Resolving Magnetopause Shadowing Using Multimission Measurements of Phase Space Density. Issue 2 (27th January 2022)

• Record Type: Journal Article
• Authors: Staples, F. A.; Kellerman, A.; Murphy, K. R.; Rae, I. J.; Sandhu, J. K.; Forsyth, C.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-27
• Subjects: radiation belt -- electron dropout -- magnetopause shadowing -- geomagnetic storm -- electron loss -- PSD; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2021JA029298
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Loss mechanisms act independently or in unison to drive rapid loss of electrons in the radiation belts. Electrons may be lost by precipitation into the Earth's atmosphere, or through the magnetopause into interplanetary space—a process known as magnetopause shadowing. While magnetopause shadowing is known to produce dropouts in electron flux, it is unclear if shadowing continues to remove particles in tandem with electron acceleration processes, limiting the overall flux increase. We investigated the contribution of shadowing to overall radiation belt fluxes throughout a geomagnetic storm starting on the 7 September 2017. We use new, multimission phase space density calculations to decipher electron dynamics during each storm phase and identify features of magnetopause shadowing during both the net‐loss and the net‐acceleration storm phases on sub‐hour time scales. We also highlight two distinct types of shadowing; "direct, " where electrons are lost as their orbit intersects the magnetopause, and "indirect, " where electrons are lost through ULF wave driven radial transport toward the magnetopause boundary. Plain Language Summary: Charged particles with extremely high energies are trapped by Earth's geomagnetic field. These particles form rings around Earth called the Van Allen radiation belts, which vary in intensity. This radiation poses a risk to satellites orbiting Earth, so it is important to understand how changes in geomagnetic conditions produce variations in the radiation belt intensity. In this work, we take measurements of electron radiation from many satellites to observe electron "dropouts, " where nearly the entire radiation belt is lost in a matter of hours. We found that it is necessary to use multimission measurements to make observations of dropouts because a dropout may occur quicker than a single satellite can traverse the radiation belt. In early September 2017, we observed that movements of the geomagnetic outer boundary, the magnetopause, were responsible for removing electrons, combined with diffusive processes. This agreed with the predictions by previous studies. We further observed that the magnetopause continued to remove electrons from the belt while electrons were simultaneously accelerated by fluctuations in the geomagnetic field. This is significant because electrons may be removed from the belt soon after they were created, limiting the overall growth of the radiation belt while the magnetopause was compressed. Key Points: Multimission phase space density observations are necessary to resolve relativistic electron dynamics during September 2017 storm Relativistic electron losses to the magnetopause were identified, which led to further diffusion of electrons toward the magnetopause Electron loss to the magnetopause was observed simultaneous to prompt local energization in the heart of the radiation belt