Akebono/Suprathermal Mass Spectrometer observations of low‐energy ion outflow: Dependence on magnetic activity and solar wind conditions

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Abstract
We present observations by the Suprathermal Mass Spectrometer (SMS) on Akebono (EXOS‐D) of ion outflow in the energy range from + and H+ outflow rates with solar radio flux (monitored by the Penticton F10.7 index), with geomagnetic activity (monitored by the Kp index), and with solar wind parameters is discussed. Comparisons of F10.7 and Kp trends to results from Polar and Dynamics Explorer‐1 (DE‐1) lead us to conclude that flows of H+ in this low energy range are entirely sufficient to account for higher‐energy flows at higher altitudes. On the other hand, we infer a substantial amount of O+ at energies above 70 eV. Both H+ and O+ outflow rates in this range exhibit a strong correlation with the solar wind kinetic pressure, the solar wind electric field, and the variability in the interplanetary magnetic field (IMF) in the hour preceding. While these factors are also associated with increased geomagnetic activity (Kp), a separate, Kp‐independent effect is also found, showing a correlation of ion outflow with solar wind density and an anticorrelation with solar wind velocity.