Frontogenesis processes in the middle and upper troposphere

Abstract

The methodology for investigation is based on analysis of simulated upper-level frontogenesis with a three-dimensional primitive-equation model. The model is a simplified version of the UCLA GCM, with 21 layers in the vertical, horizontal resolution of 1.2° lat × 1.5° long; a 60° sector of one hemisphere as periodic domain; and physics reduced to horizontal diffusion and dry convective adjustment. In the simulations, tilting associated with divergence of the across-jet ageostrophic flow is the dominant frontogenetical process upstream of the wave trough. Further, tilting associated with divergence of the ageostrophic wind along the jet also contributes to frontogenesis, but to a lesser extent. The former result is similar to that obtained with two-dimensional models in which frontogenetical vertical motions are associated with divergence of the ageostrophic wind across the front. -from Authors