拉萨河流域高山水热分布观测结果分析

Analysis of the Observation Results of Temperature and Precipitation over an Alpine Mountain, the Lhasa River Basin

利用架设在念青唐古拉山南坡9个海拔高度(4300～5500m)的自动气象站一年(2006年8月1日-2007年7月31日)的实测数据,对山坡1.5m高度的气温和季风期(6-9月)降水随海拔梯度和时间的变化进行了分析。表明4300～4950m存在一个逆温带,逆温时间自10月至翌年4月。年逆温频率为11.5%(42天)。4300～5500m年平均气温直减率为0.61℃/100m;念青唐古拉山南坡季风期各月最大降水带都在海拔5100m。最大降水高度以下,山坡降水量递增率为4～7mm/100m,最大降水高度以上,降水递减率数值上为降水递增率的1.6～2.3倍。7月和8月降水量占季风期总降水量比例大于6月和9月。降水月内分配山坡上部总体较山坡下部均匀。降水主要发生在4:00-10:00以外的时间段,而大-中雨(3～14mm/h)主要发生在18:00-22:00。山坡强降水段相对集中在4650～5100m海拔高度。

Altitudinal and temporal distribution of surface based air temperatures and monsoon period precipitation were analysed, using an original data set, spanning Aug. 1, 2006 to Jul. 31, 2007, from 9 automated weather stations set up along an altitudinal gradient from 4300 to 5500 m a.s.l, on the southern slope of Nyainqentanglha Mountains, the Lhasa River basin. Surface based inversion was found typically during October to the following April. The annual inversion frequency was 11.5% （i.e. 42 days）. The lapse rate of mean annual air temperature was 0.61℃/100m for the elevation interval of 4300-5500 m. Analysis on the precipitation indicated the presence of the maximum precipitation belt （MPB） at about 5100 m a.s.l, with an increasing rate of 4-7mm/100m below the MPB. The precipitation decreased at a rate of 1.6-2.3 times of the increasing rate over the MPB. The precipitation amounts in July and August were larger than those in June and September. The intra-month distributions of precipitation were generally more homogeneous for the upper hillslope than for the lower. The precipitation events generally occurred at any time except for 4：00-10：00, with the heavy rainfall（3-14mm/h） mainly occurring within 18：00-22：00. The larger precipitation events concentrated roughly between 4650 m a.s.l, and 5100 m a.s.l.