Analysis of heavy fog proces in Ningxia on February,3th,2009

Using the information of automatic weather stations and T213 numerical forecast products,a weather precoss of heavy fog occurrenced in most areas of Ningxia on on February,3th,2009 was analyzed from the high and low circulation,physical field and the changes of meteorological elements.Results shown: the circulation in the 500 hPa high of Eurasian continent was relatively flat westerlies,no obvious cold-air was in mid-latitude,the south branch was flat and the weather conditions was stable;on the ground,Ningxia is located behind the North China high-pressure,the background field of this fog weather process is the weak south wind and east wind near the ground.K index and pseudo-equivalent potential temperature which can characterize the atmospheric stability,are not only the forecast indicator of strong convectively severe weather,but also the instruction meaning of fog weather process.