Research On The Basic Characteristics And Precursory Signals Of Persistent Freezing Rain And Snow Events In Southern My Country During The Winter Of 1951-2017

In this paper,daily temperature and daily precipitation data about 753 stations from 1950to 2018 provided by China National Meteorological Information Center and reanalysis data provided by NCEP/NCAR were used,in order to finish the study of the climatic characteristics about the persistent frozen rain and snow events in South China from 1951 to 2017,comprehensively analyze it's spatial and temporal characteristics,regionalization,circulation characteristics.Find the critical risk factors of the events.Finally,explore the precursory signals of frozen rain and snow events by the method of atmospheric circulation study.The results showed that:1)The persistent frozen rain and snow events in South China have significant 2-3 years periodic variation,there has been a mutation around 1985,in recent years,the intensity of events showed a significant downtrend,even though,there have been a number of strong frozen rain and snow events;events which happened in the middle and west of south China have a high frequency and long period,southeast China events have a higher intensity,the 37 strong frozen rain and snow events in South China can be divided into three types:middle China type,south China type and southwest China type.The daily circulation of the three types of events in the north of China showed an anomaly of geopotential height with the Eurasian continent being high in the north and low in the south.The Mongolian high was significantly stronger and the center moved southward,which was conducive to the transport of cold air from the north to the south.In the south,the water vapor was transported to the north and the water vapor was transported to the north.The differences of the three factors lie in the Mongolia high pressure intensity,water vapor source and convergence zone.2)It is similar with the trend of events in the south of China,the southwest China type events intensity showed a downtrend from 1951 to 2017,the events before 1980 are stronger than that after 1980.The south maintains sufficient water vapor transport with the outbreak of strong cold air in mid-latitude East Asia due to the strong events,the process by which warm and cold air meets in the southwest to cause cooling and precipitation.3)The key anomaly combination index P_CA is established base on the Mongolian high pressure intensity index,the north-south position index and the southern branch though intensity index,it has significant correlation with South China PT index,so that can be used to explore the precursory signals of the frozen rain and snow events in the southwestern China;Autumn tropical Pacific sea surface temperature(160°E-90°W,5°S-5°N),the SSTA mode in North Pacific Ocean as similar as PDO cold phase,Indian Ocean cold sea surface temperature(40°E-100°E,10°S-20°N),three factors are significantly correlate with the key anomaly combination index P_CA in winter.The coupling of three key SSTA mode in autumn due to atmospheric circulation anomalies in the North Pacific and its downstream regions in winter.15-20 days ahead of events,in the mid-latitude region,there are three key regions that the mean Geopotential height are showed significant correlation with the key anomaly combination index P_CA,respectively are North Atlantic,Iceland,Caspian Sea.The Geopotential height signal in the upstream enhance the Mongolia high pressure and deepened the south trough in the downstream by the interaction of wave and current,and finally result in the strong frozen rain and snow event in the southwest region of China.According to the mean SST anomaly of the key SST model in early November and the mean geopotential height in the key regions which is 16 days before the events,predict index by sea surface temperature("_##$)and extended forecast index("_%)can be created which can used to improve the short-term climate prediction of southwestern China frozen rain and snow events.