The Met Office Unified Model Global Atmosphere 7.0/7.1 and JULES Global Land 7.0 configurations

Walters, David; Baran, Anthony J.; Boutle, Ian; Brooks, M. E.; Earnshaw, Paul; Edwards, John M.; Furtado, Kalli; Hill, Peter; Lock, A. P.; Manners, James; Morcrette, C. J.; Mulcahy, Jane; Sanchez, Cláudio José Palma; Smith, Chris; Stratton, Rachel; Tennant, Warren; Tomassini, Lorenzo; Weverberg, Kwinten Van; Vosper, Simon; Willett, Martin; Browse, Jo; Bushell, Andrew C.; Dalvi, Mohit; Essery, Richard; Gedney, Nicola; Hardiman, Steven C.; Johnson, Ben; Johnson, C. E.; Jones, Andy; Mann, G. W.; Milton, Sean; Rumbold, Heather; Sellar, Alistair; Ujiie, Masashi; Whitall, Michael; Williams, Keith D.; Zerroukat, M.

doi:10.5194/gmd-2017-291

Cited by 109 publications

(156 citation statements)

References 137 publications

(181 reference statements)

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“…Therefore it is likely that most models using these types of activation parametrization produce excessive aerosol activation in their lowest model levels. HadGEM3-GA7 (Walters et al, 2017b). Throughout most of the northern hemisphere land masses, when fog is present, the predicted droplet numbers are in excess of 150 cm .…”

Section: Discussionmentioning

confidence: 99%

Aerosol-fog interaction and the transition to well-mixed radiation fog

Boutle¹,

Price²,

Kudzotsa³

et al. 2017

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Abstract. We analyse the development of a radiation fog event and its gradual transition from optically thin fog in a stable boundary layer to well-mixed optically-thick fog. Comparison of observations and a detailed large-eddy simulation demonstrate that aerosol growth and activation is the key process in determining the onset of adiabatic fog. Weak turbulence and low supersaturations lead to the growth of aerosol particles which can significantly affect the visibility, but do not significantly interact with the long-wave radiation, allowing the atmosphere to remain stable. Only when a substantial fraction of the aerosol 5 become activated into cloud droplets can the fog interact with the radiation, becoming optically thick and well-mixed. Modifications to the parametrization of cloud droplet numbers in fog, resulting in lower and more realistic concentrations, are shown to give significant improvements to an NWP model, which initially struggled to accurately simulate the transition. Finally, consequences of this work for common aerosol activation parametrizations used in climate models are discussed, demonstrating that many schemes are reliant on an artificial minimum value when activating aerosol in fog, and adjustment of this minimum 10 can significantly affect the sensitivity of the climate system to aerosol radiative forcing.

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Section: Discussionmentioning

confidence: 99%

Aerosol-fog interaction and the transition to well-mixed radiation fog

Boutle¹,

Price²,

Kudzotsa³

et al. 2017

Preprint

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“…We use an aquaplanet setup of the Global Atmosphere configuration version 7.1 (GA7.1) of the Met Office Unified Model (Williams et al, 2018). The GA7.1 configuration is based on the GA7.0 configuration, described in detail by Walters et al (2017). Williams and Bodas-Salcedo (2017) evaluate the cloud simulation of the GA7.0 configuration with Atmospheric Model Intercomparison Project (AMIP) forcing.…”

Section: Methodsmentioning

confidence: 99%

Cloud Condensate and Radiative Feedbacks at Midlatitudes in an Aquaplanet

Bodas‐Salcedo

2018

Geophysical Research Letters

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Climate models show a robust negative feedback in the midlatitudes, coincident with an increase in cloud liquid in the mixed‐phase region of the control climate. This “mixed‐phase feedback” is normally attributed to a feedback caused by a phase change feedback (ice to liquid). Here we use an aquaplanet configuration to investigate this in more detail. We use high‐frequency instantaneous diagnostics and composite them in ascending and descending regimes. We find that a large fraction of the increase in cloud liquid water in the mixed‐phase region does not significantly contribute to the radiative feedback due to a masking effect of the ice cloud above. Using some simple arguments and approximate calculations, we estimate that about one third of the total shortwave negative radiative feedback is driven by a phase change feedback, whereas the rest of the feedback is driven by changes in ice and warm liquid clouds.

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“…The resolution of the simulation is N96 (i.e., 1.875 • ×1.25 • ) in the horizontal and 85 model levels in vertical. On top of the standard GA7.1 version described in Walters et al (2017), a modified microphysics scheme is used. On top of the standard GA7.1 version described in Walters et al (2017), a modified microphysics scheme is used.…”

Section: Model Datamentioning

confidence: 99%

Cluster‐Based Evaluation of Model Compensating Errors: A Case Study of Cloud Radiative Effect in the Southern Ocean

Schuddeboom

Varma

McDonald

et al. 2019

Geophysical Research Letters

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Model evaluation is difficult and generally relies on analysis that can mask compensating errors. This paper defines new metrics, using clusters generated from a machine learning algorithm, to estimate mean and compensating errors in different model runs. As a test case, we investigate the Southern Ocean shortwave radiative bias using clusters derived by applying self‐organizing maps to satellite data. In particular, the effects of changing cloud phase parameterizations in the MetOffice Unified Model are examined. Differences in cluster properties show that the regional radiative biases are substantially different than the global bias, with two distinct regions identified within the Southern Ocean, each with a different signed bias. Changing cloud phase parameterizations can reduce errors at higher latitudes but increase errors at lower latitudes of the Southern Ocean. Ranking the parameterizations often shows a contrast in mean and compensating errors, notably in all cases large compensating errors remain.

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The Met Office Unified Model Global Atmosphere 7.0/7.1 and JULES Global Land 7.0 configurations

Cited by 109 publications

References 137 publications

Aerosol-fog interaction and the transition to well-mixed radiation fog

Aerosol-fog interaction and the transition to well-mixed radiation fog

Cloud Condensate and Radiative Feedbacks at Midlatitudes in an Aquaplanet

Cluster‐Based Evaluation of Model Compensating Errors: A Case Study of Cloud Radiative Effect in the Southern Ocean

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