Causes of Continuous Cold Temperature Weather in Middle and Lower Reaches of Yellow River

Based on conventional observation data and temperature data of meteorological stations in China,the circulation and weather systems and causes were analyzed by principles of weather and weather dynamics and thermodynamic diagnosis for the strong cooling and the continuous low temperature weather process on 1-20 January 2010 in middle and lower reaches of the Yellow River. The results showed that cold air from polar region was transported to south by northerly airflow behind trough at 500 hPa; stable cold vortex center in Northeast Asia blocked the cold air to move east,made cold air accumulate and strengthen. Deep trough in Siberia oppressed pressure ridge to collapse,the strong cold air broke out and moved southward. The main reason for the rapid air temperature decrease and continuous cold temperature weather was the intense cold advection of temperature at 850 hPa,the evolution of the cold advection center of temperature was consistent with the strong cold air moving path. There were negative vorticity advection from the upper to the lower in Middle and Lower Reaches of Yellow River,strong negative vorticity advection was conducive to movement of the high-pressure system,the smaller the value of negative vorticity advection,the stronger cold air. The negative vorticity advection center corresponded with strong cooling center. The cold advection center appeared 12-24 h in advance than strong cooling center,and the negative vorticity advection core appeared early than strong cooling weather,these features will provide a favorable reference for weather forecast of strong cooling.