Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages

We consider the effect of field-aligned voltages on the magnetosphere-ionosphere coupling current system associated with the breakdown of rigid corotation of equatorial plasma in Jupiter's middle magnetosphere. Previous analyses have assumed perfect mapping of the electric field and flow along equipotential field lines between the equatorial plane and the ionosphere, whereas it has been shown that substantial field-aligned voltages must exist to drive the field-aligned currents associated with the main auroral oval. The effect of these field-aligned voltages is to decouple the flow of the equatorial and ionospheric plasma, such that their angular velocities are in general different from each other. In this paper we self-consistently include the field-aligned voltages in computing the plasma flows and currents in the system. A third order differential equation is derived for the ionospheric plasma angular velocity, and a power series solution obtained which reduces to previous solutions in the limit that the field-aligned voltage is small. Results are obtained to second order in the power series, and are compared to the original zeroth order results with no parallel voltage. We find that for system parameters appropriate to Jupiter the effect of the field-aligned voltages on the solutions is small, thus validating the results of previously-published analyses

A note on the ring current in Saturn's magnetosphere: Comparison of magnetic data obtained during the Pioneer-11 and Voyager-1 and -2 fly-bys

International audienceWe examine the residual (measured minus internal) magnetic field vectors observed in Saturn's magnetosphere during the Pioneer-11 fly-by in 1979, and compare them with those observed during the Voyager-1 and -2 fly-bys in 1980 and 1981. We show for the first time that a ring current system was present within the magnetosphere during the Pioneer-11 encounter, which was qualitatively similar to those present during the Voyager fly-bys. The analysis also shows, however, that the ring current was located closer to the planet during the Pioneer-11 encounter than during the comparable Voyager-1 fly-by, reflecting the more com-pressed nature of the magnetosphere at the time. The residual field vectors have been fit using an adaptation of the current system proposed for Jupiter by Connerney et al. (1981a). A model that provides a reasonably good fit to the Pioneer-11 Saturn data extends radially between 6.5 and 12.5 RS (compared with a noon-sector magnetopause distance of 17 RS), has a north-south extent of 4 RS, and carries a total current of 9.6 MA. A corresponding model that provides a qualitatively similar fit to the Voyager data, determined previously by Connerney et al. (1983), extends radially between 8 and 15.5 RS (compared with a noon-sector magnetopause distance for Voyager-1 of 23?24 RS), has a north-south extent of 6 RS, and carries a total current of 11.5 MA

PACE and EISCAT radar observations of short-lived flow bursts on the nightside

Concurrent observations from two widely spaced radar experiments of quasi periodic flow bursts in the nightside are presented. The flow bursts closely resemble single radar observations reported by Williams et al. By using the Polar Anglo-American Conjugate Experiment (PACE) HF radar array at Halley Bay in conjunction with the EISCAT Common Program (CP) 2-D experiment, the flow bursts are shown to be a global phenomenon and important information as to their development and propagation can be determined

Comparison of ionospheric electric currents and plasma convection patterns observed during substorms

Abstract. The effect of magnetospheric substorms on the global ionospheric convection pattern is widely debated. Discussed here, is a study made of ionospheric electric currents, co-incident with plasma convection at the time of substorm onset, using the HF radars of the Super Dual Auroral Radar Network (SuperDARN), and the global array of ground magnetometers. Preliminary results are presented, which utilise an ionospheric potential mapping model to produce plasma convection vectors and electric potential contours, with corresponding ionospheric currents being derived from magnetic perturbations. Clear indications of a relationship between the substorm current system and the plasma convection patterns are seen. 1

Dependence of convective flows and particle precipitation in the high-latitude dayside ionosphere on theXandYcomponents of the interplanetary magnetic field

The asymmetries in the convective flows, current systems, and particle precipitation in the high-latitude dayside ionosphere which are related to the equatorial plane components of the interplanetary magnetic field (IMF) are discussed in relation to the results of several recent observational studies. It is argued that all of the effects reported to date which are ascribed to the y component of the IMF can be understood, at least qualitatively, in terms of a simple theoretical picture in which the effects result from the stresses exerted on the magnetosphere consequent on the interconnection of terrestrial and interplanetary fields. In particular, relaxation under the action of these stresses allows, in effect, a partial penetration of the IMF into the magnetospheric cavity, such that the sense of the expected asymmetry effects on closed field lines can be understood, to zeroth order, in terms of the “dipole plus uniform field” model. In particular, in response to IMF By, the dayside cusp should be displaced in longitude about noon in the same sense as By in the northern hemisphere, and in the opposite sense to By in the southern hemisphere, while simultaneously the auroral oval as a whole should be shifted in the dawn-dusk direction in the opposite sense with respect to By. These expected displacements are found to be consistent with recently published observations. Similar considerations lead to the suggestion that the auroral oval may also undergo displacements in the noon-midnight direction which are associated with the x component of the IMF. We show that a previously published study of the position of the auroral oval contains strong initial evidence for the existence of this effect. However, recent results on variations in the latitude of the cusp are more ambiguous. This topic therefore requires further study before definitive conclusions can be drawn