Influence of ocean-atmosphere interaction on the arctic oscillation in twogeneral circulation models

The influence of ocean-atmosphere interaction on the wintertime Arctic osci llation (AO) is investigated using a hierarchy of experiments made with two general circulation models (GCMs), ranging from climatologically forced at mospheric to fully coupled ocean-atmosphere GCMs with increasing greenhouse gas concentrations. Both GCMs reproduce well the AO spatial pattern, defined by the leading hem ispheric mode of monthly sea level pressure or daily 700-hPa geopotential h eight, although the North Pacific pole is more pronounced as compared with observations. Coupling is not found to influence this spatial pattern. Power spectra are examined for evidence of ocean-atmosphere interaction in the form of spectral reddening or significant spectral peaks. No measurable influence is found. On interannual timescales, all the model AO spectra ar e approximately "white,'' with no clear evidence of any statistically signi ficant spectral peaks in the coupled experiments. Greenhouse gas-induced ch anges in sea level pressure are found to project onto the AO in one of the GCMs but not the other. On subseasonal timescales, the spectra are "red'' i n all the model configurations, but ocean-atmosphere interaction is not fou nd to amplify the redness. Significant spectral peaks are found in the 15-2 5-day period range, consistent with observed spectra. Daily histograms of the simulated AO indices are found to be negatively ske wed. A Gaussian mixture model is used to estimate the probability density f unction of daily hemispheric height maps, and yields three circulation regi mes in both the simulations and observed data. The uncoupled atmospheric GC M simulations exhibit AO-like regimes that acquire stronger wavelike charac teristics in the coupled runs.