海南岛不同强弱秋汛期暴雨的环流形势和动力特征分析

摘要

基于天气学诊断分析方法,对2000年10月11-14日、2010年10月1-8日和2003年10月4-5日、2005年10月10-11日4次不同降水强度的秋汛期暴雨过程进行了对比分析,研究结果表明:不同强度秋汛期暴雨过程的降水分布和高低层天气系统配置具有相似性,导致秋汛期暴雨出现强度差别的主要原因是天气系统强度、位置的差异.秋汛期暴雨强个例中,南亚高压中心位于海南岛上空,辐散强度是弱个例的2～3倍,南海热带低值系统相对更强,位置偏北,副高偏弱主体退缩至海上.南海中北部出现偏东风低空急流是秋汛期暴雨过程中最显著的环流特征.在不同强度的降水个例中,急流的分布形态、强度存在明显差别.强个例中低空急流的急流核强度、长度、厚度,以及急流核上方的风速梯度均远大于弱个例,且水平风随高度顺时针旋转现象十分显著,出现强的暖平流.此外,最强降水日中强个例的低空急流核位于海南岛东部近海上空,在水平方向上稳定少动,垂直方向和风速上则脉动剧烈.弱个例的急流核在水平方向上东西振荡明显,在垂直高度和风速上变化很小.秋汛期暴雨强个例的水汽主要由偏南风、偏东风和东北风3支气流输送而来,既有经向输送也有纬向输送,弱个例的水汽以经向输送为主,多为偏东气流所致.%Daily precipitation data observed by 18 stations in Hainan and NCEP/NCAR reanalysis data are used to analyze the different intensity rainfall circulation characteristics during the autumnal flood season in Hainan.Results show that,there are many similarities in circulation configurations and precipitation distributions of the rainstorms with different intensity during autumnal flood season.The difference of the intensity and position of synoptic systems results in the precipitation discrepancy of the rainstorms during the autumnal flood season.In the strong rainstorm processes,the center of South Asia High (SAH) remain over Hainan Island,and its divergence intensity is about 2-3 times stronger than weaker rainstorm processes.At middle and lower level,Western North Pacific Subtropical High (WNPSH) is weaker and retreats from Asian continent,and tropical low-pressure system is stronger and more northern in the strong rainstorm cases.The presence of strong low-level jet in north central South China Sea(SCS) is the most significant feature of rainstorm case in autumnal flood season,but the distinct characteristics are also manifested mainly in the differentia of the shape and intensity of low level jet between different rainstorm cases.In the strong cases,the strength,length,thickness and speed gradient of jet core is much larger,and that horizontal wind circumvolve clockwise along with height,all facts are conductive to the maintenance and development of rainstorm.In addition,the jet cores of strong cases are stationary and stay over the sea near the eastern Hainan Island in the maximum precipitation day,and they fluctuate wildly in the vertical direction and wind speed.But when it comes to the weak cases,the situation is reversed,the jet cores change little in height and speed,and oscillate obviously in the east-west direction.The water vapor of the strong cases transports by three airflows:northeaster,easterly and southerly,but the vapor transportation of the weak cases is mainly due to the easterly wind.