Coincident equatorial bubble detection by TIMED/GUVI and ROCSAT‐1

Abstract

The GUVI on board the NASA's TIMED satellite provides a new capability for monitoring equatorial electron density irregularities. The nighttime GUVI disk scan images of OI 135.6‐nm show numerous emission‐depleted dark features in the equatorial region. The dark features show typical equatorial bubble characteristics ‐ elongation in the north‐south direction, westward tilt, and season‐longitudinal variations in their distribution. Coincident in‐situ observations by ROCSAT‐1 satellite identify plasma depletions co‐located with the emission depletions. The individual bubble images are hardly distinguishable in the equatorial region owing to an occurrence of multiple bubbles and owing to the low background radiance at the ionization trough. Occasionally, a reversed “C”‐shaped bubble images appear on the GUVI swath of a single orbit. Those global bubble images corroborate the occurrence of plasma depletion in the whole magnetic flux tube and the presence of vertical shear of zonal bulk plasma flow in the topside ionosphere.