Large-Scale Conditions of Tibet Plateau Vortex Departure

Tibetan Plateau Vortices (TPV), when moving eastward out of the plateau, usually cause catastrophic weather in East China. Some of them even influenced the Korea peninsula and Japan. Based on the circumfluence situation of the out- and in- Tibet Plateau Vortex (TPV) from 1998 - 2004 and its weather-influencing system, multiple synthesized physical fields in the middle – upper troposphere of the out- and in-TPV are computationally analyzed by using re-analysis data from National Centers for Enviromenal Prediction and National Center for Atmospheric Research (NCEP/NCAR) of United States. Our research shows that the departure of TPV is caused by the mutual effects among the weather systems in westerlies and in the subtropical area, within the middle and the upper troposphere. This paper describes the large-scale meteorological condition and the physics image of the departure of TPV, and the main differences among the large-scale conditions for all types of TPVs. This study could be used as the scientific basis for predicting the torrential rain and the floods caused by the TPV departure.

The results indicate:

·According to the weather-influencing system, the out-TPV can be classified into two categories: one goes with a trough, and the other acts in a sheared stream field. In detail, the trough-related Out-TPV could be further classified into the westerly trough foreside sort (WTFS) and the trough north vortex south sort (TNVS). The shear Out-TPV related is further divided as the sheared stream filed sort (SSFS) and the shear line sort (SLS). The TNVS with two troughs and one ridge and the WTFS with one trough and one ridge have less difficulty migrating out from the plateau.

·The departure of TPV is caused by the mutual effects of the weather systems in the westerly belt and in the subtropical area as well as the weather systems within the middle and the upper troposphere. Although the weather-circumfluence configuration accompanied with out- and in-TPV in the eastern Asia farther north of 40°N in the same sort are named as the same, remarkably the differences exist: the weather-influencing system in the middle troposphere for out-TPV is strengthening, but it is weakening for in-TPV; out-TPV is of baroclinicity, while in-TPV is warm vortex; by comparison, the westerly or northerly related to out-TPV in the northern portion of or to the north of the plateau, and vapor transportation is stronger and becoming more so; the westerly jet on 200 hPa is sited farther south, closer to out-TPV; westerly-deflected on the 300hPa upper out-TPV is strong or gaining strength.

·The common large-scale features of the four kinds of out-TPVs include the follow: All weather- influencing systems are enhancing; out-TPVs have been infused by the cold air of baroclinicity; the northern airflow in the northern plateau or its neighborhood is reinforcing; vapor is transported stably to the eastern or southeastern plateau by the southern airflow; the ridge line of the South Asia High is situated at 24-30°N; the westerly jet on 200 hPa exists just over the weather- influencing system on 500hpPa and has reached the upper area of out-TPV; the leading airflow on 300hPa-westerly or west-southwester is strong or becoming stronger.

Key Word: Tibet Plateau vortex, Large-scale meteorological condition,physics image