Geoscientific Model Development | 2019
Description and evaluation of NorESM1-F: a fast version of the Norwegian Earth System Model (NorESM)
Abstract
Abstract. A new computationally efficient version of the Norwegian Earth System Model\n(NorESM) is presented. This new version (here termed NorESM1-F) runs about\n2.5\xa0times faster (e.g., 90 model years per day on current hardware) than the\nversion that contributed to the fifth phase of the Coupled Model\nIntercomparison project (CMIP5), i.e., NorESM1-M, and is therefore\nparticularly suitable for multimillennial paleoclimate and carbon cycle\nsimulations or large ensemble simulations. The speed-up is primarily a result\nof using a prescribed atmosphere aerosol chemistry and a tripolar ocean–sea\nice horizontal grid configuration that allows an increase of the ocean–sea\nice component time steps. Ocean biogeochemistry can be activated for fully\ncoupled and semi-coupled carbon cycle applications. This paper describes the\nmodel and evaluates its performance using observations and NorESM1-M as\nbenchmarks. The evaluation emphasizes model stability, important large-scale\nfeatures in the ocean and sea ice components, internal variability in the\ncoupled system, and climate sensitivity. Simulation results from NorESM1-F in\ngeneral agree well with observational estimates and show evident\nimprovements over NorESM1-M, for example, in the strength of the meridional\noverturning circulation and sea ice simulation, both important metrics in\nsimulating past and future climates. Whereas NorESM1-M showed a slight global\ncool bias in the upper oceans, NorESM1-F exhibits a global warm bias. In\ngeneral, however, NorESM1-F has more similarities than dissimilarities\ncompared to NorESM1-M, and some biases and deficiencies known in NorESM1-M\nremain.