Other
Scientific paper
May 1974
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974p%26ss...22..735b&link_type=abstract
Planetary and Space Science, Volume 22, Issue 5, p. 735-736.
Other
Scientific paper
Rapid measurements of the spatial and temporal variations of the Balmer beta line of hydrogen in aurorae have been obtained with a meridian-scanning photometer. The data confirm previous spectographic evidence which shows that the pre-breakup 'hydrogen arc' is a stable, weak and diffuse arc of considerable latitudinal extent. This description is consistent with theoretical calculation for the precipitation pattern of low-energy isotropic protons. The photometric data also reveal that the hydrogen emissions participate in the auroral breakup. At that time the H-beta line increases markedly in intensity, becomes spatially discrete, and appears within the bright breakup arc. Such behaviour implies an increase in the proton flux and either a large increase in the energy of the incident protons or a drastic narrowing of their pitch angle distribution. Both effects may occur, but the present data does not provide specific information on pitch angle distributions. On the other hand, the observational evidence from the concurrent behaviour of the other auroral emissions and from other types of measurements indicates that the characteristic energy of the incident protons increases from approx 15 keV to 150 keV during the breakup of an auroral display. The possibility of electron excitation of ambient hydrogen has been re-examined. Taking extreme values for the electron flux, H-beta excitation cross-section and atmospheric hydrogen density, it is possible that up to 40 per cent of the hydrogen emission observed in bright, discrete breakup arcs can be attributed to electron excitation of ambient hydrogen. However, there is insufficient data at this time to determine whether or not this mechanism is actually contributing significantly to the observed hydrogen intensity.
Belon A. E.
Romick Gerald J.
Stringer W. J.
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