New England coastal frontogenesis

Abstract New England coastal frontogenesis is investigated on the basis of individual and climatological case studies. The results suggest that differential friction plays the role of the synoptic scale geostrophic deformation in packing the isotherms together for this mesoscale boundary‐layer frontal phenomenon. An initial temperature gradient must be present for the differential friction mechanism to be effective. Geostrophic deformation is incapable of initiating coastal frontogenesis while the maximum area of observed deformation coincides with the location of the developing front. Coastal frontogenesis is associated with a pronounced sea level cold anticyclone to the north and east of New England in all cases studied. Differential friction between the northerly inland flow and the more easterly onshore flow then sets up favourable shoreline deformation and convergence fields leading to frontogenesis in the presence of differential thermal stratification. The time scale for an order‐of‐magnitude increase in the horizontal temperature gradient appears to be one‐half to one day depending upon the contribution of differential diabatic heating. The orientation of the New England shoreline is such as to favour frontogenesis across extreme eastern Massachusetts and Rhode Island. An axis of relatively high precipitation is noted just to the west of this favoured locale on the climatological charts, consistent with a thermally direct circulation about the front.