Nonlinear dynamics of Rossby waves

Several different projects have been performed examining different aspects of the nonlinear evolution of Rossby waves in the stratosphere and troposphere.

Vertical structure of Rossby wave breaking
The vertical structure of Rossby waves on the edge of polar vortices has been examined using an idealised multi-layer model. Both the linear and nonlinear evolution has been examined, with particular emphasis on the dependence of the propagation and wave breaking on the initial vortex structure. The characteristics of both features are found to be sensitive to structure of the vortex, and there are vortices that are more robust than barotropic vortices. This variation of the wave breaking on the vertical structure of the vortex may be important for understanding the seasonal variation in the evolution of the observed polar vortices.

The figure below shows the vortex structure after 12 days for simulations using the same forcing but different initial vortices.

See Waugh and Dritschel (1998) for details.

Wave breaking within the stratospheric surf zone.
The dynamics of Rossby wave breaking in the stratospheric surf zone has been exmained using idealized single-layer numerical models (Polvani et al., 1995, Waugh 1993). See publications for references.

The fine-scale transport characteristics of this wave breaking has been examined using high-resolution trajectory calculations driven by observed winds, see mixing project and references therein.

Rossby wave breaking in upper troposphere.
The characteristics of the poleward advection of upper tropospheric air have been investigated using meteorological analyses and idealized numerical models. Large poleward excursions of upper tropospheric air are observed during Rossby wave breaking events. The evolution of the tropospheric air depends on the local, meridional shear: in anticyclonic, or weak cyclonic, shear the tropospheric air tilts forwards, broadens, and wraps up anticyclonically, whereas in cyclonic shear the tropospheric air tilts backwards, thins, and is advected cyclonically. The two types of behaviour are shown in the figures below. See Peters and Waugh (1998) for details.

In a separate study, Waugh, Polvani, and Plumb (1994) , wave propagation and breaking within the tropical troposphere was examined via high-resolution barotropic simulations.

Darryn Waugh