The increase in temperature with depth in the earth is called the geothermal

Yes the answer is geothermal, but more specifically geothermal gradient.

Geothermal gradient

Explanation:

The thermal gradient is often defined as the rate of increase in temperature with respect to the increase in the subsurface depth. This accounts for more than 50% of the total heat energy of the earth. The geothermal gradient is approximately 25° C/km beneath the earth's surface. This heat results from the decay of the radioactive elements that are at great depths. In addition to this, the latent heat is also produced due to the crystallization of the core. Due to this heat energy, that is transmitted to the upper mantle, the plates are able to move over the layer of the Asthenosphere.  

This heat energy obtained from the interior of the earth is known as geothermal energy.

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.