Internal Frontogenesis: A Two-Dimensional Model in Isentropic, Semi-Geostrophic Coordinates

Abstract

A two-dimensional semi-geostrophic model in isentropic coordinates is applied to the study of internal frontogenesis induced by a geostrophic deformation field. A continuous potential vorticity distribution is considered and the upper and lower boundaries are chosen to be isentropic. In the initial conditions a jet structure is prescribed. Internal frontogenesis takes place under such conditions and is thus shown not to be a side effect of intensification of temperature gradients at the ground level. The model reproduces some of the observed features of the process, although the ageostrophic circulation is in a thermodynamically direct sense and a temperature discontinuity only forms in an infinite time.