Generation of rising‐tone chorus in a two‐dimensional mirror field by using the general curvilinear PIC code

Abstract

Recently, the generation of rising‐tone chorus has been implemented with one‐dimensional (1‐D) particle‐in‐cell (PIC) simulations in an inhomogeneous background magnetic field, where both the propagation of waves and motion of electrons are simply forced to be parallel to the background magnetic field. In this paper, we have developed a two‐dimensional (2‐D) general curvilinear PIC simulation code and successfully reproduced rising‐tone chorus waves excited from an anisotropic electron distribution in a 2‐D mirror field. Our simulation results show that whistler waves are mainly generated around the magnetic equator and continuously gain growth during their propagation toward higher‐latitude regions. The rising‐tone chorus waves are observed off the magnetic equator, which propagate quasi‐parallel to the background magnetic field with the wave normal angle smaller than 25°. Due to the propagating effect, the wave normal angle of chorus waves is increasing during their propagation toward higher‐latitude regions along an enough curved field line. The chirping rate of chorus waves is found to be larger along a field line with a smaller curvature.

Nonlinear Evolution of Counter‐Propagating Whistler Mode Waves Excited by Anisotropic Electrons Within the Equatorial Source Region: 1‐D PIC Simulations

“…This has already been confirmed by many observational works, further showing that their source region just extends to several degrees of magnetic latitude from the magnetic equator (LeDocq et al, ; Parrot et al, ; Santolík et al, ). In the source region, whistler mode waves are typically detected with opposite Poynting flux directions and very small WNAs (Li et al, ), which is also supported by the linear theory (Gary & Karimabadi, ; Omura et al, ) and particle‐in‐cell (PIC) simulations (Ke et al, ).…”

Unraveling the Correlation Between Chorus Wave and Electron Beam‐Like Distribution in the Earth's Magnetosphere

“…Chorus waves are commonly believed to be excited by anisotropic hot electrons at the magnetic equator, whose wave normal angles are typically very small Ke et al, 2017;Lu et al, 2019;Omura et al, 2008). Then, they will propagate toward high-latitude regions with increasing wave normal angles Ke et al, 2017;Lu et al, 2019). Meanwhile, the parallel electric field of chorus waves also becomes significant, which will accelerate electrons in the parallel direction through the The scatter plots of chorus events in the (E ∥ /B 0 V Ae , n h /n 0 ) plane with color-coded n b /n h for two categories (i.e., θ < 45°and θ > 45°) and (c and d) the median value of n b /n h in the (E ∥ /B 0 V Ae , n h /n 0 ) plane.…”

Theoretical analysis on lower band cascade as a mechanism for multiband chorus in the Earth’s magnetosphere

“…In the equatorial plane, the parallel counter-propagating whistler waves (either discrete or hiss-like emissions) are excited by anisotropic hot electrons, then these waves propagate to relatively higher-latitude regions and their WNA can become non-zero but a small value. 22,23 Through the type I E-t channel, the whistler-mode spectrum can turn into a banded one, where lower-band and upper-band chorus waves coexist in both electric and magnetic spectrograms. At even higher-latitude regions, lower-band whistler waves can become very oblique and quasi-electrostatic, 22 which typically have a small magnetic amplitude but a large electric amplitude.…”