GLOBAL AND REGIONAL VARIABILITY IN A COUPLED AOGCM

The variability of near surface temperature on global and regional spa tial scales and interannual time scales from a 1000 year control integ ration of the Hadley Centre coupled model (HADCM2-CTL) are compared wi th the observational record of surface temperature. The model succeeds in reproducing the observed patterns of natural variability, with hig h variability over the northern continents and low variability over mu ch of the tropics. The model global mean variability has similar stren gth to observed global mean variability on time scales less than 20 ye ars. The warming seen in the historical record is outside the range of natural variability as simulated in HADCM2-CTL. The model has El-Nino /Southern Oscillation (ENSO)-like behaviour with a central Pacific, pe ak to peak? strength of approximately 3 K. Changes in near surface tem perature in the central Pacific are strongly correlated with changes i n near surface temperature over most of the tropics, large regions of the extra-tropics and changes in tropical ocean upper 250 m heat conte nt. Tropospheric temperature changes and tropical surface pressure cha nges are also strongly correlated with changes in the central Pacific surface temperature. Oceanic regions show significant departures from an AR1 or first order Markov behaviour in the Northwest Atlantic, Nort hwest Pacific and Arctic oceans. The Northwest Atlantic region has lar ge amounts of variability over periods greater than 50 years. This var iability is associated with a jump in the strength of North Atlantic m eridional stream function. The spectra of the Western European and Con tinental US land regions are not significantly different from an AR1 p rocess. The flow through the Drake Passage has an interannual standard deviation of approximately 2.5 Sv with significant departures from an AR1 process at time scales greater than 40 years. Winter northern hem ispheric 500 hPa geopotential height shows some evidence of multiple r egimes but no year to year persistence of these regimes.