Y. Sahai et al., Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000, J GEO R-S P, 106(A11), 2001, pp. 24481-24492
Regular all-sky imaging observations of the F region OI 630 nm nightglow em
ission are carried out at Rikubetsu (43.5 degreesN) and Shigaraki (34.8 deg
reesN), 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 observa
tions during the geomagnetic storm of February 12, 2000. The airglow observ
ations were obtained between 1500 UT and 2000 UT (0000-0500 LT) on this nig
ht. Images from both Rikubetsu and Shigaraki show the presence of mesoscale
-enhanced airglow bands moving slowly (similar to 20-30 m s(-1)) to the sou
thwest direction. The mesoscale band structures were also detected by an ex
tensive network of GPS signal observations over Japan. The airglow observat
ions at Shigaraki also show intense OI 630 nm emission in the south with se
veral small-scale intensity depletion structures. We suggest that these sma
ll-scale intensity depletion structures (scale size 30-50 km) are caused by
possible nonlinear interaction between the mesoscale TIDs and enhanced reg
ions of the equatorial ionospheric anomaly. The ionosonde observations from
Wakkanai (45.4 degreesN) and Kokubunji (35.7 degreesN) show spread F signa
tures between 1130 and 2100 UT and 1215 and 1715 UT, respectively, whereas
no spread F was observed at Yamagawa (31.2 degreesN) and Okinawa (26.3 degr
eesN). The phase fluctuations of GPS signal were observed at latitudes high
er than 30 degreesN for 1400-1900 UT. These observations suggest enhanced s
torm time ionospheric disturbances were confined in the midlatitudes.