Plasma bubbles and irregularities in the equatorial ionosphere

Abstract

Using the Atmosphere Explorer satellite AE-C, we observe large-scale (10- to >200-km) irregular biteouts of up to three orders of magnitude in the ion concentration Ni in the nighttime equatorial F region associated with small-scale inhomogeneities in Ni. Similar phenomena were reported by Hanson and Sanatani but without the more complete plasma diagnostics present on AE. Simultaneous plasma velocity observations show irregular upward and westward motion of the order of 150 m s−1 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. Bubbles that move upward typically also move westward with respect to the background plasma. This may explain the east-west asymmetries seen in studies of equatorial irregularities made using HF radar, HF transequatorial propagation, and detailed 6300-Å tropical airglow mapping techniques.