Simulation study on parametric dependence of whistler-mode hiss generation in the plasmasphere

• Published in: Earth, planets, and space Vol. 73; no. 1; pp. 1 - 17
• Main Authors: Liu, Yin, Omura, Yoshiharu, Hikishima, Mitsuru
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 16.12.2021; Springer; Springer Nature B.V; SpringerOpen
• Subjects: 3. Space science; Amplitudes; Earth and Environmental Science; Earth Sciences; Electromagnetic fields; Electron density; Equatorial regions; Geology; Geophysics/Geodesy; Gradient coefficient; High temperature plasmas; Hiss; Hot electrons; Inhomogeneity; Low level; Magnetic fields; Nonlinear; Observations; Particle simulation; Plasma (Ionized gases); Plasmasphere; Plasmaspheric hiss; Simulation; Theoretical analysis; VLF/ELF Remote Sensing of Ionospheres and Magnetospheres; Wave packets; Wave propagation; Japan; Plasmaspheric hiss; Nonlinear; Gradient coefficient; Particle simulation; Electron density
• ISSN: 1880-5981; 1343-8832; 1880-5981
• DOI: 10.1186/s40623-021-01554-6

We conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of the background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, the nonlinear process is suppressed. In the simulations, as we enlarge the gradient coefficient of the background magnetic field, waves generated near the equator do not grow through propagation. By examining the range of suitable values of inhomogeneity factor S (i.e., | S | < 2 ), we find the generation of wave packets is limited to the equatorial region when the background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable S values implies that the nonlinear process occurs even at a low level of hot electron density. However, by examining J E that closely relates to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which agrees with the theoretical analysis. Graphical Abstract