Revisit the Analytical Approximation of Transit‐Time Scattering for Fast Magnetosonic Waves

Abstract

Nonresonant interactions between fast magnetosonic waves and magnetospheric particles have obtained more and more attention. Through such nonresonant interactions, magnetosonic waves can lead to the so‐called transit‐time scattering on particles. The previous analytical approximation has been demonstrated capable of capturing the main results of test particle simulations but takes a computation time about 4 order of magnitude faster than the latter. However, the typical ripples in the diffusion coefficient maps are usually left out. In this paper, we have first discussed the reason for the lack of these typical ripples produced by previous analytical approximation. Then the previous algorithm has been modified to be capable of producing typical ripples in the electron diffusion coefficient maps. Our new analytical expression can be applied to wave models with a Gaussian distribution or a rectangular distribution in wave amplitude. Finally, it is shown that the modified algorithm can be also applied to ring current protons.

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

“…To further demonstrate that the observed MS waves can cause flux enhancements of mirroring ring current ions, following the analytical approximation in Bortnik et al (2015) which can capture the main results of test particle simulations but take a computation time about 4 order of magnitude faster than the latter, we calculate the equatorial pitch angle diffusion coefficients for protons (X. Yu et al, 2020). As denoted by two green horizontal lines in Figure 2, within the anisotropic zone the intersected footprint of the RBSP‐A and NOAA 16 corresponds to about L = 5.78.…”

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

“…For each fitting process, the high determine coefficient of R 2 shows the accuracy of our model. In the future, we will study the effect of MS wave in dynamic evolution of the radiation belts and ring current protons based on this model, including transit‐time scattering on particles (Bortnik et al, 2015; Yu et al, 2020).…”

“…Additionally, MS waves have a wide MLT coverage and can exist both inside and outside the plasmapause. Some previous works have put forward that MS wave plays a role in accelerating electrons from keVs to MeVs via Landau resonance (Horne et al, 2000, 2007; Ni et al, 2018; Shprits, 2016; Shprits et al, 2013; Yu et al, 2020), as well as in scattering ring current ions (Fu et al, 2016; Yu et al, 2019; Yuan et al, 2020). Therefore, MS waves become an essential part in the inner magnetospheric kinetic process.…”

Radially Full Reflection of Fast Magnetosonic Waves Near the Cut‐Off Frequency

“…According to the quasilinear theory, MS waves are considered to play an important role in the dynamic evolution of the radiation belt electrons (Fu et al, 2019;Horne et al, 2007;Li et al, 2016;Xiao et al, 2015;J. Yu et al, 2019;X. Yu et al, 2020).…”