SAM - The Stratospheric Aerosol Model
Claudia Timmreck, René Hommel
The stratospheric aerosol model SAM (Timmreck and raf, 2001) has been developed as an extendable module for the general circulation model ECHAM (Roeckner et al., 1996; 2003). Currently SAM is implemented in the GCM cycles 4 (Timmreck, 2001) and 5 (Hommel et al., 2003). SAM is also together with the middle atmosphere GCM version MAECHAM4 (Manzini et al., 1998; 1999) and the chemistry model CHEM (Steil et al., 2003) part of a chemistry-microphysics climate model (Timmreck, 2003; Timmreck et al., 2003). In the following the model description relates to the latest development for the ECHAM5 circulation model.
SAM is a fixed sectional sulfate aerosol model with 44 separate size classes in the range of 0.3 nm and 6.2 μm, determined by mass doubling. A semi-Langrangian flux-form scheme is used for the transport of the aerosol tracers as well as for the precursers SO2, OCS, DMS and sulfuric acid vapor in terms of mass concentrations. Only liquid H2SO4/H2O droplets with a souble core are considered. The sulfuric acid mass fraction and weight percentage of the
droplets are calculated dependent on the atmospheric conditions and the partial pressure of H2SO4 and H2O.
The model use a parameterization for binary homogeneous nucleation for upper tropospheric and lower stratospheric conditions ehkamäki et al., 2002). The microphysical scheme includes condensation and evaporation of sulfate, water vapor growth, coagulation, gravitational sedimentation and a new wet deposition scheme (Stier et al., 2004). A high-resistance scheme for dry deposition of sulfate aerosol and gases is used (Ganzeveld et al., 1998).
To describe the formation and evolution of stratospheric aerosol, a tropospheric sulfur cycle (Feichter et al., 1996) is coupled to a stratospheric sulfur chemistry scheme (Timmreck, 2001). Anthropogenic and volcanic emissions of SO2 are considered. The model calculates DMS emissions online from DMS seawater concentrations. The oxidants are prescribed as monthly mean datasets taken from results of a decadal simulation of the 1990s with the MOZART2 chemisty transport model (Schultz et al., 2002). OCS and the photolysis rates of OCS, H2SO4 and SO2 prescribed monthly mean datasets taken from results of a two-dimensional chemical transport model (Grooß et al., 1998).
Model related links:
Project PARTS (Particles in the upper Troposphere and lower Stratosphere)
Feichter, J. et al., Simulation of the tropospheric sulfur cycle in a global climate model, Atmos. Environ., 30, 1693-1707, 1996.
Ganzeveld, L., J. Lelieveld and G.J. Roelofs, A dry deposition parameterization for sulfur oxides in a chemistry and general circulation model, J. Geophys. Res., 103, 5679-5694, 1998.
Grooß, J. U. et al., Impact of aircraft emissions on tropospheric and stratospheric ozone, Part I: Chemistry and 2-D model results, Atmos. Environ., 32, 3173-3184, 1998.
Hommel, R., C. Timmreck, and H.-F. Graf, Global stratospheric sulfate aerosol modeling with ECHAM5 GCM, Abstracts of the European Aerosol Conference 2003, Vol II, J. Aerosol Science, 1047-1048, 2003.
Manzini, E., J. Feichter, Simulation of the SF6 tracer with the middle atmosphere MAECHAM4 model: Aspects of the large-scale transport, J. Geophys. Res., 104, 31,097-31,108, 1999.
Manzini E., McFarlane N.A., The effect of varying the source spectrum of a gravity wave parameterization in a middle atmosphere general circulation model. J. Geophys. Res., 103, 31523-31539, 1998.
Roeckner E., et al., The atmospheric general circulation model ECHAM 5. PART I: Model description, MPI-Report 349, 127 pp, 2003.
Roeckner, E., K. Arpe, L. Bengtsson, M. Christoph, M. Claussen, L. Dümenil, M. Esch, M. Giorgetta, U. Schlese, U. Schulzweida: The atmospheric general circulation model ECHAM4: Model description and simulation of present-day climate, MPI Rep., 218, Hamburg, Germany, 1996.
Schultz, M.G. et al., Analysis of factors controlling the variability and trends of the tropospheric chemical composition, Joint int. symposium on atmos. chemistry within the earth system, Creata, Greece, 2002.
Steil B., Brühl C., Manzini E., Crutzen P.J., Lelieveld J., Rasch P.J., Roeckner E., Krueger K., A new interactive chemistry-climate model. 1. Present day climatology and interannual variability of the middle atmosphere using the model and 9 years of HALOE/UARS data., J. Geophys. Res., 108, 10.1029/2002JD002971, 2003.
Stier, P. et al., The aerosol-climate model ECHAM5-HAM, Atmos. Chem. Phys. Discuss., 4, 5551-5623, 2004.
Timmreck, C., Simulation of UT/LS aerosol with a chemistry-microphysics-climate model, Abstracts of the European Aerosol Conference 2003, Vol. II, J. Aerosol Science, 1053-1055, 2003.
Timmreck, C., H.-F. Graf and B. Steil, Aerosol chemistry interactions after the Mt. Pinatubo eruption, in Volcanism and the Earth's Atmosphere, eds. A. Robock and C. Oppenheimer, AGU Monograph, 139,
213-225, 2003.
Timmreck, C., Three-dimensional simulation of stratospheric background aerosol: First results of a multiannual GCM simulation., J. Geophys. Res., 106, 28,313-28,332, 2001.
Timmreck, C. and H.-F. Graf, A microphysical model for simulation of stratospheric aerosol in a climate model., Meteorol. Z., Vol. 9, 263-282, 2000.
Vehkamäki, H. et al., An improved parameterization for sulfuric acid/water nucleation rates for tropospheric and stratospheric conditions, J. Geophys. Res., 107, 4622, 2002.