Calculation of auroral Bahner volume emission height profiles in the upper atmosphere

Abstract

Energetic protons entering the atmosphere will either travel as auroral protons or as neutral hydrogen atoms due to charge-exchange and excitation interactions with atmospheric constituents. Our objective is to develop a simple procedure to evaluate the Balmer excitation rates of H α and H β, and produce the corresponding volume emission rates vs height, using semi-empirical range relations in air, starting from proton spectra observed from rockets above the main collision region as measured by Reasoner et al. [(1968) J. geophys. Res. 73, 4185] and Søbraas et al. [(1974) J. geophys. Res. 79, 1851]. The main assumptions are that the geomagnetic field is parallel and vertical, and that the pitch angle of the proton/hydrogen atom is preserved in collisions with atmospheric constituents before being thermalized. Calculations show that the largest energy losses occur in the height interval between 100 and 125 km, and the corresponding volume emission rate vs height profiles have maximum values in this height interval. The calculted volume emission rate height profile of H β compares favorably with that measured with a rocket-borne photometer.