An interactive atmosphere-ocean instability mechanism that reproduces some
salient properties of the observed Antarctic Circumpolar Wave and also its
manifestation in the Commonwealth Scientific and Industrial Research Organi
sation (CSIRO) Mark 2 coupled model is analyzed with a more complete treatm
ent than that studied by others. It is suggested that this interaction mech
anism is important in maintaining this phenomenon in both the model and the
real atmosphere-ocean but is not strong enough to initiate it. Through use
of a simple model consisting of a zonally periodic midlatitude beta plane
with a uniform mean north-south temperature gradient, a barotropic atmosphe
re, and a two-layer ocean with an inactive lower layer, the stability of un
iform zonal flow to small perturbations was analyzed. The perturbation equa
tions describe the velocity and temperature fields in both the atmospheric
and oceanic layers and include the exchange in momentum and heat between th
em by surface fluxes. The interaction occurs between long (most notably wav
enumbers 2 and 3) barotropic Rossby waves in the atmosphere forced by surfa
ce heat flux from the ocean and similarly long waves in the upper layer of
the ocean forced by the wind stress curl. Growth times are long-on the orde
r of several decades-indicating that modes can be sustained by the interact
ion process but that they may need to be energized by other mechanisms to r
each realistic amplitudes in a reasonable time.