Radial velocity fluctuations in a frame corotating with the gas in run M3B10 at r = 5.2r_in. The horizontal axis φ − Ω_ρt corresponds to an azimuthal coordinate in the comoving frame. The vertical axis is the density-weighted mean radial velocity ⟨v_r⟩_ρ relative to the average sound speed ⟨c_s⟩_ρ, φ. Different curves correspond to different times as color-coded in units of local orbital periods. The horizontal segment illustrates how far a signal would propagate in the φ direction at the sound speed ⟨c_s⟩_ρ, φ over this time interval.