A study of meso-scale vortex-like convective clouds observed over the seas around Japan

自1987年由地球静止气象卫星“Himawa”进行观测以来，在日本周边海域经常发现[10公里至[100公里]中尺度的涡旋对流云型。本文以观测研究、实验室和数值试验为基础，对日本海冬季中尺度涡旋对流云的季节分布、地理分布及其发展机制进行了研究，取得的主要结果如下：(1)卫星云图统计分析表明，冬季日本海有两个中尺度涡旋云多发地区：1)朝鲜半岛以东，2)北海道以西。这些具有气旋性涡度和数小时寿命的涡旋云以10ms^&lt；-1&gt；的速度向东南方向移动，其中一些在登陆日本沿海地区后消失。(2)观察到伴随水平辐合和气旋性切变的带状云，涡旋云通常形成在这样的带中：一是来自西伯利亚的北风与来自朝鲜半岛的西风的辐合带，另一条是来自西伯利亚的西北风与来自北海道的东北风的辐合带。(3)对流层上层有发达的低槽或冷涡，对流层下部有西北风季风，在日本海上空有较深的潜在不稳定层。这有利于中尺度涡旋对流云的发展，并伴随着地形引起的辐合和切变带。

Vortical convective cloud patterns in meso-scale ranging from[10km to [100km gave been frequently found over the seas around Japan, since observation by the geostationary meteorological satellite "Himawari" was available in 1987. The objectives of the present study is to elucidate seasonal and geographical distributions of meso-scale vortical convective clouds and mechanism of their development besed on an observational study and laboratory and numercal experiments.The results obtained so far are summarized as follows.(1) Statistical analyses of satellite cloud pictures show two preferred areas in the Sea of Japan in winter where meso-scale vortical clouds are most frequently observed : 1) east of Korea peninsula and 2) west of Hokkaido Island. These vortical clouds gaving cyclonic vorticity and life-time of several hours move to southeast in a speed of 10ms^<-1> and some of them vanish just after landing to coastal regions of Japan.(2)Band clouds accompanying horizontal convergence and cyclonic shear are observed and the vortical clouds are often formed in the bands : one is a convergence zone between northerly wind from Siberia and westerly wind from Korea peninsula and the other is a convergence zone between northwesterly from Siberia and northeasterly from Hokkaido. This suggests that meso-scale vortical disturbances may be formed favorably in the convergence zones.(3) A well-developed trough or a cold vortex in the upper troposphere and a northwesterly monsoon in the lower tropposphere provides a deep potentially unstable layer over the Sea of Japan. This is favorable for development of meso-scale vortical convective clouds in association with topographically induced convergence and shear zones.