Atmosphere–ocean–aerosol–chemistry–climate model SOCOLv4.0: description and evaluation

Abstract

Abstract. This paper features the new\natmosphere–ocean–aerosol–chemistry–climate model, SOlar Climate Ozone Links (SOCOL) v4.0, and its\nvalidation. The new model was built by interactively coupling the Max\nPlanck Institute Earth System Model version 1.2 (MPI-ESM1.2)\n(T63, L47) with the chemistry (99 species) and\nsize-resolving (40 bins) sulfate aerosol microphysics modules from the\naerosol–chemistry–climate model, SOCOL-AERv2. We evaluate its performance\nagainst reanalysis products and observations of atmospheric circulation,\ntemperature, and trace gas distribution, with a focus on stratospheric\nprocesses. We show that SOCOLv4.0 captures the low- and midlatitude\nstratospheric ozone well in terms of the climatological state, variability\nand evolution. The model provides an accurate representation of climate\nchange, showing a global surface warming trend consistent with observations\nas well as realistic cooling in the stratosphere caused by greenhouse gas\nemissions, although, as in previous model versions, a too-fast residual\ncirculation and exaggerated mixing in the surf zone are still present. The\nstratospheric sulfur budget for moderate volcanic activity is well\nrepresented by the model, albeit with slightly underestimated aerosol\nlifetime after major eruptions. The presence of the interactive ocean and a\nsuccessful representation of recent climate and ozone layer trends make\nSOCOLv4.0 ideal for studies devoted to future ozone evolution and effects of\ngreenhouse gases and ozone-destroying substances, as well as the evaluation\nof potential solar geoengineering measures through sulfur injections.\nPotential further model improvements could be to increase the vertical\nresolution, which is expected to allow better meridional transport in the\nstratosphere, as well as to update the photolysis calculation module and\nbudget of mesospheric odd nitrogen. In summary, this paper demonstrates that\nSOCOLv4.0 is well suited for applications related to the stratospheric ozone\nand sulfate aerosol evolution, including its participation in ongoing and\nfuture model intercomparison projects.\n