Ozone depletion at temperature warmer than TNAT in the Arctic

The unprecedented ozone destruction in the Arctic vortex in 2011 that extended until the end of March offers a unique opportunity for testing the relationship between temperature, responsible for heterogeneous chlorine activation on PSCs and aerosols and the amplitude of ozone loss. Indeed, as shown by the total ozone evolution in the vortex during that winter from the SAOZ network compared to passive ozone simulations from the REPROBUS CTM, most of the total 39% total ozone depletion occurred after mid-February at a rate of near 0.8% /day when relatively low temperatures were still present in the Arctic. The evolution of ozone depletion is shown to fully match that of the cumulative area of temperatures below the chlorine activation threshold weighted by vortex sunlight illumination, assuming, as shown by Drlda and Mueller (2010), that chlorine activation occurs at 195 K at the 475 K level. However, if instead, the total integrated backscatter for combined liquid aerosols/PSCs inside the vortex reported by CALIPSO or the cumulated PSC surface at 191 K aligned to STS threshold are used, PSCs are seen to disappear in early March, that is three weeks before the end of ozone depletion. The suggestion is thus that chlorine activation takes place at temperature significantly warmer than that of NAT or STS PSC formation, on binary aerosol, still present and accounted for in the integrated backscatter, but of smaller surface area. The same analyses applied to all past winters since 1994 confirms the ozone depletion at relatively warm temperature in the absence of PSC. The mechanism involved is explored by a variety of model simulations, including or not, liquid binary aerosols, NAT and STS.