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

Abstract

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.

Presentation and Evaluation of the IPSL‐CM6A‐LR Ensemble of Extended Historical Simulations

“…The representation of clouds is described in Madeleine et al. (2020), while Hourdin, Rio, Jam, et al. (2020) linked the reduction in SST biases to improvements in atmospheric physics.…”

The Tuning Strategy of IPSL‐CM6A‐LR

“…A specific tuning of the effect of subgrid-scale orography was done targeting the northern mid and high latitude circulation (Gastineau, Mignot, Lott, & Hourdin, 2020). Thanks to parameterization improvements and a better tuning targeting the space and time distribution of Cloud Radiative Effect (CRE) at the top of the atmosphere, the clouds and radiative fluxes are much better represented in this new version (Madeleine et al, 2020). In particular, a modification of the boundary layer convective transport model to represent marine stratocumulus (Hourdin et al, 2019) allowed the reduction of Sea Surface Temperature (SST) warm biases in the Eastern part of tropical oceans (Hourdin, Rio, Jam, et al, 2020).…”

“…Some attempts were done as well to adjust the atmospheric radiation and clouds there. In particular, this aspect was looked at when adjusting the fraction of liquid and ice in clouds (Madeleine et al., 2020). However, the lack of reliable observations of surface fluxes over the Antarctic made this exercise somewhat limited.…”

“…Individual components of the model are described in separate publications for the continental surfaces (Cheruy et al., 2020) and for the atmosphere (Hourdin, Rio, Jam, et al., 2020). Specific contributions are dedicated to the representation of clouds (Madeleine et al., 2020), the impact of sub‐grid scale orography tuning on the simulation of northern high latitude climate (Gastineau, Mignot, Lott, & Hourdin, 2020) and the reduction of the Eastern Tropical oceans warm biases (Hourdin, Rio, Jam, et al., 2020). This study is devoted to the presentation of the 3‐year collective work and of the tuning strategy that led to the final IPSL‐CM6A‐LR model configuration.…”

Representation by two climate models of the dynamical and diabatic processes involved in the development of an explosively deepening cyclone during NAWDEX

“…This uncertainty lies in the location of the extratropical cyclones and the intensity and position of the storm track (e.g. McDonald, 2011;Zappa et al, 2013b) rather than in the total number of extratropical cyclones (e.g. Finnis et al, 2007;Bengtsson et al, 2009;Catto et al, 2011;Zappa et al, 2013b).…”