The dependence of fast magnetosonic wave instability on wave normal angles

Abstract:

Equatorial noises (also known as fast magnetosonic waves) are a nearly perpendicularly propagating electromagnetic emission above proton gyro frequency and below lower hybrid resonance frequency in the Earth’s magnetosphere. The emission, which is generated through a proton ring type distribution, is important for electron acceleration in the Earth’s radiation belts. Although the wave normal angle is confined within several degrees about 90 degrees observationally, the effectiveness of electron acceleration is still sensitive to the wave normal angle in this narrow range. In this presentation, the dependence of magnetosonic waves instability on wave normal angle (up to 90 degrees) and frequency is systematically investigated. We find that magnetosonic wave growth rate can peak at 90 deg with sharp harmonic structure, and as wave normal angle decreases the growth rate becomes weaker and gradually turns continuous with respect to frequency. The importance of magnetosonic waves on electron acceleration is also discussed.