B-727 aircraft. In the frame of reference moving with the wind, the wind shear vortices normally move at half the wind speed in the direction opposite to the wind (i.e., 5 fps to the left in Fig. 3). The effect of the aircraft vortices on this motion is to speed it up on the up-wind side and to reverse it on the down-wind side. The wind shear vortices approaching from the right in Fig. 3 are swept up in the air and eventually induce the down-wind vortex to reverse its downward motion and move back up. After 60 sec, this vortex has captured wind shear vorticity of equal magnitude to its own and is moving upward at a speed comparable to its initial downward motion. The up-wind vortex, on the contrary, finds itself isolated from wind shear vorticity and therefore is influenced only by its image vortex. These motions are shown in Fig. 4 in the ground frame of reference. For comparison, the trajectories for a uniform wind are also shown. The trajectory of the up wind vortex is almost the same for the two cases, as one might expect. Although the model used here is crude, it gives a qualitative description of the observed difference in the motion of the two vortices. The effect is similar to but stronger than that proposed by Harvey and Perry1 to explain the rising of vortices. It should be noted that the effect discussed in this note is actually produced by the vertical gradient in the wind shear rather than by the wind shear directly. One can easily see that the wind shear vortices would not affect the aircraft vortex vertical motion at all if they were uniformly distributed in space. The phenomenon described in this Note pertains to relatively low cross winds. Both experimental observations and calculations indicate that other phenomena occur at much higher cross wind speeds (e.g. 30 fps instead of the 10 fps considered here).