A "nature run" is a high-quality simulation of a phenomena of interest which is used to provide data to be assimilated into a forecast model, for the purpose of evaluating the forecast model, its data assimilation scheme, and the potential utility of new observation types. We have endeavored to generate a very high-quality nature run simulation of a hurricane in the Tropcal Atlantic, using the ARW-WRF model with 1 km horizontal resolution, 60 vertical levels, and the latest physical parameterizations. The simulation is not based on a real storm, but rather one that is produced within a 6 month ECMWF global nature run that has already been produced and validated.

This presentation will describe our efforts to validate the hurricane nature run, that is, to determine the extent to which it is like a real hurricane, at least in comparison to operational forecast models. For this purpose, we will evaluate the structure of the cyclone in comparison to a number of observational diagnostics: the pressure-wind relationship, the outward slope of the eyewall, the decay of wind with height along the radius of maxium winds, the inflow depth and temperature structure of the boundary layer, and the distribution of convective versus stratiform precipitation.