In Wikipedia page of Diurnal Temperature variation, there is a statement as following: "As solar energy strikes the earth’s surface each morning, a shallow (1–3 cm) layer of air directly above the ground is heated by conduction. Heat exchange between this shallow layer of warm air and the cooler air above is very inefficient. On a warm summer’s day, for example, air temperatures may vary by 30°F from just above the ground to waist height." First of all, do you believe it? And if you do, how comes that there is such a discrete temperature separation (a difference of up to 30°F) of these two layers (the 3 cm one and the one above it)?