Magnetodisk Coordinates for Saturn

摘要

The magnetosphere of Saturn is known to be warped into a bowl shape, and the severity of the warping varies with the seasonal tilt of Saturn's spin axis in its orbital plane. This peculiar geometry complicates the analysis of many magnetospheric phenomena, because they are symmetric about the warped magnetodisk equator rather than the spin equator. To reorganize the Cassini data, a new coordinate system is proposed wherein a z_A coordinate represents the perpendicular distance above or below the warped surface, and a ρ_A coordinate represents the arc length along the surface from the origin to where the perpendicular intersects the surface. Using the Cassini spacecraft trajectory, examples show how these disk coordinates (ρ_A, z_A) significantly deviate from the standard spin-equatorial coordinates (ρ, z), especially outside the orbit of Titan. Another example indicates that fluxes of energetic electrons are well organized in this new system. Supporting information tabulates the disk coordinates as a function of time during the Cassini mission.