Planetary Wave Driven Variability in Equatorial Plasma Bubbles

A combination of whole atmosphere model simulations and NASA Global-scale Observations of the Limb and Disk (GOLD) observations are used to investigate the occurrence of periodic variability in equatorial plasma bubbles (EPBs). GOLD observations exhibit a quasi-six day oscillation in the occurrence of EPBs during early 2021. The source of the quasi-six day oscillation in EPBs is investigated using simulations in the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). WACCM-X simulations with realistic lower atmosphere and solar/geomagnetic variability exhibit a quasi-six day oscillation in the Rayleigh-Taylor (R-T) instability growth rate that is generally consistent with the GOLD observations of EPBs. The quasi-six day oscillation in the simulated R-T growth rate is coincident with an enhancement in the quasi-six day planetary wave in the mesosphere-lower thermosphere, indicating that the quasi-six day variability in EPBs is likely driven by planetary wave activity. WACCM-X simulations with constant solar and geomagnetic forcing confirm that the periodic variability in the R-T growth rate is of lower atmospheric origin. Additional analysis of the simulations reveals that the quasi-six day oscillation in the R-T growth rate is due to periodic variability in the migrating semidiurnal tide which drives variability in the pre-reversal enhancement in vertical plasma drifts.