Genesis and Trends in Marine Heatwaves Over the Tropical Indian Ocean and Their Interaction With the Indian Summer Monsoon. Issue 2 (1st February 2022)

• Record Type: Journal Article
• Authors: Saranya, J. S.; Roxy, M. K.; Dasgupta, Panini; Anand, Ajay
• Is Part Of: Journal of geophysical research. Volume 127:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-01
• Subjects: marine heatwave -- Indian Ocean -- monsoon -- ocean warming -- climate change -- global warming; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017427
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Marine heatwaves (MHWs) are extreme oceanic warm water events (above 90th percentile threshold) that significantly impact the marine environment. Recent studies have explored the genesis and impacts of MHWs in the global oceans though they are least understood in the tropical Indian Ocean. Here we investigate the genesis and trend of MHWs in the Indian Ocean during 1982–2018 and their role in modulating the Indian summer monsoon. We find that the rapid warming in the Indian Ocean plays a critical role in increasing the number of MHWs. Meanwhile, the El Niño has a prominent influence on the occurrence of MHWs during the monsoon. The Indian Ocean warming and the El Niño variability have synergistically resulted in some of the strongest and long‐lasting MHWs in the Indian Ocean. The western Indian Ocean region experienced the largest increase in MHWs at a rate of 1.2–1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.4–0.5 events per decade. Locally, the MHWs are induced by increased solar radiation, relaxation of winds, and reduced evaporative cooling. In the western Indian Ocean, the decreased winds further restrict the heat transport by ocean currents from the near‐equatorial regions toward the north. Our analysis indicates that the MHWs in the western Indian Ocean and the north Bay of Bengal lead to a reduction in monsoon rainfall over the central Indian subcontinent. On the other hand, there is an enhancement of monsoon rainfall over southwest India due to the MHWs in the Bay of Bengal. Plain Language Summary: Marine heatwaves are periods of extremely high temperatures in the ocean. Though recent studies have reported their occurrence and impacts in the global oceans, they are least understood in the tropical Indian Ocean. In the current study, we find that marine heatwaves are increasing in the Indian Ocean, with the largest increase observed over the western Indian Ocean, followed by the north Bay of Bengal. These marine heatwaves occur as a result of background ocean warming in the Indian Ocean and also in response to El Niño events in the Pacific Ocean. Locally, a peak in solar radiation and a dip in evaporative cooling due to weak winds lead to the formation of these marine heatwaves. In the western Indian Ocean, the weak winds also reduce the heat transported by ocean currents from the near‐equatorial regions toward the north, intensifying the marine heatwave. In turn, these marine heatwaves impact the monsoon by reducing the rainfall over the central Indian subcontinent while enhancing it over the southern peninsula. Key Points: An increasing trend in marine heatwaves is observed over the western Indian Ocean and the Bay of Bengal Ocean warming and El Niño events drives the genesis and trends of marine heatwaves in the Indian Ocean Marine heatwaves reduce the monsoon rainfall over the central Indian subcontinent while enhancing it over the southern peninsula