Evidence of Global-Scale 5-Day Waves in a 73-Year Pressure Record

Abstract

A 73-year record of sea-level pressure is examined for evidence of the m=1,n=2 planetary wave or wave of the second class, theoretically predicted by Laplace's tidal equations. Coherence squares and phase angles based on cross spectra averaged over 72 summers provide evidence of a westward propagating, 5-day disturbance, which are features expected for the wave. Coherence squares, estimated for the corresponding winter seasons show no similarly strong evidence. Because of likely changes in the ?Signal-to-noise? ratio from summer to winter, only a tentative conclusion is drawn about possible seasonal variations in the amplitude of the wave. Although questions arise concerning the stationarity over the 73 years of the means and of the spectral characteristics of the data, statistically significant evidence of the 5-day wave is shown to be present throughout.