Baroclinic Instability Questions and Answers

Q: Which four reservoirs appear in the Lorenz energy cycle?

The cycle divides both available potential energy and kinetic energy into zonal mean and eddy parts, giving four reservoirs connected by conversion terms. The dominant path runs from zonal available potential energy through eddy available potential energy to eddy kinetic energy and finally to zonal kinetic energy. Mapping the observed magnitudes onto that diagram summarises the general circulation compactly. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Q: Which conversion dominates the observed energy cycle?

The baroclinic conversion from zonal to eddy available potential energy, driven by the poleward eddy heat flux, is the largest term and is the first step of the dominant pathway. It is followed by conversion to eddy kinetic energy and then, during barotropic decay, to zonal kinetic energy. Direct zonal to eddy kinetic conversion is small and often of the opposite sign. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Q: Which type of weather system does baroclinic instability produce?

Travelling mid-latitude depressions with their attendant fronts are the direct manifestation of baroclinic instability, forming in the strong horizontal temperature gradients of the mid-latitudes. Tropical cyclones are driven by surface heat fluxes in a nearly barotropic environment, thunderstorms by conditional instability, and lee waves by forced flow over topography. Assigning each weather system to the instability or forcing that creates it is a useful organising exercise across the whole of dynamical meteorology.

Q: Which latitude band shows most baroclinic activity?

Baroclinic activity requires a strong horizontal temperature gradient together with an appreciable Coriolis parameter, and both conditions are met between roughly 30 and 60 degrees latitude. The tropics lack the gradient and the rotation, and the polar regions lack the gradient once inside the vortex. This is why the weather of temperate latitudes is dominated by travelling systems while tropical weather is dominated by convection.

Q: Which season shows the strongest baroclinic activity?

The equator to pole temperature contrast is greatest in winter, so the vertical shear and hence the growth rate are largest then. Storm tracks are correspondingly most active in winter in both hemispheres. Summer heating warms the whole hemisphere and actually reduces the gradient. The seasonal cycle follows directly from the thermal wind relation applied to the observed temperature distribution. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Q: Which contrast makes the ocean important for storm track position?

Cold air flowing off a winter continent over the warm Gulf Stream or Kuroshio creates intense low level baroclinicity, which anchors the entrance of each storm track. Roughness, albedo and boundary layer depth all differ between land and sea but none of them produces a horizontal temperature gradient of comparable strength. This is why ocean circulation exerts a direct influence on where mid-latitude storms form.

Q: Which term describes the region where a storm track begins?

The entrance region lies over the western boundary current where the Eady growth rate is largest, and disturbances amplify as they travel downstream through it. The exit region over the eastern ocean is where they decay. The surf zone belongs to the stratosphere and the dry slot to the structure of an individual cyclone rather than to the geography of the track.

Q: Which behaviour do disturbances show in the storm track exit region?

By the eastern side of an ocean basin the baroclinicity has weakened and the eddies enter their barotropic decay phase, transferring momentum into the mean flow and weakening. Peak amplitude is generally reached in mid-basin. Blocking can make a system stationary in the exit region, which is why the last option is plausible, but decay is the normal behaviour.

Q: Which feature can interrupt a storm track entirely?

A blocking high diverts the westerly flow around it and can halt the progression of disturbances along a storm track for a week or more. Its onset and decay remain among the least predictable events in mid-latitude meteorology. Jet streaks, cut-off lows and transitioning tropical cyclones all modify the track without arresting it in the same way.

Q: Which flow pattern characterises a block?

The classical block is a persistent anticyclone at high latitude with the westerly flow split into branches passing to its north and south, often with a cut-off low beneath it. The omega and dipole patterns are the standard varieties. A strong zonal jet is the opposite condition, and rapid short wave passage describes the unblocked progressive regime.

61.

Which four reservoirs appear in the Lorenz energy cycle?

A.Zonal and eddy available potential and kinetic energy
B.Internal, potential, kinetic and latent energy considered separately for the atmosphere as a whole
C.Radiative, latent, sensible and kinetic energy
D.Available potential energy divided among the four seasons of the year at each latitude of the globe

Answer: A

The cycle divides both available potential energy and kinetic energy into zonal mean and eddy parts, giving four reservoirs connected by conversion terms. The dominant path runs from zonal available potential energy through eddy available potential energy to eddy kinetic energy and finally to zonal kinetic energy. Mapping the observed magnitudes onto that diagram summarises the general circulation compactly. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Discuss in Forum

62.

Which conversion dominates the observed energy cycle?

A.Latent heat directly into zonal kinetic energy through the release of buoyancy in tropical convection
B.Zonal to eddy available potential energy
C.Zonal kinetic energy directly into eddy kinetic energy without any potential energy being involved at all
D.Eddy kinetic to zonal available potential

Answer: B

The baroclinic conversion from zonal to eddy available potential energy, driven by the poleward eddy heat flux, is the largest term and is the first step of the dominant pathway. It is followed by conversion to eddy kinetic energy and then, during barotropic decay, to zonal kinetic energy. Direct zonal to eddy kinetic conversion is small and often of the opposite sign. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Discuss in Forum

63.

Which type of weather system does baroclinic instability produce?

A.The thunderstorm
B.The mountain lee wave, which forms where stable flow is forced over a barrier and oscillates downstream
C.The mid-latitude cyclone
D.The tropical cyclone, which draws its energy from the latent heat supplied by a warm ocean surface

Answer: C

Travelling mid-latitude depressions with their attendant fronts are the direct manifestation of baroclinic instability, forming in the strong horizontal temperature gradients of the mid-latitudes. Tropical cyclones are driven by surface heat fluxes in a nearly barotropic environment, thunderstorms by conditional instability, and lee waves by forced flow over topography. Assigning each weather system to the instability or forcing that creates it is a useful organising exercise across the whole of dynamical meteorology.

Discuss in Forum

64.

Which latitude band shows most baroclinic activity?

A.The tropics, where the greatest supply of energy from solar heating reaches the surface of the planet
B.The polar regions
C.The subtropics, where the descending branch of the Hadley circulation produces the strongest subsidence
D.The middle latitudes

Answer: D

Baroclinic activity requires a strong horizontal temperature gradient together with an appreciable Coriolis parameter, and both conditions are met between roughly 30 and 60 degrees latitude. The tropics lack the gradient and the rotation, and the polar regions lack the gradient once inside the vortex. This is why the weather of temperate latitudes is dominated by travelling systems while tropical weather is dominated by convection.

Discuss in Forum

65.

Which season shows the strongest baroclinic activity?

A.Winter
B.Summer, when the greater solar heating supplies more energy to the atmosphere in the hemisphere concerned
C.Spring
D.Autumn, when the ocean is at its warmest and the greatest supply of heat is available to the air above

Answer: A

The equator to pole temperature contrast is greatest in winter, so the vertical shear and hence the growth rate are largest then. Storm tracks are correspondingly most active in winter in both hemispheres. Summer heating warms the whole hemisphere and actually reduces the gradient. The seasonal cycle follows directly from the thermal wind relation applied to the observed temperature distribution. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Discuss in Forum

66.

Which contrast makes the ocean important for storm track position?

A.The difference in the depth of the boundary layer over water compared with that observed over the land
B.The temperature difference between a warm current and cold continental air
C.The difference in surface roughness between the smooth ocean and the much rougher adjacent land surface
D.The difference in albedo

Answer: B

Cold air flowing off a winter continent over the warm Gulf Stream or Kuroshio creates intense low level baroclinicity, which anchors the entrance of each storm track. Roughness, albedo and boundary layer depth all differ between land and sea but none of them produces a horizontal temperature gradient of comparable strength. This is why ocean circulation exerts a direct influence on where mid-latitude storms form.

Discuss in Forum

67.

Which term describes the region where a storm track begins?

A.The surf zone
B.The dry slot, which is the descending stratospheric airstream wrapping around a developing cyclone
C.The entrance region
D.The exit region, in which the disturbances decay and return their energy to the mean flow around them

Answer: C

The entrance region lies over the western boundary current where the Eady growth rate is largest, and disturbances amplify as they travel downstream through it. The exit region over the eastern ocean is where they decay. The surf zone belongs to the stratosphere and the dry slot to the structure of an individual cyclone rather than to the geography of the track.

Discuss in Forum

68.

Which behaviour do disturbances show in the storm track exit region?

A.They reach their greatest amplitude, since the accumulated growth over the track is at its maximum there
B.They form for the first time
C.They become stationary and remain in place for several days before dissipating under surface friction
D.They decay and their energy returns to the mean flow

Answer: D

By the eastern side of an ocean basin the baroclinicity has weakened and the eddies enter their barotropic decay phase, transferring momentum into the mean flow and weakening. Peak amplitude is generally reached in mid-basin. Blocking can make a system stationary in the exit region, which is why the last option is plausible, but decay is the normal behaviour.

Discuss in Forum

69.

Which feature can interrupt a storm track entirely?

A.A blocking anticyclone
B.A tropical cyclone undergoing extratropical transition as it moves polewards into the mid-latitude flow
C.A jet streak
D.A cut-off low, which becomes detached from the westerly flow and drifts slowly for several days afterwards

Answer: A

A blocking high diverts the westerly flow around it and can halt the progression of disturbances along a storm track for a week or more. Its onset and decay remain among the least predictable events in mid-latitude meteorology. Jet streaks, cut-off lows and transitioning tropical cyclones all modify the track without arresting it in the same way.

Discuss in Forum

70.

Which flow pattern characterises a block?

A.A rapid succession of short wave troughs travelling eastward at close to the speed of the mean flow
B.A quasi-stationary high with split flow around it
C.A deep stationary low around which the westerly flow accelerates as it passes to the north of it
D.A strong zonal jet

Answer: B

The classical block is a persistent anticyclone at high latitude with the westerly flow split into branches passing to its north and south, often with a cut-off low beneath it. The omega and dipole patterns are the standard varieties. A strong zonal jet is the opposite condition, and rapid short wave passage describes the unblocked progressive regime.

Discuss in Forum

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