Ionospheric plasma blobs observed by OI 630 nm all-sky imaging in the Brazilian tropical sector during the major geomagnetic storm of April 6-7, 2000

This paper presents first observations of plasma blobs ( localized plasma density enhancements) associated with large-scale plasma density depletions ( plasma bubbles) in the nighttime low-latitude F-region during a major geomagnetic disturbance. Ground-based observations of the OI 630 nm all-sky images obtained at Cachoeira Paulista (22.7 degrees S, 45.0 degrees W), Brazil, in the Appleton anomaly region, showed the presence of plasma blobs during the major geomagnetic storm of April 6 - 7, 2000 (Sigma Kp = 38 -/ 40+; \Dst\(max) = 288 nT). The OI 630 nm emission images were used to map the spatial and temporal locations of plasma blobs and bubbles in the bottomside of the F-region. The F-region parameters, presented in this work, were obtained from ionosondes operating near the same site and also at Sao Luis (2.6 degrees S, 44.4 degrees W), Brazil. Ionospheric plasma blobs and bubbles zonal drift velocities, measured by the all-sky imaging system, showed that both the plasma blobs and the bubbles moved westward ( normally the plasma drift is eastward during nighttime) on this magnetically disturbed night. Furthermore, the plasma blobs showed typically east-west and north-south extensions in the range of 110 160 km and 200 - 450 km, respectively. It appears that the DMSP-15 satellite, orbiting at about 850 km altitude, passed through one of the blobs detected by the ground-based observations on this night while crossing the Brazilian sector. This indicates the enormous altitude extent [ from about 275 km ( OI 630.0 nm emission) to 850 km ( DMSP satellite) altitude] of the localized plasma density enhanced regions. In this work, we present and discuss several features related to the dynamics of the localized plasma density enhancements and large-scale plasma density depletions during this major geomagnetic disturbance.