Magnetosonic wave instability by proton ring distributions: Simultaneous data and modeling

Abstract

Simultaneous observations of enhanced fast magnetosonic (MS) waves and distinct proton ring distributions collected by Cluster satellite near the location L= 4-5 on 28 May 2005 are analyzed to study instability of MS waves. A sum of subtracted bi-Maxwellian components is utilized to fit the observed proton (2-10 keV) ring distributions. A ray-tracing simulation is performed to calculate the local growth rate and path-integrated gain of MS waves. Peak growth rates are found to occur at the multiples of proton gyrofrequency mainly in the range ∼ 70-120 Hz, and wave gain lies in ∼ 40-80 dB, comparable to the observation. Moreover, MS waves primarily locate within a few degrees of the geomagnetic equator and propagate either into or out of the plasmasphere through the plasmapause. The current results provide observational support for instability of fast magnetosonic waves generated by the proton ring distribution.