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The modulation of Indian summer monsoon onset processes during ENSO through equatorward migration of the subtropical jet stream
Climate Dynamics ( IF 4.6 ) Pub Date : 2021-02-22 , DOI: 10.1007/s00382-021-05700-4
Devanil Choudhury , Debashis Nath , Wen Chen

In this study, we demonstrate a new mechanism, on how the warm phase of El Niño and Southern Oscillation (ENSO) delays the Indian Summer Monsoon onset through coupled ocean-atmospheric processes. Strong basin-wide warming is prominent over North Indian Ocean (NIO) during the El Niño years. The warming is intense over the South West Indian Ocean (SWIO) due to the westward propagation of the equatorial Rossby waves from the Pacific Ocean. It increases the convective activities over the southern tropical Indian Ocean (0–10° S), adjacent to the SWIO region. The warming over the SWIO and the NIO strengthens the divergent wind from the Indian Ocean to the sub-tropics via a wind-evaporation-SST feedback mechanism, which causes more upper-level convergence within 30° N latitudes. Besides, a warmer Indian Ocean enhances the upper-level diabatic heating over the southern Arabian Peninsula and Eastern Indian landmass. These factors strengthen but shift the local Hadley circulation over the Indian Ocean more southward, with an ascending branch centered over the SWIO region. The shifting of the local Hadley circulation during the El Niño years causes the Sub Tropical Jet (STJ) to migrate more southward and centered more over the Indian subcontinent. This southward movement of the STJ over the Indian subcontinent in response to the El Niño condition inhibits the establishment and propagation of the tropical easterly jet during the monsoon season, which subsequently hinders the monsoon circulation, thus delays its onset.



中文翻译:

通过亚热带急流向赤道移动,对ENSO期间印度夏季风爆发过程的调节

在这项研究中,我们展示了一种新的机制,说明厄尔尼诺现象和南部涛动(ENSO)的暖相如何通过耦合的海洋-大气过程延迟了印度夏季风的爆发。在厄尔尼诺现象期间,整个北印度洋(NIO)都出现了强烈的全盆地变暖现象。由于来自太平洋的赤道Rossby波向西传播,西南印度洋(SWIO)的变暖加剧。它增加了靠近SWIO地区的南部热带印度洋(0-10°S)上的对流活动。SWIO和NIO的变暖通过风-蒸发-SST反馈机制增强了从印度洋到亚热带的发散风,这会在北纬30°以内引起更高的高层收敛。除了,印度洋变暖会增强阿拉伯半岛南部和东印度大陆的上层绝热加热。这些因素加强了印度洋上的哈德利环流,但将其向南移,而上升的分支则集中在SWIO地区。在厄尔尼诺时期,哈德利局部环流的转移导致次热带喷气机(STJ)向南迁移,并在印度次大陆上居中。响应厄尔尼诺现象,STJ在印度次大陆上的这种向南运动抑制了季风季节期间热带东风急流的建立和传播,从而阻碍了季风环流,从而延缓了其爆发。这些因素加强了印度洋上的哈德利环流,但将其向南移,而上升的分支则集中在SWIO地区。在厄尔尼诺时期,当地哈德利环流的转移导致次热带喷气机(STJ)向南迁移,并在印度次大陆上居中。响应厄尔尼诺现象,STJ在印度次大陆上的这种向南运动抑制了季风季节期间热带东风急流的建立和传播,从而阻碍了季风环流,从而延缓了其爆发。这些因素加强了印度洋上的哈德利环流,但将其向南移,而上升的分支则集中在SWIO地区。在厄尔尼诺时期,哈德利局部环流的转移导致次热带喷气机(STJ)向南迁移,并在印度次大陆上居中。响应厄尔尼诺现象,STJ在印度次大陆上的这种向南运动抑制了季风季节期间热带东风急流的建立和传播,从而阻碍了季风环流,从而延缓了其爆发。在厄尔尼诺时期,当地哈德利环流的转移导致次热带喷气机(STJ)向南迁移,并在印度次大陆上居中。响应厄尔尼诺现象,STJ在印度次大陆上的这种向南运动抑制了季风季节期间热带东风急流的建立和传播,从而阻碍了季风循环,从而延缓了季风的爆发。在厄尔尼诺时期,哈德利局部环流的转移导致次热带喷气机(STJ)向南迁移,并在印度次大陆上居中。响应厄尔尼诺现象,STJ在印度次大陆上的这种向南运动抑制了季风季节期间热带东风急流的建立和传播,从而阻碍了季风环流,从而延缓了其爆发。

更新日期:2021-02-22
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