Dominant Roles of High Harmonics on Interactions Between AKR and Radiation Belt Relativistic Electrons

Abstract

Auroral kilometric radiations (AKR) are widely existing superluminous waves in the magnetosphere. Due to rarely available measurements of AKR magnetic field components, we derive the explicit expression of diffusion coefficients in terms of electric field components, which can be applied to various space plasma waves. Using Van Allen Probes data, we calculate diffusion coefficients with different harmonic orders for two AKR events. It is found that the first (higher) harmonic order contributes to diffusion coefficients at small (larger) pitch angles. The effect of higher harmonic orders becomes more significant as the electron energy increases. These results are contrary to the case of chorus wave, in which the first order usually contributes much to wave‐particle interactions. Estimations show that the phase space density of 0.5 MeV electrons can increase ∼10 times within 6 hr by AKR. This study is important for better modeling of AKR‐induced radiation belt electron dynamics.

A Concise Empirical Formula for the Field‐Aligned Distribution of Auroral Kilometeric Radiation Based on Arase Satellite and Van Allen Probes

“…In addition, if the PSD of wave magnetic field and electric field are chosen to follow the same frequency distribution, the empirical formula of AKR magnetic field amplitude can be obtained based on the Maxwell’s equations and Equation . However, considering that the Arase satellite and Van Allen Probes currently provide only the electric field PSD of AKR emissions in the radiation belts, we prefer to use formulas in terms of AKR wave electric field amplitude to calculate diffusion coefficients (Zhang et al., 2020). The concise formula probably provides a very useful method to model AKR‐electron interaction.…”

“…However, their studies are limited within low latitudes due to the low latitude orbit of Van Allen Probes. Various studies (Summers et al., 2001; Xiao, Chen, He, 2010; Xiao et al., 2006; Xiao, Su, et al., 2010; Zhang et al., 2020) have found that the AKR has a potential for producing acceleration (or precipitation) of electrons in radiation belts under appropriate conditions. The aforementioned acceleration or loss of energetic electrons can yield serious damage to spacecraft by surface charging (Baker, 2002) or ozone destruction via chemistry change in atmosphere (Thorne, 1977; Callis et al., 1998; Thorne et al., 2005).…”

“…The efficiency of wave-particle interaction is determined by diffusion coefficients which depend on wave spectrum characteristics, particularly the wave amplitude because diffusion coefficients are proportional to the square of wave amplitude (Su et al, 2018;Summers, 2005;Summers et al, 2001Summers et al, , 1998Wang et al, 2020;Zhang et al, 2020). Charged particles in magnetosphere usually move along the field line, bounced back and forth between two mirror points.…”

“…Wave-particle interaction generally occurs at each point along the specific field line. Previous observations have showed that the AKR amplitude can approach to 300 mV/m in the source region (Ergun et al, 1998), and reduces to 0.287 mV/m near the equatorial plane (Zhang et al, 2020). In order to better quantify the interaction between AKR waves and electrons, it is necessary to specify the wave amplitude along the field line, but this has not been reported so far.…”

Asymmetric Distributions of Auroral Kilometric Radiation in Earth's Northern and Southern Hemispheres Observed by the Arase Satellite

“…It is well known that wave‐particle interaction is an important process of magnetosphere‐ionosphere‐atmosphere coupling and has been studied widely by researchers (Q. Yang et al., 2016; Jin et al., 2018; Guo et al., 2020; Guan et al., 2020; C. Yang et al., 2021; He et al., 2021). Various studies have proved that AKR can produce efficient acceleration or pitch angle scattering of energetic electrons under appropriate conditions (Summers et al., 2001; Xiao, Chen, & He, 2010; Xiao, Chen, He, & Yang, 2010; Xiao et al., 2006; Xiao, Su, et al., 2010; Zhang et al., 2020). Those accelerated or scattered electrons can cause ozone destruction or serious damage to spacecrafts (Baker, 2002; Callis et al., 1998; Thorne, 1977; Thorne et al., 2005).…”