Atmospheric Waves Questions and Answers

Q: Which observation identifies upward propagating gravity wave energy?

Because the group velocity is perpendicular to the phase velocity and directed on the opposite side of the horizontal, a wave carrying energy upward shows phase lines descending with time. Radiosonde and radar time-height sections are read this way routinely. Amplitude does grow with height as the density falls, but that is a separate consequence of energy conservation rather than an indicator of direction. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Q: Which consequence follows from that amplitude growth?

Once the wave amplitude is large enough to overturn the isentropes, the wave breaks, generating turbulence and depositing its momentum flux into the mean flow. This drag is the principal driver of the mesospheric circulation and must be parameterised in climate models. Reflection occurs at certain levels for other reasons, and smooth dissipation is far too slow to matter at these altitudes. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Q: Which circulation is driven largely by breaking gravity waves?

Gravity wave drag in the mesosphere forces a meridional circulation from the summer to the winter pole, which drives the summer mesopause to the coldest temperatures found anywhere in the atmosphere. Without the wave drag the mesosphere would be far closer to radiative equilibrium. The Hadley, Walker and Ferrel cells are tropospheric features driven by quite different mechanisms. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Q: Which feature of the summer mesopause demonstrates this driving?

Despite continuous sunlight, the summer mesopause reaches about 130 kelvin, far colder than the winter mesopause, because the wave-driven circulation forces strong ascent and adiabatic cooling there. It is the coldest place in the Earth's atmosphere and is where noctilucent clouds form. This departure from radiative expectation is the clearest evidence of the wave driving. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Q: Which cloud type forms at the summer mesopause?

Noctilucent or polar mesospheric clouds form near 83 kilometres in the extremely cold summer mesopause and are visible from high latitudes after sunset. Polar stratospheric and nacreous clouds form much lower, around 20 kilometres in the winter stratosphere, and cirrus is a tropospheric cloud. Their existence is direct evidence of the extreme cold that wave driving produces. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Q: Which condition allows lee waves to form downstream of a ridge?

Trapped lee waves require a stable layer with the wind increasing with height, which creates a duct that reflects wave energy downward and allows a train of waves to persist far downstream. Neutral stratification supports no waves at all, light winds cannot force them, and strong directional shear disrupts the coherence of the train. Glider pilots exploit exactly these conditions. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Q: Which cloud marks the crest of a trapped lee wave?

Lenticular cloud forms in the ascending part of each wave crest and dissipates in the descending part, so it appears stationary while the air moves through it. The clouds mark the wave train clearly from the ground and from satellite. Deep convection requires conditional instability rather than wave lifting, and the other cloud types have no particular association with lee waves. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Q: Which hazard do mountain waves present to aircraft?

Rotor turbulence beneath the wave crests and vertical currents of several metres per second can exceed the climb or descent capability of an aircraft, and several accidents have been attributed to them. Lenticular cloud is generally smooth and not a major icing hazard. Navigation and air density are not affected in the way suggested by the other options.

11.

Which observation identifies upward propagating gravity wave energy?

A.Downward phase propagation in a time-height section
B.Upward phase propagation, since energy and phase must always travel in the same direction as one another
C.Stationary phase lines
D.A steady increase in the amplitude of the oscillation with time at a fixed height above the ground

Answer: A

Because the group velocity is perpendicular to the phase velocity and directed on the opposite side of the horizontal, a wave carrying energy upward shows phase lines descending with time. Radiosonde and radar time-height sections are read this way routinely. Amplitude does grow with height as the density falls, but that is a separate consequence of energy conservation rather than an indicator of direction. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Discuss in Forum

12.

Which effect causes gravity wave amplitude to grow with height?

A.The reduction of the horizontal wavelength as the wave propagates upward through the atmosphere above
B.The decrease of density with height
C.The increase of the buoyancy frequency with height as the atmosphere becomes more stably stratified
D.The decrease of temperature

Answer: B

Conservation of wave energy flux requires the amplitude to grow as the inverse square root of density, so a wave with a one metre per second velocity perturbation in the troposphere reaches tens of metres per second in the mesosphere. That growth eventually leads to breaking. The buoyancy frequency does increase into the stratosphere but the density effect is far larger and is the conventional explanation. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Discuss in Forum

13.

Which consequence follows from that amplitude growth?

A.The wave dissipates smoothly
B.The wave slows down until it becomes stationary relative to the ground at the level of maximum amplitude
C.The wave eventually breaks and deposits its momentum
D.The wave is reflected back downward once its amplitude exceeds a critical threshold at some level

Answer: C

Once the wave amplitude is large enough to overturn the isentropes, the wave breaks, generating turbulence and depositing its momentum flux into the mean flow. This drag is the principal driver of the mesospheric circulation and must be parameterised in climate models. Reflection occurs at certain levels for other reasons, and smooth dissipation is far too slow to matter at these altitudes. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Discuss in Forum

14.

Which circulation is driven largely by breaking gravity waves?

A.The Hadley circulation, whose ascending branch lies beneath the intertropical convergence zone below
B.The Walker circulation
C.The Ferrel cell, which is the indirect meridional circulation found in the middle latitudes of each hemisphere
D.The mesospheric summer to winter pole circulation

Answer: D

Gravity wave drag in the mesosphere forces a meridional circulation from the summer to the winter pole, which drives the summer mesopause to the coldest temperatures found anywhere in the atmosphere. Without the wave drag the mesosphere would be far closer to radiative equilibrium. The Hadley, Walker and Ferrel cells are tropospheric features driven by quite different mechanisms. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Discuss in Forum

15.

Which feature of the summer mesopause demonstrates this driving?

A.It is colder than the winter mesopause
B.It is warmer than the winter mesopause, as would be expected from the distribution of solar heating there
C.It has the same temperature
D.It shows no seasonal variation at all because the radiative timescale at that altitude is extremely long

Answer: A

Despite continuous sunlight, the summer mesopause reaches about 130 kelvin, far colder than the winter mesopause, because the wave-driven circulation forces strong ascent and adiabatic cooling there. It is the coldest place in the Earth's atmosphere and is where noctilucent clouds form. This departure from radiative expectation is the clearest evidence of the wave driving. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Discuss in Forum

16.

Which cloud type forms at the summer mesopause?

A.Nacreous cloud, whose iridescent appearance results from diffraction by uniformly sized ice particles
B.Noctilucent cloud
C.Polar stratospheric cloud, which forms in the winter stratosphere at temperatures below about 195 kelvin
D.Cirrus

Answer: B

Noctilucent or polar mesospheric clouds form near 83 kilometres in the extremely cold summer mesopause and are visible from high latitudes after sunset. Polar stratospheric and nacreous clouds form much lower, around 20 kilometres in the winter stratosphere, and cirrus is a tropospheric cloud. Their existence is direct evidence of the extreme cold that wave driving produces. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Discuss in Forum

17.

Which source generates gravity waves in the troposphere?

A.Radiative cooling
B.The horizontal advection of temperature by the geostrophic wind across a region of strong thermal gradient
C.Flow over mountains
D.The condensation of water vapour into cloud droplets within a slowly ascending layer of stratiform cloud

Answer: C

Stably stratified flow forced over a mountain range generates waves whose phase lines are stationary relative to the ground, and these mountain waves are a principal source of momentum flux into the stratosphere. Convection and jet stream imbalance are the other two major sources. Radiative cooling and thermal advection act too slowly and too smoothly to excite waves of any significant amplitude. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Discuss in Forum

18.

Which condition allows lee waves to form downstream of a ridge?

A.Neutral stratification through a deep layer so that a displaced parcel experiences no restoring force
B.Very light winds
C.A wind direction that changes rapidly with height so that the flow crosses the ridge at varying angles
D.Stable stratification with wind increasing with height

Answer: D

Trapped lee waves require a stable layer with the wind increasing with height, which creates a duct that reflects wave energy downward and allows a train of waves to persist far downstream. Neutral stratification supports no waves at all, light winds cannot force them, and strong directional shear disrupts the coherence of the train. Glider pilots exploit exactly these conditions. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Discuss in Forum

19.

Which cloud marks the crest of a trapped lee wave?

A.Altocumulus lenticularis
B.Cumulonimbus, which develops where the ascending branch of the wave lifts air beyond its level of free convection
C.Stratus
D.Cirrus uncinus, whose trailing ice crystals indicate strong vertical shear at the level where they form

Answer: A

Lenticular cloud forms in the ascending part of each wave crest and dissipates in the descending part, so it appears stationary while the air moves through it. The clouds mark the wave train clearly from the ground and from satellite. Deep convection requires conditional instability rather than wave lifting, and the other cloud types have no particular association with lee waves. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Discuss in Forum

20.

Which hazard do mountain waves present to aircraft?

A.A sudden increase in air density in the descending part of the wave that overloads the wing structure
B.Severe turbulence and strong vertical currents
C.Rapid airframe icing caused by the very high liquid water content of the lenticular cloud at the crest
D.Loss of navigation signal

Answer: B

Rotor turbulence beneath the wave crests and vertical currents of several metres per second can exceed the climb or descent capability of an aircraft, and several accidents have been attributed to them. Lenticular cloud is generally smooth and not a major icing hazard. Navigation and air density are not affected in the way suggested by the other options.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Atmospheric Waves Questions and Answers || Atmospheric Waves MCQ Questions and Answers || Atmospheric Waves GK Questions and Answers || Atmospheric Waves GK MCQ Questions || Atmospheric Waves Multiple Choice Questions and Answers || Atmospheric Waves GK || GK on Atmospheric Waves || Atmospheric Dynamics Questions and Answers || Atmospheric Dynamics MCQ Questions and Answers || Atmospheric Dynamics GK Questions and Answers || GK on Atmospheric Dynamics

Atmospheric Waves Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications