The Impacts of Numerical Schemes on Asymmetric Hurricane Intensification
Steve Guimond
ESSIC
Noon in 2155
Abstract:
The fundamental pathways for tropical cyclone (TC) intensification are
explored by considering axisymmetric and asymmetric impulsive thermal
perturbations to balanced, TC;like vortices using the dynamic cores
of three different nonlinear numerical models. Attempts at
reproducing the results of previous work, which used the atmospheric
science community model WRF (Nolan and Grasso 2003; NG03), revealed a
discrepancy with the impacts of purely asymmetric thermal
forcing. The current study finds that thermal asymmetries can
have an important, largely positive role on the vortex intensification
whereas NG03 and other studies find that asymmetric impacts are
negligible.
Analysis of the spectral energetics of each numerical model indicates
that the vortex response to asymmetric thermal perturbations is
significantly damped in WRF relative to the other models.
Spectral kinetic energy budgets show that this anomalous damping is
primarily due to the increased removal of kinetic energy from the
vertical divergence of the vertical pressure flux, which is related to
the flux of inertia-gravity wave energy. The increased kinetic
energy in the other two models is shown to originate around the scales
of the heating and propagate upscale with time from nonlinear effects.
The results of this research indicate that the numerical treatment of
small-scale processes that project strongly onto inertia-gravity
wave energy can lead to significant differences in asymmetric TC
intensification. Sensitivity tests with different time
integration schemes suggest that diffusion entering into the implicit
solution procedure may be responsible for the anomalous damping of
energy. Extensions of this work to analyze the effects of various
physical parameterizations will be discussed.