Abstract
AbstractWe 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.
Highlights
A characteristic feature of Jupiter’s middle magnetosphere is that it is radially distended into a magnetodisc configuration, owing to the existence of a substantial azimuthal equatorial current sheet [e.g., Khurana et al, 2004, and references therein]
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
Given that pressure anisotropy plays a major role in the force balance in Jupiter’s magnetosphere and that the radial stretching of the field is an important parameter for the Jovian M-I coupling current system, we describe here an M-I coupling/magnetodisc model in which the azimuthal current that produces the magnetodisc field includes the contribution from hot plasma pressure anisotropy
Summary
A characteristic feature of Jupiter’s middle magnetosphere is that it is radially distended into a magnetodisc configuration, owing to the existence of a substantial azimuthal equatorial current sheet [e.g., Khurana et al, 2004, and references therein]. Where ρ is the perpendicular distance from the magnetic axis, z is the distance along this axis from the magnetic equator, and φ is the azimuthal angle The use of such a flux function, which is related to the vector potential employed in the calculation of the magnetodisc structure, allows mapping between the equator and ionosphere to be achieved by writing Fe = Fi, where subscript “e” refers to the equator and “i” refers to the ionosphere. That the ionospheric magnetic field is a spin-aligned dipole to the lowest approximation, the ionospheric flux function is given by
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