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Volume 11, issue 1 | Copyright
Geosci. Model Dev., 11, 321-338, 2018
https://doi.org/10.5194/gmd-11-321-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Development and technical paper 23 Jan 2018

Development and technical paper | 23 Jan 2018

An interactive ocean surface albedo scheme (OSAv1.0): formulation and evaluation in ARPEGE-Climat (V6.1) and LMDZ (V5A)

Roland Séférian1, Sunghye Baek2,a, Olivier Boucher2, Jean-Louis Dufresne3, Bertrand Decharme1, David Saint-Martin1, and Romain Roehrig1 Roland Séférian et al.
  • 1Centre National de Recherches Météorologiques, Météo-France/CNRS, Toulouse, France
  • 2Institut Pierre-Simon Laplace, CNRS/UPMC, Paris, France
  • 3Laboratoire de Météorologie Dynamique, CNRS/UPMC, Paris, France
  • anow at: Korea Institute of Atmospheric Prediction Systems (KIAPS), Seoul, South Korea

Abstract. Ocean surface represents roughly 70% of the Earth's surface, playing a large role in the partitioning of the energy flow within the climate system. The ocean surface albedo (OSA) is an important parameter in this partitioning because it governs the amount of energy penetrating into the ocean or reflected towards space. The old OSA schemes in the ARPEGE-Climat and LMDZ models only resolve the latitudinal dependence in an ad hoc way without an accurate representation of the solar zenith angle dependence. Here, we propose a new interactive OSA scheme suited for Earth system models, which enables coupling between Earth system model components like surface ocean waves and marine biogeochemistry. This scheme resolves spectrally the various contributions of the surface for direct and diffuse solar radiation. The implementation of this scheme in two Earth system models leads to substantial improvements in simulated OSA. At the local scale, models using the interactive OSA scheme better replicate the day-to-day distribution of OSA derived from ground-based observations in contrast to old schemes. At global scale, the improved representation of OSA for diffuse radiation reduces model biases by up to 80% over the tropical oceans, reducing annual-mean model–data error in surface upwelling shortwave radiation by up to 7Wm−2 over this domain. The spatial correlation coefficient between modeled and observed OSA at monthly resolution has been increased from 0.1 to 0.8. Despite its complexity, this interactive OSA scheme is computationally efficient for enabling precise OSA calculation without penalizing the elapsed model time.

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This paper presents a new interactive scheme for ocean surface albedo suited for the current generation of Earth system models. This scheme computes the ocean surface albedo accounting for the spectral dependence (across a range of wavelengths between 200 and 4000 nm), the characteristics of incident solar radiation (direct of diffuse), the effects of surface winds, chlorophyll content and whitecaps in addition to the canonical solar zenith angle dependence.
This paper presents a new interactive scheme for ocean surface albedo suited for the current...
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