Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000

Abstract

Regular all‐sky imaging observations of the F region OI 630 nm nightglow emission are carried out at Rikubetsu (43.5°N) and Shigaraki (34.8°N), Japan since 1998. In this paper, we present observations of the OI 630 nm emission images from these two sites with a cluster of other observations during the geomagnetic storm of February 12, 2000. The airglow observations were obtained between 1500 UT and 2000 UT (0000–0500 LT) on this night. Images from both Rikubetsu and Shigaraki show the presence of mesoscale‐enhanced airglow bands moving slowly (∼20–30 m s−1) to the southwest direction. The mesoscale band structures were also detected by an extensive network of GPS signal observations over Japan. The airglow observations at Shigaraki also show intense OI 630 nm emission in the south with several small‐scale intensity depletion structures. We suggest that these small‐scale intensity depletion structures (scale size 30–50 km) are caused by possible nonlinear interaction between the mesoscale TIDs and enhanced regions of the equatorial ionospheric anomaly. The ionosonde observations from Wakkanai (45.4°N) and Kokubunji (35.7°N) show spread F signatures between 1130 and 2100 UT and 1215 and 1715 UT, respectively, whereas no spread F was observed at Yamagawa (31.2°N) and Okinawa (26.3°N). The phase fluctuations of GPS signal were observed at latitudes higher than 30°N for 1400–1900 UT. These observations suggest enhanced storm time ionospheric disturbances were confined in the midlatitudes.