Transient Behavior of the Asian Summer Monsoon Anticyclone Associated With Eastward Eddy Shedding
Transient Behavior of the Asian Summer Monsoon Anticyclone Associated With Eastward Eddy Shedding
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DOI：
10.1029/2021jd036090
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发表时间：
2021-10
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通讯作者：
Xinyue Wang;W. Randel;L. Pan;Yutian Wu;Pengfei Zhang
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作者：
Xinyue Wang;W. Randel;L. Pan;Yutian Wu;Pengfei Zhang
亚洲季风反气旋（AMA）呈现出副涡的三峰分布，西太平洋是首选位置之一。西太平洋反气旋 (WPA) 的增强通常与 AMA 向东的涡流脱落有关，尽管这一过程尚不清楚。本研究调查了与天气尺度上对流层上层和平流层下层 WPA 出现相关的驱动向东涡流脱落的动力学。使用 1979 年至 2019 年期间的再分析数据，我们的综合分析表明，放大的 WPA 事件与先前研究中确定的欧亚大陆中纬度上游丝绸之路 (SR) 波列模式有关。准静止向东传播的涡流是由沿西风急流的斜压激发产生的，这一点可以通过相干涡流热通量和低层温度梯度的减弱来确定。高空西风急流对于确定波列的纵向锁相非常重要，波列在急流出口附近锚定并放大。菲律宾附近偶尔增强的对流也会引发反气旋涡流，这些涡流通过太平洋-日本（PJ）模式向上和向东北传播，在对流层上层形成 WPA。相关性分析表明 SR 和 PJ 机制在物理上并不相关。
The Asian monsoon anticyclone (AMA) exhibits a trimodal distribution of sub‐vortices and the western Pacific is one of the preferred locations. Amplification of the western Pacific anticyclone (WPA) is often linked with eastward eddy shedding from the AMA, although the processes are not well understood. This study investigates the dynamics driving eastward eddy shedding associated with the emergence of the WPA in the upper troposphere and lower stratosphere on synoptic scales. Using reanalysis data during 1979–2019, our composite analysis reveals that amplified WPA events are tied to the upstream Silk Road (SR) wave‐train pattern over midlatitude Eurasia as identified in previous studies. The quasi‐stationary eastward propagating eddies result from baroclinic excitation along the westerly jet, as identified by coherent eddy heat fluxes and weakening of the low‐level temperature gradient. The upper‐level westerly jet is important in determining the longitudinal phase‐locking of wave trains, which are anchored and amplify near the jet exit. Occasionally enhanced convection near the Philippines also triggers anticyclonic eddies that propagate upward and northeastward via the Pacific‐Japan (PJ) pattern, forming the WPA in the upper troposphere. Correlation analysis suggests that the SR and PJ mechanisms are not physically correlated.