Surface winds in hurricane Floyd: a comparison numerical simulations, aircraft, and QuikScat satellite data

A principal benefit of numerical simulations of hurricanes is that they provide detailed, high resolution information on the structure and evolution of the atmosphere that cannot be obtained through current observational techniques. However, simulations can be strongly dependent on the initial and boundary data as well as on the physical parameterizations in the numerical model, and so it is necessary to compare simulation results with observational data when available. The objectives of this study are to (1) validate model simulations of hurricane Floyd with all available observations, including in situ and remote sensing data sets and (2) explore the impact of the observations on high-resolution model simulations.

One important aspect of the model simulations is the surface wind field. The surface wind has a substantial impact on the fluxes of heat and moisture at the surface, which in turn have a large influence on the storm intensity and structure. Yet near the surface the model results are influenced greatly by the parameterization of boundary layer and surface processes. Hurricane Floyd presents an excellent opportunity for model-observation intercomparison of winds near the surface. Several swaths of data from NASA's QuikScat satellite were obtained while Floyd was over water. Additionally, surface winds derived from NOAA/HRD aircraft observations were obtained at several times during the life of the storm. In this study we conduct a four-day long simulation of Floyd using the PSU/NCAR nonhydrostatic mesoscale model (MM5) with one fixed mesh and two levels of moving nested grid. We compare surface winds derived from QuikScat and aircraft data to the surface winds in our numerical simulation of Floyd. Additionally, we compare vertical profiles of reflectivity and hydrometeors from the simulations with those derived from the TMI and PR instruments on NASA's TRMM satellite. Although the TRMM swaths, the Quikscat swaths, and HRD data are not coincident in time, the MM5 simulation's continuity in time allows a comparison with all observational data sources, and so the MM5 can be used as a cross-validation platform. This model-observation comparison is the first step towards the goal of assimilating observed surface winds into the MM5.