高原低涡与西南涡结伴而行的不同活动形式个例的环境场和位涡分析

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

本文利用NCEP/NCAR-FNL再分析资料、历史天气图、青藏高原低涡切变线年鉴,通过分析1998~2015年持续高原涡影响西南涡结伴而行(简称两涡伴行)过程的活动形式,并对不同活动形式的个例进行了环境场与位涡分析,得出了不同活动形式两涡伴行的环境场特征,揭示了冷空气活动、200 hPa急流对不同活动形式的两涡伴行的影响原因。结果表明:(1)两涡伴行有三种活动形式,它们是高原涡诱发西南涡、高原涡与西南涡耦合以及同一天气系统下两涡,其中以高原涡诱发西南涡的活动形式占多数。(2)两涡伴行的500 hPa环境场主要是40°N以北东亚环流经向度不强,纬向气流主导,受500 hPa低槽、冷空气活动的影响;200 hPa环境场主要与200 hPa急流的强度、距急流核距离、在急流两侧的位置密切相关;不同活动形式的西南涡上空200 hPa、500 hPa环境场特征是有差别的。(3)受500 hPa低槽、冷空气影响的两涡伴行中的西南涡的生成是通过500 hPa高位涡空气伸入西南涡上空,造成西南涡上空斜压不稳定所至;在西南涡上空500 hPa斜压不稳定增强且具有较强的斜压不稳定时西南涡加强;200 hPa西南风急流影响高原涡诱发或耦合、加强西南涡是分别在高空高位涡下传影响到高原涡与西南涡上空、西南涡的情况下实现的,同一天气系统下,高空高位涡下传只影响高原涡,而未影响西南涡。

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 hP a 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.