The magnetosphere of Jupiter has its energy supply dominated by the rotation of the planet rather than the stream velocity of the solar wind. In this respect it is intermediate between the earth's magnetosphere and that of pulsars. The dependence of the energy made available to the magnetospheric processes on the strength of the solar wind is calculated. Periodicities in the streams of energetic particles can be understood in terms of the unsymmetrical magnetic field of the planet and the external fixed orientation supplied by the solar wind.