The role of stationary eddies in shaping storm track dynamics

Transient eddies in storm tracks dominate the extratropical transport of heat, momentum, and water vapor. Yet it is unclear what controls properties such as the kinetic energy of storm track eddies, or the spatial distribution of this eddy kinetic energy. Here we show that stationary eddies play a fundamental role in shaping transient storm track dynamics, using an idealized general circulation model (GCM) with a simple representation of moisture. A local zonally asymmetric surface heat flux in the extratropics initiates storm tracks and stationary waves in the GCM. We show that on the one hand, stationary eddies lead to upgradient heat fluxes near the storm track entrance regions and thus contribute to the maintenance of the baroclinicity there, which transient eddies tend to erode. On the other hand, stationary eddies destroy baroclinicity in the storm track exit regions and thus lead to the downstream self-destruction of storm tracks; the eddy kinetic energy downstream is reduced to values lower than they would be without the zonal asymmetries that cause localized storm tracks. Water vapor fluxes by stationary eddies play a key role in both cases. Our results demonstrate an important nonlinear baroclinic coupling of stationary and transient eddy dynamics, necessitating a revision of current theoretical approaches to storm track dynamics.