Rotation of the Earth's plasmasphere at different radial distances

We have studied the rotation of the plasmasphere using a large plasmaspheric notch observed by the Extreme Ultraviolet (EUV) instrument onboard the IMAGE spacecraft on 2001/173. The time scale is more than 20 h. On the magnetic equatorial plane the notch extends over more than 1.5 Re in radial distance. By analyzing the brightness for four annuluses at different average values of L from 2.0 to 3.25 over time, we determine the rotation rate of the plasmasphere at different radial distances. The analysis reveals that, with the increase of L, the rotation rate of the plasmasphere tends to strongly decrease on the dusk side and slightly increase on the dawn side.