18A.7 The maximum intensity of hurricanes in axisymmetric numerical models

Friday, 2 May 2008: 11:45 AM
Palms GF (Wyndham Orlando Resort)
George H. Bryan, NCAR, Boulder, CO; and R. Rotunno

We use two axisymmetric numerical models to investigate the maximum intensity of simulated hurricanes. One is the code developed by Rotunno and Emanuel (1987, hereafter RE87), and the second is a newly developed code that conserves mass and energy. We investigate the effects of several approximations and settings in the two models, including: resolution, formulation of the governing equations, and settings in the turbulence parameterization. Based on a large number of simulations, we have reached the following conclusions:

1) If the turbulence parameterization is not modified, the simulations by RE87 were properly converged (maximum V → 50 m/s with increasing resolution).

2) The strongest sensitivity in axisymmetric models is the parameterization of turbulence, and essentially inviscid simulations yield unnaturally high intensity (maximum V ~110 m/s for the RE87 setup).

3) Comparison of output from the new, energy-conserving model to Emanuel's maximum intensity theory shows that the most intense (least diffusive) model-produced solution is ~30% greater than Emanuel's theoretical limit; this is somewhat less than the over-prediction of ~50% reported by Persing and Montgomery (2003) using the RE87 Model.

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