A model of force balance in Jupiter's magnetodisc including hot plasma pressure anisotropy

• Published in: Journal of geophysical research. Space physics Vol. 120; no. 12; pp. 10,185 - 10,206
• Main Authors: Nichols, J. D., Achilleos, N., Cowley, S. W. H.
• Format: Journal Article
• Language: English
• Published: 01.12.2015
• Subjects: Jupiter; magnetodisc; magnetosphere; modeling; pressure anisotropy
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2015JA021807

We present an iterative vector potential model of force balance in Jupiter's magnetodisc that includes the effects of hot plasma pressure anisotropy. The fiducial model produces results that are consistent with Galileo magnetic field and plasma data over the whole radial range of the model. The hot plasma pressure gradient and centrifugal forces dominate in the regions inward of ∼20 RJ and outward of ∼50 RJ, respectively, while for realistic values of the pressure anisotropy, the anisotropy current is either the dominant component or at least comparable with the hot plasma pressure gradient current in the region in between. With the inclusion of hot plasma pressure anisotropy, the ∼1.2 and ∼2.7° shifts in the latitudes of the main oval and Ganymede footprint, respectively, associated with variations over the observed range of the hot plasma parameter Kh, which is the product of hot pressure and unit flux tube volume, are comparable to the shifts observed in auroral images. However, the middle magnetosphere is susceptible to the firehose instability, with peak equatorial values of βh∥e−βh⊥e≃1 − 2, for Kh=2.0 − 2.5 × 107 Pa m T−1. For larger values of Kh,βh∥e−βh⊥e exceeds 2 near ∼25 RJ and the model does not converge. This suggests that small‐scale plasmoid release or “drizzle” of iogenic plasma may often occur in the middle magnetosphere, thus forming a significant mode of plasma mass loss, alongside plasmoids, at Jupiter. Key Points Hot plasma pressure anisotropy current is dominant in the middle magnetosphere Shifts main oval and Ganymede footprint from varying hot plasma pressure: comparable to observations Middle magnetosphere is near to the firehose stability limit