Signature of white bubbles in the equatorial ionosphere

Abstract

<title>Abstract</title> From airglow OI 630 nm observations in the low-latitude ionosphere, we identified an enhancement in the emission rate inside Equatorial Plasma Bubbles (EPBs) on certain occasions after local midnight during equinox seasons. On the night of 7–8 October 2021, an all-sky imager, operated at Bom Jesus da Lapa (BJL) (13.3°S, 43.5°W, dip 14.1°S), observed a dark plasma bubble transitioning into a bright one due to an enhancement of the OI 630 nm emission rate, a phenomenon we refer to as a "White Bubble" (WhB). Prior to the appearance of the WhB, the imager detected a Midnight Brightness Wave (MBW) rapidly moving southward from the equator. Concurrently, a downward movement of the F-layer's height was observed at Cachoeira Paulista (22.7°S, 45.0°W, dip 18.1°S). The WhB extended equatorward when the EPB's eastward drift speed increased. Similar WhBs were observed on seven nights during 2021–2022. These observations suggest that the MBW interacted with the EPB, causing plasma depletion within the EPB to be filled, ultimately generating a WhB.