Global and regional variability in a coupled AOGCM |
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| Authors: | S F B Tett T C Johns J F B Mitchell |
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| Institution: | (1) Hadley Centre for Climate Prediction and Research, UK Meteorological Office, London Road, Bracknell, Berkshire RG12 2SY, UK, GB |
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| Abstract: | The variability of near surface temperature on global and regional spatial scales and interannual time scales from a 1000
year control integration of the Hadley Centre coupled model (HADCM2-CTL) are compared with the observational record of surface
temperature. The model succeeds in reproducing the observed patterns of natural variability, with high variability over the
northern continents and low variability over much of the tropics. The model global mean variability has similar strength to
observed global mean variability on time scales less than 20 years. The warming seen in the historical record is outside the
range of natural variability as simulated in HADCM2-CTL. The model has El-Ni?o/Southern Oscillation (ENSO)-like behaviour
with a central Pacific, peak to peak, strength of approximately 3 K. Changes in near surface temperature in the central Pacific
are strongly correlated with changes in near surface temperature over most of the tropics, large regions of the extra-tropics
and changes in tropical ocean upper 250 m heat content. Tropospheric temperature changes and tropical surface pressure changes
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, Northwest Pacific and Arctic oceans. The Northwest
Atlantic region has large amounts of variability over periods greater than 50 years. This variability is associated with a
jump in the strength of North Atlantic meridional stream function. The spectra of the Western European and Continental US
land regions are not significantly different from an AR1 process. 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 hemispheric 500 hPa geopotential height shows some evidence of multiple regimes but no year to year persistence of
these regimes.
Received: 31 January 1996/Accepted: 22 July 1996 |
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