A simulation study of currents in the Jovian magnetosphere

We have used a global magnetohydrodynamic simulation of the interaction of Jupiterʹs magnetosphere with the solar wind to investigate the effects of the solar wind on the structure of currents in the jovian magnetosphere. A thin equatorial current sheet with currents flowing around Jupiter dominates Jupiterʹs middle magnetosphere. However, in our simulations this current is not uniform in azimuth. It is weaker on the day side than the night side with local regions where the current density decreases by more than 50%. In addition to this ring current the current sheet contains strong radial “corotation enforcement” currents. Outward radial currents are found at most local times but there are regions with currents directed toward Jupiter. The current pattern is especially complex in the local afternoon and evening regions. In the near equatorial magnetosphere the field-aligned current pattern also is complex. There are regions with currents both toward and away from Jupiterʹs ionosphere. However, when we mapped the currents from the inner boundary of the simulation to the ionosphere we found a pattern more like that expected for the ionosphere to drive corotation with currents away from Jupiter at lower latitudes and currents toward Jupiter at higher latitudes. Since upward field-aligned currents are associated with aurora at the Earth they may be associated with aurora at Jupiter. The upward field-aligned currents map to larger distances on the night side (40RJ to 60 RJ) than on the day side (20RJ to 30RJ). In the simulations changing the solar wind dynamic pressure did not make major changes in the current sheet or field-aligned currents (both were slightly stronger for higher pressures). The interplanetary magnetic field had a stronger effect on the currents with the strongest currents for northward IMF. However, it took a very long time for the magnetosphere to respond to the changes in the IMF.