Compatison of Equatorial Spread-F Bubbles seen in 135.6 nm airglow at solar maximum and solar minimum from high Earth orbit

Abstract:

Nighttime 135.6 nm airglow provides information on O+ in the ionosphere. Observations of 135.6 nm can only be made from orbit as it is quickly absorbed at altitudes below the middle thermosphere. Structures within the O+ such as equatorial spread-F bubbles are readily identified as variations in airglow brightness. While observations from low-earth orbit offer the opportunity to see these structures in high resolution, observations made from high-earth-orbit offer the opportunity to identify the motion of these structures across a period of several hours. IMAGE-FUV SI-13 provided such observations during solar maximum conditions, while GOLD provides such observations during the current solar minimum conditions. While many years separate these two datasets, a comparison of the two can reveal any fundamental differences in the equatorial spread-F bubbles seen during these two periods. Here we present the first comparison of these two powerful datasets, with a focus on the size, spacing and occurrence rates and drift speeds of the bubbles seen.