Influence of Normal Mode Rossby Waves on the Mean Field: Interference with Quasi-Stationary Waves

Abstract

The influence of normal mode Rossby waves on the mean field is investigated with the aid of TIROS-N/NOAA satellite observations by applying the Eliassen-Palm (E-P) flux diagnostics. Despite the fact that the normal mode Rossby wave is essentially a free wave without E-P fluxes, it is found that the constructive and destructive interference between the traveling free Rossby wave and the quasi-stationary forced wave induces the periodic change of the EP-flux and its divergence, which in turn gives rise to vacillations in the basic flow. Three typical cases of the interference in the stratosphere are presented for the periods of the equinoctial season when the 5-day, 10-day and 16-day waves globally appear, and it is shown that observed vacillations of the zonal mean wind are well elucidated by the quasi-periodic change of the E-P flux divergence due to the interference.