Hydrogeology of limited aquifer in a granitic terrain     

V. S. Singh  V. Krishnan  M. R. K. Sarma  C. P. Gupta  R. L. Dhar 《Environmental Geology》1999,37(1-2):90-95

 Detailed hydrogeological studies in a granitic micro-watershed have been carried out to determine the extent, behavior, and characteristics of the aquifer. The study includes analysis of lithologs, drill time log, pumping tests, and slug tests. Realistic field conditions have been taken into account for characterizing the aquifer system. Slug tests were carried out to estimate aquifer parameters at the wells which could not sustain pumping. Received: 20 November 1997 · Accepted: 23 February 1998  相似文献   

On the anomalous precipitation enhancement over the Himalayan foothills during monsoon breaks     

Ramesh K. Vellore  R. Krishnan  Jayant Pendharkar  Ayantika Dey Choudhury  T. P. Sabin 《Climate Dynamics》2014,43(7-8):2009-2031

An intriguing feature associated with ‘breaks’ in the Indian summer monsoon is the occurrence of intense/flood-producing precipitation confined to central-eastern parts of the Himalayan (CEH) foothills and north-eastern parts of India. Past studies have documented various large-scale circulation aspects associated with monsoon-breaks, however the dynamical mechanisms responsible for anomalous precipitation enhancement over CEH foothills remain unclear. This problem is investigated using diagnostic analyses of observed and reanalysis products and high-resolution model simulations. The present findings show that the anomalous precipitation enhancement over the CEH foothills during monsoon-breaks emerges as a consequence of interactions between southward intruding mid-latitude westerly troughs and the South Asian monsoon circulation in its weak phase. These interactions facilitate intensification of mid-tropospheric cyclonic vorticity and strong ascending motion over the CEH foothills, so as to promote deep convection and concentrated rainfall activity over the region during monsoon-breaks. Mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the CEH foothills as evidenced from the high-resolution model simulations. It is further noted from the model simulations that the coupling between precipitation and circulation during monsoon-breaks can produce nearly a threefold increase of total precipitation over the CEH foothills and neighborhood as opposed to active-monsoon conditions.  相似文献   

Intraseasonal SST-precipitation relationship and its spatial variability over the tropical summer monsoon region   总被引：1，自引：1，他引：0  

Mathew Roxy  Youichi Tanimoto  B. Preethi  Pascal Terray  R. Krishnan 《Climate Dynamics》2013,41(1):45-61

The SST-precipitation relationship in the intraseasonal variability (ISV) over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 (CFSv2). CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models. The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics. Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales. The response is fast over the Arabian Sea, where precipitation lags SST by ~5 days; whereas it is slow over the Bay of Bengal and South China Sea, with a lag of ~12 days. The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface. However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea. With respect to the observations, the ocean–atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship. A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow (deep) mixed layer enhances (suppress) the amplitude of the intraseasonal SST anomalies, thereby amplifying (lessening) the ISV and the active-break phases of the monsoon in the model.  相似文献   

High resolution simulation of the South Asian monsoon using a variable resolution global climate model   总被引：2，自引：1，他引：1  

T. P Sabin  R. Krishnan  Josefine Ghattas  Sebastien Denvil  Jean-Louis Dufresne  Frederic Hourdin  Terray Pascal 《Climate Dynamics》2013,41(1):173-194

This study examines the feasibility of using a variable resolution global general circulation model (GCM), with telescopic zooming and enhanced resolution (~35 km) over South Asia, to better understand regional aspects of the South Asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation. For this purpose, two sets of ten member realizations are produced with and without zooming using the LMDZ (Laboratoire Meteorologie Dynamique and Z stands for zoom) GCM. The simulations without zoom correspond to a uniform 1° × 1° grid with the same total number of grid points as in the zoom version. So the grid of the zoomed simulations is finer inside the region of interest but coarser outside. The use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields. It is found that the monsoon simulation with high-resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the Western Ghats, the northeastern mountain slopes and northern Bay of Bengal (BOB). A realistic Monsoon Trough (MT) is also noticed in the zoomed simulation, together with remarkable improvements in representing the associated precipitation and circulation features, as well as the large-scale organization of meso-scale convective systems over the MT region. Additionally, a more reasonable simulation of the monsoon synoptic disturbances (lows and disturbances) along the MT is noted in the high-resolution zoomed simulation. On the other hand, the no-zoom version has limitations in capturing the depressions and their movement, so that the MT zone is relatively dry in this case. Overall, the results from this work demonstrate the usefulness of the high-resolution variable resolution LMDZ model in realistically capturing the interactions among the monsoon large-scale dynamics, the synoptic systems and the meso-scale convective systems, which are essential elements of the South Asian monsoon system.  相似文献   

Erratum to: Changes in western disturbances over the Western Himalayas in a warming environment     

R. K. Madhura  R. Krishnan  J. V. Revadekar  M. Mujumdar  B. N. Goswami 《Climate Dynamics》2015,44(3-4):1169-1169

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Predicting sediment transport by interrill overland flow on rough surfaces     

Athol D. Abrahams  Gary Li  Chitra Krishnan  Joseph F. Atkinson 《地球表面变化过程与地形》1998,23(12):1087-1099

Modelling soil erosion requires an equation for predicting the sediment transport capacity by interrill overland flow on rough surfaces. The conventional practice of partitioning total shear stress into grain and form shear stress and predicting transport capacity using grain shear stress lacks rigour and is prone to underestimation. This study therefore explores the possibility that inasmuch as surface roughness affects flow hydraulic variables which, in turn, determine transport capacity, there may be one or more hydraulic variables which capture the effect of surface roughness on transport capacity suffciently well for good predictions of transport capacity to be achieved from data on these variables alone. To investigate this possibility, regression analyses were performed on data from 1506 flume experiments in which discharge, slope, water temperature, rainfall intensity, and roughness size, shape and concentration were varied. The analyses reveal that 89·8 per cent of the variance in transport capacity can be accounted for by excess flow power and flow depth. Including roughness size and concentration in the regression improves that explained variance by only 3·5 per cent. Evidently, flow depth, when used in combination with excess flow power, largely captures the effect of surface roughness on transport capacity. This finding promises to simplify greatly the task of developing a general sediment equation for interrill overland flow on rough surfaces. Copyright © 1998 John Wiley & Sons, Ltd.  相似文献   

Indian Ocean and monsoon coupled interactions in a warming environment   总被引：1，自引：0，他引：1  

Panickal Swapna  R. Krishnan  J. M. Wallace 《Climate Dynamics》2014,42(9-10):2439-2454

Several studies have drawn attention to the steady warming of the equatorial and tropical Indian Ocean (IO) sea surface temperature (SST) observed during recent decades. An intriguing aspect of the IO SST warming trend is that it is has been accompanied by a pronounced weakening of the large-scale boreal summer monsoon circulation. Based on a detailed diagnostic analysis of observed datasets, reanalysis products and IPCC AR4 coupled model output, this study examines how the observed changes in the summer monsoon circulation could have contributed to this SST warming trend. The present results reveal that the weakening trend of the summer monsoon cross-equatorial flow has favored a reorientation of surface westerlies towards the equatorial IO during recent decades, relative to summer monsoons of earlier decades, which were dominated by stronger cross-equatorial flow. Our analysis suggests that the weakening of the summer monsoon cross-equatorial flow has in turn significantly accelerated the SST warming in the central equatorial IO. While the trend in the equatorial westerlies has promoted downwelling and thermocline deepening in the eastern equatorial IO, the central equatorial IO warming is attributed to reduced upwelling in response to a weakening trend of the wind-stress curl. The observed trends in Indian monsoon rainfall and the near-equatorial SST warming are shown to be closely related to variations in the meridional gradient of the monsoon zonal winds. An examination of the twentieth century simulations from 22 IPCC AR4 models, suggests that some models capture the recent equatorial IO warming associated with the weakened summer monsoon circulation reasonably well. The individual member models, however, exhibit significant inter-model variations in representing the observed response of the IO and monsoon coupled system.  相似文献   

Trends and variability of meteorological drought over the districts of India using standardized precipitation index     

P Guhathakurta  Preetha Menon  P M Inkane  Usha Krishnan  S T Sable 《Journal of Earth System Science》2017,126(8):120

Meteorological drought during the southwest monsoon season and for the northeast monsoon season over five meteorological subdivisions of India for the period 1901–2015 has been examined using district and all India standardized precipitation index (SPI). Whenever all India southwest monsoon rainfall was less than ?10% or below normal, for those years all India SPI was found as ?1 or less. Composite analysis of SPI for the below normal years, viz., less than ?15% and ?20% of normal rainfall years indicate that during those years more than 30% of country’s area was under drought condition, whenever all India southwest monsoon rainfall was –15% or less than normal. Trend analysis of monthly SPI for the monsoon months identified the districts experiencing significant increase in drought occurrences. Significant positive correlation has been found with the meteorological drought over most of the districts of central, northern and peninsular India, while negative correlation was seen over the districts of eastern India with NINO 3.4 SST. For the first time, meteorological drought analysis over districts and its association with equatorial pacific SST and probability analysis has been done for the northeast monsoon over the affected regions of south peninsular India. Temporal correlation of all India southwest monsoon SPI and south peninsular India northeast monsoon SPI has been done with the global SST to identify the teleconnection of drought in India with global parameters.  相似文献   

High resolution facies record on late Holocene flood plain sediments from lower reaches of Narmada Valley,Western India     

Prabhin Sukumaran  Dhananjay A. Sant  K. Krishnan  Govindan Rangarajan 《Journal of the Geological Society of India》2012,79(1):41-52

A high resolution quantitative granulometric record for site Uchediya [21°43′2.22″ N, 73° 6′26.22″ E; 10 m a. s. l.] gives understanding towards accretion history of the late Holocene flood plain in the lower reaches of Narmada River. Two sediment facies (sandy and muddy) and seven subfacies (sandy subfacies: St_MS+FS+CS, Sm_FS+MS, Sl_FS+VFS, and St_{MS + CS}; muddy subfacies: Fm_SILT+VFS+FS, Fm_SILT+VFS (O) and Fm_SILT+VFS (T)) are identified based on cluster analysis supplemented with sedimentary structures observed in field and other laboratory data. Changes in hydrodynamics are further deduced based on various sedimentological parameters and their ratios leading to arrive at a depositional model.  相似文献   

Late holocene storm records from lower reaches of Narmada valley,Western India     

Prabhin Sukumaran  C. Rajshekhar  Dhananjay A. Sant  K. Krishnan 《Journal of the Geological Society of India》2012,80(3):403-408

Storms from the Arabian Sea are the most significant meteorological feature in western India that brings extreme rainy days together with catastrophic flooding. The present study reports two such palaeo-storm horizons at 1.16 m and 3.2 m above the present day water level in the Narmada channel, 56 km inland based on sedimentology and foraminiferal records. Both the horizons show similar sediment facies and foraminiferal assemblage. The present findings instigate to look for such new sites and build palaeo-storm records for western India.  相似文献