Radar and tower data from Hurricane Isabel have been collected during the Characterization of Atmospheric Turbulence and Flood Initiation and Validation Experiment (CAT-FIVE) in 2003. For the first time an experiment was set up in a hurricane environment to essentially acquire high spatial and temporal resolution data of hurricane boundary layer (HBL) rolls. A Shared Mobile Atmospheric Research and Teaching (SMART) radar with a gate spacing of 66.7 m and a scanning strategy focusing on the HBL was operated along with an array of 10 m instrumented towers, with an acquisition rate of 0.5 to 5 Hz. The goal of this experiment was to acquire a comprehensive high-resolution data set of HBL rolls during a landfalling hurricane in order to determine the rolls' vertical structure, evolution and impact on the surface wind field.

The Doppler velocity data from Hurricane Isabel revealed the presence of a significant number of rolls in the HBL. The rolls are easily identified on the SMART radar images, as areas of strong localized horizontal wind shear due to vertical mixing of winds of different intensities. Indeed, the counter-rotating structure of the rolls generates updraft and downdraft regions responsible for the vertical transport of momentum. Strong winds at the top of the boundary layer are then transported downward while weaker winds originally closer to the surface are moved upward, resulting in horizontal differences in wind speed as depicted on the high resolution radar images. This study will investigate this transport of momentum and its potential reflection on the surface wind field. A time domain analysis of the surface wind speed data collected from the towers will be performed. Likewise, radar data from the lowest parts of the rolls will be examined for the same time period. The two data sets will then be correlated in order to document any link that might exist between perturbations on the surface wind field and the roll circulation.