Effects of Horizontal Diffusion on Tropical Cyclone Intensity Change and Structure in Idealized Three-Dimensional Numerical Simulations
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Effects of Horizontal Diffusion on Tropical Cyclone Intensity Change and Structure in Idealized Three-Dimensional Numerical Simulations
  • Published Date:

    2015

  • Source:
    Monthly Weather Review, 143(10), 3981-3995.
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  • Description:
    This study examines the effects of horizontal diffusion on tropical cyclone (TC) intensity change and structure using idealized simulations of the Hurricane Weather Research and Forecasting Model (HWRF). A series of sensitivity experiments were conducted with varying horizontal mixing lengths (L-h), but kept the vertical diffusion coefficient and other physical parameterizations unchanged. The results show that both simulated maximum intensity and intensity change are sensitive to the L-h used in the parameterization of the horizontal turbulent flux, in particular, for L-h less than the model's horizontal resolution. The results also show that simulated storm structures such as storm size, kinematic boundary layer height, and eyewall slope are sensitive to L-h as well. However, L-h has little impact on the magnitude of the surface inflow angle and thermodynamic mixed layer height. Angular momentum budget analyses indicate that the effect of L-h is to mainly spin down a TC vortex. Both mean and eddy advection terms in the angular momentum budget are affected by the magnitude of L-h. For smaller L-h, the convergence of angular momentum is larger in the boundary layer, which leads to a faster spinup of the vortex. The resolved eddy advection of angular momentum plays an important role in the spinup of the low-level vortex inward from the radius of the maximum wind speed when L-h is small.
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