1. Transport of Mass, Momentum and Energy in Planetary Magnetodisc Regions

Abstract

The rapid rotation of the gas giant planets, Jupiter and Saturn, leads to the formation of magnetodisc regions in their magnetospheric environments. In these regions, relatively cold plasma is confined towards the equatorial regions, and the magnetic field generated by the azimuthal (ring) current adds to the planetary dipole, forming radially distended field lines near the equatorial plane. The ensuing force balance in the equatorial magnetodisc is strongly influenced by centrifugal stress and by the thermal pressure of hot ion populations, whose thermal energy is large compared to the magnitude of their centrifugal potential energy. The sources of plasma for the Jovian and Kronian magnetospheres are the respective satellites Io (a volcanic moon) and Enceladus (an icy moon). The plasma produced by these N.

Plasma transport driven by the Rayleigh‐Taylor instability

“…For an equilibrium with straight magnetic field lines and cold plasma (i.e., the environment of the plasma torus in Jupiter's inner magnetosphere), the centrifugal instability operates when the centrifugal force opposes the flux content gradient. For a homogeneous magnetic field (e.g., our simulation configuration), the onset criterion is identical to the Rayleigh‐Tayler instability [ Achilleos et al , ]. In spite of the similarities between the RT instability and the centrifugal instability, we note that the presence of magnetic field curvature and nonzero steady state velocity for the centrifugal instability in the real magnetosphere may modify the detailed dynamics.…”

“…It is widely believed that the centrifugally driven interchange instability triggers radial plasma transport [ Thomsen , ; Mauk et al , ; Achilleos et al , , and references therein]. This instability is very similar to the Rayleigh‐Taylor (RT) instability [ Chandrasekhar , ; Bateman , ], which operates when the flux tube content or the flux tube entropy decreases radially [ Southwood and Kivelson , ; Achilleos et al , , and references therein].…”

“…The stability of the inner magnetosphere has been investigated by one‐dimensional numerical simulations [ Chen , , ] and theoretical analysis [ André and Ferrière , ], showing that the Io torus is close to marginal stability against interchange. It is noteworthy that the definition of “interchange” varies with different authors [ Achilleos et al , , and references therein]. For instance, Kivelson [] suggested that “interchange” refers to the motion of entire flux tubes driven by inertial effects like gravity and the centrifugal pseudoforce.…”

A More Viscous‐Like Solar Wind Interaction With All the Giant Planets

“…Conditions at all the giant planet magnetopauses are therefore expected to typically deviate from steady state to a greater extent, likely affecting global magnetic reconnection more than the ongoing viscous-like interaction (e.g., Masters, 2017;McComas & Bagenal, 2007). Of all solar system magnetospheres, our toy magnetosphere with negligible outer magnetospheric plasma pressure is most unlike the giant magnetospheres of Jupiter and Saturn, where planetary rotation and significant internal plasma sources lead to outer magnetospheric plasma confinement to an equatorial, corotating plasma sheet (see the reviews by Achilleos et al, 2015;Bagenal, 1992;Delamere et al, 2015;Kivelson, 2014). However, outer magnetospheric plasma β > 1 clearly acts to reinforce our conclusion due to the implications for the local Alfvén speed.…”

Juno observations of large‐scale compressions of Jupiter's dawnside magnetopause

“…Jupiter's magnetosphere is the largest in the solar system, due to its strong internal magnetic field (magnetic moment~20,000 times that of Earth). Centrifugal forces generated by Jupiter's rotation result in the outward diffusion of thermal plasma, and this radial transport stretches Jupiter's dipolar magnetic field out into a magnetodisc configuration [Gledhill, 1967;Smith et al, 1974;Caudal, 1986;Caudal and Connerney, 1989;Connerney et al, 1981;Kivelson, 2014;Achilleos et al, 2015;Szego et al, 2015;Delamere et al, 2015a]. Outside of the magnetodisc is a so-called "cushion region," a region of strongly fluctuating magnetic field that forms preferentially on the dawnside of the magnetosphere from the transport of empty flux tubes back toward the dayside [Smith et al, 1976;Kivelson and Southwood, 2005;Delamere and Bagenal, 2010;Went et al, 2011;Delamere et al, 2015b].…”