First Law Applied to the Atmosphere Questions and Answers

Answer: A

Saturation means the dew point equals the temperature, so the two curves lie together, which is the signature of a cloud layer on a sounding. Divergence of the curves indicates dry air. The dew point can never exceed the temperature, so a crossing indicates an error in the data rather than a physical condition.

Answer: B

The layer in which temperature and dew point coincide is saturated and therefore cloudy, and its vertical extent gives the cloud depth directly. A dry adiabatic lapse rate indicates a well mixed layer, which may or may not be cloudy at its top. Reading cloud base, top and depth from a single plotted sounding is among the most useful practical skills the diagram provides. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: C

The parcel curve crosses the environment curve at the level of free convection on the way up and at the equilibrium level higher still, bounding the positive area between them. The lifting condensation level is where the parcel curve changes from a dry to a saturated adiabat rather than where it crosses the environment. Distinguishing the crossings from the kink is essential when computing convective energy. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: B

Total potential energy is internal energy + gravitational potential energy.

In atmospheric energetics, for a column of air in hydrostatic balance, the internal energy and the gravitational potential energy are proportional to each other and change together, so they are combined as total potential energy. Only a small part of it, the available potential energy, can be converted into kinetic energy (Lorenz).

Kinetic energy is the energy of motion and is the form into which potential energy is converted, so any option adding or subtracting kinetic energy does not define potential energy.