Global Distribution of Discrete and Continuous Spectrum Equatorial Magnetosonic Waves Observed by the Van Allen Probe‐A.

Magnetosonic (MS) waves can either be discrete or continuous in the time‐frequency spectrogram. Through the observation from Van Allen Probe‐A spacecraft, the global distribution of discrete and continuous spectrum MS waves in the region L ∼ 3–6 is determined. According to our research, the continuous spectrum MS waves are greater in amplitude than discrete spectrum MS waves. Also, the impact of changes in geomagnetic activity on continuous spectrum MS waves is much more significant than discrete spectrum MS waves. Besides, it is also demonstrated that the strong discrete spectrum MS waves have a peak wave amplitude of ∼60 pT and an occurrence rate of ∼50% at the noon sector outside the plasmapause. In comparison, the strong continuous spectrum MS waves have a peak wave amplitude of ∼300 pT and an occurrence rate of ∼60% at the postnoon sector inside the plasmapause. Plain Language Summary: Magnetosonic (MS) waves are usually assumed as the continuous spectrum in the frequency band in line with the quasi‐linear diffusion theory. However, discrete spectrum structures are also observable. Therefore, systematical statistics are generated in the occurrence rate and spatial distribution of discrete and continuous spectrum MS waves with the data from Van Allen Probe‐A spacecraft between January 2014 and December 2017. The study reveals the difference between discrete and continuous spectrum MS waves on the spatial distribution and the occurrence rate, which leads to the conclusion that the changes in geomagnetic activity have a more significant impact on the generation of continuous spectrum MS waves. Key Points: Out of the total magnetosonic (MS) waves observed, 32,474 (48.7%) were discrete spectrum MS waves, while 33,380 (50.1%) were continuous spectrum MS wavesThe wave amplitude of continuous spectrum MS waves is substantially greater compared to discrete spectrum MS wavesThe occurrence rates and wave amplitude of continuous spectrum MS waves are closely associated with AE* effects inside the plasmapause [ABSTRACT FROM AUTHOR]