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How well do regional climate models reproduce radiation and clouds in the Arctic?: An evolution of ARCMIP simulations
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0002-6908-7410
Stockholm University, Faculty of Science, Department of Meteorology .
2008 (English)In: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 47, no 9, p. 2405-2422Article in journal (Refereed) Published
Abstract [en]

Downwelling radiation in six regional models from the Arctic Regional Climate Model Intercomparison (ARCMIP) project is systematically biased negative in comparison with observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment, although the correlations with observations are relatively good. In this paper, links between model errors and the representation of clouds in these models are investigated. Although some modeled cloud properties, such as the cloud water paths, are reasonable in a climatological sense, the temporal correlation of model cloud properties with observations is poor. The vertical distribution of cloud water is distinctly different among the different models; some common features also appear. Most models underestimate the presence of high clouds, and, although the observed preference for low clouds in the Arctic is present in most of the models, the modeled low clouds are too thin and are displaced downward. Practically all models show a preference to locate the lowest cloud base at the lowest model grid point. In some models this happens also to be where the observations show the highest occurrence of the lowest cloud base; it is not possible to determine if this result is just a coincidence. Different factors contribute to model surface radiation errors. For longwave radiation in summer, a negative bias is present both for cloudy and clear conditions, and intermodel differences are smaller when clouds are present. There is a clear relationship between errors in cloud-base temperature and radiation errors. In winter, in contrast, clear-sky cases are modeled reasonably well, but cloudy cases show a very large intermodel scatter with a significant bias in all models. This bias likely results from a complete failure in all of the models to retain liquid water in cold winter clouds. All models overestimate the cloud attenuation of summer solar radiation for thin and intermediate clouds, and some models maintain this behavior also for thick clouds.

Place, publisher, year, edition, pages
2008. Vol. 47, no 9, p. 2405-2422
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-14592DOI: 10.1175/2008JAMC1845.1ISI: 000259317400009OAI: oai:DiVA.org:su-14592DiVA, id: diva2:181112
Available from: 2009-01-13 Created: 2009-01-13 Last updated: 2022-02-25Bibliographically approved
In thesis
1. Arctic clouds - interactions with radiation and thermodynamic structure
Open this publication in new window or tab >>Arctic clouds - interactions with radiation and thermodynamic structure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Clouds play in important role in the climate system through their interaction with radiation. Globally, clouds tend to cool the Earth by reflecting solar radiation and shading the surface. Over the Arctic, clouds tend to have the opposite impact, where they instead warm the surface through the cloud greenhouse effect because the surface is generally quite reflective. The magnitude and overall effect of clouds on the surface varies significantly with the surface, cloud and thermodynamic characteristics and can have large impacts on the energy budget at the surface.

Low-level central-Arctic stratus clouds interact with the thermodynamics in a manner differently than sub-tropical stratus. Observations from several Arctic observatories indicate that these clouds penetrate and persist within stable temperature inversion structures, rather than being limited to the base of the stable layer as observed in the subtropics. It is hypothesized that such interactions with the thermodynamics can impact for example the cloud phase, lifetime, and their relationship with the sub-cloud layer and surface. Analysis indicates both the thermodynamic setting and the cloud properties affect the vertical location of the cloud top relative to inversion base. Hypothetical longwave radiative impacts resulting from liquid water redistributions are identified and discussed.

Clouds primarily influence the energy at the surface via interactions with radiation. Measurements from the central Arctic suggest that the transition of season from melting to freezing was largely determined by the presence, or absence, of liquid-containing clouds and the incumbent cloud longwave warming effect. The components affecting the cloud-radiative forcing are described with relation to the energy budget and the change of season. Additionally, the influence of altering cloud condensation nuclei as a mechanism for limiting cloud liquid water is shown to have strong influences on surface temperature and lower atmospheric stability.

Finally, regional climate models, RCMs, are evaluated against an annual dataset to assess the ability of RCMs to represent cloud and radiation processes in the Arctic. It is shown that both inter-model and model-observation spread are rather significant. Biases in the cloud representations yield distinct biases in the radiative fluxes, and can result in significant local climate variations solely through these parameters.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2010. p. 46
Keywords
Arctic, stratus, radiation, thermodynamic structure, cloud radiative forcing, seasonal transition
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-43935 (URN)978-91-7447-176-2 (ISBN)
Public defence
2010-12-03, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Accepted. Paper 4: Manuscript published in Atmospheric Chemistry and Physics Discussions.Available from: 2010-11-11 Created: 2010-11-01 Last updated: 2022-02-24Bibliographically approved

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Tjernström, MichaelSedlar, Joseph

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