Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Marine heatwaves (MHWs) are prolonged warm sea condition events that can have a destructive impact on marine ecosystems. The documentation of MHWs and assessment of their impacts is largely confined to a few regional seas or to global mean studies. The north Indian Ocean received almost no attention in this regard despite the fact that this ocean basin, particularly the Arabian Sea, has been warming at the most rapid pace among the other tropical basins in recent decades. This study shows the characteristics of MHW events for the Arabian Sea during 1982â2019. Our analysis shows that the duration (frequency) of MHWs exhibits a rapidly increasing trend of <span class="inline-formula">â¼20</span>âd per decade (1.5â2 events per decade) in the northern Arabian Sea and the southeastern Arabian Sea close to the west coast of India, which is a multifold increase in MHW days (frequency) from the 80s. Notably, since the beginning of the satellite record, the years 2010 and 2016 have exhibited the maximum number of heatwave days when more than 75â% of days of the pre-monsoon and summer monsoon season experience heatwaves. The accelerated trend of the heatwave days is found to be driven by the rapid rise in the mean sea surface temperature (SST) of the Arabian Sea in the recent decade. Moreover, longer heatwave days are also associated with dominant climate modes. Among them, the Indian Ocean Basin Mode via the decaying phase of El Niño is the most influential mode contributing to more than 70â%â80â% of observed heatwave days in this basin. Further analysis of the most prolonged observed heatwave during AprilâJune 2010 indicates that surface heat flux associated with the weaker latent heat loss and the shallow mixed layer was the primary cause of this event. Further, we note that the pre-monsoon cyclonic storms in the Arabian Sea often contribute to the waning of such heatwaves in the basin.
Highlights
Sea surface temperature (SST) shows significant variability over a large spectrum of frequencies in space and time across the globe
In order to understand the dominant physical forcing in the genesis of MHWs a volume-averaged mixed layer heat budget analysis has been carried out using the temperature and velocity fields taken from the model simulation
We have investigated the trends and genesis of the MHWs in the Arabian Sea
Summary
Sea surface temperature (SST) shows significant variability over a large spectrum of frequencies in space and time across the globe. Heatwaves (MHWs) and are defined as prolonged anomalously warm ocean condition exceeding a pre-defined threshold (Pearce et al, 2011; Hobday et al, 2016) These extreme warm events are shown to be responsible for widespread coral bleaching (Hughes et al, 2017), loss of Kelp forest off the coast of Australia and New Zealand Documenting and understanding the genesis of MHWs in the Arabian Sea, in the coastal oceans which possess significant economic importance, is necessary for better prediction of these MHWs and assessment of their impacts on this region. In this study, we document MHWs in the Arabian Sea with a special emphasis on the coastal waters close to the west coast of India and try to decipher the possible physical mechanisms that influence the genesis of such heatwaves in this region.
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