Normally, even though hot air (at equal pressure) is less dense than cool air, density decreases with height in the atmosphere due to the decrease in pressure. When it doesn’t, it is called autoconvective, meaning it will constantly turn over with air dropping from higher levels and rising from lower levels. Imagine a rock on top of a life jacket in the water. As soon as it is jostled at all, the life jacket will rise and the rock will sink.
Today, using high-resolution temperature sensors at multiple low-levels, we find that the atmospheric density actually increases with height from the surface up to 40 feet, because it is so hot near the ground surface. A few minutes ago, it was over 5 degrees warmer at 1.5 feet than at 30 feet. This sets up a constant overturning near the ground, but it is not happening fast enough to offset the incoming solar radiation heating up the ground, and then the air in contact with the ground.
