Abstract：A study was carried out on the landfall typhoon 0509 Matsa，which sustained over land for a long period and was transformed into an extratropical cyclone in the end. Through the analysis, it is shown that the Matsa's extratropical transition and the re-intensification are due to the intrusion of cold air from the upper-level trough into the typhoon's circulation. From the variation of potential vortices at the upper-level, one can clearly see the mechanism that its anomaly is downward transported from the upper troposphere during the typhoon's transformation. The main course is the transformation of a symmetric perpendicular cyclone to a baroclinic asymmetric cyclone.
2007, Vol. 25 
