Strange Strobe/Anti Collision light pattern question
 

The other night I was flying Jeju Air HKG-ICN. The aircraft was a 738, ex FR (even though the cabin had been fully re-done, it still had Ryanair branded soap in the bathroom!).

Anyway, at cruising height, which I think was around 29,000ft, we entered what I would describe as a foggy area. The crew switched on the seatbelt sign, although the turbulence never got that bad. Anyway, as it was night and misty outside, the strobe light pattern was exaggerated on the clouds surrounding the plane. I noticed that they were not following any pattern at all and seemed to be resembling something similar to a lightening storm. They would flash once, with a gap of 1-2 seconds, then do a random burst of 10 or so flashes in very quick successions, followed by a kind of bright burst. It really did look like lightning flashes, however it obviously wasn't as a pilot would surely not fly right into a storm and also, the plane at this point was flying perfectly smooth, not even the slightest jolt. I would expect a 737 in the middle of a thunder cloud to be a little bumpy, but nothing.

At several points the lights which illuminate the cabin facing side of the engine also came on, as if we were approaching for landing. They seemed to vary between flashing on and off a few times a second to staying on for a few minutes at a time.

As a frequent flyer I have never seen such things happening with the lights. Is it all random? What would cause strobe lights to function in such a way? Why would the cockpit turn on the landing lights at cruise level?

It's possible that you were flying in and out of cloud. The strobes are not really visible from the cabin in clear air, so that would explain the random nature of the flashes, in that you only saw them on the occasions while you were in cloud.

Pilots sometimes turn on the landing lights at night at cruise altitude so that they can see by the reflection whether or not they are in cloud. Again, the bright reflection from the engine nacelle would be exaggerated while you were in cloud. The pilots may have been 'flashing' them as well, to check whether or not they were in cloud at a particular time.

Or simply switched on the wing light which faces along the leading edges and shines on the nacelles to check for wing icing. The 737 usually is not equipped with icing sensors so the crew has to check visually if wing de-icing is required.

Thanks for the replies, guys. It was just quite odd to see, but it makes sense now.