A numerical investigation of the February 1993 snowstorm

Despite considerable research in the study of explosively deepening oceanic storms, much less attention has been paid to coastal secondary cyclogenesis that is characterized by weak baroclinicity but heavy precipitation. In this thesis, the development of one such storm, the February 1993 cyclone, is investigated using a high-resolution version of the Canadian Regional Finite-element (RFE) model in which more realistic physical representations are incorporated. It is shown that the improved RFE model reproduces extremely well the timing and location of coastal secondary cyclogenesis along the Carolina coast, the evolution of the associated surface pressure perturbations and tropospheric baroclinic waves. The model also performs remarkably well in predicting the distribution and intensity of the storm's precipitation over the New England states, Quebec and the maritime provinces.It is found that the coastal secondary cyclogenesis occurs in response to the low-level inshore advection of warm and moist air from the maritime boundary layer and the approach of the midtropospheric short-wave trough associated with a decaying cyclone to the west. Rapid deepening of the cyclone ensues as intense precipitation falls along the warm and cold frontal zones.Diagnosis of a series of sensitivity simulations reveals that large-scale dry dynamics, latent heat release, air-sea interaction and surface characteristics act in concert to determine the cyclone's intensification and evolution. It is found that the low-level thermal advection contributes more to the cyclogenesis during the incipient stage, whereas the upper-level trough control the cyclone's rapid deepening at later stages. Overall, latent heat release accounts for about 50% of the total deepening. It is also found that ice microphysics (i.e., melting of snow) could indeed induce a thermally indirect circulation superposed onto the mean flow in the vicinity of the rain-snow boundary, but it has a weak negative impact on the cyclogenesis