Precipitation mechanism and organization of mesoscale convective systems.

1988年7月，九州地区在密集观测期间观测到一次与白球锋有关的暴雨。我们研究了造成这次强降雨的一个雨带的结构和机理。提出了一种反演雨带热力学场的方法。反演结果表明，雨滴蒸发和垂直切变对维持局地雨带有重要作用。对此次暴雨进行了数值预报试验。对观测的降雨进行了较好的模拟，并对降雨的环境条件进行了研究。采用高水平分辨率的数值模式对暴雨进行了详细的结构分析。模拟了雨带的垂直结构，明确了其垂直结构。1992年4月22日，关东平原上空随着一个温带气旋的通过而形成一条狭窄的云带。它的独特特征包括快速形成和弧形固体云墙的外观，而不是一些孤立的对流细胞的线条。它沿着一个更广泛的弱雨区的南部边缘演变，其方式类似于Bluestein和Jain（1985）所确定的嵌入式区域类型。对常规观测资料的中尺度分析表明，局地冷气团从关东平原西北部向东南方向传播。它是由与东向传播的气旋相关的水平压力梯度力驱动的。该云带是在冷潮与关东平原南部盛行的天气尺度西南气流碰撞时被迫形成的。进一步揭示了这次寒潮是一个低层中尺度气团的先导部分，称为“先导”气团。因其存在于天气尺度西北气流前方，上层低压槽前方西南气流下方而得名。

A heavy rainfall associated with the Baiu front was observed during an intensive observation period in the Kyushu District in July 1988. We studied a structure and mechanism of a rainband caused the heavy rainfall. A retrival method was developed to raveal a thermodynamic field in the rainband. The retrived field showed that the evaporation of raindrop and a vertical shear were important to maintain the inteese rainband.A numerical prediction experiment of the heavy rainfall was performed. The observed rainfall was simulated well and the environmental condition of the rainfall was stduied. A numerical model with high horizontal resolution was used to find a detailed structure of the heavy rainfall. The rainband was simulated and its vertical structure was clarified.A narrow cloud band developed over Kanto Plain on 22 April 1992 in association with the passage of an extratropical cyclone. Its unique features include the rapid formation and appcarance of an arc-shaped solid cloud wall, rather than a line of a number of isokated convective cells. It evolved along the southern edge of a much broader weak rain area in a manner similar to the embedded areal type as identified by Bluestein and Jain (1985).A mesoscale analysis of conventional observation data reveals that a local cold air mass propagated southeastward from the northwestern part of Kanto Plain. It was driven by the horizontal pressure gradient force associated with the eastward-propagiting cyclone. The cloud band was found to be forced to form when and where the cold surge collided with the synopic scale southwesterly flow which was prevailing over the southern part of Kanto Plain.It is further revealed that the cold surge was a leading part of a low-level mesoscale air mass which was termed as "forerunner". It was so named since it existed in front of the sysnoptic scale northwesterly flow and beneath the southwesterly flow ahead of the upper-level trough.