Evaluating regional climate models for simulating sub-daily rainfall extremes     

Virginia Edith Cortés-Hernández  Feifei Zheng  Jason Evans  Martin Lambert  Ashish Sharma  Seth Westra 《Climate Dynamics》2016,47(5-6):1613-1628

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Origin of Ti-rich garnets in the groundmass of Wajrakarur field kimberlites,southern India: insights from EPMA and Raman spectroscopy     

Ashish N. Dongre  K. S. Viljoen  N. V. Chalapathi Rao  A. Gucsik 《Mineralogy and Petrology》2016,110(2-3):295-307

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Evaluation of the SWAT model for water balance study of a mountainous snowfed river basin of Nepal     

Birsingh Dhami  Sushil Kumar Himanshu  Ashish Pandey  Amar Kant Gautam 《Environmental Earth Sciences》2018,77(1):21

In this study, a semi-distributed hydrologic model Soil and Water Assessment Tool (SWAT) has been employed for the Karnali River basin, Nepal to test its applicability for hydrological simulation. Further, model was evaluated to carry out the water balance study of the basin and to determine the snowmelt contribution in the river flow. Snowmelt Runoff Model (SRM) was also used to compare the snowmelt runoff simulated from the SWAT model. The statistical results show that performance of the SWAT model in the Karnali River basin is quite good (p-factor = 0.88 and 0.88, for daily calibration and validation, respectively; r-factor = 0.76 and 0.71, for daily calibration and validation, respectively). Baseflow alpha factor (ALPHA_BF) was found most sensitive parameter for the flow simulation. The study revealed that the average annual runoff volume available at the basin outlet is about 47.16 billion cubic metre out of which about 12% of runoff volume is contributed by the snowmelt runoff. About 25% of annual precipitation seems to be lost as evapotranspiration. The results revealed that both the models, SWAT and SRM, can be efficiently applied in the mountainous river basins of Nepal for planning and management of water resources.  相似文献   

Why is Indian Ocean warming consistently?     

Suryachandra A. Rao  Ashish R. Dhakate  Subodh K. Saha  Somnath Mahapatra  Hemantkumar S. Chaudhari  Samir Pokhrel  Sobhan K. Sahu 《Climatic change》2012,110(3-4):709-719

Observations have shown that the Indian Ocean is consistently warming and its warm pool is expanding, particularly in the recent decades. This paper attempts to investigate the reason behind these observations. Under global warming scenario, it is expected that the greenhouse gas induced changes in air–sea fluxes will enhance the warming. Surprisingly, it is found that the net surface heat fluxes over Indian Ocean warm pool (IOWP) region alone cannot explain the consistent warming. The warm pool area anomaly of IOWP is strongly correlated with the sea surface height anomaly, suggesting an important role played by the ocean advection processes in warming and expansion of IOWP. The structure of lead/lag correlations further suggests that Oceanic Rossby waves might be involved in the warming. Using heat budget analysis of several Ocean data assimilation products, it is shown that the net surface heat flux (advection) alone tends to cool (warm) the Ocean. Based on above observations, we propose an ocean-atmosphere coupled positive feedback mechanism for explaining the consistent warming and expansion of IOWP. Warming over IOWP induces an enhancement of convection in central equatorial Indian ocean, which causes anomalous easterlies along the equator. Anomalous easterlies in turn excite frequent Indian ocean Dipole events and cause anti-cyclonic wind stress curl in south-east and north-east equatorial Indian ocean. The anomalous wind stress curl triggers anomalous downwelling oceanic Rossby waves, thereby deepening the thermocline and resulting in advection of warm waters towards western Indian ocean. This acts as a positive feedback and results in more warming and westward expansion of IOWP.  相似文献   

The hemispheric asymmetry of solar activity during the last century and the solar dynamo     

Ashish Goel Arnab Rai Choudhuri 《中国天文和天体物理学报》2009,9(1)

We believe the Babcock-Leighton process of poloidal field generation to be the main source of irregularity in the solar cycle. The random nature of this process may make the poloidal field in one hemisphere stronger than that in the other hemisphere at the end of a cycle. We expect this to induce an asymmetry in the next sunspot cycle. We look for evidence of this in the observational data and then model it theoretically with our dynamo code. Since actual polar field measurements exist only from the 1970s, we use the polar faculae number data recorded by Sheeley (1991, 2008) as a proxy of the polar field and estimate the hemispheric asymmetry of the polar field in different solar minima during the major part of the twentieth century. This asymmetry is found to have a reasonable correlation with the asymmetry of the next cycle. We then run our dynamo code by feeding information about this asymmetry at the successive minima and compare the results with observational data. We find that the theoretically computed asymmetries of different cycles compare favorably with the observational data, with the correlation co-efficient being 0.73. Due to the coupling between the two hemispheres, any hemispheric asymmetry tends to get attenuated with time. The hemispheric asymmetry of a cycle ei-ther from observational data or from theoretical calculations statistically tends to be less than the asymmetry in the polar field (as inferred from the faculae data) in the preceding minimum. This reduction factor turns out to be 0.43 and 0.51 respectively in observational data and theoretical simulations.  相似文献   

Oxygen and carbon stable isotope studies onGloborotalia menardii from Pleistocene DSDP Cores in northern Indian Ocean and their paleoclimatic and paleoceanographic implications     

Ashish Sarkar  Asit K Guha  Supriyo Chakraborty 《Journal of Earth System Science》1996,105(2):119-129

Stable isotope ratios of oxygen (δ¹⁸O) and carbon (δ¹³C) in tests ofGloborotalia menardii from samples at 25 cm intervals of top 900 cm cores, representing different thicknesses of the Pleistocene, from DSDP Sites 219, 220 and 241 in the northern Indian Ocean have been measured. Based on the δ¹⁸O stratigraphy, glacial and interglacial phases during the Pleistocene have been recognized, which are in good agreement with the standard Quaternary planktonic foraminiferal/climatic zones i.e., Ericson zones at these sites, based onG. menardii abundances. The GIA (glacial interglacial amplitude) at Sites 241, 219 and 220 are of the order of 1·2, 1·4 and 1·9‰ respectively. The last glacial and interglacial maxima (18 ka BP and 125 ka BP respectively) could be identified in DSDP Cores 241, and 219 with some precision. ‘Isotopic ages’ could be assigned to the different levels of these core sections based on the correlation of δ¹⁸O record from these sites with the SPECMAP record (Imbrieet al 1984). Changes in sediment accumulation rates at different levels of the Pleistocene have been worked out on the basis of changes in oxygen isotopic ratio. Oscillations in δ¹³C stratigraphy at Site 241 indicated southwest monsoon induced increase in upwelling and productivity during warmer periods. At Sites 219 and 220, variations in the δ¹³C record were due to the mixing of bottom water.  相似文献   

Growth and water relation parameters in drought-stressed Coriaria nepalensis seedlings     

Kiran Bargali  Ashish Tewari 《Journal of Arid Environments》2004,58(4):1593

In the present study, growth and water relation parameters were analysed in drought-stressed Coriaria nepalensis Wall. seedlings. C. nepalensis seedlings were subjected to four drought cycles of 7, 14, 21, and 28-days, and to one control level (watered on alternate days) in a glasshouse. The seedlings failed to survive a 28-days drought during summer. Osmotic adjustment (defined as the decrease in osmotic potential at zero or full turgor in response to water deficit) was measured as the difference between the osmotic potential of seedlings watered on alternate days (control) and those subjected to 21-days drought cycle. Seedlings subjected to 21-days drought had a predawn water potential of −2.60 MPa, and showed an osmotic adjustment of −1.95 MPa at full turgor and −2.17 MPa at zero turgor. The growth of seedlings was positively related to moisture and with water potential. With decline in soil moisture the root:shoot ratio increased while leaf weight ratio decreased. Leaf characteristics, such as leaf number, leaf area, leaf area ratio, specific leaf area and leaf drop, were also affected by moisture stress. This study has indicated that osmotic adjustment is a major adaptive mechanism of C. nepalensis that aids successful regeneration of seedlings in degraded sites with inhospitable soil conditions.  相似文献   

The effect of inertial coupling on seismic reflection amplitudes     

Ashish Arora  S.K. Tomar 《Geophysical Prospecting》2008,56(5):643-654

A problem of reflection and transmission of elastic waves at a plane interface between a uniform elastic solid half-space and a porous elastic half-space containing two immiscible fluids is investigated. The theory developed by Lo, Sposito and Majer for porous media containing two immiscible fluids is employed to find out the reflection and transmission coefficients. The incident wave is assumed to propagate through the uniform elastic half-space and two cases are considered. In the first case, a beam of plane longitudinal wave is assumed to be incident and in the second case, a beam of transverse wave is assumed to be incident at the interface. By taking granite as impervious elastic medium and columbia fine sandy loam containing air-water mixture as porous medium, reflection and transmission coefficients are obtained. By neglecting the inertial coupling coefficients, these coefficients are reduced to those obtained by Tomar and Arora using the theory of Tuncay and Corapcioglu. It is found that the inertial coupling parameters significantly affect the phase speeds and the amplitude ratios of the transmitted waves.  相似文献   

Potential of support vector regression for prediction of monthly streamflow using endogenous property   总被引：2，自引：0，他引：2  

Rajib Maity  Parag P. Bhagwat  Ashish Bhatnagar 《水文研究》2010,24(7):917-923

In the recent past, a variety of statistical and other modelling approaches have been developed to capture the properties of hydrological time series for their reliable prediction. However, the extent of complexity hinders the applicability of such traditional models in many cases. Kernel‐based machine learning approaches have been found to be more popular due to their inherent advantages over traditional modelling techniques including artificial neural networks(ANNs ). In this paper, a kernel‐based learning approach is investigated for its suitability to capture the monthly variation of streamflow time series. Its performance is compared with that of the traditional approaches. Support vector machines (SVMs) are one such kernel‐based algorithm that has given promising results in hydrology and associated areas. In this paper, the application of SVMs to regression problems, known as support vector regression (SVR), is presented to predict the monthly streamflow of the Mahanadi River in the state of Orissa, India. The results obtained are compared against the results derived from the traditional Box–Jenkins approach. While the correlation coefficient between the observed and predicted streamflows was found to be 0·77 in case of SVR, the same for different auto‐regressive integrated moving average (ARIMA) models ranges between 0·67 and 0·69. The superiority of SVR as compared to traditional Box‐Jenkins approach is also explained through the feature space representation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Relativistic static spheres filled with infinitely conducting charged fluids     

G. G. Asgekar  S. M. Aherkar 《Astrophysics and Space Science》1992,190(2):191-196

A class of spherically-symmetric cosmological models for space-time filled with infinitely conducting relativistic perfect fluids with constant magnetic permeability is developed for a specified choice of matter density and fluid pressure. Some salient features of all these solutions are discussed.  相似文献