Southeastern Peninsular India witnessed heavy rainfall events (HRE) during the recent El Nino year 2015 and La Nina year 2021 in November and early December. Both these events were associated with enhanced easterly wave activity and active Madden Julian Oscillation (MJO) over the Maritime continent. The MJO was on the fourth (MJO-4) phase for 15 and 17 days in November 2015 and 2021 respectively. A weakening in the positive correlation between El Nino and Northeast monsoon rainfall and a strengthening in the positive correlation between the MJO-4 days and HRE is observed in very recent years. This study revealed that the unequal changes in Sea Surface Temperature (SST) in the Indo-Pacific region i.e., warming over the eastern Indian Ocean (IO) and cooling over the western Pacific Ocean can be favourable for the increased occurrence of MJO-4 days as well as HRE over southern Peninsular India. The easterly wind anomalies towards the southern Bay of Bengal (BoB) and southeastern Peninsular India and westerly wind anomalies over the central equatorial Indian Ocean are significantly correlated with HRE in the recent epoch (2001−2021). Warming in eastern IO brings easterlies from the cool western Pacific and westerlies from the western IO, which helps the MJO to remain active over maritime continent and inhibits its further eastward propagation. The HREs in the recent epoch are associated with the low-pressure systems and cyclonic circulation over southern Peninsular India, in which moisture transport is from the Arabian Sea to Peninsular India. The HRE in the early epoch (1981–2000) is related to the anticyclonic circulation over BoB region and the moisture transport is from BoB and southeastern IO. A proposed mechanism for the HRE in the recent epoch is as follows. The SST gradient in the Indo-Pacific Ocean is conducive for the moistening of MJO-4 region and is favourable for the enhanced easterly wave activity and the formation of low-pressure systems, which get strengthened while moving towards southern Peninsular India due to the presence of strong equatorial westerlies over IO. These strengthened low pressure systems leads to strong ascending wind anomalies over southern Peninsular India and strong descending anomalies over Central IO and HREs over southern Peninsular India.

中文翻译：

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理清东北季风季节强降雨事件 (HRE) 的动态，并探索其与印度洋变暖和马登朱利安涛动的联系


印度半岛东南部在最近的2015年厄尔尼诺现象和2021年11月和12月初的拉尼娜现象中出现了强降雨事件（HRE）。这两个事件都与海洋大陆上增强的东波活动和活跃的马登朱利安涛动（MJO）有关。 MJO 于 2015 年 11 月和 2021 年分别处于第四阶段 (MJO-4) 15 天和 17 天。近年来，厄尔尼诺现象与东北季风降雨之间的正相关性减弱，而 MJO-4 天与 HRE 之间的正相关性增强。这项研究表明，印度洋-太平洋地区海面温度 (SST) 的不均匀变化，即东印度洋 (IO) 变暖和西太平洋变冷，可能有利于 MJO-4 天的发生增加以及印度半岛南部的神罗。近时期（2001−2021年）孟加拉湾南部（BoB）和印度半岛东南部的东风异常以及赤道印度洋中部的西风异常与HRE显着相关。 IO东部的变暖带来了来自凉爽的西太平洋的东风和来自IO西部的西风，这有助于MJO在海洋大陆上保持活跃并抑制其进一步向东传播。近代的 HRE 与印度半岛南部的低压系统和气旋性环流有关，其中水汽从阿拉伯海输送到印度半岛。早期(1981-2000年)的HRE与BoB地区的反气旋环流有关，水汽输送来自BoB和IO东南部。最近时期 HRE 的拟议机制如下。 印度太平洋海温梯度有利于MJO-4区域的增湿，有利于东波活动增强和低压系统的形成，并在向印度半岛南部移动时因存在而得到加强IO 上空强烈的赤道西风。这些增强的低压系统导致印度半岛南部出现强烈的上升风异常，并导致印度半岛南部的中央IO和HRE出现强烈的下降异常。