Classification and mechanisms for different types of marine heatwaves in the western Indian Ocean during the past three decades

Marine heatwaves (MHWs) in the western Indian Ocean (WIO) have become more intense and frequent since the 1990s, but the underlying mechanisms driving different types of MHWs have not yet been investigated. In this study, a self-organizing map–based clustering method is applied to classify the boreal summer WIO MHW events from 1993 to 2024, and four clusters are identified from the total of 92 MHW events, according to the first three leading EOF principal components. It is found that the first three clusters of MHW events are all triggered by the suppression of evaporative cooling related to weak wind, but their underlying mechanisms exhibit substantial differences. The occurrence of Cluster 1 events is accompanied by the strengthening of advective heat transport, and the warming trend is dampened due to the deepening of the Great Whirl. For the Cluster 2 events, the warming effects by positive anomalous air–sea fluxes become more pronounced due to the shallow mixed layer. However, the warm center of Cluster 3 events locates over the central Indian Ocean in the Southern Hemisphere. As for Cluster 4 events, they are strongly associated with the long-term suppression of upwelling over the western boundary caused by the positive Indian Ocean Dipole. These findings have significant implications for discerning the features of MHWs in the WIO and improving their predictability through the identification of precursor signals. 本文采用了基于自组织映射的聚类方法, 将1993至2024年间发生于西印度洋的92次夏季海洋热浪事件分为四种类型.前三类事件均伴随因风速下降导致的蒸发冷却被抑制.但后续发展机制存在差异:第一类事件随平流热输送增强;第二类事件因混合层变浅促使增温加剧;第三类事件的暖中心发生区域较为特殊, 位于南半球.而第四类事件则由印度洋偶极子正位相导致的上升流受抑制引起.这些发现对理解西印度洋MHW特征及提高其预测性具有重要意义.