Idealized numerical study of tropical cyclone intensification on a beta-plane

In this study, we investigate the development and structure of an idealized tropical cyclone in an otherwise quiescent environment on a beta plane using a non-hydrostatic mesoscale model. Experiments are conducted using a nominal horizontal grid spacing of 5 km and a simple physics package (e.g. explicit latent heating scheme and Bulk-aerodynamic boundary layer scheme).

A series of experiments are carried out with small random perturbations in the boundary layer moisture field (- 0.5 g/kg to 0.5 g/kg). We show that:

i)There is an intrinsic variability of vortex intensity among ensemble members once rapid intensification commences.

ii)During the early phase of rapid intensification the inner-core asymmetries are dominated by vortical hot towers (VHTs) as found in the corresponding f-plane experiments. The mean intensity of ensemble members does not differ significantly from the mean intensity of corresponding f-plane experiments.

iii) The ensemble average asymmetry in the inner-core does not show a dominant wavenumber-one pattern.

iv) The large-scale asymmetry associated with the beta-gyre is virtually the same among ensemble members. This asymmetry causes the vortex to move in the north-northwest direction, with a maximum difference in storm position of any two members of about 60 km after 96 hours.

Some of these findings differ profoundly from previous research and we provide the beginning of an insightful explanation of the influence of the beta effect on the structure and intensity of numerically simulated hurricanes.