Multiscale numerical simulation of tropical cyclone Debby (2006) and validation with NAMMA data

Tropical cyclone Debby (2006) formed from an African wave only a short distance off the west African coast. Because it formed during the African Monsoon Multidisciplinary Analyses (AMMA) program, there are more data than usual for model initialization over the African continent. The NASA downstream addition to AMMA (NAMMA) provides a unique opportunity to validate these numerical simulations with a detailed description of the structure of Debby with data from the DC-8 aircraft flight of August 23. This dataset is particularly valuable because it includes clear evidence of the wind, cloud, precipitation, and aerosol distribution as a function of height, never before obtained on a storm in the east Atlantic.

A nested-grid WRF model at resolution of 36, 12, 4, and 1.33 km is initialized with NCEP global forecast system final analysis about 36 hours before the tropical storm formation. A total of 5 days of simulation is conducted to depict the structure and evolution of the tropical cyclone Debby. Numerical simulation results are then compared with the observations obtained during NAMMA. Initial results show that the high-resolution simulation has captured some observed structural features of Debby (e.g., warm core, eyewall, dry air outside of rainbands etc.). More detailed results from comparison and evaluation will be presented. In addition, the sensitivity of numerical simulation to model resolution, cloud microphysics and boundary layer parameterizations will be addressed. The environmental factors that affect Debby's development will also be discussed.