Open AccessCosmic radio noise absorption related to structures in auroral luminosity
Author(s) -
Stoker P. H.,
Mathews M. J.,
Scourfield M. W. J.
Publication year - 1997
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/96ja03493
Subject(s) - riometer , physics , astrophysics , ionosphere , luminosity , absorption (acoustics) , sky , electron precipitation , magnetic field , radio wave , astronomy , magnetosphere , optics , galaxy , quantum mechanics
Digitized all‐sky white light images of auroral optical emissions, recorded by a low‐light level TV system at Sanae (70.3°S, 2.4°W, L = 4.0), have been mapped onto the angular sensitivity functions of the inner four beams of a 16‐element imaging riometer. Cosmic radio waves of 5–10 m wavelengths appeared to be absorbed more strongly in directions through regions adjacent to discrete auroral arcs than through the arc regions themselves. These stronger absorptions may be due either to enhanced electron temperatures, caused by the Farley‐Buneman two‐stream instability in the presence of large electric fields around auroral arcs in the E region, or to D region absorption caused by energetic electrons precipitating along magnetic field lines passing through regions adjacent to auroral arcs. The two auroral events before local magnetic midnight reported in this paper started with high luminosity and small ionospheric absorption. The absorption increased as the event developed. Auroral luminosities and structures were changing in all four viewing directions during the event on May 10, 1992, with variations in absorptions following variations in luminosity after a delay of 30 s. The event on June 8, 1992, involved a pulsating arc structure. Changes in absorption appeared to be delayed relative to changes in luminosity that varied from 0 to 60 s in a particular viewing direction. The auroral event after local magnetic midnight on April 14, 1993, differed from the former two events in the appearance of pulsating auroral patches and in slower temporal variations, but, occasionally, changes in absorption of cosmic radio noise in the four beam directions were still delayed relative to changes in luminosity. The observed spatial and temporal differences in regions of optical emissions and ionospheric absorption should be of magnetospheric origin rather than ionospheric origin on account of the long delay times.