thomas W.; Betancourt, Julio L.

1998-12-01

138

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

NASA Astrophysics Data System (ADS)

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

Committee On Earth Science; Applications From Space

139

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

140

Have Aerosols Caused the Observed Atlantic Multidecadal Variability?  

E-print Network

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

Zhang, Rong

141

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

142

Morbidity and mortality in common variable immune deficiency over 4 decades.  

PubMed

The demographics, immunologic parameters, medical complications, and mortality statistics from 473 subjects with common variable immune deficiency followed over 4 decades in New York were analyzed. Median immunoglobulin levels were IgG, 246 mg/dL; IgA, 8 mg/dL; and IgM, 21 mg/dL; 22.6% had an IgG less than 100 mg/dL. Males were diagnosed earlier (median age, 30 years) than females (median age, 33.5 years; P = .004). Ninety-four percent of patients had a history of infections; 68% also had noninfectious complications: hematologic or organ-specific autoimmunity, 28.6%; chronic lung disease, 28.5%; bronchiectasis, 11.2%; gastrointestinal inflammatory disease, 15.4%; malabsorption, 5.9%; granulomatous disease, 9.7%; liver diseases and hepatitis, 9.1%; lymphoma, 8.2%; or other cancers, 7.0%. Females had higher baseline serum IgM (P = .009) and were more likely to develop lymphoma (P = .04); 19.6% of patients died, a significantly shorter survival than age- and sex-matched population controls (P < .0001). Reduced survival was associated with age at diagnosis, lower baseline IgG, higher IgM, and fewer peripheral B cells. The risk of death was 11 times higher for patients with noninfectious complications (hazard ratio = 10.95; P < .0001). Mortality was associated with lymphoma, any form of hepatitis, functional or structural lung impairment, and gastrointestinal disease with or without malabsorption, but not with bronchiectasis, autoimmunity, other cancers, granulomatous disease, or previous splenectomy. PMID:22180439

Resnick, Elena S; Moshier, Erin L; Godbold, James H; Cunningham-Rundles, Charlotte

2012-02-16

143

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

144

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)

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

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

2008-06-01

145

Observing Variable Stars, Novae and Supernovae  

NASA Astrophysics Data System (ADS)

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

North, Gerald; James, Nick

2014-08-01

146

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

Microsoft Academic Search

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

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

1998-01-01

147

Decadal-Scale Tropical North Atlantic Climate Variability Recorded in Slow Growing Cape Verde Corals  

NASA Astrophysics Data System (ADS)

The decadal to century scale climate variability of the tropical North Atlantic has major implications for both neighboring coastal and inland areas. Changes in patterns of sea surface temperature (SST) and SST anomalies (SSTA) in the tropical North Atlantic are known to affect rainfall in Florida, South America, and sub-Saharan Africa, as well as the number of major hurricanes formed in the Atlantic. Because of the significance of these connections, it is important to further increase our predictive capacity for the recognition of trends and cycles in tropical North Atlantic SST and SSTA. Located at 15° N latitude off the west coast of sub-Saharan Africa, the Cape Verde Islands are an ideal geographic location to search for records of the Tropical North Atlantic Index (TNA). Such patterns are present in proxy indicators of climate (O, C, Sr/Ca and Mg/Ca) recorded in the skeletons of slow growing corals, such as Siderastrea radians, found in Cape Verde (growth rate = 1-2 mm/yr). These corals represent an archive for SST and SSTA records that exceed the instrumental period of the eastern tropical North Atlantic. We cored corals from several different locations within the Cape Verde archipelago and analyzed them for stable isotopes (?13C and ?18O) and minor elements (Sr, Mg, and Ba). The ?18O signal present in these corals shows a distinct relationship to the TNA over the better part of the last 100 years. In addition, the ?18O record in several of these corals also records the onset of the latest Sahel (11°-18° N in Africa) drought which began in 1970. The Sr/Ca and Mg/Ca records of these corals indicate a slight warming of the waters around Cape Verde during the last 100 years, as well as accurately recording the El Niño events of 1982-83 and 1997-98. The correlations present between the records in these corals and the known instrumental record for the eastern tropical North Atlantic suggests that the fluctuations recorded in the proxy indicators may be accurately used as a tool to study both the intensity and duration of SST and SSTA cycles as far back as the 1880's.

Moses, C. S.; Swart, P. K.; Dodge, R. E.; Helmle, K. P.; Thorrold, S.

2002-12-01

148

Patients with cardiac disease: Changes observed through last decade in out-patient clinics  

PubMed Central

AIM: To describe current profile of patients with cardiovascular disease (CVD) and assessing changes through last decade. METHODS: Comparison of patients with established CVD from two similar cross-sectional registries performed in 1999 (n = 6194) and 2009 (n = 4639). The types of CVD were coronary heart disease (CHD), heart failure (HF) and atrial fibrillation (AF). Patients were collected from outpatient clinics. Investigators were 80% cardiologist and 20% primary care practitioners. Clinical antecedents, major diagnosis, blood test results and medical treatments were collected from all patients. RESULTS: An increase in all risk factors, except for smoking, was observed; a 54.4% relative increase in BP control was noted. CHD was the most prevalent CVD but HF and AF increased significantly, 41.5% and 33.7%, respectively. A significant reduction in serum lipid levels was observed. The use of statins increased by 141.1% as did all cardiovascular treatments. Moreover, the use of angiotensin-renin system inhibitors in patients with HF, beta-blockers in CHD patients or oral anticoagulants in AF patients increased by 83.0%, 80.3% and 156.0%, respectively (P < 0.01). CONCLUSION: The prevalence of all cardiovascular risk factors has increased in patients with CVD through last decade. HF and AF have experienced the largest increases. PMID:24009818

Cordero, Alberto; Bertomeu-Martinez, Vicente; Mazon, Pilar; Facila, Lorenzo; Cosin, Juan; Bertomeu-Gonzalez, Vicente; Rodriguez, Moises; Andres, Eva; Galve, Enrique; Lekuona, Inaki; Gonzalez-Juanatey, Jose R

2013-01-01

149

An Overview of the Impacts of Pacific Decadal Climate Variability on Marine Ecosystems  

NASA Astrophysics Data System (ADS)

Over the past few decades a wealth of evidence has pointed to strong associations between multi-decadal climate changes and marine ecosystem changes in the Pacific. The period from the late 1970's through the mid-1990's, for example, saw sustained high productivity for most Pacific salmon at the northern end of their range coinciding with sustained low productivity for Pacific salmon at the southern end of their range. It is now recognized that this "north-south inverse production pattern" for Pacific salmon played out over much of the 20th Century in response to Pacific Decadal climate variations. There is abundant direct and indirect evidence for decadal scale climate impacts on many other Pacific marine species, including (among others) sardines and anchovies in the Humboldt and California Currents, and pollock and crab in the Bering Sea. In special cases, interdecadal ecosystem changes have been termed "ecosystem regime shifts", wherein evidence points to large-scale ecosystem restructuring at both lower and upper trophic levels. Understanding the mechanisms linking decadal variations in climate to ecosystems has proven to be a major challenge, and the lack of understanding poses a serious barrier to predicting ecosystem changes at the time-space scales important to resource managers and the fishing industry.

Mantua, N.

2006-12-01

150

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

151

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

NASA Astrophysics Data System (ADS)

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

Lemeshko, Natalia; Eitzinger, Josef; Kubu, Gerhard

2013-04-01

152

Decadal Challenges in Ground-Based Observations for Solar and Space Physics (Invited)  

NASA Astrophysics Data System (ADS)

Ground-based observations of the sun and near-Earth space have long provided the fundamental information needed to achieve a better understanding of the coupled Sun-Earth system and the processes responsible for solar activity and its effects on Earth's magnetosphere, ionosphere, and atmosphere. Observations based on both active and passive radio wave and optical techniques provide measurements throughout Earth's atmosphere, geospace, the heliosphere, and the Sun. Although the number of observing instruments, the capabilities of the instruments, and the variety of ground-based assets continue to open new frontiers and enable scientific discoveries, gaps still exist, not only in terms of the spatial coverage of the measurements, but also in the properties of the system that are observed and the cadence and frequency of the observations. Fortunately, new technologies have provided the tools by which these challenges can be overcome. This is an opportune time to develop an integrated strategy for development, deployment, operation, and data analysis of ground-based assets. These include, for example, advanced networking technologies, crowd-sourced data acquisition, and multi-use observational platforms. Ground-based observations can also be optimized through the development of smart sensors, that operate at low power and are easily deployable, reconfigurable, and remotely operable. Furthermore, the data from ground-based observations will be collected, archived, and disseminated in ways that will enable effective and productive data mining, image and pattern recognition, cross-correlation among diverse data sets, and broadly-based collaborative research. These capabilities are especially important as we attempt to understand the system aspects of the solar-terrestrial environment. The next decade will undoubtedly see new understanding and discoveries resulting from improved and expanded ground-based instruments, as well as in their strategic deployment and operation.

Robinson, R. M.

2013-12-01

153

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

NASA Astrophysics Data System (ADS)

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

Elguindi, N.; Giorgi, F.

2006-02-01

154

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

NASA Astrophysics Data System (ADS)

This presentation investigates causes for the formation and the variability of the Sea Surface Salinity (SSS) maximum of the South Pacific Ocean over the 1990-2011 period at the seasonal timescale and above. We use a monthly 1ºx1º gridded product of SSS based on in-situ measurements, high-resolution along-track Voluntary Observing Ships thermosalinograph data, SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a zonal seasonal cycle of the location of the high (above 36 pss) SSS core barycentre of about 400 km in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show an interannual westward shift of the barycentre of 1400 km. The possible origins of this shift, that could not be linked to the El Nino Southern Oscillation phenomena, are discussed. In the model, the processes maintaining the 22-year equilibrium of the high salinity in the mixed layer are the surface forcing (~+7 pss/yr), the horizontal salinity advection (~-3.5 pss/yr) and processes occurring at the mixed layer base (~-3.5 pss/yr).

Hasson, Audrey; Delcroix, Thierry; Boutin, Jacqueline

2014-05-01

155

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

NASA Technical Reports Server (NTRS)

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

Sandford, Stephen P.

2010-01-01

156

Pacific decadal oscillation and variability of the Indian summer monsoon rainfall  

Microsoft Academic Search

Recent studies have furnished evidence for interdecadal variability in the tropical Pacific Ocean. The importance of this phenomenon in causing persistent anomalies over different regions of the globe has drawn considerable attention in view of its relevance in climate assessment. Here, we examine multi-source climate records in order to identify possible signatures of this longer time scale variability on the

R. Krishnan; M. Sugi

2003-01-01

157

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

NASA Astrophysics Data System (ADS)

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

Pistotnik, Georg; Groenemeijer, Pieter

2014-05-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

159

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

160

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

SciTech Connect

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

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

1994-08-01

161

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

NASA Astrophysics Data System (ADS)

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

Hayashi, Masaki; Farrow, Christopher R.

2014-08-01

162

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

NASA Astrophysics Data System (ADS)

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

Bruhwiler, L. M.; Matthews, E.

2007-12-01

163

Decadal Trends and Variability in Special Sensor Microwave / Imager (SSM/I) Brightness Temperatures and Earth Incidence Angle  

NASA Astrophysics Data System (ADS)

The Goddard Satellite-based Surface Turbulent Fluxes (GSSTF) dataset is a valuable tool for monitoring air-sea fluxes over the global ocean. The most recently released version of GSSTF, Version 2b, uses Remote Sensing Systems (RSS) Version-6 Special Sensor Microwave / Imager (SSM/I) brightness temperature (TB) dataset in its production. Analysis of long-term trends from 1987 to 2008 in GSSTF showed a surprising result: while column-integrated water vapor has a small positive trend (less than 1%/decade), the lowest 500-m water vapor (WB) has a large negative trend (-3.4%/decade). Through collaboration between our two groups, we determined that the trends in WB are due to trends in the earth incidence angle (EIA) of SSM/I TB measurements. The effect of these EIA trends must be removed from TB to get accurate trends in WB. This presentation characterizes EIA trends and variability in the SSM/I dataset, and explains their effect on TB. The entire dataset is analyzed, including all six sensors operating from 1987-2009. The methodology used to calculate EIA is explained, which provides insight into the sources of EIA variability. The main source of variability is the change in altitude over an orbit, however this is modulated by the precession of perigee that varies with a four month period. The physical relationship between EIA and TB is explained with RSS radiative transfer model. The relationship is not constant, but depends on the meteorological conditions in the satellite footprint, which is the key difficulty in removing EIA effects. Since the SSM/I satellites are gradually falling over time, EIA has a trend of -0.14°/decade. This produces a -0.3 K/decade trend in vertical polarization TB. RSS has always handled EIA variations using its retrieval algorithms that are parameterized in terms of EIA. In order to use legacy algorithms that do not include EIA dependence (e.g., Schulz WB retrieval algorithm), an algorithm to normalize TB to a nominal EIA is derived and its accuracy is characterized. The algorithm performs very well in all meteorological conditions, and provides highly accurate decadal trends. The performance of the algorithm is assessed for WB retrievals. These retrievals are used by GSSTF in the calculation of latent heat flux. Before normalization, WB has a trend of -3.4%/decade, and the algorithm reduces this trend to -0.9%/decade.

Hilburn, K. A.; Shie, C.

2011-12-01

164

Multiwavelength observations of eleven cataclysmic variables  

SciTech Connect

A study of 11 cataclysmic variables in the UV, optical and IR ranges has indicated that the alpha index of the UV flux distribution for five systems at quiescence is relatively flat and constrained, implying a narrow range in mass transfer rate. This may be correlated with the mechanism for mass transfer in short orbital period systems. Near maximum light, the alpha index is steep and consistent with steady state models. 42 references.

Szkody, P.

1985-09-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

166

[Intestinal infarct: a critical review of the cases observed in the decade of 1981-1991].  

PubMed

The authors consider the causes of bowel infarction and report the up-to-date diagnostic tools for optional treatment. They verify management and outcome of 97 cases treated during the last decade. PMID:8286184

Diviacco, P; Muià, R; Danovaro, L; Pasero, E; Boaretto, R; Pianezza, M; Berardi, L; Mereto, E; Casaccia, M; Lombardi, A

1993-09-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

168

Observations of Variables used in the Higgs Machine Learning Challenge  

E-print Network

In this project observations were made to the the variables needed for the Higgs Machine Learning challenge. Usually, a Machine Learning algorithm is used to learn a set of data. What the project did is to observe the behavior of different variables and use some judgment (or Human Learning) before a Machine algorithm was used to learn from the data.

Alvarez, Justin

2014-01-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

170

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

NASA Astrophysics Data System (ADS)

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

Qu, X.; Huang, G.

2014-08-01

171

Tradition and Change in the Social Studies: Some Observations on a Decade of Reform.  

ERIC Educational Resources Information Center

Trends in social studies education in the 1960's which appeared significant and which may well affect the developments of the next decade include: (1) curriculum evangelism--the zealous, uncritical pursuit of fashionable educational ideas--and the institutionalization of innovative changes, (2) restraints on intellectual freedom by the radical…

Lunstrum, John P.

172

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

173

Three Decades of Field Experiments Show Minimal Variability in Maximum Preferential Flow Speed  

NASA Astrophysics Data System (ADS)

Evaluation of about 50 published field tests shows that the maximum transport speed in macropores and other preferential channels varies surprisingly little. The tests differ substantially: in type of medium, including fractured rock and various soil textures; in travel distance, ranging from less than 1 to more than 1000 m; in type of tracer; and in vertical or horizontal flow direction. One factor that significantly affects transport speed is the supply of water that generates the flow. Continuous application of water at the land surface, such as ponding or steady irrigation, as opposed to a sporadic supply such as natural rainfall, causes preferential flow that is faster and that varies less among studies. For continuously supplied water, nearly all observations of maximum transport speed fall between 1 and 100 m/d, suggesting that a value in that range could serve as a guideline for expected transport speed under comparable conditions. For sporadically applied water, if transport speeds are adjusted by a factor equal to the fraction of time during which water is applied, the adjusted values also fall in a range of about 1 to 100 m/d. Results suggest that in some common modes of preferential flow, certain mechanisms tend to compensate for factors that would normally cause substantial differences in flow rate. For example, an increase in water content within an unsaturated fracture may not affect the speed of solute transport in thick films if the greater water content is accommodated not by changing film thickness but by covering a larger portion of fracture-wall surface. The generalization that certain transport speeds are predictable to a large extent from water input conditions may improve the reliability and ease of predicting worst-case contaminant travel times and other quantities of hydrologic importance.

Nimmo, J. R.

2005-12-01

174

(abstract) Mount Rainier: New Remote Sensing Observations of a Decade Volcano  

NASA Technical Reports Server (NTRS)

Mount Rainier was selected as a Decade Volcano by the International Association of Volcanology and Chemistry of the Earth's Interior. The purpose of this selection is to focus scientific and public attention on Mount Rainier during the current decade, the United Nations-designated International Decade of Natural Hazard Reduction. The Mount Rainier science plan calls for remote sensing surveys to monitor the volcano. To date, we have conducted airborne surveys with visible and near-infrared, thermal infrared, and interferometric radar instruments. Our preliminary analysis of some night-time time-series thermal infrared survey data sets of the summit suggests that, aside from seasonal variations in snow cover, there have been no qualitative changes in the size or pattern of the summit hot spots. Day-time airborne surveys were done to record the current surface appearance of the volcano and map hydrothermal alteration in the summit region. An interferometric radar survey yielded a high-resolution digital elevation model (DEM) which serves as a base for the registration of the other remote sensing data sets. More importantly, the DEM documents the current topography of glaciers and valleys. Planned biannual radar survey of mount rainier will produce a data set from which seasonal changes in glacier and valley topography can be characterized. Such characterization is essential if we are to recognize geothermally induced changes in snow and ice cover.

Realmuto, V. J.; Zebker, H. A.; Frank, D.

1994-01-01

175

Long-term trends and decadal variability of upper mesosphere/lower thermosphere gravity waves at midlatitudes  

NASA Astrophysics Data System (ADS)

Mesosphere/lower thermosphere (MLT) winds over Germany as measured with a low-frequency spaced receiver system at Collm 1984-2007 have been analysed with respect to variations at the time scales of gravity waves. Background winds are also registered to analyse possible gravity wave-mean flow interactions at decadal and interdecadal time scales. In both winter and summer an increasing mesospheric zonal wind jet with time is registered, which is accompanied with increasing gravity wave variances. At greater altitudes in summer, the mean wind jet trend reverses, and negative trends of gravity wave variances are found. This connection between gravity waves and mean wind is also observed on a quasi-decadal scale: during solar maximum stronger mesospheric zonal wind jets as well as larger gravity wave amplitudes are observed. This results in a solar cycle modulation of gravity waves with larger amplitudes during solar maximum. The observed positive correlation between gravity wave amplitudes and the mean zonal wind may follow the theory of saturated waves in the atmosphere, such that stronger mesospheric zonal winds are connected with larger gravity wave amplitudes.

Jacobi, Christoph

2014-10-01

176

Einstein x-ray observations of cataclysmic variables  

SciTech Connect

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

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

1982-01-01

177

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

178

Observed Climate Variability and Trends Coral reef, Funafuti, Tuvalu  

E-print Network

51 Chapter 3 Observed Climate Variability and Trends Coral reef, Funafuti, Tuvalu #12;52 Climate and in the oceans", and that "greenhouse gas forcing has very likely caused most of the observed global warming over Fourth Assessment Report (Hergerl et al., 2007) concluded that "anthropogenic warming of the climate

Phipps, Steven J.

179

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

NASA Technical Reports Server (NTRS)

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

Markevitch, Maxim

2012-01-01

180

Observing Variable Stars, A Guide for the Beginner  

NASA Astrophysics Data System (ADS)

David Levy's entertaining, well-researched book is aimed at the amateur enthusiast who likes to learn enjoyably. Beginning with advice on binoculars and telescopes, and how to observe the night sky effectively, the author goes on to describe thoroughly the field of variable star observation, a field in which amateurs have made important contributions. He shows how to interpret variations in light output in terms of the life of a star, from birth through to sometimes violent death. All of the major variable stars are described and classified, as well as other variable objects such as active galaxies, asteroids, comets and the sun. The book also contains a guide to the seasonal night sky. Throughout, practical observations serve to complement the text, producing an exciting, very readable introduction to this fascinating subject.

Levy, David H.

181

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

182

First catalogue of variable sources observed by INTEGRAL/OMC  

NASA Astrophysics Data System (ADS)

The Optical Monitoring Camera (OMC) onboard INTEGRAL provides photometry in the V Johnson band. With an aperture of 50 mm and a field of view of 5°×5°, OMC is able to detect optical sources brighter than around V˜18 from a previously selected list of potential targets of interest. This first catalogue of variable sources observed by OMC contains more than 5000 variables objects. The long time interval of the observations (more than 7 years) allowed us to study the potential periodicity of these sources determining periods for more than 1000 objects.

Alfonso-Garzón, J.; Domingo, A.; Mas-Hesse, J. M.

2013-05-01

183

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

NASA Astrophysics Data System (ADS)

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 observe the previously reported relationship between Gamma and the ratio of L x to the Eddington luminosity.

Mattson, Barbara Jo

2008-10-01

184

Temporal variability of observed and simulated hyperspectral reflectance  

NASA Astrophysics Data System (ADS)

Multivariate analysis techniques were used to quantify and compare the spectral and temporal variability of observed and simulated shortwave hyperspectral Earth reflectance. The observed reflectances were measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument between 2002 and 2010. The simulated reflectances were calculated using climate Observing System Simulation Experiments (OSSEs), which used two Intergovernmental Panel on Climate Change AR4 scenarios (constant CO2 and A2 emission) to drive Moderate Resolution Atmospheric Transmission simulations. Principal component (PC) spectral shapes and time series exhibited evidence of physical variables including cloud reflectance, vegetation and desert albedo, and water vapor absorption. Comparing the temporal variability of the OSSE-simulated and SCIAMACHY-measured hyperspectral reflectance showed that their Intertropical Convergence Zone-like Southern Hemisphere (SH) tropical PC1 ocean time series had a 90° phase difference. The observed and simulated PC intersection quantified their similarity and directly compared their temporal variability. The intersection showed that despite the similar spectral variability, the temporal variability of the dominant PCs differed as in, for example, the 90° phase difference between the SH tropical intersection PC1s. Principal component analysis of OSSE reflectance demonstrated that the spectral and centennial variability of the two cases differed. The A2 PC time series, unlike the constant CO2 time series, exhibited centennial secular trends. Singular spectrum analysis isolated the A2 secular trends. The A2 OSSE PC1 and PC4 secular trends matched those in aerosol optical depth and total column precipitable water, respectively. This illustrates that time series of hyperspectral reflectance may be used to identify and attribute secular climate trends with a sufficiently long measurement record and high instrument accuracy.

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

2014-09-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

188

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

Microsoft Academic Search

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

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

2008-01-01

189

Ginga and ROSAT observations of the cataclysmic variable S193  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

190

Understanding selection effects in observed samples of cataclysmic variables  

E-print Network

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

Magaretha L. Pretorius; Christian Knigge; Ulrich Kolb

2006-10-21

191

Variability of Arctic Sea Ice as Determined from Satellite Observations  

NASA Technical Reports Server (NTRS)

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

Parkinson, Claire L.

1999-01-01

192

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

NASA Astrophysics Data System (ADS)

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 are of acceptably high quality. The formats and data structures used by the seismological community are esoteric. IRIS and its FDSN partners are developing web services that can transform the data holdings to structures that are more easily used by broader scientific communities. For instance, atmospheric scientists are interested in using global observations of microbarograph data but that community does not understand the methods of applying instrument corrections to the observations. Web processing services under development at IRIS will transform these data in a manner that allows direct use within such analysis tools as MATLAB® already in use by that community. By continuing to develop web-service based methods of data discovery and access, IRIS is enabling broader access to its data holdings. We currently support data discovery using many of the Open Geospatial Consortium (OGC) web mapping services. We are involved in portal technologies to support data discovery and distribution for all data from the EarthScope project. We are working with computer scientists at several universities including the University of Washington as part of a DataNet proposal and we intend to enhance metadata, further develop ontologies, develop a Registry Service to aid in the discovery of data sets and services, and in general improve the semantic interoperability of the data managed at the IRIS DMC. Finally IRIS has been identified as one of four scientific organizations that the External Research Division of Microsoft wants to work with in the development of web services and specifically with the development of a scientific workflow engine. More specific details of current and future developments at the IRIS DMC will be included in this presentation.

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

2009-04-01

193

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

PubMed Central

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

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

2014-01-01

194

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

PubMed Central

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

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

2010-01-01

195

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

SciTech Connect

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

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

2013-01-01

196

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

197

Cataclysmic variables to be monitored for HST observations  

NASA Astrophysics Data System (ADS)

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

Waagen, Elizabeth O.

2012-09-01

198

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

PubMed

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

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

2014-01-01

199

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

NASA Astrophysics Data System (ADS)

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

Piskozub, Jacek; Gutowska, Dorota

2014-05-01

200

Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode*  

E-print Network

, to the South Pacific near Antarctica­South America, and then bending northward toward Africa. This patternDecadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed Polar Research Center, and Atmospheric Sciences Program, Department of Geography, The Ohio State

Howat, Ian M.

201

Observing soil moisture temporal variability under fluctuating climatic conditions  

Microsoft Academic Search

The paper focuses on the observation of interannual and intra-annual climate variability impact on soil moisture temporal patterns and variation, for an experimental site located in Southern Italy and characterized by a typical Mediterranean climate. Analysed data consist of three years soil water content time series measured during the period 2004-2007, under intermediate (2004\\/2005), wet (2005\\/2006) and dry (2006\\/2007) climatological

A. Longobardi

2008-01-01

202

Analysis of Marine Stratocumulus Drizzle Variability Using In Situ Observations  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

203

Observability of Antarctic Surface Temperature Variations on Decadal Time Scales, With High Spatial Resolution, Using Satellite Observations of Thermal Microwave Emission and Sparse Ground Measurements  

NASA Astrophysics Data System (ADS)

Knowledge of Antarctic surface temperature variations in space and time is presently based on instrumental records and interpretation of ice cores, both of which are, by practical necessity, sparse point measurements. The sufficiency of spatial sampling by such measurements remains uncertain. Spatially extensive satellite observations of 0.8 cm-wavelength (37 GHz) thermal emission can be interpreted in terms of snow surface temperature to address this problem, but such interpretation is presently limited in two important respects: (1) interpretation is restricted to regions of space and time near instrumental or other independent temperature data that are needed to infer an effective microwave emissivity; and (2) the record of suitable observations extends back only 22 years, a duration which is short compared to the timescale of many prospective temperature variations of interest. The first limitation can be addressed by estimating long-term (centennial-scale) mean surface temperature independently from satellite observations of 4.5 cm-wavelength (6.7 GHz) emission. I present the essential physical and observational validation for this estimation, and show how, together with the shorter wavelength observations, the estimation can be used to characterize microwave emissivity at 0.8 cm-wavelength (for a simplified, though usefully approximate model in which firn properties are independent of depth within the range from which the shorter-wavelength emission originates). The second limitation can be addressed using emission observations at wavelengths longer than 0.8 cm - in particular, emission at 1.8 cm - and longer-wavelengths (i.e., frequencies of 19 GHz and lower) carries information on temperature variations on decadal scales. I present a simple calculation that shows how this occurs, and note approximate agreement of the calculation with recent results by Shuman and by Fahnestock and co-workers. The underlying physics thus supports, in principle, the use of existing and prospective satellite microwave emission observations to characterize ice sheet temperature variations during a significant part of the 20th century - the key question is whether available accuracies compare well with the expected magnitudes of such temperature variations. I address this question using basic but modern geostatistical methods to estimate the accuracy of "calibration" of the satellite temperature estimates using sparse ground observations. From this follows directly an assessment of the observability of Antarctic surface temperature variations on decadal time scales, both with present data and with data likely to become available in the next decade.

Winebrenner, D. P.

2001-12-01

204

New Observations of Accretion Phenomena in Magnetic Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

We present an overview of the ongoing observational, theoretical and modelling work on magnetically controlled accretion phenomena in magnetic cataclysmic variables. With SAAO's high speed polarimeter, HIPPO, we have discovered polarized Quasi-Periodic Oscillations, on a timescale of several minutes. We have investigated various scenarios in which such QPOs can be created, all of them requiring some interaction between the ballistic accretion flow and the magnetic field of the accreting white dwarf. With high speed photometry, including observations with SALT, we are investigating the nature of high frequency QPOs (~sub-few seconds) from the accretion shocks in mCVs. We also present some high speed photometric observations revealing the magnetic accretion spots on the accreting White Dwarfs. Developments in the use of Doppler tomography are also presented. Our new "inside-out" visualization gives an alternative way of calculating Doppler tomograms that can better emphasize the ballistic and magnetically confined accretion flows.

Buckley, D. A. H.; Potter, S. B.; Kotze, E.; Kotze, M.; Breytenbach, H.

2014-01-01

205

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

206

ROTSE-III observation of a Cataclysmic Variable new outburst  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

208

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

NASA Astrophysics Data System (ADS)

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

Chereskin, T. K.; Koenig, Z.

2012-12-01

209

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

PubMed

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

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

2014-01-01

210

Subtropical Gyre Variability Observed by Ocean Color Satellites  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

211

Ground based observations of Io plasma torus variability  

NASA Astrophysics Data System (ADS)

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

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

212

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

213

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

214

OBSERVATIONS OF THERMAL FLARE PLASMA WITH THE EUV VARIABILITY EXPERIMENT  

SciTech Connect

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

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

2013-06-20

215

A Preliminary Observational Search for Circumbinary Disks around Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

Circumbinary (CB) disks have been proposed as a mechanism to extract orbital angular momentum from cataclysmic variables (CVs) during their evolution. As proposed by Taam & Spruit, these disks extend outward to several astronomical units and should be detected observationally via their infrared flux or by absorption lines in the ultraviolet spectra of the CV. We have made use of archival HST/STIS spectra, as well as our own near-IR imaging, to search for observational evidence of such CB disks in seven CVs. Based on the null result, we place an upper limit on the column density of the disk of NH~1017cm-2. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work was started while three of the authors (K. E. B., N. S., S. B. H.) were at the Planetary Science Institute, Tucson, AZ.

Belle, Kunegunda E.; Sanghi, Neeru; Howell, Steve B.; Holberg, J. B.; Williams, Peter T.

2004-07-01

216

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

NASA Astrophysics Data System (ADS)

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

Sun, Bo; Wang, Huijun

2014-07-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

218

North American Climate in CMIP5 Experiments. Part II: Evaluation of Historical Simulations of Intraseasonal to Decadal Variability  

E-print Network

of California, Los Angeles, Los Angeles, California f International Pacific Research Center, School of Ocean and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California k Department variability in the eastern Pacific and most models capture the midsummer drought over Central America

219

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

Microsoft Academic Search

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

Vincent Moron

1997-01-01

220

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

NASA Astrophysics Data System (ADS)

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 peripheral basins of Iowa, and may be obscured in the central basins where extreme flows strongly affect annual concentration trends.

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

2013-12-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

223

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

224

Ionospheric Variability as Observed by the CTECS and CORISS Sensors  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

225

Follow up Observations of SDSS and CRTS Candidate Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

226

Observed and simulated multidecadal variability in the Northern Hemisphere  

Microsoft Academic Search

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

T. L. Delworth; M. E. Mann

2000-01-01

227

Climate feedbacks and predictability in the Nordic Seas area: a view based on oceanic observations and atmospheric reanalysis data in recent decades  

NASA Astrophysics Data System (ADS)

Prospects for short-term (seasonal-to-interannual) prediction of extratropical climate variability depend on the strength of feedbacks between different components of the climate system, the atmosphere and ocean in particular. Our recent studies indicate that such feedbacks are particularly strong in the Nordic (Greenland-Iceland-Norwegian and Barents) Seas area where anomalous air-sea interactions are enhanced by a large amplitude of the seasonal cycle of the sea ice cover, especially in the Barents Sea. We have shown that wintertime sea ice extent anomalies in this area are strongly linked to half a year earlier anomalies of Atlantic water temperature at the entrance to the Barents Sea and to local air-sea interactions and sea surface temperature anomalies in the preceding winter-to-spring season. We have also shown a substantial predictability of wintertime anomalies of surface air temperature and winds over the Nordic Seas from oceanic heat anomalies and proposed mechanisms responsible for a long persistence of the atmospheric anomalies. We will review these concepts and provide further evidence of a strong atmospheric response in the Nordic Seas and adjacent areas to oceanic heat anomalies based on ocean temperature observations and atmospheric reanalysis data from recent decades. We will show that significant oceanically-driven air temperature and wind anomalies extend to the tropopause and explain mechanisms responsible for such a deep response.

Schlichtholz, Pawel

2014-05-01

228

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

Microsoft Academic Search

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

D. BESTLE; M. ZEITZ

1983-01-01

229

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

NASA Astrophysics Data System (ADS)

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

Chappell, N. A.; Jones, T.

2013-12-01

230

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

NASA Astrophysics Data System (ADS)

The movement of the Adria plate is important in the understanding of the seismicity of Italy and the Dalmatian region. Its northern margin delineates the most seismic area of the Alps and has been hit by destructive earthquakes. The deformation of the margin has been observed over four decades in a natural cave with long-base highly stable and sensitive instruments. We discuss the observed deformation on the decadal time scale. We show that the movement is the superposition of a steady state deformation rate, and a time varying deformation with half-period of about twenty years. The station is near to the Adriatic Sea, wherefore a sea loading effect is present. The change of sea-level in time involves also a steady state as well as decadal scale variations. We model the geodetic observations in terms of the deformation due to the plate-tectonic movement and discuss the deformation due to the sea-loading.

Braitenberg, C.; Nagy, I.; Papacchioli, S.

2004-12-01

231

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

232

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

Microsoft Academic Search

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

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

1998-01-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

234

Mythological Evidence for Ancient Observations of Variable Stars  

NASA Astrophysics Data System (ADS)

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.

Wilk, Stephen R.

235

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

237

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

USGS Publications Warehouse

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

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

2007-01-01

238

Variability of Attention Processes in ADHD: Observations from the Classroom  

ERIC Educational Resources Information Center

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

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

2009-01-01

239

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

Microsoft Academic Search

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

A. Grötzner; M. Latif; T. P. Barnett

1998-01-01

240

Direct observation of homoclinic orbits in human heart rate variability  

NASA Astrophysics Data System (ADS)

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

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

2003-05-01

241

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

SciTech Connect

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

Lai, Chung-Chieng A.

1997-10-01

242

First Catalogue of Optically Variable Sources Observed by OMC Onboard INTEGRAL  

NASA Astrophysics Data System (ADS)

In this work, we present the first catalogue of optically variable sources observed by the Optical Monitoring Camera (OMC), with information about the variability of more than 5000 objects and periodicity of ~ 1000 sources.

Alfonso-Garzón, Julia; Domingo, Albert; Miguel Mas-Hesse, José

2012-04-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

244

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

NASA Astrophysics Data System (ADS)

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

Aculinin, Alexandr; Smicov, Vladimir

2010-05-01

245

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

246

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

NASA Astrophysics Data System (ADS)

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

Cazenave, Anny; Benveniste, Jérôme; Legeais, JeanFrancois

247

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

ERIC Educational Resources Information Center

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…

Adamson, Reesha M.; Wachsmuth, Sean T.

2014-01-01

248

Variability in Tropical Tropospheric Ozone as Observed by SHADOZ  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

249

Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei  

E-print Network

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

Mushotzky, Richard F; Baumgartner, Wayne H; Gandhi, Poshak

2011-01-01

250

Observations from over a decade of experience in developing faster, better, cheaper missions for the NASA small explorer program  

NASA Astrophysics Data System (ADS)

The Small Explorer (SMEX) Project at NASA Goddard Space Flight Center (GSFC) has accumulated nearly a decade of experience building missions with the underlying philosophy of "Faster, Better, Cheaper" (FBC). Five satellites are now successfully operating on-orbit with only one serious instrument anomaly. Together this Project has accumulated 14.6 years of on-orbit experience without a spacecraft bus failure. Additionally, this project, under the Explorer Technology Infusion effort, has developed a protoflight version of a 21 st Century FBC spacecraft bus that has just completed environmental qualification and has been selected at the base spacecraft for NASA's Triana mission. Design and production of these six high performance spacecraft, in just ten years time, has provided a unique base of experience from which to draw lessons learned. This paper will discuss the fundamental practices that have been used by the SMEX Project in achieving this record of success.

Watzin, Jim

2001-03-01

251

Comparison of temperature variability in observations and sixteen climate model simulations  

NASA Astrophysics Data System (ADS)

Understanding how much, if any, of observed climate changes are anthropogenic depends upon understanding the magnitude and spatial patterns of natural climate variability. We have compared simulated surface air temperature (SAT) variability in 16 coupled ocean-atmosphere-sea ice climate model simulations to observed temperature variability. The majority of the simulations exhibit excessive air temperature variability over land while simulated temperature variability over oceans is generally too low. The ratio of variability over land to over oceans is too high in all the simulations, relative to observations. We have identified several factors which may contribute to the differences in temperature variability. In particular, many of the models use ``bucket'' land surface schemes which produce greater temperature variability over land, due to lower levels of soil moisture, than more realistic land surface schemes produce.

Bell, J.; Duffy, P.; Covey, C.; Sloan, L.

252

Comparison of temperature variability in observations and sixteen climate model simulations  

NASA Astrophysics Data System (ADS)

Understanding how much, if any, of observed climate changes are anthropogenic depends upon understanding the magnitude and spatial patterns of natural climate variability. We have compared simulated surface air temperature (SAT) variability in 16 coupled ocean-atmosphere-sea ice climate model simulations to observed temperature variability. The majority of the simulations exhibit excessive air temperature variability over land while simulated temperature variability over oceans is generally too low. The ratio of variability over land to over oceans is too high in all the simulations, relative to observations. We have identified several factors which may contribute to the differences in temperature variability. In particular, many of the models use ”bucket” land surface schemes which produce greater temperature variability over land, due to lower levels of soil moisture, than more realistic land surface schemes produce.

CMIP Investigators; Bell, J.; Duffy, P.; Covey, C.; Sloan, L.

253

Equatorial F2 characteristic variability: A review of recent observations  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

254

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

255

Anne S. Young: Professor and Variable Star Observer Extraordinaire  

NASA Astrophysics Data System (ADS)

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.

Bracher, Katherine

2011-05-01

256

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

PubMed Central

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

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

2009-01-01

257

The Semiregular Variable Star Observing Program at Grinnell College  

NASA Astrophysics Data System (ADS)

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

Cadmus, Robert R.

2014-06-01

258

Patterns and Variability in Global Ocean Chlorophyll: Satellite Observations and Modeling  

NASA Technical Reports Server (NTRS)

Recent analyses of SeaWiFS data have shown that global ocean chlorophyll has increased more than 4% since 1998. The North Pacific ocean basin has increased nearly 19%. These trend analyses follow earlier results showing decadal declines in global ocean chlorophyll and primary production. To understand the causes of these changes and trends we have applied the newly developed NASA Ocean Biogeochemical Assimilation Model (OBAM), which is driven in mechanistic fashion by surface winds, sea surface temperature, atmospheric iron deposition, sea ice, and surface irradiance. The model utilizes chlorophyll from SeaWiFS in a daily assimilation. The model has in place many of the climatic variables that can be expected to produce the changes observed in SeaWiFS data. This enables us to diagnose the model performance, the assimilation performance, and possible causes for the increase in chlorophyll. A full discussion of the changes and trends, possible causes, modeling approaches, and data assimilation will be the focus of the seminar.

Gregg, Watson

2004-01-01

259

An Evaluation of CMIP5 Precipitation Variability for China Relative to Observations and CMIP3  

NASA Astrophysics Data System (ADS)

Precipitation represents an important link between the atmosphere, hydrosphere, and biosphere and is thus a key component of the climate system. As indicated by the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), global surface air temperatures increased by 0.74°C during the 20th century, with further warming of 0.2°C/decade projected by the 2030s. Projected changes in precipitation, however, are much more variable, and exhibit more complex temporal and spatial patterns. This presentation focuses on precipitation variability based on 20 general circulation models (GCMs) participating in the fifth coupled model intercomparison project (CMIP5). Specifically, we focus on China and provide a comprehensive evaluation of the CMIP5 models compared to historical 20th century precipitation variability from two observational precipitation products: the University of East Anglia's Climatic Research Unit (CRU) time series (TS) dataset version 3.10, and the Global Precipitation Climatology Centre (GPCC) version 6. We also reassess the performance of the third CMIP (CMIP3) to quantify potential improvements in CMIP5 over the previous generation of GCMs. Finally, we provide 21st century precipitation projections for China based on three representative concentration pathways (RCP): RCP 8.5, 4.5, and 2.6. These future precipitation projections are presented in light of the observed 20th century biases in the models. We find that CMIP5 models are able to better reproduce the general spatial pattern of observed 20th century precipitation than CMIP3. However, for China as a whole, the annual precipitation magnitude is overestimated in CMIP5, more so than in CMIP3. This smaller overestimation in CMIP3 was primarily driven by a large underestimation of summer precipitation. Spatially, overestimated precipitation magnitudes are evident for most regions of China, especially along the eastern margin of the Tibetan Plateau. Over southeastern China during summer, the precipitation amounts are underestimated. The multidecadal precipitation variability in CMIP5 is muted relative to observations, but improved when compared to CMIP3. We also assess precipitation trends and correlations relative to observations, and again find better agreement for CMIP5 than for CMIP3. Both observations and models indicated precipitation increases over parts of northwestern China, and decreases over the Tibetan Plateau throughout the 20th century. However, for the southeastern and northern regions of China there is poor agreement in precipitation trends. Precipitation is projected to increase across all of China under all the three emission scenarios during the 21st century. The largest significant trend is evident for RCP 8.5, which projects a precipitation increase of 1.5 mm/year, resulting in a 16% increase in precipitation by the end of the century. The smallest increases are projected to occur under the RCP 2.6 scenario, resulting in only a +6% change by 2100. The regions of greatest precipitation increases are the Tibetan Plateau and eastern China during summer, suggesting a potential change in the monsoonal circulation in the future.

Frauenfeld, O. W.; Chen, L.

2013-12-01

260

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

SciTech Connect

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

Fox-Rabinovitz, M; Cote, J

2009-06-05

261

Improvements in observed and relative survival in follicular grade 1-2 lymphoma during 4 decades: the Stanford University experience.  

PubMed

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

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; Advani, Ranjana H

2013-08-01

262

Decade Volcanoes  

NSDL National Science Digital Library

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

263

Observed Multi-Decade DD and DT Z-Pinch Fusion Rate Scaling in 5 Dense Plasma Focus Fusion Machines  

SciTech Connect

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.

Hagen, E. C. [National Security Technologies, LLC; Lowe, D. R. [National Security Technologies, LLC; O'Brien, R. [University of Nevada, Las Vegas; Meehan, B. T. [National Security Technologies, LLC

2013-06-18

264

Spatial variability and its scale dependency of observed and modeled soil moisture over different climate regions  

NASA Astrophysics Data System (ADS)

Past studies on soil moisture spatial variability have been mainly conducted at catchment scales where soil moisture is often sampled over a short time period; as a result, the observed soil moisture often exhibited smaller dynamic ranges, which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness) of in situ soil moisture, modeled and satellite-retrieved soil moisture obtained in a warm season (198 days) were examined over three large climate regions in the US. The study found that spatial moments of in situ measurements strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean when statistics from dry, intermediate, and wet climates were combined. This upward convex shape was vaguely or partially observable in modeled and satellite-retrieved soil moisture estimates due to their smaller dynamic ranges. Despite different environmental controls on large-scale soil moisture spatial variability, the correlation between spatial variability and mean soil moisture remained similar to that observed at small scales, which is attributed to the boundedness of soil moisture. From the smaller support (effective area or volume represented by a measurement or estimate) to larger ones, soil moisture spatial variability decreased in each climate region. The scale dependency of spatial variability all followed the power law, but data with large supports showed stronger scale dependency than those with smaller supports. The scale dependency of soil moisture variability also varied with climates, which may be linked to the scale dependency of precipitation spatial variability. Influences of environmental controls on soil moisture spatial variability at large scales are discussed. The results of this study should be useful for diagnosing large scale soil moisture estimates and for improving the estimation of land surface processes.

Li, B.; Rodell, M.

2013-03-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

266

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

ERIC Educational Resources Information Center

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

Vermunt, Jeroen K.

2005-01-01

267

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

NASA Astrophysics Data System (ADS)

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

Hajek, P.

2006-06-01

268

Decadal changes of ENSO persistence barrier in SST and ocean heat content indices: 1958–2001  

Microsoft Academic Search

Decadal changes of El Niño-Southern Oscillation (ENSO) persistence barriers in various indices of sea surface temperature (SST) and ocean heat content (OHC) are examined in this study using observations and ocean data assimilation products for the period 1958–2001. It is found that the SST indices in the eastern and central equatorial Pacific exhibit very different decadal barrier variability. The variability

Jin-Yi Yu; Hsun-Ying Kao

2007-01-01

269

Cassini UVIS Observations of the Io Plasma Torus. III. Observations of Temporal and Azimuthal Variability  

E-print Network

In this third paper in a series presenting observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS) of the Io plasma torus, we show remarkable, though subtle, spatio-temporal variations in torus properties. The Io torus is found to exhibit significant, near-sinusoidal variations in ion composition as a function of azimuthal position. The azimuthal variation in composition is such that the mixing ratio of S II is strongly correlated with the mixing ratio of S III and the equatorial electron density and strongly anti-correlated with the mixing ratios of both S IV and O II and the equatorial electron temperature. Surprisingly, the azimuthal variation in ion composition is observed to have a period of 10.07 hours--1.5% longer than the System III rotation period of Jupiter, yet 1.3% shorter than the System IV period defined by Brown (1995). Although the amplitude of the azimuthal variation of S III and O II remained in the range of 2-5%, the amplitude of the S II and S IV compositional variation ranged between 5-25% during the UVIS observations. Furthermore, the amplitude of the azimuthal variations of S II and S IV appears to be modulated by its location in System III longitude, such that when the region of maximum S II mixing ratio (minimum S IV mixing ratio) is aligned with a System III longitude of ~200 +/- 15 degrees, the amplitude is a factor of ~4 greater than when the variation is anti-aligned. This behavior can explain numerous, often apparently contradictory, observations of variations in the properties of the Io plasma torus with the System III and System IV coordinate systems.

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

2005-08-01

270

On the 3-5 ?m variability of young variables in Vela-D through Spitzer-WISE observations  

NASA Astrophysics Data System (ADS)

Flux variability is a common feature of Young Stellar Objects (YSOs), which is often related to intermittent events of disk accretion (EXors events in case of 3-4 magnitudes variations). Recently, thanks to the surveys carried out by the space missions Spitzer and WISE, it has become possible to perform statistical studies on the mid-IR variability on large samples of YSOs. As a follow-up of our recent statistical study on five star forming regions (Antoniucci et al., Astrophys. J. 782:51, 2014), we present the 3-5 ?m variability study of the YSOs population of the Vela-D star forming region. We have compared the 3.6 ?m and 4.5 ?m Spitzer-IRAC fluxes of 181 YSOs in Vela-D with their WISE fluxes at 3.4 ?m and 4.6 ?m and selected those objects simultaneously varying in both bands. We have identified a robust sample of 34 variables. On the base of the infrared excess of the Spectral Energy Distribution (SED) and the magnitude vs. color variations, we select 5 EXors candidates, which will be systematically monitored to firmly ascertain their nature. The selected 34 variables represent ˜18 % of the YSOs detected with Spitzer and WISE, a percentage higher than that of other young star forming regions. Conversely, the percentage of candidate EXors (2.7 %) is quite similar to that measured in Perseus, Ophiuchus and Serpens, and also equals that found in Vela-D on the base of Spitzer variability (Giannini et al., Astrophys. J. 704:606, 2009). Consistently with our finding presented in Antoniucci et al. (2014), this fraction equals the probability of observing the source once in burst and once in quiescence, under the hypothesis that the time elapsed between the two events is of about 0.5-1 year. Of the 5 selected EXors candidates, 3 are Class I sources, and 2 are flat-spectrum sources, a circumstance that suggests that accretion-driven variability is a common phenomenon during the earlier phases of the protostellar evolution. In the light of the new WISE data, we also re-examine a sample of 10 variables, which we had already selected in Giannini et al. (2009). From the inspection of their light curves, we select two flat-spectrum sources as the best EXors candidates.

Giannini, T.; Lorenzetti, D.; Antoniucci, S.; Li Causi, G.; Elia, D.; Strafella, F.

2014-08-01

271

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

272

Interpreting intraseasonal variability of subsurface tracers observed by a profiling float  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

273

Spatial variability and its scale dependency of observed and modeled soil moisture under different climate conditions  

NASA Astrophysics Data System (ADS)

Past studies on soil moisture spatial variability have been mainly conducted in catchment scales where soil moisture is often sampled over a short time period. Because of limited climate and weather conditions, the observed soil moisture often exhibited smaller dynamic ranges which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness) of in situ soil moisture measurements (from a continuously monitored network across the US), modeled and satellite retrieved soil moisture obtained in a warm season (198 days) were examined at large extent scales (>100 km) over three different climate regions. The investigation on in situ measurements revealed that their spatial moments strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean across dry, intermediate, and wet climates. These climate specific features were vaguely or partially observable in modeled and satellite retrieved soil moisture estimates, which is attributed to the fact that these two data sets do not have climate specific and seasonal sensitive mean soil moisture values, in addition to lack of dynamic ranges. From the point measurements to satellite retrievals, soil moisture spatial variability decreased in each climate region. The three data sources all followed the power law in the scale dependency of spatial variability, with coarser resolution data showing stronger scale dependency than finer ones. The main findings from this study are: (1) the statistical distribution of soil moisture depends on spatial mean soil moisture values and thus need to be derived locally within any given area; (2) the boundedness of soil moisture plays a pivoting role in the dependency of soil moisture spatial variability/skewness on its mean (and thus climate conditions); (3) the scale dependency of soil moisture spatial variability changes with climate conditions.

Li, B.; Rodell, M.

2012-09-01

274

Comparing variability and trends in observed and modelled globalmean surface temperature  

E-print Network

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

275

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

Microsoft Academic Search

In order to investigate the nature of the winds of cataclysmic variables the authors present an observational and theoretical study of the P Cygni profiles of these systems, giving particular attention to the profiles of the dwarf nova HL CMa. After presenting the IUE observations of HL CMa, the authors give the results of a synthetic spectral code, which is

Christopher W. Mauche; John C. Raymond

1987-01-01

276

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

277

Constraining land carbon cycle process understanding with observations of atmospheric CO2 variability  

NASA Astrophysics Data System (ADS)

We evaluate our understanding of the land biospheric carbon cycle by benchmarking a model and its variants to atmospheric CO2 observations and to an atmospheric CO2 inversion. Though the seasonal cycle in CO2 observations is well simulated by the model (RMSE/standard deviation of observations <0.5 at most sites north of 15N and <1 for Southern Hemisphere sites) different model setups suggest that the CO2 seasonal cycle provides some constraint on gross photosynthesis, respiration, and fire fluxes revealed in the amplitude and phase at northern latitude sites. CarbonTracker inversions (CT) and model show similar phasing of the seasonal fluxes but agreement in the amplitude varies by region. We also evaluate interannual variability (IAV) in the measured atmospheric CO2 which, in contrast to the seasonal cycle, is not well represented by the model. We estimate the contributions of biospheric and fire fluxes, and atmospheric transport variability to explaining observed variability in measured CO2. Comparisons with CT show that modeled IAV has some correspondence to the inversion results >40N though fluxes match poorly at regional to continental scales. Regional and global fire emissions are strongly correlated with variability observed at northern flask sample sites and in the global atmospheric CO2 growth rate though in the latter case fire emissions anomalies are not large enough to account fully for the observed variability. We discuss remaining unexplained variability in CO2 observations in terms of the representation of fluxes by the model. This work also demonstrates the limitations of the current network of CO2 observations and the potential of new denser surface measurements and space based column measurements for constraining carbon cycle processes in models.

Collatz, G. J.; Kawa, S. R.; Liu, Y.; Zeng, F.; Ivanoff, A.

2013-12-01

278

A decade's overview of Io's volcanic activity  

NASA Technical Reports Server (NTRS)

Over the past decade some aspects of Io's volcanic activity have changed greatly, while others have essentially remained constant. This contrast has emerged from our study of multi-wavelength, infrared, observations of Io's thermal emission. From 1983 to 1992 we observed the disk integrated flux density of Io from the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Our spectral coverage allows us to separate out the emission components due to volcanic thermal anomalies which are warmer than the background emission caused by solar heating. Our temporal coverage allows us to resolve individual eruptions and also to obtain the disk-integrated flux density as a function of longitude (or, equivalently, orbital phase angle). Characteristics that persisted over the decade involve Loki's location and intensity of emission, the leading hemisphere emission, and the average heat flow. The variable aspects of Io over the decade include Loki's hotter area(s) and the outbursts in the leading hemisphere.

Matson, D. L.; Veeder, G. J.; Johnson, T. V.; Blaney, D. L.; Goguen, J. D.

1993-01-01

279

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

280

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

E-print Network

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

R. Smith; S. Vaughan

2007-01-08

281

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

282

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

283

Natural variability of observed hourly SO 2 and CO concentrations in St. Louis  

NASA Astrophysics Data System (ADS)

Observed hourly pollutant concentrations are stochastic or turbulent variables. For constant given mean wind speed, wind direction, stability and source emissions, observed hourly concentration can be expected to vary from hour to hour. In this study the variable C/ Q is used, where C is hourly concentration of CO or SO 2 observed in the St. Louis RAPS network (there are 25 monitoring stations) and Q is the total hourly emissions observed in the region. Wind speed, wind direction and stability are broken down into 10, 18 and 7 classes, respectively. Calculations of the standard deviation of ln( C/ Q) for joint meteorological classes using hourly data from 1976 indicate that there is a factor of two natural variability in hourly concentrations, independent of the meteorological parameters that are used. There is about 40% more variability in SO 2 concentrations than in CO concentrations, probably due to the dominance of point sources for SO 2 and area sources for CO. A perfect air quality model of the Gaussian type, predicting ensemble average hourly concentrations, cannot hope to produce results that are better than this natural variability.

Hanna, Steven R.

284

Upper Ocean Heat Variability and its Impact on H i I t it d St t D d l PHurricane Intensity and Structure: Decadal Progress  

E-print Network

and Structure: Decadal Progress Objective: To quantify the ocean's role on hurricane intensity and structure h f-sea heat and moisture transfers. Perlroth (68) related ocean thermal structure between the surface and 200 these phenomena. L i d V l (72) i d th h H i h i l t tLeipper and Volgenau (72) coined the phrase: Hurricane heat

Kuligowski, Bob

285

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

NASA Astrophysics Data System (ADS)

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

Famiglietti, J. S.

2012-12-01

286

Recent Results from High Energy Observations of Cataclysmic Variables: AM Canum Venaticorum and DW Ursae Majoris  

NASA Astrophysics Data System (ADS)

We present preliminary results from high energy observations of two cataclysmic variables that are prototypes of the classes to which they belong. The first is AM Canum Venaticorum, prototype of the AM CVn class of interacting binary white dwarfs. We have obtained average and time-resolved far-ultraviolet spectra of AM CVn with FUSE. The second is DW Ursae Majoris, one of the four founding members of the SW Sextantis class of novalike cataclysmic variable. We have observed DW UMa using XMM.

Hoard, D. W.; Homer, L.; Szkody, P.; Wachter, S.

2006-09-01

287

Events per variable for risk differences and relative risks using pseudo-observations.  

PubMed

A method based on pseudo-observations has been proposed for direct regression modeling of functionals of interest with right-censored data, including the survival function, the restricted mean and the cumulative incidence function in competing risks. The models, once the pseudo-observations have been computed, can be fitted using standard generalized estimating equation software. Regression models can however yield problematic results if the number of covariates is large in relation to the number of events observed. Guidelines of events per variable are often used in practice. These rules of thumb for the number of events per variable have primarily been established based on simulation studies for the logistic regression model and Cox regression model. In this paper we conduct a simulation study to examine the small sample behavior of the pseudo-observation method to estimate risk differences and relative risks for right-censored data. We investigate how coverage probabilities and relative bias of the pseudo-observation estimator interact with sample size, number of variables and average number of events per variable. PMID:24420649

Hansen, Stefan Nygaard; Andersen, Per Kragh; Parner, Erik Thorlund

2014-10-01

288

The regional MiKlip decadal forecast ensemble for Europe  

NASA Astrophysics Data System (ADS)

Funded by the German Ministry for Education and Research (BMBF) a major research project called MiKlip (Mittelfristige Klimaprognose, Decadal Climate Prediction) was launched and global as well as regional predictive ensemble hindcasts have been generated. The aim of the project is to demonstrate for past climate change whether predictive models have the capability of predicting climate on time scales of decades. This includes the development of a decadal forecast system, on the one hand to support decision making for economy, politics and society for decadal time spans. On the other hand, the scientific aspect is to explore the feasibility and prospects of global and regional forecasts on decadal time scales. The focus of this paper lies on the description of the regional hindcast ensemble for Europe generated by COSMO-CLM and on the assessment of the decadal variability and predictability against observations. To measure decadal variability we remove the long term bias as well as the long term linear trend from the data. Further, we applied low pass filters to the original data to separate the decadal climate signal from high frequency noise. The decadal variability and predictability assessment is applied to temperature and precipitation data for the summer and winter half-year averages/sums. The best results have been found for the prediction of decadal temperature anomalies, i.e. we have detected a distinct predictive skill and reasonable reliability. Hence it is possible to predict regional temperature variability on decadal timescales, However, the situation is less satisfactory for precipitation. Here we have found regions showing good predictability, but also regions without any predictive skill.

Mieruch, S.; Feldmann, H.; Schädler, G.; Lenz, C.-J.; Kothe, S.; Kottmeier, C.

2013-11-01

289

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

NASA Astrophysics Data System (ADS)

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

Rivett, Michael O.; Turner, Ryan J.; Glibbery (née Murcott), Penny; Cuthbert, Mark O.

2012-10-01

290

Sea Surface Salinity Variability from Simulations and Observations: Preparing for Aquarius  

NASA Technical Reports Server (NTRS)

Oceanic fresh water transport has been shown to play an important role in the global hydrological cycle. Sea surface salinity (SSS) is representative of the surface fresh water fluxes and the upcoming Aquarius mission scheduled to be launched in December 2010 will provide excellent spatial and temporal SSS coverage to better estimate the net exchange. In most ocean general circulation models, SSS is relaxed to climatology to prevent model drift. While SST remains a well observed variable, relaxing to SST reduces the range of SSS variability in the simulations (Fig.1). The main objective of the present study is to simulate surface tracers using a primitive equation ocean model for multiple forcing data sets to identify and establish a baseline SSS variability. The simulated variability scales are compared to those from near-surface argo salinity measurements.

Jacob, S. Daniel; LeVine, David M.

2010-01-01

291

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

E-print Network

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

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

2014-01-01

292

An Observational and Computational Variable Tagging System for Climate Change Informatics  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

293

Recent advances in satellite observations of solar variability and global atmospheric ozone  

NASA Technical Reports Server (NTRS)

A description is given of the temporal behavior of the sun as an ultraviolet variable star in relation to daily zonal means of atmospheric ozone from the total amount to that above the 10-mb and 4-mb pressure levels. A significant correlation has been observed between enhancements in the ultraviolet solar irradiances and terrestrial passages of the solar magnetic field sector boundary structure. However, it has not yet been possible to separate solar from the dynamical effects on the variability in the zonal means of ozone. Attention is given to global changes in ozone which have been derived from the satellite observations in terms of season, solar variability, and major stratospheric disturbances such as stratospheric warmings.

Heath, D. F.

1974-01-01

294

Observations of entrainment and time variability in the HH 47 jet  

NASA Technical Reports Server (NTRS)

We present new Fabry-Perot images of the HH 47 jet that show the first clear evidence for entrainment in a jet from a young star. The material in the jet moves faster down the axis of the flow and slower at the edges, similar to viscous flow in a pipe. The higher excitation lines occur along the edges of the jet, as expected if entrainment accelerates and heats the ambient material. We confirm previous observations of multiple bow shocks in this system. Together, time variability and entrainment produce much of the observed shock-excited gas in this object. Our data show that the 'wiggles' along the jet are not caused by jet material tied to a spiraling magnetic field, but instead result from time variability, variable ejection angles, or inhomogeneities in the flow. The gas entrained in the HH 47 jet may be atomic; our results do not provide direct evidence that stellar jets drive molecular outflows.

Hartigan, Patrick; Morse, Jon A.; Heathcote, Steve; Cecil, Gerald

1993-01-01

295

Decadal variability of northern northeast Brazil rainfall and its relation to tropical sea surface temperature and global sea level pressure anomalies  

Microsoft Academic Search

Decadal (9–14 year) relations of the northern northeastern Brazil (NEB) rainfall to the sea surface temperature (SST) in the 60°N–30°S oceanic sector and to the global sea level pressure (SLP) anomalies are investigated for the 1871–1991 period. Indices are defined for the precipitation and for the SST anomalies in the tropical North Atlantic (TNA), in the tropical South Atlantic (TSA),

Mary Toshie Kayano; Rita Valéria Andreoli

2004-01-01

296

Decadal variability of northern northeast Brazil rainfall and its relation to tropical sea surface temperature and global sea level pressure anomalies  

Microsoft Academic Search

Decadal (9-14 year) relations of the northern northeastern Brazil (NEB) rainfall to the sea surface temperature (SST) in the 60°N-30°S oceanic sector and to the global sea level pressure (SLP) anomalies are investigated for the 1871-1991 period. Indices are defined for the precipitation and for the SST anomalies in the tropical North Atlantic (TNA), in the tropical South Atlantic (TSA),

Mary Toshie Kayano; Rita Valéria Andreoli

2004-01-01

297

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

Microsoft Academic Search

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

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

298

Compact imaging spectrometer with visible-infrared variable filters for Earth and planet observation  

Microsoft Academic Search

Compact spectrometers are of interest for space applications for both Earth observation and analysis of planet soil. The spectrometer here described is dedicated to Land imaging and is based on the use of linear variable filters for wavelength selection. This kind of filter is able to transmit the radiation in a narrow band (<20 nm) centered on a wavelength that

A. Piegari; A. Sytchkova; J. Bulir; M. Dami; G. Aroldi; B. Harnisch

2011-01-01

299

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

SciTech Connect

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

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

2013-03-15

300

Observed Variability of Ocean Wave Stokes Drift, and the Eulerian Response to Passing Groups  

E-print Network

Observed Variability of Ocean Wave Stokes Drift, and the Eulerian Response to Passing Groups JEROME 2005, in final form 13 September 2005) ABSTRACT Waves and currents interact via exchanges of mass and momentum. The mass and momentum fluxes associated with surface waves are closely linked to their Stokes

Smith, Jerome A.

301

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

ERIC Educational Resources Information Center

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

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

2012-01-01

302

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

Microsoft Academic Search

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

J. R. Lesh; P. R. Wesselius

1979-01-01

303

Observed variability of chlorophyll-a using Argo profiling floats in the southeastern Arabian Sea  

E-print Network

Observed variability of chlorophyll-a using Argo profiling floats in the southeastern Arabian Sea M 2012 Keywords: Chlorophyll-a Oxygen minimum zone Subsurface chlorophyll maxima Wind speed Southeastern Arabian Sea Air­sea interaction a b s t r a c t The time series of temperature, salinity, chlorophyll

Riser, Stephen C.

304

Observed Interannual Variability of the Florida1 Current: Wind Forcing and the North Atlantic2  

E-print Network

in FC transport along10 with sea level differences and direct ocean current measurements (SchottObserved Interannual Variability of the Florida1 Current: Wind Forcing and the North Atlantic2 School of Marine and Atmospheric Science, University of Miami, Miami,8 Florida9 10 Lewis J. Gramer11

Miami, University of

305

Observed Interannual Variability of the Florida Current: Wind Forcing and the North Atlantic Oscillation  

E-print Network

along with sea level differ- ences and direct ocean current measurements (Schott and Zantopp 1985Observed Interannual Variability of the Florida Current: Wind Forcing and the North Atlantic, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida WILLIAM E. JOHNS

306

The anatomy of decision support during inpatient care provider order entry (CPOE): Empirical observations from a decade of CPOE experience at Vanderbilt  

PubMed Central

The authors describe a pragmatic approach to the introduction of clinical decision support at the point of care, based on a decade of experience in developing and evolving Vanderbilt’s inpatient “WizOrder” care provider order entry (CPOE) system. The inpatient care setting provides a unique opportunity to interject CPOE-based decision support features that restructure clinical workflows, deliver focused relevant educational materials, and influence how care is delivered to patients. From their empirical observations, the authors have developed a generic model for decision support within inpatient CPOE systems. They believe that the model’s utility extends beyond Vanderbilt, because it is based on characteristics of end-user workflows and on decision support considerations that are common to a variety of inpatient settings and CPOE systems. The specific approach to implementing a given clinical decision support feature within a CPOE system should involve evaluation along three axes: what type of intervention to create (for which the authors describe 4 general categories); when to introduce the intervention into the user’s workflow (for which the authors present 7 categories), and how disruptive, during use of the system, the intervention might be to end-users’ workflows (for which the authors describe 6 categories). Framing decision support in this manner may help both developers and clinical end-users plan future alterations to their systems when needs for new decision support features arise. PMID:16290243

Miller, Randolph A.; Waitman, Lemuel R.; Chen, Sutin; Rosenbloom, S. Trent

2006-01-01

307

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

NASA Astrophysics Data System (ADS)

Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (i) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the 20th century reanalysis v2 (20CRv2), (ii) to isolate the high frequency meteorological variability of MSL from longer-term changes, (iii) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (iv) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October to March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude. Reference: Dangendorf, S., Wahl, T., Nilson, E., Klein, B., Jensen, J. (2013): A new atmospheric proxy for sea level variability in the southeastern North Sea: observations and future ensemble projections, Climate Dynamics, doi:10.1007/s00382-013-1932-4.

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

2014-05-01

308

Photometric Variability Properties of 21 T Tauri and Related Stars from AAVSO Visual Observations  

NASA Astrophysics Data System (ADS)

T Tauri variables are sun-like stars in various stages of their birth. We have analyzed long-term AAVSO visual observations of 21 T Tauri and related stars, using Fourier and self-correlation techniques. This follows our previous study of eleven such stars in JAAVSO 35, 290 (2006). Only a few of the variables showed periodic behavior, but self-correlation analysis makes it possible to construct a "variability profile" - amount of variability versus time scale - for all the stars, not just the periodic ones. For some of the periodic variables, we have studied the long-term behavior of the periods and amplitudes: T Cha and HT Lup appear to be rotating variables with stable periods less than 10 days; RU Lup, UX Ori, and TU Phe appear to show transient cycles of typically 50-500 days, probably arising in the accretion disc. R CrA has a stable 66-day period, which would be unusually long for a rotation period; its cause is not clear. We also discuss interesting but spurious low-amplitude one-year and one-month periodicities which occur in a few of the stars. Finally: we comment on the star AQ Dra, an RR Lyrae star, originally classified as a T Tauri star with a 5.5-day period.

Percy, J. R.; Esteves, S.; Glasheen, J.; Lin, A.; Long, J.; Mashintsova, M.; Terziev, E.; Wu, S.

2010-12-01

309

A stepwedge-based method for measuring breast density: observer variability and comparison with human reading  

NASA Astrophysics Data System (ADS)

Breast density is positively linked to the risk of developing breast cancer. We have developed a semi-automated, stepwedge-based method that has been applied to the mammograms of 1,289 women in the UK breast screening programme to measure breast density by volume and area. 116 images were analysed by three independent operators to assess inter-observer variability; 24 of these were analysed on 10 separate occasions by the same operator to determine intra-observer variability. 168 separate images were analysed using the stepwedge method and by two radiologists who independently estimated percentage breast density by area. There was little intra-observer variability in the stepwedge method (average coefficients of variation 3.49% - 5.73%). There were significant differences in the volumes of glandular tissue obtained by the three operators. This was attributed to variations in the operators' definition of the breast edge. For fatty and dense breasts, there was good correlation between breast density assessed by the stepwedge method and the radiologists. This was also observed between radiologists, despite significant inter-observer variation. Based on analysis of thresholds used in the stepwedge method, radiologists' definition of a dense pixel is one in which the percentage of glandular tissue is between 10 and 20% of the total thickness of tissue.

Diffey, Jenny; Berks, Michael; Hufton, Alan; Chung, Camilla; Verow, Rosanne; Morrison, Joanna; Wilson, Mary; Boggis, Caroline; Morris, Julie; Maxwell, Anthony; Astley, Susan

2010-04-01

310

Quantifying spatial and seasonal variability in atmospheric ammonia with in situ and space-based observations  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

311

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

312

Excitation of Earth Rotation Variations "Observed" by Time-Variable Gravity  

NASA Technical Reports Server (NTRS)

Time variable gravity measurements have been made over the past two decades using the space geodetic technique of satellite laser ranging, and more recently by the GRACE satellite mission with improved spatial resolutions. The degree-2 harmonic components of the time-variable gravity contain important information about the Earth s length-of-day and polar motion excitation functions, in a way independent to the traditional "direct" Earth rotation measurements made by, for example, the very-long-baseline interferometry and GPS. In particular, the (degree=2, order= 1) components give the mass term of the polar motion excitation; the (2,O) component, under certain mass conservation conditions, gives the mass term of the length-of-day excitation. Combining these with yet another independent source of angular momentum estimation calculated from global geophysical fluid models (for example the atmospheric angular momentum, in both mass and motion terms), in principle can lead to new insights into the dynamics, particularly the role or the lack thereof of the cores, in the excitation processes of the Earth rotation variations.

Chao, Ben F.; Cox, C. M.

2005-01-01

313

Multi-decadal river flow variations in France  

NASA Astrophysics Data System (ADS)

In this article, multi-decadal variations in the French hydroclimate are investigated, with a specific focus on river flows. Based on long observed series, it is shown that river flows in France generally exhibit large multi-decadal variations in the instrumental period (defined in this study as the period from the late 19th century to the present), especially in spring. Differences of means between 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations. Multi-decadal spring river flow variations are associated with variations in spring precipitation and temperature. These multi-decadal variations in precipitation are themselves found to be driven by large-scale atmospheric circulation, more precisely by a multi-decadal oscillation in a sea level pressure dipole between western Europe and the eastern Atlantic. It is suggested that the Atlantic Multidecadal Variability, the main mode of multi-decadal variability in the North Atlantic-Europe sector, controls those variations in large-scale circulation and is therefore the main ultimate driver of multi-decadal variations in spring river flows. Potential multi-decadal variations in river flows in other seasons, and in particular summer, are also noted. As they are not associated with significant surface climate anomalies (i.e. temperature, precipitation) in summer, other mechanisms are investigated based on hydrological simulations. The impact of climate variations in spring on summer soil moisture, and the impact of soil moisture in summer on the runoff-to-precipitation ratio, could potentially play a role in multi-decadal summer river flow variations. The large amplitude of the multi-decadal variations in French river flows suggests that internal variability may play a very important role in the evolution of river flows during the next decades, potentially temporarily limiting, reversing or seriously aggravating the long-term impacts of anthropogenic climate change.

Boé, J.; Habets, F.

2014-02-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

316

Methods to interpolate soil categorical variables from profile observations: Lessons from Iran  

Microsoft Academic Search

The paper compares semi-automated interpolation methods to produce soil-class maps from profile observations and by using multiple auxiliary predictors such as terrain parameters, remote sensing indices and similar. The Soil Profile Database of Iran, consisting of 4250 profiles, was used to test different soil-class interpolators. The target variables were soil texture classes and World Reference Base soil groups. The predictors

Tomislav Hengl; Norair Toomanian; Hannes I. Reuter; Mohammad J. Malakouti

2007-01-01

317

Observations of the cataclysmic variable SDSS J081321.91+452809.4  

E-print Network

Our observations of the first reported outburst of SDSS J081321.91+452809.4 during 2008 April show that this cataclysmic variable is a dwarf nova. The outburst amplitude was at least 3.1 magnitudes and the outburst appears to have been rather short-lived at around 3 days with a rapid decline to quiescence of 0.73 mag/day.

Jeremy Shears; Ian Miller; Steve Brady

2008-12-12

318

The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR  

NASA Astrophysics Data System (ADS)

We present a broadband (~0.5-79 keV) spectral and temporal analysis of multiple NuSTAR observations combined with archival Suzaku and Chandra data of NGC 4945, the brightest extragalactic source at 100 keV. We observe hard X-ray (>10 keV) flux and spectral variability, with flux variations of a factor of two on timescales of 20 ks. A variable primary continuum dominates the high-energy spectrum (>10 keV) in all states, while the reflected/scattered flux that dominates at E <10 keV stays approximately constant. From modeling the complex reflection/transmission spectrum, we derive a Compton depth along the line of sight of ?Thomson ~ 2.9, and a global covering factor for the circumnuclear gas of ~0.15. This agrees with the constraints derived from the high-energy variability, which implies that most of the high-energy flux is transmitted rather than Compton-scattered. This demonstrates the effectiveness of spectral analysis at constraining the geometric properties of the circumnuclear gas, and validates similar methods used for analyzing the spectra of other bright, Compton-thick active galactic nuclei (AGNs). The lower limits on the e-folding energy are between 200 and 300 keV, consistent with previous BeppoSAX, Suzaku, and Swift Burst Alert Telescope observations. The accretion rate, estimated from the X-ray luminosity and assuming a bolometric correction typical of type 2 AGN, is in the range ~0.1-0.3 ?Edd depending on the flux state. The substantial observed X-ray luminosity variability of NGC 4945 implies that large errors can arise from using single-epoch X-ray data to derive L/L Edd values for obscured AGNs.

Puccetti, Simonetta; Comastri, Andrea; Fiore, Fabrizio; Arévalo, Patricia; Risaliti, Guido; Bauer, Franz E.; Brandt, William N.; Stern, Daniel; Harrison, Fiona A.; Alexander, David M.; Boggs, Steve E.; Christensen, Finn E.; Craig, William W.; Gandhi, Poshak; Hailey, Charles J.; Koss, Michael J.; Lansbury, George B.; Luo, Bin; Madejski, Greg M.; Matt, Giorgio; Walton, Dominic J.; Zhang, Will

2014-09-01

319

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

320

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

Microsoft Academic Search

In paper 1 (Cheng et al. 2001) we have shown that the soft X-ray spectra of\\u000atwo types of Seyfert 1 galaxies statistically vary differently with increasing\\u000aintensity. In order to understand how the spectrum of blazars changes, the\\u000aspectral shape variability of 18 blazars observed by ROSAT\\/PSPC mode are\\u000astudied by presenting the correlation of Hardness Ratio 1 versus

Linpeng Cheng; Yongheng Zhao; Janyan Wei

2001-01-01

321

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

Microsoft Academic Search

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

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

2006-01-01

322

Summertime tropospheric ozone variability over the Mediterranean basin observed with IASI  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

323

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

NASA Technical Reports Server (NTRS)

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

Mauche, Christopher W.; Raymond, John C.

1987-01-01

324

Amateur Observing Patterns and Their Potential Impact on Variable Star Science  

NASA Astrophysics Data System (ADS)

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

Templeton, M. R.

2012-06-01

325

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

SciTech Connect

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

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

2013-08-20

326

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

PubMed Central

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

2014-01-01

327

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

328

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

PubMed Central

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

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

2012-01-01

329

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

NASA Astrophysics Data System (ADS)

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

Portugal, E. W.; Belmont, P.

2012-12-01

330

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

331

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

PubMed Central

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

2010-01-01

332

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

333

Observations and a model of gravity-wave variability in the middle atmosphere  

NASA Technical Reports Server (NTRS)

A major goal was to determine what portion of the gravity-wave frequency spectrum accounted for the majority of the momentum flux and divergence, as this has important implications for the middle atmosphere response. It was found that approx. 70% of the total flux and divergence was due to wave motions with observed periods less than 1 hour, consistent with expectations based on the shape of the observed gravity-wave spectrum (FrItts, 1984). This dominance of the momentum flux and divergence by high-frequency motions implies a potential for the modulation of those quantities by large-amplitude motions at lower frequencies. A second, striking aspect of the velocity and momentum flux data is its dramatic diurnal variability, particularly at certain levels. This variability is illustrated with the momentum flux, computed in 8-hr blocks. The dominant contributions here are due to waves with periods less than 1 hr. The variability with height and size of the mean square velocity in the west beam and the momentum flux, energed over the 3-day period. A detailed analysis of the various tidal motions present during this data interval was performed, and it was determined that variations in the zontal wind profile imposed by the diurnal tidal motion are probably responsible for the modulation of the gravity-wave amplitudes and momentum fluxes.

Fritts, D. C.; Vincent, R. A.

1986-01-01

334

The intraday variable quasar 0917+624: VLBI and X-ray observations.  

NASA Astrophysics Data System (ADS)

We present the first VLBI images of the extremely rapidly variable radio source 0917+624, at frequencies ranging from 2.3 to 22GHz. They reveal a compact core containing ~75% of the total flux density, and a jet extending to the northwest at position angle -20deg. The jet is curved on the sub-milliarcsecond scale, and one of the jet components is elongated perpendicular to the jet direction. This component displays apparent superluminal motion with a speed of ?_app_h=7.8+/-0.8 (H_0_=100h.km/s/Mpc; q_0_=0.5). A first detection of X-rays from 0917+624 with the ROSAT satellite enables us to estimate the magnetic field and the Doppler factor from synchrotron self-Compton theory. The observational results are compared with models for the rapid variability. The orientation of the jet on the sky is consistent with a prediction from two-component models that were developed to explain the polarization variations in 0917+624. The physical parameters derived from the new observations can be accomodated both by intrinsic (shock-in-jet or coherent emission) and extrinsic (interstellar scattering) explanations of the variability.

Standke, K. J.; Quirrenbach, A.; Krichbaum, T. P.; Witzel, A.; Otterbein, K.; Alef, W.; Eckart, A.; Alberdi, A.; Marcaide, J. M.; Ros, E.; Lesch, H.; Steffen, W.; Kraus, A.; Zensus, J. A.

1996-02-01

335

Coherent interannual and decadal variations inthe atmosphere-ocean system  

NASA Technical Reports Server (NTRS)

We investigate the source of poleward propagating atmospheric zonal wind anomalies, originating at the equator and penetrating to high latitudes in both hemispheres in conjunction with ENSO [Dickey et al.,1992], and report the discovery of similar variability on decadal and longer timescales. Since atmospheric dissipation times are generally on the order of a month or less, we examine the ocean as a 'memory' source for these globally coherent anomalies. This hypothesis is substantiated by the observation of complementaryoscillation in the sea surface temperature (SST) field; further, we detect a robust decadal variability (1012 yrs)in both the SST and contemporaneous atmospheric angular momentum (AAM) series. Analyzing GISST SST data beginning in 1902, we confirm this decadal mode and find signatures of longer (multidecadal) SST variability centered in the equatorial and North Pacific.

Dickey, J. O.; Marcus, S. L.; DeViron, O.

2003-01-01

336

Simultaneous Observations of Variability at All Atmospheric Levels of V824 Arae (HD 155555)  

NASA Astrophysics Data System (ADS)

We conducted a multiwavelength campaign observing V824 Ara (HD 155555, G5 IV+K0 IV-V) continuously throughout one complete orbital cycle (~1.7 days) in early May of 1996. At the core of this campaign were observations using the GHRS on the Hubble Space Telescope (HST). In all, about 48,000 spectra, many in rapid readout mode, were obtained with the GHRS covering the C IV, Mg II, and Fe XXI wavelength regions at 11-15 separate phases. Simultaneous observations were made with the Extreme Ultraviolet Explorer (EUVE). Radio observations (3.5 and 6 cm) were conducted at the Australian Telescope, while ground-based visual spectroscopic and photometric observations were made at European Southern Observatory, Cerro Tololo Inter-American Observatory, the Anglo-Australian Telescope, and South African Astronomical Observatory. Additional ground-based observations were obtained before, during, and after the campaign. Our primary intent was to obtain a three-dimensional model of the atmosphere extending from the photosphere to the corona. Variability was clearly detected, including several flares observed in the HST, EUVE, and radio data. We present results from modeling the ultraviolet transition region lines using an anisotropic macroturbulence model. Previous studies of transition region lines in late-type active stars have used multiple Gaussians to fit the observed line profiles, adding broad components to account for the extended wings observed in several active systems, including V711 Tau (HR 1099). This broad component has been interpreted as arising from the continuous presence of microflaring. We demonstrate that anisotropic macroturbulence models can also explain the observed Mg II profiles. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Dempsey, Robert C.; Neff, James E.; Lim, Jeremy

2001-07-01

337

The Beaufort Gyre Fresh Water Reservoir: State and Variability From Observations  

NASA Astrophysics Data System (ADS)

We investigate basin-scale mechanisms regulating anomalies in fresh water content (FWC) in the Beaufort Gyre (BG) of the Arctic Ocean using historical observations, data collected in 2003-2007 by the Beaufort Gyre Exploration Project, and measurements obtained from drifting Ice-Tethered Profilers. The major cause of the large FWC in the BG is the process of Ekman pumping associated with the climatological anticyclonic atmospheric circulation over the Canada Basin centered in the BG. The mechanically-forced seasonal variability of FWC in the central BG follows wind curl changes with a maximum in November - January and a minimum in June-August tracking seasonal changes in the atmospheric circulation. The atmospheric and oceanic thermal regimes regulate seasonal transformations of liquid FWC due to the seasonal cycle of sea ice melt and growth. Combination of the two mechanisms, reflected in the seasonal cycle of total BG FWC, has two pronounced peaks separated by approximately 3-4 months. The first peak (June-July) is observed when the sea ice thickness reaches its minimum (maximum fresh water release from sea ice to the ocean) and when the Ekman pumping is very close to its weakest. The second maximum is observed in November- January when the wind curl is strongest (maximum Ekman pumping) and the salt flux from the growing sea ice has not reached its maximum. One conclusion from this study is that the observational practice to sample the Arctic Ocean hydrography in August-September (when the sea ice coverage is at its seasonal minimum and the Arctic is accessible by research icebreakers) and April-May (using aircraft when the sea ice is sufficiently strong and there is adequate daylight) misses natural FWC seasonal variability and underestimates the seasonal variability of hydrographic fields, their gradients and circulation patterns.

Proshutinsky, A.; Krishfield, R.; Timmermans, M.; Toole, J.; Carmack, E.; McLaughlin, F.; Itoh, M.; Shimada, K.; Zimmermann, S.

2008-12-01

338

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

NASA Astrophysics Data System (ADS)

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

Zampieri, Matteo; Scoccimarro, Enrico; Gualdi, Silvio

2014-05-01

339

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

E-print Network

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

M. J. Ireland; M. Scholz

2006-01-18

340

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

SciTech Connect

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

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

2013-12-01

341

Filtering and Gridding Satellite Observations of Cloud Variables to Compare with Climate Model Output  

NASA Astrophysics Data System (ADS)

Global climate models have improved considerably over the years, yet clouds still represent a large factor of uncertainty for these models. Comparisons of model-simulated cloud variables with equivalent satellite cloud products are the best way to start diagnosing the differences between model output and observations. Gridded (level 3) cloud products from many different satellites and instruments are required for a full analysis, but these products are created by different science teams using different algorithms and filtering criteria to create similar, but not directly comparable, cloud products. This study makes use of a recently developed uniform space-time gridding algorithm to create a new set of gridded cloud products from each satellite instrument's level 2 data of interest which are each filtered using the same criteria, allowing for a more direct comparison between satellite products. The filtering is done via several variables such as cloud top pressure/height, thermodynamic phase, optical properties, satellite viewing angle, and sun zenith angle. The filtering criteria are determined based on the variable being analyzed and the science question at hand. Each comparison of different variables may require different filtering strategies as no single approach is appropriate for all problems. Beyond inter-satellite data comparison, these new sets of uniformly gridded satellite products can also be used for comparison with model-simulated cloud variables. Of particular interest to this study are the differences in the vertical distributions of ice and liquid water content between the satellite retrievals and model simulations, especially in the mid-troposphere where there are mixed-phase clouds to consider. This presentation will demonstrate the proof of concept through comparisons of cloud water path from Aqua MODIS retrievals and NASA GISS-E2-[R/H] model simulations archived in the CMIP5 data portal.

Pitts, K.; Nasiri, S. L.; Smith, N.

2013-12-01

342

A Review of Predictability Studies of Atlantic Sector Climate on Decadal Time Scales  

Microsoft Academic Search

This review paper discusses the physical basis and the potential for decadal climate predictability over the Atlantic and its adjacent land areas. Many observational and modeling studies describe pronounced decadal and multidecadal variability in the Atlantic Ocean. However, it still needs to be quantified to which extent the variations in the ocean drive variations in the atmosphere and over land.

M. Latif; M. Collins; H. Pohlmann; N. Keenlyside

2006-01-01

343

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

SciTech Connect

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

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

2012-01-01

344

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

345

Mechanisms for Diurnal Variability of Global Tropical Rainfall Observed from TRMM  

NASA Technical Reports Server (NTRS)

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

Yang, Song; Smith, Eric a.

2006-01-01

346

An Halpha-selected sample of cataclysmic variables -- I. Observations of newly discovered systems  

E-print Network

Strong selection effects are present in observational samples of cataclysmic variables (CVs), complicating comparisons to theoretical predictions. The selection criteria used to define most CV samples discriminate heavily against the discovery of short-period, intrinsically faint systems. The situation can be improved by selecting CVs for the presence of emission lines. For this reason, we have constructed a homogeneous sample of CVs selected on the basis of Halpha emission. We present discovery observations of the 14 CVs and 2 additional CV candidates found in this search. The orbital periods of 11 of the new CVs were measured; all are above 3 h. There are two eclipsing systems in the sample, and one in which we observed a quasi-periodic modulation on a \\sim 1000 s time-scale. We also detect the secondary star in the spectrum of one system, and measure its spectral type. Several of the new CVs have the spectroscopic appearance of nova-like variables (NLs), and a few display what may be SW Sex star behaviour. In a companion paper, we discuss the implications of this new sample for CV evolution.

Magaretha L. Pretorius; Christian Knigge

2008-01-07

347

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

SciTech Connect

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

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

2005-05-13

348

A new observation of acro-cardio-facial syndrome substantiates interindividual clinical variability.  

PubMed

We report on a baby presenting with ectrodactyly, heart defects, and mild facial dysmorphisms, an association recognized as acro-cardio-facial syndrome (ACFS). Based on the first three observations, the acronym CCGE, cleft palate, cardiac defect, genital anomalies, and ectrodactyly had been proposed to embrace the most consistent features of this syndrome. A subsequent report and the present patient point to an obvious interindividual and intrafamilial variability of this autosomal recessive disorder in which ectrodactyly was the sole characteristic shared by all affected individuals. PMID:15937946

Mingarelli, Rita; Zuccarello, Daniela; Digilio, Maria Cristina; Dallapiccola, Bruno

2005-07-01

349

X-ray and optical observations of 2 new cataclysmic variables  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

351

Satellite-observed biological variability in the equatorial Pacific during the 2009-2011 ENSO cycle  

NASA Astrophysics Data System (ADS)

The event of 2009-2011 El Niño Southern Oscillation (ENSO) provides an opportunity to gain insight into the biological variability of the equatorial Pacific Ocean for an entire ENSO cycle with satellite and in situ observations. Even though El Niño and La Niña in general led to respectively weakened and enhanced chlorophyll-a concentration and net primary production (NPP) along the equatorial Pacific Ocean during the 2009-2011 ENSO cycle, biological responses were highly disparate along the equator and attributed to different driving mechanisms. In the eastern equatorial Pacific east of 150°E, the El Niño-La Niña biological change was in general small except for the transition period even though sea surface temperature (SST) showed over ?5 °C drop from El Niño to La Niña. In the central-eastern (170°W-140°W) equatorial Pacific, moderate change of biological activity is attributed to the changes of thermocline driven by the eastward propagating equatorial Kelvin waves and changes of zonal currents and undercurrents. Highest biological response in this ENSO cycle was located in the central (170°E-170°W) and central-western (150°E-170°E) equatorial Pacific with quadruple chlorophyll-a concentration and over ?400 mg C m-2 d-1 increase of NPP from El Niño in 2009 to La Niña in 2010. However, spatial pattern of ENSO biological variability as represented with NPP is not exactly the same as chlorophyll-a variability. Wind-driving mixing of nutrients and eastward advection of the oligotrophic warm pool waters are attributed to this significant biological variability in this region.

Shi, Wei; Wang, Menghua

2014-11-01

352

X-ray variability of NGC 2516 stars in the XMM-Newton observations  

E-print Network

We present the characteristics of the X-ray variability of stars in the cluster NGC2516 as derived from XMM-Newton/EPIC/pn data. The X-ray variations on short (hours), medium (months), and long (years) time scales have been explored. We detected 303 distinct X-ray sources by analysing six EPIC/pn observations; 194 of them are members of the cluster. Stars of all spectral types, from the early-types to the late-M dwarfs, were detected. The Kolmogorov-Smirnov test applied to the X-ray photon time series shows that, on short time scales, only a relatively small fraction (ranging from 6% to 31% for dG and dF, respectively) of the members of NGC2516 are variable with a confidence level $\\geq$99%; however, it is possible that the fraction is small only because of the poor statistics. The time X-ray amplitude distribution functions (XAD) of a set of dF7-dK2 stars, derived on short (hours) and medium (months) time scales, seem to suggest that medium-term variations, if present, have a much smaller amplitude than those on short time scales; a similar result is also obtained for dK3-dM stars. The amplitude variations of late-type stars in NGC2516 are consistent with those of the coeval Pleiades stars. Comparing these data with those of ROSAT/PSPC, collected 7-8 years earlier, and of ROSAT/HRI, just 4-5 years earlier, we find no evidence of significant variability on the related time scales, suggesting that long-term variations due to activity cycles similar to the solar cycle are not common among young stars. Indications of spectral variability was found in one star whose spectra at three epochs were available.

A. Marino; G. Micela; I. Pillitteri; G. Peres

2008-01-15

353

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

E-print Network

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

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

2006-04-29

354

Analysis of variability of TW Hya as observed by MOST and ASAS in 2009  

E-print Network

As a continuation of our previous studies in 2007 and 2008, new photometric observations of the T Tauri star TW Hya obtained by the MOST satellite and the ASAS project over 40 days in 2009 with temporal resolution of 0.2 days are presented. A wavelet analysis of the combined MOST-ASAS data provides a rich picture of coherent, intermittent, variable-period oscillations, similarly as discovered in the 2008 data. The periods (1.3 - 10 days) and systematic period shortening on time scales of weeks can be interpreted within the model of magneto-rotationally controlled accretion processes in the inner accretion disk around the star. Within this model and depending on the assumed visibility of plasma parcels causing the oscillations, the observed shortest-period oscillation period may indicate the stellar rotation period of 1.3 or 2.6 d, synchronized with the disk at 4.5 or 7.1 solar radii, respectively.

Siwak, Michal; Matthews, Jaymie M; Pojmanski, Grzegorz; Kuschnig, Rainer; Guenther, David B; Moffat, Anthony F J; Sasselov, Dimitar; Weiss, Werner W

2010-01-01

355

First XMM-Newton observations of a Cataclysmic Variable I: Timing studies of OY Car  

E-print Network

We present XMM-Newton observations of the eclipsing, disc accreting, cataclysmic variable OY Car which were obtained as part of the performance verification phase of the mission. The star was observed 4 days after an outburst and then again 5 weeks later when it was in a quiescent state. There is a quasi-stable modulation of the X-rays at ~2240 sec, which is most prominent at the lowest energies. We speculate that this may be related to the spin period of the white dwarf. The duration of the eclipse ingress and egress in X-rays is 20--30 sec. This indicates that the bulk of the X-ray emission originates from the boundary layer which has a negligible height above the surface of the white dwarf. The eclipse profile implies a white dwarf of mass M_{1}=0.9-1.1Msun and a secondary star of M_{2}=0.08-0.11Msun.

Gavin Ramsay; Tracey Poole; Keith Mason; France Cordova; William Priedhorsky; Alice Breeveld; Rudi Much; Julian Osborne; Dirk Pandel; Stephen Potter; Jennifer West; Peter Wheatley

2000-10-18

356

UHF Coherent Backscatter Observations of Mid-Latitude Electric Field Structures and Variability  

NASA Astrophysics Data System (ADS)

Mid-latitude ionospheric regions located near the plasmasphere boundary layer (PBL) respond with large spatial and temporal variability to geomagnetic and solar disturbances. In particular, those areas on field lines connected to asymmetric ring currents in the magnetosphere equatorial plane experience large poleward and eastward electric fields during disturbance periods. These fields interact with conductivity gradients in the dusk and evening periods to create large ExB sub-auroral polarization stream (SAPS) flows and steep storm-enhanced density (SED) structures in a complex magnetosphere/ionosphere feedback system. Farley-Buneman two stream irregularities frequently accompany these dynamic conditions, creating coherent wave structures which perturb existing operational systems such as GPS but which can be also exploited for radar remote observations. The Millstone Hill UHF 440 MHz radar, when operated in a high-resolution coherent backscatter mode, is a sensitive diagnostic of these intense electric fields and dramatic variability. We present observations and interpretation of mid-latitude UHF coherent backscatter events at 34 cm wavelength in the L=3.5 to 4 region (55 to 60 degrees invariant latitude) showing a wide range of spatial and temporal variability. Very large electric field gradients of up to 4 mV/m per kilometer and total electric field increases of more than 40-50 mV/m can occur within the 3 to 5 degree wide SAPS region, moving at cross-L-shell velocities of 250-400 m/s. These very narrow sub-auroral ion drift (SAID) configuration structures are superimposed on the main background SAPS velocity channel and have lifetimes as short as 1.5 minutes. We will also illustrate the range of spatial scales seen and discuss their implications for generation of amplitude and phase scintillation disturbances in transiting radio signals.

Erickson, P. J.; Foster, J. C.; Lind, F. D.

2004-12-01

357

SABER Observations of the OH Meinel Airglow Variability Near the Mesopause  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

358

X-ray observations of a large sample of cataclysmic variable stars using the Einstein Observatory  

NASA Technical Reports Server (NTRS)

This paper presents the results of an X-ray survey of 31 known or suspected cataclysmic variables. Eighteen of these close binary systems are detected with inferred luminosities in the 0.1-4.0 keV band of between 10 to the 30th and 10 to the 32nd erg/sec. The majority have relatively hard X-ray spectra (kT greater than 2 keV) irrespective of luminosity state. Of seven dwarf novae observed during optical outbursts only U Gem exhibited enhanced ultrasoft X-ray emission (kT of about 10 eV) in addition to weak, hard X-ray emission. Variability of the X-ray flux is observed in many of these stars, on time-scales ranging from tens of seconds to hours. The contribution to the flux from extended X-ray emission is investigated for SU UMa and GK Per. Several possibilities for the origin of the hard X-rays are considered.

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

1984-01-01

359

Investigating the origins of observed variability of slow slip events with fault slip simulations  

NASA Astrophysics Data System (ADS)

Slow slip events (SSEs) in subduction zones around the world exhibit a wide range of recurrence intervals, durations, and spatial extents. In some regions, most notably Cascadia, distinct along-strike segmentation of these SSE characteristics have been observed. Yet the temporal extent of the SSE record is insufficient to determine whether along-strike variation in segmentation of SSEs persists beyond human time-scales. Here we employ the earthquake simulator RSQSim to model a simple, planar megathrust, which consists of seismogenic, slow slip, and continuous creep sections. The slow slip section is segmented to explore potential causes of along-strike variability in recurrence intervals, durations, and spatial extent, by varying parameters such as the effective normal stress, frictional properties, slip rates, and fault geometry. RSQSim enables simulations of long histories of SSEs over all orders of magnitude to allow for robust characterization of the variation in parameters. Preliminary results suggest even small variations in these parameters have a significant effect on observable characteristics of SSEs, which may illuminate the primary controls on along-strike variability and help establish a framework for understanding SSEs worldwide.

Watkins, W. D.; Colella, H.; Brudzinski, M. R.; Dieterich, J. H.; Richards-Dinger, K. B.

2013-12-01

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

SciTech Connect

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

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

2012-01-01