Profiler Observations of the Boundary Layer within Hurricanes Georges and Earl during Landfall

Detailed wind profiles and other boundary layer (BL) properties of Hurricane Georges and Earl, during landfall, are described using measurements from a mobile Doppler profiling system (915 MHz profiler, Doppler sodar, and ceilometer). This paper focuses on the properties of wind profiles, turbulence, and cloud patterns within the boundary layer of these two landfalling tropical cyclones. During maximum wind conditions of George's landfall, the wind profile within the eyewall assumed the form of a jet, with peak winds of 44 m s-1 within the 0.5-1.0 km AGL layer. Considerable shear existed above and below this jet core. We define the BL depth as the region within which turbulence, as inferred from the variance of the Doppler spectrum along the vertical beam, is enhanced. We find that the BL depth is roughly proportional to the BL wind magnitude. For Hurricane Georges, the BL attained a maximum height of about 2 km AGL during maximum measured winds of 44 m s-1 within the 0.5-1.0 km AGL layer. The BL contains resolvable eddies, consisting of updrafts and downdrafts of 1-3 m s-1 magnitude, that may be associated with the vertical branches of horizontal convective rolls recently identified within landfalling hurricanes. Measurements of cloud base height also reveal large fluctuations within the cloud-filled BL of these two dissimilar hurricanes.