A Comparison of Wave-Induced Residual and Lagrangian Transport in the Stratosphere

The global mass circulation in the stratosphere is caused in part by the downward control principle. Extratropical stratospheric wave drag, produced by the breaking and dissipation of planetary waves, acts as a pump, drawing tracers from the equator to the pole and resulting in the observed Brewer-Dobson circulation.

At present, the theoretical understanding of this process has limitations. Although it can be shown, under certain assumptions, that the Lagrangian velocities and the transformed Eulerian mean velocities are the same and are a direct result of the wave drag, it is not clear that this relationship holds in general. In particular, the theory assumes linear, small-amplitude waves while the atmosphere is clearly a nonlinear system with breaking planetary waves in the surf zone. Thus, while the existence of the wave-induced circulation is not under debate, its quantitative determination remains problematic.

The purpose of this work is to include the effects of nonlinear, breaking waves by using a 3d primitive equations model to study the effect of the wave forcing on the traditional diagnostic quantities (the Eliassen-Palm flux divergence and the residual circulation) and to use offline particle advection to quantify the resulting Lagrangian transport. It will be shown that while the theory holds for small-amplitude and weakly nonlinear regimes, it does not do so well in the nonlinear regime. In particular, the correspondence between the residual circulation and the Lagrangian transport becomes poor in regions where the flow is permitted to develop smaller scales through wave breaking.