Preprints
https://doi.org/10.5194/gmd-2020-277
https://doi.org/10.5194/gmd-2020-277

Submitted as: model evaluation paper 11 Nov 2020

Submitted as: model evaluation paper | 11 Nov 2020

Review status: a revised version of this preprint is currently under review for the journal GMD.

Vertical cloud radiative heating in the tropics: Confronting the EC-Earth model with satellite observations

Erik Johansson1,2,3, Abhay Devasthale1, Michael Tjernström2,3, Annica M. L. Ekman2,3, Klaus Wyser4, and Tristan L'Ecuyer5 Erik Johansson et al.
  • 1Atmospheric Remote Sensing, Research and development department, Swedish Meteorological and Hydrological Institute (SMHI), Norrköping, Sweden
  • 2Department of Meteorology, Stockholm University (MISU), Stockholm, Sweden
  • 3Bolin Center for Climate Research, Stockholm University, Stockholm, Sweden
  • 4Rossby Centre, Research and development department, Swedish Meteorological and Hydrological Institute (SMHI), Norrköping, Sweden
  • 5Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, USA

Abstract. Understanding the coupling of clouds to large-scale circulation is one of the grand challenges for the global climate research community. In this context, realistically modelling the vertical structure of cloud radiative heating/cooling (CRH) in Earth system models is a key premise to understand these couplings. Here, we evaluate CRH in two versions of the European Community Earth System Model (EC-Earth) using retrievals derived from the combined radar and lidar data from the CloudSat and CALIPSO satellites. One model version is also used with two different horizontal resolutions. Our study evaluates large-scale intraseasonal variability in the vertical structure of CRH and cloud properties and investigates the changes in CRH during different phases of the El Niño Southern Oscillation (ENSO), a process that dominates the interannual climate variability in the tropics.

EC-Earth generally captures both the intraseasonal and meridional pattern of variability in CRH over the convectively active and stratocumulus regions and the CRH during the positive and negative phases of ENSO. However, two key differences between model simulations and satellite retrievals emerge. First, the magnitude of CRH over the convectively active zones is up to twice as large in the models compared to the satellite data. Further dissection of net CRH into its shortwave and longwave components reveals noticeable differences in their vertical structure. The shortwave component of the radiative heating is overestimated by all model versions in the lowermost troposphere and underestimated in the middle troposphere. These over- and underestimates of shortwave heating are partly compensated by an overestimate of longwave cooling in the lowermost troposphere and heating in the middle troposphere. The biases in CRH can be traced back to disagreements in cloud amount and cloud water content. There is no noticeable improvement of CRH by increasing the horizontal resolution in the model alone. Our findings highlight the importance of evaluating models with satellite observations that resolve the vertical structure of clouds and cloud properties.

Erik Johansson et al.

 
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Erik Johansson et al.

Erik Johansson et al.

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Short summary
Understanding the coupling of clouds to large-scale circulation is a grand challenge for the climate community. Cloud radiative heating (CRH) is a key parameter in this coupling and is therefore essential to model realistically. We, therefore, evaluate a climate model against satellite observations. Our findings indicate good agreement in the seasonal pattern of CRH even if the magnitude differs. We also find that increasing the horizontal resolution in the model has little effect on the CRH.