The northeast-southwest oscillating equatorial mode of the tropical instability wave and its impact on equatorial mixing
The northeast-southwest oscillating equatorial mode of the tropical instability wave and its impact on equatorial mixing
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热带不稳定波的东北-西南振荡赤道模式及其对赤道混合的影响
DOI：
10.1029/2018gl080226
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发表时间：
2019
影响因子：
5.2
通讯作者：
Liu Zhiyu
中科院分区：
文献类型：
--
作者：
Liu Chuanyu;Wang Xiaowei;Köhl Armin;Wang Fan;Liu Zhiyu
东太平洋热带不稳定波（TIWs）由中心周期约为33天和17天的波动组成。虽然前者表现为赤道以北的涡旋，并且已知调节其南部边缘的横辐混合，但后者在很大程度上仍未被探索。本文基于长期的现场观测和再分析资料，研究了17天TIW的结构及其影响赤道混合的机制。与公认的纬向速度振荡不同，17天的TIW被发现诱导东北-西南（NE-SW）的速度振荡。它们被限制在赤道内，但不对称于赤道，不同于自由柳井波，它们通常被认为是类似的。与向西的异常速度相关联的垂直切变叠加在平均流的切变上，从而导致在上部温跃层中的最强切变，这有望促进其中的穿透混合。
The tropical instability waves (TIWs) in the eastern Pacific consist of waves with central periods of about 33 and 17 days. While the former manifest as vortices north of the equator, and are known to modulate diapycnal mixing at their southern edge, the latter remain largely unexplored. Here the structure of the 17‐day TIWs and the mechanism through which they may influence equatorial mixing are investigated based on long term in situ measurements and reanalysis data. Different from the well‐recognized meridional velocity oscillation, the 17‐day TIWs are found to induce northeast‐southwest (NE‐SW) velocity oscillations. They are confined within but asymmetric about the equator, differing from free Yanai waves, which they were commonly assumed to resemble. The vertical shear associated with the westward anomalous velocity superimposes on the shear of the mean flow, resulting in the strongest shear in the upper thermocline that is expected to facilitate diapycnal mixing therein.