Dynamical Boundary-Layer Depths in Hurricanes Derived from Surface Wind Observations

Recent composite analysis of GPS dropwindsonde vertical profiles in hurricanes has documented characteristic boundary layer depth as a function of radial distance from the storm center (Zhang et al., 2011). Results suggest that dynamical and thermodynamic boundary-layer depths do not generally coincide, and furthermore that traditional scaling methods such as the height of critical Richardson number are not consistent with observed boundary layer depths. To understand the implications for these results, the directly-observed depth is compared with characteristic depths estimated from azimuthally-averaged SFMR surface wind speed radial profiles obtained in over 25 hurricanes assuming a steady-state momentum balance. The resulting depth value is equivalent to the height were the wind stress vanishes, or approximately, the height of the maximum wind speed. As the computed depth is also sensitive to the specified drag coefficient and cross-isobar inflow angle, a range of variability due to uncertainty in these quantities is estimated. Finally, we will compare these observationally-based depths with values derived from numerous cases of HWRF simulated surface winds.