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We present simultaneous Juno and Hubble Space Telescope of Jupiter's far-ultraviolet auroras obtained as part of a programme of observations covering 3 years of Juno's Extended Mission. We show that bright, expanded dusk-side southern main emission is associated with large-scale convection dynamics, dusk-side main emission arcs are associated with field-aligned currents, and equatorward diffuse emission and patches are associated with plasma injections in the middle magnetosphere occurring within intervals of enhanced plasma density, ongoing interchange motion and magnetospheric convection. These results shed light on the relation between the main auroral emission and magnetosphere-ionosphere coupling currents, and radial force balance in the magnetosphere. We also report on unusually bright and expanded southern auroral emissions observed during PJ 43.

Cassini's 2017 proximal orbits provided the opportunity to examine the auroral field-aligned currents in the northern hemisphere dawn sector in relation to wider magnetospheric conditions. We combine three recent studies to examine the response of the dawn region auroral field-aligned currents and the azimuthal ring currents to compressions and expansions of the Saturnian magnetosphere. For compressions of Saturn's magnetosphere resulting in tail reconnection, the currents within the downward current sheet, located equatorward of the main auroral oval, increases in strength with increasing total ring current and location of the peak downwards current moves inwards toward Saturn. While the inverse relation occurs during intervals of quiet or expanded magnetospheric conditions. During compression events there is an increase in the energetic particle intensities, in particular in the protons (35–506 keV), within the downward current region. This current system is akin to an Earth-like “region 2” field aligned current within Saturn's magnetosphere, with tail reconnection occurring when the magnetosphere is compressed resulting in a partial nightside ring current closed by a downward current near to dawn. Within the upward current sheet, mapping to Saturn's main auroral oval, both non-rotating subcorotating current and the rotating Planetary Period Oscillations (PPOs) currents flow. The upward current is strongly modulated by the PPOs but also increases in strength, with enhanced high-energy protons, during intervals of magnetospheric compressions and tail reconnection. We conclude that the enhanced plasma injected into the midnight-dawn sector during tail reconnection events results in an enhanced subcorotation current system.

We present a comparison of magnetic field data collected by the NASA Juno spacecraft, with the magnetosphere-ionosphere (MI) coupling model for the Jovian system developed by the University of Leicester. We study the magnetic field of Jupiter, in the Northern Hemisphere, for Perijoves 1-13. By virtue of the offset of the magnetic field to the rotation axis and the subsequent “wobble” of the Juno trajectory in magnetic coordinates, these northern hemisphere portions of PJs 1-13 see the spacecraft traversing the magnetic field lines connecting to the inner, middle, outer and tail regions of the magnetosphere. As such, even away from the close Perijove period, the observations contain evidence of the expected magnetic field perturbations associated with field-aligned currents associated with this fundamental MI coupling. In this study, therefore, we focus on investigating the nature of the field-aligned current signatures evident in the residual azimuthal field (having subtracted the Connerney et al 2018 JRM09 internal magnetic field model) along the magnetic field lines outside of the close periapsides. We map the residual azimuthal field signatures into the ionosphere, and calculate the corresponding ionospheric Pedersen current on an orbit by orbit basis. We compare the magnitude and distribution of these field-aligned current signatures to those expected from the Leicester model, and consider the observed orbit-by-orbit variation as a function of ionospheric colatitude and longitude. We deduce estimates for the field-aligned current densities on auroral field lines for each observation using the Pedersen currents and their distribution in co-latitude, and compare to the previous work of Kotsiaros et al [2019]. We discuss possible reasons for the variations we see, and present the next steps of our broader analysis.

Prolonged operation of the Joint European Torus (JET) in a set-up involving all ITER partners will be beneficial for ITER. Experiments at JET with its ITER-like wall and using a D-T plasma mixture will help to mitigate risks in the ITER research plan. Training of the ITER operators, technicians and engineers at JET will safe valuable time when ITER comes into operation. Moreover, the way in which the future ITER experiments will be organized can already be experienced at JET, by imposing a similar organisational structure. This paper will present arguments in favour of an extension of JET and additionally briefly discuss a number of enhancements that will make experiments on JET even more relevant for ITER. For complete list of authors see http://dx.doi.org/10.1007/s10894-015-0009-2

We present SuperDARN radar observations of the nightside high-latitude ionospheric flow during two 6-hour intervals of quasi-steady northward interplanetary magnetic field (IMF). During both intervals (01:30–07:30 UT on 2 December and 21:00–03:00 UT on 14/15 December 1999), the solar wind and IMF remained relatively steady with Bz positive and By negative, such that the IMF clock angle was ~ - 50° to - 60°. Throughout both intervals the radar data clearly indicate the presence of a highly distorted By-dominated twin cell flow pattern, indicative of an open magnetosphere, which is confirmed by DMSP and auroral data. Estimates of the changes in open flux present during each interval indicate approximately balanced dayside and nightside reconnection at rates of ~ 30–35 kV over the full 6 h. However, strong bursts of flow with speeds of over ~ 1000 ms-1 are observed near magnetic midnight on time scales of ~ 1 h, which are associated with increases in the transpolar voltage. These are indicative of the net closure of open flux by recon-nection in the tail. During one large flow burst, the night-side reconnection rate is estimated to have been ~ 1.5 times the dayside rate, i.e. ~ 45–60 kV compared with ~ 30–40 kV. Magnetic bays, which would indicate the formation of a sub-storm current wedge, are not observed in association with these bursts. In addition, no low-latitude Pi2s or geostationary particle injections were observed, although some local, small amplitude Pi2-band (5–50 mHz) activity does accompany the bursts. Coincident measurements of the flow and of the low amplitude magnetic perturbations reveal nightside ionospheric conductances of no more than a few mho, indicative of little associated precipitation. Therefore, we suggest that the flow bursts are the ionospheric manifestation of bursty reconnection events occurring in the more distant geomagnetic tail. The main implication of these findings is that, under the circumstances examined here, the convection cycle is not equivalent to the usual substorm cycle that occurs for southward IMF. Key words. Ionosphere (plasma convection; ionosphere-magnetosphere interactions) – Magnetospheric Physics (magnetotail)