How is the Jovian main auroral emission affected by the solar wind?

The influence of the solar wind on Jupiter's magnetosphere is studied via three-dimensional global MHD simulations. We especially examine how solar wind density variations affect the main auroral emission. Our simulations show that a density increase in the solar wind has strong effects on the Jovian magnetosphere: the size of the magnetosphere decreases, the field lines are compressed on the dayside and elongated on the nightside (this effect can be seen even deep inside the magnetosphere), and dawn-dusk asymmetries are enhanced. Our results also show that the main oval becomes brighter when the solar wind is denser. But the precise response of the main oval to such a density enhancement in the solar wind depends on the local time: on the nightside the main oval becomes brighter, while on the dayside it first turns slightly darker for a few hours and then also becomes brighter. Once the density increase in the solar wind reaches the magnetosphere, the magnetopause moves inward, and in less than 5 h, a new approximate equilibrium position is obtained. But the magnetosphere as a whole needs much longer to adapt to the new solar wind conditions. For instance, the total electrical current closing in the ionosphere slowly increases during the simulation and it takes about 60 h to reach a new equilibrium. By then the currents have increased by as much as 45%.