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1.
Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical
incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline
earth elements to total cations and HCO3>Cl + SO4 reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO4, and NO3 are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO3 type progressively evolves to Ca + Na–HCO3 and Na–Ca–HCO3 class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry
is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly
to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO3 and Ca + Mg vs HCO3 supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase
feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation
of CaCO3 supported by improved correlation coefficients between Na + Ca vs HCO3 and negative correlation of Ca vs HCO3, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function
of selective dissolution of olivine > pyroxene followed by plagioclase feldspar.
The data suggest siallitization (L < R and R
k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite)
products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component
range from 6.98 to 36.65 tons/km2/yr, respectively. The values of the CO2 consumption rates range between 0.18 × 106 mol//km2/yr (groundwater) and 0.9 × 106 mol/km2/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO2 consumption, an inference, that is, not taken into contemplation in most of the studies. 相似文献
2.
Frequency, intensity, areal extent (AE) and duration of rain spells during summer monsoon exhibit large intra-seasonal and inter-annual variations. Important features of the monsoon period large-scale wet spells over India have been documented. A main monsoon wet spell (MMWS) occurs over the country from 18 June to 16 September, during which, 26.5 % of the area receives rainfall 26.3 mm/day. Detailed characteristics of the MMWS period large-scale extreme rain events (EREs) and spatio-temporal EREs (ST-EREs), each concerning rainfall intensity (RI), AE and rainwater (RW), for 1 to 25 days have been studied using 1° gridded daily rainfall (1951–2007). In EREs, ‘same area’ (grids) is continuously wet, whereas in ST-EREs, ‘any area’ on the mean under wet condition for specified durations is considered. For the different extremes, second-degree polynomial gave excellent fit to increase in values from distribution of annual maximum RI and RW series with increase in duration. Fluctuations of RI, AE, RW and date of occurrence (or start) of the EREs and the ST-EREs did not show any significant trend. However, fluctuations of 1° latitude–longitude grid annual and spatial maximum rainfall showed highly significant increasing trend for 1 to 5 days, and unprecedented rains on 26–27 July 2005 over Mumbai could be a realization of this trend. The Asia–India monsoon intensity significantly influences the MMWS RW. 相似文献
3.
In this paper, the changes in convective activity over heat-low region over northwest India during contrasting phases of effective strength index (ESI) tendency have been examined. During contrasting phases of ESI tendency, evolution of surface pressure and temperature field over India from winter to spring is exactly opposite, and hence, the heat-low over northwest India depicts temporal and spatial variations in magnitude and location. During positive ESI tendency, the evolution of surface cooling and high surface pressure from winter to spring suggests reduced convective activity over heat-low region, while during the negative phase of ESI tendency, anomalously warm surface temperatures and low surface pressure evolve from winter to spring suggesting enhanced convective activity over the heat low region. The temporal variability in the relationship between surface temperature/pressure over heat-low region and Indian summer monsoon rainfall (ISMR) is also examined in this paper. During positive ESI tendency, heat-low temperature anomaly in February is significantly associated with ISMR, whereas during negative ESI tendency, both temperature/pressure over heat-low region in May are significantly associated with ISMR. These parameters may help in long range forecasting of ISMR. 相似文献
4.
Ashwini Kulkarni Ramesh Kripalani Sudhir Sabade Madhavan Rajeevan 《Climate Dynamics》2011,36(5-6):1005-1021
The day-to-day behavior of Indian summer monsoon rainfall (IMR) is associated with a hierarchy of quasi-periods, namely 3?C7, 10?C20 and the 30?C60?days. These two periods, the 10?C20?days and the 30?C60?days have been related with the active and break cycles of the monsoon rainfall over the Indian sub-continent. The seasonal strength of Indian summer monsoon rainfall may depend on the frequency and duration of spells of break and active periods associated with the fluctuations of the above intra-seasonal oscillations (ISOs). Thus the predictability of the seasonal (June through September) mean Indian monsoon depends on the extent to which the intra-seasonal oscillations could be predicted. The primary objective of this study is to bring out the dynamic circulation features during the pre-monsoon/monsoon season associated with the extreme phases of these oscillations The intense (weak) phase of the 10?C20 (30?C60) days oscillation is associated with anti-cyclonic circulation over the Indian Ocean, easterly flow over the equatorial Pacific Ocean resembling the normal or cold phase (La Nina) of El Nino Southern Oscillation (ENSO) phenomenon, and weakening of the north Pacific Sub-tropical High. On the other hand the weak phase of 10?C20?days mode and the intense phase of 30?C60?days mode shows remarkable opposite flow patterns. The circulation features during pre-monsoon months show that there is a tendency for the flow patterns observed in pre-monsoon months to persist during the monsoon months. Hence some indications of the behavior of these modes during the monsoon season could be foreshadowed from the spring season patterns. The relationship between the intensity of these modes and some of the long-range forecasting parameters used operationally by the India Meteorological Department has also been examined. 相似文献
5.
Alexander Z. Bochev Karel Kudela Iren A. Dimitrova Petko Nenovski Ashwini K. Sinha Marián Slivka 《Studia Geophysica et Geodaetica》2009,53(4):537-556
Examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere,
observed by INTERBALL-Auroral satellite during January 11, April 11 and June 28, 1997 are shown. Identification of corresponding
magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured simultaneously
onboard the spacecraft. The examined Pc5 pulsations reveal a compressional character. A fairly good correlation is demonstrated
between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The ULF Pc5 wave occurrence
is observed in both upward and downward FACs. 相似文献
6.
India’s annual weather cycle consists mainly of wet and dry periods with monsoonal rains being one of the significant wet periods that shows strong spatiotemporal variability. This study includes the climatological characteristics, fluctuation features, and periodic cycles of annual, seasonal, and monthly rainfall of seven river basins across the eastern Gangetic Plain (EGP) using the longest possible instrumental area-averaged monthly rainfall series (1829–2012). Understanding the relationships between these parameters and global tropospheric temperature changes and El Niño and La Niña climatic signals is also attempted.Climatologically, mean annual rainfall in the EGP varies from 1070.5?mm in the Tons River basin to 1508.6?mm in the Subarnarekha River basin. The highest rainfall in the EGP occurs during monsoon (1188?mm). The annual rainfall in all river basins and monsoon rainfall in four river basins is normally distributed. Annual and monsoonal rainfall in the Brahmani and Son River basins show a significant decreasing long-term trend. Over the last 20 years, annual rainfall in all river basins and monsoonal rainfall in five river basins show a decreasing trend. The power spectra for all rainfall series are characterized by consistent significant wavelength peaks at 3–5 years, 10–20 years, 40 years, and more than 80 years. Short-term fluctuations with a period less than 10 years is the major contributor to total variance in annual and/or monsoon rainfall (77.6%), followed by decadal variations with a period of 10–30 years (13.1%) and a long-term trend with a period greater than 30 years (9.3%).Temperature and thickness gradients from the Tibet–Himalaya–Karakoram–Hindu Kush highlands to eight strong highs show a significant correlation with rainfall during the onset and withdrawal phases of summer monsoon in the EGP. 相似文献
7.
Projected changes in South Asian summer monsoon by multi-model global warming experiments 总被引：1，自引：0，他引：1
S. S. Sabade Ashwini Kulkarni R. H. Kripalani 《Theoretical and Applied Climatology》2011,103(3-4):543-565
South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) dataset. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices, middle (2031–2050) and end of the twenty-first century (2081–2100), in the non-mitigated Special Report on Emission Scenarios B1, A1B and A2 .There is large inter-model variability in the simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of the 25 models are able to simulate space–time characteristics of the South Asian monsoon precipitation reasonably well. The response of these selected ten models has been examined for projected changes in seasonal monsoon rainfall. The multi-model ensemble of these ten models projects a significant increase in monsoon precipitation with global warming. The substantial increase in precipitation is observed over western equatorial Indian Ocean and southern parts of India. However, the monsoon circulation weakens significantly under all the three climate change experiments. Possible mechanisms for the projected increase in precipitation and for precipitation–wind paradox have been discussed. The surface temperature over Asian landmass increases in pre-monsoon months due to global warming and heat low over northwest India intensifies. The dipole snow configuration over Eurasian continent strengthens in warmer atmosphere, which is conducive for the enhancement in precipitation over Indian landmass. No notable changes have been projected in the El Niño–Monsoon relationship, which is useful for predicting interannual variations of the monsoon. 相似文献
8.
Geology, petrochemistry, and genesis of the bimodal lavas of Osham Hill, Saurashtra, northwestern Deccan Traps 总被引：1，自引：0，他引：1
Hetu C. Sheth Ashwini Kumar ChoudharyCiro Cucciniello Sudeshna BhattacharyyaRamesh Laishram Trupti Gurav 《Journal of Asian Earth Sciences》2012,43(1):176-192
The Saurashtra region in the northwestern Deccan continental flood basalt province (India) is notable for compositionally diverse volcano-plutonic complexes and abundant rhyolites and granophyres. A lava flow sequence of rhyolite-pitchstone-basaltic andesite is exposed in Osham Hill in western Saurashtra. The Osham silicic lavas are Ba-poor and with intermediate Zr contents compared to other Deccan rhyolites. The Osham silicic lavas are enriched in the light rare earth elements, and have εNd (t = 65 Ma) values between −3.1 and −6.5 and initial 87Sr/86Sr ratios of 0.70709-0.70927. The Osham basaltic andesites have initial εNd values between +2.2 and −1.3, and initial 87Sr/86Sr ratios of 0.70729-0.70887. Large-ion-lithophile element concentrations and Sr isotopic ratios may have been affected somewhat by weathering; notably, the Sr isotopic ratios of the silicic and mafic rocks overlap. However, the Nd isotopic data indicate that the silicic lavas are significantly more contaminated by continental lithosphere than the mafic lavas. We suggest that the Osham basaltic andesites were derived by olivine gabbro fractionation from low-Ti picritic rocks of the type found throughout Saurashtra. The isotopic compositions, and the similar Al2O3 contents of the Osham silicic and mafic lavas, rule out an origin of the silicic lavas by fractional crystallization of mafic liquids, with or without crustal assimilation. As previously proposed for some Icelandic rhyolites, and supported here by MELTS modelling, the Osham silicic lavas may have been derived by partial melting of hot mafic intrusions emplaced at various crustal depths, due to heating by repetitively injected basalts. The absence of mixing or mingling between the rhyolitic and basaltic andesite lavas of Osham Hill suggests that they reached the surface via separate pathways. 相似文献
9.
N. Ranganath Ashok Kumar Padhi Ajoy Kumar Padhi Ashwini Kumar Rai 《Journal of the Geological Society of India》2009,74(5):591-596
Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn
area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities.
The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both
as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental
distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests
their sedimentary origin. 相似文献
10.
Shared nearest neighbour (SNN) cluster algorithm has been applied to seasonal (June–September) rainfall departures over 30 sub-divisions of India to identify the contiguous homogeneous cluster regions over India. Five cluster regions are identified. Rainfall departure series for these cluster regions are prepared by area weighted average rainfall departures over respective sub-divisions in each cluster. The interannual and decadal variability in rainfall departures over five cluster regions is discussed. In order to consider the combined effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO), an index called effective strength index (ESI) has been defined. It has been observed that the circulation is drastically different in positive and negative phases of ESI-tendency from January to April. Hence, for each phase of ESI-tendency (positive and negative), separate prediction models have been developed for predicting summer monsoon rainfall over identified clusters. The performance of these models have been tested and found to be encouraging. 相似文献