Two types of wave breaking in an aquaplanet GCM

The characteristics of two distinct types of wave breaking in an aquaplanet general circulation model (GCM) are described. A systematic analysis of wave breaking is possible because when a baroclinic wave packet is present, the wave breaking tends to occur in the vicinity of the packet center. Although the refractive index is strictly valid only for linear, quasigeostrophic flows, in this GCM the refractive index is shown to be useful for categorizing two types of wave breaking. Empirical orthogonal function (EOF) analysis is performed using the refractive index obtained (by averaging over one carrier wavelength) at the center of the wave packet. Composite Eliassen-Palm fluxes and upper-level potential vorticity, corresponding to either phase of the first EOF of the refractive index, are consistent with the two types of wave breaking. It is found that the strength of the meridional shear in the upper troposphere is related to the type of wave breaking. Implications of these results for storm track variability in the atmosphere are also discussed.