The Evaluation Of Low-Temperature Reanalysis Data And The Analysis Of Low Frequency Characteristics Of Low-Temperature Events In Southern China

Used the daily minimum temperature of 192 gauge stations in China from 1979 to 2013 and the reanalysis minimum temperature of NCEP/NCAR,NCEP/DOE,JRA-55,ERA-Interim,and homogenization data from 1979 to 2004,the low-temperature thresholds were calculated,features and differences between reanalysis and observations were explored on climatology,interannual variation,long-term trend and spatial changes.Furtherly,counted continuous low-temperature events in south China,characteristics of intraseasonal oscillation and corresponding circulation in east route cold events were discussed and thermodynamic diagnosis was performed.Results are as follows:(1)Compared with the observations,the thresholds of homogenization data is lower in northeast China,western Inner Mongolia,Guangdong and Guangxi while higher in the east of the Tibetan Plateau,northern Xinjiang and Yellow River,but the linear trend is the opposite.(2)The thresholds of reanalysis data is lower in south China while higher in the northeast,their credibility is better in east China than that in the west.Reanalysis data can capture the features of cooling trend over northern Xinjiang and western Inner Mongolia and warming trend over the Tibetan Plateau in nearly 35 years,but there are differences in values and ranges,nor underestimate the significant warming in North China Plain.According to the EOF decomposition,four reanalysis data can depict the characteristics of nationwide consistent and reverse between the northeast and other regions in observation thresholds.The feature of interannual variation can be caught,but only JRA-55 and ERA-Interim can reappear the interdecadal variation.(3)There is a strong 10-20 day quasi-biweekly oscillation period in minimum temperature in southern China,and the amplitude is enhanced during 22 low-temperature events.10-20 day oscillation kinetic energy mainly concentrate in the high latitude North Pacific and Atlantic in lower troposphere while it is zonal distributed in upper troposphere in northern hemisphere winter.(4)The event in February 1996 showed when circulation centre was born on Europe,moved southeastward to the lower reaches especially in middle latitudes.The anomalous northerly winds guiding cold air to the south was the main reason of continuous low temperature events.Meanwhile,the study also found that the low frequency system over North America moves westward.And the cold air lead to baroclinicity on East Asian coast.Thermodynamic diagnosis thought that the cooling was mainly affected by advection and diabatic cooling,cold advection was the key to maintain a low-temperature process.Different from the former,the case 2 showed the temperature in southern China was much lower than that in other years,while higher in the north.In addition to the southeast path,low frequency systems also moved eastward at lower latitudes.However,the cooling process was mainly caused by the strong cold advection,the diabatic term played the role of heating in the event.