Lower stratosphere waves during 1986—89 Southern Springs

This paper describes the horizontal structure of ozone and 50 mb height waves for the 1986-1989 springs of the Southern Hemisphere using global NMC height analyses and Nimbus 7 TOMS Grid-T Version 6 data. Empirical Orthogonal Functions (EOFs) are obtained for the ozone and height data independently to identify the meridional structure of observed long waves as well as their propagation characteristics. It is found that the leading EOFs for both the ozone and 50 mb height waves exhibit wavenumber 1 and 2 patterns. The wave 1 pattern is usually centred at 60-65°S and it either propagates eastward with a period of 30 days or longer (1986, 1987, 1989) or it is quasi-stationary (1988). This wave is weak during 1987, a year with low ozone values which persisted into summer. The wave 2 pattern travels eastward with a period of 10-12 days. It is best defined while the polar vortex is strong and its amplitude in the ozone field is observed to decay sharply after onset of the summer regime. The correlation coefficients between ozone and 50 mb height principal components are high. These indicate high/low ozone values associated with high/low values of 50 mb heights. This distribution is consistent with the advection of ozone by planetary waves south of the ozone maximum, as shown by a simple linear wave model. This model consists of an equivalent barotropic wave between 5 and 150 mb. The observed total ozone amplitudes for waves 1 and 2 for most years are consistent with the total ozone predictions by the wave model. In contrast, during 1989, a year with a well defined vertically propagating wave 1, the linear model overpredicts the observed ozone wave amplitude by a factor of 2.