PRELIMINARY ANALYSIS ON THE INTENSITY AND STRUCTURE OF TYPHOON MORAKOT (2009) DURING ITS LANDING PROCESS

NCEP GFS (Global Forecast System) analytical data (available 4 times per day), satellite cloud image data and real-time observations of path and intensity of Typhoon Morakot are employed to investigate the variation of synoptic dynamics in its intensity and structure before and after the landing. This study intends to offer some hints for the forecast of intensity and structure of typhoons. Results show that in the tangential direction, the averaged asymmetry amplitude of wind on the radius of a large-value center of the low-level wind can be used as an important parameter for diagnosing the intensity of typhoons. Besides, the maximum of the upper dry potential vorticity in Morakot’s center tends to extend downward along the intensive gradient of tangential wind situated on the inner side of a large-value center of the low-level tangential wind. Additionally, the radial advection of the tangential wind determines the variation of tangential wind in conjunction with the vertical transmission of the tangential wind, the inertial centrifugal force and the Coriolis force. These four items are dominant in the motion equation of tangential wind based on a cylindrical coordinate without the effects of friction and turbulence. Moreover, the low-level convergence center of the typhoon has a tendency of shifting and developing along the intensive gradient of the tangential wind in the tangential direction.