Engine nacelles are optimized for cruise performance. At high angles of attack, their shape results in some rather awkward flow properties which can influence the wing performance above and behind them. In order to control things, you will see small vanes attached to one or both sides of the nacelle that generate a vortex that stabilizes the flow somewhat. As an aircraft rotates at takeoff, the strength of this vortex increases and it will often become visible as moisture in the air condenses within in. This vortex will stream back up and over the leading edge of the wing.
When you are inside the aircraft, this is pretty easy to see provided the conditions are right. From head on or aft they are also quite conspicuous. It isn’t often that you get a good view from above. When I was flying over LAX in the helicopter, the aircraft departing from the north complex had better light on them. However, the runways are offset so the rotation point is further west and beyond the area in which we are allowed to fly. However, you can get a view from above and behind as the jets get airborne. An El Al 777 took off while I was up and I managed to get some shots of it as it rotated and climbed away and the vortices were clear to see as the angle of attack increased.
The light was getting low in the sky and I was needing to drop my rental car back at the lot to get my flight home but a Finnair A350 was on approach. I could see it was coming in to the south complex so the Proud Bird parking lot would be the spot for me. The nice evening light was going to work out well. I had shot a Finnair A350 once before when one came to SFO but this would be only my second encounter. No point in missing it. The sky was warming up nicely so it was hard to miss getting the shot.
