A Wavenumber-Frequency Analysis of the 500 mb Geopotential at 50°N

Abstract

A space-time spectral analysis is applied to the daily 500 mb geopotential field (gridded along 50° N) of five winter seasons (1972–77). The results are displayed in the wavenumber-frequency domain as two-sided frequency spectra of meridional geostrophic wind and one-sided spectra of geopotential. They show three isolated spectral peaks: stationary ultralong waves (k = 1–4, p ≈ 25 days), and eastward propagating long (k = 5–6, p ≈ 10 days, c ≈ 6 m s−1) and short waves (k = 7–8, p = 4–6 days, c ≈ 10 m s−1). In the wave-number-frequency domain only the magnitudes of the peaks vary from one season to the other.