The atmosphere is composed of billions of billions of molecules, 1043 molecules to be exact. Each molecule is zooming at hundreds of meters per second but colliding with other molecules each billionth of a second, exchanging kinetic energy (½ mv2), momentum (mv), and internal energy (rotations and vibrations). It’s impossible to calculate what all of these molecules will do, so instead we study the energy and energy changes of volumes of molecules and use this information in our forecast models. This study is called thermodynamics. Thermodynamics has some difficult concepts to master, but it is also part of your everyday experience. In this lesson, you will learn the fundamental laws of thermodynamics and see how they describe our atmosphere’s pressure and temperature structure. You will learn why the atmosphere is sometimes stable and what happens when it isn’t.
By the end of this lesson, you should be able to:
- use the fundamental gas laws - Ideal Gas Law, Dalton’s Law – to determine the relative densities of different air masses
- derive the hydrostatic equilibrium equation from force balance to show why atmospheric pressure decreases with height
- use the 1st Law of Thermodynamics and conservation of energy (i.e., adiabatic processes) to explain air parcel temperature changes
- determine stability for different dry environmental temperature profiles
- calculate buoyancy and vertical velocity with time
If you have any questions, please post them to the Course Questions discussion forum. I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.