On I(5577 Å) and I (7620 Å) auroral emissions and atomic oxygen densities

Abstract

A model of auroral electron deposition processes has been developed using Monte Carlo techniques to simulate electron transport and energy loss. The computed differential electron flux and pitch angle were compared with in situ auroral observations to provide a check on the accuracy of the model. As part of the energy loss process, a tally was kept of electronic excitation and ionization of the important atomic and molecular states. The optical emission rates from these excited states were computed and compared with auroral observations of <eta>(3914 Å), <eta>(5577 Å), <eta>(7620 Å) and <eta>(N₂VK). In particular, the roles played by energy transfer from N₂(A³<Sigma>⁺_u) and by other processes in the excitation of O(¹S) and O₂(b¹<Sigma>⁺_g) were investigated in detail. It is concluded that the N₂(A³<Sigma>⁺_u) mechanism is dominant for the production of OI(5577 Å) in the peak emission region of normal aurora, although the production efficiency is much smaller than the measured laboratory value; above 150 km electron impact on atomic oxygen is dominant. Atomic oxygen densities in the range of 0.75±0.25 MSIS-86 [O] were derived from the optical comparisons for auroral latitudes in mid-winter for various levels of solar and magnetic activity.