The impacts of resolution and boundary layer parameterization on the structure of the wind field in high resolution simulations of Hurricane Isabel (2003)

We present detailed analyses of high resolution simulations of Hurricane Isabel (2003) initialized from GFDL model initial conditions at 00Z on Sept. 12th, 2003. The effects of horizontal resolution, vertical resolution, nested grid size, and boundary layer parameterization on the accuracy of the simulation are illustrated. In particular, the vertical structures of the inner-core wind fields are evaluated by direct comparison to the wind fields observed with pseudo-dual-Doppler radar analyses, and the boundary layer winds are evaluated by comparisons with dropsondes and stepped descent observations from CBLAST flights into the storm. Simulations with 4 km, 1.33 km, and 444 m resolution are considered.

On the 12th and 13th of September, the simulated boundary layer structures compare remarkably well with those observed, with the YSU PBL scheme using the Donelan et al. correction for the drag coefficient giving the best results. Increasing the vertical resolution in the boundary layer does not give notably improved results. The azimuthally averaged wind fields compare amazingly well to radar and dropsonde analyses. Some additional improvements can be made by making small changes to the boundary layer parameterizations.