Electron Scattering, Transport and Energization by Alfvénic Turbulence in Earth's Outer Radiation Belt

• Published in: Geophysical research letters 2023-07, Vol.50 (13), p.n/a
• Main Author: Chaston, C. C.
• Format: Article
• Language: English
• Subjects: Alfeven waves; Alfven waves; Belt conveyors; Chorus waves; Coefficients; Deformation; Deviation; Drift; Drift estimation; Earth; Electromagnetic fields; Electrons; Energetic particles; Energy; Explosive impact tests; Geomagnetic field; Geomagnetic storms; Geomagnetism; Jupiter; Magnetic storms; Magnetohydrodynamic waves; Mathematical models; Momentum; Numerical experiments; Orbits; Outer radiation belt; particle acceleration; particle transport; Populations; Radiation; Radiation belts; Scattering; Solar energy; Space weather; Statistical analysis; Statistical methods; Statistics; Storms; Transport; Transport properties; Turbulence; Variation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL104243

The transport of energetic electrons immersed in Alfvénic turbulence in Earth's outer radiation belt is explored. It is shown how electrons subject to the action of an empirically derived 3‐D spectrum of Alfvénic field fluctuations experience rapid transport across L‐shells, pitch‐angle and through momentum space. Timescales for radial transport are less than a drift period while scattering at large pitch‐angle occurs at a similar rate. Transport through momentum space occurs at a rate comparable to that in whistler mode chorus and is particularly rapid below 100 keV. Bounce‐averaged transport coefficients for these processes are consistent with quasi‐linear estimates for drift‐bounce resonances, albeit with enhanced values. A super‐diffusive to sub‐diffusive transition with increasing energy is identified. Plain Language Summary Space weather events known as geomagnetic storms drive rapid variations in near‐Earth energetic particle distributions with potentially catastrophic effect. Populations of energetic electrons trapped for months in Earth's outer radiation belt during these storms are sometimes lost in a matter of hours. While large‐scale deformation of the geomagnetic field due to the impact of explosive solar energy releases is an obvious driver of this variability, turbulent storm‐time electromagnetic fluctuations known as Alfvén waves on the scale of energetic electron orbits may also drive rapid changes. Motivated by coincident observations of this turbulence and rapid variations in Earth's outer radiation belt, a numerical experiment is performed to evaluate the effectiveness of these fluctuations in modifying radiation belt electron populations. Using the statistical properties of the observed wavefields and of the supporting plasma, a wave model equivalent to that observed is created. Energetic electrons within this model experience erratic deviations from their usual orbits. Statistical analyses quantifying these deviations indicate anomalous transport rates through space on timescales of the order of minutes along with rapid variations in particle momentum and energy. The results from this numerical experiment suggest that turbulent electromagnetic fields may play an important role in storm‐time radiation belt dynamics. Key Points A semi‐empirical model for turbulent Alfvénic fields in the storm‐time inner‐magnetosphere is created Alfvénic turbulence drives rapid radiation belt electron transport across L‐shells, through pitch‐angles and i