青藏高原低云量的年际变化及其稳定性

利用青藏高原80个测站1961-2000年1～12月低云量资料,分析了青藏高原低云量的年际变化规律.结果表明:青藏高原的低云量从东南向西北减少,云量的稳定性夏季高于冬季,南部高于北部.江河上游区域、藏东谷地、川西高原、甘南高原和祁连山区是青藏高原低云量多,且比较稳定的地区;青藏高原西部低云量月变化振幅大,尤以西南部为最,夏季云量最多;高原东南部江河上游区和藏东谷地3～9月低云量多,且起伏变化小,6月和9月出现峰值;高原东南部低云量稳定性较好;低云量的年际变化总体呈下降趋势, 江河上游区和高原东南部的低云量变化缓慢,高原西北部有显著上升趋势;变化趋势在季节上表现为冬、春、夏、秋西北上升西南下降,春、秋季中东部持平,夏、冬略降.

Study on the Annual Change and Stability of Low-cloud Amount over the Qinghai-Tibetan Plateau

In this paper,the annual change and stability of low-cloud amount over the Qinghai-Tibetan Plateau since recent 40 years are analyzed based on the monthly-averaged low-cloud amount data observed by 80 observational stations during the period from January 1961 to December 2000.The results reveal that the low-cloud amount over the study area decreases from the southeast to the northwest,and the stability of low-cloud amount is higher in summer than that in winter and over the south than that over the north.The low-cloud amount is high and stable over the upper reaches of the rivers,valleys in east Tibet,plateau in west Sichuan Province,and Gannan Plateau and Qilian Mountains in Gansu Province.The monthly change of low-cloud amount over the west Qinghai-Tibetan Plateau is high,especially over the southwest plateau where the low-cloud amount is the highest in summer.The low-cloud amount is high and relatively stable over the upper reaches of the rivers in the southeast Qinghai-Tibetan Plateau and the valleys in Tibetan during the period from March to September,and the peak values occur in June and September respectively.Stability of low-cloud amount over the southeast Qinghai-Tibetan Plateau is high.The annual low-cloud amount over the plateau is generally in a decrease trend,the change of low-cloud amount over the upper reaches of the rivers and the southeast plateau is low,and the low-cloud amount over the northwest plateau increases significant.Seasonally,the low-cloud amount increases over the northwest plateau but decreases over the southwest plateau,it over the central and east plateau is stable in spring and autumn but decreases slightly in summer and winter.