Wingtip vortices occur when a wing is generating lift. Air from below the wing is drawn around the wingtip into the region above the wing by the lower pressure above the wing, causing a vortex to trail from each wingtip. Wake turbulence exists in the vortex flow behind the wing. The strength of wingtip vortices is determined primarily by the weight and airspeed of the aircraft.[1] Wingtip vortices make up the primary and most dangerous component of wake turbulence.
Lift is generated by high pressure below the wing and low pressure above the wing. As the high-pressure air moves around the wingtip to the low pressure, (high pressure always moves towards lower pressure areas) the air rotates, or creates a horizontal "tornado" behind the wings. This tornado sinks lower and lower until it dissipates.
Wake turbulence is especially hazardous in the region behind an aircraft in the takeoff or landing phases of flight. During take-off and landing, aircraft operate at high angle of attack. This flight attitude maximizes the formation of strong vortices. In the vicinity of an airport there can be multiple aircraft, all operating at low speed and low height, and this provides extra risk of wake turbulence with reduced height from which to recover from any upset.