Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations

摘要

The geometrical structure of the Pc 5 compressional wave is important in judging its generation mechanism and the wave-particle interaction process. In this work, 117 magnetic troughs (where magnetic field strength transiently decreases) identified from 50 Pc 5 compressional wave events in the duskside (15.5–18.5 local time) magnetosphere are studied based on the Magnetospheric Multiscale (MMS) data. We derived the three dimensional geometry of the magnetic trough by including the normal and velocity information at its boundaries from the multi-spacecraft analysis method. The magnetic trough has a magnetic bottle shape along the magnetic field line with the most probable center (with weakest magnetic field) located at θ = 75? , while the widest part of the magnetic bottle located around θ = 65? (θ denotes the angle between spacecraft position vector and the ambient magnetic field). The cross section of the magnetic trough is eccentric and has a “wedgelike” shape whose average open angle is ~23° toward radial outward. It is found that the radial component of the current density is the dominant one at the boundaries, and the value is generally proportional to the depth of the magnetic trough. The generation of these Pc 5 compressional waves can be attributed to the drift Alfvén ballooning mirror instability. This work reveals the possible changes of magnetic field configuration caused by the Pc 5 compressional wave in the magnetosphere and may bring new ideas to the interaction way between wave field and ring current particles.