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

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) B-z component. The data cover altitudes between 6000 and 13,500 km, 0600-18 00 magnetic local time (MLT), and 65 degrees-90 degrees invariant latitude (ILAT). We present an automated algorithm using principal component analysi s to categorize and classify the upflowing ions into beams, conics, and hyb rids. Conics dominate the ion outflow (number flux) in the cusp region; whi le beams are the main contributor to the outflow prenoon and postnoon outsi de the cusp region. Generally, the highest average number flux is found in the cusp region. The outflow intensity and the region of energetic ion outf low are different for positive and negative IMF B-z. However, this differen ce is not as strong as the difference in outflow intensity and active regio n observed for AE <50 and AE >200. The results imply that the dayside energ etic ion outflow is controlled partly by nightside (driven by the release o f 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 B-z co mponent) activity. The effect of the directly driven component (IMF B-z) is strongest in the cusp and the postnoon region.