Analysis of Environmental Background and Potential Vorticity of Different Accompanied Moving Cases of Tibetan Plateau Vortex and Southwest China Vortex

By using NCEP/NCAR-FNL data, historical weather maps and Tibetan Plateau vortex and shear line yearbooks, the sustained activity patterns of Tibetan Plateau vortex (TPV) accompanied with Southwest China vortex (SCV) during the period of 1998 to 2015 were analyzed. The environmental background and potential vorticity fields corresponding to typical activity patterns of various cases of the two accompanying vortices were calculated and analyzed. Characteristics of different environmental fields of the two accompanying vortices and the reasons for influences of cold air activities and jet stream at 200 hPa in the vortices were revealed. The main results are as follows:(1) The two accompanying vortices have 3 types of activity pattern, i.e. TPV induced SCV type, TPV coupled with SCV type, and two vortices with the same weather system type. The most active type is the TPV induced SCV type. (2) The environmental background of accompanying two vortices is characterized by low troughs and cold airmass at 500 hPa with weak meridional circulation to the north of 40°N, where zonal flows prevail. The environmental variables at 200 hPa have a close relation with the intensity of jet, the distance to the jet core and the position on both sides of the jet. Different types of vortices activity pattern have different environmental fields at 500 hPa and 200 hPa. (3) The generation of SCV of the two accompanying vortices is influenced by cold air related to low trough at 500 hPa, i.e. the high potential vorticity air flow extends to the upper level of the SCV, leading to baroclinic instability in the upper. The SCV intensifies when baroclinic instability enhances, and there exists strong baroclinic instability above the SCV at 500 hPa. The southwesterly jet at 200 hPa influences on the TPV induced or coupled SCV and intensification of SCV are respectively through downward extending of the high potential vorticity to TPV and the upper level of SCV, and to the SCV. Under the same weather condition, the downward extending of high potential vorticity only influences the TPV and has no influence on the SCV.