LOCATION AND SHAPE OF THE JOVIAN MAGNETOPAUSE AND BOW SHOCK

Following Galileo's arrival at Jupiter in fall 1995, a total of six sp acecraft have now sampled the Jovian magnetosphere. Using these data s ets to investigate the average location and shape of the Jovian bounda ries, we fit ellipse profiles to the observations, allowing for the di sk-like shape of the magnetosphere and taking account of variable sola r wind pressure. We find that the subsolar magnetopause location varie s with solar wind dynamic pressure to power between -1/5 and -1/4, in contrast to the terrestrial -1/6 power; this is a well-known differenc e attributed to the presence of hot plasma and centrifugal stretching in the Jovian magnetodisk that lessens the pressure gradients in the o uter magnetosphere, resulting in its unusual responsiveness to compres sion. The magnetopause is less flared than the bow shock as expected, and the magnetopause shape is especially streamlined (least flared and more bulletlike) during the higher solar wind dynamic pressure condit ions encountered, The average subsolar shock-to-magnetopause standoff ratio is approximately 6/5, while at low incident solar wind dynamic p ressure the ratio rises to around 4/3 suggesting a blunter Earth-type magnetopause shape under these conditions. In particular, our analysis confirms that the magnetopause boundary shape is influenced by the ra dially inflated magnetodisk, as has been previously inferred from the stretched magnetic field lines seen within the magnetosphere. Our fits to the observations reveal that the average magnetopause boundary is indeed contracted on the north-south axis about the magnetic equator. The bow shock is not found to be so asymmetric in shape, suggesting th at there is little effect of external magnetic field direction, and su pporting our conclusion that the internal magnetodisk shape is the cau se of the magnetopause polar flattening.