CLIMATE DRIFT IN A MULTICENTURY INTEGRATION OF THE NCAR-CLIMATE-SYSTEM-MODEL

The National Center for Atmospheric Research's Climate System Model is a comprehensive model of the physical climate system. A 300-yr integr ation of the model has been carried out without flux correction. The s olution shows very little drift in the surface temperature distributio n, set-ice extent, or atmospheric circulation. The lack of drift in th e surface climate is attributed to relatively good agreement in the es timates of meridional heat transport in the uncoupled ocean model and that implied by the uncoupled atmospheric model. On the other hand, th ere is significant drift in the temperature and salinity distributions of the deep ocean. The ocean loses heat at an area-averaged rate of 0 .35 W m(-2), the upper ocean becomes fresher, and the deep ocean becom es colder and saltier than in the uncoupled ocean model equilibrium or in observations. The cause of this drift is an unreasonably large mer idional transport of freshwater in the sea ice model, resulting in the production of excessively cold and salty Antarctic Bottom Water. Ther e is also significant drift in the Arctic basin, with the complete ero sion of the surface halocline early in the coupled integration.