MJO-Induced Intraseasonal Mixed Layer Depth Variability in the Equatorial Indian Ocean and Impacts on Subsurface Water Obduction
MJO-Induced Intraseasonal Mixed Layer Depth Variability in the Equatorial Indian Ocean and Impacts on Subsurface Water Obduction
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DOI：
10.1175/jpo-d-20-0179.1
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发表时间：
2021-01
影响因子：
3.5
通讯作者：
Lingling Liu;Yuanlong Li;Fan Wang
中科院分区：
文献类型：
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作者：
Lingling Liu;Yuanlong Li;Fan Wang
海洋表面混合层深度（MLD）的变化对表层和次表层海洋的垂直交换至关重要，并调节着不同时间尺度上的表面温度变化。在马登-朱利安涛动（MJO）开始的赤道印度洋（EIO），现场观测记录了MLD以30 - 105天为周期的显著季节内变率（ISV）。混合坐标海洋模式（HYCOM）的模拟结果表明，在70°-95°E， 3°S-3°N的EIO区域，季节内MLD变异最大，标准差约为14 m。HYCOM的敏感性试验表明，在所有mjo相关强迫效应中，风驱动的下潜和混合是季内MLD加深的主要原因，占总ISV的83.7%。MLD的ISV引起了地下水的高频夹带，导致年夹带率提高了34%。然而，只有一小部分的携带事件（<20%）可以有效地促成1.36 Sv的年诱发率，这是全年温跃层水重新表面量的一个量化，主要发生在夏季风季节（5 - 10月）。在4 - 5月，MLD的ISV达到最大强度，对后续的内倾有很大影响。基于HYCOM模拟的估计表明，mjo总体上使夏季风季的诱入率降低了53%。提出了一个概念性的示意图来说明由MJO风引起的春季季节性MLD加深事件如何缩小了有效夹带的时间窗口，从而抑制了温跃层水的逆冲。
Change of oceanic surface mixed layer depth (MLD) is critical for vertical exchanges between the surface and subsurface oceans and modulates surface temperature variabilities on various time scales. In situ observations have documented prominent intraseasonal variability (ISV) of MLD with 30–105-day periods in the equatorial Indian Ocean (EIO) where the Madden–Julian oscillation (MJO) initiates. Simulation of Hybrid Coordinate Ocean Model (HYCOM) reveals a regional maximum of intraseasonal MLD variability in the EIO (70°–95°E, 3°S–3°N) with a standard deviation of ~14 m. Sensitivity experiments of HYCOM demonstrate that, among all of the MJO-related forcing effects, the wind-driven downwelling and mixing are primary causes for intraseasonal MLD deepening and explain 83.7% of the total ISV. The ISV of MLD gives rise to high-frequency entrainments of subsurface water, leading to an enhancement of the annual entrainment rate by 34%. However, only a small fraction of these entrainment events (<20%) can effectively contribute to the annual obduction rate of 1.36 Sv, a quantification for the amount of resurfacing thermocline water throughout a year that mainly (84.6%) occurs in the summer monsoon season (May–October). The ISV of MLD achieves the maximal intensity in April–May and greatly affects the subsequent obduction. Estimation based on our HYCOM simulations suggests that MJOs overall reduce the obduction rate in the summer monsoon season by as much as 53%. A conceptual schematic is proposed to demonstrate how springtime intraseasonal MLD deepening events caused by MJO winds narrow down the time window for effective entrainment and thereby suppress the obduction of thermocline water.