The influence of large-scale eddy flux variability on the zonal mean ozone distribution

The influence of the variability of large-scale eddy heat and momentum fluxes on interannual and decadal changes in the zonal mean ozone distribution is investigated based on a two-dimensional circulation model with interactively coupled transport and chemistry. The large-scale eddy fluxes are prescribed according to observations, that is, in terms of monthly mean eddy mixing coefficients that are derived from ECMWF reanalysis 1979 - 93 (ERA-15). The results show that the eddy-forced changes in the lower-stratospheric residual circulation and eddy mixing processes induce coherent changes in temperature, ozone, and other chemical tracers. Significant ozone declines are found mainly in the lower stratosphere during winter, with maximum values of about -1.2 Dobson units (DU) per kilometer per decade at midlatitudes and more than -2 DU km(-1) decade(-1) at polar latitudes. The seasonal and vertical structure of the observed Northern Hemispheric ozone trend is captured in a remarkable way. It is also shown that, at midlatitudes, maximum declines in the zonal mean lower-stratospheric ozone are mainly related to the eddy mixing processes, and, at polar latitudes, to the induced changes in the lower-stratospheric temperatures.