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Future Summertime Marine Heatwaves in the Indian Ocean in Response to Enhanced Variability of the Western North Pacific Subtropical High Under Warming Climate.

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Title: Future Summertime Marine Heatwaves in the Indian Ocean in Response to Enhanced Variability of the Western North Pacific Subtropical High Under Warming Climate.
Authors: Sandaruwan, Jayarathna W. N. D.1,2 (AUTHOR), Zhou, Wen3 (AUTHOR) wen_zhou@fudan.edu.cn, Collins, Mat2 (AUTHOR), Wang, Xuan1 (AUTHOR)
Source: Journal of Geophysical Research. Oceans. Sep2025, Vol. 130 Issue 9, p1-18. 18p.
Subject Terms: *Marine heatwaves, *Ocean-atmosphere interaction, *Climate change, *Ocean, *Atmospheric circulation, Ecological resilience, Atmospheric models
Geographic Terms: Indian Ocean
Abstract: Marine heatwaves (MHWs) pose significant threats to marine ecosystems and associated services, necessitating a deeper understanding of their driving mechanism. This study examines how the intensification of the Western North Pacific Subtropical High (WNPSH) influences future summer MHW occurrences in the Indian Ocean through complex ocean‐atmosphere coupling. Over two thirds of CMIP6 models project more frequent an intense strong WNPSH years by the end of the 21st century, resulting in prolonged and extreme summer MHWs in the future. Westward extension of stronger WNPSH generates pronounced anomalous anticyclonic circulation, producing easterly winds that extend into the north and equatorial Indian Ocean and oppose climatological monsoon winds. While these anomalous easterlies suppress key cooling mechanisms, such as wind driven evaporative cooling and upwelling, the westward propagating downwelling Rossby waves dynamically precondition the warming in the western Indian Ocean by deepening the thermocline. This coupled system creates sustained surface and subsurface warming extending from preceding seasons into summer. Regional differences emerge in future summer MHWs through cloud‐sea surface temperature (SST) feedback mechanisms. The central and northeastern Indian Ocean experiences more extreme MHWs due to reduced cloud cover, enhanced solar radiation exposure, and suppressed evaporative cooling through positive low cloud‐SST feedback. Conversely, the western Indian Ocean exhibits enhanced convection and cloud formation, moderating extreme warming through negative SST‐cloud feedback, exposing the region only to strong‐moderate MHWs. These findings highlight the critical role of multiseasonal, coupled ocean‐atmospheric interactions in shaping future summer MHW patterns, emphasizing the enhanced vulnerability of marine ecosystems. Plain Language Summary: Marine heatwaves (MHWs) are periods of unusually warm ocean temperatures that can have long lasting impacts on marine ecosystems, fisheries, and coastal communities. Our study explores how MHWs in the Indian Ocean might change in the future, using climate model simulations under high greenhouse gas emissions. We focus on summer MHWs and their connection to a large atmospheric system called the Western North Pacific Subtropical High (WNPSH), which influences weather patterns across the region. We found that the WNPSH is likely to become stronger and extend further westward by the end of the century. This shift creates unusual wind patterns over the Indian Ocean that weaken natural cooling processes in the region, such as wind‐driven evaporation and upwelling, leading to longer and intense MHWs. The central and northeastern Indian Ocean is expected to experience the most extreme MHWs, hence worst impacts to marine ecosystem as reduced cloud cover allows more sunlight to heat the ocean surface and weaker winds reduce cooling through evaporation. In contrast, the western Indian Ocean is projected to experience less severe MHWs. Although the region is subject to warming from reduced upwelling, this effect is largely counteracted by increased cloud cover, which limits incoming solar radiation. Key Points: Intensifying Western North Pacific Subtropical High (WNPSH) drives prolonged and extreme summer marine heatwaves (MHWs) in Indian OceanThe suppression of climatological cooling by WNPSH‐induced anomalous easterly winds plays a major role in generating MHWs in the summerFuture summertime MHWs may pose the greatest risk to marine ecosystems in the central and northeastern parts of the Indian Ocean [ABSTRACT FROM AUTHOR]
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Abstract:Marine heatwaves (MHWs) pose significant threats to marine ecosystems and associated services, necessitating a deeper understanding of their driving mechanism. This study examines how the intensification of the Western North Pacific Subtropical High (WNPSH) influences future summer MHW occurrences in the Indian Ocean through complex ocean‐atmosphere coupling. Over two thirds of CMIP6 models project more frequent an intense strong WNPSH years by the end of the 21st century, resulting in prolonged and extreme summer MHWs in the future. Westward extension of stronger WNPSH generates pronounced anomalous anticyclonic circulation, producing easterly winds that extend into the north and equatorial Indian Ocean and oppose climatological monsoon winds. While these anomalous easterlies suppress key cooling mechanisms, such as wind driven evaporative cooling and upwelling, the westward propagating downwelling Rossby waves dynamically precondition the warming in the western Indian Ocean by deepening the thermocline. This coupled system creates sustained surface and subsurface warming extending from preceding seasons into summer. Regional differences emerge in future summer MHWs through cloud‐sea surface temperature (SST) feedback mechanisms. The central and northeastern Indian Ocean experiences more extreme MHWs due to reduced cloud cover, enhanced solar radiation exposure, and suppressed evaporative cooling through positive low cloud‐SST feedback. Conversely, the western Indian Ocean exhibits enhanced convection and cloud formation, moderating extreme warming through negative SST‐cloud feedback, exposing the region only to strong‐moderate MHWs. These findings highlight the critical role of multiseasonal, coupled ocean‐atmospheric interactions in shaping future summer MHW patterns, emphasizing the enhanced vulnerability of marine ecosystems. Plain Language Summary: Marine heatwaves (MHWs) are periods of unusually warm ocean temperatures that can have long lasting impacts on marine ecosystems, fisheries, and coastal communities. Our study explores how MHWs in the Indian Ocean might change in the future, using climate model simulations under high greenhouse gas emissions. We focus on summer MHWs and their connection to a large atmospheric system called the Western North Pacific Subtropical High (WNPSH), which influences weather patterns across the region. We found that the WNPSH is likely to become stronger and extend further westward by the end of the century. This shift creates unusual wind patterns over the Indian Ocean that weaken natural cooling processes in the region, such as wind‐driven evaporation and upwelling, leading to longer and intense MHWs. The central and northeastern Indian Ocean is expected to experience the most extreme MHWs, hence worst impacts to marine ecosystem as reduced cloud cover allows more sunlight to heat the ocean surface and weaker winds reduce cooling through evaporation. In contrast, the western Indian Ocean is projected to experience less severe MHWs. Although the region is subject to warming from reduced upwelling, this effect is largely counteracted by increased cloud cover, which limits incoming solar radiation. Key Points: Intensifying Western North Pacific Subtropical High (WNPSH) drives prolonged and extreme summer marine heatwaves (MHWs) in Indian OceanThe suppression of climatological cooling by WNPSH‐induced anomalous easterly winds plays a major role in generating MHWs in the summerFuture summertime MHWs may pose the greatest risk to marine ecosystems in the central and northeastern parts of the Indian Ocean [ABSTRACT FROM AUTHOR]
ISSN:21699275
DOI:10.1029/2025JC022626