Development of Banded Structure in a Numerically Simulated Hurricane

Abstract

The developments of the propagating and the stationary bands in a three-dimensional model of a hurricane (Isbell, 1964) are investigated. Propagating bands in the vertical motion fields in the middle and the upper troposphere form in the regions of strong heating in the upper troposphere and weak cooling in the middle troposphere. The structures of the wind, temperature and pressure fields in these bands are similar to those observed in the outer radar bands of hurricanes. Strong, nearly stationary bands form close to the center in the intense storm stage. Results of two experiments, one (M1) in which the so-called nonconvective release of latent heat in the upper troposphere is included and the other (M2) in which this heating is not incorporated, are compared. Convective release of latent heat is included in both experiments. The stationary bands in which form in M1, also develop in M2. The propagating bands which form in M1, however, do not develop in M2. The rate of intensification of the simulated storm in M1 is nearly the same as observed in Isbell; it is, however, significantly weaker in M2. It is shown that the inclusion of nonconvective release of latent heat in M1 enhances the upper tropospheric outflow which induces strong zones of convergence in the boundary layer. The resulting increase in the upward motion at the top of the boundary layer augments the convective release of latent heat and leads to a rapid intensification of the disturbance.