Propagation of Rossby Waves of Nonzero Frequency

The propagation of Rossby waves of positive and negative frequency, corresponding to eastward and westward phase speeds, respectively, is investigated. The techniques used are theoretical analysis, ray tracing, and initial value problems in barotropic and baroclinic numerical models. The basic states considered are a superrotation flow and December–February climatological zonally symmetric and zonally asymmetric flows. It is found that positive and negative frequency Rossby waves can differ significantly from each other and from stationary, zero frequency Rossby waves in many aspects. Negative frequency waves tend to have larger total wavelengths and increased meridional group velocities. Enhanced meridional propagation and, indeed, cross-equatorial propagation are found for westward moving sources in both barotropic and baroclinic models. However, general deductions from studies of stationary Rossby waves, such as the existence of subtropical jet waveguides, are still found to be valid.