MODEL DESCRIPTION & PARAMETRIC CONFIGURATIONS: Linking Atmosphere-Only and Coupled Climate Simulations Through Perturbed Parameter Ensembles

Wave45 Parametric Configuration – IPSL-CM6.5.2 PPE Ensemble Publication for this dataset is under review Linking Atmosphere-Only and Coupled Climate Simulations Through Perturbed Parameter Ensembles B. S. Ferster1†,2, J. Mignot2, G. Gastineau2, F. Hourdin3, M. Coulon–Decorzens3, J. Deshayes2, G.Gachon2, J. Puyssegur2 1CECI-CERFACS (Université de Toulouse, CNRS, IRD), Toulouse, France. 2LOCEAN-IPSL (Sorbonne Université, CNRS, IRD, MNHN), Paris, France. 3LMD-IPSL, Sorbonne University, CNRS, Paris, France. This dataset contains the outputs of the Wave45 perturbed parameter ensemble (PPE) conducted with the IPSL coupled climate model IPSL-CM6.5.2, derived from the CMIP6 IPSL-CM6A-LR configuration (Boucher et al., 2020) with updated ocean and sea-ice components and minor bug corrections. The ensemble is designed to explore structural and parametric uncertainty in coupled climate simulations using a constrained subset of physically relevant parameters obtained through iterative history matching. Model configuration The coupled model consists of the following components: Atmosphere: LMDZ6 (Hourdin et al., 2020) Land surface: ORCHIDEE (Krinner et al., 2005) Ocean: NEMO v4.2 (Madec et al., 2022) Sea ice: SI3 (Vancoppenolle et al., 2023) The atmospheric grid has a horizontal resolution of 144 × 143 points (≈2.5° × 1.25°) with 79 vertical levels up to ~80 km. The ocean uses the ORCA1 tripolar grid (~1° nominal resolution) with 75 vertical levels. The land model shares the atmospheric grid and includes 11 hydrological soil layers (2 m depth) with a deeper thermal diffusion extension to 90 m. All simulations are forced with fixed CMIP6 year-2000 greenhouse gas and aerosol concentrations. Experimental design The Wave45 ensemble is part of a perturbed parameter ensemble (PPE) framework constructed using a history-matching and iterative refocusing approach (implemented via HighTune Explorer; building from Hourdin et al., 2023). The full parameter exploration is based on 12 free parameters spanning atmosphere, land, ocean, and sea ice processes (P1–P12). These include: Cloud microphysics and convection parameters (P1–P5) Boundary layer and orographic drag (P4–P6) Land surface hydrology and snow albedo (P7–P8) Sea ice albedo and thermal properties (P9–P10) Upper ocean mixing processes (P11–P12) These parameters are selected based on their known or suspected influence on climate sensitivity, radiation balance, and atmosphere–ocean coupling. Wave45 selection The Wave45 ensemble corresponds to 45 parameter combinations selected from the final Not Ruled Out Yet (NROY) parameter space after iterative history matching with HighTune. These parameter vectors represent a constrained subset of physically plausible model states consistent with observed climate metrics and emulator-based filtering. Each simulation in Wave45 uses a unique parameter vector applied consistently across the atmosphere-only and coupled model components, found within the attached wave45_params.txt. Reproducibility To reproduce this ensemble, users should: Obtain IPSL-CM6.5.2 model code (LMDZ6–ORCHIDEE–NEMO–SI3 coupled system) Apply the 12-dimensional parameter vectors corresponding to the Wave45 NROY subset for both the LMDZOR and IPSLCM6 models Run 2 years of LMDZOR and 20 of IPSLCM6 for analysis The parameter space and selection procedure follow the iterative history matching framework described in Hourdin et al. (2023) and related references. Data access The original full model outputs are stored on TGCC Irene and can be accessed upon request, as it exceeds the 50 gb maximum of the repository. Contact For questions or requests: [e-mail] / [e-mail]