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Ann. Geophys., 16, 1308-1321, 1998
www.ann-geophys.net/16/1308/1998/
© European Geosciences Union 1998
Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam
M. Galand1, J. Lilensten2, W. Kofman2, and D. Lummerzheim3
1High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA
Fax: +1 303 497 1589; e-mail: galand@hao.ucar.edu
2Centre d'Etudes des Phénomènes Aléatoires et Géophysiques, St Martin d'Hères, France
3Geophysical Institute, University of Alaska, Fairbanks, Alaska, USA
Abstract. We investigate the influence of magnetic
mirroring and elastic and inelastic scattering on the angular redistribution in
a proton/hydrogen beam by using a transport code in comparison with
observations. H-emission Doppler profiles viewed in the magnetic zenith exhibit
a red-shifted component which is indicative of upward fluxes. In order to
determine the origin of this red shift, we evaluate the influence of two angular
redistribution sources which are included in our proton/hydrogen transport
model. Even though it generates an upward flux, the redistribution due to
magnetic mirroring effect is not sufficient to explain the red shift. On the
other hand, the collisional angular scattering induces a much more significant
red shift in the lower atmosphere. The red shift due to collisions is
produced
by <1 -keV protons and is so small as to require an instrumental bandwidth
<0.2 nm. This explains the absence of measured upward proton/hydrogen fluxes
in the Proton I rocket data because no useable data concerning protons <1 keV
are available. At the same time, our model agrees with measured ground-based
H-emission Doppler profiles and suggests that previously reported red shift
observations were due mostly to instrumental bandwidth broadening of the
profile. Our results suggest that Doppler profile measurements with higher
spectral resolution may enable us to quantify better the angular scattering in
proton aurora.
Key words. Auroral ionosphere ยท Particle precipitation
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