Chorus intensification in response to interplanetary shock

Abstract

, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites observed a significant intensification of chorus in response to the interplanetary shock in the Earth's dayside plasma trough. We analyze the wave-particle interaction and reveal that the chorus intensification can be caused by the gyroresonance between the chorus and the energetic electrons. When the electrons are scattered from resonance points to low-density regions along the diffusion curves, a part of their energy can be lost and then transferred to amplify the chorus. During the compression of the magnetosphere, the temperature anisotropy of electrons is enhanced. This makes the electron diffusion and chorus intensification very effective. The maximum growth rate after the shock is about 50% greater than that before the shock. The lower-energy (15-25 keV) electrons contribute more to the growth of chorus due to the larger density gradient along the diffusion curve. The <10 keV electrons are almost isotropic, so they contribute little to the amplification of chorus. We investigate the free energy for the chorus intensification and find that it can be generated through the local betatron acceleration and radial diffusion processes. The local betatron acceleration results from the shock-induced compression of the magnetosphere. The linear and nonlinear growth rates are also compared. We find that the linear diffusion process works well for the present case.

Electron Distribution Functions Around a Reconnection X‐Line Resolved by the FOTE Method

“…3. the electron distribution measured by MMS 2 and 3, in the magnetosheath-side inflow region with nullspacecraft distance of 20 or 30 km (2-D distance; see Figure 3m), is cigar-type (T // > T ⊥ ) at low-energy channels but exhibits a loss feature in the antiparallel direction at high-energy channels (Figures 3f and 3g and 3j and 3k). This scenario is somewhat similar to that in the radiation belt, where quasi-perpendicular electrons have mirror points close to the magnetic equator and the ionospheric collision leads to the loss cone distribution (Fu et al, 2011(Fu et al, , 2012. In this way, these quasiperpendicular electrons (population B and C) will be stably trapped in the inflow region and get energized via the Fermi process during the multiple bounces between the mirror points, as the case measured by MMS 4 in the magnetosphere-side inflow region.…”

Observation of Oblique Lower Band Chorus Generated by Nonlinear Three‐Wave Interaction

“…These waves frequently exhibit a two-band structure with a power minimum near 0.5f ce0 (Burtis & Helliwell, 1976;H. Usually observed outside the plasmapause, chorus waves consist of narrow band discrete emissions with frequency chirping due to nonlinear wave-particle interactions.…”

PENGUIn/AGO and THEMIS conjugate observations of whistler mode chorus waves in the dayside uniform zone under steady solar wind and quiet geomagnetic conditions

“…Dayside whistler mode chorus is at times related to sudden enhancements of the solar wind dynamic pressure. It has been reported that a sudden magnetospheric compression triggers chorus or increases its intensity [ Gail and Inan , 1990; Gail et al , 1990; Salvati et al , 2000; Fu et al , 2012]. This type of dayside chorus is attributed to compression‐related adiabatic heating leading to electron anisotropy and thus increases in the chorus wave growth rate.…”