6C.6
A simple model of the hurricane boundary layer
Roger K. Smith, University of Munich, Munich, Germany
A simple steady axisymmetric slab boundary layer model for the hurricane boundary layer is investigated. High-resolution solutions of the boundary layer equations are obtained by integrating inwards from some large radius, at which it is assumed that geostrophic balance exists. A new feature of these solutions is the existence of spatial oscillations in vertical velocity (with both positive and negative values) at the top of the boundary layer, inside the radius of maximum tangential wind speed. There are associated annular regions in which the tangential flow is supergradient. The existence of boundary layer induced oscillations in vertical velocity in reality would have implications for the organization of convection in the core region of a hurricane. It is shown that an approximation to determine the radial flow in the boundary layer suggested by Willoughby overestimates the vertical motion at the top of the boundary layer by a factor of about two.
We examine also the thermodynamic structure of the boundary layer and the distribution of surface fluxes as a function of radius for vortices of different widths. It is found that the radial gradient of boundary layer equivalent potential temperature in the eyewall region, which is related to the radial gradient of virtual temperature above the boundary layer, is relatively insensitive to the vortex size for wide range of vortex profiles, but has some dependence on size for the narrowest profiles. In contrast, the strength and radial distribution of the latent heat flux varies markedly with the radial structure of the vortex.
Session 6C, Tropical Cyclone Simulation: Dynamics I (Parallel with Sessions 6A, 6B, and 6D)
Tuesday, 30 April 2002, 2:00 PM-3:30 PM
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