Chaotic precipitation of relativistic electrons driven by large amplitude whistler waves

Summary form only given. It has for some time been known that electrons trapped by Earth's magnetic field can precipitate along the geomagnetic field lines into the polar regions. Here the secondary ionizations caused by the electrons impacting into the ionosphere can perturb VLF signals propagating in the Earth-ionosphere waveguide. The correspondence of these precipitation events with the presence magnetospheric whistler waves has led to much study of the interaction of whistler waves with the magnetospheric plasma. Most theories have considered Doppler shifted gyroresonant interactions. However, due to the directional nature of these interactions, they are unable to explain the simultaneous observation of precipitation events in geomagnetically conjugate regions in both hemispheres. Therefore we will investigate the interaction on a single test electron with a large amplitude nonresonant wave. We show that the interaction of a whistler wave with a trapped bouncing electron can lead to chaos in the electron trajectory. The dynamics of the electron trajectory depend strongly on both particle energy and wave amplitude. In order to induce chaos with physically realistic wave amplitudes, the particle energy must be quite large, and thus relativistic effects are important. Inclusion of relativistic effects also has the effect of decreasing the required threshold wave field for the onset of chaos for a wide range of particle energies. The end result of chaotic behavior is to enhance the electron's axial kinetic energy, which decreases the particles pitch angel allowing it to be scattered into the mirror field loss cone.