Interhemispheric transit-time distributions and path-dependent lifetimes constrained by measurements of SF6, CFCs, and CFC replacements

Abstract:

We constrain tropospheric transport from Northern-Hemisphere midlatitudes to the Southern-Hemisphere (SH) surface using measurements of SF₆, CFCs, and CFC replacement gases and a novel maximum-entropy-based inversion approach. We provide the first estimate of the width Δ of the tropospheric interhemispheric transit-time distribution (TTD). We find that Δ has a value of ~1.3 years that varies little with SH latitude, compared to the mean transit time Γ that increases from ~1.1 years in the SH tropics to ~1.4 years at the South Pole. The TTD shape parameter Δ/Γ is thus larger in the SH tropics than at mid and high SH latitudes. Our analysis introduces a simple path-dependent lifetime that parameterizes chemical losses. The path-dependent lifetimes are estimated for CFC replacements and systematic differences between path-dependent and global lifetimes are interpreted. The path-dependent lifetimes have the potential to provide new observational constraints on tropospheric and stratospheric loss processes.