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<p>Marine Heatwaves (MHWs) severely disrupt marine ecosystems and affect the societal economy by altering monsoon and cyclone activity. This study focuses on delineating the drivers of prolonged and intense (category-2) MHW that occurred during the Southwest (SW) monsoon of 2020 over the Bay of Bengal (BoB), which was a neutral El Niño–Southern Oscillation and Indian Ocean Dipole year. It was found that Net Surface Heat Flux (NSHF) plays a dominant role in the MHW evolution. This NSHF was predominantly driven by anomalously strong Shortwave Radiation (SWR) to the ocean and reduced heat loss via Latent Heat Flux (LHF). Reduced winds and low-surface salinity also led to weaker vertical mixing, further intensifying the MHW. In contrast, reduced SWR to the ocean, increased LHF from the ocean, along with strong winds and high salinity, promoting stronger mixing, helped in MHW decay. Crucially, this study reveals a detailed mechanistic connection between the evolution of MHWs and Monsoon Intra-Seasonal Oscillations (MISO), whose intensity during 2020 was anomalously high. The results demonstrate that MHW formation (decay) coincided with MISO break (active) phases, characterized by clear (cloudy) skies, and enhanced (reduced) incoming SWR and suppressed (enhanced) LHF. The MHW was found to lead the rainfall by about 10 days, where the MHW preconditioned the atmosphere for strong convective instability, leading to a stronger-than-normal active MISO phase. The cumulative heat budget analysis revealed a more pronounced MISO-MHW coupling in the northern BoB than southern BoB.</p>

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Evolution of marine heatwaves and air-sea interactions during the 2020 Southwest Monsoon in the Bay of Bengal

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Hitesh Gupta,
  • Piyali Goswami,
  • Arkaprava Ray,
  • Arpan Bhattacharjee,
  • Sourav Sil

摘要

Marine Heatwaves (MHWs) severely disrupt marine ecosystems and affect the societal economy by altering monsoon and cyclone activity. This study focuses on delineating the drivers of prolonged and intense (category-2) MHW that occurred during the Southwest (SW) monsoon of 2020 over the Bay of Bengal (BoB), which was a neutral El Niño–Southern Oscillation and Indian Ocean Dipole year. It was found that Net Surface Heat Flux (NSHF) plays a dominant role in the MHW evolution. This NSHF was predominantly driven by anomalously strong Shortwave Radiation (SWR) to the ocean and reduced heat loss via Latent Heat Flux (LHF). Reduced winds and low-surface salinity also led to weaker vertical mixing, further intensifying the MHW. In contrast, reduced SWR to the ocean, increased LHF from the ocean, along with strong winds and high salinity, promoting stronger mixing, helped in MHW decay. Crucially, this study reveals a detailed mechanistic connection between the evolution of MHWs and Monsoon Intra-Seasonal Oscillations (MISO), whose intensity during 2020 was anomalously high. The results demonstrate that MHW formation (decay) coincided with MISO break (active) phases, characterized by clear (cloudy) skies, and enhanced (reduced) incoming SWR and suppressed (enhanced) LHF. The MHW was found to lead the rainfall by about 10 days, where the MHW preconditioned the atmosphere for strong convective instability, leading to a stronger-than-normal active MISO phase. The cumulative heat budget analysis revealed a more pronounced MISO-MHW coupling in the northern BoB than southern BoB.