Recall from physics that kinetic energy relates to the motion of objects, while potential energy relates to the attraction between objects. These energies can apply on the macroscale — to large-scale objects consisting of many molecules. They can also apply on the microscale — to individual molecules, atoms, and subatomic particles. Energy on the microscale is known as internal energy, and a portion of internal energy is what we call heat.
Energy can change forms between kinetic, potential, and other energy types. It can also change scale. The conversion between microscale and macroscale energies was studied extensively during the industrial revolution to design better engines. This study is called thermodynamics. The field of thermodynamics also applies to the atmosphere. The microscale energy of heat can cause the macroscale motions we call winds. Microscale attractions enable water-vapor molecules to condense into macroscale cloud drops and rain. In this chapter, we will investigate the interplay between internal energy and macroscale effects in the atmosphere. First, focus on internal energy.
Thumbnail: A constant pressure balloon stays aloft for weeks at an altitude of 100,000 ft so that the instruments in the attached gondola can make long-term measurements. Credit: National Scientific Balloon Facility, Palestine TX.