On the Relationship between the Stratospheric QBO and the Tropospheric SO.

Two oscillations in the tropical atmosphere with similar oscillation period - the stratospheric QBO and the Southern Oscillation (SO) — and the relationship between these two oscillations, are examined using the Principal Oscillation Pattern (POP) analysis technique. The POP analysis of the equatorial stratospheric data set provides a compact description of the QBO. The oscillation features identified by the POP analysis, namely the spatial structure, the characteristic times of the oscillation, and the asymmetry in downward propagation, are almost identical to those found by earlier studies using more conventional studies. The simultaneous POP analysis of the equatorial zonal surface wind and sea surface temperature indicates a well—defined cyclic behavior of the SO. In contrast to the very regular QBO, the SO appears to be much more noisy with intermittent quiet phases. A spectral analysis of the QBO time series and the Southern Oscillation Index reveals a negligible correlation between the two processes. A POP analysis of the combined equatorial data set of stratospheric wind, zonal surface wind and SST also indicates no relation between the QBO and the S0. Two independent modes are identified, one of them completely describing the QBO and the other representing the entire SO. No linear relationship is found between the two modes either in space or in time. It is concluded that the SO and the QBO are two independent processes with similar time scales, and that is misleading to refer to the quasi-biennial component of the SO by the expression "QBO"