On the alignment of velocity and magnetic fields within magnetosheath jets

Abstract. Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on MMS jet observations and corresponding superposed epoch analyses of the angles φ between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, the effect is small: Typically, reductions in φ of only 10° are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of angles φ pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of φ: 0° to 90°. This variability is commonly somewhat larger within jets than outside, masking the systematic decrease in φ at core regions of individual jets.