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   

Influence of coronal mass ejection on geomagnetic activity during 1988–1993     

Shrivastava  Pankaj Kumar  Singh  G. N. 《Earth, Moon, and Planets》2002,91(1):1-8

The most rapid and dramatic evolution in the solar corona occurs in events now known as Coronal Mass Ejections (CMEs). There have considerable importance for our understanding of the evolution of the mass and energy injected into the interplanetary medium. In this work, we have studied the relation of CMEs with geomagnetic activity for the period of 1988 to 1993. Not all CMEs are capable of producing geomagnetic disturbances. Our study indicates that the maximum chance of a geomagnetic disturbance occurs two to three days after a CME in association with B-type solar flares.  相似文献   

Fast versus slow response in climate change: implications for the global hydrological cycle   总被引：3，自引：2，他引：1  

Govindasamy Bala  K. Caldeira  R. Nemani 《Climate Dynamics》2010,35(2-3):423-434

Recent studies have shown that changes in global mean precipitation are larger for solar forcing than for CO₂ forcing of similar magnitude. In this paper, we use an atmospheric general circulation model to show that the differences originate from differing fast responses of the climate system. We estimate the adjusted radiative forcing and fast response using Hansen’s “fixed-SST forcing” method. Total climate system response is calculated using mixed layer simulations using the same model. Our analysis shows that the fast response is almost 40% of the total response for few key variables like precipitation and evaporation. We further demonstrate that the hydrologic sensitivity, defined as the change in global mean precipitation per unit warming, is the same for the two forcings when the fast responses are excluded from the definition of hydrologic sensitivity, suggesting that the slow response (feedback) of the hydrological cycle is independent of the forcing mechanism. Based on our results, we recommend that the fast and slow response be compared separately in multi-model intercomparisons to discover and understand robust responses in hydrologic cycle. The significance of this study to geoengineering is discussed.  相似文献   

The effect of horizontal resolution on simulation of very extreme US precipitation events in a global atmosphere model   总被引：1，自引：0，他引：1  

Michael F. Wehner  Richard L. Smith  G. Bala  Phillip Duffy 《Climate Dynamics》2010,34(2-3):241-247

We investigate the ability of a global atmospheric general circulation model (AGCM) to reproduce observed 20 year return values of the annual maximum daily precipitation totals over the continental United States as a function of horizontal resolution. We find that at the high resolutions enabled by contemporary supercomputers, the AGCM can produce values of comparable magnitude to high quality observations. However, at the resolutions typical of the coupled general circulation models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, the precipitation return values are severely underestimated.  相似文献   

High-resolution climate simulation of the last glacial maximum     

Seong-Joong Kim  Thomas J. Crowley  David J. Erickson  Bala Govindasamy  Phillip B. Duffy  Bang Yong Lee 《Climate Dynamics》2008,31(1):1-16

The climate of the last glacial maximum (LGM) is simulated with a high-resolution atmospheric general circulation model, the NCAR CCM3 at spectral truncation of T170, corresponding to a grid cell size of roughly 75 km. The purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography. The LGM simulations were forced with modified CLIMAP sea ice distribution and sea surface temperatures (SST) reduced by 1°C, ice sheet topography, reduced CO₂, and 21,000 BP orbital parameters. The high-resolution model captures modern climate reasonably well, in particular the distribution of heavy precipitation in the tropical Pacific. For the ice age case, surface temperature simulated by the high-resolution model agrees better with those of proxy estimates than does the low-resolution model. Despite the fact that tropical SSTs were only 2.1°C less than the control run, there are many lowland tropical land areas 4–6°C colder than present. Comparison of T170 model results with the best constrained proxy temperature estimates (noble gas concentrations in groundwater) now yield no significant differences between model and observations. There are also significant upland temperature changes in the best resolved tropical mountain belt (the Andes). We provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells. A longstanding model-data discrepancy therefore appears to be resolved without invoking any unusual model physics. The response of the Asian summer monsoon can also be more clearly linked to local geography in the high-resolution model than in the low-resolution model; this distinction should enable more confident validation of climate proxy data with the high-resolution model. Elsewhere, an inferred salinity increase in the subtropical North Atlantic may have significant implications for ocean circulation changes during the LGM. A large part of the Amazon and Congo Basins are simulated to be substantially drier in the ice age—consistent with many (but not all) paleo data. These results suggest that there are considerable benefits derived from high-resolution model regarding regional climate responses, and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent.  相似文献   

On out of plane equilibrium points in photo-gravitational restricted three-body problem     

M. K. Das  Pankaj Narang  S. Mahajan  M. Yuasa 《Journal of Astrophysics and Astronomy》2009,30(3-4):177-185

We have investigated the out of plane equilibrium points of a passive micron size particle and their stability in the field of radiating binary stellar systems Krüger-60, RW-Monocerotis within the framework of photo-gravitational circular restricted three-body problem. We find that the out of plane equilibrium points (L _i , i = 6, 7, 8, 9) may exist for range of β ₁ (ratio of radiation to gravitational force of the massive component) values for these binary systems in the presence of Poynting-Robertson drag (hereafter PR-drag). In the absence of PR-drag, we find that the motion of a particle near the equilibrium points L _6,7 is stable in both the binary systems for a specific range of β ₁ values. The PR-drag is shown to cause instability of the various out of plane equilibrium points in these binary systems.  相似文献   

Testing isotropy of cosmic microwave background radiation     

Pramoda Kumar Samal  Rajib Saha  Pankaj Jain  John P. Ralston 《Monthly notices of the Royal Astronomical Society》2008,385(4):1718-1728

We introduce new symmetry-based methods to test for isotropy in cosmic microwave background (CMB) radiation. Each angular multipole is factored into unique products of power eigenvectors, related multipoles and singular values that provide two new rotationally invariant measures mode by mode. The power entropy and directional entropy are new tests of randomness that are independent of the usual CMB power. Simulated Galactic plane contamination is readily identified. The ILC– WMAP data maps show seven axes well aligned with one another and the direction Virgo. Parameter free statistics find 12 independent cases of extraordinary axial alignment, low power entropy, or both having 5 per cent probability or lower in an isotropic distribution. Isotropy of the ILC maps is ruled out to confidence levels of better than 99.9 per cent, whether or not coincidences with other puzzles coming from the Virgo axis are included. Our work shows that anisotropy is not confined to the low l region, but extends over a much larger l range.  相似文献   

Late Cambrian microbial build-ups,Llano Area,Central Texas: A three-phase morphological evolution     

Pankaj Khanna  Heath H. Hopson  André W. Droxler  Dylan A. Droxler  Daniel Lehrmann  Brian Kubik  Jacob Proctor  Pulkit Singh  Paul M. Harris 《Sedimentology》2020,67(2):1135-1160

Although Late Cambrian microbial build-ups were recognized in the Point Peak Member of the Wilberns Formation in Central Texas (USA) nearly 70 years ago, only a few studies focused specifically on the build-ups themselves. This study focuses on the interpretation of the regional (15 measured sections described in literature representing an area of 8000 km²) and local (field and drone photogrammetry studies in a 25 km² area from within south Mason County) microbial build-up occurrence, describes their growth phases and details their interactions with the surrounding inter-build-up sediments. The study establishes the occurrence of microbial build-ups in the lower and upper Point Peak members (the Point Peak Member is informally broken up into the lower Point Peak and the upper Point Peak members separated by Plectotrophia zone). The lower Point Peak Member consists of three <1 m thick microbial bioherms and biostrome units, in addition to heterolithic and skeletal/ooid grainstone and packstone beds. One, up to 14 m thick, microbial unit associated with inter-build-up skeletal and ooid grainstone and packstone beds, intercalated with mixed siliciclastic–carbonate silt beds, characterizes the upper Point Peak member. The microbial unit in the upper Point Peak member displays a three-phase growth evolution, from an initial colonization phase on flat based, rip-up clast lenses, to a second aggradation and lateral expansion phase, into a third well-defined capping phase. The ultimate demise of the microbial build-ups is interpreted to have been triggered by an increase of water turbidity caused by a sudden influx of fine siliciclastics. The lower Point Peak member represents inner ramp shallow subtidal and intertidal facies and the upper Point Peak member corresponds to mid-outer ramp subtidal facies. Understanding the morphological architecture and depositional context of these features is of importance for identifying signatures of early life on Earth.  相似文献   

Multi isotopic approach to study temporal variation of groundwater quality in coastal aquifer of Saijo plain, Shikoku Island, Japan     

Pankaj Kumar 《Water Resources》2012,39(5):601-609

In order to delineate geochemical processes and its relation with groundwater quality evolution, hydrochemical and isotopic analysis were carried out in coastal groundwater of Saijo plain, western Japan. From analytical results, even within a small distance from the coast; ionic concentration of water samples varies a lot which infers non-homogenous and patchy distribution of different aquifer system (complex geology). From stable isotopic results, it was found that most of sample points plotted near the local meteoric water line (LMWL) i.e. origin of ground water is meteoric in principle; however point away from the LMWL might favors exchange with rock minerals.  相似文献   

Measurement of radon exhalation rate in various building materials and soil samples     

Pankaj Bala  Vinod Kumar  Rohit Mehra 《Journal of Earth System Science》2017,126(2):31

Indoor radon is considered as one of the potential dangerous radioactive elements. Common building materials and soil are the major source of this radon gas in the indoor environment. In the present study, the measurement of radon exhalation rate in the soil and building material samples of Una and Hamirpur districts of Himachal Pradesh has been done with solid state alpha track detectors, LR-115 type-II plastic track detectors. The radon exhalation rate for the soil samples varies from 39.1 to 91.2 mBq kg^?1 h^?1 with a mean value 59.7 mBq kg^?1 h^?1. Also the radium concentration of the studied area is found and it varies from 30.6 to 51.9 Bq kg^?1 with a mean value 41.6 Bq kg^?1. The exhalation rate for the building material samples varies from 40.72 (sandstone) to 81.40 mBq kg^?1 h^?1 (granite) with a mean value of 59.94 mBq kg^?1 h^?1.  相似文献