The Characteristics of EMIC Waves in the Magnetosphere Based on the Van Allen Probes and Arase Observations

Abstract

Electromagnetic ion cyclotron (EMIC) waves constitute a significant loss process of energetic protons and sub-relativistic electrons through pitch-angle scattering by wave-particle interactions (e.g., Anderson et al., 1992aAnderson et al., , 1992bThorne, 2010). These interactions contribute to the generation of the isolated proton auroras at subauroral latitudes (e.g.,

Effects of EMIC Wave‐Driven Proton Precipitation on the Ionosphere

“…For L < 6 Re, this statistical distribution of He‐band EMIC wave is similar to that of the recent work by Jun et al. (2021), such that both show the peak occurrence in the noon‐to‐dusk sector (i.e., 12–21 MLT). But the used statistical distribution of H‐band EMIC wave shows wider MLT coverage than that of Jun et al.…”

“…For L < 6 Re, this statistical distribution of He-band EMIC wave is similar to that of the recent work byJun et al (2021), such that both show the peak occurrence in the noon-to-dusk sector (i.e., 12-21 MLT). But the used statistical distribution of H-band EMIC wave shows wider MLT coverage than that ofJun et al (2021), which mainly occurs in the noon sector (i.e., 10-14 MLT). Based on such wave intensity, the pitch angle diffusion coefficient ⟨ ⟩ is calculated from quasi-linear theory, as a function of energy and pitch angle.Figures 2c and 2d show such coefficients at MLT = 18 and L = 4.…”

“…But the used statistical distribution of H‐band EMIC wave shows wider MLT coverage than that of Jun et al. (2021), which mainly occurs in the noon sector (i.e., 10–14 MLT). Based on such wave intensity, the pitch angle diffusion coefficient $$< {D}_{\alpha \alpha } > $$ is calculated from quasi‐linear theory, as a function of energy and pitch angle.…”

Amplitude Dependence of Nonlinear Precipitation Blocking of Relativistic Electrons by Large Amplitude EMIC Waves

“…The ion concentration is assumed to be constant with latitude, with the commonly used ratios n H /n e = 0.77, n He /n e = 0.2, and n O /n e = 0.03 (Albert & Bortnik, 2009;Jordanova et al, 2008). The wave frequencies adopted for regions b and c were f b = 1.9 Hz and f c = 0.77 Hz corresponding to typical H-band and He-band wave frequencies at L = 5, respectively (Jun et al, 2021), with a field-aligned wave normal angle. The latitudinal amplitude variation was taken similar to Bortnik et al (2008), that is, increasing smoothly in the equatorial region to its maximum value 𝐴𝐴 𝐴𝐴 0 𝑤𝑤 over the span of a few degrees, and is given by…”

“…• The range of nonlinear responses of energetic electrons interacting with intense ElectroMagnetic Ion Cyclotron (EMIC) waves is studied using a test-particle code • Resonant energetic electrons at low pitch angles experience nonlinear force bunching which rapidly advects them to large pitch angles • Increasing EMIC wave amplitudes enhances the force bunching positive advection relative to diffusion resulting in precipitation blocking Meredith et al, 2014;Min et al, 2012;Saikin et al, 2015;Usanova et al, 2012Usanova et al, , 2013, the recent availability of high-resolution, long-term, multi-spacecraft, full-spatial coverage datasets has allowed an unprecedented level of detail to be achieved in such observations. For example, using a combined dataset of Van Allen Probes (Mauk et al, 2013) and Arase (Miyoshi et al, 2018) observations, Jun et al (2021) demonstrated that EMIC waves tend to naturally group into four distinct occurrence regions, each with its own unique morphology and driving conditions, shown in the central panel of Figure 1, labeled a-d.…”