Revisit the Analytical Approximation of Transit‐Time Scattering for Fast Magnetosonic Waves. Issue 16 (14th August 2020)

• Record Type: Journal Article
• Authors: Yu, Xiongdong; Yuan, Zhigang; Yu, Jiang
• Is Part Of: Geophysical research letters. Volume 47:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-14
• Subjects: fast magnetosonic waves -- transit‐time scattering -- diffusion coefficient -- nonresonant interactions -- radiation belt electrons -- ring current protons; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088434
• Languages: English
• ISSNs: 0094-8276

Abstract

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. Plain Language Summary: Transit‐time scattering of magnetosonic waves due to their spatial confinement has been demonstrated to play an important role in the evolution of magnetospheric energetic particles. One generally uses test particle simulations to study this well‐known effect, which cost a rather long computation time to obtain a diffusion coefficient map. Alternatively, analytical approach has been proposed, which captures the main portion but leaves out the typical ripples in the diffusion coefficient maps. Here we show that these typical ripples are smeared out because of the large‐ y problem in previous algorithm. The typical ripples can be captured when the appropriate value is set for the integral bound to solve the large‐ y problem successfully. The study also verifies the availability of the modified algorithm to be applied to radiation belt electrons and ring current protons. Key Points: Previous analytical expressions of transit‐time scattering for fast magnetosonic waves have been modified Typical ripples in diffusion coefficient maps can be captured by the modified algorithm The modified algorithm works well for both radiation belt electrons and ring current protons