The SOCOL version 3.0 chemistry–climate model: description, evaluation, and implications from an advanced transport algorithm

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 modifi-cations compared to the previous model version are: (1) the dynamical core has beenupdated with the fifth generation of the middle-atmosphere general circulation model5MA-ECHAM, and (2) the advection of the chemical species is now calculated by amass-conserving and shape-preserving flux-form transport scheme instead of the pre-viously used hybrid advection scheme. The whole chemistry code has been rewrittenaccording to the ECHAM5 infrastructure and transferred to Fortran95. In contrast to itspredecessors, SOCOLvs3 is now fully parallelized. The performance of the new SO-10COL version is evaluated on the basis of transient model simulations (1975–2004) withdifferent horizontal (T31 and T42) resolutions, following the approach of the CCMVal-1model validation activity. The advanced advection scheme significantly reduces the ar-tificial loss and accumulation of tracer mass in regions with strong gradients that wasobserved in previous model versions. Compared to its predecessors, SOCOLvs3 gen-15erally shows more realistic distributions of chemical trace species, especially of totalinorganic chlorine, in terms of the mean state, but also of the annual and interannualvariability. Advancements with respect to model dynamics are for example a better rep-resentation of the stratospheric mean state in spring, especially in the Southern Hemi-sphere, and a slowdown of the upward propagation in the tropical lower stratosphere.20Despite a large number of improvements model deficiencies still remain. Examples in-clude a too fast vertical ascent and/or horizontal mixing in the tropical stratosphere, thecold temperature bias in the lowermost polar stratosphere, and the overestimation ofpolar total ozone loss during Antarctic springtime.