Variation Characteristics of Global Radiation and the Associated Climatic Factors over Yunnan-Guizhou Plateau in the Southwestern Part of China for 1961-2005

The variation characteristics of the global radiation and the meteorological factors such as cloud cover, humidity, wind speed, visibility, and sunshine duration which may impact the global radiation over the Yunnan-Guizhou Plateau in the southwestern part of China were studied by mathematical statistics method, with which the data of nine radiation observation stations and about 200 weather stations from 1961 to 2005 were involved. The results show that the spatial distribution characteristics of annual global radiation are higher in the western part than the eastern part, and the highest is at Lijiang station(6207 MJ·m-2·a-1), the lowest is at Zunyi station(3340 MJ·m-2·a-1). The global radiations in six out of nine stations have no significant linear trend (P>0.1) in interannual variation, but the other three stations (Mengzi, Guiyang, and Zunyi) have a significant decline (P<0.001) from the 1960s to the 1980s, and then followed by slight (Mengzi) or significant increasing (Guiyang). The main reason of the global radiation declining in Mengzi may owe to the visibility decreasing, and that in Guiyang is concerned with the increasing total cloud cover which result in sunshine duration decreasing. The cloud cover increasing and visibility decreasing are the reasons of the global radiation decline in Zunyi. Overall, interannual or decada1 time scale variations of the global radiation are relative to the cloud cover and sunshine duration on the Yunnan-Guizhou Plateau during 1961-2005. The sunshine duration at city stations (Kunming and Guiyang) decreased with visibility reducing.