NCAR Seminar MMM

To study the maximum possible intensity of hurricanes, previous investigators have used analytic theory, observations, and/or numerical models. Each approach has advantages and drawbacks. This talk will focus on the use of time-dependent numerical models. The primary advantage of this approach is that little input is required from the model user. By simply placing a weak vortex into a specified, homogeneous environment, the simulated hurricane typically intensifies rapidly and achieves a steady state of maximum intensity. The primary drawback of the approach is that numerical models can sometimes produce unnatural results. For example, using a state-of-the-art numerical model, I will show that sustained tangential velocity can exceed 120 m/s, despite a maximum observed intensity of only 60 m/s for the same environment. A systematic study of various components of the numerical model (e.g. governing equations, numerical techniques, specification of unresolved physical processes, etc.) has revealed that this unnatural result is mostly attributable to the model's specification of subgrid/unresolved turbulence in the horizontal (radial) direction. Unfortunately, the effects of turbulent processes in hurricanes remain poorly understood. A pathway toward better parameterization and understanding of turbulence in hurricanes will be demonstrated using output from a large eddy simulation of an idealized hurricane.