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<p>Time series measurements of the high-resolution vertical profiles of temperature, salinity, current velocity and surface meteorological parameters from a moored buoy at 17.8° N, 89.5° E in the northern Bay of Bengal (BoB) are used to document differences in the marine heatwaves (MHW) conditions between summer (defined as June to September) 2019 and 2020 and its plausible connection with northward propagating monsoon intraseasonal oscillation (MISO). It was found that the summer of 2020 exhibited significantly warmer SST anomalies in the northern BoB with magnitudes exceeding 1&#xa0;°C north of 15° N, compared to the near climatological state in 2019. Consequently, MHW metrics reveal a moderate and persistent MHW state in the summer of 2020, in contrast to the sporadic and weak MHW conditions in 2019. In the summer of 2019, the northern BoB experienced progressive cooling, modulated by the sequential occurrence of MISO events without a significant break period between the events. Despite a similar number of MISO activities in 2020, seasonal cooling was absent, leading to persistent MHW conditions with a peak magnitude in August 2020. A mixed-layer heat budget analysis using flux mooring data indicates that the enhanced net shortwave radiation (<i>NSW</i>) was the primary factor responsible for the MHW in 2020. The westward extension of an anomalous anticyclone over the northwestern Pacific into the BoB reduced cloud cover, thereby increasing <i>NSW</i> heating at the ocean surface in 2020. This mechanism weakened MISO-driven cooling, allowing SST to remain anomalously warm in 2020, along with a prolonged break between the events.</p>

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The causes of the difference in marine heat wave conditions during the summers of 2019 and 2020 in the Northern Bay of Bengal

  • 期刊论文

  • 发表日期：

    2025年8月12日

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  • M. S. Girishkumar,
  • V. R. Sherin,
  • E. Pattabhi Rama Rao

摘要

Time series measurements of the high-resolution vertical profiles of temperature, salinity, current velocity and surface meteorological parameters from a moored buoy at 17.8° N, 89.5° E in the northern Bay of Bengal (BoB) are used to document differences in the marine heatwaves (MHW) conditions between summer (defined as June to September) 2019 and 2020 and its plausible connection with northward propagating monsoon intraseasonal oscillation (MISO). It was found that the summer of 2020 exhibited significantly warmer SST anomalies in the northern BoB with magnitudes exceeding 1 °C north of 15° N, compared to the near climatological state in 2019. Consequently, MHW metrics reveal a moderate and persistent MHW state in the summer of 2020, in contrast to the sporadic and weak MHW conditions in 2019. In the summer of 2019, the northern BoB experienced progressive cooling, modulated by the sequential occurrence of MISO events without a significant break period between the events. Despite a similar number of MISO activities in 2020, seasonal cooling was absent, leading to persistent MHW conditions with a peak magnitude in August 2020. A mixed-layer heat budget analysis using flux mooring data indicates that the enhanced net shortwave radiation (NSW) was the primary factor responsible for the MHW in 2020. The westward extension of an anomalous anticyclone over the northwestern Pacific into the BoB reduced cloud cover, thereby increasing NSW heating at the ocean surface in 2020. This mechanism weakened MISO-driven cooling, allowing SST to remain anomalously warm in 2020, along with a prolonged break between the events.