On the alignment of velocity and magnetic fields within magnetosheath jets

• Main Authors: F. Plaschke, M. Jernej, H. Hietala, L. Vuorinen
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-03-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/38/287/2020/angeo-38-287-2020.pdf
• ISSN: 0992-7689; 1432-0576

<p>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 Magnetospheric Multiscale (MMS) jet observations and corresponding superposed epoch analyses of the angles <span class="inline-formula"><i>ϕ</i></span> between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in <span class="inline-formula"><i>ϕ</i></span> of around 10<span class="inline-formula">^∘</span> are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of <span class="inline-formula"><i>ϕ</i></span> pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of <span class="inline-formula"><i>ϕ</i></span>: 0 to 90<span class="inline-formula">^∘</span>. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in <span class="inline-formula"><i>ϕ</i></span> at core regions of individual jets.</p>