Power spectra of I, , and ϕ_diff in blue, purple, and yellow, respectively, observed along the crest ridge combining crests 3 and 4 (Fig. 10). The amplitudes are scaled to conveniently show the three power spectra on the same plot. The red solid lines indicate the best fit linear function (in log-log) to the observed power spectra. The derived best fit slopes are given in the bottom left of the plot, α_I in blue, α_χ in purple, and α_ϕ in yellow, forthe power spectra of I, , and ϕ_diff, respectively. The vertical black solid line indicates the 14′′ HPBW of the data at 850 μm (s ~ 2.7 arcmin⁻¹), which is also the highest frequency data point used to fit the power-law.