GCM simulations of intraseasonal variability in the Pacific/North American region

• Published in: Journal of the atmospheric sciences 1993-07, Vol.50 (13), p.1991-2007
• Main Authors: Schubert, Siegfried, Suarez, Max, Park, Chung-Kyu, Moorthi, Shrinivas
• Format: Article
• Language: English
• Subjects: Atmosphere; Climate; Earth, ocean, space; Exact sciences and technology; External geophysics; General circulation. Atmospheric waves; Marine; Meteorology; Meteorology And Climatology; Wind
• ISSN: 0022-4928; 1520-0469
• DOI: 10.1175/1520-0469(1993)050<1991:GSOIVI>2.0.CO;2

General circulation model (GCM) simulations of low-frequency variability with time scales of 20 to 70 days are analyzed for the Pacific sector during boreal winter. The GCM's leading mode in the upper-tropospheric zonal wind is associated with fluctuations of the East Asian jet; this mode resembles, in both structure and amplitude, the Pacific/North American (PNA) pattern found in the observations on these time scales. In both the model and observations, the PNA anomaly is characterized by: (1) a linear balance in the upper-tropospheric vorticity budget with no significant Rossby wave source in the tropics, (2) a barotropic conversion of kinetic energy from the time mean Pacific jet, and (3) a north/south displacement of the Pacific storm track. In the GCM, the latter is associated with synoptic eddy heat flux and latent heat anomalies that appear to contribute to a strong lower-tropospheric source of wave activity over the North Pacific. This is in contrast to the observations, which show only a weak source of wave activity in this region.