Bow Shock Generator Current Systems: MMS Observations of Possible Current Closure. Issue 1 (10th January 2018)

• Record Type: Journal Article
• Authors: Hamrin, M.; Gunell, H.; Lindkvist, J.; Lindqvist, P.‐A.; Ergun, R. E.; Giles, B. L.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 1(2018)
• Page Start: 242
• Page End: 258
• Publication Date: 2018-01-10
• Subjects: bow shock -- current closure -- Magnetospheric Multiscale mission; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024826
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We use data from the first two dayside seasons of the Magnetospheric Multiscale (MMS) mission to study current systems associated with quasi‐perpendicular bow shocks of generator type. We have analyzed 154 MMS bow shock crossings near the equatorial plane. We compute the current density during the crossings and conclude that the component perpendicular to the shock normal ( J ⊥ ) is consistent with a pileup of the interplanetary magnetic field (IMF) inside the magnetosheath. For predominantly southward IMF, we observe a component J n parallel (antiparallel) to the normal for GSM Y > 0 (<0), and oppositely directed for northward IMF. This indicates current closure across the equatorial magnetosheath, and it is observed for IMF clock angles near 0 ∘ and 180 ∘ . To our knowledge, these are the first observational evidence for bow shock current closure across the magnetosheath. Since we observe no clear signatures of | J ⊥ | decreasing toward large | Y | we suggest that the main region of current closure is further tailward, outside MMS probing region. For IMF clock angles near 90 ∘, we find indications of the current system being tilted toward the north‐south direction, obtaining a significant J z component, and we suggest that the current closes off the equatorial plane at higher latitudes where the spacecraft are not probing. The observations are complicated for several reasons. For example, variations in the solar wind and the magnetospheric currents and loads affect the closure, and J n is distributed over large regions, making it difficult to resolve inside the magnetosheath proper. Key Points: These are the first observations of bow shock current closure across the magnetosheath and toward the magnetosphere For large IMF | B z |, there are indications of current closure in the equatorial plane For large IMF | B y |, the current system is tilted and closure may occur at higher latitudes