The fields of influence and associated tornadoes descend 800 to 900 feet below the aircraft and drift with the wind until they dissipate. Atmospheric turbulence will hasten their dissipation and is often visible in the contrails. The vortex dissipates as a function of time, not distance, although there is a correlation. At flight levels with a high TAS, a three-minute vortex could persist 25 miles. At terminal area speeds, the three-minute vortex could linger for nine miles.
Vortices can be powerful enough to roll business jets and airliners and cause structural damage.
If the vortices reach the ground, they will move outward from the aircraft at about two to three knots in calm wind conditions. If there is an ambient wind, then the net movement of the vortices will be the sum of the ambient wind velocity and the no-wind motion of each vortex. An aircraft departing or arriving too close behind a large aircraft can be subjected to rolling moments exceeding the roll-control authority of the encountering aircraft, which cannot be compensated by any flight maneuver. Counter control is usually effective and induced roll minimal in cases where the wingspan and ailerons are outside the rotational flow of the vortex. You should fly at or above the preceding aircraft's flight path, altering course laterally as necessary to avoid the area below and behind the generating aircraft.