Characteristics of Large-Scale Atmospheric Fields during Heavy Rainfall Events in Western Japan: Comparison with an Extreme Event in Early July 2018
Characteristics of Large-Scale Atmospheric Fields during Heavy Rainfall Events in Western Japan: Comparison with an Extreme Event in Early July 2018
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日本西部强降雨事件期间大范围大气场特征：与2018年7月上旬极端事件的比较
DOI：
10.2151/jmsj.2020-062
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Kazuto Takemura
中科院分区：
文献类型：
--
作者：
Y. Harada;H. Endo;Kazuto Takemura
为了探索造成日本西部大范围强降雨事件的大尺度大气因子，利用日本55年再分析资料对该地区过去强降雨事件的大气场进行了综合分析。在强降雨事件中，大气场的特征是朝鲜半岛上空的对流层低槽、日本以东的对流层高脊、日本东南部的地面高压系统和西南方向的水汽通量。综合分析表明，西伯利亚极锋急流准平稳罗斯比波包传播（RWPP）导致的清晰波列往往在极端事件发生前出现。进一步考虑大气各时间尺度变化的分析表明，日本东南部的地面高压异常以25 ~ 90 d周期的变率为主，而与KP周围对流层上层槽发展有关的东海低气压异常以8 ~ 25 d周期的变率为主。我们还研究了2018年7月初发生的一次极端强降雨事件（HR18）期间的大气场。HR18期间的大气特征与其他强降雨事件基本相似。然而，2018年6月下旬，副热带急流（STJ）沿线发生了一次显著的RWPP，并增强了日本东南部的地面高压系统。此外，在日本南部有一个持续了8 - 25天的低压系统，该低压系统与沿STJ的显著RWPP引起的破波有关，并向西北方向传播到ECS，然后到达日本。高低压系统的同时发展导致了极偏南的水汽流进入日本西部。HR18的另一个特征是在KP上空有一个尖锐的对流层上层槽，以周期< 8天的高频变率为主。
In order to explore large-scale atmospheric factors causing heavy rainfall events that occurred widely in western Japan, a composite analysis of atmospheric fields during the past heavy rainfall events in the region is conducted using the Japanese 55-year Reanalysis. During heavy rainfall events, atmospheric fields are characterized by an upper-tropospheric trough over the Korean Peninsula (KP), an upper-tropospheric ridge to the east of Japan, a surface high-pressure system to the southeast of Japan, and southwesterly moisture flux. The composite analysis indicates that a clear wave train due to quasi-stationary Rossby wave packet propagation (RWPP) along the polar front jet over Siberia tends to occur just before extreme events. Further analysis considering various time scale variabilities in the atmosphere reveals that surface high-pressure anomalies to the southeast of Japan are dominated by variability with a 25 – 90 day period, whereas variability with an 8 – 25 day period dominates lower-pressure anomalies over the East China Sea (ECS) in relation to the development of the upper-tropospheric trough around the KP. We also investigate atmospheric fields during an extreme heavy rainfall event that occurred in early July 2018 (HR18). Atmospheric features during HR18 are generally similar to those of the other heavy rainfall events. However, a remarkable RWPP occurred along the subtropical jet (STJ) in late June 2018 and intensified a surface high-pressure system to the southeast of Japan. Additionally, a low-pressure system with an 8 – 25 day period to the south of Japan developed in association with wave breaking induced by the remarkable RWPP along the STJ and propagated northwestward toward the ECS and then to Japan. The simultaneous development of highand low-pressure systems contributed to the extreme southerly moisture flux into western Japan. HR18 is also characterized by a sharp upper-tropospheric trough over the KP that is dominated by high frequency variability with a period < 8 days.
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