Comprehensive imaging observations of midlatitude ionospheric disturbancesduring storm time substorms

This paper reports comprehensive imaging observations of 630-nm airglow enh ancements and related phenomena in the nighttime F region over Japan. We fo und 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 Au gust 26; 1998, and February 18, 1999. Total electron content (TEC) observat ions by more than 900 GPS receivers over Japan show a clear TEC enhancement of similar to 10-40 Ya at latitudes below 40 degrees, which coincides with the airglow enhancements and the substorms. On the other hand, 2-MHz virtu al heights obtained by bottomside sounding at four ionosonde stations show equatorward moving large-scale structures! which do not coincide with the a ir glow enhancements. Vertical ion drift data at an altitude of similar to 800 km obtained by the Defense Meteorological Satellite Program satellites show upward ion motion in midlatitudes just. after the substorm onset for t he February event. These observations suggest, that the midlatitude airglow and TEC enhancements are caused by upward electron motion (fountain) in th e low latitudes due to penetration of eastward electric field associated wi th the storm time substorms.