On the Characteristic Height Scales of the Hurricane Boundary Layer

Abstract

In this study, data from 794 GPS dropsondes deployed by research aircraft in 13 hurricanes are analyzed to study the characteristic height scales of the hurricane boundary layer. The height scales are defined in a variety of ways: the height of the maximum total wind speed, the inflow layer depth, and the mixed layer depth. The height of the maximum wind speed and the inflow layer depth are referred to as the dynamical boundary layer heights, while the mixed layer depth is referred to as the thermodynamical boundary layer height. The data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights. Consistent with previous studies on the boundary layer structure in individual storms, the dynamical boundary layer height is found to decrease with decreasing radius to the storm center. The thermodynamic boundary layer height, which is much shallower than the dynamical boundary layer height, is also found to decrease with decreasing radius to the storm center. The results also suggest that using the traditional critical Richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer. These different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations.

Contributions of Surface Sensible Heat Fluxes to Tropical Cyclone. Part I: Evolution of Tropical Cyclone Intensity and Structure

“…Consistent with observational and modeling results (e.g., Zhang et al 2008;Green and Zhang 2013), the LHX are distinctly larger than SHX in magnitudes. A predominant finding is that although the values of peak SHX could account for nearly 30% of those of the total surface latent and sensible heat fluxes, the influences of SHX on TC intensity are nonetheless not significant.…”

“…2) possess typical structures of real TCs: the radial inflow in the boundary layer, radial outflow in the upper troposphere, secondary outflow jet immediately above the boundary layer, slantwise upward motion, and tangential winds with peak values within the inflow layer (Kepert and Wang 2001;Zhang et al 2011). Consistent with their intensity relationship, the strengths of winds for two runs are also similar, while the eyewall in NOSH is much thinner than in CTRL as indicated by the radial extent of updraft.…”

Near-surface coherent structures explored by large eddy simulation of entire tropical cyclones

“…These changes possibly due to the difference in the eddy viscosity are consistent with previous studies 26 , and might affect the change in the eyewall radius. The heights of the boundary layer and the maximum tangential wind (301 m and 275 m at r  = 15 km, respectively) in the LES run are somewhat lower than those estimated by dropsonde observations over many TCs, which is higher than 500 m 27, 28 .…”

Signature of Large Aspect Ratio Roll Vortices in Synthetic Aperture Radar Images of Tropical Cyclones

“…As mentioned above, Doppler radar analyses show that PBL roll vortices that tend to align close to the surface wind direction and that have subkilometer to multikilometer wavelengths, but nearly always at aspect ratios comparable to those seen in standard rolls, are a frequent feature of the hurricane boundary layer (Wurman and Winslow, 1998;Morrison et al, 2005;Lorsolo et al, 2008;Ellis and Businger, 2010). The dynamical hurricane boundary layer depth can be subkilometer near the storm center, and it tends to increase with increasing radius from the center (Zhang et al, 2011). The smallest-scale rolls may also be related to surface layer streaks (Foster, 1997;Drobinski and Foster, 2003;Foster et al, 2006).…”