Investigation of the Physical Mechanisms of the Formation and Evolution of Equatorial Plasma Bubbles During a Moderate Storm on 17 September 2021

We investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global-scale Observations 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 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to similar to 30 degrees 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 similar to 30 degrees magnetic latitude during the night of 17 September. Equatorial plasma bubbles (EPBs) are frequently observed in the equatorial region after sunset and have been the focus of ionospheric research. They are an important space weather phenomenon that often significantly impact trans-ionospheric radio wave signals. During geomagnetic storms, the occurrence and evolution of EPBs are more complicated, and their physical mechanisms are worthy of further investigation. In this study, we used Global-scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model-eXtended (WACCM-X) simulations to study the occurrence and evolution of EPBs during a moderate storm on 17 September 2021. GOLD observations show that EPBs occurred after the storm commencement on 17 September, whereas no EPBs were observed on 16 September. Additionally, these EPBs extend to similar to 30 degrees magnetic latitude. According to the WACCM-X simulation analysis, the rapid enhancement of the prompt penetration electric fields (PPEFs) after the sudden storm commencement resulted in a significant Rayleigh-Taylor instability (RTI) on 17 September, triggering the occurrence of EPBs. Furthermore, quantitative analysis revealed that PPEF induces enhanced vertical plasma drifts, which are the main reason for the strengthening RTI and the large latitudinal extension of the EPBs on 17 September. Equatorial plasma bubbles (EPBs) extended poleward to similar to 30 degrees magnetic latitude during a moderate storm on 17 September 2021Diagnostic analysis reveals that occurrence of EPBs was due to rapidly enhanced eastward prompt penetration electric field (PPEF) after the sudden storm commencementPPEF-driven upward drifts are the main factor causing large Rayleigh-Taylor instability, and thus the formation and large latitudinal extension of the EPBs