The Unknown Hydrogen Exosphere: Space Weather Implications

Abstract

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere‐Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

Coincident Observations by the Kharkiv IS Radar and Ionosonde, DMSP and Arase (ERG) Satellites, and FLIP Model Simulations: Implications for the NRLMSISE‐00 Hydrogen Density, Plasmasphere, and Ionosphere

“…• The NRLMSISE-00 model underestimated thermospheric hydrogen density by~100% during 2016-2018 • An unusually strong response to the minor storm of 24 December 2017 was observed from the inner plasmasphere to the F2-layer peak region • The Kharkiv IS radar results are consistent with ionosonde, DMSP, and Arase (ERG) satellite measurements Krall et al, 2018;Richards & Torr, 1985). Hydrogen from the upper thermosphere is also the source of the geocorona, which significantly affects the ring current decay during the recovering phase of magnetic storms (Ilie et al, 2013;Krall et al, 2018). Thus, accurate knowledge of the upper thermosphere H density is crucially important for comprehensive investigations of a wide range of important space weather phenomena in the near-Earth environment.…”

“…Thus, atomic hydrogen (H) in the Earth's upper thermosphere is primarily responsible for the formation the plasmasphere. It directly impacts plasmasphere refilling after strong magnetic storms (Kersley et al, ; Krall et al, ; Richards & Torr, ). Hydrogen from the upper thermosphere is also the source of the geocorona, which significantly affects the ring current decay during the recovering phase of magnetic storms (Ilie et al, ; Krall et al, ).…”

“…It directly impacts plasmasphere refilling after strong magnetic storms (Kersley et al, ; Krall et al, ; Richards & Torr, ). Hydrogen from the upper thermosphere is also the source of the geocorona, which significantly affects the ring current decay during the recovering phase of magnetic storms (Ilie et al, ; Krall et al, ). Thus, accurate knowledge of the upper thermosphere H density is crucially important for comprehensive investigations of a wide range of important space weather phenomena in the near‐Earth environment.…”

Evolution of Field‐Aligned Electron and Ion Densities From Whistler Mode Radio Soundings During Quiet to Moderately Active Period and Comparisons With SAMI2 Simulations

“…The modeled plasmaspheric densities are sensitive to neutral hydrogen density (Krall et al, 2018;Richards et al, 2000). The neutral densities in SAMI2 are specified using the NRLMSISE00 model.…”

Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres

“…At these altitudes, the H atoms are the primary participants of ion‐neutral interactions, energetically and dynamically coupling the upper atmosphere with the ionosphere, plasmasphere, and magnetosphere. Accurate quantification of this key atmospheric constituent is critical for many disparate investigations in aeronomy and magnetospheric physics, including MLT chemistry and energetics, thermosphere/ionosphere coupling, long‐term atmospheric evolution, and energy dissipation in the ring current following geomagnetic storms (Daglis et al, ; Fahr & Shizgal, ; Krall et al, ; Shizgal & Arkos, ; Zoennchen et al, ). Moreover, in the studies of Venus and Mars atmospheres, H density estimation is critical for the investigation of the role that loss of gas to space has played in climate change over time in order to explore the history of the habitability of these planets (Chaffin et al, , ; McClintock et al, ; Svedhem et al, ).…”