Next imagine our two jumpers jumping from a tethered
balloon in a wind. Because the balloon is tethered, the groundspeed is
zero. The jumpers drift with the wind in freefall and also when under
canopy. Note that the light trails are the same (dashed line). However,
the smoke trails are separate and distinct for the two jumpers, because
they drift downwind. Separate smoke trails mean each has his/her own
column of air. Their separation is satisfactory despite the zero
groundspeed of the jumpship.