Prediction of Nine Explosive Cyclones over the Western Atlantic Ocean with a Regional Model

Abstract

A series of 14 numerical experiments were conducted using the Pennsylvania State University/National Center for Atmospheric Research mesoscale model on nine cases of explosive marine cyclogenesis. The main objective was to identify key factors that are important to short-range prediction of explosive cyclones. We found that the intensity and structure of the simulated cyclones were sensitive to the details of precipitation parameterization. The grid-resolvable-scale precipitation associated with the mesoscale slantwise ascent in the vicinity of the warm front was crucial for rapid development. The upright convective precipitation played a relatively unimportant role. Surface energy fluxes had little effect on the development during the 24-h period of rapid cyclogenesis. The pattern of upward and downward fluxes while the storms were in progress was not favorable for storm intensification. Small case-to-case variation was found among the nine-case ensemble in the resulting deepening due to changes in physical parameterizations or in horizontal and vertical resolutions; however, a substantial variation existed in the fundamental characteristics of these storms. Some storms were more dynamically driven, while others were more diabatically forced. Some cyclones were more sensitive to uncertainties in the initial conditions, and were therefore less predictable, than others. Averaged over the nine cases, the model components crucial for short-range (0?24 h) prediction of rapid deepening?in order of decreasing importance?were: 1) initial conditions, 2) horizontal grid resolution, 3) precipitation parameterization, and 4) lateral boundary conditions. The parameterization of the surface energy fluxes and the vertical resolution generally had lesser impacts.