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The possibility of supersonic plasma flow in a collapsing post-sunset ionosphere.As a result of the rapidly decreasing pressure in the topside ionosphere during twilight hours, a rapid downward flow of hydrogen plasma from the protonosphere takes place. In the case of steady state, isothermal, frictionless flow, the criterion for the existence of a critical point (transition to supersonic flow) above 1000 km is that the plasma temperature be lower than a certain limiting temperature which is a function of the field line considered. In the latitude region between 40 and 70 deg, this upper temperature limit varies from 963 to 1066 K. Since these temperatures are considerably lower than the observed temperatures, it follows that in the case of steady state, isothermal flow the velocities will always remain subsonic. When the effect of the neglected terms is examined, the temperature gradient is shown to exert the strongest influence on the nature of the flow. It is concluded that there is a definite possibility that supersonic downward flows in a post-sunset topside ionosphere may occur.
Document ID
19720035233
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Fontheim, E. G.
(Michigan, University Ann Arbor, Mich., United States)
Banks, P. M.
(California, University La Jolla, Calif., United States)
Date Acquired
August 6, 2013
Publication Date
January 1, 1972
Publication Information
Publication: Planetary and Space Science
Volume: 20
Subject Category
Geophysics
Accession Number
72A18899
Funding Number(s)
CONTRACT_GRANT: NGR-23-005-015
CONTRACT_GRANT: NGR-05-009-075
Distribution Limits
Public
Copyright
Other

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