The dynamic response of the Earth’s exosphere to the 10-11 May 2024 Superstorm

The exosphere is the outermost layer of the terrestrial atmosphere which is mainly comprised of atomic hydrogen (H) and extends from several hundreds of kilometers (~500 km) to several Earth radii (~60 RE). Knowledge of the 3-D structure and spatial distribution of H densities, especially during geomagnetic storms, is crucial to understand (i) the mechanisms that may enhance its permanent escape to space and (ii) its significant role in governing the transient response of the terrestrial plasma environment to space weather. Current analysis of this vast neutral region is carried out via remote sensing measurements of scattered FUV emissions by H atoms, specifically at Lyman-Alpha ~121.6 nm. Zoennchen et al., (2017) and Cucho-Padin & Waldrop., (2019) have conducted multi-event studies of storm-time exospheres using observations from the Lyman-Alpha Detectors (LADs) onboard NASA’s Two-Wide angle Imaging Neutral-atom Spectrometers (TWINS) mission. They found that H densities significantly increased during the main phase of the storm followed by a slow recovery period to quiet-time conditions. Such increase in the number density is theorized to be caused by changes in the temperature and density at its lower boundary, the exobase at ~500 km, during geomagnetic storms. In this work, we investigate the response of the terrestrial exosphere to the geomagnetic superstorm that occurred between  May 10-11, 2024, using the Kinetic-based Terrestrial Exospheric (KITE) model which solves the kinetic equation of the H atoms using the finite volume method. Our simulations show a vertical redistribution of atomic H that varies with location. Near the ecliptic plane, there is a depletion of H of up to ~35% with respect to quiet time condition below 3RE altitude, but there is an increase of ~20% above this transition point. Near the north pole, there is a constant increase of atomic H that reaches up to 60% variation at 1.2 RE altitude. We intend to compare these simulations to actual observations of the geocoronal H Lyman-Alpha emission obtained by the Cosmic Origins Spectrograph (COS) instrument onboard the Hubble Space Telescope.