1971-2004年青藏高原总云量时空变化及其影响因子

利用青藏高原及其周边地区75 个地面气象台站的云量日均值资料，采用正交经验函数(EOF) 和线性倾向估计等方法，分析了高原地区1971-2004 年总云量的时空变化特征。结果表明，高原总云量分布呈自东南向西北减少的态势，且年与四季总云量变化都存在显著下降趋势。进而，研究了高原总云量变化与其他气候因子的相关性。其中，(1) 高原总云量与日照时数、日较差之间存在较好的负相关。本文从云的辐射效应出发，解释了存在这种负相关关系的原因；(2) 青藏高原总云量与相对湿度之间有很好的正相关性，受地形因素、不同云型和云水路径等因素共同影响，高原总云量与降水之间的关系却不显著。在此基础上，重点讨论了高原总云量与气溶胶和臭氧等因子之间的复杂关系。指出：青藏高原总云量减少趋势可能与高原大气气溶胶特别是吸收性气溶胶的增加以及臭氧的损耗有关。

Variation of Total Cloud Amount and Its Possible Causes over the Qinghai- Xizang Plateau during 1971-2004

The Qinghai-Xizang (Tibet) Plateau plays a crucial role in global change and the climate of East Asia. It is indispensable to analyze the characteristic of cloudiness variation over the Plateau,which will promote the understanding of climatic change and of cloud-radiation feedback mechanisms in climate models. With EOF and trend analysis method adopted,the spatio-temporal variation of total cloud amount is analyzed for 75 stations over the Plateau during the period of 1971-2004. Analysis indicates that the distribution of total cloud amount is characterized by remarkable regional features,which decreases from the southeast to the northwest of the Plateau. In addition,the annual and seasonal variation of total cloud amount shows a declining tendency over the past decades. Correlation analysis demonstrates that total cloud amount is negative with sunshine duration and diurnal temperature range (DTR),and is positive with precipitation and relative humidity,respectively. The negative correlation is consistent with the radiative effect of cloud,while the positive correlation between total cloud amount and precipitation is obscured because of topographic factor. Discussion implies that the decrease of total cloud amount is possibly due to the variation of atmospheric aerosol content and ozone concentration over the Plateau,although it is difficult to quantify the driving forcing mechanism up to now.