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 typical auroral hydrogen emission is characterized by a broad line profile whose shape depends on the energy and pitch angle distributions of the initial proton beam whereas its total brightness reflects the proton energy flux precipitated into the auroral upper atmosphere. Global remote sensing of proton aurora through its ultraviolet signature makes it is increasingly important to relate the characteristics of the emission to the physical properties of the precipitated proton flux.
We present a numerical model of proton and hydrogen flux transport and kinetics based on the Direct Simulation Monte Carlo method. 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.
We show that consideration of the stochastic character of the H atom velocity redistribution after collisions produces line profiles different from those obtained in the strictly forward or mean scattering angle approximations previously used in proton transport codes. In particular, the predicted fraction of photons due to backscattered particles is considerable larger when stochastic collision scattering is considered than in the strictly forward or mean scattering angle approximations. In addition, the wavelength of the peak in the line profile shows an inverse dependence on the proton energy.
Applications of the model to interpretation of the IMAGE satellite data and ground based observations are discussed.
Created 2010-10-07 02:36:40 by Mats HolmstrÃ¶m Last changed 2010-10-13 10:57:02 by Mats HolmstrÃ¶m