On type 3 auroral VHF coherent radar backscatter

Journal Article · Tue Mar 31 23:00:00 EST 1992 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA02829· OSTI ID:5368787

Haldoupis, C ^[1]; Schlegel, K; Nielsen, E ^[2]

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1. Univ. of Crete, Iraklion (Greece)
2. Max-Planck-Inst. fuer Aeronomie, Katlenburg-Lindau (West Germany)

Type 3 echoes of radar aurora relate to coherent backscatter signals with narrow power spectra peaking below ion acoustic Doppler speeds in the 100- to 300-m/s range and preferentially close to 200 m/s. The first observations, all made at 50 MHz, suggested that these echoes are due to electrostatic ion cyclotron (EIC) plasma waves generated at altitudes well above the electrojet where ions become magnetized. In the present paper, after a brief review of past studies and an update of the problem, the authors present new evidence of type 3 auroral scatter obtained at 140 MHz from cross-beam radar measurements made at optimum magnetic aspect angles. The observations do not favor the EIC mechanism, and they show that type 3 waves resemble in several ways in type 1 waves generated by the two-stream instability, e.g., they propagate in the same direction inside the same azimuthal sector at small angles to the electrojet E {times} B flow. This suggests a direct role for the ambient electric field in generating type 3 plasma waves as well. Further, type 3 and type 1 echoes can occur simultaneously over extended ionospheric areas and thus possibly originate at different altitudes. Prompted by the present results, the authors consider the option that type 3 echoes are simply due to type 1 waves originating in narrow sporadic E{sub s} layers located at lower electrojet altitudes, and they investigate the effect of both an enhanced mean ionic mass and a large destabilizing electron density gradient component on lowering the phase velocity well below typical ion acoustic speed values.

• OSTI ID: 5368787
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 97:A4; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAE
BACKSCATTERING
CYCLOTRON FREQUENCY
DRIFT INSTABILITY
E REGION
EARTH ATMOSPHERE
ELECTRIC FIELDS
ELECTRON DENSITY
INSTABILITY
ION WAVES
IONOSPHERE
MEASURING INSTRUMENTS
PLANETARY IONOSPHERES
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
PLASMA WAVES
RADAR
RANGE FINDERS
SCATTERING
SPORADIC E
TWO-STREAM INSTABILITY
WAVE PROPAGATION