Abstract
Abstract. We present the third generation of the coupled chemistry–climate model (CCM) SOCOL (modeling tools for studies of SOlar Climate Ozone Links). The most notable modifications compared to the previous model version are (1) the dynamical core has been updated with the fifth generation of the middle-atmosphere general circulation model MA-ECHAM (European Centre/HAMburg climate model), and (2) the advection of the chemical species is now calculated by a mass-conserving and shape-preserving flux-form transport scheme instead of the previously used hybrid advection scheme. The whole chemistry code has been rewritten according to the ECHAM5 infrastructure and transferred to Fortran95. In contrast to its predecessors, SOCOLvs3 is now fully parallelized. The performance of the new SOCOL version is evaluated on the basis of transient model simulations (1975–2004) with different horizontal (T31 and T42) resolutions, following the approach of the CCMVal-1 model validation activity. The advanced advection scheme significantly reduces the artificial loss and accumulation of tracer mass in regions with strong gradients that was observed in previous model versions. Compared to its predecessors, SOCOLvs3 generally shows more realistic distributions of chemical trace species, especially of total inorganic chlorine, in terms of the mean state, but also of the annual and interannual variability. Advancements with respect to model dynamics are for example a better representation of the stratospheric mean state in spring, especially in the Southern Hemisphere, and a slowdown of the upward propagation in the tropical lower stratosphere. Despite a large number of improvements model deficiencies still remain. Examples include a too-fast vertical ascent and/or horizontal mixing in the tropical stratosphere, the cold temperature bias in the lowermost polar stratosphere, and the overestimation of polar total ozone loss during Antarctic springtime.
Highlights
The accurate calculation of the advective transport of chemical species is of fundamental importance for the overall performance of coupled chemistry–climate models (CCMs)
This paper presents the third generation of the coupled chemistry–climate model SOCOL
Compared to the previous model version, the underlying general circulation model has been updated from MA-ECHAM4 to MA-ECHAM5, and the former hybrid advection algorithm has been replaced by a mass-conserving and shape-preserving flux-form semi-Lagrangian scheme
Summary
The accurate calculation of the advective transport of chemical species is of fundamental importance for the overall performance of coupled chemistry–climate models (CCMs). As shown by Schraner et al (2008), several deficiencies of the first version (vs1.0) of the CCM SOCOL (modeling tool for studies of SOlar Climate Ozone Links, Egorova et al, 2005) were directly related to deficiencies of the semiLagrangian advection scheme (Ritchie, 1985; Williamson and Rasch, 1989) applied for horizontal tracer transport. Compared to Cly or Bry the stratospheric lifetime of the Ox family is much shorter, and, mass conservation during advection becomes less critical than for tracers with a lifetime longer than one year From all of this it is obvious that a more satisfying approach to the advection problem requires the semi-Lagrangian scheme to be replaced by a more advanced, mass-conserving approach. Differences from the previous model version SOCOLvs are documented
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