Abstract
Abstract. The submodel PSC of the ECHAM5/MESSy Atmospheric Chemistry model (EMAC) has been developed to simulate the main types of polar stratospheric clouds (PSC). The parameterisation of the supercooled ternary solutions (STS, type 1b PSC) in the submodel is based on Carslaw et al. (1995b), the thermodynamic approach to simulate ice particles (type 2 PSC) on Marti and Mauersberger (1993). For the formation of nitric acid trihydrate (NAT) particles (type 1a PSC) two different parameterisations exist. The first is based on an instantaneous thermodynamic approach from Hanson and Mauersberger (1988), the second is new implemented and considers the growth of the NAT particles with the aid of a surface growth factor based on Carslaw et al. (2002). It is possible to choose one of this NAT parameterisation in the submodel. This publication explains the background of the submodel PSC and the use of the submodel with the goal of simulating realistic PSC in EMAC.
Highlights
Polar stratospheric clouds are necessary for ozone depletion in polar spring
(R4) (R5) (R6) (R7) (R8) (R9) (R10) (R11). The products of these reactions: molecular chlorine (Cl2), molecular bromine (Br2), hypochlorous acid (HOCl), hypobromous acid (HOBr), nitryl chloride (ClNO2) and bromine chloride (BrCl) are in gas phase (g); HNO3 and H2O are in liquid (l) or solid phase (s)
Besides the submodel PSC for the simulation of polar stratospheric clouds and MECCA1 for the gas-phase chemistry we have used for our performed ECHAM5/MESSy Atmospheric Chemistry model (EMAC) simulation the following submodels: OFFLEM for offline emissions of trace gases and aerosols (Kerkweg et al, 2006b), TNUDGE for tracer nudging (Kerkweg et al, 2006b), DRYDEP for dry deposition of trace gases and aerosols (Kerkweg et al, 2006a), SEDI for the sedimentation of aerosol particles (Kerkweg et al, 2006a), JVAL for the calculation of photolysis rates (Landgraf and Crutzen, 1998), SCAV for the scavenging and liquid phase chemistry in cloud and precipitation (Tost et al, 2006a), CONVECT for the parameterization of convection (Tost et al, 2006b), LNOX for the source of NOx produced by lightning (Tost et al, 2007b), PTRAC
Summary
Polar stratospheric clouds are necessary for ozone depletion in polar spring. The activation of inorganic chlorine and bromine substances takes place on their surfaces during the polar winter leading to ozone depletion in polar spring and the denitrification of nitrogen substances and the dehydration of water vapour (H2O) is caused through the sedimentation of NAT and ice particles. Theoretical work suggests that the second formation mechanism, the heterogeneous nucleation of ice out of SSA or STS with mineral oxide or soot as nuclei, may occur at temperatures warmer than those required for homogeneous nucleation (DeMott et al, 1997; Jensen and Toon, 1997). This mechanism is perhaps possible for the upper troposphere, where these nuclei exist, but improbable for the stratosphere (Fortin et al, 2003). In the laboratory studies of Fortin et al (2003) only a supercooling of 0.1 K to 1.3 K was necessary for the formation
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