The North American monsoon system in the Hadley Centre coupled ocean-atmosphere GCM

The North American monsoon system (NAMS) as represented in the second-gener ation Hadley Centre coupled ocean-atmosphere model is examined using high-t ime-resolution (six-hourly) records of model output. A current-climate simu lation gives a realistic depiction of the NAMS, with date of onset and prec ipitation trends agreeing with observations. The model reproduces the obser ved negative relationship between precipitation over the southwestern U.S. and that over the central U.S. Changes in tropospheric circulation and mois ture after onset are consistent with observed changes although mid-level mo istening is less than is observed.: An enhanced greenhouse-gas simulation g ives higher precipitation and stronger tropospheric dynamical and moisture changes after onset.