Storm Structure and Rainfall Evolution in Hurricane Dennis (2005)

Rainfall and diabatic heating distributions in a hurricane is one of the key parameters in understanding the dynamic process in storm development and evolution. Detailed analysis of a high-resolution model simulation of Hurricane Dennis (2005) is used to examine the characteristics of rainfall and vertical velocity fields during the early development and later intensification stages. Dennis was one of the cases extensively observed during the NASA Tropical Cloud System and Processes (TCSP) experiment in 2005. In addition, we have evaluated model simulated rainfall by comparing the results from Dennis to model simulations and the observations from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and Microwave Imager (TMI) rainfall data from a number of Atlantic hurricanes from 1998-2005. The models used in this study are PSU/NCAR MM5 and the Weather Research and Forecast (WRF) model. Both have a vortex-following movable grid with the finest resolution at 1.67 km in the inner-most domain. The conditional probability density function (PDF) is used to quantify the overall statistical rainrate distributions in the model simulations and the TRMM data. We stratify the comparisons according to storm intensity, lifecycle, and inner-core and outer rainband structures. Preliminary results indicate that the model simulated rainrate is closer to the PR data than that of TMI in high rainrates because of the lower resolution in TMI. Overall both MM5 and WRF simulations produce higher rainrates than observations, The WRF simulations produce relatively more rainrate values in the range of 10~50 mm h-1 than MM5 and TRMM data. MM5 tends to produce more extreme rainrates (> 50 mm h-1) than both WRF and TRMM data. More detailed analysis is underway to identify various physical and dynamical processes that are responsible for the different characteristics in model simulated rainfall in the early development and later intensification stages in Dennis and other Atlantic hurricanes.