Glacial mass balance changes in the Karakoram and Himalaya based on CMIP5 multi-model climate projections   总被引：1，自引：0，他引：1  

Rajiv K. Chaturvedi  Anil Kulkarni  Yogesh Karyakarte  Jaideep Joshi  G. Bala 《Climatic change》2014,123(2):315-328

The impact of future climate change on the glaciers in the Karakoram and Himalaya (KH) is investigated using CMIP5 multi-model temperature and precipitation projections, and a relationship between glacial accumulation-area ratio and mass balance developed for the region based on the last 30 to 40 years of observational data. We estimate that the current glacial mass balance (year 2000) for the entire KH region is -6.6?±?1 Gta^?1, which decreases about sixfold to -35?±?2 Gta^?1 by the 2080s under the high emission scenario of RCP8.5. However, under the low emission scenario of RCP2.6 the glacial mass loss only doubles to -12?±?2 Gta^?1 by the 2080s. We also find that 10.6 and 27 % of the glaciers could face ‘eventual disappearance’ by the end of the century under RCP2.6 and RCP8.5 respectively, underscoring the threat to water resources under high emission scenarios.  相似文献   

Transport of Crustacean Larvae Between a Low-Inflow Estuary and Coastal Waters     

Steven G. Morgan  Jennifer L. Fisher  Skyli T. McAfee  John L. Largier  Seth H. Miller  Megan M. Sheridan  Joseph E. Neigel 《Estuaries and Coasts》2014,37(5):1269-1283

The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast.  相似文献   

Early In-orbit Performance of Scanning Sky Monitor Onboard AstroSat     

M. C. Ramadevi  B. T. Ravishankar  N. Sitaramamurthy  G. Meena  Brajpal Singh  Anand Jain  Reena Yadav  Anil Agarwal  V. Chandra Babu  Kumar  Ankur Kushwaha  S. Vaishali  Nirmal Kumar Iyer  Anuj Nandi  Girish V.  Vivek Kumar Agarwal  S. Seetha  Dipankar Bhattacharya  K. Balaji  Manoj Kumar  Prashanth Kulshresta 《Journal of Astrophysics and Astronomy》2017,38(2):32

We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ \(\times \) 2.5\(^\circ \) and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.  相似文献   

A Long-Term Decrease of the Mid-Size Segmentation Lengths Observed in the He <Emphasis Type="SmallCaps">ii</Emphasis> (30.4 nm) Solar EUV Emission     

Leonid Didkovsky  Seth Wieman  Elena Korogodina 《Solar physics》2017,292(2):32

Power spectra of segmentation-cell length (a dominant length scale of EUV emission in the transition region) from full-disk He?ii extreme ultraviolet (EUV) images observed by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during periods of quiet-Sun conditions for a time interval from 1996 to 2015 were analyzed. The spatial power as a function of the spatial frequency from about 0.04 to 0.27 (EIT) or up to 0.48 (AIA) Mm^?1 depends on the distribution of the observed segmentation-cell dimensions – a structure of the solar EUV network. The temporal variations of the spatial power reported by Didkovsky and Gurman (Solar Phys. 289, 153, 2014) were suggested as decreases at the mid-spatial frequencies for the compared spectra when the power curves at the highest spatial frequencies of 0.5 pix^?1 were adjusted to match each other. This approach has been extended in this work to compare spectral ratios at high spatial frequencies expressed in the solar spatial frequency units of Mm^?1. A model of EIT and AIA spatial responses allowed us to directly compare spatial spectral ratios at high spatial frequencies for five years of joint operation of EIT and AIA, from 2010 to 2015. Based on this approach, we represent these ratio changes as a long-term network transformation that may be interpreted as a continuous dissipation of mid-size network structures to the smaller-size structures in the transition region. In contrast to expected cycling of the segmentation-cell dimension structures and associated spatial power in the spectra with the solar cycle, the spectra demonstrate a significant and steady change of the EUV network. The temporal trend across these structural spectra is not critically sensitive to any long-term instrumental changes, e.g. degradation of sensitivity, but to the change of the segmentation-cell dimensions of the EUV network structure.  相似文献   

Forbush Decrease: A New Perspective with Classification     

Anil Raghav  Zubair Shaikh  Ankush Bhaskar  Gauri Datar  Geeta Vichare 《Solar physics》2017,292(8):99

Sudden short-duration decreases in cosmic ray flux, known as Forbush decreases (FDs), are mainly caused by interplanetary disturbances. A generally accepted view is that the first step of an FD is caused by a shock sheath and the second step is due to the magnetic cloud (MC) of the interplanetary coronal mass ejection (ICME). This simplistic picture does not consider several physical aspects, such as whether the complete shock sheath or MC (or only part of these) contributes to the decrease or the effect of internal structure within the shock-sheath region or MC. We present an analysis of 16 large (\({\geq}\,8 \%\)) FD events and the associated ICMEs, a majority of which show multiple steps in the FD profile. We propose a reclassification of FD events according to the number of steps observed in their respective profiles and according to the physical origin of these steps. This study determines that 13 out of 16 major events (\({\sim}\,81\%\)) can be explained completely or partially on the basis of the classic FD model. However, it cannot explain all the steps observed in these events. Our analysis clearly indicates that not only broad regions (shock sheath and MC), but also localized structures within the shock sheath and MC have a significant role in influencing the FD profile. The detailed analysis in the present work is expected to contribute toward a better understanding of the relationship between FD and ICME parameters.  相似文献   

Some Bianchi-type cosmological models in a new scalar-tensor theory     

T. Singh  Anil Kumar Agrawal 《Astrophysics and Space Science》1991,182(2):289-312

Bianchi type I, III, V, VI₀, and Kantowski-Sachs type models have been investigated in a scalar tensor theory developed by Saez and Ballester (1985) and Saez (1985). The dynamical behaviour of the models has also been analyzed.  相似文献   

Anoxia over the western continental shelf of India: bacterial indications of intrinsic nitrification feeding denitrification     

Krishnan KP  Fernandes SO  Loka Bharathi PA  Krishna Kumari L  Nair S  Pratihary AK  Rao BR 《Marine environmental research》2008,65(5):445-455

Studies on the Arabian Sea coastal anoxia have been of immense interest, but despite its ecological significance there is sparse understanding of the microbes involved. Hence, observations were carried out off Goa (15 degrees 30'N, 72 degrees 40'E to 15 degrees 30'N, 72 degrees 59'E) to understand the processes that mediate the changes in various inorganic nitrogen species in the water column during anoxia. Water column chemistry showed a clear distinct oxic environment in the month of April and anoxic condition in October. Our study based on microbial signatures indicated that oxygen deficit appeared as a well-defined nucleus almost 40 km away from the coast during the oxic period (April) and spreads there after to the entire water column synchronizing with the water chemistry. Striking results of net changes in inorganic nitrogen species in nitrification blocked and unblocked experimental systems show that denitrification is the predominant process in the water column consuming available nitrate ( approximately 0.5 microM) to near zero levels within approximately 72 h of incubation. These observations have been supported by concomitant increase in nitrite concentration ( approximately 4 microM). Similar studies on denitrification-blocked incubations, demonstrate the potential of nitrification to feed denitrification. Nitrification could contribute almost 4.5 microM to the total nitrate pool. It was found that the relation between ammonium and total dissolved inorganic nitrogen (DIN) pool (r=0.98, p<0.001, n=122) was significant compared to the latter with nitrite and nitrate. The occurrence of high ammonium under low phosphate conditions corroborates our observations that ammonium does not appear to be locked under low oxygen regimes. It is suggested that ammonium actively produced by detrital breakdown (ammonification) is efficiently consumed through nitrification process. The three processes in concert viz. ammonification, nitrification and denitrification appear to operate in more temporal and spatial proximity than hitherto appreciated in these systems and this gives additional cues on the absence of measurable nitrate at surface waters, which was earlier attributed only to efficient algal uptake. Hence we hypothesize that the alarming nitrous oxide input into the atmosphere could be due to high productivity driven tighter nitrification-denitrification coupling, rather than denitrification driven by extraneous nitrate.  相似文献   

GPS for real-time earthquake source determination and tsunami warning systems   总被引：1，自引：0，他引：1  

Geoffrey Blewitt  William C. Hammond  Corné Kreemer  Hans-Peter Plag  Seth Stein  Emile Okal 《Journal of Geodesy》2009,83(3-4):335-343

We identify the key design aspects of a GPS-based system (and in the future, GNSS-based systems) that could contribute to real-time earthquake source determination and tsunami warning systems. Our approach is based on models of both transient and permanent displacement of GPS stations caused by large earthquakes, while considering the effect of GPS errors on inverted earthquake source parameters. Our main conclusions are that (1) the spatial pattern, magnitude, and timing of permanent displacement of GPS stations can be inverted for the earthquake source and so predict the 3D displacement field of the ocean bottom, thus providing the initial conditions for tsunami models, and (2) there are no inherently limiting factors arising from real-time orbit and positioning errors, provided sufficient near-field GPS stations are deployed. This signal could be readily exploited by GPS networks currently in place, and will be facilitated by the IGS Real-Time Project as it comes to fruition.  相似文献   

Star formation and feedback in smoothed particle hydrodynamic simulations – I. Isolated galaxies     

Greg Stinson  Anil Seth  Neal Katz  James Wadsley  Fabio Governato  Tom Quinn 《Monthly notices of the Royal Astronomical Society》2006,373(3):1074-1090

  相似文献   

Resolving mechanisms of toxicity while pursuing ecotoxicological relevance?     

Hinton DE  Kullman SW  Hardman RC  Volz DC  Chen PJ  Carney M  Bencic DC 《Marine pollution bulletin》2005,51(8-12):635-648

In this age of modern biology, aquatic toxicological research has pursued mechanisms of action of toxicants. This has provided potential tools for ecotoxicologic investigations. However, problems of biocomplexity and issues at higher levels of biological organization remain a challenge. In the 1980s and 1990s and continuing to a lesser extent today, organisms residing in highly contaminated field sites or exposed in the laboratory to calibrated concentrations of individual compounds were carefully analyzed for their responses to priority pollutants. Correlation of biochemical and structural analyses in cultured cells and tissues, as well as the in vivo exposures led to the production and application of biomarkers of exposure and effect and to our awareness of genotoxicity and its chronic manifestations, such as neoplasms, in wild fishes. To gain acceptance of these findings in the greater environmental toxicology community, “validation of the model” versus other, better-established often rodent models, was necessary and became a major focus. Resultant biomarkers were applied to heavily contaminated and reference field sites as part of effects assessment and with investigations following large-scale disasters such as oil spills or industrial accidents.

Over the past 15 years, in the laboratory, small aquarium fish models such as medaka (Oryzias latipes), zebrafish (Danio rerio), platyfish (Xiphophorus species), fathead minnow (Pimephales promelas), and sheepshead minnow (Cyprinodon variegatus) were increasingly used establishing mechanisms of toxicants. Today, the same organisms provide reliable information at higher levels of biological organization relevant to ecotoxicology. We review studies resolving mechanisms of toxicity and discuss ways to address biocomplexity, mixtures of contaminants, and the need to relate individual level responses to populations and communities.  相似文献