Change characteristics of convective cloud in the Qilian Mt. region under background of global warming

Based on the climatic data of cloud form and surface air temperature at 29 meteorological stations during 1961-2000 in Qilian Mountain and the surrounding areas,the climatic characteristics of cloud form,its variation features and the relationship between cloud form and air temperature were studied by linear regression analysis,correlation analysis and wavelet transforms using the Mexican Hat Function.The results showed that:⑴The occurrence frequency of convective cloud in the Qilian Mt.Region was higher than Qaidam basin and Gansu corridor.⑵The annual mean air temperature increased 1.3℃ with the increase rate of 0.32 ℃/10a in the Qilian Mt.region over the recent 40 years,especially since the mid-1980's.⑶The occurrence frequency of convective cloud decreased 10% in the Qilian Mt.region over the recent 40 years,especially since the mid-1980's,corresponding to the synchronous remarkable warming.⑷In the time scale of more than 30 years,the occurrence frequency of convective cloud and air temperature present reverse phase changed in Qilian mountain areas.In the time scale of 15 years,10 years and 5 years their characteristics of variations were in opposite phase before 1980's,but in synchronous phase after 1980's.⑸The correlation analysis indicated that there is a obvious negative relation between the occurrence frequency of convective cloud and annual mean air temperature in Qilian Mountain.when the average temperature increased 1℃,the occurrence frequency of convective cloud was found to decrease 2%～5% over the majority region of Qilian mountain area,and decreased by 4%～5.7% mostly over its middle area.