A study of hurricane dynamics using a two-fluid axisymmetric model

Summary A model of a frictionless rotating axisymmetric flow in an incompressible fluid is extended to the spun-up flow in the lower of two incompressible fluids, the upper fluid remaining at rest. It is shown that a steady state can be maintained only if the upper fluid extends to the surface in an inner core (the eye), the surface radius of which is determined by the strength of the tangential flow, as is the configuration of the eye wall. A secondary (meridional) circulation may also be present provided that the tangential flow has its maximum strength at middle levels.In order to relate this idealised model of a mature hurricane to the physical processes involved in its evolution, the eye wall, treated as a flow separation discontinuity in the idealised case, is considered as a transition zone between the fluids. The physical processes involved in the creation of this zone from a pre-existing ring of deep moist convection are proposed. Finally, the dynamics of the inflow layer, taking account of momentum transfer by small-scale eddies, is considered using a boundary layer model based on a modification of the classical Ekman-Taylor spiral.With 7 Figures