Statistical Characteristics of the Subauroral Ion Drifts

Abstract:

A database of subauroral ion drifts (SAIDs) is established using long-term observations by the DMSP satellites during 1987–2012. Based on this database, statistical investigations on SAIDs are carried out, including the occurrence location and probability, the solar cycle, seasonal, and diurnal variations, the correlations among SAIDs, field-aligned currents (FACs), and electron precipitation, and the correlations among SAIDs, mid-latitude ionospheric troughs (MITs) and plasmapause (PP). Statistical results show that SAIDs occur mostly at 60.1° invariant latitude and 2230 magnetic local time with a typical half width of 0.57°, move equatorward during high solar activities with large widths, and have two occurrence peaks in spring and fall equinoxes and two valleys in summer and winter solstices. The seasonal variation of SAID latitude has two valleys in spring and fall, and SAID width has a valley distribution with a minimum in summer. SAIDs exhibit a clear day-to-night difference in latitude. The diurnal variation of SAID width has a morning valley and an afternoon peak. The generation mechanism of SAID associated with the electron precipitation and the downward field-aligned current is also supported by the statistics. The polar boundaries of SAIDs overlap with the plasmapause and are more poleward than the polar boundaries of MITs. The arrangement of SAID, MIT, and PP is in such a pattern that PP is the most poleward, MIT is the most equatorward, and SAID is between MIT and PP.