Genesis and trends in marine heatwaves over the tropical Indian Ocean
and their interaction with the Indian summer monsoon
Abstract
Marine heatwaves (MHWs) are extreme oceanic warm water events (above
90th percentile threshold) that significantly impact the marine
environment. Several studies have recently explored the genesis and
impacts of MHWs 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 monsoon.
We find that the rapid warming in the Indian Ocean plays a critical role
in increasing the number of MHWs. Meanwhile, the El Nino has a prominent
influence on the occurrence of MHWs during the summer monsoon. The
Indian Ocean warming and the El Nino variability have synergistically
resulted in some of the strongest and long-lasting MHWs in the Indian
Ocean. The western Indian Ocean (WIO) 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 towards 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.