THE EXTRATROPICAL 40-DAY OSCILLATION IN THE UCLA GENERAL-CIRCULATION MODEL .2. SPATIAL STRUCTURE

Intraseasonal oscillations in a 3-yr, perpetual-January simulation are examined using a version of the UCLA GCM that produces no self-sustai ned Madden-Julian oscillation in the Tropics. A robust, 40-day oscilla tion is found to arise in the model's Northern Hemisphere (NH) extratr opics when standard topography is present. Part I of this study addres sed the zonally averaged component of the GCM oscillation, manifested in wind- and pressure-induced variations in atmospheric angular moment um (AAM). The focus here is on the spatial features of the oscillation as manifested in the variability of the 500-mb height field. A standi ng, wavenumber-two pattern is found in the NH extratropics, which unde rgoes tilted-trough vacillation in conjunction with the model's AAM os cillation. High (low) values of AAM are associated with low (high) 500 -mb heights over the northeast Pacific and Atlantic Oceans; the two ce nters' of action slightly different frequencies give rise to a long-pe riod modulation (of about 300 days) in the amplitude of the intraseaso nal oscillation. Global correlations with the leading empirical orthog onal functions of the NH extratropical 500-mb height field show northe ast-southwest teleconnection patterns extending into the Tropics, simi lar to those found in observational studies. The zonally averaged late nt heating in the Tropics exhibits no intraseasonal periodicity, but a 39-day oscillation is found in cumulus precipitation over the western Indian Ocean. The latter shows significant coherence with EOF 1 but i s absent in three shorter no-mountain experiments (see Part I), indica ting that it may be remotely forced by the intraseasonal oscillation t hat arises in the model's NH extratropics only in the standard-topogra phy experiment.