Explosive East Coast Cyclogenesis: Numerical Experimentation and Model-Based Diagnostics

Abstract

Numerical experimentation of explosive East Coast cyclogenesis is performed using the Florida State University Global Spectral Model (FSUGSM). The three cases examined here are the Presidents'Day storm of 18?19 February 1979 and the North Atlantic and Pacific bombs of 18?20 January 1979 which formed off the east coasts of the United States and Japan respectively. The use of a global model provides a framework for studying the phenomena on the 3?5 day time scale. The forecast verifications of the numerical experiments indicate that the FSUGSM was able to adequately predict the phase, intensity, and synoptic-scale structure of three aforementioned cases. These results justify the use of model data for diagnostic studies of the bomb. The model data are used to quantify the role of the adiabatic and diabatic forcing in the explosive cyclogenetic process using surface pressure tendency (SPT) to gauge development. The results of the partioning technique substantiate the fact that the bomb is fundamentally a baroclinic phenomenon in which the dynamical forcing initiates and sustains explosive development. Convective and noncenvective latent heat release were the primary physical mechanisms responsible for generating at most, roughly 40% during the later phase of case 1. The remaining physical processes that are parameterized in the FSUGSM, including the, surface fluxes of heat, moisture, and momentum, do not directly or instantaneously impact bomb development as they force less than 10% of the negative SPT.