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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
https://doi.org/10.5194/gmd-2018-212
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Methods for assessment of models 18 Oct 2018

Methods for assessment of models | 18 Oct 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

The Cloud_cci simulator for the ESA Cloud_cci climate data record and its application to a global and a regional climate model

Salomon Eliasson1, Karl Göran Karlsson1, Erik van Meijgaard2, Jan Fokke Meirink2, Martin Stengel3, and Ulrika Willén1 Salomon Eliasson et al.
  • 1Swedish Meteorological and Hydrological Institute (SMHI), Sweden
  • 2Koninklijk Nederlands Meteorologisch Instituut (KNMI), the Netherlands
  • 3Deutscher Wetterdienst (DWD), Germany

Abstract. The Cloud_cci satellite simulator has been developed to enable comparisons between the Cloud_cci Climate Data Record (CDR) and climate models. The Cloud_cci simulator is applied here to the EC-Earth Global Climate Model as well as the RACMO Regional Climate Model. We demonstrate the importance of using a satellite simulator that emulates the retrieval process underlying the CDR as opposed to taking the model output directly. The impact of not sampling the model at the local overpass time of the polar-orbiting satellites used to make the dataset was shown to be large, yielding up to 100% error in Liquid Water Path (LWP) simulations in certain regions. The simulator removes all clouds with optical thickness smaller than 0.2 to emulate the Cloud_cci CDR's lack of sensitivity to very thin clouds. This reduces Total Cloud Fraction (TCF) globally by about 10% for EC-Earth and by a few percent for RACMO over Europe. Globally, compared to the Cloud_cci CDR, EC-Earth is shown to be mostly in agreement on the distribution of clouds and their height, but it generally underestimates the high cloud fraction associated with tropical convection regions, and overestimates the occurrence and height of clouds over the Sahara and the Arabian sub-continent. In RACMO, TCF is higher than retrieved over the northern Atlantic Ocean, but lower than retrieved over the European continent, where in addition the Cloud Top Pressure (CTP) is underestimated. The results shown here demonstrate again that a simulator is needed to make meaningful comparisons between modelled and retrieved cloud properties. It is promising to see that for (nearly) all cloud properties the simulator improves the agreement of the model with the satellite data.

Salomon Eliasson et al.
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Salomon Eliasson et al.
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Short summary
To enable fair comparisons of clouds between Climate models and the ESA cloud_cci Climate Data Record (CDR), we present a tool called the Cloud_cci simulator. The tool takes into account the geometry and cloud detection capabilities of the Cloud_cci CDR to allow fair comparisons. We demonstrate the simulator on two climate models. We find the impact of time sampling has a large effect on simulated cloud water amount, and that the simulator reduces the cloud cover by about 10 % globally.
To enable fair comparisons of clouds between Climate models and the ESA cloud_cci Climate Data...
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