Impact of Cloud Microphysical Processes on the Intensity Forecast of Tropical Cyclones: High Resolution Numerical Simulations and Doppler Radar Data Assimilation

Cloud microphysical processes have a significant impact on the forecasting of the structure and intensity of tropical cyclones (TCs). Results from our recent study showed that the numerical simulation of rapid intensification of Hurricane Emily (2005) is very sensitive to different microphysical schemes in the WRF model. It is also shown that the major difference among the various microphysical schemes is the different distribution of microphysical properties each scheme produced. However,cloud microphysical properties are not analysis variables in most of the current advanced data assimilation systems. Therefore, it is difficult to understand the impact of accurate initial cloud microphysical variables on TC intensity forecasts.

Doppler radar reflectivity data provide distributions of hydrometeors at a high spatial and temporal resolution. The data are very useful in depicting the realistic structure of microphysical properties of TC vortices. In this study, the airborne Doppler radar reflectivity data are assimilated into the mesoscale WRF model to improve the initial specification of cloud microphysical properties in the inner core of the Hurricane Dennis (2005). The impact of the data in representing cloud microphysical properties and convection distributions in the initial vortex is examined. High-resolution numerical simulations are then conducted with the improved initial conditions. By analyzing the model simulations, the impact of the radar reflectivity on the forecasts of the intensity, track, and the storm inner core dynamic and thermodynamic structures for Hurricane Dennis is investigated. The physical mechanisms through which the cloud microphysical processes influence TC intensity change are also discussed.