Description and evaluation of the UKCA stratosphere-troposphere chemistry scheme (StratTrop vn 1.0) implemented in UKESM1

Archibald, Alexander T.; O’Connor, Fiona M.; Abraham, N. L.; Archer‐Nicholls, Scott; Chipperfield, Martyn P.; Dalvi, Mohit; Folberth, Gerd; Dennison, Fraser; Dhomse, Sandip; Griffiths, Paul; Hardacre, Catherine; Hewitt, Alan J.; Hill, R. E.; Johnson, C. E.; Keeble, James; Köhler, Marcus O.; Morgenstern, Olaf; Mulcahy, Jane; Ordóñez, Carlos; Pope, Richard J.; Rumbold, Steven T.; Russo, M. R.; Savage, Nick; Sellar, Alistair; Stringer, Marc; Turnock, Steven T.; Wild, Oliver; Zeng, Guang

doi:10.5194/gmd-2019-246

Cited by 24 publications

(74 citation statements)

References 82 publications

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“…• Ocean biogeochemistry: MEDUSA (Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification; Yool et al, 2013), with the addition of a diagnostic submodel for DMS surface seawater concentration (Anderson et al, 2001) to support interactive DMS emissions to the atmosphere. • Atmospheric composition: UKCA (United Kingdom Chemistry and Aerosol model; Archibald et al, 2019;Mulcahy et al, 2018) with unified stratospheric-tropospheric chemistry and close coupling between chemistry and aerosols. UKESM1 is a successor to HadGEM2-ES (Collins et al, 2011), and many of its components, namely, the land surface, atmospheric chemistry, and the core physical model, have been developed from that model's components.…”

Section: Component Models and Couplingmentioning

confidence: 99%

“…A thorough evaluation of the chemistry performance of UKESM1 can be found in Archibald et al (2019); here we focus on those aspects which represent major enhancements relative to HadGEM2-ES, namely, stratospheric chemistry, interactive photolysis, and biogenic emissions of VOCs.…”

Section: Atmospheric Chemistrymentioning

confidence: 99%

“…Atmospheric composition in UKESM1 is simulated by the U.K. Chemistry and Aerosols (UKCA) model. UKCA has several chemistry configurations available; the specific configuration used in UKESM1 is described in Archibald et al (2019) and comprises a combination of the stratospheric scheme of Morgenstern et al (2009) (with minor updates to reaction rates as in Morgenstern et al, 2017) and the "TropIsop" tropospheric chemistry of O'Connor et al (2014), which includes extensions to the volatile organic compound (VOC) representation relative to the tropospheric chemistry in HadGEM2-ES. The merged scheme thus simulates interactive chemistry from the surface to the top of the model (85 km), enabling a holistic treatment of ozone, the third most important radiatively active gas in the atmosphere and the primary source of the hydroxyl radical (OH) in the troposphere.…”

Section: A4 Atmospheric Chemistrymentioning

confidence: 99%

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UKESM1: Description and Evaluation of the U.K. Earth System Model

Sellar

Jones

Mulcahy

et al. 2019

J Adv Model Earth Syst

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567

461

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We document the development of the first version of the U.K. Earth System Model UKESM1.The model represents a major advance on its predecessor HadGEM2-ES, with enhancements to all component models and new feedback mechanisms. These include a new core physical model with a well-resolved stratosphere; terrestrial biogeochemistry with coupled carbon and nitrogen cycles and enhanced land management; tropospheric-stratospheric chemistry allowing the holistic simulation of radiative forcing from ozone, methane, and nitrous oxide; two-moment, five-species, modal aerosol; and ocean biogeochemistry with two-way coupling to the carbon cycle and atmospheric aerosols. The complexity of coupling between the ocean, land, and atmosphere physical climate and biogeochemical cycles in UKESM1 is unprecedented for an Earth system model. We describe in detail the process by which the coupled model was developed and tuned to achieve acceptable performance in key physical and Earth system quantities and discuss the challenges involved in mitigating biases in a model with complex connections between its components. Overall, the model performs well, with a stable pre-industrial state and good agreement with observations in the latter period of its historical simulations. However, global mean surface temperature exhibits stronger-than-observed cooling from 1950 to 1970, followed by rapid warming from 1980 to 2014. Metrics from idealized simulations show a high climate sensitivity relative to previous generations of models: Equilibrium climate sensitivity is 5.4 K, transient climate response ranges from 2.68 to 2.85 K, and transient climate response to cumulative emissions is 2.49 to 2.66 K TtC −1 . Plain Language SummaryWe describe the development and behavior of UKESM1, a novel climate model that includes improved representations of processes in the atmosphere, ocean, and on land. These processes are inter-related: For example, dust is produced on the land and blown up into the atmosphere where it affects the amount of sunlight falling on Earth. Dust can also be dissolved in the ocean, where it affects marine life. This in turn changes both the amount of carbon dioxide absorbed by the ocean and the material emitted from the surface into the atmosphere, which has an affect on the formation of clouds. UKESM1 includes many processes and interactions such as these, giving it a high level of complexity. Ensuring realistic process behavior is a major challenge in the development of our model, and we have carefully tested this. UKESM1 performs well, correctly exhibiting stable results from a continuous pre-industrial simulation (used to provide a reference for future experiments) and showing good agreement

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Section: Component Models and Couplingmentioning

confidence: 99%

Section: Atmospheric Chemistrymentioning

confidence: 99%

Section: A4 Atmospheric Chemistrymentioning

confidence: 99%

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UKESM1: Description and Evaluation of the U.K. Earth System Model

Sellar

Jones

Mulcahy

et al. 2019

J Adv Model Earth Syst

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567

461

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“…The UKESM1 model (Sellar et al, 2020)is includes an interactive stratosphere-troposphere gas-phase chemistry scheme (Archibald et al, 2019) using the UK Chemistry and Aerosol (UKCA; (Morgenstern et al, 2009;O'Connor https://doi.org/10.5194/acp-2019-1205 Preprint. Discussion started: 13 March 2020 c Author(s) 2020.…”

Section: Modelsmentioning

confidence: 99%

“…Dust is modelled independently using the bin scheme of (Woodward, 2001). The UKCA chemistry and aerosol schemes are coupled such that the secondary aerosol (SO4, OA) formation rates depend on oxidants from the stratosphere-troposphere chemistry scheme (Archibald et al, 2019;Sellar et al, 2020), Mulcahy et al 2019, in prep). Aerosol particles are activated into cloud droplets using the activation scheme of (Abdul-Razzak and Ghan, 2000) which is dependent on aerosol size distribution, aerosol composition, and meteorological conditions.…”

Section: Modelsmentioning

confidence: 99%

Effective Radiative forcing from emissions of reactive gases and aerosols – a multimodel comparison

Thornhill¹,

Collins²,

Kramer³

et al. 2020

Preprint

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Abstract. This paper quantifies the effective radiative forcing from CMIP6 models of the present-day anthropogenic emissions of NOx, CO, VOCs, SO2, NH3, black carbon and primary organic carbon. Effective radiative forcing from pre-industrial to present-day changes in the concentrations of methane, N2O and halocarbons are quantified and attributed to their anthropogenic emissions. Emissions of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, secondary inorganic and organic aerosol and methane. We therefore break down the ERFs from each emitted species into the contributions from the composition changes. The 1850 to 2014 mean ERFs are 1.1 ± 0.07 W m−2 for sulfate, −0.24 ± 0.01 W m−2 for organic carbon (OC), and 0.15 ± 0.04 W m−2 for black carbon (BC), and for the aerosols combined it is −0.95 ± 0.03 W m−2. The means for the reactive gases are 0.69 ± 0.04 W m−2 for methane (CH4), 0.06 ± 0.04 W m−2 for NOx, −0.09 ± 0.03 W m−2 for volatile organic carbons (VOC), 0.16 ± 0.03 W m−2 for ozone (O3), 0.27 W m−2 for nitrous oxide (N2O) and −0.02 ± 0.06 W m−2 for hydrocarbon (HC). Differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.

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The Common Representative Intermediates Mechanism version 2 in the United Kingdom Chemistry and Aerosols Model

Archer‐Nicholls

Abraham

Shin

et al. 2020

Preprint

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We document the implementation of the Common Representative Intermediates Mechanism version 2, reduction 5 into the United Kingdom Chemistry and Aerosol model (UKCA) version 10.9. The mechanism is merged with the stratospheric chemistry already used by the StratTrop mechanism, as used in UKCA and the UK Earth System Model, to create a new CRI-Strat mechanism. CRI-Strat simulates a more comprehensive treatment of non-methane volatile organic compounds (NMVOCs) and provides traceability with the Master Chemical Mechanism. In total, CRI-Strat simulates the chemistry of 233 species competing in 613 reactions (compared to 87 species and 305 reactions in the existing StratTrop mechanism). However, while more than twice as complex than StratTrop, the new mechanism is only 75% more computationally expensive. CRI-Strat is evaluated against an array of in situ and remote sensing observations and simulations using the StratTrop mechanism in the UKCA model. It is found to increase production of ozone near the surface, leading to higher ozone concentrations compared to surface observations. However, ozone loss is also greater in CRI-Strat, leading to less ozone away from emission sources and a similar tropospheric ozone burden compared to StratTrop. CRI-Strat also produces more carbon monoxide than StratTrop, particularly downwind of biogenic VOC emission sources, but has lower burdens of nitrogen oxides as more is converted into reservoir species. The changes to tropospheric ozone and nitrogen budgets are sensitive to the treatment of NMVOC emissions, highlighting the need to reduce uncertainty in these emissions to improve representation of tropospheric chemical composition. Plain Language SummaryTo understand the climate and predict how it will change in the future, we need to understand its chemical composition-the trace gases and small particles that exist in tiny quantities in the atmosphere. A key tool we use to do this are computer models which simulate the atmosphere and processes within it. Key processes include the formation of ozone, a harmful pollutant and greenhouse gas in the lower atmosphere. However, the chemistry involved in forming ozone is very complicated, so computer simulations of the atmosphere must greatly simplify the chemistry. These simple schemes may introduce errors in the model. We also have much more complex chemical mechanisms which simulate our best understanding of all chemical reactions, but these complex schemes require too much computational power to be used when simulating the whole atmosphere. In this paper, we describe the implementation of a chemical mechanism that sits between these levels of complexity, realistically simulating the formation and destruction of ozone without being too slow to run. We compare this new mechanism against measurements taken of the atmosphere and the preexisting, simpler chemical mechanism and show that the new mechanism greatly enhances the amount of ozone that is produced.

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Description and evaluation of the UKCA stratosphere-troposphere chemistry scheme (StratTrop vn 1.0) implemented in UKESM1

Cited by 24 publications

References 82 publications

UKESM1: Description and Evaluation of the U.K. Earth System Model

UKESM1: Description and Evaluation of the U.K. Earth System Model

Effective Radiative forcing from emissions of reactive gases and aerosols – a multimodel comparison

The Common Representative Intermediates Mechanism version 2 in the United Kingdom Chemistry and Aerosols Model

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