Wingtip vortices are circular patterns of rotating air left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. Wingtip vortices are sometimes named trailing or lift-induced vortices because they also occur at points other than at the wing tips.
Indeed, vorticity is trailed at any point on the wing where the lift varies span-wise (a fact described and quantified by the lifting-line theory); it eventually rolls up into large vortices near the wingtip, at the edge of flap devices, or at other abrupt changes in wing planform.
Wingtip vortices are associated with induced drag, the imparting of downwash, and are a fundamental consequence of three-dimensional lift generation. Careful selection of wing geometry (in particular, aspect ratio), as well as of cruise conditions, are design and operational methods to minimize induced drag.
Wingtip vortices form the primary component of wake turbulence. Depending on ambient atmospheric humidity as well as the geometry and wing loading of aircraft, water may condense or freeze in the core of the vortices, making the vortices visible.
They’re swirling tunnels of air that form on your wingtips. High pressure air from the bottom of your wing escapes around the wingtip, moving up towards the lower pressure area on the top of the wing. This movement creates a vortex or tunnel of air, rotating inwards behind the wing.
They’re strongest when the air pressure difference between the top and the bottom of the wing is the greatest – which happens when you’re generating the most induced lift. This occurs when you’re at high angles of attack.
During takeoff and landing, you’re slow – so you’re at a high angle of attack and generating strong wingtip vortices.
When you’re cruising at high altitudes, like a jet in the flight levels, the air is thin. So, you need a high angle of attack to generate enough lift to stay level, even though you’re moving fast. Your wingtip vortices are stronger here, too.