The effects of ice microphysics on the inner core thermal structure of the hurricane boundary layer

The effects of five cloud microphysics parameterizations on the mean thermal structure of the tropical cyclone boundary layer (TCBL) are examined by numerical experiments with an axisymmetric, non-hydrostatic model. It is shown that although the radial and azimuthal velocity remains slaved to the gradient flow above the TCBL, the strength of the boundary layer updrafts (and downdrafts) and the location of the cloud base (which is connected to the location of the stable layer within the TCBL) depend sensitively on the microphysics parameterization. From an analysis of the potential temperature and water vapor mixing ratio budgets, it is found that latent heat release within the eyewall above the cloud base is balanced by the strong cooling tendency due to vertical advection above the cloud base. Below the cloud base, it is found that the downward flux of high theta is largely balanced by rain evaporation. Near the surface, it is shown that warm rain microphysical parameterizations enhance near-surface evaporation rates compared to their ice microphysics counterparts (which affect the thermal structure of the surface layer). Finally, it is shown that diagnostic TCBL models generally underestimate rainwater evaporation rates compared to the full non-hydrostatic model.