UK Global Ocean GO6 and GO7: a traceable hierarchy of model resolutions

Versions 6 and 7 of the UK Global Ocean configuration (known as GO6 and GO7) will form the ocean components of the Met Office GC3.1 coupled model and UKESM1 earth system model to be used in CMIP6note-anchorfna_Ch1.Footn1#fn_Ch1.Footn1¹ simulations. The label “GO6” refers to a traceable hierarchy of three model configurations at nominal inline-formula1, inline-formula1∕4 and inline-formula $M3inlinescrollmathml\mathrm{normal\; 1}/{\mathrm{normal\; 12}}^{\circ }$ 31pt14ptsvg-formulamathimg52d83408a281a6be147fb692aa06146b gmd-11-3187-2018-ie00001.svg31pt14ptgmd-11-3187-2018-ie00001.png resolutions. The GO6 configurations are described in detail with particular focus on aspects which have been updated since the previous version (GO5). Results of 30-year forced ocean-ice integrations with the inline-formula $M4inlinescrollmathml\mathrm{normal\; 1}/{\mathrm{normal\; 4}}^{\circ }$ 25pt14ptsvg-formulamathimg1336b0c128a3cdfeedc0b3d16a0bf247 gmd-11-3187-2018-ie00002.svg25pt14ptgmd-11-3187-2018-ie00002.png model are presented, in which GO6 is coupled to the GSI8.1 sea ice configuration and forced with CORE2note-anchorfna_Ch1.Footn2#fn_Ch1.Footn2² fluxes. GO6-GSI8.1 shows an overall improved simulation compared to GO5-GSI5.0, especially in the Southern Ocean where there are more realistic summertime mixed layer depths, a reduced near-surface warm and saline biases, and an improved simulation of sea ice. The main drivers of the improvements in the Southern Ocean simulation are tuning of the vertical and isopycnal mixing parameters. Selected results from the full hierarchy of three resolutions are shown. Although the same forcing is applied, the three models show large-scale differences in the near-surface circulation and in the short-term adjustment of the overturning circulation. The GO7 configuration is identical to the GO6 inline-formula $M5inlinescrollmathml\mathrm{normal\; 1}/{\mathrm{normal\; 4}}^{\circ }$ 25pt14ptsvg-formulamathimgb3e7aebd1bc2e8d9f3c98042acad90ea gmd-11-3187-2018-ie00003.svg25pt14ptgmd-11-3187-2018-ie00003.png configuration except that the cavities under the ice shelves are opened. Opening the ice shelf cavities has a local impact on temperature and salinity biases on the Antarctic shelf with some improvement in the biases in the Weddell Sea.