A primitive equation (PE) model is used to study the structure and maintenance of westerly jets in the atmosphere. The PE model experiment is controlled by introducing two key parameters into an idealized radiative equilibrium temperature profile: one is tropical heating which modulates the intensity of the Hadley cell and subtropical jet, and the other is high-latitude cooling which is designed to modulate the meridional width of the baroclinic zone.

In a statistically steady state, an eddy-driven jet, distinctively separated from the subtropical jet, emerges as (1) the tropical heating decreases, which weakens the subtropical jet, or (2) the high latitude cooling increases causing the baroclinic zone to broaden. If the above two parameter values do not satisfy these conditions, then the statistically steady state is characterized by just a single jet. The above results are further accentuated when moist processes are included in the model. While equatorial moist heating strengthens the subtropical jet, midlatitude moist heating shifts the barocliniczone poleward, isolating the eddy-driven jet from the subtropical jet.

The characteristics of the simulated jets, as well as the corresponding regimes for the two parameters, are compared with the observed conditions for all seasons and for both the Northern and Southern hemispheres. We conclude that the the model results are broadly consistent with the observations. Hence the results provide useful insight into the observed general circulation.