2013年浙江省夏季异常高温天气特征及其成因分析

Characteristics and causes of an extremely high-temperature event in the summer of 2013 in Zhejiang Province

本文利用常规气象站观测资料及欧洲数值预报中心ERA-Interim(0.75°×0.75°)再分析资料,对2013年浙江省夏季异常高温天气的特征及其成因进行了分析。结果表明:2013年夏季浙江省出现了自1951年以来最严重的一次高温天气,7—8月全省平均气温、高温日数和极端最高气温均为1951年以来的最高纪录;梅雨期偏短,台风影响程度小,是浙江省此次高温天气发生的背景。浙江省此次高温天气的6个阶段中,第四个阶段高温持续时间最长和强度最强。浙江省此次异常高温天气主要是由于夏季偏强偏西的副热带高压和偏强偏东的南亚高压控制浙江地区的高低层,受下沉气流影响,对流活动受到抑制;极涡中心位置偏向北美北部地区,冷空气偏弱,中高纬度地区低压槽相对浅薄,不利于冷空气深入南下,副热带高压7月中旬开始稳定维持在长江中下游地区,并在8月上旬形成带状高压坝,使冷暖气流辐合偏北,降水落区偏北;西风急流位置偏北,影响副热带高压西伸,导致高温区受下沉气流影响增温。

The characteristics and causes of an extreme high-temperature event in the summer of 2013 in Zhejiang Province were analyzed using the conventional automatic weather station observations and the European Center for Medium-Range Weather Forecasts（ ECMWF） Re-Analyses（ ERA） Interim reanalysis data（ resolution with 0. 75°× 0. 75°）. The results showthat the highest temperature appears in the summer of 2013 since 1951 over Zhejiang Province. Its mean value of temperature in July and August,the number of the high-temperature days and extreme value of the maximum temperature all break the highest records since 1951. The short-time period of Meiyu and less impact of the typhoon are the backgrounds for this high-temperature weather. Among its six high-temperature stages,the fourth is the one that lasts the longest and has the strongest intensity. The main reasons for the high temperature are as follows. First,the stronger westward subtropical high and stronger eastward South Asia high in the summer together control the high and lowlevels over Zhejiang region. It leads to the convective activity is inhibited by the sinking airflow. Second,the center of polar vortex tends to the north of the North America. So the cold air coming from the polar vortex is weak at Zhejiang region. Meanwhile,the troughs in the middle and high latitudes are relatively shallow. It is not favorable for the cold air to move southwards. Furthermore,the subtropical high occupies over the middle and lower reaches of the Yangtze River from mid-July and then forms a banding high-pressure dam in early August. Under this situation,the convergence zone of cold and warm airs is located northwards,and the precipitation areas are also northward. Third,the westerly jet lies northward. It impedes the subtropical high moving westwards. Under the influence of the sinking airflow,it leads to the temperature increasing at this region.