Statistical study of relationships between high-altitude and high-latitude O+ ion outflows and solar/geomagnetic activity
S. Arvelius, M. Yamauchi, H. Nilsson, Y. Hobara, I. Sandahl, R. Lundin, H. Reme, and the Cluster/CIS team
The terrestrial-origin O+ ion outflow, which is persistently observed by the Cluster CIS/CODIF instrument was statistically studied in the high-altitude (from 3 up to 11 Re), and high-latitude (from 70 to ~90 degrees invariant latitude, ILAT) polar region. We studied its occurrence and distribution in terms of the solar wind parameters (including the interplanetary magnetic field, IMF, conditions) as well as the geomagnetic activity (so far, referred by planetary disturbance index, Kp). We found the following; (1) Outflowing O+ ions with more than 1 keV are observed above 10 Re and near the pole (>85 degrees ILAT); (2) The velocity filter effect can explain all the energy dispersion of O+ outflow only below 8 Re but not above; (3) The tendency to observe outflowing O+ ions with the energy of more than keV at both higher altitudes and higher latitudes shows a clear Kp-dependence. Furthermore, regarding (1) and (2) above that suggest additional energization/acceleration process(es) acting on outflowing O+ ions occur at high altitudes and high latitudes, three candidate processes are assessed. With respect to (3) above, relationships between Kp and solar wind parameters are first investigated, then the correlations between the properties of outflowing O+ ions (maximum differential particle flux and its energy) and solar wind parameters in time scale of from tens of minutes to a hour are shown.
Created 2005-04-01 13:23:13 by Rick McGregor Last changed 2005-04-01 13:23:41 by Rick McGregor