Is the residual vertical velocity a good proxy for stratosphere-troposphere exchange of ozone?

Stratosphere-troposphere exchange (STE) of ozone (O3 ) is key in the budget of tropospheric O3 , in turn affecting climate forcing and global air quality. We compare three commonly used diagnostics meant to quantify cross-tropopause O3 fluxes with a Chemistry-Transport Model driven by two distinct European Centre forecast fields. Our reference case calculates accurate, geographically resolved net transport across an isosurface in artificial tracer e90 representing the tropopause. Hemispheric fluxes derived from the ozone mass budget of the lowermost stratosphere yield similar results. Use of the Brewer-Dobson residual vertical velocity as a scaled proxy for ozone flux, however, fails to capture the interannual variability. Thus, the common notion that the strength of stratospheric overturning circulation is a good measure for global STE does not apply to O3 . Climatic variability in the modeled O3 flux needs to be diagnosed directly rather than indirectly through the overturning circulation.