I still don’t understand how icing can occur without visible moisture since there are no particles which could form on the aircraft surface.
The only thing I now how icing in clear air can happen is this way:
One area where you may witness clear-air icing is in the vicinity of convective storms. During times of updraft supercooled droplets can be expelled through the tops of the “anvil” and fall outside of the storm itself. In other words, it could be raining even though there is no cloud above the area. If an aircraft is in this rainshower of supercooled droplets, it may experience icing despite being VMC.
However, the droplets from the nearby storm satisfy the requirement of visible moisture necessary for ice formation.