## MOMB20 Figure Caption

Snapshot of the temperature field (red is warm ~25°C, blue is cold ~2°C)
after 600 years of integration of a primitive equation ocean model
(the GFDL Modular Ocean Model) at fairly high resolution (20 km).

One can easily picture the turbulent nature of the field, with mushroom-like
structures and isolated vortices. In fact, even with no wind forcing, the
circulation is almost as turbulent as the real ocean (as measured by
turbulent kinetic energy or sea surface height variations).

Apart from this mesoscale turbulence, the model produces large-amplitude
interdecadal variations of the meridional overturning (the thermohaline
circulation). That was in fact the scientific rationale for these experiments,
since such long-term oscillations were found at low resolution (160 km
horizontal grid spacing) and explained as driven by unstable planetary waves.
This longwave baroclinic instability relies on large eddy-mixing, such that
its interactions with the most energetic traditional mesoscale baroclinic
instability was not straightforward.

The domain geometry is a Cartesian beta-plane centered at 40°N,
extending from 20°N to 60°N (4470 km), 5120 km wide, 4500 m deep.
The forcing is purely thermal, consisting of prescribed zonally-uniform
surface heat flux linearly varying with latitude from +45 W/m² at 20°N to
-45 W/m² at 60°N.
Sub-grid-scale parameterizations are uniform, with biharmonic diffusion
of momentum and tracer on the horizontal (4 10^{10} m^4/s), and standard
eddy-difusivity on the vertical (10^{-4} m²/s for temperature and
10^{-3} m²/s for momentum).
The model was initialized at year 0 by an interpolation of a 40-km-resolution
previous 1000-yr run, itself initialized from a 3000-yr 80-km-resolution run,
itself initialized from a 6000-yr 160-km run, such that the thermohaline
circulation can be safely considered as statiscally stationnary.
**References**

Huck, T., 1997: Modélisation de la circulation thermohaline: Analyse de sa
variabilité interdécennale. Thèse de doctorat, Université de Bretagne
Occidentale, Brest, France, 250 p.
Huck, T., G. K. Vallis, and A. Colin de Verdière, 2001: On the robustness
of the interdecadal modes of the thermohaline circulation.
*Journal of Climate*, **14**, 940-963.