Max Planck Institute Earth System Model (MPI-ESM1.2) for the High-Resolution Model Intercomparison Project (HighResMIP)

Abstract

As a contribution towards improving the climate mean state of the atmosphere and the ocean in Earth system models (ESMs), we compare several coupled simulations conducted with the Max Planck Institute for Meteorology Earth System Model (MPI-ESM1.2) following the High-ResMIP protocol. Our simulations allow to analyse the separate effects of increasing the horizontal resolution of the ocean (0.4 to 0.1 • ) and atmosphere (T127 to T255) submodels, and the effects of substituting the Pacanowski and Philander (PP) vertical ocean mixing scheme with the K-profile parameterization (KPP).The results show clearly distinguishable effects from all three factors. The high resolution in the ocean removes biases in the ocean interior and in the atmosphere. This leads to the important conclusion that a high-resolution ocean has a major impact on the mean state of the ocean and the atmosphere. The T255 atmosphere reduces the surface wind stress and improves ocean mixed layer depths in both hemispheres. The reduced wind forcing, in turn, slows the Antarctic Circumpolar Current (ACC), reducing it to observed values. In the North Atlantic, however, the reduced surface wind causes a weakening of the subpolar gyre and thus a slowing down of the Atlantic meridional overturning circulation (AMOC), when the PP scheme is used. The KPP scheme, on the other hand, causes stronger open-ocean convection which spins up the subpolar gyres, ultimately leading to a stronger and stable AMOC, even when coupled to the T255 atmosphere, thus retaining all the positive effects of a higher-resolved atmosphere.

Description of the resolution hierarchy of the global coupled HadGEM3-GC3.1 model as used in CMIP6 HighResMIP experiments

“…Hence, given a new protocol, together with model resolutions which range wider than those used in previous CMIP exercises, we need to assess the efficacy of this experimental design, finding its strengths and weaknesses, in addition to using it to assess the impact of model horizontal resolution. Similar assessments with other global climate models are ongoing and can be found in C. D. , Cherchi et al (2019), Voldoire et al (2019), Gutjahr et al (2019), Sidorenko et al (2019), Haarsma et al (2019) and Caldwell et al (2019).…”

“…The simulations described here follow the CMIP6 High-ResMIP protocol (Haarsma et al, 2016) in terms of the forcing datasets used. The spinup-1950 and control-1950 experiments ( Fig.…”

“…interactive aerosol schemes, Earth system components). CMIP6 HighResMIP (Haarsma et al, 2016) is a new experimental design that specifically focuses on assessing the impact of increased horizontal resolution on mean state biases, using model configurations designed for this purpose. The protocol encourages minimal model changes as resolution is increased, the use of a common, simplified aerosol optical property scheme (MACv2-SP; Stevens et al, 2017), as well as common initial conditions and other standard CMIP6 forcings (Eyring et al, 2016).…”

Assessment of the Finite-volumE Sea ice-Ocean Model (FESOM2.0) – Part 1: Description of selected key model elements and comparison to its predecessor version

“…With the increase of computational resources, the ocean modeling community aims at resolving the mesoscale eddies in the ocean by increasing resolution of computational grids. As discussed in Hallberg (2013), the resolution of two grid points per Rossby radius of deformation should be the target in the near future. Considering that the Rossby radius can be as small as a few kilometers in high latitudes and even less than 1 km in high-latitude shelf regions, the size of the computational grid needed to resolve mesoscales globally is far larger than those which are currently employed in climate models.…”

“…In order to appropriately simulate mesoscale eddies, the Rossby deformation radius needs to be resolved with several grid points (Hallberg, 2013). Sein et al (2017) introduced a mesh where the Rossby radius is resolved by two grid cells with the minimum resolution set to 4 km in the Northern Hemisphere and 7 km in the Southern Hemisphere (the mesh with ∼ 5.01 M surface vertices; Fig.…”