We present evidence that shows some aspects of the global atmospheric dynamic responses to the eruption of Mount St. Helens on May 18, 1980. Although events such as volcanic eruptions may excite a number of acoustic‐gravity wave modes in the atmosphere, the observed surface pressure perturbations and distant ionospheric perturbations can be explained only in terms of propagation of Lamb modes with a horizontal propagation velocity slightly above 300 m/s. Results from model computations show good agreements with the observational data. Ground level pressure perturbations created by this event are only slightly smaller than those created by the historical Great Siberian Meteor.

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Previous attempts to detect Eclipse-induced acoustic gravity waves (AGWs) have met with varying degrees of success. In this study the speed and direction of the waves have been determined at two widely spaced locations by an HF Doppler technique. The AGW activity following the eclipse was different to the background waves detected before the event in amplitude, speed and direction. The velocity vectors are consistent with a generating mechanism for the waves based on the supersonic passage of the cooled region of the atmosphere during the eclipse.

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