Bimodal size of Jupiter's magnetosphere

Observations of Jovian magnetopause crossing by a number of different spacecraft have established that Jupiter's magnetosphere has a generally bimodal size distribution, with typical standoff distances at the nose of ∼63 and ∼92 R_J. Here we examine both the external solar wind structure and time constants and the internal magnetospheric time constants for shedding and refilling material in the Jovian plasma disk. We show that these latter time constants are ∼ hours to ∼10 h, comparable to the compression time of the magnetopause, but shorter than the typically several day expansion time when the solar wind dynamic pressure decreases. Together, we show that it is the well-developed compressions and rarefactions in the solar wind at ∼5 AU that produced the generally bimodally structured solar wind dynamic pressure and hence Jovian magnetospheric size.