  A new framework is proposed for the evaluation of stochastic subgrid-scale
parameterizations in the context of MAOOAM, a coupled ocean-atmosphere model of
intermediate complexity. Two physically-based parameterizations are
investigated, the first one based on the singular perturbation of Markov
operator, also known as homogenization. The second one is a recently proposed
parameterization based on the Ruelle's response theory. The two
parameterization are implemented in a rigorous way, assuming however that the
unresolved scale relevant statistics are Gaussian. They are extensively tested
for a low-order version known to exhibit low-frequency variability, and some
preliminary results are obtained for an intermediate-order version. Several
different configurations of the resolved-unresolved scale separations are then
considered. Both parameterizations show remarkable performances in correcting
the impact of model errors, being even able to change the modality of the
probability distributions. Their respective limitations are also discussed.
