| Autor: |
Ross, J. P. J.1 (AUTHOR) johros@bas.ac.uk, Glauert, S. A.1 (AUTHOR), Horne, R. B.1 (AUTHOR), Meredith, N. P.1 (AUTHOR) |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Space Physics. Sep2022, Vol. 127 Issue 9, p1-10. 10p. |
| Abstrakt: |
The banded structure of electromagnetic ion cyclotron (EMIC) wave spectra and their resonant interactions with radiation belt electrons depend on the cold ion composition. However, there is a great deal of uncertainty in the composition in the inner magnetosphere due to difficulties in direct flux measurements. Here, we show that the hydrogen and helium band wave spectra are most consistent with a helium and oxygen composition of a few percent. Less than 10% of hydrogen band wave intensity is consistent with a high helium fraction of ∼20%. Similarly, only ∼20% helium band wave intensity is consistent with an oxygen torus ion composition. Furthermore, we find that the decay of the ultra‐relativistic electrons in the radiation belts by EMIC waves depends on the ion composition. The decay is most sensitive to the helium fraction, and the strongest agreement with Van Allen Probes data is found when the helium fraction is a few percent. We suggest that more observations of the cold ion composition would significantly help understand and set constraints on the decay of ultrarelativistic electrons in the radiation belts. Plain Language Summary: The radiation belts are rings of charged particles around the Earth that are largely confined by the Earth's magnetic field. Electromagnetic waves can interact with these particles, leading to acceleration, transport, and loss. In the outer belt, electrons can be rapidly accelerated during geomagnetic storms leading to a large population of ultrarelativistic electrons. Electromagnetic ion cyclotron waves are particularly important for the decay of this ultrarelativistic population, as they are effective at scattering these electrons into the atmosphere, removing them from the belts. In this work, we show that the cold ion composition is important in determining the rate of decay of these electrons and find that the strongest agreement between models and observations when the He+ fraction is only a few percent. Key Points: Electromagnetic ion cyclotron wave spectra are most consistent with low helium and oxygen fractionsRadiation belt simulations are most sensitive to the cold ion helium fractionStronger agreement with observations is found using ion compositions with low helium fractions [ABSTRACT FROM AUTHOR] |
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GreenFILE |
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