Energetic ion outflow from the dayside ionosphere: Categorization, classification, and statistical study

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The energetic ion outflow (40 eV – 1.2 keV) from the dayside ionosphere has been investigated using 2 weeks (70 orbits) of Viking ion data when the AE index showed little dependence on the interplanetary magnetic field (IMF) Bz component. The data cover altitudes between 6000 and 13,500 km, 0600–1800 magnetic local time (MLT), and 65°–90° invariant latitude (ILAT). We present an automated algorithm using principal component analysis to categorize and classify the upflowing ions into beams, conies, and hybrids. Conies dominate the ion outflow (number flux) in the cusp region, while beams are the main contributor to the outflow prenoon and postnoon outside the cusp region. Generally, the highest average number flux is found in the cusp region. The outflow intensity and the region of energetic ion outflow are different for positive and negative IMF Bz. However, this difference is not as strong as the difference in outflow intensity and active region observed for AE <50 and AE >200. The results imply that the dayside energetic ion outflow is controlled partly by nightside (driven by the release of stored energy in the magnetotail, as observed in the AE index) and partly by dayside (directly driven, as observed in the polarity in the IMF Bz component) activity. The effect of the directly driven component (IMF Bz) is strongest in the cusp and the postnoon region.