STOCHASTIC VARIABILITY AT THE AIR-SEA INTERFACE ON DECADAL TIMESCALES

Multiple integrations of an atmospheric general circulation model (AGC M) exhibit differences in the decadal mean of the surface heat flux, Q . The differences (typically 2-3 Wm(-2)) can be as large as 10 Wm(-2) in places, which are shown to produce sea-surface temperature (SST) ch anges up to approximately 0.5 degrees C in a hybrid coupled atmosphere /ocean/sea-ice model or HCM. This underscores a significant mechanism by which long-lived SST anomalies can arise, independent of any intern al ocean variability, for which there is very little predictive capabi lity. Consequently, AGCM integrations using prescribed SSTs provide up per bounds on the predictability of atmospheric variability. The HCM i s used to estimate the magnitude of the drift in the climatology of co upled models if flux adjustments are based on AGCM integrations of dec adal duration. The random interannual fluctuations in Q averaged over the ocean are most closely associated with fluctuations in surface lat ent heating and long wave radiation to space. The same fluctuations ar e not associated with land surface variability. The impact of variabil ity in other fluxes on SST in the HCM was also analysed. Changes due t o wind-stress were approximately half those due to heating, while chan ges due to freshwater forcing were relatively unimportant except at po lar latitudes.