Impact Of Changbai Mountain And SST In The Japan Sea On Northeast Cold Vortex

Based on reanalysis data of FNL provided by NCEP/NCAR and SST (Sea surfacetemperature) data from Hadley Center, numerical simulation and experiments onrepresentative cold vortex over northeast China (NECV) by WRF model have beenmade, including sensitivity experiments on the topography of Changbai Mountain andSST anomaly in the Japan Sea.Diagnostic analysis to NECV shows that intrusion of dry and cold air in themiddle and upper troposphere, the strength and location of low-level jet have madegreat influence on precipitation from NECV. By contrasting model output whichChangbai Mountain has been cut off with control experiment, it has been found thattopography in north and west slope significantly affect upward movement before thefront and downward movement after the front. Besides, the positive vorticity centerresulting from lee wave propagation promotes local precipitation at the east of thesouth branch of Changbai Mountain. By contrasting model output of warmer andcolder SST anomaly in the Japan Sea with control experiment, it has been found thatSST anomaly can affect geopotential height field in850hPa and the strength andlocation of precipitation by affected water vapor content and upward movement.Sensitivity experiment to Changbai Mountain shows that uplift of trumpet shapedtopography strengthens upward movement and water vapor convergence in the lowlevel when NECV go through Changbai Mountain. At the north of mountain, upwardmovement when NECV passes and downward movement after NECV has beenweaken and strengthen, respectively. It makes less precipitation when NECV passesand small high after NECV. Besides, the emergence of positive vorticity in low levelreinforce water vapor convergence and upward movement which result in moreprecipitation when lee wave has been emergence at the east of the south branch of Chanbgai Mountain. The sensitivity experiment about SST anomaly in the Japan Seashows that warmer SST anomaly favors more water evaporating and stronger upwardmovement, which reduces geopotential height in850hPa. At the same time, vapor fluxhas been strengthened, resulting to more precipitation.Days of NECV has been used to represent intensity of NECV, which shows thatNCV is the most strong in summer and weak in autumn. In a long tendency, days ofNCV increases notably in winter. The anomaly regions of NCV strengthcorresponding to500hPa geopotential height are different in four seasons. It isconnected with blocking high in Okhotsk in summer. But Aleutian Low and IcelandicLow become more sensitive in winter and spring. Regions which have a closeconnection with intensity of NCV in SST field include Equatorial and North Pacific,Indian Ocean and south of Iceland.