A robust feature of transient greenhouse-gas increase integrations of the GFDL coupled ocean-atmosphere general circulation model is a significant lag in the lower-tropospheric global-warming in the Southern Hemisphere, as compared to the Northern Hemisphere. This lag is attributable to oceanic heat-storage and vertical-mixing effects. There is also a difference between the meridional distributions of warming in the two hemispheres that is of dynamical interest. In the Northern Hemisphere, the warming increases with latitude and as a result the magnitude of the northern-hemispheric lower tropospheric meridional temperature gradient is reduced. By contrast, the Southern Hemisphere warming seems to take place in two stages. At an early stage, the Southern Hemisphere lag in warming is most pronounced over the latitudes of the Southern Oceans, 50S to 70S, so that the lower-tropospheric baroclinicity between these latitudes and the tropics is increased. At a later stage, a transition to a distribution with a local maximum in warming occurs over the Southern Oceans,
leading to a more complicated pattern of baroclinicity.
This paper examines the extratropical atmospheric response to these large-scale changes in the Southern Hemisphere near-surface emperatures. In one transient greenhouse-gas increase integration of the R30 model, at the early stage referred to above, accompanying the changed baroclinicity pattern is a poleward shift and strengthening of the westerlies over the Southern Oceans that extends from the surface to the upper troposphere, with a maximum at the tropopause. At the later stage, the westerlies shift back and weaken. Changes to the eddy
circulation statistics also occur: there is an upward displacement of the upper-tropospheric eddy kinetic energy maximum, a shift in the eddy momentum flux consistent with the displacement of the surface westerlies, and a significant weakening of the poleward heat flux. The paper will focus on the extent to which these circulation changes can be modeled as forcings of internal dynamical modes of variability, and the role of coupling to the wind-driven ocean circulation in driving or supressing these signals.