Weak Turbulence and Quasilinear Diffusion for Relativistic Wave-Particle Interactions Via a Markov Approach

Allanson, Oliver; Elsden, T.; Watt, Clare E. J.; Neukirch, T.

doi:10.3389/fspas.2021.805699

Cited by 18 publications

(24 citation statements)

References 79 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Each of the wave-particle resonant interactions should be considered independently, that is, we assume no correlation of electron gyrophase between two successive resonant interactions. Such correlations may significantly modify the efficiency of electron scattering by waves (see discussion in, e.g., Allanson et al, 2022;Osmane & Lejosne, 2021), but for realistic, inhomogeneous magnetic fields and realistic whistler-mode wave amplitudes, effects due to phase correlations are negligibly weak (see discussions in Artemyev et al, 2020b;Artemyev et al, 2020a). 3.…”

Section: Theory Of Nonlinear Landau Resonancementioning

confidence: 99%

On the Nature of Intense Sub‐Relativistic Electron Precipitation

et al. 2022

View full text Add to dashboard Cite

Energetic electron precipitation into Earth's atmosphere is an important process for radiation belt dynamics and magnetosphere‐ionosphere coupling. The most intense form of such precipitation is microbursts—short‐lived bursts of precipitating fluxes detected on low‐altitude spacecraft. Due to the wide energy range of microbursts (from sub‐relativistic to relativistic energies) and their transient nature, they are thought to be predominantly associated with energetic electron scattering into the loss cone via cyclotron resonance with field‐aligned intense whistler‐mode chorus waves. In this study, we show that intense sub‐relativistic microbursts may be generated via electron nonlinear Landau resonance with very oblique whistler‐mode waves. We combine a theoretical model of nonlinear Landau resonance, equatorial observations of intense very oblique whistler‐mode waves, and conjugate low‐altitude observations of <200 keV electron precipitation. Based on model comparison with observed precipitation, we suggest that such sub‐relativistic microbursts occur by plasma sheet (0.1 − 10 keV) electron trapping in nonlinear Landau resonance, resulting in acceleration to ≲200 keV energies and simultaneous transport into the loss cone. The proposed scenario of intense sub‐relativistic (≲200 keV) microbursts demonstrates the importance of very oblique whistler‐mode waves for radiation belt dynamics.

show abstract

Section: Theory Of Nonlinear Landau Resonancementioning

confidence: 99%

On the Nature of Intense Sub‐Relativistic Electron Precipitation

et al. 2022

View full text Add to dashboard Cite

show abstract

“…There are also important upper limits to the time over which diffusion coefficients should be estimated from observations. An important upper limit is a timescale of the order of D −1 αα (Lemons, 2012;Liu et al, 2012;Allanson et al, 2022). For many observation-specific diffusion coefficients used in this study, this timescale is at least a few days.…”

Section: Diffusion Coefficients Modelled Using Quasi-linear Theorymentioning

confidence: 95%

“…Quasi-linear diffusion coefficients must be calculated on timescales that are long compared to the wave period T ~Ω−1 e , and the particle de-correlation time τ C ~T, where τ C increases for decreasing wave amplitude (Lemons, 2012;Liu et al, 2012;Allanson et al, 2020;Allanson et al, 2022). For whistler mode waves in the terrestrial magnetosphere, these timescales are short and usually much less than 1 s. As a result, individual wave-spectra observations from spacecraft such as the NASA Van Allen Probes have already averaged over timescales longer that the appropriate minimum timescale.…”

Section: Diffusion Coefficients Modelled Using Quasi-linear Theorymentioning

confidence: 99%

Temporal variability of quasi-linear pitch-angle diffusion

Watt

Allison

Bentley

et al. 2022

Front. Astron. Space Sci.

Self Cite

View full text Add to dashboard Cite

Kinetic wave-particle interactions in Earth’s outer radiation belt energize and scatter high-energy electrons, playing an important role in the dynamic variation of the extent and intensity of the outer belt. It is possible to model the effects of wave-particle interactions across long length and time scales using quasi-linear theory, leading to a Fokker-Planck equation to describe the effects of the waves on the high energy electrons. This powerful theory renders the efficacy of the wave-particle interaction in a diffusion coefficient that varies with energy or momentum and pitch angle. In this article we determine how the Fokker-Planck equation responds to the temporal variation of the quasi-linear diffusion coefficient in the case of pitch-angle diffusion due to plasmaspheric hiss. Guided by in-situ observations of how hiss wave activity and local number density change in time, we use stochastic parameterisation to describe the temporal evolution of hiss diffusion coefficients in ensemble numerical experiments. These experiments are informed by observations from three different example locations in near-Earth space, and a comparison of the results indicates that local differences in the distribution of diffusion coefficients can result in material differences to the ensemble solutions. We demonstrate that ensemble solutions of the Fokker-Planck equation depend both upon the timescale of variability (varied between minutes and hours), and the shape of the distribution of diffusion coefficients. Based upon theoretical construction of the diffusion coefficients and the results presented here, we argue that there is a useful maximum averaging timescale that should be used to construct a diffusion coefficient from observations, and that this timescale is likely less than the orbital period of most inner magnetospheric missions. We discuss time and length scales of wave-particle interactions relative to the drift velocity of high-energy electrons and confirm that arithmetic drift-averaging is can be appropriate in some cases. We show that in some locations, rare but large values of the diffusion coefficient occur during periods of relatively low number density. Ensemble solutions are sensitive to the presence of these rare values, supporting the need for accurate cold plasma density models in radiation belt descriptions.

show abstract

“…In the absence of a modeling framework able to account for 1) the effects of both diffusive and non-diffusive (i.e., rapid, significant and coherent) radial transport, as well as 2) the effects of local acceleration (including nonlinear effects), it is not possible to quantify the importance of local vs. radial acceleration unequivocally. Given current computational advances, time may have come to go beyond a purely diffusion-driven model, towards a more realistic modeling framework (e.g., Artemyev et al, 2021;Lukin et al, 2021;Allanson et al, 2022). That said, improved radiation belt modeling would also require improved knowledge of the characteristics of trapped particle interactions with VLF and ULF waves-via experimental determination of the correlation decay time for instance (e.g., Ukhorskiy and Sitnov, 2013).…”

Section: Topic Overviewmentioning

confidence: 99%

Differentiating Between the Leading Processes for Electron Radiation Belt Acceleration

Lejosne

Allison

Blum

et al. 2022

Front. Astron. Space Sci.

View full text Add to dashboard Cite

Many spacecraft fly within or through a natural and variable particle accelerator powered by the coupling between the magnetosphere and the solar wind: the Earth’s radiation belts. Determining the dominant pathways to plasma energization is a central challenge for radiation belt science and space weather alike. Inward radial transport from an external source was originally thought to be the most important acceleration process occurring in the radiation belts. Yet, when modeling relied on a radial diffusion equation including electron lifetimes, notable discrepancies in model-observation comparisons highlighted a need for improvement. Works by Professor Richard M. Thorne and others showed that energetic (hundreds of keV) electrons interacting with whistler-mode chorus waves could be efficiently accelerated to very high energies. The same principles were soon transposed to understand radiation belt dynamics at Jupiter and Saturn. These results led to a paradigm shift in our understanding of radiation belt acceleration, supported by observations of a growing peak in the radial profile of the phase space density for the most energetic electrons of the Earth’s outer belt. Yet, quantifying the importance of local acceleration at the gyroscale, versus large-scale acceleration associated with radial transport, remains controversial due to various sources of uncertainty. The objective of this review is to provide context to understand the variety of challenges associated with differentiating between the two main radiation belt acceleration processes: radial transport and local acceleration. Challenges range from electron flux measurement analysis to radiation belt modeling based on a three-dimensional Fokker-Planck equation. We also provide recommendations to inform future research on radiation belt radial transport and local acceleration.

show abstract

Weak Turbulence and Quasilinear Diffusion for Relativistic Wave-Particle Interactions Via a Markov Approach

Cited by 18 publications

References 79 publications

On the Nature of Intense Sub‐Relativistic Electron Precipitation

On the Nature of Intense Sub‐Relativistic Electron Precipitation

Temporal variability of quasi-linear pitch-angle diffusion

Differentiating Between the Leading Processes for Electron Radiation Belt Acceleration

Contact Info

Product

Resources

About