I quote from the Private Pilot Manual - in Chapter 1:
Ground Effect
When an airplane wing operates within a wingspan distance above the ground, induced drag is significantly reduced. Within this height above the ground, the strength of wingtip vortices and the wing downwash is significantly reduced, since these forces are restricted in downward movement.
Therefore, as the aircraft nears the ground, drag effects are reduced rapidly; just before touchdown drag can be decreased as much as 40%. The low-wing airplane is more subject to ground effect than mid- or high-wing airplanes because the wing is closer to the ground.
Further:
Wind
Wind direction and velocity affect takeoff performance. For example, a headwind shortens the takeoff run, while crosswinds, and especially tailwinds, lengthen the takeoff roll and reduce the subsequent angle of climb. Decreased controllability and takeoff performance can make crosswind takeoffs undesirable and downwind takeoffs hazardous.
It doesn't say anything about wind causing or increasing ground effect. But then it doesn't say anything about wind making the hamburgers better at the aiport cafeteria either.

It does however clearly state that a headwind
decreases the takeoff roll. Ground affect doesn't care if the plane is taking off or landing - it only cares how close the plane is to the ground. That's why some planes could only fly *in* ground effect. Therefore, the effect of a headwind is to decrease the distance required to land. It isn't quoted in the above passages, but it is in every text and INDN even states this in his response telling me I'm wrong.
INDN, you can't have it both ways. Ground effect tends to lengthen the distance required to land - not shorten it. You can't then tell me that a wind coming down the runway causes ground effect but also shortens the distance. Your logic is just wrong.
Wind will/can cause turbulence, however, and maybe the pilots were referring to rougher than normal landing conditions and not to the tendency of the airplane to float. Air coming across water would also tend to be more humid and therefore less dense - meaning lower performance and faster speeds required for takeoff or landing which would extend distances. But it isn't "ground effect".
There is no need to cloud the issue with wind shear, flaps, or anything of the sort. I would be very interested in hearing how a wind blowing down the runway causes ground effect, however. Please feel free to quote whatever references you have available.
And Thunder, we aren't density altitude here either. We are talking about a wind coming down the runway causing a plane to float. No more. No less. Not thrust. Not weight. Not temperature. No comparisons between high and low airports. Certainly all of the above affect takeoff and landing but aren't the issue.
Prove me wrong and I'll shut up - but I don't think you'll be able to. Either of you.
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