What is the typical speed at which vortices will travel laterally across the surface if there is no wind?

The typical speed at which vortices will travel laterally across the surface in calm air conditions, without wind, is generally recognized to be in the range of 2-3 knots. This lateral movement is a result of the wake turbulence created by an aircraft as it generates lift and displaces air.

In the absence of wind, the vortices will drift downwind at this speed, influenced primarily by the characteristics of the aircraft that created them, such as its weight and speed during takeoff or landing. Understanding this speed is crucial for ensuring safe separation distances on the ground, especially during takeoff and landing phases, where the impact of these vortices can significantly affect smaller aircraft.

The values outside this range, such as 1-2 knots or 4-5 knots, do not accurately reflect the typical conditions observed, underscoring the importance of recognizing the correct speed associated with lateral vortex movement in calm conditions.