孟加拉湾海洋热浪季节变化特征与可能成因

本文基于1982−2021年的NOAA最优插值海表温度等资料，分析了孟加拉湾海洋热浪季节分布特征与可能成因。结果表明：大致以斯里兰卡岛与缅甸伊洛瓦底江河口连线为界，孟加拉湾西北部与东南部海域海洋热浪频率和天数呈现出不同的季节变化特征。在湾西北部海域，海洋热浪频率和天数季节变化较显著，均在夏季达到最大，春、秋季次之，冬季最少。而在湾东南部海域，二者的季节变化相对较弱。依据海洋热浪累积强度将海洋热浪从弱至强分为I～IV4种等级。分析显示，I类和II类较弱海洋热浪主要发生于夏、秋季的湾西部或西北部海域；III类以上严重海洋热浪则多发于春季的安达曼海和湾东南部海域以及夏季的缅甸西南部海域。进一步分析表明，在春、夏和秋季大部分海洋热浪活跃区，较浅的混合层及海表净热通量的变化对这些海区海洋热浪活动可能起主要作用，而冬季湾东南部海域海洋热浪形成与维持可能主要与赤道远地强迫有关。

Seasonal variability and mechanism of marine heatwaves in the Bay of Bengal

Based on the NOAA optimal interpolated sea surface temperature and other data from 1982 to 2021, seasonal variability of marine heatwave in the Bay of Bengal and associated formation mechanism were analyzed in this study. The results show that, bounded by the connection between Sri Lanka Island and the mouth of the Irrawaddy river in Myanmar, the frequency and days marine heatwave show different seasonal variation characteristics in the northwest and southeast of the Bay of Bengal. In the northwestern of the bay, both the frequency and the number of days of marine heatwaves are the largest in summer followed by spring and autumn, and the least in winter. In the southeastern of the bay, the seasonal variation of both is relatively weak. According to the cumulative intensity of marine heatwave, marine heatwaves are divided into four categories from weak to strong: I−IV. The analysis shows that the weak marine heatwave of category I and II mainly occurred in western or northwestern of the bay in summer and autumn; severe marine heatwaves of category 3 and above are mostly found in the Andaman Sea and the southeastern of the bay in spring and off southwestern Myanmar in summer. Further analysis shows that in most active areas of marine heatwaves in spring, summer and autumn, the change of net surface heat flux and the shallow mixed layer depth play a major role in these areas, while the formation and maintenance of marine heatwave in the southern of bay may be related to the remote forcing from the equator.