On diagnosing the hurricane boundary layer: inertial stability versus Richardson number

The hurricane boundary layer thickness as determined through the uniform constant BL depth model and varying prescribed BL depth model presented by Smith and Vogl (2008) is compared to the Troen and Mahrt (1986) method. Smith and Vogl presented the uniform constant BL depth approach from Emanual (1986) and a spatially varying prescribed BL depth based on inertial stability from the gradient wind. The Troen and Mahrt method of diagnosing the boundary layer thickness using the Richardson number is a basis for the Hong and Pan or MRF boundary layer schemes available in many hurricane models including WRF and MM5.

A hurricane, developed in the CM1 without a specified boundary layer formulation, is analyzed for comparing methods in determining the boundary layer thickness. The inertial stability method and the Troen and Mahrt method of determining the boundary layer thickness differed with depths increasing with increasing radius away from the radius of maximum wind for the inertial stability method and depths decreasing with increasing radius away from the radius of maximum wind with the Troen and Mahrt method.