2D spatial power spectra of the velocity fields measured at four bisector levels, for the same scan as shown in Fig. 2. The upper row shows two power maps corresponding to the velocity fields measured at the bisectors 0.2 (left) and 0.5 (right). The second row corresponds to the velocity fields measured at the bisectors 0.75 (left) and line core (right). The axes are the wave numbers k_x and k_y. The power is color coded from red (maximum power) to green (minimum power). The insets show the corresponding mean azimuthal power P_a . The small circles mark the wave number at which the signal disappears below a certain common threshold.