Variability in hurricane boundary layer characteristics observed in a long-term NOAA dropsonde archive

Abstract

The statistical properties of five boundary layer height definitions were examined in 6,593 NCAR GPS dropsonde observations of the hurricane environment. Based on similar composite analysis studies, these boundary layer height estimates were divided into two categories based on their analytical characteristics. Three dynamical methods of estimating the boundary layer height were combined with two thermodynamical methods of estimating the mixed layer depth to numerically interrogate the physical properties of hurricanes within two primary modes of variability: azimuthal and geographic region. The results confirmed the vertical bifurcation of dynamical and thermodynamical height estimates and indicated a consistent distinction in the radial variability of each class. Moreover, the tangential wind field was well-described by the modified Rankine vortex. A characteristic decrease in boundary layer height with decreasing radius to the storm center was expressed in four of the five definitions. The non-uniform azimuthal distribution of relative radial winds and ill-behaved inflow layer depths precluded meaningful comparisons of boundary layer height in the rear storm-relative semicircle. While boundary layer height estimates failed to exhibit any significant regional variability, the right-front storm-relative quadrant appeared to exhibit non-trivial increases in mean boundary layer height.