Quasi-Stationary Front and Stratification Structure of the Freezing Rain and Snow Storm over Southern China in January 2008

The weather pattern,moisture flux,the eastward propagating convective systems from Tibetan Plateau and surface temperature,stratification conditions for severe freezing rain and snow storm process during 25—29 January 2008 is diagnosed.The results show that,the east-west oriented quasi-stationary front(or shear line) located along Yangtze River Basin was the most important system producing freezing rain and snow storm.The warm layer and inversion of western part of front was stronger than its eastern part,the former was very favorable for the formation of freezing rain.The strongest moisture convergence occurred ahead the front at low-level and then climbed slantly along the front to middle level.The low-level moisture convergence in eastern part of the front was stronger than that in western part.It is maybe the main reason why the precipitation amount in eastern part of the front was relatively large.The convections were very active over the Tibetan Plateau during January 2008,propagated eastward and impacted East China several times.There were three times eastward propagation of convective systems from the Tibetan Plateau during 25—29 January 2008.The favorable condition for freezing rain was ground surface temperature at-1—-3 ℃ and weaker wind.The middle level frozen layer,warm layer and inversion layer existed while freezing rain occurred,at the same time,the formation of freezing rain was sensible to the thickness of the warm layer and frozen layer.Base on these,the physical model of quasi-stationary front and stratification condition related with freezing rain has been proposed.