6A.4 Large Eddy Simulations of an Idealized Tropical Cyclone

Tuesday, 29 April 2008: 11:00 AM
Palms GF (Wyndham Orlando Resort)
Yongsheng Chen, NCAR, Boulder, CO; and R. Rotunno, C. Davis, W. Wang, J. Dudhia, and G. Holland

The Weather Research and Forecasting (WRF) model, employing resolution high enough to capture three-dimensional turbulent motions, has been used to study an idealized tropical cyclone. The present study is motivated by previous work using axisymmetric numerical models, wherein all the turbulent motions of the idealized tropical cyclone had to be parameterized. The present model uses similar initial conditions to those of the previous studies, but by virtue of its three dimensionality, it can and does develop energetic turbulent eddies. It is found that the ability of the model to produce vigorous turbulent eddies occurs when the grid interval falls below approximately 100m; for larger grid intervals, the simulated turbulent motion is weak and the simulations depend sensitively on the subgrid turbulence parameterizations. Analysis shows that once the large-amplitude, high-frequency fluctuations are filtered out (using a 10-min window) the idealized (on an f-plane with constant sea-surface temperature and no environmental wind) vortex reaches a nearly steady state. Analyses of the time- and azimuthally averaged vortex structure and eddy fluxes will be presented
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