Atmospheric Waves Questions and Answers

Q: Which tracer is used to estimate the age of stratospheric air?

Long lived tracers whose tropospheric concentration is increasing steadily provide a clock: the lag between a stratospheric measurement and the matching tropospheric value gives the mean transit time. Ages of up to six years are found at high latitudes. Ozone is chemically active, water vapour is modified by the cold trap, and nitrous oxide is destroyed rather than produced in the stratosphere. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Q: Which wave signature is seen in stratospheric water vapour observations?

The annual cycle of tropical cold point temperature imprints alternating moist and dry layers on the ascending air, and these propagate upward over several years like the signal on a tape recorder. Tracking them gives a direct measurement of the ascent rate of the Brewer-Dobson circulation. Methane oxidation does add water vapour with height, which makes that a plausible distractor, but the tape recorder signal is the striking observation.

Q: Which region of the winter stratosphere is called the surf zone?

The mid-latitude surf zone is where planetary waves break irreversibly, mixing potential vorticity and forming a broad region of weak gradients between the tropics and the vortex edge. The vortex edge itself acts as a transport barrier. The name captures the analogy with ocean waves breaking on a shelving beach, and the sharp gradients at its edges are a striking feature of potential vorticity maps.

Q: Which consequence does that isolation have for polar ozone?

Because the vortex is isolated, air depleted of ozone by heterogeneous chemistry on polar stratospheric clouds is not replaced, and the depletion accumulates through the winter and spring. This is why the ozone hole is a southern hemisphere phenomenon, the southern vortex being colder and more isolated than the northern one. Descent does occur but the air remains extremely cold.

Q: Which hemisphere shows the stronger and more isolated polar vortex?

The southern vortex is colder, stronger and far less disturbed by planetary waves, because the southern hemisphere has weaker stationary wave forcing from topography and land-sea contrast. That is precisely why the ozone hole forms over Antarctica and not over the Arctic. The vortex is a winter feature, forming as the pole enters polar night.

Q: Which event can disrupt the vortex in mid-winter?

Breaking planetary waves can decelerate and reverse the vortex within a few days, raising polar stratospheric temperatures by tens of kelvin and sometimes splitting the vortex in two. Such major warmings occur in roughly half of northern winters and very rarely in the south. The spring reversal is the ordinary seasonal transition, and volcanic and tropospheric influences act far more slowly.

91.

Which tracer is used to estimate the age of stratospheric air?

A.Water vapour
B.Nitrous oxide, whose concentration increases with altitude as it is produced within the stratosphere itself
C.Sulphur hexafluoride or carbon dioxide
D.Ozone, whose concentration falls steadily with time as it is destroyed by catalytic chemical reactions

Answer: C

Long lived tracers whose tropospheric concentration is increasing steadily provide a clock: the lag between a stratospheric measurement and the matching tropospheric value gives the mean transit time. Ages of up to six years are found at high latitudes. Ozone is chemically active, water vapour is modified by the cold trap, and nitrous oxide is destroyed rather than produced in the stratosphere. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

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92.

Which feature of the tropical tropopause controls stratospheric water vapour?

A.The height of the tropopause, which determines the total mass of air able to enter the stratosphere above
B.The strength of the trade winds
C.The concentration of ozone at the tropopause, which absorbs radiation and warms the air passing through it
D.The cold point acting as a freeze drier

Answer: D

Air entering the stratosphere through the tropical tropopause is dehydrated to the saturation mixing ratio at the cold point, typically a few parts per million, which sets the humidity of the whole stratosphere. This is the Brewer mechanism, proposed to explain the observed dryness. Tropopause height and ozone influence the temperature but the freeze drying is the direct control. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

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93.

Which name is given to the layer just below the tropical tropopause?

A.The tropical tropopause layer
B.The planetary boundary layer, within which turbulent stress transmits the drag of the surface upward
C.The Ekman layer
D.The entrainment zone, across which free tropospheric air is mixed into the convective boundary layer below

Answer: A

The tropical tropopause layer between about 14 and 19 kilometres is a transition region with properties intermediate between troposphere and stratosphere, and it is where air is dehydrated as it enters the stratosphere. Its detailed structure controls the stratospheric water vapour budget. The boundary layer, Ekman layer and entrainment zone all lie within the lowest kilometres of the atmosphere and have nothing to do with stratospheric entry.

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94.

Which wave signature is seen in stratospheric water vapour observations?

A.A signal that oscillates with the same period as the quasi-biennial oscillation of the equatorial winds
B.The tape recorder signal of the annual cycle
C.A steady increase with height reflecting the production of water vapour by methane oxidation up there
D.No signal at all

Answer: B

The annual cycle of tropical cold point temperature imprints alternating moist and dry layers on the ascending air, and these propagate upward over several years like the signal on a tape recorder. Tracking them gives a direct measurement of the ascent rate of the Brewer-Dobson circulation. Methane oxidation does add water vapour with height, which makes that a plausible distractor, but the tape recorder signal is the striking observation.

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95.

Which quantity does the tape recorder signal measure directly?

A.The strength of the polar vortex
B.The frequency at which planetary waves are breaking in the surf zone of the winter stratosphere above
C.The tropical ascent rate in the lower stratosphere
D.The rate at which methane is being oxidised into water vapour within the middle stratosphere above it

Answer: C

By following the upward progress of a given annual maximum or minimum through successive years of observation, the mean vertical velocity of the tropical branch of the Brewer-Dobson circulation can be read off directly. Values around 0.3 millimetres per second are found. It is one of the few direct measurements of a large scale vertical velocity anywhere in the atmosphere.

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96.

Which region of the winter stratosphere is called the surf zone?

A.The tropical region in which air rises slowly across the tropopause into the stratosphere above it
B.The polar vortex interior
C.The layer immediately above the tropopause where the static stability increases sharply with height
D.The mid-latitude region where planetary waves break

Answer: D

The mid-latitude surf zone is where planetary waves break irreversibly, mixing potential vorticity and forming a broad region of weak gradients between the tropics and the vortex edge. The vortex edge itself acts as a transport barrier. The name captures the analogy with ocean waves breaking on a shelving beach, and the sharp gradients at its edges are a striking feature of potential vorticity maps.

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97.

Which property does the polar vortex edge have?

A.It acts as a barrier to horizontal transport
B.It permits free exchange of air between the vortex interior and the surrounding mid-latitude air mass
C.It moves with the mean flow
D.It coincides exactly with the position of the polar night jet at every level within the stratosphere

Answer: A

Strong potential vorticity gradients at the vortex edge inhibit mixing, so air inside remains isolated for months, which is what allows the chemical processing responsible for the ozone hole to proceed undiluted. The barrier is not perfect but is remarkably effective. The jet is associated with the edge but the two are not exactly coincident at every level.

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98.

Which consequence does that isolation have for polar ozone?

A.The vortex air warms steadily through the winter as it is compressed by descent within the circulation
B.Chemically processed air is not replenished from outside
C.Ozone rich air from the tropics is continually mixed into the vortex, offsetting any chemical loss there
D.There is no consequence

Answer: B

Because the vortex is isolated, air depleted of ozone by heterogeneous chemistry on polar stratospheric clouds is not replaced, and the depletion accumulates through the winter and spring. This is why the ozone hole is a southern hemisphere phenomenon, the southern vortex being colder and more isolated than the northern one. Descent does occur but the air remains extremely cold.

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99.

Which hemisphere shows the stronger and more isolated polar vortex?

A.Both equally
B.Neither, since the vortex forms only in the hemisphere experiencing summer at the time of the observation
C.The southern hemisphere
D.The northern hemisphere, where the greater land-sea contrast produces a more vigorous circulation aloft

Answer: C

The southern vortex is colder, stronger and far less disturbed by planetary waves, because the southern hemisphere has weaker stationary wave forcing from topography and land-sea contrast. That is precisely why the ozone hole forms over Antarctica and not over the Arctic. The vortex is a winter feature, forming as the pole enters polar night.

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100.

Which event can disrupt the vortex in mid-winter?

A.The seasonal reversal of the winds in spring as sunlight returns to the polar region after the winter
B.A volcanic eruption
C.The passage of a deep tropospheric cyclone directly beneath the centre of the polar region concerned
D.A sudden stratospheric warming

Answer: D

Breaking planetary waves can decelerate and reverse the vortex within a few days, raising polar stratospheric temperatures by tens of kelvin and sometimes splitting the vortex in two. Such major warmings occur in roughly half of northern winters and very rarely in the south. The spring reversal is the ordinary seasonal transition, and volcanic and tropospheric influences act far more slowly.

Discuss in Forum

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