Characteristics of Low-Harmonic Magnetosonic Waves in the Earth's Inner Magnetosphere

Magnetosonic (MS) waves are electromagnetic waves that play important roles in the acceleration and scattering of radiation belt electrons. However, previous statistical analyses of the global MS wave distribution were mainly restricted to magnetic field measurements. In this study, we first report a low-harmonic MS wave event observed only by the electric field instrument in Van Allen Probes. The MS wave frequencies follow the local proton gyrofrequency (f(cp)), which suggests the characteristics of nearly local generation. We further statistically investigate similar wave events using Van Allen Probes data. The identified MS wave power exhibits peaks between 4f(cp) and 10f(cp), regardless of the L-shell, but it shows a dependence on magnetic local time. This work is supplemental to previous MS wave frequency spectra and provides new insights to better understand the source region of MS waves in the Earth's magnetosphere.