Period and space distribution characteristics of high temperature (above 35 ℃) at 7 weather stations in Shenyang City from 1951 to 2008 were analyzed in this study.The results revealed that the occurrence period of high temperature in northern Shenyang was longer than the southern and eastern parts.The northwestern part had the most days of high temperature,the southeastern part came next,and the mid-eastern and southwestern parts had the least.The distribution characteristics of high temperature period were increasing frequency,enhanced intensity and expanded range after 1990s.The occurrence frequency of high temperature was the highest in June and the lowest in August.The hot late summer weather in the middle period of August in 2009 was caused by anomaly atmospheric circulation and subtropical high pressure (stronger and the more westward).
By using the monthly mean grid data of NCAR/NCEP reanalysis at 500 hPa geopotential height from 1958 to 1997,the relationship between the Northeast cold vortex and the western Pacific subtropical high was analyzed.The influence of the sea surface temperature(SST) and outgoing longwave radiation(OLR) on the Northeast cold vortex and subtropical high was studied.As was shown in the results,in summer,there was a positive correlation between the Northeast cold vortex and the subtropical high,and an anti-phase relationship existed between the threshold characteristic line of GMS-SST=28 ℃ and the height index of the Northeast cold vortex and the subtropical high.With the gradual northward moving of the threshold characteristic line,the subtropical high was weakening,and the Northeast cold vortex was increasing and strengthening.
