Answer:
3.5 °F/1000 ft
Step-by-step explanation:
The "normal lapse rate" is the average rate at which normal air temperature decreases with increasing altitude. It is on the order of 3.5 °F per 1000 ft or 6.5 °C per km.
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The actual lapse rate depends on a number of factors, including radiation, convection, and condensation. An "inversion" is characterized by increasing temperature with altitude.