Study on Climatic Change and Anomaly of Low Cloud Amount over Qilian Mountain Area

Using the low cloud amount of 34 observational stations over Qilian mountain area from January to December in the period of 1961-2000,the spatial anomaly features and time evolution rule of low amount for 40 years were analyzed with EOF and REOF methods.The results show the first three principal components can reflect the whole anomaly structure of season low cloud amount,namely the consistent type in the whole,\!+-+ type of east and west changes,north and south change contrary type.The first three loading vector fieldsof REOFcan represent the three principal amount anomaly areas: Chaidamu basin,Qilian mountain area and Hexi corridor.Its turn in to have the different trends,Chaidamu basin′scloud amount had increased trend in each season,especially the amount of cloud notable increased after 1985.Hexi corridor′s cloud amounttrend hadn′t obviously changed in spring and summer,but in 1990′sthe amount obviously decreasedin summer.Qilian mountain area′s trend didn′t obviously change in spring and autumn,but the autumn′s amount trend increased in 1990′sand decreased in summer.