The interaction of a cyclone with topography on a b-plane

The interaction of a cyclone with topography on a b-plane has been carefully explored by a joint numerical computation and laboratory experiment, which was used to simulate a typhoon vortex encountering the island of Taiwan. Based on a dissipative formulation of rotating shallow-water flow, a physical viscosity has been incorporated in the momentum equations to model the diffusive nature of the geophysical flow. In the present laboratory experiment, the effects of Froude number, dimensionless Coriolis parameter and dimensionless b-parameter have been examined by properly choosing the angular speed of the turn-table, the size and strength of a generated vortex, the depth of water and the slope of bottom topography. It is so hoped that the essential dynamics of an ideal typhoon vortex at the mid-altitudes was captured. Both qualitative flow visualization and PIV (particle image velocimetry) measurement were performed in the turn-table experiment. Results show a good agreement between two approaches- numerical computation and turn-table experiment. Results indicate that, for example, on a cyclone encountering the center portion of the topography, a secondary cyclonic vortex was induced on the lee-side of topography. Due to the combined effect of the topographic and background b-gyres, both the primary and secondary vortices first moved towards north along the topography and then merged and left near the northwest of the topography. These phenomena are similar to what were observed in the case of typhoon encountering the center portion of Taiwan. Some other types of trajectories of cyclones were also investigated in detail in the present study.