A statistical comparison of the outflow of N-2(+), NO+ and O-2(+) molecular ions with that of atomic O+ ions using Polar/TIMAS observations

Ion composition data from the first 22 months of operation (until the end o f 1997) of the Polar/TIMAS instrument, covering the 15-eV/e to 33-keV/e ene rgy range, have been surveyed to determine the typical abundance of N-2(+), NO+ and O-2(+) ions as a group (M/Q similar to 30) in the auroral ion outf low, as compared to that of the better known O+ ions. The results, obtained at and near solar minimum, indicate that molecular ions have roughly the s ame energy distribution as the O+ ions, with maximum differential flux occu rring below 400 eV, but are far less abundant, by two orders of magnitude o n average. The molecular ions also differ from the O+ ions in that they see m more specifically associated with enhanced geomagnetic activity, possibly with some electrodynamic threshold being surpassed in the ionosphere. The most intense fluxes of molecular ions, 10(5)-10(6) (cm(2) s ster keV/e)(-1) , are usually encountered near the Polar perigee in the southern auroral zo ne (at R similar to 2R(E)), but the longer lasting encounters, 30 min or mo re, are closer to the Polar apogee in the northern hemisphere, often well i nside the polar cap (at R similar to 4-9 R-E). The molecular ions are obser ved at varying local time but too infrequently to yield a significant measu re of local time distribution. (C) 2000 Elsevier Science Ltd. All rights re served.