The Classification Of Winter Persistent Abnormal Events In Southern China And Their Large-scale Atmospheric Conditions

The persistent low-temperature freezing rain events exert severe influences on both human activity and agricultural production,and are the major meteorological disasters over southern China in winter.This study is based on the abnormal precipitation and temperature events to analysis the relation and difference of circulation between 4 kinds of persistent abnormal events.The persistent abnormal events have dual characteristics of weather and climate.Based on the 2747 stations daily observational datasets of precipitation and temperature in China during 1981-2010,results of multiple-variable combine EOFs objectively show the area where the meteorological disaster occurs frequently in south China in winter.Furthermore,the persistent abnormal events are identified and classified into four types in southern China by the daily precipitation and temperature anomaly in this area.Their large-scale atmospheric conditions are composited and compared using NCEP-NCAR(National Centers for Environmental Prediction/ National Center for Atmospheric Research)reanalysis data.The anomalous “north high-south low” pattern in geopotential height over Eurasia in the mid-high latitudes results in a weaker-than-normal temperate jet and a stronger-than-normal subtropical jet,so that favorable for the southward invading of cold air.In the other hand,the anomalous “west low–east high” pattern over middle latitude leads the subtropical western Pacific high to be stronger and locate farther north than normal and,meanwhile,southern branch trough to be deep and active.During this period,the water vapor transmission and the precipitation increase in South China.The various persistent abnormal events during winter in south China are jointly affected by anomalous circulations both in high latitudes and in middle latitudes,while the wet-cold event appears when afected by two above anomalous patterns in succession.The circulation indices of precipitation()and temperature()are defined with the differences of key circulation system.And the indices are the proceeding signals to predict persistent precipitation and low-temperature event.Therefore,our results suggest that improvements could be made in pr edicting severe freezing disaster weather event over southern China when taking into account the differences of wet-cold event and other events and critical systems for cold-wet event.The characteristics of precipitation and temperature event are analyzed over southern China during January 2016.Results show a persistent abnormal cold-dry event occurs over southern China from 20 to 25 January.The index of “north high-south low” going positive value is 8 days before,and the index of “west low–east high” turning negative value is 4 days before.This clarifies again that the indices are the proceeding signals to predict persistent precipitation and low-temperature event.Moreover,the present study analyzs the results of Arctic warming and the influence mechanism of Arctic warming on this cold-dry event over China.Persistent warm SST anomalies on the east coast of North America excite teleconnection wave train from North America to North Europe,and then a disturbance wind field on average temperature gradient tansport processes result in Arctic warming.The rapid Arctic warming leads to polar vortex and polar cold air from Arctic to mid-high latitude,and severe winter cold events across China.