Kushwaha Vikas Kumar, Kumar S Prasanna, Feba F, Ashok Karumuri
Centre for Earth, Ocean and Atmospheric Science, University of Hyderabad, Hyderabad, India.
CSIR-National Institute of Oceanography, Dona Paula, Goa, 403002, India.
Sci Rep. 2022 Jul 29;12(1):13037. doi: 10.1038/s41598-022-17025-1.
A cross-equatorial low-level wind, known as Findlater Jet (FJ), modulates the thermocline in the Arabian Sea (AS) during summer monsoon (June to September). By analysing ocean and atmospheric data, we show that the FJ signal gets 'trapped' in the AS in the form of upper ocean heat content till the following winter months (December to February). This memory is the consequence of the combined effect of FJ-induced wind stress curl and the annual downwelling Rossby waves in the AS. During the summer monsoon months, the strong low-level westerly winds cause a negative wind stress curl in the south of the FJ axis over the central AS, resulting in a deep thermocline and high magnitude of heat being trapped. In winter monsoon months, though the wind stress curl is positive over large parts of the AS and could potentially shoal the thermocline and reduce the upper ocean heat content in the central AS, this does not happen due to two reasons. Firstly, winds are weaker, and spread over a larger area over the AS making the magnitude of the wind stress curl low. Secondly, westward propagating downwelling Rossby wave radiated from the eastern AS deepens the thermocline and prevents ventilation of the trapped heat. During the following spring, the collapse of the Rossby waves leads to the shoaling and mixing of underlying waters with surface waters thereby resurfacing of the trapped heat. The resurfacing of the trapped heat makes the AS a memory bank of the FJ induced signal.
一种被称为芬德莱特急流（FJ）的跨赤道低空风，在夏季风（6月至9月）期间调节着阿拉伯海（AS）的温跃层。通过分析海洋和大气数据，我们发现FJ信号以上层海洋热含量的形式“被困”在阿拉伯海，直到接下来的冬季月份（12月至2月）。这种记忆是FJ引起的风应力旋度和阿拉伯海年度下沉罗斯贝波共同作用的结果。在夏季风月份，强烈的低空西风在阿拉伯海中部FJ轴以南造成负风应力旋度，导致温跃层加深以及大量热量被困。在冬季风月份，尽管阿拉伯海大部分区域的风应力旋度为正，并且可能使温跃层变浅并减少阿拉伯海中部上层海洋的热含量，但由于两个原因这种情况并未发生。首先，风力较弱，且在阿拉伯海上分布更广，使得风应力旋度的幅度较低。其次，从阿拉伯海东部辐射出的向西传播的下沉罗斯贝波加深了温跃层，并阻止了被困热量的通风。在接下来的春季，罗斯贝波的崩溃导致下层水体与表层水体变浅并混合，从而使被困热量重新浮出水面。被困热量的重新浮出水面使阿拉伯海成为FJ诱导信号的记忆库。
