International Master’s Programme in Space Sciences

Coronal Mass Ejections (CMEs) often travel in the interplanetary space faster than the ambient solar wind. When their relative velocities exceed the local magnetosonic speed, a shock wave forms. The region between the shock front and the leading edge is known as a sheath region. Sheaths are compressed regions characterized by turbulent magnetic field and plasma properties and they can cause significant space weather disturbances. Within the sheath region, it is possible to find fine structures such as planar magnetic structures (PMSs). The magnetic field vectors in a PMS are characterized by abrupt changes in direction and magnitude, but they all remain for a time interval of several hours nearly parallel to a single plane that includes the interplanetary magnetic field (IMF) spiral direction. PMSs have been associated to several regions and phenomena in the heliosphere, but many of them occur in CME sheath regions. This suggests that CMEs play a central role in the formation of PMSs, probably by provoking the amplification and the alignment of pre-existing discontinuities by compression of the solar wind at the CME-driven shock or because of the draping of the magnetic field lines around the CME ejecta. The presence of PMSs in sheath regions, moreover, suggests that PMSs themselves can be related to space weather effects at Earth, therefore a comprehensive stud