Large-Scale Environmental Conditions Related to Midsummer Extreme Rainfall Events around Japan in the TRMM Region
Large-Scale Environmental Conditions Related to Midsummer Extreme Rainfall Events around Japan in the TRMM Region
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DOI：
10.1175/jcli-d-17-0632.1
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发表时间：
2018-07
影响因子：
4.9
通讯作者：
A. Hamada;Y. Takayabu
中科院分区：
文献类型：
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作者：
A. Hamada;Y. Takayabu
研究了TRMM观测区域日本周边13年卫星数据确定的8月极端事件降水特征及其与大尺度环境条件的关系。在每个分析网格框中分别使用每个事件中的最大近地表降雨量和最大 40 dB Z 回波顶高度来定义两种类型的极端事件：极端降雨和极端对流事件。两类极端事件的降水特征存在明显差异。极端降雨事件是比极端对流事件更有组织的降水系统，具有相对较低的回波顶高度和非常低的闪电活动。相关环境条件也存在明显差异，与极端降雨事件相关的环境对流稳定，几乎整个对流层都非常潮湿。这些事实与我们之前的研究一致，并强调了暖雨过程在极强降水产生中的重要性。与极端降雨事件相关的环境在中国南部至日本东部的自由对流层中表现出纬向扩展的湿润异常，这表明大规模气流从西部输送的过量水分可能在一定程度上产生了有利于极端降雨的环境条件。另一方面，与极端对流事件相关的环境与自由对流层湿气流入无关。还研究了与热带气旋和对流层上层动力场的关系，发现极端降雨事件和极端对流事件之间存在明显不同。
The precipitation characteristics of extreme events in August determined from 13 years of satellite data around Japan in the TRMM observation region and their relationship with large-scale environmental conditions are examined. Two types of extreme events, extreme rainfall and extreme convective events, are defined in each analysis grid box using maximum near-surface rainfall and maximum 40-dB Z echo-top height in each event, respectively. There are clear differences in precipitation characteristics between the two types of extreme events. Extreme rainfall events are more organized precipitation systems than the extreme convective events, with relatively lower echo-top heights and very low lightning activity. There are also clear differences in the related environmental conditions, where the environments related to the extreme rainfall events are somewhat convectively stable and very humid in almost the entire troposphere. These facts are consistent with our previous studies and reinforce the importance of warm-rain processes in extremely intense precipitation productions. The environments related to the extreme rainfall events exhibit a zonally extended moist anomaly in the free troposphere from southern China to the east of Japan, indicating that the excessive moisture transported from the west by a large-scale flow may partially play a role in producing environmental conditions favorable for extreme rainfall. On the other hand, the environments related to extreme convective events are not associated with free-tropospheric moisture inflow. The relationships with the tropical cyclones and upper-tropospheric dynamical fields are also examined, and are found to be clearly different between the extreme rainfall events and extreme convective events.