Ultra-low frequency waves in the Hermean magnetosphere: On the role of the morphology of the magnetic field and the foreshock

Ultra-low frequency (ULF) waves have been observed in the Mercury's magnetosphere by the Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry and Ranging missions. The observed ∼2 s (∼0.6 Hz) period waves in the magnetic field are proposed to be generated by dynamic processes in the Mercury's magnetosphere. We investigate the Hermean ULF waves with a global hybrid model. We found evidence for ∼2-s circularly polarized right-handed waves in Mercury's magnetosphere at the closest approach of BepiColombo mission's first Mercury flyby in the model. The most intense wave power occurs on the dawn side closed magnetic field lines. These waves were found to be generated on the hemisphere which is magnetically directly connected to the interplanetary magnetic field on the dayside and to the foreshock region. It is therefore possible that the generation mechanism of these waves is associated with the precipitating ion flux or with the wave activity in the foreshock region.