Beam-driven ECH waves: A parametric study

It is well known that electron cyclotron harmonic (ECH) waves can effectively precipitate hundreds of eV to tens of keV electrons into the upper atmosphere, resulting in the production of diffuse aurora. To deepen our outstanding of the contributions of ECH waves to diffuse aurora, in this study we perform a detailed analysis of the sensitivity of ECH wave‐induced electron scattering to ambient magnetic field intensity, total electron density and density ratio between hot and cold electrons. Our results show that for various parameter sets, ECH waves can cause the precipitation loss of diffuse auroral electrons at energies of 100 eV to several keV and are capable of accelerating 100 eV to keV electrons at intermediate pitch angle, therefore contributing to the formation of butterfly pitch angle distribution. We also find that the variations of background parameters significantly change the magnitude of diffusion coefficients and resonant pitch angle range of < ∼1 keV electrons, while the scattering efficiency of >∼1 keV electrons is almost unaffected. For <∼1 keV electrons, an increase of magnetic field intensity or density ratio between hot and cold electrons weakens the electron scattering efficiency and narrows the resonant region to lower pitch angles, while an increase of total electron density generally plays an opposite role. In addition, the momentum diffusion can be stronger than pitch angle diffusion at large pitch angles for <∼1 keV electrons, while it can be negligible at higher energies.

Section: Introductionmentioning

confidence: 99%

Parametric Sensitivity of Electron Scattering Effects by Electrostatic Electron Cyclotron Harmonic Waves

Lou

Cao

et al. 2022

“…Although ECH waves are typically generated by transversely anisotropic electrons [see the first event from Figure 1 and Ashour‐Abdalla and Thorne (1977) and Karpman et al. (1975)], field‐aligned electron streams may also drive ECH generation (see X. Zhang, Angelopoulos, Artemyev, Zhang, & Liu, 2021; X. Zhang, Angelopoulos, Artemyev, & Zhang, 2021, and references therein). Therefore, we may suggest that the difference between events from Figures 1 and 2 are different electron populations responsible for the ECH wave generation: hot, anisotropic electrons trapped into δB ‖ minima for the first event and cold, field‐aligned electron streams observed at δB ‖ maxima for the second event.…”

Section: Spacecraft Instruments and Data Setmentioning

confidence: 99%

“…There is no preferential MLT sector for events with correlation or anti‐correlation of whistler‐mode and ECH waves, that is, correlation/anti‐correlation mechanisms shall not be attributed to ULF wave properties or background plasma characteristics, but may depend on properties of electron velocity distributions (relative densities of hot, transversely anisotropic and cold, field‐aligned anisotropic populations, see discussion in X. Fu et al. (2014); X. Zhang, Angelopoulos, Artemyev, and Zhang (2021); Frantsuzov et al. (2022)).…”

Section: Spacecraft Instruments and Data Setmentioning

confidence: 99%

Statistical Analysis of Concurrent Electron Cyclotron Harmonic and Whistler Waves Driven by ULF Waves

Waheed¹,

Bashir

Artemyev

et al. 2023

Self Cite

Plasma sheet electron precipitation to the diffuse aurora is one of the primary mechanisms of magnetospheric energy transport to the Earth’s atmosphere. Such precipitation is provided by electron resonant interactions with electron cyclotron harmonics (ECH) and whistler‐mode waves in the near‐Earth plasma sheet. ECH and whistler‐mode wave generation is traditionally attributed to two main sources of free energy: the loss‐cone anisotropy and the temperature anisotropy due to transverse electron heating during earthward convection or plasma sheet injections. This paper considers a third free energy source for ECH and whistler‐mode wave generation—the electron distribution modulation by compressional ultra‐low‐frequency (ULF) waves. We conduct statistics of ECH and whistler‐mode wave bursts associated with ULF waves and show that: (a) such bursts are mostly observed on the dawn flank, (b) 83% of events show a correlation between ECH and whistler‐mode bursts, and the rest 17% show anti‐correlation, (c) ECH and whistler‐mode wave intensities are comparable with those observed around the night‐side injection region. We investigate the main characteristics of ECH and whistler‐mode waves modulated by ULF waves and provide an empirical model for these characteristics. This model can be directly incorporated into simulation frameworks, so as to include these ULF‐modulated wave bursts in simulations of the magnetosphere‐ionosphere coupling and radiation belt dynamics.

“…The most intense ECH waves occur at L = 5–9, but moderately strong ECH emissions can still be observed up to L = 12 (Zhang et al., 2013), while they generally intensify with increasing geomagnetic activity (Ni, Thorne, Horne, et al., 2011). ECH waves are thought to be excited by the loss cone instability of the ambient plasma sheet electrons (Ashour‐Abdalla & Kennel, 1978), although other generation mechanisms like wave‐wave interactions between chorus waves and ECH waves (Gao et al., 2018) or the excitation by an electron beam distribution (e.g., Zhang, Angelopoulos, Artemyev, & Zhang, 2021; Zhang, Angelopoulos, Artemyev, Zhang, & Liu, 2021) are possible.…”

Section: Introductionmentioning

confidence: 99%

Variation of Electron Lifetime Due To Scattering by Electrostatic Electron Cyclotron Harmonic Waves in the Inner Magnetosphere With Electron Distribution Parameters

Stoll,

Pick,

Wang

et al. 2023

Through resonant wave‐particle interactions with electrostatic electron cyclotron harmonic (ECH) waves, low‐energy plasma sheet electrons can be scattered into the atmospheric loss cone and precipitate. This process can be investigated by calculating bounce‐averaged quasi‐linear diffusion coefficients. However, the numerical calculation of ECH wave‐induced scattering rates requires the specification of several parameters, including the properties of the hot plasma sheet electrons responsible for the wave excitation. The dependence of the diffusion coefficients on these parameters and the exact contribution of scattering by ECH waves to diffuse auroral precipitation is still poorly understood and has not been carefully quantified yet. In this study, we calculate bounce‐averaged quasi‐linear scattering rates and compare the resulting lifetimes to the strong diffusion limit. We vary the temperature, plasma density, and loss cone parameters of the hot component in the electron loss cone distribution over a large range based on previous studies and observations. By adopting a new model that derives the wave normal angle from the midpoint and the angular width of the growth rate profile, our findings suggest that the electron lifetime near the loss cone is not significantly affected by the hot electron temperature and loss cone parameters. However, there is an increase in electron lifetimes with increasing plasma density. For an electric field amplitude of 1 mV/m, the electron lifetime is below or equal to the lifetime calculated using the strong diffusion limit up to E = 0.25 keV when n = 1.5 cm−3, and up to E = 0.22 keV when n = 9 cm−3.