Southern hemisphere medium‐scale waves and total ozone disturbances in a spectral general circulation model

The ozone distribution and its variability is simulated with a general circulation model (GCM), which includes self‐consistent representation of the physical processes and an accurate parameterization of the ozone photochemical sources and sinks. Emphasis is placed on analysis of the action of atmospheric waves on the O 3 distribution. In particular, the model generates the medium‐scale waves which are often observed in the southern hemisphere. These waves tend to form quasi‐regular O 3 patterns with zonal wave numbers 4, 5, and 6, in fairly good agreement with the observations. Baroclinic instability generates the waves in the lower troposphere, but it is their equivalent barotropic structure in the upper troposphere‐lower stratosphere which produces the signal on the total ozone column, since O 3 disturbances are nearly in phase in this altitude range. Episodes of large amplitude of the medium‐scale waves occur when the transient waves interact with a stationary wave. This standing wave has a zonal wave number close to 4 and appears to result from the large convective activity within the South Pacific Convergence Zone and its southward extension at mid‐latitudes. This study gives a good illustration of the important role played by GCMs in understanding the interactions between dynamical and physical processes in the troposphere and wave activity and O 3 distribution in the lower stratosphere.