Subseasonal Mode Of Cold And Wet Climate In China And Its Variations During The Cold Season

Based on in-situ surface air temperature(SAT)and rainfall in China,NCEP/NCAR reanalysis data,sea surface temperature(SST)from the Met Office Hadley Sea Ice and SST,we investigated the dominant mode of climatological intraseasonal oscillation(CISO)of winter cold and wet climate in China,and its relationship with the Arctic circulation.Besides,we discussed the cooperative effects and interdecadal difference of ENSO and North Atlantic SST on winter climate in China,as well as subseasonal changes.The main conclusions are as follows.The dominant mode of CISO displays a cold-dry climate in North China,whereas a cold-wet pattern prevails in South China,which is characterized by a quasi-30-day oscillation during the peak winter season.,The ISO of SAT in SC plays a leading role.Evidence shows that under the combined effect of the negative phase of Arctic Oscillation and a pair of propagating ISO modes at the 500-hPa geopotential height,cold air always moves southward,resulting in the cold-wet climate over SC.Therefore,the cold-air activity acts as a precursor for subseasonal rainfall forecasting in South China.Under different interdecadal background,there are significant interannual differences in the tropical Pacific(TP)and North Atlantic(NA)SST anomalies(SSTAs)patterns and their effects on winter climate in China.Since 1990 s,the cooperative effect of TP and NA SSTAs on the winter rainfall of southern China has become significant.Whereas during 1965-1985,the respective impacts of the TP and NA SSTAs are offset,resulting an insignificant cooperative effect.Since 1995,the SSTAs center in the TP moves westward,and the westward anomalous anticyclone over the western North Pacific(WNP)strengthened,causing the rainbelt northward to the Yangtze River basin.And compared to the previous dipole SSTA,the recent northward tri-pole SSTA in the NA is related to anomalous cylonic circulation in the South Asia with positive rainfall anomaly in the south edge of South China.As for SAT,TP SSTAs in the combined mode are conductive to a wide warming in China.Recently,the impact of NA on ISO is stronger than that of TP.Along with global SAT warming,the intensity of subseasoanl mode of winter cold and wet climate in China strengthed,and the period becomes longer.And the former results from ISO of rainfall,while the latter comes from ISO of SAT.The enhanced cold air in the mid-high latitudes and the northwest Pacific anomalous anticyclone in the low latitudes are conducive to the maintenance of the subseasonal mode.