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Contrasting upper atmospheric response to cyclones in the north Indian Ocean during the pre-monsoon and the post-monsoon seasons
  • Vineet Kumar Singh,
  • Roxy Mathew Koll,
  • Medha Sachin Deshpande
Vineet Kumar Singh
Indian Institute of Tropical Meteorology

Corresponding Author:vineetsingh.jrf@tropmet.res.in

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Roxy Mathew Koll
Indian Institute of Tropical Meteorology
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Medha Sachin Deshpande
Indian Institute of Tropical Meteorology, Pashan Road, Pune, INDIA.
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Cyclones in the north Indian Ocean evolve differently during the pre-monsoon (April-June) and post-monsoon (October-December) seasons. While several studies have investigated the near-surface ocean-atmospheric interactions, there is a lack of understanding of the upper-atmospheric response during cyclones. In the current study, we find that cyclones in this basin induce warming of 3–4°C at the upper tropospheric levels (300–400 hPa) during the pre-monsoon season, for the period 1982–2019. However, during the post-monsoon season, the upper-level warming is only ~1°C. The contrasting atmospheric response to cyclones in the two seasons is attributed to the contrasting ocean-cyclone-atmosphere coupled interaction. In the pre-monsoon season, higher SSTs coupled with higher wind forcing and moisture disequilibrium enhance the latent heat flux from the ocean to the atmosphere during the cyclones. This enhances convection resulting in enhanced latent heat release and anomalous upper-level warming in the atmosphere. During the post-monsoon season, the SSTs are cooler, and wind forcing and moisture disequilibrium is less than in the pre-monsoon season. As a result, the latent heat flux exchange is weak, leading to weaker convection, reduced latent heat release and weak upper-level warming. The lower atmospheric response to cyclones is also different in the two seasons, with enhanced evaporative cooling due to a drier lower atmosphere in the pre-monsoon season as compared to the post-monsoon season. Since the Indian Ocean is warming rapidly, it is essential to closely monitor the atmospheric temperature changes accompanying the cyclones in this basin since they can potentially influence largescale atmospheric dynamics and circulation.