Zonal-Wind Oscillations over the Western Hemisphere during Winter: Further Evidence of a Zonal-Eddy Relationship

Abstract

Abstract The European Centre for Medium-Range Weather Forecasts (ECMWF) 500-mb height analyses and 7-day forecasts are examined during ten winters (1981–90) for oscillations of geostrophic zonal wind over the western hemisphere. A well-defined zonal-wind oscillation is isolated in the first two eigenvectors. This zonal-wind oscillation accounts for about 55% of the total zonal-wind variance over the western hemisphere during this ten-winter period. The oscillation is characterized by zonal-wind anomalies that are in phase between 30° and 70°N and out of phase with zonal-wind anomalies along 50°N. The oscillation clearly displays southward propagation from 85° through 30°N, with standing components along 30°, 50°, and 70°N. The dominant temporal period associated with the oscillation is found to be in the range of 15–35 days with large interannual variability. Composites of 500-mb heights through 25 cycles of zonal-wind oscillations over ten winters were performed for unfiltered and 15–39-day filtered data...