A Diagnosis of a Model-Simulated Explosively Developing Extratropical Cyclone

Abstract

This paper examines a simulation of the explosive development phase of the ERICA IOP 4 extratropical cyclone case obtained from the 70-km Limited Area Mesoscale Prediction System. A detailed diagnosis of the simulated cyclone is performed using the Zwack?Okossi equation to examine the forcing mechanisms influencing the near-surface synoptic-scale pressure tendency. The diagnosis includes two special features, the inclusion of forcing terms representing synoptic-subsynoptic exchange processes and a unique approach to evaluating the contribution of individual levels to the vertically integrated forcing. Explosive cyclogenesis was initiated by the combined effects of warm-air advection, cyclonic vorticity advection, and latent heat release, the first two maximizing above 400 mb and the latter below 750 mb. At the cyclone center the temperature advection profiles also featured a secondary warm-air advection maximum below 800 mb whose impact on surface pressure tendency was often equal to or greater than the upper-level maximum. The end of explosive development was signaled by a marked decrease in development rate that corresponded to a reversal in sign of the temperature advection contribution. Finally, subsynoptic processes contributed significantly through the synoptic-subsynoptic exchange of temperature.