Analysis of the hurricane boundary layer kinematic structure using Doppler radar profiles

The hurricane intensity forecast problem has long been one of the main challenges of the hurricane research and forecasting community. To better understand hurricane intensity change and thus improve intensity forecast, one of the goals of the Hurricane Research Division is to improve our understanding of the physical processes that influence intensity change from large-scale to turbulence scales, and from surface layer up to the upper levels. Recent studies have shown that the hurricane boundary layer (HBL) plays an important role in the intensification mechanism; it is therefore critical to obtain an accurate representation of the HBL structure. Moreover, with recent efforts in the modeling community to use high-resolution numerical models, it has become increasingly important to evaluate critical regions such as the HBL depicted in the models. The present study provides a thorough analysis of the kinematic structure of the HBL using airborne Doppler radar data.

For several decades, the Hurricane Research Division of NOAA has been collecting Doppler radar data starting at 150 m above sea level. Over 200 radar vertical profiles are processed from 8 hurricanes at various intensities and stages of their lifecycle and composites analyses of the lowest 3 km, generally radially extending up to 4 times the radius of maximum wind are presented here. Statistical analyses of the various characteristics of the HBL structure (inflow layer depth, inflow/outflow magnitude, turbulent kinetic energy…) are performed and the potential relationships of these characteristics with TC strength, intensity change, vertical wind shear magnitude and location with respect to the shear direction are investigated. Such analysis offers a unique opportunity for a detailed representation of both the radial and vertical structure of the HBL, and could provide insights on the HBL processes involved in the intensification process.