On my flight back from Singapore to Darwin we entered some cloud and encountered some slight turbulence. The Air Crew put on the seatbelt sign during that period. Looking out of the window I had a view of the wing shrouded in a translucent haze, rather obviously what we would call mist or fog on the ground. I watched the light patterns caused by the red and white navigation lights for a while. Then I noticed that there were smaller flashes on parts of the wings including the flaps, the ailerons and the things protruding backward from under the wing (nacelles?).
I assumed that it was static electricity, but why it was doing what it was doing I could not work out. The individual sparks were such as you might see on a child's sparkler, but randomly dotted around, not a long continuous burn. As we left the cloud the sparks ceased. It was an intriguing sight, one that I have not encountered before.
On returning home I was able to look it up and find that it is indeed static electricity and it is the rain droplets causing a sudden discharge that causes the flash. This is common in all metal air planes and in fact they are designed to funnel static charges to the wings where they are discharged by "Static Discharge Wicks".In fact the view of the A320 that they show is almost identical to the view that I had.
The Bludger learnt something today.