Mesoscale Frontogenesis: An Analysis of Two Cold Front Case Studies

A comparative analysis of mesoscale-Beta frontogenesis is presented for two case studies of cold fronts that originated west of the Appalachians and moved across North Carolina during the Genesis of Atlantic Lows Experiment (GALE). The evolution of the fronts is depicted with a detailed three- dimensional analysis. The two cold fronts are compared to the classic model of fronts established by the Norwegian school. Diagnostic computations of divergence, vorticity, dynamical forces and frontogenesis were performed. The individual contributions of shear, confluence, and diabatic terms were determined to assess their relative importance in frontogenetical forcing. The diabatic process of differential cloud shading and its thermal impact at the surface contributed significantly to the development of a zone of strong temperature gradient ahead of both wind shift lines. A more extensive cloud free area contributed to more widespread diabatic forcing in case 1 as compared to case 2. Meteograms, satellite imagery and diagnostic computations of divergence, vorticity and frontogenesis confirm that only the extreme eastern portion of both wind shift lines over the coastal plain and adjacent waters of North Carolina remained active and well-defined. The confluence term dominated frontogenetical forcing over this region. It is hypothesized that the pre- existing baroclinic zone over the cold Atlantic shelf waters had a pronounced influence on the regeneration of the frontal boundaries along extreme eastern North Carolina. Results of other relevant studies confirm this possibility. The dynamical force balance and parcel trajectories were computed at selected times.