西藏拉萨达孜夏季降水日变化特征

Diurnal Variation of Precipitation in Summer in Dazi County of Tibet

利用西藏自治区拉萨市达孜县2014—2015年夏季逐时降水数据,研究达孜县日降水量、降水频次、降水强度以及不同持续时间降水等指标。结果表明:降水主要集中于晚上,尤其是后半夜,白天降水较少。降水量最多的时段为1:00—7:00,降水次多时间段为19:00—23:00,降水量最少的时段为12:00—18:00,降水量最大值出现在凌晨4:00,而最少为午后13:00;降水最易发生于21:00至次日9:00,最不容易产生降水的时间段为13:00—17:00,降水次数最多时间为凌晨4:00,与降雨量最大值出现的时刻相吻合;降水强度最大时段为20:00—22:00和1:00—7:00,降水强度最大值出现在21:00,其次为22:00,最小值则出现在13:00;降水量与降水频次以及降水强度均呈显著的正相关,降水量的变化受降水频次影响程度较降水强度的大;达孜县夏季降雨以短时间段的降水为主,短时降水频次比长持续时间降水次数多,且短时降水对总降水量的贡献大于较长时间的降水。

By using hourly precipitation data in summer at Dazi county,Lhasa City,Tibet Autonomous Region,China during 2014—2015,four precipitation indices（ daily precipitation,precipitation frequency,precipitation intensity,different duration precipitation） were studied and analyzed. The results showed that rainfalls were mainly concentrated at nights,especially in the latter half of the night,and the precipitation less in the afternoon. The peak period of precipitation was at 1： 00 to 7： 00,the less of that at 19： 00 to 23： 00,the least of that at 12： 00 to 18： 00.The maximum rainfall value appeared at 4： 00,while the minimum value appeared at 13： 00. The precipitation occurred at 21： 00 to 9： 00 next day easily,but it was not easy to generate at 13： 00 to 17： 00. The high value of rainfall frequency took place at 4： 00,and it was accorded with the time of maximum rainfall value. The maximum precipitation intensity took place at 20： 00 to 22： 00 and 1： 00 to 7： 00. The highest rainfall intensity appeared at21： 00,and the higher intensity was at 22： 00,and the minimum intensity generally occurred at 13： 00. The correlation among precipitation,precipitation frequency and precipitation intensity was significantly positive. The variation of precipitation was closely related to precipitation frequency,and less affected by precipitation intensity. The short time precipitation was mainly occurring in summer of Dazi County. The short time precipitation frequency events took place more than long duration precipitation events,and short time precipitation had great contribution to total precipitation,as compared with that of long duration precipitation events.