Study on Source Region and Generation Mechanism of Oblique Whistler‐Mode Waves in the Earth's Magnetosphere

Abstract

Whistler-mode waves are very common electromagnetic emissions falling within the frequency range of 0.1-0.8 𝐴𝐴 𝐴𝐴ce (where 𝐴𝐴 𝐴𝐴ce is the equatorial electron gyrofrequency) in the Earth's magnetosphere. They are also known as chorus waves, appearing as a series of repetitive coherent emissions (Gao et al., 2022;Lu et al., 2021). There usually exists a power gap around 0.5 𝐴𝐴 𝐴𝐴ce in the spectrum, dividing the spectrum into lower and upper bands (

Intense chorus waves are the cause of flux-limiting in the heart of the outer radiation belt

“…The flux of relativistic electrons trapped in the Earth's Van Allen radiation belts can vary by several orders of magnitude in response to solar wind forcing (e.g., 1 ), and a number of wave-particle interactions have been proposed as contributing to the observed dynamics. For example, chorus waves are responsible for local acceleration (e.g., see [2][3][4][5][6][7][8][9][10][11] ), longer period ultra-low frequency (ULF) waves are responsible for particle acceleration as a result of inward radial diffusion (e.g., see [12][13][14][15][16][17][18][19][20][21] ), in addition to other wave-particle interactions such as electromagnetic ion-cyclotron (EMIC) waves that are responsible for loss of radiation belt electrons (e.g., see 22,23 ), manmade VLF transmitter waves (e.g., 24 ) and plasmaspheric hiss (e.g., 25 ) are also thought to be able to scatter the electrons into the loss cone and lead to the corresponding evolution of the electron flux. In this paper, we examine the chorus wave activity that accompanies a flux-limiting process in the inner magnetosphere that occurs during geomagnetic storms, and demonstrate that the theoretical predictions of Kennel and Petschek 26 accurately depict the behaviour of waves and electron fluxes in the outer Van Allen belt.Recent work associated with the capping of ~ 10-100 keV electron flux by Olifer et al 27 has revisited the dynamics of the energetic electron population in the outer electron radiation belt, revealing evidence for an energy-dependent limit to the electron flux in the belts (see also 28 , and references therein).…”

Butterfly Distributions of Energetic Electrons Driven by Ducted and Nonducted Chorus Waves

“…Chorus waves can be ducted (quasi‐parallel) in a density structure and propagate nearly along the magnetic field lines (e.g., R. Chen et al., 2021; Ke et al., 2021; Liu et al., 2021; Streltsov et al., 2006). However, nonducted chorus waves tend to become oblique‐propagating gradually (e.g., Breuillard et al., 2012; Gao, Lu, et al., 2022; Lu et al., 2019) after leaving their equatorial sources (e.g., LeDocq et al., 1998; W. Li et al., 2009; Santolík et al., 2005). The relations between nonducted chorus waves and electron butterfly PADs at tens of keV is less well‐known.…”