NOAA/AOML Hurricane Research Division
For this presentation a commonly used and relatively sophisticated microphysical parameterization scheme used in high-resolution tropical cyclone simulations is compared to airborne radar and microphysical probe data collected from storms over many years. Statistics of vertical motion, reflectivity, and hydrometeor concentrations are compared for the two datasets (observations versus simulations) to identify potential deficiencies in the microphysical scheme and areas for improvement to the scheme. Such improvements can lead to better forecasts of tropical cyclone intensity and rainfall.
Comparisons of the two populations show that the model reproduces many of the gross features seen in the observations, though notable differences are evident. The general distribution of vertical motion is similar between the observations and simulations, with the strongest up- and downdrafts comprising a small percentage of the overall population in both datasets, but the magnitudes of vertical motion are weaker in the simulations. The model produces reflectivities that are much higher than observed, and correlations between vertical motion and hydrometeor concentration and reflectivity show a much stronger relationship in the model than what is observed.
These comparisons show that there are several likely areas of deficiency in the parameterization, such as with the parameterization of the production, conversion, and fallout of frozen hydrometeors. Preliminary results from attempts at improving these defeciencies will also be presented, with the goal of improving the statistics in the simulations. The comparison technique presented here provides a reliable method for testing simulations against observations, and it provides a framework for conducting comparisons using other observational platforms. As operational models achieve higher resolutions over the coming years, these sorts of evaluation techniques can be applied to them as well.