摘要
利用地面观测资料和NCEP/NCAR 1°×1°再分析资料,对2013年7月17—18日四川境内的区域暴雨(7.18暴雨)进行了分析,并用WRF模式对该次暴雨过程进行了数值模拟。研究表明:7.18暴雨是一次典型的低涡暴雨,其主要强降水时段发生在北京时间18日凌晨01—02时,具有明显的夜雨特征;WRF模式对夜雨的模拟效果要好于白天,这说明WRF模式对地形复杂的四川地区白天降水的模拟能力尚需进一步提高;导致7.18暴雨的中尺度低涡具有类似锋区的斜压特征,异常陡峭的θse的分布,使得倾斜不稳定涡旋发展;较强的正涡度中心大值区有利于中小尺度低涡的形成。
In China, the Southwest Vortex （a special type of mesoscale convective system） is second only to that caused by tropical cyclones when it comes to the severity of heavy precipitation.During 11--12 July 2013 ,heavy rainfall（referred to as the ＂7. 18 rainfall＂ hereafter） occurred over Sichuan Province in China,resulting in cata- strophic flooding.Based on rain gauge data--including conventional meteorological observations and those of au- tomatic weather stations--provided by the Meteorological Information Center of the China Meteorological Admin- istration, and NCEP FNL （Final） Operational Global Analysis data with a horizontal resolution of 1 ~x 1 ~ and pre- pared operationally every six hours,synoptic diagnostic methods and mesoscale numerical modeling were used to study the 7. 18 heavy rainfall with the Weather Research and Forecasting（WRF） model.Numerical experiments were performed to （1） test the capability of WRF in simulating nighttime precipitation over complex terrain, such as that of Sichuan Province ; （2） examine the characteristics of the Southwest Vortex ; and （3） elucidate the cause of the 7. 18 heavy rainfall with respect to the large-scale precipitation conditions.The main results can be summa- rized as follows： （ 1 ） The 7. 18 heavy rainfall was influenced by a typical mesoscale vortex, and the period of the largest a- mount of precipitation was 0100--0200 Beijing standard time（BST） 18 July 2013. Accompanying the development and disappearance of the mesoscale vortex at 500 hPa, the intensity of precipitation gradually changed from strong to weak and, finally, stable, meaning the 7.18 heavy rainfall possessed obvious characteristics of nighttime rainfall. （2）The main weather systems of influence were a westerly trough at 500 hPa（nearby at 0000 UTC） and a mesoscale vortex at 700 hPa over Sichuan Province.Meanwhile,meridionally, the western Pacific subtropical high （WPSH） extended towards the west and formed a typical ＂western trough--eastern high＂ pattern;and under the obstruction of the stable WPSH, the westerly trough at 500 hPa developed a low pressure vortex, before weakening gradually and ultimately disappearing. Sichuan Province suffered long-duration precipitation during 11--12 July 2013 because there was a westerly trough at 500 hPa and a mesoscale vortex at 700 hPa stagnated o- ver Sichuan Province for a long period under the blocking of the WPSH. The typical ＂western trough-eastern high＂ pattern allowed warm and wet flow to arrive from the ocean to the south, and dry and cold flow from the north, which converged over Sichuan Province. In addition, Sichuan Province was influenced by strong atmospheric upward motion, and these conditions led to the occurrence of the 7.18 heavy rainfall. （3） The low vortex at 700 hPa had a baroclinic feature similar to that of a frontal zone, and was under the in-fluence of unusually steep potential pseudo-equivalent temperature （ 0se ）, meaning slantwise and unstable vorticity could develop gradually.As the stronger and higher value positive vorticity center would have been beneficial to the formation of small and mesoscale vortexes,the formation and development of such vortexes could have pro- vided favorable dynamic conditions for the heavy rainfall. （4） The simulation results from the WRF model showed that WRF was able to simulate the location of the rain belt near Ziyang well,but the location of the rain belt near Guangyuan was shifted to the north and east.Mo- reover, the intensity of the simulated precipitation was greater than observed.Regarding the temporal evolution of precipitation occurrence, the simulation results of WRF were better for nighttime than daytime, indicating that WRF needs to be further improved for simulating daytime precipitation over complex terrain like that of Sichuan Province.
出处
《大气科学学报》
CSCD
北大核心
2016年第5期702-711,共10页
Transactions of Atmospheric Sciences
基金
国家自然科学基金资助项目(91337215
41305131)
重庆市气象局开放式研究基金项目(KFJJ-201102)
博士后科研项目特别资助项目(渝xm201103028)
公益性行业(气象)科研专项(GYHY201406020)
关键词
四川暴雨
数值模拟
WRF模式
Sichuan Province
heavy rainfall
numerical simulation
WRF model
