Baroclinic Instability Questions and Answers

Answer: C

The first two statements are correct, but storm tracks are strongest in winter when the equator to pole temperature contrast and hence the vertical shear are greatest. The seasonal cycle follows directly from the thermal wind relation and the dependence of the growth rate on shear, so the third statement contradicts the mechanism the other two describe.

Answer: D

The barotropic model has no vertical shear at all and therefore cannot exhibit baroclinic growth, so the last pairing is wrong. The other three are correctly matched. Setting the models out side by side, each with the feature that distinguishes it, is the most efficient way to keep the family straight and to know which one answers a given question.

Answer: A

The initial wave stage already shows a westward tilt, since that is what allows it to grow at all, so describing it as upright is wrong. The other three pairings are correct. Tracing the tilt through the life cycle from wave through growth to occlusion and decay is a compact summary of the whole energetics of a mid-latitude cyclone.

Answer: B

Latent heat release amplifies baroclinic growth substantially but is not required, as the entirely dry Eady and Charney models demonstrate. Vertical shear, stable stratification and a sign change in the potential vorticity gradient are all necessary ingredients. Distinguishing what a mechanism requires from what merely enhances it is a habit worth cultivating throughout this subject. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: C

An upper potential vorticity anomaly arriving upstream of a strong surface thermal anomaly is the classic configuration for rapid deepening, and the western Atlantic in winter supplies both the baroclinicity and the moisture. Mutual amplification proceeds while the westward tilt is maintained. Alignment marks the end rather than the beginning of the development. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: D

The Sanders and Gyakum criterion scales the 24 hectopascal threshold by the sine of the latitude relative to 60 degrees, giving about 21 hectopascals at 55 degrees, which the forecast exceeds. Such rates are well documented over the western oceans. Latent heat contributes but dry dynamics alone can produce very rapid deepening in a sufficiently baroclinic environment. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: A

Available potential energy is the small portion of the total potential energy that could be converted to kinetic energy by an adiabatic rearrangement of mass. Lorenz showed it to be about 0.5 per cent of the total, yet ten times the kinetic energy of the general circulation. Internal, kinetic and latent energies are distinct reservoirs in the same budget. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: B

The cycle runs from an initial small wave through baroclinic growth to maximum amplitude and then barotropic decay, giving 2, 4, 3, 1. The tilt changes from westward to upright to eastward as the cycle proceeds, and the energy conversion reverses accordingly. Tracing the tilt is the quickest way to identify which stage an observed system has reached.

Answer: C

Eady works on an f-plane between two rigid lids, Charney on a beta plane with no upper boundary, and the two-level model on a beta plane with the vertical structure reduced to two discrete levels. Each isolates a different aspect of the problem, and the differences between their predictions are precisely what reveal the role of each ingredient.

Answer: D

Lorenz defined available potential energy as the difference between the actual potential energy and that of a reference state obtained by adiabatic rearrangement to a horizontally uniform stratification. That definition made the atmospheric energy cycle quantitative for the first time. Potential enstrophy, helicity and the Eliassen-Palm flux are all useful diagnostics introduced for other purposes. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.