我国西南部降水日变化特征分析

The Characteristics of Rainfall Diurnal Variation over the Southwestern China

利用1991—2004年台站观测的逐时降水资料分析了我国西南部降水日变化的基本特征和区域差异。结果表明,西南部降水"夜雨"特征明显,但存在午后次峰值,且区域差异显著。降水频次和降水强度亦存在明显日变化,夜间降水量峰值主要来自于降水频次的贡献,而午后降水量峰值以降水强度的贡献为主。在25°N以北,降水量的峰值位相超前于降水频次1～2 h,且自西向东存在区域差异。西部降水量主峰值在凌晨03—04时,而中、东部在01—02时;中部和东部的区别主要在降水强度的日变化上,中部的强度日变化为午夜单峰值结构,而东部的午后强度较大。25°N以南地区的降水日变化特征与北部明显不同,南部降水量主峰值出现在午后,且主要是强度的贡献,次峰值出现在凌晨05—06时,以频次贡献为主。

Diurnal variations of precipitation over the southwestern China and its regional features are studied using hourly rain-gauge data from 72 stations during 1991-2004.Results show that nocturnal rainfall dominates this region,but there is a secondary peak in the late afternoon.Precipitation in this region has large diurnal variations with considerable regional differences.Moreover,the contribution of rainfall frequency and intensity to the diurnal variation of rainfall amount varies with the hours.The night peak of rainfall amount mainly comes from precipitation frequency while the amount peak in the afternoon is resulted from precipitation intensity.In the region north of 25°N in the southwestern China,the peak phase of rainfall amount precedes that of frequency about 1 or 2 hours and varies from the west to east.Over the western region,precipitation is characterized by the diurnal peaks at 3-4 LST.In the middle and eastern regions,rainfall peaks take place at 1-2 LST,and their major difference lies on diurnal variation of intensity.In the region south of 25°N,the diurnal features of precipitation differ from that in the north.The main peak of amount occurs in the afternoon,mainly as a result of the contribution of intensity,while the secondary peak is at 5-6 LST and comes from the contribution of frequency.