ULF Modulations on Plasma Environment and Coherent Waves of Mercury's Magnetosphere: MESSENGER's Observation

Abstract

AbstractUltra low frequency (ULF) waves are fundamental waves that can energize, transport, and scatter charged particles in planetary magnetospheres. With the measurements from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER), we investigate the proton flux fluctuations and coherent waves associated with a series of ULF waves on the flanks of Mercury's magnetosphere. The ULF waves are mainly compressional with a frequency of ∼15 mHz and significantly modulate the intensity of proton flux. The coherent waves accompanied by the ULF waves correspond to a higher frequency (∼1 Hz). The wave power and compressibility of the coherent waves vary quasi‐periodically with the ∼15 mHz ULF waves. We conclude that the compressional ULF waves modulate the coherent waves with higher frequency. This modulation might result from the associated periodic proton flux changes and helps us understand the nature of the ∼1 Hz waves better.