Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines

Abstract

Abstract. We consider the contribution of the solar winddriven Dungey-cycle to flux transport in Jupiter's and Saturn's magnetospheres, the associated voltages being based on estimates of the magnetopause reconnection rates recently derived from observations of the interplanetary medium in the vicinity of the corresponding planetary orbits. At Jupiter, the reconnection voltages are estimated to be ∼150 kV during several-day weak-field rarefaction regions, increasing to ∼1 MV during few-day strong-field compression regions.The corresponding values at Saturn are ∼25 kV for rarefaction regions, increasing to ∼150 kV for compressions. These values are compared with the voltages associated with the flows driven by planetary rotation. Estimates of the rotational flux transport in the "middle" and "outer" magnetosphere regions are shown to yield voltages of several MV and several hundred kV at Jupiter and Saturn respectively, thus being of the same order as the estimated peak Dungeycycle voltages. We conclude that under such circumstances the Dungey-cycle "return" flow will make a significant contribution to the flux transport in the outer magnetospheric regions. The "return" Dungey-cycle flows are then expected to form layers which are a few planetary radii wide inside the dawn and morning magnetopause. In the absence of significant cross-field plasma diffusion, these layers will be characterized by the presence of hot light ions originating from either the planetary ionosphere or the solar wind, while the inner layers associated with the Vasyliunas-cycle and middle magnetosphere transport will be dominated by hot heavy ions originating from internal moon/ring plasma sources. The temperature of these ions is estimated to be of the order of a few keV at Saturn and a few tens of keV at Jupiter, in both layers.

Properties of Near-Earth Magnetic Reconnection from In-Situ Observations

“…However, in the case of both giant planets, and in contrast to Earth, it has yet to be established to what extent magnetotail reconnection is driven externally (e.g., by dayside reconnection with the solar wind field) or internally (e.g., through the centrifugally driven stretching of mass-loaded flux tubes on the nightside) (cf. Kivelson and Southwood 2005;Badman and Cowley 2007). Reconnection has also been shown to occur at Mercury (Russell and Walker 1985;Slavin et al 2009).…”

Mapping Magnetospheric Equatorial Regions at Saturn from Cassini Prime Mission Observations

“…Although internal plasma and energy sources in the saturnian magnetosphere are thought to dominate in driving magnetospheric dynamics, the effects of dayside reconnection and Dungeycycle convection have been estimated in a number of studies (e.g., Jackman et al 2004;Badman and Cowley 2007). In these studies the rate at which reconnection can proceed can be estimated using the "half-wave rectifier" function (e.g., Perrault and Akasofu 1978) where the reconnection voltage (equal to the magnetic flux opened per unit time) is given by = v SW B ⊥ L 0 cos 4 (θ/2) where v SW is the solar wind speed, B ⊥ is the magnetic field perpendicular to the magnetic dipole, L 0 is a length scale set to the width of the magnetopause and θ is the "clock angle" of the field (see Jackman et al 2004 for details).…”

IMF dependence of Saturn's auroras: modelling study of HST and Cassini data from 12–15 February 2008

“…While the dynamics of Saturn's magnetosphere are generally believed to be dominated by flows driven by the planet's rotation (e.g. Badman and Cowley, 2007), the auroras and related radio emissions are also known to respond strongly to increases in solar wind dynamic pressure that occur at interplanetary shocks Crary et al, 2005;Jackman et al, 2005;Bunce et al, 2006;Badman et al, 2008). Saturn's system thus appears to combine aspects that are related both to the Earth, where auroral processes are driven primarily by solar wind-magnetosphere coupling (e.g.…”