重庆夏季低涡无暴雨的气候学分析

The Summery without Heavy Rainfall Climatic Characteristics Associated with the Mesocale Low Vortex over Chongqing

为了研究对流层中低层中尺度低涡未给重庆夏季带来暴雨的原因,使用1979～2011年1°×1°的ERA-Interim再分析资料和重庆市逐日降水资料,采用天气学诊断、合成分析等方法,从天气、气候学角度,对重庆上空有低涡无暴雨日的天气形势和大尺度降水条件进行分析,结果表明,30余年来,虽然54例低涡未给重庆带来暴雨,但是从气候上讲,大约有1/3的低涡能给重庆带来小于暴雨等级的降水;未给重庆带来暴雨的低涡主要由来自于新疆、过河西走廊及川北地区较干的西北气流和西风带过青藏高原较干的绕流、在重庆上空形成;该低涡在垂直结构上虽然也具有在对流层中低层为气旋性辐合,中高层为反气旋性辐散的特征,但是由于重庆大部分地区并不位于高空急流右侧的辐散区,使高空急流对低层大气的抽吸作用受到限制,加之在低涡日,来自孟加拉湾、南海的水汽主要在广西、湖南以及江西一带形成的水汽大值区,重庆远离该大值区,这些都使重庆难以发生暴雨。

To study the reason that why the mesoscale low vortex in the lower troposphere can not form the heavy rainfall in the Chongqing area during summer. Based on the daily precipitation data from 34 stations in Chongqing and ERA-Interim daily reanalysis datasets from 1979-2011 the synoptic situation and large-scale precipitation conditions when exist low vortex can not form the heavy rainfall is analyzed by means of composite analysis combining diagnostics methods. The result show that in the last 30 years,there are 54 produc low vortex while not form the heavy rain and about one third of the low vortex will produce precipitation The low vortex in Chongqing which not produce heavy rainfall is formed by the drier airflow com from Xinjiang though the north of Sichuan and the Hexi Corridor bypassing the Tibetan plateau. The low vortex vertical structure show that cyclonic convergence in the middle and lower troposphere,anticyclonic divergence in the middle and higher troposphere,but the most area of Chongqing is not on the right side of the divergence of the upper-level jet stream he upper-jet stream pumping action has been restricted esides in the low vortex of the day,the distance between Chongqing and the high value of the water vapor which come from the Bay of Bengai and South China Sea,all of these makes it hard for Chongqing.