Commercial jets fly in the lower stratosphere. What happens to the exterior temperature of these planes as they leave the ground and rise to enter the stratosphere?

Hello!

The exterior temperature of these planes as they leave the ground and rise to enter the stratosphere decreases and then increases.

That happens because the airplane first goes up through the troposphere. In this layer of the atmosphere, the temperature decreases as the plane go higher. When the plane enters the frontier between the troposphere and the stratosphere (the tropopause), temperature rises. That increase in temperature is caused by the Ozone Layer, which is in the stratosphere and absorbs ultraviolet radiation from the Sun's rays, causing an increase in temperature.

Have a nice day!