The dynamic diagnosis on easterwards moving characteristics and developing mechanism of two Tibetan Plateau Vortex processes

Abstract By using NCEP reanalysis data, physical variables calculating and combining application of observatory data, satellite data and radiosonde data, the characteristics and development mechanism of twice Tibetan Plateau Vortex processes which happened during 19-22 July ,2008 and 29 July to 1 August, 2007 are analyzed from dynamic point of view. The results show that the positive vorticity eastwards moving is obvious along with the Plateau Vortex moves eastwards. If the Plateau Vortex is sequentially enhanced after moved out of the Plateau, it behaves as follows: Deep positive vorticity accompanies with the deep air vertical up movement as well as accompanies with strong convergence in middle and low troposphere level before the Plateau Vortex moves out of the Plateau. The positive vorticity is strengthened with the stronger air vertical up movement and stronger convergence in middle and low troposphere level and stronger divergence in middle and upper troposphere level after the Plateau Vortex moves out of the Plateau. If the Plateau Vortex is sequentially weakened after moved out of the Plateau, it behaves as follows: Positive vorticity is weaker and accompanies with the weaker deep air vertical up movement, accompanies with less convergence in middle and low troposphere level before the Plateau Vortex moves out of the Plateau. The positive vorticity is weakened with the weaker air vertical up movement and less convergence whole troposphere after the Plateau Vortex moves out of the Plateau. When the Plateau Vortex moving over the Plateau, the area of positive vorticity change rate center almost agrees with the area of positive vorticity center. The positive vorticity area maintenance, development and weakening dynamic mechanism which is close related with the development of the Plateau Vortex are mainly controlled by the total vorticity source's generation, development and weakening. The maintenance and development of convergence or divergence fields has important influence on total vorticity source and takes an important part in the maintenance and development of low vortex. The dynamic influence of topography makes the Plateau Vortex easier to develop on lee slope side of the big topography. The nearby and north area leaning north direction winds is favorable to the development of the Plateau Vortex. The vertical vorticity transition is not favorable to the strengthening of Plateau Vortex in the middle and low level troposphere. The results also show that stream fields convergence is stronger, the movements of cold and warm air are more active and the congregation of instability energy is more obvious during "7.21"process than during "7.31"process. The release of instability energy triggered by cold air is an important mechanism of low vortex development. That the meeting of cold and warm air leads to the maintaining and strengthening of convergence stream fields is the important factor of maintaining and strengthening of low vortex .