At what speed do vortices typically move laterally outward when contacting the ground?

The typical lateral movement speed of vortices as they interact with the ground is approximately 5 knots. This speed is significant in understanding how wake turbulence behaves after an aircraft has landed or taken off. Vortices are generated by the lift produced by an aircraft, and when they come into contact with the ground, they spread out laterally. At around 5 knots, the vortices can drift away from the runway, creating potential hazards for following aircraft. Understanding this speed is crucial for pilots and air traffic controllers to ensure safe operations, especially during takeoff and landing phases.