AWI-CM3 coupled climate model: description and evaluation experiments for a prototype post-CMIP6 model

Abstract

Abstract. We developed a new version of the Alfred Wegener Institute Climate Model (AWI-CM3), which has higher skills in representing the observed climatology and better computational efficiency than its predecessors. Its ocean component FESOM2 (Finite-volumE Sea ice–Ocean Model) has the multi-resolution functionality typical of unstructured-mesh models while still featuring a scalability and efficiency similar to regular-grid models. The atmospheric component OpenIFS (CY43R3) enables the use of the latest developments in the numerical-weather-prediction community in climate sciences. In this paper we describe the coupling of the model components and evaluate the model performance on a variable-resolution (25–125 km) ocean mesh and a 61 km atmosphere grid, which serves as a reference and starting point for other ongoing research activities with AWI-CM3. This includes the exploration of high and variable resolution and the development of a full Earth system model as well as the creation of a new sea ice prediction system. At this early development stage and with the given coarse to medium resolutions, the model already features above-CMIP6-average skills (where CMIP6 denotes Coupled Model Intercomparison Project phase 6) in representing the climatology and competitive model throughput. Finally we identify remaining biases and suggest further improvements to be made to the model.

Multi-year simulations at kilometre scale with the Integrated Forecasting System coupled to FESOM2.5/NEMOv3.4

“…After the initialization, the pan-hemispheric sea ice model performance is similar for the three configurations, and attributing the error differences to the use of different model resolution or complexity is not obvious, confirming previous findings (e.g., Streffing et al 2022;Selivanova et al, 2023). Overall, the model errors for the first year of simulations are in line with state-of-the-art seasonal prediction systems (Johnson et al 2019;Mu et al 2020;Mu et al 2022),…”

East Asian summer precipitation in AWI‐CM3: Comparison with observations and CMIP6 models

“…Besides the uncertainty from the comparison between the equilibrium simulation and the transient observation and CMIP6 results, we could not run the high‐resolution AWI‐CM3 simulations for enough model years as the typical CMIP6 simulations to fully reach equilibrium states, which also induces uncertainties to this study. Despite those, Streffing et al (2022) showed that the AWI‐CM3 transient simulation with TCo159 already outperforms CMIP6 in many large‐scale climatologies, and features above CMIP6‐average skills. We here confirm this conclusion for specific aspects of more regional climate (i.e., the East Asian precipitation), although model setups different from those employed by Streffing et al (2022) are applied.…”

“…Despite those, Streffing et al (2022) showed that the AWI‐CM3 transient simulation with TCo159 already outperforms CMIP6 in many large‐scale climatologies, and features above CMIP6‐average skills. We here confirm this conclusion for specific aspects of more regional climate (i.e., the East Asian precipitation), although model setups different from those employed by Streffing et al (2022) are applied. Furthermore, we conclude that employing AWI‐CM3 at a higher spatial resolution of the atmosphere model indeed improves the simulation of the EAP.…”

“…The AWI-CM3 consists of two major components: the atmosphere module is the global Integrated Forecasting System (IFS) in the version OpenIFS (version 43R3V1;ECMWF, 2017aECMWF, , 2017bECMWF, , 2017c developed at the European Centre for Medium-Range Weather Forecast, and the ocean module is the second version of the Alfred Wegener Institute's global ocean model, the Finite volumE Sea ice-Ocean Model (FESOM2) with unstructured meshes (Danilov et al, 2017). The OpenIFS has a superior computational efficiency owing to its semi-Lagrangian semi-implicit advection scheme, allowing for advection distances beyond the Courant-Friedrichs-Lewy condition, and is consequently numerically stable at much longer time steps than equivalent Eulerian integrations, which enables us to run high-resolution simulations with affordable computational resources (Streffing et al, 2022).…”

“…Here, we employ the third generation of climate model developed at the Alfred Wegener Institute (AWI‐CM3) introduced by Streffing et al (2022) and evaluate its simulation of the climatological summer EAP for a modern climate state against observations and the ensemble of CMIP6 models. Streffing et al (2022) has shown that, from the viewpoint of reproduction of observed global climatology, the AWI‐CM3 has higher skill than the average of the models that participated in CMIP6. The influence of horizontal resolution was analysed for its atmosphere model on systematic errors, cloud radiative forcing and extratropical cyclone characteristics (Jung et al, 2006; Potter, 1995; Tibaldi et al, 1990).…”