Unusual Weather due to Irregular Activity of Polar Airmass and Associated Heavy Rainfall.

位于亚洲大陆东部的日本，极地气团主导着天气。在极地气团和热带气团之间形成的白乌锋和秋雨锋与极地气团的活动有关。极地气团的不规则行为有时会导致日本出现异常天气。本文以极区气团活动异常和强降水为研究对象，利用国家气象中心（NMC）格点资料，对极区气团活动进行了统计分析。南半球夏季和北方冬季500 hPa高度场的相关性较强。南半球的高度距平在纬向上与北方的高度距平比较一致。当旋转装置是轴对称的时，轴对称流是不稳定的，并且产生非轴对称扰动。1988年7月，在九州地区的密集观测期间，观测到了与白宇锋有关的暴雨。研究了一次强降水过程中雨带的结构和形成机制。发展了一种反演雨带热力场的方法。反演结果表明，雨滴蒸发和垂直切变是维持强雨带的重要因素。1“ORI”是“海洋研究所”的简称。对观测到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。利用一个高水平分辨率的数值模式对这次暴雨进行了详细的结构分析。对雨带进行了数值模拟，并阐明了雨带的垂直结构。

The polar airmass dominates the weather in Japan which is located in the east of the Asian Continent. Baiu and Akisame fronts which form between the polar airmass and the tropical airmass are related to an activity of the polar airmass. An irregular behavior of the polar airmass sometimes causes unusual weather in Japan. Objectives of this research are the unusual weather due to the irregular activity of the polar airmass and the associated heavy rainfall.The NMC grid point data were analyzed by means of a statistic method to investigate the activity of polar airmass. High correlations were found in 500hPa height field during summer season in the southern hemisphere and during winter season in the northern hemisphere. A height anomaly in the southern hemisphere was relatively uniform in the zonal direction in comparison with that in the northern hemisphere.Behavior of the polar airmass was simulated in a laboratory experiment. While a rotating apparatus was axisymmetric, the axisymmetric flow was not stable and a non-axisymmetric disturbance developed. The pattern of the non-axisymmetric flow was similar to that of a polar air outbreak.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 reinfall. A retrieval method was developed to reveal a thermodynamic field in the rainband. The retrieved field showed that the evaporation of raindrop and a vertical shear were important to maintain the intense rainband.^1 "ORI" is the abbreviation of "Ocean Research Institute".A numerical prediction experiment of the heavy rainfall was performed. The observed rainfall was simulated well and the environmental condition of the rainfall was studied. 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.