A statistical study of ion beams and conics from the dayside ionosphere during different phases of a substorm

Abstract

The increase of upflowing ions from the dayside ionosphere during substorms has been investigated using Viking ion data and 1‐min values of the AE index. An automated algorithm using principal component analysis has been used to categorize and classify the upflowing ions (UFIs), that is, beams, conies, and hybrids. The data cover altitudes between 6000 and 13,500 km, 0600–1800 magnetic local time, and 65°–90° invariant latitude. The distribution and AE dependence agree with low‐altitude perpendicular ion heating and Kp dependence observed by the Freja satellite near 1700 km, suggesting that heated ions become beams or conies at midaltitude. One‐minute AE values provide a higher time resolution for the geomagnetic activity level than Kp and make it possible to investigate the ionospheric outflow during different substorm phases. The highest average UFI number flux is observed during expansion phase when the flux increase from quiet conditions ( AE < 100) is a factor of 2, but even during growth and recovery phase the average UFI number flux is 30% higher than for quiet conditions. The UFI frequency of occurrence increases significantly from AE <50 to AE >200, but stays rather constant during growth, expansion, and recovery phase. During substorms ( AE >100) a strong increase in the UFI occurrence rate with AE is observed mainly in the cusp region, although a smaller increase is also observed in the postnoon sector.