GOLD Namx on September 16-17, 2021. Left panels show the observations on the night of September 16th, while right panels show the observations on the night of September 17th. The red dotted lines represent the magnetic dip equator.
Space Weather: We investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on September 17th, 2021, using Global-scale Observation of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model-eXtended (WACCM-X) simulations. GOLD observations show that there were no EPBs on September 16th before the storm but EPBs occurred after the storm commencement on September 17th. The EPBs extended to ~ 30° magnetic latitude. A diagnostic analysis of WACCM-X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh-Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ~ 30° magnetic latitude during the night of September 17th.