An idealized nonlinear model of the Northern Hemisphere winter storm tracks: Formulation and applications

In this study, a nonlinear dry model, forced by fixed radiative forcing alone, has been constructed to simulate the Northern Hemisphere winter storm tracks. A procedure has been devised to iterate the radiative equilibrium temperature profile such that at the end of the iterations the model climate closely resembles the desired target climate.

This iterative approach is applied to simulate the climatological storm tracks in January. It is found that, when the three-dimensional temperature distribution in the model resembles the observed distribution, the model storm tracks are much too weak. It is hypothesized that this is due to the fact that eddy development is suppressed in a dry atmosphere, owing to the lack of latent heat release in the ascending warm air. To obtain storm tracks with realistic amplitudes, the static stability of the target climate is reduced to simulate the enhancement in baroclinic energy conversion due to latent heat release. With this modification, the storm tracks in the model simulation closely resemble those observed except that the strength of the Atlantic storm track is slightly weaker than observed. The model, when used as a forecast model, also gives high-quality forecasts of the evolution of observed eddies.

The model can be applied to examine the dynamics and variability of the Northern Hemisphere winter storm tracks. In this presentation, application of this model, along with simulations made using a stationary wave model, to understand the interactions between the Pacific and Atlantic storm tracks, will be highlighted. In another presentation (Chang and Zurita-Gotor), application of the model to simulate the seasonal cycle of the Northern Hemisphere storm tracks will be discussed.