Seasonal variations in Saturn's plasma sheet warping

Composite images of hydrogen and oxygen energetic neutral atoms (ENA) obtained from 2005 through 2015 from the Ion Neutral Camera on Cassini reveal the structure of Saturn's plasma sheet out to similar to 40 R-s (1 R-s=60,268km). Seen from either the dawnside or duskside at low latitude, these composites reveal that the plasma sheet is concave upward (northward) near Saturn's southern solstice, has no concavity near equinox, and is concave downward (southward) near Saturn's northern solstice. This seasonal variation confirms the Arridge bowl model developed early in the Cassini mission based on limited magnetometer data, with the concavity depending on the tangent of the Sun's latitude at Saturn and a hinge parameter r(H). The best fits to the ENA data indicate r(H)approximate to 25-30 R-s, which is close to the 29 R-s originally suggested by the magnetometer results. The bowl structure suggests other magnetodisks in the solar system and beyond may also undergo similar warping dynamics and may not have a flat geometry.