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- Title
MeV Electron Precipitation During Radiation Belt Dropouts.
- Authors
Freund, Domenique; Blum, Lauren; Vidal‐Luengo, Sergio; Bruno, Alessandro; Kataoka, Ryuho
- Abstract
To gain deeper insights into radiation belt loss into the atmosphere, a statistical study of MeV electron precipitation during radiation belt dropout events is undertaken. During these events, electron intensities often drop by an order of magnitude or more within just a few hours. For this study, dropouts are defined as a decrease by at least a factor of five in less than 8 hours. Van Allen probe measurements are employed to identify dropouts across various parameters, complemented by precipitation data from the CALorimetric Electron Telescope instrument on the International Space Station. A temporal analysis unveils a notable increase in precipitation occurrence and intensity during dropout onset, correlating with the decline of SYM‐H, the north‐south component of the interplanetary magnetic field, and the peak of the solar wind dynamic pressure. Moreover, dropout occurrences show correlations with the solar cycle, exhibiting maxima at the spring and autumn equinoxes. This increase during equinoxes reflects the correlation between equinoxes and the SYM‐H index, which itself exhibits a correlation with precipitation during dropouts. Spatial analysis reveals that dropouts with precipitation penetrate into lower L‐star regions, mostly reaching L‐star <4, while most dropouts without precipitation don't penetrate deeper than L‐star 5. This is consistent with the larger average dimensions of dropouts associated with precipitation. During dropouts, precipitation is predominantly observed in the dusk‐midnight sector, coinciding with the most intense precipitation events. The results of this study provide insight into the contribution of precipitation to radiation belt dropouts by deciphering when and where precipitation occurred. Plain Language Summary: The outer radiation belt encircles Earth, trapping energetic electrons due to the planet's magnetic field. Under certain conditions, such as during geomagnetic storms, there can be a significant loss of these trapped electrons over a short period, known as a dropout. One reason for this can be particles reentering Earth's atmosphere, leading to their removal from the outer radiation belt. This is referred to as precipitation. This study investigates the role of precipitation for dropouts, focusing on when and where precipitation occurs during those events. To accomplish this, data from the Van Allen Probe spacecraft, measuring electron density, and the CALorimetric Electron Telescope instrument aboard the International Space Station, measuring precipitation, are utilized. The findings reveal a correlation between dropouts, whether aligned with precipitation or not, and the solar cycle and seasons. Seasonal variations are likely connected to the intensity of disturbances in the magnetosphere, consequently raising the probability of precipitation. Spatial investigations reveal that dropouts accompanied by precipitation penetrate deeper into lower regions of stably trapped particles. Furthermore, precipitation predominantly occurs on the dusk and midnight side of Earth, where the strongest precipitation measurements are also recorded. Key Points: MeV electron dropouts with and without associated precipitation show dependencies on solar cycle and seasonsAn increase in precipitation occurrence and intensity during MeV dropouts aligns with the decline in SYM‐H and Bz, and the peak in PdynDropouts with MeV electron precipitation, on average, spread over a wider radial extent, with occurrences related to SYM‐H
- Subjects
INTERPLANETARY magnetic fields; RADIATION belts; SOLAR cycle; MAGNETIC storms; AUTUMNAL equinox; SOLAR wind
- Publication
Journal of Geophysical Research. Space Physics, 2024, Vol 129, Issue 8, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2024JA032759