Shock-like Structures in the Tropical Cyclone Boundary Layer

Flight-level tangential and radial wind observations from the boundary layer of tropical cyclones, such as Hurricanes Allen (1980) and Hugo (1989), show abrupt jumps over several kilometers. To understand how these features form, we use an axisymmetric, f-plane slab boundary layer model with a prescribed pressure forcing in conjunction with two local, steady-state models. With this series of models, we evaluate the role of shock dynamics arising from the nonlinear terms in the radial momentum equation and assess conditions necessary for the development of shock-like features in the tropical cyclone boundary layer through varying the intensity and radial extent of the winds in the initial vortex. We find that the local models adequately represent the boundary layer winds for weak vorticity. However, in strong, small vortices, we see that shock-like structures readily develop in the region where the hyperbolic nature of the boundary layer dominates. We also find that this development can be hindered by the formation of a secondary inflow maximum in vortices with a large wind field. We will show that the formation of this secondary inflow maximum precedes the formation of a secondary eyewall.