If we accept this number and the typical flow velocity reported by Frank et al. This value is 43 Io cross-sections or a radial extent of 6.5 R Io . That distance is quite consistent with the region of disturbed flow shown in Figure 4 . Finally, the temperature of the picked up ions also gives a clue to the nature of the interaction since the thermal velocity of the picked up ion equals the bulk velocity at the pick up point. At the edges of the interaction region where the flow velocity increases as it expands behind Io the picked up ions are their hottest.
Data are in the corotation frame.
The newly added plasma slows the flow in front of Io, while the magnetospheric ends of the field continue to move past Io at nearly their undisturbed velocity. The wake currents increase the vertical field in the region immediately behind Io. The observations made by Voyager 1 and Galileo in their Io flyby passes are quite consistent in this regard. The magnetic perturbation seen by Voyager and the flow disturbance seen by Galileo are very similar. The flow passing directly over the moon that is moving much slower than the surrounding torus plasma produces cold plasma.