A NUMERICAL STUDY OF TROPICAL CYCLONE MOTION USING A BAROTROPIC MODEL .2. MOTION IN SPATIALLY-VARYING LARGE-SCALE FLOWS

The motion of an initially symmetric vortex in a spatially-varying large-scale flow on a beta plane is investigated using a nondivergent, barotropic numerical model. The calculations extend those carried out for the case of zero basic flow in Part I. The large-scale flows are provided by meridionally-varying zonal flows, or single-mode, stationary, finite-amplitude planetary waves in a channel. Interest is focused on the evolution of vortex asymmetries and their role in determining vortex motion relative to the basic large-scale flow. As in Part I, the calculations are used to assess averaging procedures for computing the environmental wind field of a tropical cyclone from observed wind data. It is shown that averaging over an annular region centred on the vortex is, in principle, more accurate when there is a basic flow, in comparison with the case of zero basic flow.