UNSPECIFIED (2000) Plasma sounding at the upper hybrid frequency. JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 105 (A6). pp. 13103-13117. ISSN 0148-0227

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Abstract

A sounder measures the density of plasmas in various parts of the solar system. The sounder emits wave pulses into the ambient plasma and listens to the response. Intensity peaks in the wave response are typically related to two mechanisms. One is provided by waves that are reflected off plasma inhomogeneities and propagate back to the emitting antenna, where they are then detected. The second is provided by waves propagating with the same group velocity as that of the receiving antenna. In the second case the waves stay close to the antenna and thus yield a long-lasting response. Response peaks to sounding at the upper hybrid (UH) frequency have, in most cases, been related to reflected waves. In this work we examine if accompanying waves can give rise to the UH response peak. We examine quantitatively how the plasma response to sounding at the UH frequency depends on the plasma density, on the electron temperature, and on the emission amplitude. For the first two parameters this is done by solving the linear dispersion relation. The well-known property of the UH waves to change from having a zero group velocity to propagating waves, depending on how the electron density compares to the electron cyclotron frequency, is applied to Alouette sounder data. It is discussed how the change in the group velocity may affect the spectral profile of the UH resonance. We present results from numerical particle in cell (PIC) simulations which show that in the case of nonpropagating UH waves, energy can be coupled into the plasma even though the vanishing group velocity of the UH waves should not allow this. The PIC simulations and sounder data from the Alouette mission show that in the case of propagating UH waves the response duration to sounding may be used to determine the electron temperature. Emission amplitudes that are typical for plasma sounders are also shown to suppress the generation of certain electron cyclotron harmonic waves.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Journal or Publication Title:	JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Publisher:	AMER GEOPHYSICAL UNION
ISSN:	0148-0227
Date:	1 June 2000
Volume:	105
Number:	A6
Number of Pages:	15
Page Range:	pp. 13103-13117
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/13343

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