Generation of Electromagnetic Waves by Ion Beams at the Magnetopause

Abstract

We present a theory for the generation of both long and short wavelength (in comparison with the ion gyroradius) electromagnetic waves that are triggered by ion beams at the Earth's magnetopause. We use a fluid model for long wavelength limit, and a hybrid approach (a kinetic theory for ion response and a fluid model for electron response) for short wavelength limit, and derive the linear dispersion relations for both cases. The latter are analyzed numerically for parameters corresponding to the Earth's magnetopause. It is shown that the ion beam with a speed greater than the ion thermal speed and the plasma density inhomogeneity with scalelength less than the electron skin-depth destabilize the electromagnetic waves of lower-hybrid frequencies. The present study may be useful for understanding the origin of numerous scale-sized fluctuations that are observed at the Earth's magnetopause.