Baroclinic Instability Questions and Answers

Q: Consider the following statements about storm tracks. 1. They coincide with maxima of the Eady growth rate parameter. 2. They are anchored by western boundary current temperature gradients. 3. They are strongest in summer. Which of the statements given above is or are correct?

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.

Q: Consider the following pairs of model and feature. Eady - two rigid lids Charney - beta plane with no upper lid Two-level - critical shear for instability Barotropic - baroclinic growth How many of the pairs given above are correctly matched?

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.

Q: Consider the following pairs of stage and structure. Growing - westward tilt with height Mature - vertically upright Decaying - eastward tilt Wave stage - vertically upright How many of the pairs given above are correctly matched?

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.

Q: Which of the following is not required for baroclinic instability? Latent heat release Vertical shear Stable stratification A sign change in the PV gradient

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.

Q: A model forecasts a cyclone deepening 30 hectopascals in 24 hours at 55 degrees north. How should this be described?

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.

Q: The energy released when the atmospheric mass is rearranged to lower its centre of gravity is called _____ energy.

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.

Q: Arrange the stages of the baroclinic eddy life cycle in order. 1. Barotropic decay 2. Initial wave 3. Maximum amplitude 4. Baroclinic growth Select the correct sequence.

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.

Q: Match each model with its distinguishing assumption. List I A. Eady B. Charney C. Two-level List II P. beta plane with unbounded atmosphere Q. f-plane with two rigid lids R. beta plane with two discrete levels Select the correct match.

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.

Q: Which quantity did Lorenz introduce to quantify the energy cycle?

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.

51.

Consider the following statements about storm tracks.

1. They coincide with maxima of the Eady growth rate parameter.

2. They are anchored by western boundary current temperature gradients.

3. They are strongest in summer.

Which of the statements given above is or are correct?

A.2 and 3 only
B.1, 2 and 3
C.1 and 2 only
D.1 and 3 only

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.

Discuss in Forum

52.

Consider the following pairs of model and feature.

Eady - two rigid lids

Charney - beta plane with no upper lid

Two-level - critical shear for instability

Barotropic - baroclinic growth

How many of the pairs given above are correctly matched?

A.Only one
B.Only two
C.All four
D.Only three

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.

Discuss in Forum

53.

Consider the following pairs of stage and structure.

Growing - westward tilt with height

Mature - vertically upright

Decaying - eastward tilt

Wave stage - vertically upright

How many of the pairs given above are correctly matched?

A.Only three
B.Only one
C.Only two
D.All four

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.

Discuss in Forum

54.

Which of the following is not required for baroclinic instability?

Latent heat release

Vertical shear

Stable stratification

A sign change in the PV gradient

A.A sign change in the PV gradient
B.Latent heat release
C.Vertical shear
D.Stable stratification

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.

Discuss in Forum

55.

A forecaster observes an upper trough approaching a strong low level baroclinic zone over the western Atlantic in January.

What development is expected?

A.No development
B.Development only if the upper trough moves ahead of the surface feature before the two become aligned
C.Rapid cyclogenesis through mutual amplification of the anomalies
D.Slow filling of the surface low as the upper trough passes overhead without any interaction occurring

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.

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56.

A model forecasts a cyclone deepening 30 hectopascals in 24 hours at 55 degrees north.

How should this be described?

A.Ordinary development, since the threshold of 24 hectopascals applies only at 60 degrees of latitude exactly
B.Impossible
C.A tropical transition, since deepening at that rate can only occur through the release of latent heat
D.Explosive cyclogenesis, since the latitude adjusted threshold is met

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.

Discuss in Forum

57.

The energy released when the atmospheric mass is rearranged to lower its centre of gravity is called _____ energy.

A.available potential
B.internal energy, which is by far the largest of the atmospheric energy reservoirs but is mostly unavailable
C.kinetic
D.latent heat energy, which is released when water vapour condenses within an ascending parcel of moist air

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.

Discuss in Forum

58.

Arrange the stages of the baroclinic eddy life cycle in order.

1. Barotropic decay

2. Initial wave

3. Maximum amplitude

4. Baroclinic growth

Select the correct sequence.

A.4, 2, 1, 3
B.2, 4, 3, 1
C.1, 2, 3, 4
D.2, 3, 4, 1

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.

Discuss in Forum

59.

Match each model with its distinguishing assumption.

List I

A. Eady

B. Charney

C. Two-level

List II

P. beta plane with unbounded atmosphere

Q. f-plane with two rigid lids

R. beta plane with two discrete levels

Select the correct match.

A.A-R, B-P, C-Q
B.A-Q, B-R, C-P
C.A-Q, B-P, C-R
D.A-P, B-Q, C-R

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.

Discuss in Forum

60.

Which quantity did Lorenz introduce to quantify the energy cycle?

A.Potential enstrophy, which is the domain integral of one half the square of the potential vorticity field
B.Helicity
C.The Eliassen-Palm flux, which measures the interaction between the eddies and the zonal mean flow present
D.Available potential energy

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.

Discuss in Forum

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