Physics
Scientific paper
May 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986jgr....91.5755h&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 91, May 1, 1986, p. 5755-5767. NSERC-supported research.
Physics
28
E Region, Ion Acoustic Waves, Plasma Waves, Polar Regions, Angular Distribution, Auroral Echoes, Doppler Effect, Radio Auroras, Summer
Scientific paper
A series of 50-MHz Doppler experiments have been performed during three consecutive summers to investigate auroral backscatter properties at different magnetic aspect angles ranging from about 1 degree to 14 degrees. The large data base is used to study a particular class of echoes, namely the ion acoustic-type echoes. In the present understanding of radio aurora, this category of scatter, with characteristics reminiscent of equatorial type 1 echoes, is attributed to electrostatic plasma waves generated by the Farley-Buneman instability. The observations reported show that type 1 auroral echoes at 50 MHz occur regularly in the entire aspect angle range from about 0 degrees to 14 degrees. Thus, the corresponding 3-m irregularities could have finite wavevector components along the magnetic field, with ratios of k (parallel) to k (perpendicular) as large as 0.25. On the average, the echoes appear to be weakly aspect sensitive at a rate near -1.5 dB/degree. The observed phase velocities decrease slowly with aspect angle at a rate of about 7 m/s per degree and, in general, have values in the nominal ion acoustic speed range of the plasma. The observations might be explained within the framework of the tw-stream instability, by invoking a very high anomalous electron collision frequency, since that would have a strong destabilizing effect at the larger aspect angles. At present, however, there is no theoretical justification for this interpretation and the aspect sensitivity of radio aurora remains an open and challenging problem.
Haldoupis Christos
Koehler James A.
Sofko George J.
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