Emission angle variation Ω_θ versus the difference in rotational angular speed between the apparent DAM arcs (Ω_DAM) and the source footprints for the emissions (Ω_FP) on the dawn side (a) and the dusk side (b). Emission angle variation Ω_θ = ∆θ/∆t where ∆θ means the overall change in the emission angle over the observation time ∆t. The values were normalized by the rotational angular speed of Jupiter Ω_J.