Quantitative evaluation of the "self-development" processes in extratropical cyclogenesis.

Abstract

The objective of this study is to assess quantitatively the process of "self-development" (Sutcliffe and Forsdyke, 1950) in extratropical cyclogenesis. The basic approach is to determine within the framework of the quasi-geostrophic equations the contributions of thermal advection and latent heat release to changes occurring in the intensification rate of a surface cyclone which result from modifying the field of vorticity advection. The relevant concepts and equations are applied to a major cyclone over the central United States and to a structurally simple analytic model of a cyclonic disturbance for which varying horizontal and vertical distributions of latent heat release are prescribed. Results of computations utilizing the analytic model indicate that the effect of latent heat release in self-development can be comparable with that of thermal advection. The separate and, more so, the collective influence of these mechanisms upon acceleration of the deepening rate are considered synoptically significant; however, the influence of translation of the vorticity maximum aloft with respect to the surface system appears to dominate changes in the rate of development. The quantitative reliability of the results obtained for the real data case are in doubt because of apparent difficulties in the objective scheme (HOBAN) employed in analysis of input data.