An analysis of summer rain showers over central Japan and its relation with the thermally induced circulation
An analysis of summer rain showers over central Japan and its relation with the thermally induced circulation
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日本中部夏季阵雨分析及其与热诱发环流的关系
DOI：
10.2151/jmsj1965.75.2_513
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发表时间：
1997
影响因子：
3.1
通讯作者：
T. Kuwagata
中科院分区：
文献类型：
--
作者：
T. Kuwagata
本文利用气象站常规观测资料，对1985年夏季日本中部地区在晴朗天气条件下发生的夏季阵雨过程进行了研究。统计分析表明，降水的日循环在1800LST附近有一个明显的峰值，而0000~1200LST之间降水较少。这一明显的峰值与下午炎热的陆地表面上形成的夏季阵雨有关。当大气可降水量超过40 mm时，干(湿)对流的大气静力稳定度降低，雨簇射活动增加。暴雨集中在水平尺度约为100公里的多条山脉组成的山区。暴雨主要集中的地区并没有随着时间的推移而移动。然而，在较高的活动条件下，阵雨的空间集中程度较弱。在春季到夏季的晴朗天气和弱天气风条件下，白天在日本中部地区发展了一种热力诱导的局地环流。这种环流对地形有很强的依赖性，并在山区辐合。根据前人的研究，白天的热力环流通过平原和盆地地区的湿空气平流使山区上空水汽含量增加，当地形水平尺度接近100公里时，下午晚些时候山区上空积累的水汽最多。在山区测得的比湿度在下午出现最大值，超过了盆地底部的下午。山区上空水汽的增加预计将有助于积云的发展，山区上空下午晚些时候的日照时数减少证实了这一点。这些结果表明，夏季山区的阵雨是由热力诱导的局地环流引发的。
The summer rain shower which develop in central Japan under otherwise fair-weather conditions during the summer of 1985 were investigated, making use of routine observational data from weather stations. According to the statistical analysis, the diurnal cycle of precipitation exhibited a distinct peak around 1800 LST, while little rainfall occurred from 0000 to 1200 LST. This distinct peak was associated with the summer rain shower developed over the heated land surface during the afternoon. The rain shower activity increased as the atmospheric static stability for dry (or moist) convection decreased, under conditions that the atmospheric precipitable water exceeded 40 mm. The rain shower was concentrated in the mountainous regions which consist of several mountain ranges having the horizontal scale of about 100 km. The areas where the rain shower was concentrated largely did not move with time. The degree of spatial concentration of the rain showers however was weaker under higher activity conditions of the rain showers. A thermally induced local circulation developed over central Japan during the daytime under fair weather and weak synoptic wind conditions from the spring to summer seasons. This circulation was strongly dependent on the topography, and converged in the mountainous regions. According to the previous study, the daytime thermally induced circulation contributes to an increase in the water vapor content over the mountainous regions through the moist air advection from the plain and basin regions, and the greatest amounts of water vapor are accumulated over the mountainous regions in the late afternoon when the horizontal scale of topography is close to 100 km. Specific humidity measured in the mountainous area displayed an afternoon maximum, exceeding that at the basin bottom in the afternoon. The increase in water vapor over the mountainous regions is expected to contribute to the development of cumulus clouds, which was confirmed by decreased sunshine duration during the late afternoon over the mountainous regions. These results suggest that summer rain showers are triggered over the mountainous regions by the thermally-induced local circulation.