  This paper describes a reduced-order quasi-geostrophic coupled
ocean-atmosphere model that allows for an arbitrary number of atmospheric and
oceanic modes to be retained in the spectral decomposition. The modularity of
this new model allows one to easily modify the model physics. Using this new
model, coined the "Modular Arbitrary-Order Ocean-Atmosphere Model" (MAOOAM), we
analyse the dependence of the model dynamics on the truncation level of the
spectral expansion, and unveil spurious behaviour that may exist at low
resolution by a comparison with the higher-resolution configurations. In
particular, we assess the robustness of the coupled low-frequency variability
when the number of modes is increased. An "optimal" configuration is proposed
for which the ocean resolution is sufficiently high, while the total number of
modes is small enough to allow for a tractable and extensive analysis of the
dynamics.
