A Three-Dimensional Study of Frontogenesis Using a Model Formulated in Stream-Axis Coordinates

Abstract

A jet-based model is proposed to study the dynamics of frontal zone-jet stream systems. The model is developed in non-orthogonal stream-axis coordinates with a condition of gradient flow in the direction of the jet (no assumption is made on the flow in the cross-jet direction). Approximating functions are used to represent the spatial dependence of the variables, and the forecast is advanced using a Galerkin technique with an Euler-backward time extrapolation scheme. Three-dimensional forecast experiments are performed using a baroclinic zonal jet with a superimposed perturbation of the type studied numerically by Mudrick (1974). The model forecast develops surface and mid-tropospheric frontal zones which compare well with the results obtained by Madrick. The forecast frontogenesis mechanisms and circulation patterns are determined, and effects due to the trajectory curvature calculation and the resolution of the approximating functions are considered.