25  Touchdown Rotation  Wake ends  Wake begins  Figure 5-14.  Avoid turbulence from another aircraft.  Figure 5-15.  When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the  ground at a speed of 2 or 3 knots (top). A crosswind will decrease the lateral movement of the upwind vortex and increase the movement  of the downwind vortex. Thus a light wind with a cross runway component of 1 to 5 knots could result in the upwind vortex remaining in  the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway (bottom).  5-10  Vortex Movement Near Ground - with Cross Winds  Vortex Movement Near Ground - No Wind  3K Wind  6K  (3K + 3K)  3K  No Wind  3K  0 (3K - 3K) 