Theory and observations of the short‐period normal mode oscillations of the atmosphere

Abstract

Virtually all previous work on the subject of atmospheric normal modes has concentrated on the relatively long‐period Rossby modes, such as the familiar “5‐day” and “16‐day” waves. However, theory does predict the existence of shorter‐period Rossby‐gravity, Kelvin, and gravity modes. In the present investigation, long time series of hourly and 3‐hourly barometric observations from several tropical stations were employed in a search for these high‐frequency modes. Evidence was found for several spectral peaks that can be identified with various Rossby‐gravity, Kelvin, and gravity wave normal modes. Particularly prominent is the zonal wave number 1 Kelvin normal mode with a period of about 33 hours. This mode was found to undergo systematic seasonal and interannual variations. The theory of short‐period normal modes in the Martian atmosphere is also briefly examined. Such modes might be detectable in the surface pressure time series obtained in the Viking missions to Mars.