1976-2007年乌鲁木齐可降水量及其降水转化率

Study on Precipitable Water and Precipitation Conversion Efficiency in Urumqi during the Period of 1976-2007

采用乌鲁木齐1976-2007年探空逐日观测资料和各月降水资料,分析乌鲁木齐可降水量的变化特征及其与实测降水的相关关系,同时对该地区的降水转化率进行分析。发现乌鲁木齐的可降水量年内分配不均,7月平均可降水量最大,1月最低;夏季可降水量最大,冬季最低。年平均可降水量为11.46 mm,可降水量上升趋势不明显。同时发现探空资料计算的乌鲁木齐水汽含量和实测降水量存在明显的正相关关系。通过对降水转化率的计算分析,发现4月的降水转化率最高,为11.89%,8月的降水转化率最低,为4.28%,月平均降水转率为7.46%。春季降水转化率较高,夏季较低,秋季和冬季相当,夏、冬季降水转化率呈显著增加趋势。降水转化率的月和年际变化较大,说明开发潜力大。

In this paper, the change features of precipitable water and its mutual relationships with observed precipitation and local precipitation conversion efficiency are analyzed on the basis of daily radio soundings and monthly precipitation in Urumqi during the period of 1976 -2007. It is found that the mean annual precipitable water in Urumqi was 11.46 mm, its maximum （12.85 mm） occurred in 1999 and 12% higher than the average, its minimum （9.83 mm） occurred in 2007 and 14% lower than the average. The difference between the maximum and minimum was 3.02 mm, and it passed successfully the significance test and M-K sharp change test. The increase trend of annual precipitable water was not so significant. The annual distribution of precipitation was uneven, its curve was unimodal, and its monthly variance was significant. Its peak value （21.74 ram） occurred in July, and its minimum （5.22 mm） occurred in January. The water vapor content in upper air was the highest in summer and the lowest in winter. Moreover, there was a positive correlation between the water vapor content calculated from soundings and the observed precipitation. The annual variance of preeipitable water volume was trivial, but that of precipitation was quite high. The water vapor content over Urumqi reached its peak value in summer while the subtropical westerly current was over Xinjiang and the short wave movement was frequent, thus , the summertime rainfall was the most abundant. The precipitable water volume in spring was similar to that in autumn. The conversion efficiency from water vapor to rainfall for a certain period in Urumqi could be approximately measured by the conversion efficiency from precipitation to precipitable water volume. The monthly conversion efficiency of precipitation was the highest （ 11.89% ） in April and the lowest （4.28%） in August, and its average was 7.46%. Seasonally, the conversion efficiency of precipitation was high in spring, low in summer and similar in autumn and winter; however, its increase trend was significant in summer and winter.