'I suggest that with respect to the description of wind turbine noise it is a matter of terminology that needs a shift as follows:

The language should be pulsations at an infrasound rate.
Modulation of the entire signal at an infrasound rate. (Zwicker and Fastl call this fluctuation as a sensation detected by the ear).
AM is present as some discrete low frequencies modulated at the bpf.
UK method of AM is determining the modulation index of the fluctuating signal (not technically AM).
You can determine the Modulation Index of the low frequency noise that is AM.' -Steven Cooper.