Diurnal Variation of Precipitation and Moisture Transport by Local Circulations

本研究揭示了由海陆对比或山谷对比产生的局地环流对降水概率与水汽输送的影响关系。进行了现场试验、数据分析和数值试验。利用全球定位系统（GPS）获得的可降水量进行分析。结果表明，关东地区夏季无风晴日降水具有以下特征：1.夏季无风晴日降水；降水概率密度日变化明显，在傍晚或傍晚达到最大值。降水概率密度的水平分布与地形有很好的相关性。地形效应大于陆海对比效应。下午山区降水概率密度变大，然后高概率密度区向平原延伸。这些结果表明，局地环流的水汽输送与夏季山区对流降水的发展有着密切的关系。对这些对流降水，即雷暴的预报来说，观测可降水量是非常重要的。

This study reveals the relation of probability of precipitation and moisture transport by the local circulations, which are generated by the contrast of land /sea or mountain/valley. Field experiments, data analysis and numerical experiments are carried out. Precipitable water vapor obtained by GPS (Gloval Positioning System) are also used for the analysis.As the results, it was shown that the precipitation in the Kanto area on the calm clear days in summer has the following characteristics :1.Probability density of precipitation has clear diurnal variation with the maximum in late afternoon or early evening.2.Horizontal distribution of probability density of precipitation correlate well with orograpy.3.The orographic effects is lareger than the effect of the contrast of land and sea.4. Probability density of precipitation becomes large in the mountainous region in the afternoon, and then high probability density area extends toward the plain.These results show that the moisture transport by local circulations has strong relationship with convective precipitation developed over mountainous region in summer. For the prediction of these convective precipitation, i.e., thunder storms, observing precipitable water vapor is very important.