2021年汉江上游秋雨异常偏多及成因分析

Analysis on the causes of autumn rain anomalies in the upstream of Hanjiang River in 2021

利用统计学方法,对2021年汉江上游秋雨异常特征和成因进行分析。2021年汉江上游秋雨具有开始早、历时长、雨日多、雨量大、阶段性降雨强等特点,其环流特征表现为200 hPa华北有稳定的急流中心,汉江上游上空处于高空辐散区;500 hPa欧亚中高纬环流在巴尔喀什湖至贝加尔湖及蒙古地区同为负距平,利于西北冷空气的南下;西太平洋副热带高压异常偏强偏西、脊线位置稳定于30°N附近,利于雨带的长时间维持。此外,赤道中东太平洋秋季海温表现为负距平,与我国华西秋雨异常偏多、年“拉尼娜”型海温异常具有较好的一致性。

Based on the meteorological and hydrological data,statistical methods were used to analyze the abnormal characteristics and causes of rainfall in the autumn flood season in the upstream of Hanjiang River in 2021.The results show that the autumn rain in the upstream of Hanjiang River in 2021 has the characteristics of early onset,long duration,more rain days,large rainfall,and periodic heavy rainfall.The circulation characteristics are as follows:there is a stable jet stream center in North China at 200 hPa,and the upstream of Hanjiang River is in a upper air divergence area.At 500 hPa,the circulation pattern in middle and high latitudes of Eurasia is negative anomaly from Balkhash lake to Baikal Lake and Mongolia region,which is conducive to the southward movement of cold air from northwest.The subtropical high over the Western Pacific is abnormally strong and westward,and the ridge line is stable near 30°N,which is conducive to the longterm maintenance of the rain belt.In addition,there is a negative anomaly in autumn SST over the equatorial Middle Eastern Pacific with more autumn rains in the upstream of Hanjiang River,which is consistent with the La Nina typical SST anomalies in western China.