The Dynamical Diagnosis And Numerical Study Of Typhoon Morakot (0908)

Tropic cyclones are the most dangerous weather system on the earth.The TC structure and intensity changes could still not well be understood due to the limit of observation in the ocean. Based on Ncep reanalysis data, TBB data from the Fy-2c satellite data and TRMM 3B42 precipitation data, the asymmetrical characteristics of landing Typhoon Morakot are analyzed, the result shows that water vapor transport by the southwest wind is the main vapor source of heavy rain. The eye of typhoon shows an obvious expansion when landing in Taiwan.By invoking numerical model output, satellite imagery and radar echo pictures, etc., the structures of Typhoon Morakot (2009) are analyzed.The WRF model with three nested domains is used to perform numerical simulation to understand the terrain effect on the structure of the Typhoon Morakot. The model initial conditions are generated from a WRF three-dimensional variational data assimilation (3DVAR) system. The typhoon structure is resolved over the finest domain with grid size of 2km and verification against observations and best track data is carried out. The simulation reasonably reproduces the typhoon track,its intensity and the principal rainband maintaining in the south of Typhoon Morakot.Vertical motion triggered near the edge of eyewall is more stronger than other regions, this matches with the observation that light precipitation exists in the eye and intensitively convective precipitation occurs near the inner edge of eyewall. It is found that outward-sloping eyewall clouds exist in the south part of Typhoon, which is maintained by strong radial air transport upward from boundary layer.The simulation results show that highly asymmetric structure of the Typhoon is associated with the asymmetric distribution of the strong tangential wind and the temperature anomaly. The model reproduces the hollow PV tower structure in the core region, the maintenance and late breakdown of PV tower in the landing process affect the symmetric structure and distribution of deep convections. The PV budget also shows that the change of PV generation rate in rainband play an important role in the asymmetric distribution of heavy rain. The vortex Rossby wave redistributes the PV in radial direction though mixing the PV between the core and eyewall, it indicates the strong wave-flow interaction in the Typhoon. The distribution of high wavenumber eddy kinetic energy outside the eyewall is closely related to the isolated hot tower activities. The breakdown of the western part of eyewall was induced by the mixing between warm air from boundary layer and cold air from high levels when landing Chinese Mainland. The forward trajectory analysis shows air parcel with high moisture entropy mixing to eyewall from the eye. The tangential wind budget shows the friction and the enhanced radical wind make the decrease of tangential wind and induce the structure become more asymmetric.The high value area of hail matches well with the distribution of rain mixing, it indicates the cold cloud precipitation is the main micro physic mechanism in landing Typhoon Morakot.Some dynamical parameter is calculated with NCEP/NCAR global final analysis data in heavy-rainfall events of Typhoon Morakot. The result shows that the positive high-value area of the parameter vertically integrated well covered the observed 6h-accumulated surface rainfall.The baroclinic inertial-gravity invariant describes the heavy rain in the "fast-manifold" for severe weather effectively.