The Research Of Circulation During Freezing Over Southwest China

By using the freezing data of Erlang Sichuan in January, daily meteorological data of Southwest China, Plateau monsoon index and NCEP/NCAR reanalysis general circulation data, the method of composite analysis and correlation analysis to study the atmospheric circulation, atmospheric stratification and reasons of icing over the Southwestern China, the main conclusions are as follows:Most icing generate at an altitude of 1500 to 4000 meters. Because of lower humidity above 4000 meters and higher temperature below 1500 meters, there are both few icing. The cold air from North China, which tempeter between -10℃and 0℃, and warm air from South China, which humidity more than 80 percent, converge at Yunnan, Guizhou and Sichuan over Southwestern China, and form inversion layer at about 1500m to 2500m. They are all conditions of icing over Southwestern China.By calculating accumulated days of icing shows that it has well interannual and decadal change in recently 50 years.2008 is the most severe icing year, the weakest icing year is 1987, from 1963 to 1974 year the number of icing days grew rapidly, from 1975 to 1987 year reduce slowly, from 1988 to 1996 year the number of icing days grew slowly, from 1997 to 2004 year reduce, and from 2005 its increase rapidly, and has a great growth rate.when strong icing,500hPa height anomaly field is "north-higher and "south-lower" in Eurasia, and no-icing has opposite status. when strong icing year,500hPa height anomaly field is "north-higher and "south-lower" in Eurasia, "west-higher and east-lower" in the high latitude, "west-lower and east-higher" in the low latitude, and Ural mountain pressure is much higher, Caspian Sea trough is much lower and the subtropical high is stronger, so warm and cold air converge in southwest China. By using data of Erlang to study the icing process of atmospheric circulation, we can known that there is a maximum negative center of strong cold air around Baikal and the cold air can extend to the Southwest China, the source of vapor is mainly the southwest air from Arabian Sea, Bay of Bengal and southeast air from South China Sea.The index of the Middle East jet stream and the icing in Southwest China have great relationship, and the the best areas of relation are most serious icing areas on climate field, they are most areas of Guizhou province, the junction of Sichuan, Chongqing and Yunnan, the junction of north Yunnan and southeast Xizang, southwest of Shanxi, and Erlang of Sichuan. The bond of the index of the Middle East jet stream and the icing in Southwest China is anomaly of atmospheric circulation over Eurasia. The activity of low pressure trough over Central Asia and hyperbar over Tibetan Plateau, can make the the Middle East jet stream and the icing in Southwest China linking.Establishing a conceptual model of impact the icing in southwest China:If prior sea surface temperature of bermuda in north Atlantic is colder in December, the Middle East jet stream is much stronger, the low pressure trough over Central Asia is much stronger and winter monsoon over Tibetan Plateau is weaker, then there wil be strong icing in southwest China.