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Ann. Geophys., 25, 941-951, 2007
www.ann-geophys.net/25/941/2007/
© European Geosciences Union 2007
Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines
S. V. Badman and S. W. H. Cowley
Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. We consider the contribution of the solar wind-driven
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
Dungey-cycle 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.
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