First Law Applied to the Atmosphere Questions and Answers

Answer: C

Because the ocean has not yet equilibrated with the existing forcing, some further warming is already committed even if concentrations were held constant from today. The transient response and the equilibrium sensitivity are related but distinct measures of how much warming a given forcing produces. Distinguishing the three quantities carefully is essential when reading assessment reports. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

The imbalance is under one watt per square metre against fluxes of 240, which is beyond the absolute accuracy of satellite radiometry, so it is inferred from the rate at which the ocean is warming. The Argo float array made that measurement possible. Satellite data constrain the variability of the imbalance well even though they cannot give its absolute value. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: A

Nearly four thousand autonomous profiling floats now measure temperature and salinity to two kilometres depth every ten days, giving the first genuinely global picture of ocean heat content. Before Argo the coverage was confined largely to shipping routes in the northern hemisphere. Altimetry measures total sea level change, which combines thermal expansion with the addition of mass from melting ice. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: B

Specific volume, denoted alpha, is the reciprocal of density and appears in the first law as the coefficient of the pressure change. Using it rather than density keeps the thermodynamic equations in a per unit mass form throughout, which is convenient when following a parcel. Its value at sea level is about 0.82 cubic metres per kilogram, the reciprocal of the familiar 1.225 kilograms per cubic metre. Keeping the two reciprocals straight is worth a moment's care when substituting into a formula.

Answer: C

The work done per unit mass is the pressure times the increase in specific volume, which is the area beneath the process on a pressure volume diagram. At constant pressure that area is a simple rectangle. Not all the supplied heat becomes work, since some raises the internal energy, which is exactly why the two specific heats differ.

Answer: D

On a pressure volume diagram the area under the curve is the work done, while on a temperature entropy diagram the corresponding area is the heat exchanged. The tephigram is a temperature entropy diagram in disguise, which is why areas on it represent energy. Recognising which quantity an area represents on each diagram is what makes them usable for calculation rather than merely for display. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: A

Because the tephigram plots temperature against entropy, an area on it has the dimensions of energy per unit mass, which is what allows convective available potential energy to be measured directly. This property is shared by the skew-T and emagram and is the defining requirement of a usable thermodynamic diagram. Diagrams lacking it, such as the Stuve, trade the property for simplicity. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: B

The skew-T log-p diagram plots temperature skewed at 45 degrees against the logarithm of pressure and is the standard in the United States. The tephigram is used in Britain and Canada and the emagram in much of Europe. All three preserve the area-energy property and differ mainly in which lines are straight, so a forecaster trained on one adapts to another quickly. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: C

On a skew-T the isotherms run as straight lines at 45 degrees and the isobars are straight and horizontal, while the dry adiabats are gently curved and the saturated adiabats strongly so. Saturated adiabats cannot be straight on any diagram that also preserves the area property. Knowing which families are curved prevents misreading a plotted sounding.

Answer: D

A sounding is plotted as two curves, the temperature and the dew point, and the separation between them at each level shows how far the air is from saturation. The parcel curve is constructed rather than observed. The wet bulb curve can be added but is not part of the standard plot, which is why the separation of the two principal curves is what the eye is trained to read. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.