Its because the atmosphere is heated by the ground, not the sun.
Air is transparent. Sunlight will go right through it without transferring much heat at all. Instead the sunlight keeps going until it hits the earth.
The ground or water absorbs the heat from the sun, which heats the air just above it, which then rises and mixes with the colder air around it.
The heated air can only rise so far, so most of that heat stays near the ground, hence the temperature gradient between the surface and airplane cruising altitudes.
Its because the atmosphere is heated by the ground, not the sun.
Air is transparent. Sunlight will go right through it without transferring much heat at all. Instead the sunlight keeps going until it hits the earth.
The ground or water absorbs the heat from the sun, which heats the air just above it, which then rises and mixes with the colder air around it.
The heated air can only rise so far, so most of that heat stays near the ground, hence the temperature gradient between the surface and airplane cruising altitudes.