Impact of microphysical parameterizations on the structure and intensity of simulated hurricanes: Using satellite data to determine the parameterizations that produce most realistic storms

Many factors determine a tropical cyclone's intensity. Ultimately, though, intensity is dependent on the magnitude and distribution of the latent and radiative heating that accompany the hydrometeor production during the convective process. Hence, the microphysical processes and their representation in hurricane models are of crucial importance for accurately simulating hurricane intensity and evolution. The accurate modeling of the microphysical processes becomes increasingly important when running high-resolution models that should properly reflect the convective processes in the hurricane eyewall.

We study the impact of microphysical assumptions on the structure and the intensity of the simulated hurricanes. In particular we compare and contrast the members of high-resolution ensemble WRF model simulations of Hurricane Rita (2005). The members of the ensemble include simulations with three different microphysical schemes and a number of different Particle Size Distribution (PSD) assumptions within one of the microphysical schemes.

We investigate the impact of the microphysical assumptions on the thermodynamic structure of the simulated storms, their primary and secondary circulations. We find that the choice of microphysical scheme and the choice of particle size distribution parameters have significant implications for the intensity and structure of the simulated storms.

As a next step, we compare the simulated storms to a set of satellite observations. To facilitate the comparison, we employ instrument simulators that use as input the geophysical fields produced by WRF and simulate satellite observables (microwave brightness temperatures, radar reflectivity, scatterometer–observed surface backscattering cross-section). We compare the forward simulated satellite observables to a multi-parameter set of observations available from the JPL Tropical Cyclone Information System (TCIS).

We find that such comparisons can help discriminate between simulations with different microphysical assumptions. In particular, assuming hydrometeor distributions with larger number of smaller particles results in model simulations with radiometric signatures that compare more closely to observations.

To test the robustness of the conclusion, we compare and contrast two simulations of hurricane Isabel (2003), each using different PSD assumptions. Again, we use satellite observations to discriminate between the two simulations.