No abstract

Abstract. We investigate the in¯uence 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 pro®les viewed in the magnetic zenith exhibit a red-shifted component which is indicative of upward¯uxes. In order to determine the origin of this red shift, we evaluate the in¯uence of two angular redistribution sources which are included in our proton/ hydrogen transport model. Even though it generates an upward¯ux, the redistribution due to magnetic mirroring eect is not sucient to explain the red shift. On the other hand, the collisional angular scattering induces a much more signi®cant 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`0X2 nm. This explains the absence of measured upward proton/hydrogen¯uxes 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 pro®les and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the pro®le. Our results suggest that Doppler pro®le measurements with higher spectral resolution may enable us to quantify better the angular scattering in proton aurora.