Dual baroclinic jets and the organization of midlatitude storm tracks

A striking feature of the large-scale midlatitude wintertime flow is the existence of time-mean zonal velocity maxima - termed jets - over the eastern edges of the Asian and North American continents. These two jets are located upstream of regions characterized by enhanced transient eddy activity; these regions are termed storm tracks. Most previous theoretical modeling studies of midlatitude storm tracks have considered background flows that consist of a single jet.

Here we consider a zonally asymmetric basic state consisting of dual, zonally aligned baroclinic jets, and examine how the structure, strength, and spacing of these jets affect the organization of midlatitude storm tracks. In particular, we examine the linear and nonlinear time-mean energetics and spatial structure of storm tracks that develop on a basic state consisting of two zonally aligned jets using a two-layer quasigeostrophic model of the wintertime Northern Hemispheric flow. Emphasis is placed on examining separately and in combination the effects of jet separation and zonal variations in local stability on the storm tracks. We show that these background flow features play a significant role in the morphology and intensity of the storm tracks.

The storm track responses are also modulated by the strength of the basic flow between the jets. By changing the spatial patterns of the time-mean physical processes that contribute to the growth and decay of the eddies, the strength and location of the storm tracks are altered in ways that differ from predictions based on studies involving isolated baroclinic regions.