Principal components of stratospheric circulation and trace constituents from UKMO analyses and HALOE observations

The variability of zonally averaged stratospheric circulation is examined using daily gridded analyses from the U.K. Meteorological Office (UKMO) for 1991-1998, corresponding to the period observed by the Upper Atmosphere Research Satellite (UARS). Application of rotated principal component analysis to the dataset reveals dominant modes of variability consisting of annual, semiannual, and quasi-biennial oscillations, together with intraseasonal variability in the winter hemisphere. New results of this study include the observation of poleward propagating zonal wind anomalies at the northern winter stratopause, a sudden deceleration of the subtropical mesospheric jet in northern midwinter each year, and the identification of two types of wintertime evolution in the polar upper stratosphere. One is characterized in high latitudes by relatively strong flow in early winter and weakened flow after solstice, the other by relatively weak flow in early winter and strengthening flow after solstice.

The climatology and interannual variability of trace constituents in the stratosphere is examined using methane, water vapor, and ozone data from the Halogen Occultation Experiment (HALOE) aboard the Upper Atmosphere Research Satellite (UARS) in 1992-1997. Application of rotated principal component analysis to the dataset reveals dominant modes of variability consisting of annual, semiannual, and quasi-biennial oscillations (QBO), together with `subbiennial' variations evidently due to nonlinear interaction between the annual cycle and QBO. The structure of quasi-biennial variability is approximately symmetric about the equator, while subbiennial variability is approximately antisymmetric and confined mostly to the subtropics.

The leading modes of climatological water vapor reveal asymmetric Brewer-Dobson upwelling in the upper stratosphere and the atmospheric `tape recorder' effect in the tropical lower stratosphere; these effects appear in combination, in the same mode. Some latitudinal propagation of the tape recorder signal is observed in addition to the well-known vertical propagation.

The vertical structure and downward propagation of the ozone QBO at the equator is described by a pair of symmetric EOFs having separate amplitude maxima in the lower and upper stratosphere. A second pair of modes explains the seasonal dependence of subtropical ozone anomalies. For each tracer, the subtropical anomaly is considerably larger in the northern hemisphere. More years of data will be required in order to determine whether this asymmetry is a permanent feature, or the result of sampling during the UARS observing period in which only certain combinations of annual cycle and QBO have been realized.