In fact, aircraft create vortices at every point where there is a difference in the speed at which air flows across one surface relative to another. This happens at wingtips, for instance, where the air flowing over different portions of the wingtip moves at different speeds, creating a circular pattern of air movement as the wind continues to move forward \cite{1995}21.
However, the major driving force behind the powerful vortices created by modern aircraft is from jet wash, or the high-speed winds created by exhaust propelled out of jet engines \cite{hxl0ej}22. Friction between these winds and surrounding air creates powerful and persistent vortices. All aircraft create two counter-rotating vortices, circulating in opposite directions and pulling in surrounding air; as these expand following the passage of the aircraft, they interact with existing wind patterns.
Wind also has the ability to change the speed and direction of a vortex depending on the direction the vortex is rotating and wind is blowing. And crucially, atmospheric circulation tends to flow in one direction due to Earth’s rotation. Thus, under the influence of existing wind patterns, one of the vortices left by an aircraft’s jet engines will tend to be disrupted and will disperse, while the other will persist and become stronger. Twin-engine aircraft are thus likely to be a major new source of powerful, long-lasting atmospheric vortices. A common misconception is that wingtips are the source of the destructive driving force behind wake turbulence, this is incorrect. Although difference in flow speed from the aerodynamics of the aircraft and friction between the aircraft and the air surrounding it will cause vortices to form, the power behind the hazardous vortices that follow behind modern aircraft can be attributed to high speed jet exhaust winds. The same effects can be seen in a boat's wake. For example, a small tugboat pulling a large ship will have a much larger wake than the non-powered ship itself will. The friction between the jet of water that is forced through the propellers creates powerful vortices in comparison to the displacement of water from the ship. Think of the Earth's atmosphere as a lake. This is why, for instance, flocks of birds are able to fly in large V-formations with small spacing between each bird whereas jet powered aircraft cannot.
3.2. Wake turbulence, water vapor, and global warming
The significance of aircraft-produced vortices is that they last long enough to accumulate (\citet{Jacquin_2005a}; \citep*{Spalart_1998})23,24. Specifically, along high traffic routes channeled within narrow corridors, the passage of many twin-engine aircraft results in hundreds of vortices being formed within just a few hours \citep*{Sausen_1998}25. These vortices can combine, creating massive vortices on the scale of those that form naturally at land-water boundaries. More importantly, as long as air traffic continues to flow along a given route, the vortex there will consistently be reinforced (Figure \ref{616266}).