Stratospheric ozone depletion during the 1995-1996 Arctic winter: 3-D simulations on the potential role of different PSC types

The sensitivity of modelled ozone depletion in the winter Arctic stratosphe re to different assumptions of prevalent PSC types and PSC formation mechan isms is investigated. Three-dimensional simulations of the winter 1995/96 a re performed with the COlogne Model of the Middle Atmosphere (COMMA) by app lying different PSC microphysical schemes. Model runs are carried out consi dering either liquid or solid PSC particles or a combined microphysical sch eme. These simulations are then compared to a model run which only takes in to account binary sulfate aerosols, The results obtained with the three-dim ensional model agree with trajectory-box simulations performed in previous studies. The simulations suggest that conditions appropriate for type la PS C existence (T < T-NAT) occur over longer periods and cover larger areas wh en compared to conditions of potential type lb PSC existence. Significant d ifferences in chlorine activation and ozone depletion occur between the sim ulations including only either liquid or solid PSC particles. The largest d ifferences, occurring over large spatial scales and during prolonged time p eriods, are modelled first, when the stratospheric temperatures stay below T-NAT, but above the threshold of effective liquid particle growth and seco nd, in the case of the stratospheric temperatures remaining below this thre shold, but not falling below the ice frost point. It can be generally concl uded from the present study that differences in PSC microphysical schemes c an cause significant fluctuations in ozone depletion modelled for the winte r Arctic stratosphere.