The quasi-electrostatic mode of chorus waves and electron nonlinear acceleration

Selected Time History of Events and Macroscale Interactions During Substorms observations at medium latitudes of highly oblique and high-amplitude chorus waves are presented and analyzed. The presence of such very intense waves is expected to have important consequences on electron energization in the magnetosphere. An analytical model is therefore developed to evaluate the efficiency of the trapping and acceleration of energetic electrons via Landau resonance with such nearly electrostatic chorus waves. Test-particle simulations are then performed to illustrate the conclusions derived from the analytical model, using parameter values consistent with observations. It is shown that the energy gain can be much larger than the initial particle energy for 10 keV electrons, and it is further demonstrated that this energy gain is weakly dependent on the density variation along field lines. Key Points Chorus may propagate in a quasi-electrostatic mode The parallel component of wave electric field is about 25% The large parallel wave electric field can trap electrons into Landau resonance