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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 4
Ann. Geophys., 23, 1473–1480, 2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 1473–1480, 2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  03 Jun 2005

03 Jun 2005

A Monte Carlo model of auroral hydrogen emission line profiles

J.-C. Gérard1, V. I. Shematovich2, D. V. Bisikalo2, and D. Lummerzheim3 J.-C. Gérard et al.
  • 1Laboratoire de Physique Atmosphérique et Planétaire, Université de Liège, Liège, Belgium
  • 2Institute of Astronomy RAS, Moscow, Russian Federation
  • 3Geophysical Institute, University of Alaska, Fairbanks, Alaska, USA

Abstract. Hydrogen line profiles measured from space-borne or ground-based instruments provide useful information to study the physical processes occurring in the proton aurora and to estimate the proton flux characteristics. The line shape of the hydrogen lines is determined by the velocity distribution of H atoms along the line-of-sight of the instrument. Calculations of line profiles of auroral hydrogen emissions were obtained using a Monte Carlo kinetic model of proton precipitation into the auroral atmosphere. In this model both processes of energy degradation and scattering angle redistribution in momentum and charge transfer collisions of the high-energy proton/hydrogen flux with the ambient atmospheric gas are considered at the microphysical level. The model is based on measured cross sections and scattering angle distributions and on a stochastic interpretation of such collisions. Calculations show that collisional angular redistribution of the precipitating proton/hydrogen beam is the dominant process leading to the formation of extended wings and peak shifts in the hydrogen line profiles. All simulations produce a peak shift from the rest line wavelength decreasing with increasing proton energy. These model predictions are confirmed by analysis of ground-based H-β line observations from Poker Flat, showing an anti-correlation between the magnitude of the peak shift and the extent of the blue wing of the line. Our results also strongly suggest that the relative extension of the blue and red wings provides a much better indicator of the auroral proton characteristic energy than the position of the peak wavelength.

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