Effects of MJO Vertically Tilted Structure on Its Phase Speed from the Moisture Mode Theory Perspective
Effects of MJO Vertically Tilted Structure on Its Phase Speed from the Moisture Mode Theory Perspective
复制标题
从湿模理论视角MJO垂直倾斜结构对其相速度的影响
DOI：
10.1175/jcli-d-20-0732.1
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发表时间：
2021
影响因子：
4.9
通讯作者：
Li, Tim
中科院分区：
文献类型：
--
作者：
Hu, Feng;Li, Tim
通过对1979-2012年ERA-Interim再分析资料的诊断，研究了MJO的垂直倾斜结构（VTS）对其位相传播速度的影响。共选择了84个向东传播的MJO事件。结果发现，所有MJO事件在其整个生命周期内平均均表现出明显的VTS，并且倾斜强度与相速度显着正相关。研究了VTS影响相速度的物理机制。一方面，一个更强的VTS导致更强的垂直翻转环流和更强的下降在前面，这导致更大的正湿静力能量（MSE）的趋势，通过增强垂直MSE平流在原地。MSE趋势梯度越大，则东向相速度越快。另一方面，MJO对流前的翻转环流增强，导致边界层顶部东风/低压异常增强，引起边界层辐合增强，对流层低层上升增强。这加强了边界层湿度的不对称性，有利于更快的东移速度。
The effect of vertically tilted structure (VTS) of the MJO on its phase propagation speed was investigated through the diagnosis of ERA-Interim reanalysis data during 1979–2012. A total of 84 eastward propagating MJO events were selected. It was found that all MJO events averaged throughout their life cycles exhibited a clear VTS, and the tilting strength was significantly positively correlated to the phase speed. The physical mechanism through which the VTS influenced the phase speed was investigated. On the one hand, a stronger VTS led to a stronger vertical overturning circulation and a stronger descent in the front, which caused a greater positive moist static energy (MSE) tendency in situ through enhanced vertical MSE advection. The stronger MSE tendency gradient led to a faster eastward phase speed. On the other hand, the enhanced overturning circulation in front of MJO convection led to a stronger easterly/low pressure anomaly at the top of the boundary layer, which induced a stronger boundary layer convergence and stronger ascent in the lower troposphere. This strengthened the boundary layer moisture asymmetry and favored a faster eastward propagation speed.