Fine-scale Dual-Doppler analysis of the boundary layer in Hurricane Frances (2004)

Dual-Doppler data were collected by the DOW radars in the northern eyewall and eye of Hurricane Frances (2004) as it made landfall near Stuart, FL. A 5.7 km baseline was established south and east of Fort Pierce, FL. The dual-Doppler domain was chosen to optimize coverage and spatial and temporal resolution. As such, the horizontal domain comprised a 5.5 km x 5.5 km region, with a grid spacing of 20 m, thereby allowing for the resolution of horizontal structures with a characteristic size of O ~ 80m. Furthermore, the domain captured the boundary layer flow on both the windward and leeward sides the barrier island, which allowed for the assessment of the impact of the barrier island on the onshore flow. Three-dimensional wind analyses of the boundary layer revealed the presence of linear coherent structures with a characteristic wavelength of 400 – 500 m near the surface and increase in size and become more cellular in shape with height. Updraft and downdraft structures were associated with the boundary layer rolls. Characteristic wavelengths of coherent features in the boundary layer structure were determined through a 1-dimensional Fourier decomposition. Structures were examined both windward and leeward of the barrier islands, as well as over the entire domain. Horizontal cross-sections through were analyzed for characteristic wavelengths. The results of these analyses and implications on turbulent kinetic energy and boundary layer momentum fluxes will be presented.