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

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

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Atmosphere-Ocean-Aerosol-Chemistry-Climate Model SOCOLv4.0: description and evaluation

10.5194/gmd-2021-35 ◽

2021 ◽

Author(s):

Timofei Sukhodolov ◽

Tatiana Egorova ◽

Andrea Stenke ◽

William T. Ball ◽

Christina Brodowsky ◽

...

Keyword(s):

Surf Zone ◽

Climate Model ◽

Stratospheric Ozone ◽

Warming Trend ◽

Sulfate Aerosol ◽

Residual Circulation ◽

Aerosol Chemistry ◽

Meridional Transport ◽

Surface Warming ◽

Recent Climate

Abstract. This paper features the new Atmosphere-Ocean-Aerosol-Chemistry-Climate Model SOCOLv4.0 and its validation. The new model was built by interactively coupling the MPI-ESM1.2 Earth System Model (T63, L47) with the chemistry (99 species) and size-resolving (40 bins) sulfate aerosol microphysics modules from the Aerosol-Chemistry-Climate Model SOCOL-AERv2. We evaluate its performance against reanalysis products and observations of atmospheric circulation, temperature, and trace gases distribution, with a focus on stratospheric processes. We show that SOCOLv4.0 captures the low- and mid-latitude stratospheric ozone well in terms of the climatological state, variability and evolution. The model provides an accurate representation of climate change, showing a global surface warming trend consistent with observations as well as realistic cooling in the stratosphere caused by greenhouse gas emissions, although, as in previous model versions, a too fast residual circulation and exaggerated mixing in the surf zone are still present. The stratospheric sulfur budget for moderate volcanic activity is well represented by the model, albeit with slightly underestimated aerosol lifetime after major eruptions. The presence of the interactive ocean and a successful representation of recent climate and ozone layer trends make SOCOLv4.0 ideal for studies devoted to future ozone evolution and effects of greenhouse gases and ozone-destroying substances, as well as the evaluation of potential solar geoengineering measures through sulfur injections. Potential further model improvements could be to increase the vertical resolution, which is expected to allow better meridional transport in the stratosphere, as well as to update the photolysis calculation module and budget of mesospheric odd nitrogen. In summary, this paper demonstrates that SOCOLv4.0 is well suited for applications related to the stratospheric ozone and sulfate aerosol evolution, including its participation in ongoing and future model intercomparison projects.

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Improved tropospheric and stratospheric sulfur cycle in the aerosol–chemistry–climate model SOCOL-AERv2

Geoscientific Model Development ◽

10.5194/gmd-12-3863-2019 ◽

2019 ◽

Vol 12 (9) ◽

pp. 3863-3887 ◽

Cited By ~ 2

Author(s):

Aryeh Feinberg ◽

Timofei Sukhodolov ◽

Bei-Ping Luo ◽

Eugene Rozanov ◽

Lenny H. E. Winkel ◽

...

Keyword(s):

Climate Model ◽

Model Performance ◽

Stratospheric Aerosol ◽

Sulfur Cycle ◽

Sulfate Aerosol ◽

Tropospheric Chemistry ◽

Sulfur Deposition ◽

Aerosol Chemistry ◽

Deposition Fluxes ◽

Aerosol Model

Abstract. SOCOL-AERv1 was developed as an aerosol–chemistry–climate model to study the stratospheric sulfur cycle and its influence on climate and the ozone layer. It includes a sectional aerosol model that tracks the sulfate particle size distribution in 40 size bins, between 0.39 nm and 3.2 µm. Sheng et al. (2015) showed that SOCOL-AERv1 successfully matched observable quantities related to stratospheric aerosol. In the meantime, SOCOL-AER has undergone significant improvements and more observational datasets have become available. In producing SOCOL-AERv2 we have implemented several updates to the model: adding interactive deposition schemes, improving the sulfate mass and particle number conservation, and expanding the tropospheric chemistry scheme. We compare the two versions of the model with background stratospheric sulfate aerosol observations, stratospheric aerosol evolution after Pinatubo, and ground-based sulfur deposition networks. SOCOL-AERv2 shows similar levels of agreement as SOCOL-AERv1 with satellite-measured extinctions and in situ optical particle counter (OPC) balloon flights. The volcanically quiescent total stratospheric aerosol burden simulated in SOCOL-AERv2 has increased from 109 Gg of sulfur (S) to 160 Gg S, matching the newly available satellite estimate of 165 Gg S. However, SOCOL-AERv2 simulates too high cross-tropopause transport of tropospheric SO2 and/or sulfate aerosol, leading to an overestimation of lower stratospheric aerosol. Due to the current lack of upper tropospheric SO2 measurements and the neglect of organic aerosol in the model, the lower stratospheric bias of SOCOL-AERv2 was not further improved. Model performance under volcanically perturbed conditions has also undergone some changes, resulting in a slightly shorter volcanic aerosol lifetime after the Pinatubo eruption. With the improved deposition schemes of SOCOL-AERv2, simulated sulfur wet deposition fluxes are within a factor of 2 of measured deposition fluxes at 78 % of the measurement stations globally, an agreement which is on par with previous model intercomparison studies. Because of these improvements, SOCOL-AERv2 will be better suited to studying changes in atmospheric sulfur deposition due to variations in climate and emissions.

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Ozone Loss and Recovery and the Preconditioning of Upward-Propagating Planetary Wave Activity

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0259.1 ◽

2013 ◽

Vol 70 (12) ◽

pp. 3977-3994 ◽

Cited By ~ 5

Author(s):

John R. Albers ◽

Terrence R. Nathan

Keyword(s):

Ozone Depletion ◽

Planetary Wave ◽

Climate Model ◽

Stratospheric Ozone ◽

Polar Vortex ◽

Wave Drag ◽

Late Winter ◽

Residual Circulation ◽

Wave Amplification ◽

Ozone Loss

Abstract A mechanistic chemistry–dynamical model is used to evaluate the relative importance of radiative, photochemical, and dynamical feedbacks in communicating changes in lower-stratospheric ozone to the circulation of the stratosphere and lower mesosphere. Consistent with observations and past modeling studies of Northern Hemisphere late winter and early spring, high-latitude radiative cooling due to lower-stratospheric ozone depletion causes an increase in the modeled meridional temperature gradient, an increase in the strength of the polar vortex, and a decrease in vertical wave propagation in the lower stratosphere. Moreover, it is shown that, as planetary waves pass through the ozone loss region, dynamical feedbacks precondition the wave, causing a large increase in wave amplitude. The wave amplification causes an increase in planetary wave drag, an increase in residual circulation downwelling, and a weaker polar vortex in the upper stratosphere and lower mesosphere. The dynamical feedbacks responsible for the wave amplification are diagnosed using an ozone-modified refractive index; the results explain recent chemistry–coupled climate model simulations that suggest a link between ozone depletion and increased polar downwelling. The effects of future ozone recovery are also examined and the results provide guidance for researchers attempting to diagnose and predict how stratospheric climate will respond specifically to ozone loss and recovery versus other climate forcings including increasing greenhouse gas abundances and changing sea surface temperatures.

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Exploring accumulation-mode-H2SO4 versus SO2 stratospheric sulfate geoengineering in a sectional aerosol-chemistry-climate model

10.5194/acp-2018-1070 ◽

2018 ◽

Author(s):

Sandro Vattioni ◽

Debra Weisenstein ◽

David Keith ◽

Aryeh Feinberg ◽

Thomas Peter ◽

...

Keyword(s):

Radiative Forcing ◽

Surf Zone ◽

Climate Model ◽

Continuous Production ◽

Short Wave ◽

Stratospheric Aerosol ◽

Aerosol Chemistry ◽

Accumulation Mode ◽

So2 Flux ◽

Direct Emission

Abstract. Stratospheric sulfate geoengineering (SSG) could contribute to avoiding some of the adverse impacts of climate change. We used the global 3D-aerosol-chemistry-climate model, SOCOL-AER, to investigate 21 different SSG scenarios, each with 1.83 Mt S yr−1 injected either in the form of accumulation-mode-H2SO4 droplets (AM-H2SO4), gas-phase SO2, or as combinations of both. For most scenarios, the sulfur was continuously emitted at 50 hPa (≈ 20 km) altitude in the tropics and subtropics, zonally and latitudinally symmetric about the equator (ranging from &pm;3.75° to &pm;30°). In the SO2 emission scenarios, continuous production of tiny nucleation mode particles results in increased coagulation, which together with condensation produces larger coarse mode particles. These larger particles are less effective for backscattering solar radiation and sedimentation out of the stratosphere is faster. On average, AM-H2SO4 injection increases stratospheric aerosol residence times by 32 % and stratospheric aerosol burdens 37–41 % when comparing to SO2 injection. The modelled all-sky (clear-sky) short-wave radiative forcing for AM-H2SO4 injection scenarios is up to 17–70 % (44 %–57 %) larger than is the case for SO2. Aerosol burdens have a surprisingly week dependence on the latitudinal spread of emissions with emission in the stratospheric surf zone (> 15° N–15° S) decreasing burdens by only about 10 %. This is because the faster removal through stratosphere-to-troposphere transport via tropopause folds found when injection is spread farther from the equator is roughly balanced by a decrease in coagulation. Increasing injection altitude is also surprisingly ineffective because the increase in burden is compensated by an increase in large aerosols due to increased condensation. Increasing the local SO2 flux in the injection region by pulse or point emissions reduces the total global annual nucleation. Coagulation is also reduced due to the interruption of the continuous flow of freshly formed particles. The net effect of pulse or point emission of SO2 is to increase stratospheric aerosol residence time and radiative forcing. Pulse or point emissions of AM-H2SO4 has the opposite effect—decreasing stratospheric aerosol burden and radiative forcing by increasing coagulation. In summary, this study corroborates previous studies with uncoupled aerosol and radiation modules, suggesting that, compared to SO2 injection, the direct emission of AM-H2SO4 results in more radiative forcing for the same sulfur equivalent mass injection strength and that sensitivities to different injection strategies may vary for different forms of injected sulfur.

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Contributions to stratospheric ozone changes from ozone depleting substances and greenhouse gases

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-9647-2010 ◽

2010 ◽

Vol 10 (4) ◽

pp. 9647-9694 ◽

Cited By ~ 3

Author(s):

D. A. Plummer ◽

J. F. Scinocca ◽

T. G. Shepherd ◽

M. C. Reader ◽

A. I. Jonsson

Keyword(s):

Greenhouse Gases ◽

21St Century ◽

Climate Model ◽

Stratospheric Ozone ◽

Three Dimensional ◽

Ocean Model ◽

Residual Circulation ◽

Chemical Effects ◽

Ozone Depleting Substances ◽

Year 2000

Abstract. A state-of-the-art chemistry climate model coupled to a three-dimensional ocean model is used to produce three experiments, all seamlessly covering the period 1950–2100, forced by different combinations of long-lived Greenhouse Gases (GHGs) and Ozone Depleting Substances (ODSs). The experiments are designed to investigate the mechanisms by which GHGs and ODSs affect the evolution of ozone, including changes in the Brewer-Dobson circulation of the stratosphere and cooling of the upper stratosphere by CO2. Separating the effects of GHGs and ODSs on ozone, we find the decrease in upper stratospheric ozone from ODSs up to the year 2000 is approximately 30% larger than the actual decrease in ozone due to the offsetting effects of cooling by increased CO2. Over the 21st century, as ODSs decrease, continued cooling from CO2 is projected to account for more than 50% of the projected increase in upper stratospheric ozone. Changes below 20 hPa show a redistribution of ozone from tropical to extra-tropical latitudes with an increase in the Brewer-Dobson circulation, while globally averaged the amount of ozone below 20 hPa decreases over the 21st century. Further analysis by linear regression shows that changes associated with GHGs do not appreciably alter the recovery of stratospheric ozone from the effects of ODSs; over much of the stratosphere ozone recovery follows the decline of halogen concentrations within statistical uncertainty, though the lower polar stratosphere of the Southern Hemisphere is an exception with ozone concentrations recovering more slowly than indicated by the halogen concentrations. These results also reveal the degree to which climate change, and stratospheric CO2 cooling in particular, mutes the chemical effects of N2O on ozone in the standard future scenario used for the WMO Ozone Assessment. Increases in the residual circulation of the atmosphere and chemical effects from CO2 cooling more than halve the increase in reactive nitrogen in the mid to upper stratosphere that results from the specified increase in N2O between 1950 and 2100.

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The response of stratospheric ozone and dynamics to changes in atmospheric oxygen

10.5194/egusphere-egu21-12783 ◽

2021 ◽

Author(s):

Iga Józefiak ◽

Timofei Sukhodolov ◽

Tatiana Egorova ◽

Eugene Rozanov ◽

Gabriel Chiodo ◽

...

Keyword(s):

Molecular Oxygen ◽

Climate Model ◽

Atmospheric Oxygen ◽

Stratospheric Ozone ◽

Ozone Layer ◽

Self Healing ◽

Oxygen Level ◽

Meridional Transport ◽

Regional Patterns ◽

Total Column Ozone

Photolysis of molecular oxygen (O2) maintains the stratospheric ozone layer, protecting living organisms on Earth by absorbing harmful ultraviolet radiation. The atmospheric oxygen level has not always been constant, and has been held responsible for species extinctions via a thinning of the ozone layer in the past. On paleo-climate timescales, it ranged between 10 and 35% depending on the level of photosynthetic activity of plants and oceans. Previous estimates, however, showed highly uncertain ozone (O3)&#160;responses to atmospheric O2 changes, including monotonic positive or negative correlations, or displaying a maximum in O3 column around a certain oxygen level. Motivated by these discrepancies we reviewed how the ozone layer responds to atmospheric oxygen changes by means of a state-of-the-art chemistry-climate model (CCM). We used the CCM SOCOL-AERv2 to assess the ozone layer sensitivity to past and potential future concentrations of atmospheric oxygen varying from 5 to 40 %. Our findings are at odds with previous studies: we find that the current mixing ratio of O2, 21 %, indeed maximizes the O3 layer thickness and, thus, represents an optimal state for life on Earth. In the model, any alteration in atmospheric oxygen would result globally in less total column ozone and, therefore, more UV reaching the troposphere. Total ozone column in low-latitude regions is less sensitive to the changes, because of the &#8220;self-healing&#8221; effect, i.e. more UV entering lower levels, where O2 photolyzes, can partly compensate the O3 lack higher up. Mid- and high-latitudes, however, are characterized by &#177;20 DU ozone hemispheric redistributions even for small (&#177;5 %) variations in O2 content. Additional regional patterns result from the hemispheric asymmetry of meridional transport pathways via the Brewer-Dobson circulation (BDC). We will discuss the different ozone responses resulting from changes in the BDC. These effects are further modulated by the influence of ozone on stratospheric temperatures and thus on the BDC. Lower O2 cases result in a deceleration of the BDC. This renders the relation between ozone and molecular oxygen changes non-linear on both global and regional scales.

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Impact of ENSO on stratospheric ozone

10.5194/egusphere-egu21-7665 ◽

2021 ◽

Author(s):

Samuel Benito-Barca ◽

Natalia Calvo ◽

Marta Abalos

Keyword(s):

Climate Model ◽

Southern Oscillation ◽

Global Climate ◽

Stratospheric Ozone ◽

Boreal Winter ◽

Residual Circulation ◽

Central Pacific ◽

Large Variability ◽

Enso Events ◽

Middle Latitudes

El Ni&#241;o&#8208;Southern Oscillation (ENSO) is the main source of interannual variability in the global climate. Previous studies have shown ENSO has impacts on stratospheric ozone concentrations through changes in stratospheric circulation. The aim of this study is to extend these analysis by examining the anomalies in residual circulation and mixing associated with different El Ni&#241;o flavors (Eastern Pacific (EP) and Central Pacific (CP)) and La Ni&#241;a in boreal winter. For this purpose, we use four 60-year ensemble members of the Whole Atmospheric Community Climate Model version 4, reanalysis and satellite data.Significant ozone anomalies are identified in both tropics and extratropics. In the northern high-latitudes (70-90N), significant positive ozone anomalies appear in the middle stratosphere in early winter during both CP and EP El Ni&#241;o, which propagates downward during winter to the lower stratosphere only during EP-El Ni&#241;o events. Anomalies during La Ni&#241;a events are opposite to EP-El Ni&#241;o. The analysis of the different terms in the continuity equation for zonal-mean ozone concentration reveals that Arctic ozone changes during ENSO events&#160; are mainly driven by advection due to residual circulation, although contributions of mixing and chemistry are not negligible, especially in upper stratosphere.The ENSO impact on total ozone column (TOC) is also investigated. During EP-El Ni&#241;o, a significant reduction of TOC appears in the tropics and an increase in the middle latitudes. During La Ni&#241;a the response is the opposite. The TOC response to CP El Ni&#241;o events is not as robust. In the Northern Hemisphere polar region the TOC anomalies are not significant, probably due to its large variability associated with sudden stratospheric warmings in this region.

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Radiative and dynamical contributions to past and future Arctic stratospheric temperature trends

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-6707-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 6707-6728

Author(s):

P. Bohlinger ◽

B.-M. Sinnhuber ◽

R. Ruhnke ◽

O. Kirner

Keyword(s):

Planetary Wave ◽

Climate Model ◽

Stratospheric Ozone ◽

Warming Trend ◽

Wave Activity ◽

The Arctic ◽

The Past ◽

Stratospheric Temperature ◽

The Future ◽

Cooling Trend

Abstract. Arctic stratospheric ozone depletion is closely linked to the occurrence of low stratospheric temperatures. There are indications that cold winters in the Arctic stratosphere have been getting colder, raising the question if and to what extent a cooling of the Arctic stratosphere may continue into the future. We use meteorological re-analyses from ERA-Interim for the past 32 yr together with calculations of the chemistry-climate model EMAC and CCM models from the CCMVal project to infer radiative and dynamical contributions to long-term Arctic stratospheric temperature changes. For the past three decades ERA-Interim shows a warming trend in winter and cooling trend in spring and summer. Changes in winter and spring are caused by a corresponding change of planetary wave activity with increases in winter and decreases in spring. During winter the increase of planetary wave activity is counteracted by a radiatively induced cooling. Stratospheric radiatively induced cooling is detected throughout all seasons being highly significant in spring and summer. This means that for a given dynamical situation, in ERA-Interim the annual mean temperature of the Arctic lower stratosphere has been cooling by −0.41 ± 0.11 K decade−1 at 50 hPa over the past 32 yr. Calculations with state-of-the-art models from CCMVal and the EMAC model confirm the radiatively induced cooling for the past decades, but underestimate the amount of radiatively induced cooling deduced from ERA-Interim. EMAC predicts a continued annual radiatively induced cooling for the coming decades (2001–2049) of −0.15 ± 0.06 K decade−1 where the projected increase of CO2 accounts for about 2/3 of the cooling effect. Expected decrease of stratospheric halogen loading and resulting ozone recovery in the future counteracts the cooling tendency due to increasing greenhouse gas concentrations and leads to a reduced future cooling trend compared to the past. CCMVal multi-model mean predicts a future annual mean radiatively induced cooling of −0.10 ± 0.02 K decade−1 which is also smaller in the future than in the past.

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A novel approach to sulfate geoengineering with surface emissions of carbonyl sulfide

10.5194/acp-2021-813 ◽

2021 ◽

Author(s):

Ilaria Quaglia ◽

Daniele Visioni ◽

Giovanni Pitari ◽

Ben Kravitz

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Indirect Effects ◽

Radiative Forcing ◽

Climate Model ◽

Stratospheric Ozone ◽

Carbonyl Sulfide ◽

Sulfate Aerosol ◽

Stratospheric Water Vapor ◽

Surface Emission

Abstract. Sulfate geoengineering (SG) methods based on lower stratospheric tropical injection of sulfur dioxide (SO2) have been widely discussed in recent years, focusing on the direct and indirect effects they would have on the climate system. Here a potential alternative method is discussed, where sulfur emissions are located at the surface in the form of carbonyl sulfide (COS) gas. A time-dependent chemistry-climate model experiment is designed from year 2021 to 2055, assuming a 40 Tg-S/yr artificial global flux of COS, geographically distributed following the present day anthropogenic COS surface emissions. The budget of COS and sulfur species is discussed, as well as the effects of SG-COS on the stratospheric sulfate aerosol optical depth (Δ τ = 0.080 in years 2046–2055), aerosol effective radius (0.46 μm), surface SOx deposition (+8.7 %) and tropopause radiative forcing (RF) (−2.0 W/m2 for clear sky conditions and −1.5 W/m2 including the cloud adjustment). Indirect effects on ozone, methane and stratospheric water vapor are also considered, along with the COS direct contribution (with an overall gas phase global radiative forcing of +0.23 W/m2). According to our model results, the resulting net RF of this SG-COS experiment is −1.3 W/m2 for the year 2050, and it is comparable to the corresponding RF of −1.7 W/m2 obtained with a sustained injection of 4 Tg-S/yr in the tropical lower stratosphere in the form of SO2 (SG-SO2, able to produce a comparable increase of the sulfate aerosol optical depth). Significant changes of the stratospheric ozone response are found in SG-COS with respect to SG-SO2 (+4.9 DU versus +1.5 DU, globally). According to the model results, the resulting UVB perturbation at the surface accounts to −4.3 % as a global-annual average (versus −2.4 % in the SG-SO2 case), with a springtime Antarctic decrease of −2.7 % (versus a +5.8 % increase in the SG-SO2 experiment). Overall, we find that an increase in COS surface emission may be feasible, and produce a more latitudinally-uniform forcing without the need for the deployment of stratospheric aircrafts.

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Improved tropospheric and stratospheric sulfur cycle in the aerosol-chemistry-climate model SOCOL-AERv2

10.5194/gmd-2019-138 ◽

2019 ◽

Author(s):

Aryeh Feinberg ◽

Timofei Sukhodolov ◽

Bei-Ping Luo ◽

Eugene Rozanov ◽

Lenny H. E. Winkel ◽

...

Keyword(s):

Climate Model ◽

Model Performance ◽

Stratospheric Aerosol ◽

Sulfur Cycle ◽

Sulfate Aerosol ◽

Tropospheric Chemistry ◽

Sulfur Deposition ◽

Aerosol Chemistry ◽

Deposition Fluxes ◽

Aerosol Model

Abstract. SOCOL-AERv1 was developed as an aerosol-chemistry-climate model to study the stratospheric sulfur cycle and its influence on climate and the ozone layer. It includes a sectional aerosol model that tracks the sulfate particle size distribution in 40 size bins, between 0.39 nm to 3.2 µm. Sheng et al. (2015) showed that SOCOL-AERv1 successfully matched observable quantities related to stratospheric aerosol, including a simulated stratospheric aerosol burden of 109 Gg of sulfur (S), very close to the satellite-derived estimate available in 2015, 112 Gg S. In the meantime, both the satellite retrieval and SOCOL-AER have undergone significant improvements. In producing SOCOL-AERv2 we have implemented several updates to the model: adding interactive deposition schemes, improving the sulfate mass and particle number conservation, and expanding the tropospheric chemistry scheme. We compare the two versions of the model with background stratospheric sulfate aerosol observations, stratospheric aerosol evolution after Pinatubo, and ground-based sulfur deposition networks. SOCOL-AERv2 shows similar levels of agreement as SOCOL-AERv1 with satellite-measured extinctions and in situ optical particle counter (OPC) balloon flights. Also, the volcanically quiescent total stratospheric aerosol burden simulated in SOCOL-AERv2, 160 Gg S, agrees very well with the new satellite estimate of 165 Gg S. However, SOCOL-AERv2 simulates too high cross-tropopause transport of tropospheric SO2 and/or sulfate aerosol, leading to an overestimation of lower stratospheric aerosol. Due to the current lack of upper tropospheric SO2 measurements and the neglect of organic aerosol in the model, the lower stratospheric bias of SOCOL-AERv2 was not further improved. Model performance under volcanically perturbed conditions has also undergone some changes, resulting in a slightly lower shorter volcanic aerosol lifetime after the Pinatubo eruption. With the improved deposition schemes of SOCOL-AERv2, simulated sulfur wet deposition fluxes are within a factor of 2 of measured deposition fluxes at 78 % of the measurement stations globally, an agreement which is on par with previous model intercomparison studies. Because of these improvements, SOCOL-AERv2 will be better suited to studying changes to atmospheric sulfur deposition due to variations in climate and emissions.

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