Time-distance plots of ν_∥ (top) and ν_⊥ (bottom) along x = 3.81 Mm. The red and white lines are as in Figure 2. From the origin, a straight diagonal line represents the trajectory of an object travelling with the initial sound speed c₀ = 8.49 km/s and a curved black line indicates the position of an object travelling vertically with the Alfvén velocity. The dashed and dash-dotted lines indicate the trajectory of an object travelling with the negative initial sound speed.