Winter Extratropical Cyclogenesis Over The Northern Gulf of Mexico
1996
Peters, Daniel A.
Winter extratropical cyclogenesis over the northern Gulf of Mexico is examined by assigning a synoptic classification to each winter cyclone which developed during the 41-season period 1950-51 to 1990-91. The classifications of 'frontal' and 'nonfrontal' cyclogenesis are used to differentiate between those cyclones which were analyzed to have formed along pre-existing, airmass-type frontal boundaries, and those which developed in the absence of such boundaries. Spatial distributions of cyclogenesis events indicate that the open water of the northwest Gulf tends to be a preferred region for cyclone initiation, for both the frontal and the nonfrontal cases. This is particularly evident during the coldest months, when sea surface temperatures exhibit a strong gradient along the continental shelf break. Case studies reveal that after a cold air outbreak, air which resides for an extended period of time over the continental shelf of the northwest Gulf becomes differentially modified by spatially varying fluxes of heat and moisture from the sea surface, resulting in the formation of an atmospheric baroclinic zone which lies well to the north of the polar front. A solenoidal circulation develops within the boundary layer, increasing convergence and cyclonic vorticity, and inducing a horizontal discontinuity in atmospheric stability. Thus, this region is a favored location for further cyclonic intensification, provided that the upper-level paftem is also favorable. Although a lack of surface data makes the processes which induce cyclogenesis in this region difficult to resolve, visible satellite imagery is suggested to be beneficial.
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