We explore the sensitivity of Southern Ocean surface and deep ocean
temperature and salinity biases in the FOCI coupled climate model to
atmosphere-ocean coupling time step and to lateral diffusion in the
ocean with the goal to reduce biases common to climate models.
The reference simulation suffers from a warm bias at the sea surface
which also extends down to the seafloor in the Southern Ocean and is
accompanied by a too fresh surface, in particular along the Antarctic
Reducing the atmosphere-ocean coupling time step from 3 hours to 1 hour
results in increased sea-ice production on the shelf and enhanced
melting to the north which reduces the fresh bias of the shelf water
while also strengthening the meridional density gradient favouring a
stronger Antarctic Circumpolar Current (ACC).
With the shorter coupling step we also find a stronger meridional
overturning circulation with more upwelling and downwelling south and
north of the ACC respectively, as well as a reduced warm bias at almost
Tuning the lateral ocean mixing has only a small effect on the model
biases, which contradicts previous studies using a similar model
We note that the latitude of the surface westerly wind maximum has a
northward bias in the reference simulation and that this bias is
unchanged as the surface temperature and sea-ice biases are reduced in
the coupled simulations.
Hence, the surface wind biases over the Southern Hemisphere midlatitudes
appear to be unrelated to biases in sea-surface conditions.