1951—2017年热带气旋对湖南降水的影响及环流异常特征分析

揭示热带气旋在湖南的降水规律可为热带气旋影响湖南的降水预报提供技术支撑。采用近67 a的热带气旋影响资料,通过统计方法,分析了影响湖南降水的热带气旋特点及环流异常特征。结果表明:7—9月是影响的高峰季节,以在广东、福建沿海登陆的热带气旋对湖南影响次数最多、程度最重,浙江、福建沿海登陆的热带气旋在湖南形成的降水范围最大,热带气旋对湖南影响所产生的降水主要集中在湖南省东南部,热带气旋对湖南产生的强降水范围有增大的趋势,降水强度有增强的趋势。福建和广东沿海登陆对湖南影响的热带气旋的环流特征为南亚高压偏强、偏东、偏北,导致西太平洋副热带高压偏强、偏西、偏北,引导副热带高压南侧的东南气流与南海和菲律宾以东洋面的西南风气流汇合,形成季风槽,中国华南和华东沿海为东南气流,有利于热带气旋在该区域登陆影响中国。只是前者表现为南亚高压位置较后者偏北更明显,西太平洋副热带高压更偏北,季风槽更偏东,导致福建登陆对湖南影响的热带气旋在湖南大部为气旋性环流控制,湖南全省降水偏多;而广东登陆对湖南影响的热带气旋在湖南省东南部为气旋性环流控制,该区域降水偏多。

Impact of tropical cyclones on precipitation and characteristics of circulation anomalies in Hu'nan province during 1951-2017

Understanding on the precipitation patterns influenced by tropical cyclones in Hu'nan province can provide technical support for precipitation forecast in relation to tropical cyclones in this region.Using tropical cyclone data in recent 67 years, we statistically analyzed the impact of tropical cyclones on precipitation in Hu'nan province and the characteristics of circulation anomalies.The results indicate that precipitation in relation to tropical cyclones in Hu'nan province mainly occurs from July to September.Tropical cyclones landing in coastal areas of Guangdong and Fujian provinces have the most frequent and severest effects on precipitation in Hu'nan province, and those landing in Zhejiang and Fujian provinces contribute to the widest precipitation area in Hu'nan province.These precipitation events mainly concentrate in the southeast Hu'nan province, and the heavy precipitation events have exhibited an increase in area and intensity in the past 67 years.Atmospheric circulation in relation to tropical cyclones landing in coastal regions of Guangdong and Fujian provinces is characterized by a strong South Asia High, with its location more east- and northwards, and thus a strong West Pacific Subtropical High, with its location more west- and northwards.The two high-pressure systems contribute to the convergence of southeasterly flows on the southern side of the West Pacific Subtropical High and southwesterly winds over the South China Sea and the eastern Philippine Ocean, and thus the formation of a monsoon trough.Finally, southeasterly flow over southern and eastern China favors the landing of tropical cyclones and then precipitation in these regions.Tropical cyclones landing in Fujian province, in comparison with those landing in Guangdong province, are usually accompanied with South Asia High and the West Pacific Subtropical High located further northward and the monsoon trough more eastward, which can result in a cyclonic circulation and substantial precipitation in most regions in Hu'nan province.However, tropical cyclones landing in Guangdong province were mostly controlled by a cyclonic circulation and substantial precipitation in the southeastern region of Hu'nan province.