M. Galand et al., PROTON TRANSPORT MODEL IN THE IONOSPHERE - 2 - INFLUENCE OF MAGNETIC MIRRORING AND COLLISIONS ON THE ANGULAR REDISTRIBUTION IN A PROTON-BEAM, Annales geophysicae, 16(10), 1998, pp. 1308-1321
We investigate the influence of magnetic mirroring and elastic and ine
lastic scattering on the angular redistribution in a proton/hydrogen b
eam by using a transport code in comparison with observations. H-emiss
ion Doppler profiles viewed in the magnetic zenith exhibit a red-shift
ed component which is indicative of upward fluxes. In order to determi
ne the origin of this red shift, we evaluate the influence of two angu
lar redistribution sources which are included in our proton/hydrogen t
ransport model. Even though it generates an upward flux, the redistrib
ution due to magnetic mirroring effect is not sufficient to explain th
e red shift. On the other hand, the collisional angular scattering ind
uces a much more significant red shift in the lower atmosphere. The re
d shift due to collisions is produced by <1-keV protons and is so smal
l as to require an instrumental bandwidth <0.2nm. This explains the ab
sence 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 II-emis
sion Doppler profiles and suggests that previously reported red shift
observations were due mostly to instrumental bandwidth broadening of t
he profile. Our results suggest that Doppler profile measurements with
higher spectral resolution may enable us to quantify better the angul
ar scattering in proton aurora.