Reexamining the Moisture Mode Theories of the Madden–Julian Oscillation Based on Observational Analyses
Reexamining the Moisture Mode Theories of the Madden–Julian Oscillation Based on Observational Analyses
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基于观测分析重新审视马登朱利安振荡的水分模态理论
DOI：
10.1175/jcli-d-20-0441.1
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发表时间：
2021
影响因子：
4.9
通讯作者：
Hao, Lisheng
中科院分区：
文献类型：
--
作者：
Hu, Feng;Li, Tim;Gao, Jianyun;Hao, Lisheng
用1979-2012年的观测资料对MJO现有的两种水汽模式理论进行了验证，其中一种强调边界层水汽不对称性(MA)，另一种强调柱积分湿静力(MSE)趋势不对称性(TA)。总共选择了2343个MJO日。虽然所有这些日子都显示出边界层水汽的明显位相领先，但这些日子中有20%在MJO对流(非TA)之前没有表现出正的柱积分MSE趋势。进一步的MSE收支分析表明，非TA合成和TA合成的不同之处在于MJO对流前异常垂直翻转环流的纬向范围。提出了一个背景平均降水调制机制来解释这种不同的环流响应。根据MJO位置的不同，季节平均和ENSO诱发的降水场对加热的异常鳃响应有很大的调制作用。尽管非TA组在MJO对流前有负的MSE趋势，但由于边界层增湿的作用，系统继续向东移动，促进了MJO对流前的对流不稳定层结。分析结果表明，第一类水汽模式理论--水汽不对称机制显得更为稳健，尤其是在东太平洋大陆和西太平洋地区。
Two existing moisture mode theories of the MJO, one emphasizing boundary layer moisture asymmetry (MA) and the other emphasizing column-integrated moist static energy (MSE) tendency asymmetry (TA), were validated with the diagnosis of observational data during 1979–2012. A total of 2343 MJO days are selected. While all these days show a clear phase leading of the boundary layer moisture, 20% of these days do not show a positive column-integrated MSE tendency in front of MJO convection (non-TA). A further MSE budget analysis indicates that the difference between the non-TA composite and the TA composite lies in the zonal extent of anomalously vertical overturning circulation in front of the MJO convection. A background mean precipitation modulation mechanism is proposed to explain the distinctive circulation responses. Dependent on the MJO location, an anomalous Gill response to the heating is greatly modulated by the seasonal mean and ENSO induced precipitation fields. Despite the negative MSE tendency in front of MJO convection in the non-TA group, the system continues moving eastward due to the effect of the boundary layer moistening, which promotes a convectively unstable stratification ahead of MJO convection. The analysis result suggests that the first type of moisture mode theories, the moisture asymmetry mechanism, appears more robust, particularly over the eastern Maritime Continent and western Pacific.