The Effects of an Upper-Tropospheric Trough on the Heavy Rainfall Event in July 2018 over Japan
The Effects of an Upper-Tropospheric Trough on the Heavy Rainfall Event in July 2018 over Japan
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DOI：
10.2151/jmsj.2020-013
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发表时间：
2020
影响因子：
3.1
通讯作者：
C. Yokoyama;H. Tsuji;Y. Takayabu
中科院分区：
文献类型：
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作者：
C. Yokoyama;H. Tsuji;Y. Takayabu
在这项研究中，我们研究了2018年7月5日至8日给日本西部大部分地区带来强降雨的降雨系统的特征，以及在事件期间停留在广泛降雨区后部的对流层上部槽所发挥的作用。全球降水测量核心卫星上的双频降水雷达揭示了降雨量的重要贡献，其顶部低于10公里，层状降雨覆盖的广阔空间范围，以及嵌入大型层状降雨区的对流降雨。这些特征是有组织的降雨系统的特征。根据气象资料的分析，与气候学相比，与该事件有关的大尺度环境条件相对稳定，对流层大部分地区非常潮湿。这种大规模的环境，这是与以前的极端降雨事件的统计结果是一致的，是目前在日本的广泛地区。我们发现，槽在维持有利于降雨组织的环境方面发挥了重要作用。动力上升与槽采取行动，产生垂直水汽通量的辐合在对流层中上部和对流层，并潮湿的大部分对流层与水平水汽通量辐合。对流层中低层的潮湿条件有利于对流层低层对流不稳定时深对流的发展。一旦深层对流以这种方式得到促进，对流本身就可以通过非绝热上升进一步润湿对流层中上部，从而使自由对流层充满水分。动力效应和非绝热效应之间的协同作用增强了条件，使一个组织良好的降雨系统在日本大部分地区产生了非常强的降雨。
In this study, we examined the characteristics of a rainfall system that brought heavy rainfall to a broad portion of western Japan on July 5 – 8, 2018, and the role played by an upper-tropospheric trough which stayed at the rear of the extensive rainfall area during the event. The Dual-Frequency Precipitation Radar onboard the core satellite of the Global Precipitation Measurement revealed the significant contribution of rainfall with its top below 10 km, the broad spatial extent covered by stratiform rainfall, and the presence of convective rainfall embedded in the large stratiform rainfall area. These features are characteristic of well-organized rainfall systems. Based on the analysis of meteorological data, large-scale environmental conditions related to the event were found to be relatively stable and very humid throughout most of the troposphere compared with the climatology. This largescale environment, which is consistent with previous statistical results for extreme rainfall events, was present across an extensive area of Japan. We found that the trough played an important role in the maintenance of an environment favorable for rainfall organization. Dynamical ascent associated with the trough acted to produce vertical moisture flux convergence in the mid-troposphere and upper troposphere and moistened most of the troposphere in conjunction with horizontal moisture flux convergence. Humid conditions in the midto lower troposphere enhanced the development of deep convection when the lower troposphere was convectively unstable. Once deep convection was promoted in this way, convection itself could moisten the midto upper troposphere further through diabatic ascent, thereby loading the free troposphere with moisture. This synergy between the dynamical effect and the diabatic effect enhanced the conditions that allowed for a well-organized rainfall system that produced very heavy rainfall over a large portion of Japan.