• A K Srivastava

      Articles written in Journal of Earth System Science

    • Detection of major geological structures in the Eastern offshore of India using Geosat altimeter data

      T J Majumdar K K Mohanty A K Srivastava

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      Satellite altimetry can be used to infer subsurface geological structures analogous to gravity anomaly maps generated through ship-borne survey. The Eastern offshore was taken up for analysis using Geosat Exact Repeat Mission (ERM) altimeter data. A methodology is developed to use altimeter data as an aid to offshore hydrocarbon exploration. Processing of altimeter data involves corrections for various atmospheric and oceanographic effects, stacking and averaging of repeat passes, cross-over correction, removal of deeper earth and bathymetric effects, spectral analysis and conversion into free-air gravity anomaly. The final processed results were derived for Eastern offshore in the form of prospecting geoid and gravity anomaly maps and their spectral components. The highs and lows observed in those maps were derived in terms of a number of prominent megastructures e.g., gravity linears, 85°E and 90°E ridges, the Andaman trench complex etc. Satellite-derived gravity profiles along 12°N latitude match well with the existing structures.

    • Numerical study for production of space charge within the stratiform cloud

      A K Srivastava S N Tripathi

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      One dimensional numerical model has been developed to predict the production of space charge and variations in other electrical parameters within the low level stratiform type of cloud having very weak vertical motion.Non-linear coupled differential equations which govern ion concentrations,charged and neutral droplet concentrations and electric field were used.Symmetry has been observed in all the electrical parameters within the cloud.The magnitude of average positive ion concentrations was observed to be high as compared to the negative ion concentrations,which is due to low scavenging rate of positive ions than the negative ions,highly attributed to their mobilities.The rate of scavenging of ions affects the concentration of charged droplets,which eventually influence the electric field and thus the space charge density within the cloud.Maximum electric field (𝐸_max) was observed at middle of the cloud whereas minimum was observed at both the edges of the cloud.Minimum electric field (𝐸_min) was found to be equal and constant (∼27Vm−1)for any drop concentration.Net positive and negative space charges were observed at the top and bottom of the cloud,respectively.The simulated results show some discrepancies to the natural condition, which are due to simulations made under some basic assumptions and limitations and that will be incorporated in the future studies for natural cloud condition.

    • Has influence of extratropical waves in modulating Indian summer monsoon rainfall (ISMR) increased?

      A K Srivastava Somenath Dutta S R Kshirsagar Kavita Srivastava

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      In the paper, influence of extratropical circulation features on Indian Summer Monsoon Rainfall (ISMR) is examined. Energetics of extra tropics, north of Indian subcontinent for deficient and nondeficient ISMR years, during two periods 1951–1978 and 1979–2005, are calculated and critically analyzed. It is observed that for the period 1951–1978, only two out of the 10 energetic parameters, viz., the zonal available potential energy (high) and conversion of zonal available potential with kinetic energy to eddy kinetic energy (low) differed significantly in JJA months of the deficient years from that of the nondeficient years. However, during the 1979–2005 period, as many as six out of the 10 energetic parameters, viz., eddy available potential energy, zonal available potential energy, eddy kinetic energy, generation of zonal available potential energy, conversion of zonal available potential energy to zonal kinetic energy and conversion of zonal kinetic energy to eddy kinetic energy differed significantly in JJA months of the deficient years from that of the nondeficient years. These results confirm growing influence of the transient stationary waves in deficient years after the climate shift year, 1979. Analysis of energetic parameters of the pre-monsoon season of the two periods also reveals similar results. This suggests that forcings apparently responsible for energetics in JJA months of the deficient years of the later period were present even before the advent of Indian summer monsoon season.

    • Heat islands over Mumbai as revealed by autorecorded thermograph data

      A K Srivastava James Voogt S R Kshirsagar Kavita Srivastava

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      This study examined hourly temperature data of two locations of Mumbai metropolitan city. One data point (Coloba, Mumbai) is in centre of the city and the other one (Santacruz, Mumbai) is at the airport. The study finds that there were many occasions when night-time hourly temperatures over the city centre were considerably higher than that of the airport, even though temperature at the time of sunset at both the places was nearly same. In this study, the occasions, when hourly night-time temperature over city was more than that of the airport by objectively defined threshold value (3.0°C in this study) for most of the hours in the night, were termed as heat island events. Analysis of the study reveals that these events are mostly confined to November–February months. The study also found that frequency of such events has doubled in recent two decades in comparison to the earlier two decades.

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