Abstract. This paper presents global comparisons of fundamental global
climate variables from a suite of four pairs of matched low- and
high-resolution ocean and sea ice simulations that are obtained following
the OMIP-2 protocol (Griffies et al., 2016) and integrated for one cycle
(1958–2018) of the JRA55-do atmospheric state and runoff dataset (Tsujino et
al., 2018). Our goal is to assess the robustness of climate-relevant
improvements in ocean simulations (mean and variability) associated with
moving from coarse (∼ 1∘) to eddy-resolving
(∼ 0.1∘) horizontal resolutions. The models
are diverse in their numerics and parameterizations, but each low-resolution
and high-resolution pair of models is matched so as to isolate, to the
extent possible, the effects of horizontal resolution. A variety of
observational datasets are used to assess the fidelity of simulated
temperature and salinity, sea surface height, kinetic energy, heat and
volume transports, and sea ice distribution. This paper provides a crucial
benchmark for future studies comparing and improving different schemes in
any of the models used in this study or similar ones. The biases in the
low-resolution simulations are familiar, and their gross features –
position, strength, and variability of western boundary currents, equatorial
currents, and the Antarctic Circumpolar Current – are significantly improved in
the high-resolution models. However, despite the fact that the
high-resolution models “resolve” most of these features, the improvements
in temperature and salinity are inconsistent among the different model
families, and some regions show increased bias over their low-resolution
counterparts. Greatly enhanced horizontal resolution does not deliver
unambiguous bias improvement in all regions for all models.