Final answer:
The vertical air current created by temperature variations is an example of heat transfer by convection, which involves the movement of fluid mass due to changes in density and temperature.
Step-by-step explanation:
A vertical air current that is generated by temperature-induced density differences is an example of heat transfer by convection. Convection is characterized by the macroscopic movement of a fluid, with warmer, less dense material rising and cooler, denser material sinking. This is commonly observed in weather systems and is essentially heat transfer due to the motion of a fluid resulting from temperature differences.