An official website of the United States government
Abstract 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 acrossL‐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.
more »
« less
Driving Earth's Outer Radiation Belt With Alfvénic Turbulence
Abstract Semi‐empirical coefficients for electron transport in Alfvénic turbulence are used to drive the global evolution of energetic electron distributions through Earth's outer radiation belt. It is shown how these turbulent fields facilitate radial transport and pitch‐angle scattering that drive losses through the magnetopause, into the plasma sheet, through the plasmapause and to the atmosphere. Butterfly distributions are formed due to pitch‐angle scattering and the combined effect of the loss processes. For the observed spectrum of oscillations, it is estimated that Alfvénic turbulence drives order of magnitude depletions of outer radiation belt electron fluxes at relativistic energies over a period of a few hours. On the other hand, at lower energies, energization in transverse Alfvénic electric fields leads to enhancements of the electron spectrum to provide a source population for subsequent acceleration to higher energies and, in concert with the loss processes, provides exponential spectral form as a function of energy.
more »
« less
- PAR ID:
- 10585791
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 8
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler‐mode waves and relativistic electrons using Juno measurements and wave‐particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV atMshell ∼11 near the magnetic equator during perijove‐31. The electron injections are related to chorus wave bursts at 0.05–0.5fcefrequencies, wherefceis the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90° pitch angle, and the fluxes are high during injections. We calculate the whistler‐mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler‐mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1–10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave‐particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler‐mode waves in Jupiter's outer radiation belt.more » « less
-
Abstract During geomagnetic storms relativistic outer radiation belt electron flux exhibits large variations on rapid time scales of minutes to days. Many competing acceleration and loss processes contribute to the dynamic variability of the radiation belts; however, distinguishing the relative contribution of each mechanism remains a major challenge as they often occur simultaneously and over a wide range of spatiotemporal scales. In this study, we develop a new comprehensive model for storm‐time radiation belt dynamics by incorporating electron wave‐particle interactions with parallel propagating whistler mode waves into our global test‐particle model of the outer belt. Electron trajectories are evolved through the electromagnetic fields generated from the Multiscale Atmosphere‐Geospace Environment (MAGE) global geospace model. Pitch angle scattering and energization of the test particles are derived from analytical expressions for quasi‐linear diffusion coefficients that depend directly on the magnetic field and density from the magnetosphere simulation. Using a study of the 17 March 2013 geomagnetic storm, we demonstrate that resonance with lower band chorus waves can produce rapid relativistic flux enhancements during the main phase of the storm. While electron loss from the outer radiation belt is dominated by loss through the magnetopause, wave‐particle interactions drive significant atmospheric precipitation. We also show that the storm‐time magnetic field and cold plasma density evolution produces strong, local variations of the magnitude and energy of the wave‐particle interactions and is critical to fully capturing the dynamic variability of the radiation belts caused by wave‐particle interactions.more » « less
-
Abstract We investigate the dynamics of relativistic electrons in the Earth's outer radiation belt by analyzing the interplay of several key physical processes: electron losses due to pitch angle scattering from electromagnetic ion cyclotron (EMIC) waves and chorus waves, and electron flux increases from chorus wave‐driven acceleration of 100–300 keV seed electrons injected from the plasma sheet. We examine a weak geomagnetic storm on 17 April 2021, using observations from various spacecraft, including GOES, Van Allen Probes, ERG/ARASE, MMS, ELFIN, and POES. Despite strong EMIC‐ and chorus wave‐driven electron precipitation in the outer radiation belt, trapped 0.1–1.5 MeV electron fluxes actually increased. We use theoretical estimates of electron quasi‐linear diffusion rates by chorus and EMIC waves, based on statistics of their wave power distribution, to examine the role of those waves in the observed relativistic electron flux variations. We find that a significant supply of 100–300 keV electrons by plasma sheet injections together with chorus wave‐driven acceleration can overcome the rate of chorus and EMIC wave‐driven electron losses through pitch angle scattering toward the loss cone, explaining the observed net increase in electron fluxes. Our study emphasizes the importance of simultaneously taking into account resonant wave‐particle interactions and modeled local energy gradients of electron phase space density following injections, to accurately forecast the dynamical evolution of trapped electron fluxes.more » « less
-
Abstract Whistler‐mode chorus and hiss waves play an important role in Earth's radiation belt electron dynamics. Direct measurements of whistler wave‐driven electron precipitation and the resultant pitch angle distribution were previously limited by the insufficient resolution of low Earth orbit satellites. In this study, we use recent measurements from the Electron Losses and Fields INvestigation CubeSats, which provide energy‐ and pitch angle‐resolved electron distributions to statistically evaluate electron scattering properties driven by whistler waves. Our survey indicates that events with increasing precipitating‐to‐trapped flux ratios (evaluated at 63 keV unless otherwise specified) correlate with increasing trapped flux at energies up to ∼750 keV. Weak precipitation events (precipitation ratio <0.2) are evenly distributed, while stronger precipitation events tend to be concentrated atL > 5 over midnight‐to‐noon local times during disturbed geomagnetic conditions. These results are crucial for characterizing the whistler‐mode wave driven electron scattering properties and evaluating its impact on the ionosphere.more » « less
