Physical and Mathematical Properties of a Quasi-Geostrophic Model of Intermediate Complexity of the Mid-Latitudes Atmospheric Circulation

TL;DR

This paper investigates a quasi-geostrophic model of mid-latitude atmospheric circulation, analyzing how changes in temperature gradient influence the system's transition from stationary to chaotic regimes and examining the sensitivity of physical and dynamical properties.

Contribution

It introduces a detailed analysis of a quasi-geostrophic model, highlighting the impact of temperature forcing on regime transitions and the sensitivity of attractor and physical observables to model resolution.

Findings

Transition from stationary to chaotic regimes with increasing TE

Attractor properties are sensitive to model resolution

Physical observables are less sensitive to resolution, but detailed structures depend on it

Abstract

A quasi-geostrophic intermediate complexity model is considered, providing a schematic representation of the baroclinic conversion processes which characterize the physics of the mid-latitudes atmospheric circulation. The model is relaxed towards a given latitudinal temperature profile, which acts as baroclinic forcing, controlled by a parameter TE determining the forced equator-to-pole temperature gradient. As TE increases, a transition takes place from a stationary regime to a periodic regime, and eventually to an earth-like chaotic regime where evolution takes place on a strange attractor. The dependence of the attractor dimension, metric entropy, and bounding box volume in phase space is studied by varying both TE and model resolution. The statistical properties of observables having physical relevance, namely the total energy of the system and the latitudinally averaged zonal wind, are also examined. It is emphasized that while the attractor's properties are quite sensitive to model resolution, the global physical observables depend less critically on it. For more detailed physical observables, such as the latitudinal profiles of the zonal wind, model resolution again may be critical: the effectiveness of the zonal wind convergence, acting as barotropic stabilization of the baroclinic waves, heavily relies on the details of the latitudinal structure of the fields. The necessity and complementarity of both the dynamical systems and physical approach is underlined.