Planetary Wave Diagnostics on the QBO Effects on the Deceleration of the Polar-night Jet in the Southern Hemisphere.

Abstract

A composite analysis with respect to the phases of the equatorial quasi-biennial oscillation (QBO) is made for the zonal-mean zonal flow and the Eliassen-Palm (EP) flux during late winter to spring in the Southern Hemisphere. It is shown that deceleration in the lower stratosphere in September to October is more rapid in the easterly phase of the QBO than in the westerly phase, which makes the stratospheric zonal wind in November weaker. Such deceleration is consistent with the larger convergence of the EP flux observed in the easterly phase, which is associated with the stronger upward flux from the troposphere. It is also found that the equatorward flux in the upper troposphere is stronger in the westerly phase. These results for the EP flux diagnostics are discussed in terms of angular momentum budget of the atmosphere within a supposed zonally symmetric “body-of-rotation”. The composite difference of the upward flux is dominated by zonal wavenumber 1-3 component, whereas wavenumber 4-6 is predominant for the equatorward flux. Accordingly, it is suggested to be inappropriate to explain the difference of these fluxes between the QBO phases by considering the alternative directions of propagation of particular wave components due to change in refractive index. It seems that activities of wave disturbances in both scales are modified respectively by the QBO.