• Ashish Kumar

      Articles written in Journal of Earth System Science

    • Validation of a satellite-based cyclogenesis technique over the North Indian Ocean

      Suman Goyal M Mohapatra Ashish Kumar S K Dube Kushagra Rajendra P Goswami

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      Indian region is severely affected by the tropical cyclones (TCs) due to the long coast line of about 7500 km. Hence, whenever any low level circulation (LLC) forms over the Indian Seas, the prediction of its intensification into a TC is very essential for the management of TC disaster. Satellite Application Centre (SAC) of Indian Space Research Organization (ISRO), Ahmedabad, has developed a techniqueto predict TCs based on scatterometer-derived winds from the polar orbiting satellite, QuikSCAT and Oceansat-II. The India Meteorological Department (IMD) has acquired the technique and verified it for the years 2010–2013 for operational use. The model is based on the concept of analogs of the sea surfacewind distribution at the stage of LLC or vortex (T1.0) as per Dvorak’s classifications, which eventually leads to cyclogenesis (T2.5). The results indicate that the developed model could predict cyclogenesis with a probability of detection of 61% and critical success index of 0.29. However, it shows high overpredictionof the model is better over the Bay of Bengal than over Arabian Sea and during post-monsoon season (September–December) than in pre-monsoon season (March–June).

    • Satellite-based technique for nowcasting of thunderstorms over Indian region

      Suman Goyal Ashish Kumar M Mohapatra L S Rathore S K Dube Rahul Saxena R K Giri

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      India experiences severe thunderstorms during the months, March–June. But these systems are not predicted well, mainly due to the absence of mesoscale observational network over Indian region and the expert system. As these are short lived systems, the nowcast is attempted worldwide based on satellite and radar observations. Due to inadequate radar network, satellite plays the dominant role for nowcast of these thunderstorms. In this study, a nowcast based algorithm ForTracc developed by Vila et al. (Weather Forecast 23:233–245, 2008) has been examined over the Indian region using Infrared Channel (10.8 μm) of INSAT-3D for prediction of Mesoscale Convective Systems (MCS). In this technique, the current location and intensity in terms of Cloud Top Brightness Temperature (CTBT) of the MCS are extrapolated. The purpose of this study is to validate this satellite-based nowcasting technique for Convective Cloud Clusters that helps in optimum utilization of satellite data and improve the nowcasting. The model could predict reasonably the minimum CTBT of the convective cell with average absolute error (AAE) of <7 K for different lead periods (30–180 min). However, it was underestimated for all the lead periods of forecasts. The AAE in the forecasts of size of the cluster varies from about 3×104 km2 for 30-min forecast to 7×104 km2 for 120-min forecast. The mean absolute error in prediction of size is above 31–38% of actual size for different lead periods of forecasts from 30 to 180 min. There is over estimation in prediction of size for 30 and 60 min forecasts (17% and 2.6% of actual size of the cluster, respectively) and underestimation in 90 to 180-min forecasts (–2.4% to –28%). The direct position error (DPE) based on the location of minimum CTBT ranges from 70 to 144 km for 30–180-min forecast respectively.

    • Identification of significant subsurface geological structural feature using gravity and magnetic survey in parts of Kamrup district, Assam and West Khasi Hills district, Meghalaya

      ASHISH KUMAR RAJESH KUMAR CHANDRAI MURMU UMA SHANKAR NABENDU MAJUMDAR

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      Gravity and magnetic survey have been carried out in parts of the Kamrup district of Assam and the West Khasi Hills district of Meghalaya. The objective of the survey is to delineate the subsurface geological structure and identify the mineralization potential zone. Regional-residual separation, radially averaged power spectrum, Euler’s depth solutions and 2D-depth model maps mainly have been analyzed for interpretation. High Bouguer anomalies were observed over exposed Assam–Meghalaya gneissic complex (AMGC) rocks whereas low anomalies were observed over quaternary sediments. The generaltrend of the gravity and magnetic contours are in the NE–SW direction which is also the trend of geological formations, i.e., AMGC and older metamorphic group rocks. Based on Bouguer contours several inferred contact/lineament/faults have been identified. These contact/lineament/faults are very well validated with Euler’s depth solutions and total horizontal gradient of gravity anomaly. Significant high magnetic anomalies have been observed over older metamorphic group rocks and the Assam–Meghalaya gneissic complex. After the correlation with the physical properties of rock samples, geology and interpretation of gravity and magnetic maps, a potential zone has been identified for detailed investigation from a mineralization point of view.

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