Abstract
Some properties of planetary Rossby waves and zonal flow acceleration by them on a β-plane are investigated analytically by using the two-scale method. The zonal flow (u) is assumed to be westerly channel flow and is allowed to have both lateral and (small) vertical shear. We also assume u=0 at two zonal walls.
It is shown that the lateral structure of planetary waves has the following properties: The lateral scale of planetary waves is larger than that of the mean zonal flow. When the zonal flow is weak, the maximum of the wave amplitude appears at a latitude different from that of the maximum zonal wind and, as the zonal wind speed increases, the lateral profile of the wave amplitude becomes close to that of the mean flow. In general, the phase lags in latitudes where the zonal flow is fast in a positive vertical shear flow and it leads there in a dissipative medium. In an asymmetric (with respect to the center of the flow channel) flow, the phase maximum of dissipative waves shifts toward the jet side for a weak zonal flow and toward the opposite side of the jet for a strong mean flow. It is also found that, the stronger is the mean zonal flow, the smaller is the phase inclination with latitude.
The zonal flow acceleration by dissipative waves in a symmetric jet flow has the following nature: When the zonal flow is intense and the jet is sharp, the easterly acceleration is largest near the jet latitude. Except in such cases, the easterly acceleration is largest near boundaries. In an asymmetric jet flow, the jet shifts toward a lateral boundary for a weak zonal flow and toward the center for a strong zonal flow.
Thus, planetary waves and the associated zonal flow acceleration show the distinct differences in their properties depending on the magnitude of the zonal wind speed. Moreover, the inclination of the latitudinal phase of planetary waves and the lateral profile of the zonal flow acceleration are sensitive to the ratio of the radiative damping rate to the mechanical one.
