Conjugate observations of the mid-latitude electric field fluctuations with the MU radar and the Freja satellite

• Conjugate Freja satellite and MU radar observations were conducted from 1993 to 1995 to clarify the generation mechanism of mid-latitude electric field fluctuations (MEFs) which were found from DE-2 satellite observations. The detection of MEFs at higher altitudes than 1000 km by the Freja satellite confirms that the MEFs are transmitted along the geomagnetic held line without any significant damping. On one night of such conjugate observations, MEFs were observed in a traveling ionospheric disturbance (TID). On the other nights when the MEFs were observed by Freja, large scale density structures in the ionosphere were observed with the MU radar. Spread-F phenomena were also observed by ionosondes associated with these structures. The large scale modulation of the ionosphere, such as TIDs, might cause small scale modulations which grow through ionospheric instabilities. The linear growth rate is evaluated using a set of equations describing the growth of the mid-latitude ionospheric irregularities. The growth rate is shown to be too small under average conditions; however, when the neutral wind in TIDs is included, it is large enough to generate MEFs. (C) 1998 Elsevier Science Ltd. All rights reserved.

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NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

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