15A.5 Sensitivity of Idealized Hurricane Intensity and Structure to Different Resolutions and physics schemes in HWRF

Friday, 3 July 2015: 9:00 AM
Salon A-2 (Hilton Chicago)
Lin Zhu, NOAA/NCEP/EMC, College Park, MD

A series of 5-day numerical simulations of idealized hurricane vortices under the influence of different background flows is performed by varying resolution in different portions of the atmosphere and model physics with the operational version of the Hurricane Weather Research and Forecasting Model in order to study the sensitivity of hurricane intensity forecasts to different resolutions and physics. Increasing the horizontal resolution slightly increases storm intensity. It enhances the storm outflow and concentration. While increasing vertical resolution from 21 to 43 levels produces stronger hurricanes, whereas increasing it further to 64 levels does not intensity the storm further, but intensity fluctuations are much reduced. Moreover, increasing the low-level vertical resolution generates stronger storms, but the opposite is true for increased upper-level vertical resolutions. On average, adding mean flow increasing intensity fluctuations and variability (between the strongest and weakest hurricanes), whereas adding vertical shear delays hurricane intensity variability and bifurcation rate occur at later stage. These intensity differences are found to be closely related to inner-core structural changes, and they are attributable to how much latent heat could be release in higher-vertical resolution layers, followed by how much moisture content in nearby layers is converged. Hurricane intensity with higher vertical resolutions is shown to be much less sensitive to varying background flows, and stronger hurricane vortices at the model initial time are less sensitive to the vertical distribution of vertical resolutions with a near-parabolic or Ω-shape tend to produce smoother intensity variations and more typical inner-core structures. Also, storm is very sensitive to physics scheme. Both the storm intensity and structure will be impact a lot using different physics schemes.
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