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Transient emissions on the wavelength of helium I, 5876 Å recorded during auroral break-up |
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| Authors: | W Stoffregen |
| Institution: | Uppsala Ionospheric Observatory, Research Institute of Swedish National Defence, Stockholm, Sweden |
| Abstract: | During the break-up phase of two strong auroral events, emissions of short duration on the wavelength of He I, 5876 Å have been observed. These records are accurate within  0.5 Å and intensities of up to 120 R have been measured. This high value is not consistent with the theoretical limit suggested by other authors. Simultaneous observations of H , 6563 Å show that the He I and H emissions are not closely related to each other with time, which may be one reason for explaining the discrepancy with the predicted intensity derived from observed ratios of He++/H+ in the solar wind. The emission on 5876 Å has only been detected at the lowest border of very intense ray bundles towards north but not yet in auroral arcs and diffuse glow. It is suggested that two principally different helium events in aurora may be observable, one resulting in a low level He emission lasting for longer time and another in a stronger He emission of short duration. The observational difficulties caused by the presence of OH bands are discussed. |
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