The Statistical Properties of a Zonal Jet in a Baroclinic Atmosphere: A Semilinear Approach. Part I: Quasi-geostrophic, Two-Layer Model Atmosphere

Abstract

A semilinear (the wave-dynamics are linear with the time-evolution operator determined by the time-varying zonal flow while the zonal flow is fully nonlinear in the eddy fluxes) model of a baroclinic zonal jet is integrated, under macroscopic conditions realistic for the earth's atmosphere, for a time period of 20 years in a high resolution pseudospectral version and its asymptotic (in time) statistical properties are determined. The model is studied as a dynamical system, both by following sequences of bifurcations from the stable. Hadley circulation and by embedding in lower dimension spaces. The model turns out to be far from amenable to weakly nonlinear approximations common in atmospheric and oceanographic literature. The analysis of propagation of disturbances in the turbulent jet demonstrates the inadequacy of mean-field approximations usually adopted in studies of kinematics of Rossby waves, teleconnections, etc.