Field-aligned ion motions in the e and F regions

Abstract

Characteristics of field-aligned (FA) ion motions in the E and Fregion (below F peak) ionosphere have been determined based on an analysis of European incoherent scatter (EISCAT) Svalbard and Kiruna-Sodankylä-Tromso (KST) data. Sporadic/burst upward FA ion motions are observed in southward electric field enhancement regions or in the postmidnight region, while relatively stable downward FA ion motions are seen in northward electric field enhancement regions or in other regions. Long-term (diurnal) variations of these upward and downward FA ions are likely driven by the large-scale from day-to-night thermospheric wind. However, each short-lived upward FA flow has neither one-to-one correspondence to an enhancement (or depletion) of the electric field nor that of electron density. The driving mechanism of the short-lived upward flow cannot thus be understood yet, although atmospheric gravity waves can be one of the possible mechanisms to create the short-term upward FA ion motions in the southward electric field region or in the postmidnight region. Copyright 2002 by the American Geophysical Union.