Large-amplitude traveling ionospheric distrubance produced by the May 18, 1980, explosion of Mount St. Helens
A remarkable long-lived, large-scale traveling ionospheric disturbance (TID), excited by the May 18, 1980, explosion of Mount St. Helens, has been detected in total electron content monitor data. Oscillatory perturbations in the electron column density of the ionosphere with amplitudes about 10% of the nominal daytime content were detected at three stations whose ionospheric penetration points lie between 1610 and 1890 km from Mount St. Helens. Smaller perturbations were detected at five of six additional stations between 3760 and 4950 km away. The period of the TID increased linearly with great-circle distance from Mount St. Helens, ranging from roughly-equal37 min at the nearest station to roughly-equal116 min at the most distant one. The TID persisted for at least four cycles at the three close stations and three cycles at the more distant stations and was qualitatively similar to TID's produced by the low-altitude thermonuclear detonations of the 1960's. The disturbance front of this TID accelerated from an average velocity of roughly-equal350 m/s between Mt. St. Helens and the close stations to an average velocity of roughly-equal550 m/s to the more distant ones.A model based on the free wave response of an isothermal atmosphere to a point disturbance provides a good fit to the data at the three closest stations, but no such model can account for all of the data. Modeling of the long-distance behavior of the Mount St. Helens TID in terms of upper-atmosphere guided gravity waves is complicated by the requirement of exciting them by a ground-level explosion. There was no evidence for a strong supersonic shock wave in the ionosphere. As a result, the Mount St. Helens disturbance may prove to be a cleaner test of detailed theories of the point excitation and propagation of gravity waves in a realistic atmosphere than were TID's excited by thermonuclear weapons.
- Research Organization:
- Physics Department, Brandeis University, Waltham, Massachusetts 02254
- OSTI ID:
- 7063313
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:A8
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MT ST HELENS
TRAVELLING IONOSPHERIC DISTURBANCE
ELECTRON DENSITY
ERUPTION
GRAVITY WAVES
VOLCANOES
WAVE PROPAGATION
CASCADE MOUNTAINS
DISTURBANCES
FEDERAL REGION X
IONOSPHERIC STORMS
MOUNTAINS
NORTH AMERICA
USA
WASHINGTON
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena