Some jet airplanes fly in a layer of the atmosphere where temperature generally increases with altitude
What is this layer of the atmosphere?

Above the troposphere lies the stratosphere where jet airplanes fly. Temperatures increase with altitude because of increasing amounts of ozone. The ozone layer within the stratosphere absorbs harmful ultraviolet rays of sunlight. As the mesosphere extends upward above the stratosphere, temperatures decrease.

The answer should be geothermal i hope i’m right message me if i’m wrong and i’ll change my answer and fix it for you