Plasma bubbles and irregularities in the equatorial ionosphere

The Atmosphere Explorer satellite observed large-scale (10 to 200-km) irregular biteouts of up to three orders of magnitude in the ion concentration in the nighttime equatorial F region associated with small-scale inhomogeneities in the ion concentration. Simultaneous plasma velocity observations show irregular upward and westward motion of the order of 150 m/s associated with some of these 'bubbles', while others move more slowly or move with approximately the velocity of the background plasma. The plasma composition signatures indicate that most of the bubbles observed have recently moved upward. Several features of recent VHF radar observations can be understood as resulting from these plasma bubbles, e.g., the 'plume' features and very high apparent velocities seen on range-time-intensity spread F maps and the very complex and/or wide spectral features observed using such radars.