Diurnal Variation of Precipitation and Moisture Transport by Local Circulations

研究揭示了由海陆对比或山谷对比所产生的局地环流与降水概率和水汽输送的关系。进行了现场试验、数据分析和数值试验。结果表明，关东地区夏季风平浪静晴朗的降水具有以下特征：1.降水概率密度日变化明显，最大值出现在下午晚些时候或傍晚早些时候；2.降水概率密度的水平分布与地形有较好的相关性；3.地形的影响远小于陆海对比的影响。午后山区降水概率密度变大，随后高概率密度区向平原扩展，这说明夏季局地环流的水汽输送与山区对流降水发展有很强的关系。对于这些对流降水，即雷暴的预报，观测可降水水汽是非常重要的。

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.