Large-Eddy Simulation of an Idealized Tropical Cyclone

©2009 American Meteorological Society A dvances in computing have allowed presentday numerical weather-prediction models to forecast and/or simulate tropical cyclones (TCs) with high resolution (horizontal grid spacing ~1 km). While these numerical models of TCs can capture many of their important structural features (eyewall, rainbands, etc.), the effects of small-scale [~O (100 m)], three-dimensional turbulence must still be parameterized. No objective basis has yet been found for such parameterizations, yet the maximum wind speeds in axisymmetric numerical TC models have been shown to be highly sensitive to the radial turbulent transfer and diffusion at these scales. As there is little observational guidance on the nature of radial turbulent diffusion in a TC, the present study was conceived to indicate the impact of these effects through computation of the small-scale scale turbulence (i.e., a large-eddy simulation, or LES) using a numerical weather prediction model applied to an idealized tropical cyclone. The numerical experiments reported on herein were carried out with the Advanced Research Weather research and forecasting (ARW) model, version 2.2, using six nested grids centered on the TC. As the ARW model is nonhydrostatic, it can and has been used as an LES model,1 and therefore one can expect the numerical solutions to capture turbulent eddies, Large-Eddy Simulation of an Idealized Tropical Cyclone