• KASTURI SINGH

      Articles written in Journal of Earth System Science

    • Robustness of best track data and associated cyclone activity over the North Indian Ocean region during and prior to satellite era

      KASTURI SINGH JAGABANDHU PANDA M MOHAPATRA

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      There are few studies focusing on analysing climatological variation in cyclone activity by utilising the best track data provided by the India Meteorological Department (IMD) over the North Indian Ocean (NIO). The result of such studies has been beneficial in decision-making by government and meteorological agencies. It is essential to assess the quality and reliability of the currently available version of the dataset so that its robustness can be established and the current study focuses on this aspect. The analysis indicates that there is an improvement over the years in the quality and availability of the data related to cyclones over NIO, especially in terms of frequency of genesis, intensity, landfall etc. The available data from 1961 onwards has been found robust enough with the advent of satellite technology. However, there can be still missing information and inaccuracy in determining the location and intensity of cyclones during the polar satellite era (1961–1973). The study also indicates undercount of severe cyclones during the pre-satellite era. Considering the relatively smaller size of NIO basin, these errors can be neglected and thus, the IMD best track data can be considered as reliable enough for analysing cyclone activity in this region.

    • Simulated dynamics and thermodynamics processes leading to the rapid intensification of rare tropical cyclones over the North Indian Oceans

      ARPITA MUNSI AMIT KESARKAR JYOTI BHATE KASTURI SINGH ABHISHEK PANCHAL GOVINDAN KUTTY RAMKUMAR GIRI

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      The life cycle dynamics and intensification processes of three long-duration tropical cyclones (TCs), viz., Fani (2019), Luban (2018), and Ockhi (2017) formed over the North Indian Ocean (NIO) have been investigated by developing a high-resolution (6 km ${\times}$ 6 km) mesoscale analysis using WRF and En3DVAR data assimilation system. The release of CAPE in nearly saturated middle-level relative humidity caused intense diabatic heating, leading to an increase in low-level convergence triggering rapid intensification (RI). The strengthening of the relative vorticity tendency terms was due to vertical stretching (TC Fani) and middle tropospheric advection (TCs Luban and Ockhi). The increase or decrease in uppertropospheric divergence led to RI through two different mechanisms. The increase in upper divergence strengthens the vortical convection (in TC Luban and Fani) by enhancing the moisture and heat transport, whereas its decrease caused a reduction in the upper-level ventilation flow at 200 hPa followed by moisture accumulation, enhanced diabatic heating, and strengthened the warm core (TC Ockhi). The RI caused the vortex of three cyclones to extend up to the upper troposphere. The well organised wind during RI led the unorganised, weak, discontinuous vertical vortex columns to become organised with intense vertical velocity throughout the column. Spatial distributions of Okubo–Wiess (OW) parameter showed TC core dominated by vorticity than strain, since deep depression (DD) stages.

      $\bf{Highlights}$

      $\bullet$ The saturated middle-level relative humidity caused intense diabatic heating, and then release of CAPE led to a rise in low-level spin-up triggering the RI.

      $\bullet$ The strengthening of the relative vorticity tendency terms was due to stretching (TC Fani) and middle tropospheric advection (TCs Luban and Ockhi).

      $\bullet$ The increase or decrease in upper-tropospheric divergence led to RI through two different mechanisms.

      $\bullet$ The RI caused the vortex of three cyclones to extend up to the upper troposphere.

      $\bullet$ RI led unorganised, weak, discontinuous vertical vortex columns to become organised with intense vertical velocity throughout the column.

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