A new perspective concerning the influence of the solar wind on the Jovian magnetosphere

The solar wind exerts a strong influence on the Jovian magnetosphere in changing its volume, in energizing plasma, and in stimulating the aurora and a host of other associated effects. However, whereas at Earth the dominant solar terrestrial coupling process is magnetic reconnection, the dominant energy reservoir in Jupiter's magnetospheric plasma, continually present, is the kinetic energy of its rotating plasma disk. This flywheel' produces effects with no terrestrial analogy, some of which we describe here. The most surprising prediction from the analysis of this paper is that remotely sensed symptoms of Jovian magnetospheric activity are likely to occur in conjunction with solar wind pressure decreases. Compressions of the magnetosphere produced by forward shocks and other solar wind pressure increases will heat the magnetospheric plasma but substantially reduce the ionosphere-magnetosphere current systems. The intensity of dayside aurora and of radio wave emissions associated with increased ionospheric-magnetospheric current systems will tend to anticorrelate with magnetospheric compressions and correlate with expansions. The link to the aurora is based on an argument that the auroral zone maps to the plasma disk of the middle magnetosphere and is thus linked to plasma sheet dynamics. The effect of expansion on the plasma sheet is to increase the parallel pressure, setting up conditions that can produce detached plasma blobs and enhance mass loss. The analysis is particularly apposite in light of the opportunities for observing Solar wind-Jovian interactions using data from both the Galileo and the Cassini spacecraft during the Cassini flyby of Jupiter in late 2000, ideally supplemented by auroral imaging with ground-based and Hubble telescopes.