Dual spacecraft observations of a compression event within the Jovian magnetosphere: Signatures of externally triggered supercorotation?

Abstract

By using Cassini as an upstream solar wind monitor, we are able to infer increases in the interplanetary dynamic pressure upstream of Jupiter as the spacecraft approached the planet. Observations are made of the effect that these pressure increases had upon both the fields and particles within the Jovian magnetosphere as measured by the Galileo orbiter, which had subsequently reentered the magnetosphere on the duskside. As the external pressure increased, so too did the total field magnitude at Galileo (in particular the Bz and Bϕ components). In addition, strongly leading field angles were observed following the onset of the compression and strongly lagging fields during reexpansion. These observations are consistent with the concept of external control of the angular velocity of the magnetospheric plasma due to conservation of angular momentum within the system. Heating of the plasma can be seen as a pronounced increase in particle flux as measured by the Energetic Particles Detector (EPD) instrument aboard Galileo. Changes in plasma velocity inferred from energetic particle anisotropies at Galileo appear to be consistent with the behavior of the changing magnetic field angle. The overall behavior and response time of the system appears to be consistent with recently published theoretical modeling of the Jovian magnetosphere‐ionosphere coupling system.