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Hydrogen line profiles measured from space-borne or ground-based instrumentsprovide useful information to study the physical processes occurring in theproton aurora and to estimate the proton flux characteristics. The lineshape of the hydrogen lines is determined by the velocity distribution of Hatoms along the line-of-sight of the instrument. Calculations of lineprofiles of auroral hydrogen emissions were obtained using a Monte Carlokinetic model of proton precipitation into the auroral atmosphere. In thismodel both processes of energy degradation and scattering angleredistribution in momentum and charge transfer collisions of the high-energyproton/hydrogen flux with the ambient atmospheric gas are considered at themicrophysical level. The model is based on measured cross sections andscattering angle distributions and on a stochastic interpretation of suchcollisions. Calculations show that collisional angular redistribution of theprecipitating proton/hydrogen beam is the dominant process leading to theformation of extended wings and peak shifts in the hydrogen line profiles.All simulations produce a peak shift from the rest line wavelengthdecreasing with increasing proton energy. These model predictions areconfirmed by analysis of ground-based H-β line observations fromPoker Flat, showing an anti-correlation between the magnitude of the peakshift and the extent of the blue wing of the line. Our results also stronglysuggest that the relative extension of the blue and red wings provides amuch better indicator of the auroral proton characteristic energy than theposition of the peak wavelength

A Monte Carlo model of auroral hydrogen emission line profiles