Improved Representation of Clouds in the Atmospheric Component LMDZ6A of the IPSL-CM6A Earth System Model

Madeleine, Jean-Baptiste ; Hourdin, Frédéric ; Grandpeix, Jean-Yves ; Rio, Catherine ; Dufresne, Jean-Louis ; Vignon, Etienne ; Boucher, Olivier ; Konsta, Dimitra ; Cheruy, Frédérique ; Musat, Ionela ; Idelkadi, Abderrahmane ; Fairhead, Laurent ; Millour, Ehouarn ; Lefebvre, Marie-Pierre ; Mellul, Lidia ; Rochetin, Nicolas ; Lemonnier, Florentin ; Touzé-Peiffer, Ludovic ; Bonazzola, Marine

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<p align=justify>The cloud parameterizations of the LMDZ6A climate model (the atmospheric component of the IPSL-CM6 Earth system model) are entirely described, and the global cloud distribution and cloud radiative effects are evaluated against the CALIPSO-CloudSat and CERES observations. The cloud parameterizations in recent versions of LMDZ favor an object-oriented approach for convection, with two distinct parameterizations for shallow and deep convection and a coupling between convection and cloud description through the specification of the subgrid-scale distribution of water. Compared to the previous version of the model (LMDZ5A), LMDZ6A better represents the low-level cloud distribution in the tropical belt, and low-level cloud reflectance and cover are closer to the PARASOL and CALIPSO-GOCCP observations. Mid-level clouds, which were mostly missing in LMDZ5A, are now better represented globally. The distribution of cloud liquid and ice in mixed-phase clouds is also in better agreement with the observations. Among identified deficiencies, low-level cloud covers are too high in mid-latitude to high-latitude regions, and high-level cloud covers are biased low globally. However, the cloud global distribution is significantly improved, and progress has been made in the tuning of the model, resulting in a radiative balance in close agreement with the CERES observations. Improved tuning also revealed structural biases in LMDZ6A, which are currently being addressed through a series of new physical and radiative parameterizations for the next version of LMDZ.</p>
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