PROPAGATION OF LOW-FREQUENCY ROSSBY WAVE WITH DIVERGENT WIND

The effect of divergent wind excited by external thermal forcing on propagation of lowfrequency Rossby wave is investigated in a barotropic atmosphere. The dispersion relation and group velocity expression of low-frequency Rossby wave with divergent wind are derived. Theoretical analysis shows that for α∈(0,π) whereαis phase difference between stream function and velocity potential, divergent wind may reduce frequency of Rossby wave and increase zonal group velocity. The modification to meridional group velocity made by divergent wind is much more complicated than that to zonal group velocity. Rossby wave ray analysis indicates that for the constant zonal basic flow, the path along which Rossby wave with divergent wind propagates from initial location to reflection latitude is regarded as a piece of smooth arc. For 30-day period, the zonal and meridional propagation distances of Rossby waves with k=3,4 will lengthen when divergent wind weaken. The calculation of Rossby wave amplitude reveals that for weakened divergent wind, the meridional range in which Rossby wave with k=3 is propagable is extended and the amplitude decreases.