Numerical simulation of asymmetric hurricanes on a ?-plane with vertical shear
Madala, Rangarao V.
Piacsek, Steve A.
- Publisher: Co-Action Publishing
(issn: 1600-0870, eissn: 0280-6495)
A three-layer, semi-implicit model was developed to simulate moving and asymmetric hurricanes on a ?-plane, using Kuo's method of cumulus parametrization. Sensible and latent heat transfer from ocean to atmosphere was included implicitly in the model. In order to predict hurricane movement over a large area and yet resolve finer details near the eye, a multi-grid network was used with a movable finest grid of 20 km mesh size, surrounded by two coarse grid nets with mesh spacings of 60 km and 180 km, respectively. A comparison of the results with f-plane calculations shows that the vortex on the ?-plane intensified at a slower rate before the storm stage, but at the same rate thereafter. The ?-plane hurricane was asymmetric throughout its life cycle, and these asymmetrics looked similar to those observed in real hurricanes. The vortex moved on the ?-plane with a phase velocity of 4.3 km hour?1 for the westerly and 3.3 km hour?1 for the northerly components. The model was also integrated for two cases where the initial vortex was superimposed on a vertically varying basic current. Results showed that the strength of the simulated hurricane depends very much upon the magnitude of the vertical shear of the basic current; for a large shear (? 15 m sec?1/12 km) the vortex failed to intensify into a hurricane. Computations showed that the pressure weighted mean of the basic current between the surface and 12 km level agreed very well with the magnitude of the steering current. As a result of the interaction between the hurricane circulation and the basic current, the hurricane moved in an oscillatory path with an amplitude of 30 km and a period of about 20 hours.DOI: 10.1111/j.2153-3490.1975.tb01699.x