Signature of white bubbles in the equatorial ionosphere

Abstract

<title>Abstract</title> From airglow OI 630 nm observations in the low-latitude ionosphere, we observed an enhancement of the emission rate inside of plasma bubbles (EPBs). It occurred, on some occasions, after the local midnight during the equinox seasons. The all-sky imager has been operated at Bom Jesus da Lapa (BJL) (13.3°S, 43.5°W, dip.14.1°S). In the night of 7–8 October 2021, a dark plasma bubble turned into a bright one due to an enhancement of the OI 630 nm emission rate, which we call it as White Bubble (WhB). Prior to the WhB appearance, the imager detected a presence of Midnight Brightness Wave (MBW) moving rapidly from the equator to the south of BJL. At the same time, a downward movement of the height of the F-layer was observed at Cachoeira Paulista (22.7 °S, 45.0 °W, dip. 18.1°S). We further observed that the WhB extended equatorward when the EPB eastward drift increased. Similar WhBs were observed on seven nights during 2021–2022. These observational facts suggested that the MBW interacted with EPB, causing the depletion inside of EPB to be filled with plasma, resulting in the generation of WhB.