2015年1月中国南方大范围持续暴雨的过程分析

An Analysis on A Heavy Rain Weather Process During 8-13 January, 2015 in Southern China

2015年1月中国南方地区出现了一次长达6天的大范围持续性极端强降水过程,多地降水量突破同期极值。本文利用NCEP再分析资料和全国194站降水观测资料,使用合成和诊断分析方法,对此次降水的成因进行了分析。分析结果表明:(1)降水过程的环流型为经向环流型,副热带地区的波动中心更为明显,波动振幅更大。Rossby波能量在地中海中东部-里海地区侵入副热带西风急流,随后波动能量沿急流波导向中国南方传播,约2天后南支槽发展加深。中国南方地区处在高空东亚西风急流的入口区,西风分量小,Rossby波移动缓慢,南支槽能够在中国南方地区维持一段时间,为降水提供了稳定的环流形势。(2)持续偏强的南支槽和西太平洋副热带高压使得暖湿空气源源不断的从孟加拉湾和中国南海输送到中国南方,降水区域随着南支槽和副高的东移而移动。对流层高层强烈的辐散运动为强降水天气的发生提供了动力性上升条件,上升运动区和水汽辐合区对应良好。(3)地中海中东部-里海位势高度异常中心的强度和位相变化超前中国南方降水两天左右,所以分析地中海中东部-里海地区的位势高度变化,对预测我国南方地区的降水有着很好的指示作用。

A heavy rain affected the Southern China during 8-13, January, 2015. The heavy rain storm mainly occurred from Yunnan, Guangxi, Guangdong, Fujian to Zhejiang Province. It’s unusual that an extreme storm happened in winter, especially in Yunnan Province. Based on the daily rainfall observation data, and NCEP-NCAR interval reanalysis data, the atmosphere processes associated with the storm has been analyzed through composite and diagnostic methods. The results show that:(1) In the precipitation process, a strong westerly jet meandered from the northern Africa, Arabian Peninsula, South China to the northwest Pacificin the upper troposphere. There were two distinct wave-like divergence(convergence) branches, the south branch constrained within the subtropical westerly jet stream was more distinct. Rossby wave energy intruded the subtropical westerly jet in the Caspian Sea and eastern Mediterranean, and then the wave energy propagated along the waveguide to southern China, forming a trough over southern China and a ridge over the northwest Pacific. Because of continuous energy inputting in the upstream, the south branch trough could be deepened and maintained for a period of time in southern China. In addition, the western Pacific subtropical high expanded northward. Southern China located in the enter port of Asian westerly jet, meridional wind was smaller relatively. As a result, the phasevelocity of Rossby wave in southern China was slow, providing a stable circulation for the precipitation.(2) The persistent strong southern branch trough and the western Pacific subtropical high transported the warm and wet air to the southern China persistently. The moisture of precipitation mainly came from the Bay of Bengal and the South China Sea. The strong divergence in the upper troposphere provided a dynamic rising condition for the occurrence of the heavy precipitation, and the ascending vertical motion region corresponded to water vapor flux convergence region well. It was also one of the direct reasons about the heavy rain.(3) The intensity and phase changes of the cyclonic anomalous circulation center in the Caspian Seaand eastern Mediterranean was ahead of the changes in the cyclonic anomalous circulation center of the southern branch trough for about 2 days. If the south branch trough could be deepened and move to southern China, couples with enough moisture, then it will be highly possible that rain can occur there. Consequently, it may be useful to analysis the change of geopotential height in the Caspian Sea and eastern Mediterranean for the precipitation forecast in southern China.