Analysis And Research On Weather And Climatology Of The Northwest Vortex

The northwest vortex generated near Qinghai or Qaidam in China has an important impact on the weather and climate in the local and downstream regions.The paper uses the CFSR reanalysis data of four times a day during 1979~2016,in the definition of the statistical scope of the northwest vortex,uses the routine statistical method,the synthesis analysis method and the synoptic diagnosis method,and secondly,from the angle of weather and climatology,this paper analyses the differences of the atmospheric circulation situation,structural characteristics and water vapor conditions between the stagnant Northwest Vortex and the Northwest vortex-shifting,and obtains the following conclusions:(1)Climatically speaking,The appearance of northwest vortex mainly centralized in two position,one lay in 37.5°~38.5°N,97.5°~99°E,which accounted for 22.4%,another lay in 35°N,97.5°~100.5°E accounting for 15.5%.(2)In the past 38 years,a total of 1,306 northwest vortexes have occurred in summer with an average of 34.4 every year.The northwest vortex has significant interdecadal and interannual changes,and its long-term changes have a decreasing trend.From the climatic,during the three months in summer,the number of vortexes in June was more than the other two months,followed by July and the number of those in August was at least.The possibility of the vortexes appearing in the day was also higher than that in the night.(3)41.2% of the vortexes were removal type among all the northwest vortex.The time of maintenance of northwest vortex was short,about two thirds of those could last one day or less.Those which could last two days or more mainly appeared in July,and 91% of them were removal type.(4)In the past 38 years,those northwest removal-type vortexes in summer,which could last more than one day,mainly moved towards southeast,east,south and northeast.And most of them moved to southeast,and those northwest eddies which could last more than one day mainly moved to northeast and east.(5)From the climatic point of view,the stagnant Northwest vortex is a shallow vortex at 700 h Pa altitude,and there is an anti-cyclone circulation center downstream of the low vortex center,which has a role in blocking the movement of the vortex.In the 500 h Pa height of troposphere,corresponding to a weak fluctuation,in the upper troposphere 200 h Pa,there is the absence of high-altitude jet and higher value system.In the vertical space,the stagnant northwest vortex shows the lower troposphere as the cyclonic vorticity field,and the upper level is the inverse cyclone vorticity field.The vertical distribution of the divergence field is low convergence,middle level divergence.The vortex is warm center structure,but the cyclone ring flows to the low Vortex Center to bring cold air and restrain the maintenance and development of the warm center structure.The low humidity and large amount of water vapor flux are mainly located in the south of Gansu,but there is no water vapor source in the South area,and the water vapor cannot be carried to the center of low vortex.(6)From the climatic point of view,the migration of Northwest vortex is still a shallow system,but its structural characteristics than the stagnation of the Northwest vortex more prominent,the specific characteristics of the lower troposphere is mainly a strong cyclone vortex,and the surrounding humidity is near saturation.Corresponding to a deep upper trough in the troposphere,there is a high pressure control in the troposphere,near the low vortex,and at the same time there is a high altitude jet,which makes the high-altitude of the northwest low vortex have obvious divergence,which is advantageous to the development of the lower vortex.The interaction of the lower layer in the situation field may be the foundation of the vortex occurrence and development.In the perpendicular space,the moving Northwest vortex still shows the lower troposphere as the cyclonic vorticity field,and the upper troposphere as the inverse cyclone vorticity field.The vertical distribution of the divergence field is lower convergence,but the divergence on vortex center is not obvious.The Northwest vortex is still a warm center structure.The low vortex center is mainly controlled by the warm advection,and the decompression effect formed by the warm advection may be the important reason for the vortex to develop and move eastward.The water vapor in the south of the north-west vortex is abundant,the vortex is at the center edge of the enormous value area of the water vapor flux,and the cyclone ring flows to the low Vortex Center to supply the water vapor.