“9608”号台风登陆北上引发北方特大暴雨的中尺度对流系统研究

A STUDY ON MESOSCALE CONVECTIVE SYSTEMS OF THE SEVERE HEAVY RAINFALL IN NORTH CHINA BY “9608” TYPHOON

中文关键词:  台风暴雨，中尺度对流系统，中尺度高空急流

英文关键词:Heavy rainfall in typhoon,Mesoscale convective system,Mesoscale upper-level jet.

中文摘要:

      利用NCEP再分析资料和常规观测资料，对1996年8月3—5日发生在河北和山西的特大暴雨过程进行了分析和模拟研究，并对模拟结果用部分特殊观测资料进行了证实。天气形势的分析表明，“96.8”暴雨过程中登陆减弱的台风低压并未出现“75.8”暴雨中的台风与中纬度西风槽发生相互作用，入侵的弱冷空气是由华北高压南侧的偏东风引导至台风倒槽外围，是属于比较少见的登陆台风北上受高压阻挡停滞类型；台风倒槽内发生发展的2个中尺度对流云团是造成此次暴雨的直接影响系统，对流层低层的偏南风低空急流对中尺度对流云团的发展具有重要作用；暴雨期间，低空急流不仅强度大，而且伸展高度也相对较高；伴随强对流系统的主要入流和出流气流分别有2支，其中对流层高层的高空中尺度急流中心主要由强出流气流形成。分析还表明太行山对对流系统的阻挡可能是导致强降水长时间维持在石家庄附近的原因之一。

英文摘要:

      A diagnosis and simulation study have been conducted to reveal the features of the severe heavy rainfall in Hebei province during 3—5 August 1996. The weather pattern of the mesocale systems are diagnosed firstly, and then PSU/NCAR MM5 is used to simulate the process. The simulation results also are employed to study the structure and the development of mesoscale systems. Although the landing typhoon propagating northward is a key system producing heavy rainfall over North China, but the weather pattern of present case is different from most of this kind cases. It is the standstill or slow-moving of landing typhoon stopped by high pressure in the continent, which is rarely happened over North China. During the heavy rainfall process, the interaction of westerly trough and the landing typhoon was not found, but the weak cold air from the southern part of anticyclone in North China invading to the outmost of landing typhoon, which was favorable to the initiation of convection. It is indicated that two mesoscale convective systems were related directly with the severe heavy rainfall in Hebei province. The center of severe heavy rainfall occurred around Shijiazhang area during 20:00 3—08:00 5 August. The analysis of sounding shows that the instability is obvious and the moisture in lower and middle troposphere increases gradually prior to the occurrence of heavy rainfall. The moisture transportation of south low-level jet (LLJ) was very important to the development of convection. The height of LLJ was relatively higher than that in Meiyu front. The most simulation results from MM5 consistent with observation although some deficiency is found. The simulation results reproduce the formation and development of the mesoscale convective systems producing the heavy rainfall. It is shown that the upper-level mesoscale jet formed by the upper level outflow of convection occurred during the evolution of convection. The low-level jet (LLJ) and upper-level jet (ULJ) intensify with the development of convective system. There existed two inflows and two outflows of convection system producing heavy rainfall. The inflow in lower troposphere is from southerly LLJ. The two outflows occur at lower and upper level, respectively. The interaction of LLJ and mesoscale ULJ could maintain and accelerate the development of convective system. It is also shown that the northwards propagation of convection systems was blocked by Taihang Mountain, which was one of the reasons the heavy rainfall persisting over Shijiazhang, Hebei province.