The Impact Of Extratropical Transition Of Tropical Cyclone On The Midlatitude Downstream Flow

The midlatitude downstream flow would be influenced with the tropical cyclone (TC) undergoing extratropical transition (ET),and this has been discussed heatedly nowadays. TC will gradually close to and into the downstream jet when moving forward to the high latitude, and the downstream jet would be enhanced in strengthen and instability at the same time. Then the downstream flow change eventually, and new ridge-trough couplet in the downstream region would form. The influence of ridge-trough couplet in the downstream region and downstream jet are different due to the different situation of initial field of TC. The control experiment and sensitivity experiments were carried out to discuss the influence of ET process to the downstream flow when TC was different initially using the WRF mode based on the10*10FNL data. The initial fields were improved by Kurihara’s filter method and bogus method.The the contract of one control experiment and four sensitivity experiments results showed that:(1) The downstream flow is sensitive to the strength of TC in the initial field.The powerful TC undergoning ET makes the development of downstream ridge-trough couplet and downstream jet strongly; and the weak TC undergoning ET makes the development of downstream ridge-trough couplet and downstream jet weakly.(2) The downstream flow is sensitive to the position of TC relative to the upstream trough, when the postion is northwestward (i.e. closer to the upstream trough), TC undergoing ET makes the development of downstream ridge-trough couplet and downstream jet strongly; when the postion is southeastward (that is far away from upstream trough), TC undergoing ET makes the development of downstream ridge-trough couple and downstream jet weakly.