Fine-Scale Hurricane Boundary Layer Structure

In order to characterize the hurricane boundary layer structures over a range of hurricane intensities, the Doppler on Wheels radars (DOWs) deployed in several hurricanes during the 2020 season, obtaining both dual-Doppler and rapid single-Doppler observations in the boundary layer of landfalling hurricanes. Results will be presented from three hurricanes:  Hurricane Laura, Hurricane Sally, and Hurricane Delta. These results will be discussed in the context of standard hurricane wind models.

Two DOWs targeted landfalling Category 4 Hurricane Laura. The DOWs deployed in southwestern Louisiana during landfall.  As is usual, the DOW radars operated in the most intense wind regions of the hurricane, collecting fine-scale, near-surface data in the eyewall near landfall.  The dual-DOW baseline was a very short ~6.3 km, providing ~60 m spatial resolution in the center of the dual-Doppler lobes. Anemometer data at 1 Hz were collected from DOW masts ~8-10 m above radar level (ARL). Laura is the 1st ever fine-scale dual-Doppler deployment sampling the HBL and eyewall in a Category 4 hurricane at landfall.   

Single-Doppler radar data were collected in Hurricanes Sally and Delta.  This allowed for the two-dimensional quantification rapidly evolving of boundary layer structures.  An array of surface based instruments, including a prototype, “POLENET”, which attaches existing infrastructure, allowing for a customizable observation level, were deployed in Hurricane Delta in order to correlate observations at radar level with surface observations.  Using corrections based on turbulence statistics and roughness lengths, a reduction factor was derived for the radar winds, allowing  for comparison between radar level winds and winds observed at 1, 2, and 10 m.  

The HBL is comprised of coherent structures that are potentially responsible for significant transport of turbulent fluxes throughout the HBL as well as regions of enhanced damage at the surface.  These coherent structures are not well understood and consequently their effects are poorly represented in numerical models.  In order to characterize the HBL structures over a range of hurricane intensities, DOWs deployed in several hurricanes during the 2020 season, obtaining both dual-Doppler and rapid single-Doppler observations in the boundary layer of landfalling hurricanes.