Study of the structure and motion of Pc5 compressional waves by MMS observations

Abstract:

Pc5 compressional waves are frequently observed in the outer magnetosphere, and their source is usually considered to be drift mirror instability. Due to the limited spatial coverage of spacecraft, their overall structure is still poorly understood. In this work, the wave structure and motion characteristics are statistically investigated based on the MMS data from September to October 2015. During this period, the apogees of the MMS spacecraft orbits were located in the outer dusk magnetosphere, and the spacecraft has regular tetrahedral configuration that facilitates the application of multi-spacecraft analysis techniques. From our database, we identify about 1100 magnetic valley boundaries, and the normal direction, current density and velocity are calculated. We found that the “magnetic bottle” is an important element for the Pc5 compressional wave, and the spacecraft locates at the southside of the magnetic bottle, if the position angle between the spacecraft position vector and the background magnetic field is of ~ 60 degree. The boundaries mainly move sunward in the GSE XY plane with average speed of ~26km/s. The average time duration of the magnetic bottle is 3.7 min. The maximum current density is detected at the boundary of the magnetic bottle, which is mainly along the radial direction. Interestingly, the leading and trailing edges of most magnetic bottles are not parallel, but we need further study to pursue their reasons.