Refer to figure.
When an aircraft is flying, the wingtip vortices produced by the aircraft slowly descend behind the airplane. When the aircraft touches down, the vortices end. By flying your airplane above their flight path, and landing beyond their touchdown point, you're almost guaranteed to avoid a wake turbulence encounter.
Wake turbulence vortices sink slowly downwards and outwards, so high (above) and upwind should keep you clear.
In simple words, by upwind it basically means that the wind is “hitting” your airplane first and then the other. Downwind means it is hitting the large plane first and, therefore, will move the vortices in the direction of your airplane (which is undesirable). In other words, if the wind is coming from the right, you should fly on the right side (and above) of the track of the preceding aircraft. Being the goal not to cross the flight path of the heavy aircraft.
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