Local onset and demise of the Indian summer monsoon     

Misra  Vasubandhu  Bhardwaj  Amit  Mishra  Akhilesh 《Climate Dynamics》2018,51(5-6):1609-1622

This paper introduces an objective definition of local onset and demise of the Indian summer monsoon (ISM) at the native grid of the Indian Meteorological Department’s rainfall analysis based on more than 100 years of rain gauge observations. The variability of the local onset/demise of the ISM is shown to be closely associated with the All India averaged rainfall onset/demise. This association is consistent with the corresponding evolution of the slow large-scale reversals of upper air and ocean variables that raise the hope of predictability of local onset and demise of the ISM. The local onset/demise of the ISM also show robust internannual variations associated with El Nino and the Southern Oscillation and Indian Ocean dipole mode. It is also shown that the early monsoon rains over northeast India has a predictive potential for the following seasonal anomalies of rainfall and seasonal length of the monsoon over rest of India.

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Delineation of ground water potential zones in a hard Rock Terrain of Bargarh District, Orissa using IRS data     

Pankaj K Srivastava  Amit K Bhattacharya 《Journal of the Indian Society of Remote Sensing》2000,28(2-3):129-140

In the present paper, various groundwater potential zones for the assessment of groundwater availability in a hard rock terrain have been delineated with the help of hydrogeological parameters using satellite IRS- 1B-LISS-II digital data. Area selected for this study is a part of Bargarh district, Orissa, India covering an area of about 680 square km. Satellite data has been used to prepare geological-cum-lineaments, geomorphological, landuse and drainage maps. The various thematic maps have been integrated with the help of Geographic Information System to demarcate the poor to excellent groundwater potential zones. Weightage has been given to various groundwater controlling factors to the total groundwater potential in each segment of study area. Subsequently, several sites were selected and pumping tests carded out in the area. The results show that among others, lineaments as well as drainage density are the most important contributory factors in the groundwater potential of various geomorphic units in the area of investigation.  相似文献   

Linking frequency of rainstorms,runoff generation and sediment transport across hyperarid talus-pediment slopes     

Yuval Shmilovitz  Efrat Morin  Yair Rinat  Itai Haviv  Genadi Carmi  Amit Mushkin  Yehouda Enzel 《地球表面变化过程与地形》2020,45(7):1644-1659

Documenting hillslope response to hydroclimatic forcing is crucial to our understanding of landscape evolution. The evolution of talus-pediment sequences (talus flatirons) in arid areas was often linked to climatic cycles, although the physical processes that may account for such a link remain obscure. Our approach is to integrate field measurements, remote sensing of rainfall and modeling to link between storm frequency, runoff, erosion and sediment transport. We present a quantitative hydrometeorological analysis of rainstorms, their geomorphic impact and their potential role in the evolution of hyperarid talus-pediment slopes in the Negev desert, Israel. Rainstorm properties were defined based on intensity–duration–frequency curves and using a rainfall simulator, artificial rainstorms were executed in the field. Then, the obtained measured experimental results were up-scaled to the entire slope length using a fully distributed hydrological model. In addition, natural storms and their hydro-geomorphic impacts were monitored using X-band radar and time-lapse cameras. These integrated analyses constrain the rainfall threshold for local runoff generation at rain intensity of 14 to 22 mm h^-1 for a duration of five minutes and provide a high-resolution characterization of small-scale runoff-generating rain cells. The current frequency of such runoff-producing rainstorms is ~1–3 per year. However, extending this local value into the full extent of hillslope runoff indicates that it occurs only under rainstorms with ≥ 100-years return interval, or 1% annual exceedance probability. Sheetwash efficiency rises with downslope distance; beyond a threshold distance of ~100 m, runoff during rainstorms with such annual exceedance probability are capable of transporting surface clasts. The erosion efficiency of these discrete rare events highlights their potential importance in shaping the landscape of arid regions. Our results support the hypothesis that a shift in the properties and frequency of extreme events can trigger significant geomorphic transitions in areas that remained hyperarid during the entire Quaternary. © 2020 John Wiley & Sons, Ltd.  相似文献   

Hydroclimatic significance of stable isotopes in precipitation from glaciers of Garhwal Himalaya,Upper Ganga Basin (UGB), India          下载免费PDF全文

Akshaya Verma  Amit Kumar  Anil K. Gupta  Sameer K. Tiwari  Rakesh Bhambri  Suneet Naithani 《水文研究》2018,32(12):1874-1893

Stable isotopic composition of precipitation as preserved in continental proxy climate archives (e.g., ice cores, lacustrine sediments, tree rings, groundwater, and organic matter) can sensitively record fluctuations in local meteorological variables. These are important natural climatic tracers to understand the atmospheric circulation patterns and hydrological cycle and to reconstruct past climate from archives. Precipitation was collected at Dokriani Glacier to understand the response of glaciers to climate change in the Garhwal Central Himalaya, Upper Ganga Basin. The local meteoric water line deviates from the global meteoric water line and is useful for the identification of moisture source in the region. The data suggest different clusters of isotopic signals, that is, summer (June–September) and winter (November–April); the mean values of δ¹⁸O, δD, and d ‰ during summer are ?13.03‰, ?84.49‰, and 19.78 ‰, respectively, whereas during winter, the mean values of δ¹⁸O, δD, and d ‰ are ?7.59‰, ?36.28‰, and 24.46 ‰, respectively. Backward wind trajectory analysis ascertains that the major source of precipitation during summer is from the Indian Summer Monsoon and during winter from the westerlies. Regression analysis has been carried out in order to establish interrelationship between the precipitation isotopic signatures and meteorological variables such as air temperature, relative humidity, and precipitation. Temperature and precipitation have good correlation with the isotopic signatures of precipitation with R² values >.5, suggesting that both temperature and amount effects prevail in the study region. Multiple regression analysis found strong relationships for both the seasons. The relationship of deuterium excess with δ¹⁸O, relative humidity, and precipitation are significant for the winter season. No significant relationships of deuterium excess were found with other meteorological variables such as temperature and radiation. The correlation and regression analysis performed are significant and valuable for interpretation of processes in the hydrological cycle as well as for interpretation of palaeoclimate records from the region.  相似文献   

Compositions and petrogenetic significance of the eudialyte group minerals from Sushina,Purulia, West Bengal   总被引：1，自引：0，他引：1  

Aniket Chakrabarty  Kamal L. Pruseth  Amit Kumar Sen 《Journal of the Geological Society of India》2012,79(5):449-459

The eudialyte-group of minerals (EGM) is one of the most important index minerals of the peralkaline (agpaitic) nepheline syenites. They crystallize in varied physico-chemical conditions ranging from the early-magmatic (orthomagmatic) to late-magmatic and even in the post-magmatic (hydrothermal) stage. In India, the only agpaitic nepheline syenite gneisses of the Sushina Hill region contain both late-magmatic as well as hydrothermal eudialytes. Compositionally these are Mn-Nb-Ca rich eudialytes and are comparable to the other EGM occurrences such as Ilímaussaq (Greenland), Tamazeght (Morocco), Mont-Saint Hilaire (Canada) and Pilansberg (South Africa). High Mn content (>6.5 wt.%) for both varieties of the Sushina EGM indicates that they are highly evolved in nature. In terms of the calculated site occupancy, particularly the [M(3)] and [M(2)], the Sushina eudialytes mimic some Pilansberg eudialytes. In addition to the eudialyte, the host nepheline syenite gneiss also contains an unknown Na-Zr-silicate (NZS) which is often found to be replacing both types of eudialytes. Compositionally these NZS can be tentatively represented as Na₂Zr₂S₆O₁₇. These NZS are characterized by much higher Zr, but lower Mn and Nb concentrations compared to the associated eudialytes. Two distinct varieties of eudialyte and NZS indicate subtle changes in the alkalinity during their formations. The formation of the late-magmatic as well as hydrothermal eudialyte essentially took place at somewhat elevated pH conditions. The replacement or alteration of eudialytes by NZS indicates a decreasing pH condition. In terms of the chemical composition the late-magmatic eudialytes can be represented as a solid-solution series between the kentbrooksite-taseqite-aqualite while the hydrothermal eudialyte represents solid-solution between kentbrooksitetaseqite -Ce-zirsilite.  相似文献   

Identification and analysis of groundwater potential zones in Ken–Betwa river linking area using remote sensing and geographic information system     

Ram Avtar  C. K. Singh  Satyanarayan Shashtri  Amit Singh 《国际地球制图》2013,28(5):379-396

The use of remote sensing data with other ancillary data in a geographic information system (GIS) environment is useful to delineate groundwater potential zonation map of Ken–Betwa river linking area of Bundelkhand. Various themes of information such as geomorphology, land use/land cover, lineament extracted from digital processing of Landsat (ETM+) satellite data of the year 2005 and drainage map were extracted from survey of India topographic sheets, and elevation, slope data were generated from shuttle radar topography mission (SRTM) digital elevation model (DEM). These themes were overlaid to generate groundwater potential zonation (GWPZ) map of the area. The final map of the area shows different zones of groundwater prospects, viz., good (5.22% of the area), moderate (65.83% of the area) poor (15.31% of the area) and very poor (13.64% of area).  相似文献   

The Himalayan foreland basin crust and upper mantle     

S. Mitra  Sribharath M. Kainkaryam  Amit Padhi  S.S. Rai  S.N. Bhattacharya 《Physics of the Earth and Planetary Interiors》2011,184(1-2):34-40

Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average V_s of 3.7 km s^?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal V_p/V_s shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle V_s is also significantly lower beneath the eastern Ganga basin (4.30 km s^?1) compared to the west (4.44 km s^?1).  相似文献   

Groundwater chemistry and redox processes: Depth dependent arsenic release mechanism     

Ashis Biswas  Santanu MajumderHarald Neidhardt  Dipti Halder  Subhamoy BhowmickAishwarya Mukherjee-Goswami  Amit KunduDebasree Saha  Zsolt BernerDebashis Chatterjee 《Applied Geochemistry》2011,26(4):516-525

Patchy occurrences of elevated As are often encountered in groundwater from the shallow aquifers (<50 m) of the Bengal Delta Plain (BDP). A clear understanding of various biogeochemical processes, responsible for As mobilization, is very important to explain this patchy occurrence and thus to mitigate the problem. The present study deals with the periodical monitoring of groundwater quality of five nested piezometeric wells between December 2008 and July 2009 to investigate the temporal changes in groundwater chemistry vis-a-vis the prevalent redox processes in the aquifer. Geochemical modeling has been carried out to identify key phases present in groundwater. A correlation study among different aqueous redox parameters has also been performed to evaluate prevailing redox processes in the aquifer. The long term monitoring of hydrochemical parameters in the multilevel wells together with hydrogeochemical equilibrium modeling has shown more subtle differences in the geochemical environment of the aquifer, which control the occurrence of high dissolved As in BDP groundwater. The groundwater is generally of Ca-HCO₃ type. The dissolved As concentration in groundwater exceeded both WHO and National drinking water standard (Bureau of Indian Standards; BIS, 10 μg L⁻¹) throughout the sampling period. The speciation of As and Fe indicate persistent reducing conditions within the aquifer [As(III): 87-97% of As_T and Fe(II): 76-96% of Fe_T]. The concentration of major aqueous solutes is relatively high in the shallow aquifer (wells A and B) and gradually decreases with increasing depth in most cases. The calculation of SI indicates that groundwater in the shallow aquifer is also relatively more saturated with carbonate minerals. This suggests that carbonate mineral dissolution is possibly influencing the groundwater chemistry and thereby controlling the mobilization of As in the monitored shallow aquifer. Hydrogeochemical investigation further suggests that Fe and/or Mn oxyhydroxide reduction is the principal process of As release in groundwater from deeper screened piezometric wells. The positive correlations of U and V with As, Fe and Mn indicate redox processes responsible for mobilization of As in the deeper screened piezometric wells are possibly microbially mediated. Thus, the study advocates that mobilization of As is depth dependent and concentrations of As in groundwater depends on single/combined release mechanisms.  相似文献   

Developing Spectral Library of Major Plant Species of Western Himalayas Using Ground Observations     

K. R. Manjunath  Amit Kumar  Mehra Meenakshi  R. Renu  S. K. Uniyal  R. D. Singh  P. S. Ahuja  S. S. Ray  Sushma Panigrahy 《Journal of the Indian Society of Remote Sensing》2014,42(1):201-216

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Precipitation analysis over southwest Iran: trends and projections   总被引：1，自引：1，他引：0  

Amit G. Dhorde  Mohammad Zarenistanak  R. H. Kripalani  B. Preethi 《Meteorology and Atmospheric Physics》2014,124(3-4):205-216

Analysis of trends and projection of precipitation are of significance for the future development and management of water resource in southwest Iran. This research has been divided into two parts. The first part consists of an analysis of the precipitation over 50 stations in the study region for the period 1950–2007. The trends in this parameter were detected by linear regression and significance was tested by t test. Mann–Kendall rank test was also employed to confirm the results. The second part of the research involved future projection of precipitation based on four models. The models used were Centre National de Recherches Meteorologiques (CNRM), European Center Hamburg Model (ECHAM), Model for Interdisciplinary Research on Climate (MIROCH) and United Kingdom Meteorological Office (UKMOC). Precipitation projections were done under B1 and A1B emissions scenarios. The results of precipitation series indicated that most stations showed insignificant trend in annual and seasonal series. The highest numbers of stations with significant trends occurred in winter while no significant trends were detected by statistical tests in summer precipitation. No decreasing significant trends were detected by statistical tests in annual and seasonal precipitation series. The result of projections showed that precipitation may decrease according to majority of the models under both scenarios but the decrease may not be large, except according to MIROCH model. Autumn precipitation may increase with higher rates than other seasons at the end of this century.  相似文献