The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using polar/TIMAS and DE-1/EICS data

Abstract

We study the occurrence frequency of upward auroral ion beams as a function of altitude using three years of Polar/TIMAS ion data combined with 11 years of DE1/EICS ion data, in order to reach a complete altitude coverage between 5000 and 30 000 km. The most interesting result is that there is a peak in ion beam occurrence frequency and invariant energy flux and invariant particle flux at ∼ 3 RE radial distance. The peak exists at about the same altitude in both the evening and midnight MLT sectors. No solar cycle effects are found. We suggest that the peak could be due to a preferred altitude of auroral potential structures at ∼ 3 RE. To substantiate the suggestion, we also present a simple Monte Carlo simulation of ion beams. Another result is that the ion beam occurrence frequency and invariant (mapped to ionospheric altitude) energy and particle fluxes increase in the radial distance range 4-6 RE, suggesting that wave heating processes may take place in this altitude range.