a Case Study Analysis of Intense Oceanic Cyclones.

Three intense oceanic cyclones along the east coast of North America were examined in this paper. For each case explosive cyclogenesis was initiated on a strong lower tropospheric baroclinic zone when a middle/upper tropospheric short wave trough, with its accompanying quasi -geostrophic ascent, approached the incipient cyclone. This mid/upper level feature was accompanied by a cyclonic potential vorticity anomaly in the lower and middle troposphere. The advection of this high potential vorticity air along isentropic surfaces from the stratosphere into the troposphere helped to enhance the differential cyclonic vorticity advection associated with the migratory trough. An upper-level front of varying degrees of intensity was located upstream of each cyclone. Evidence from one of the cases suggests that the upper-level front played an active role in the subsequent explosive cyclogenesis through the advection of high vorticity air within the front towards the developing cyclone. Each cyclone in its incipient stage developed in a reduced static stability environment, as measured by the surface-based lifted index. For two of the cyclones strong oceanic fluxes of heat and moisture were responsible for this destabilization. Latent heat release was significant for the two cases it was computed for. This latent heating may well have aided the explosive cyclogenesis process by enhancing the vertical velocity, thermal, and vorticity fields associated with the cyclones. For one case there was a tenfold increase in isentropic potential vorticity along trajectories near the center of the intense oceanic cyclone. It appears that diabatic effects, probably due to latent heating, were responsible for the non-conservation of potential vorticity. It appears that the cyclones analyzed here are the result of intense baroclinic wave development aided by diabatic processes.