The Synoptic Verisimilitude of a Mid-Latitude Cyclone Generated in a Southern Hemisphere General Circulation Model

Abstract

A detailed examination has been made of the synoptic and physical behavior of an initially diffluent, large-amplitude but representative trough that formed in a Southern Hemisphere general circulation model after approximately 60 model days. The model is essentially the stereographic GFDL model of Manabe et al. (1965) with 9 levels and 30 points between equator and pole. The trough developed in a manner characteristic of the real atmosphere in that a jet maximum moved round to the apex of the trough, then to the leading edge. However, a baroclinic zone persisting in the rear of the trough prevented collapse of the cold air and the release of eddy kinetic energy. Vertical velocity fields were partitioned into components associated with differential vorticity advection and the Laplacian of thermal advection, and comparisons made with Krishnamurti's (1968) results. It is suggested that model developments are too strongly controlled by the vorticity and thermal terms. The model polar-front jet was located at a level close to the subtropical jet and was overshadowed by it. Trajectory analyses showed that despite this discrepancy, little interaction occurred between the two major jet streams.