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Abstract:
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".
