Comprehensive imaging observations of midlatitude ionospheric disturbances during storm time substorms

This paper reports comprehensive imaging observations of 630-nm airglow enhancements and related phenomena in the nighttime F region over Japan. We found two events during which the airglow intensity increases up to 300 R at the lower-latitude side of Japan associated with storm time substorms of August 26, 1998, and February 18, 1999. Total electron content (TEC) observations by more than 900 GPS receivers over Japan show a clear TEC enhancement of ∼10–40 % at latitudes below 40°, which coincides with the airglow enhancements and the substorms. On the other hand, 2-MHz virtual heights obtained by bottomside sounding at four ionosoride stations show equatorward moving large-scale structures, which do not coincide with the airglow enhancements. Vertical ion drift data at an altitude of ∼800 km obtained by the Defense Meteorological Satellite Program satellites show upward ion motion in midlatitudes just after the substorm onset for the February event. These observations suggest that the midlatitude airglow and TEC enhancements are caused by upward electron motion (fountain) in the low latitudes clue to penetration of eastward electric field associated with the storm time substorms.