Atmospheric Waves Questions and Answers

Answer: A

The flow accelerates down the lee slope and then jumps abruptly back to a slower deeper state, exactly as water does downstream of a weir, and the analogy has proved quantitatively useful. The turbulent jump region is where the damaging gusts and the rotor turbulence occur. Vortex rings describe microbursts and Kelvin-Helmholtz billows describe shear instability at an interface. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: B

Where the vertical shear is strong enough to overcome the stratification, with a Richardson number below one quarter, the interface rolls up into a train of billows that are sometimes made visible by a thin cloud layer. The same instability generates clear air turbulence near the jet stream. Rayleigh-Benard convection, baroclinic instability and symmetric instability all operate on quite different scales and mechanisms. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: C

Miles and Howard showed that a Richardson number below one quarter somewhere in the flow is a necessary condition for instability of a stratified shear layer. Above that value the stratification suppresses the growth. The criterion is necessary rather than sufficient, so a flow may satisfy it and still remain stable, which is a distinction worth keeping in mind.

Answer: D

Strong shear near the tropopause can reduce the Richardson number below the critical value, producing Kelvin-Helmholtz billows in cloud-free air that give sudden severe turbulence with no visual warning. It is a significant cause of in-flight injury. Icing requires cloud, ash requires an eruption, and wake vortices are generated by aircraft rather than by the atmosphere. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: A

Significant weather charts for aviation mark areas of expected clear air turbulence together with their vertical extent and severity, based on shear and stability diagnostics from model output. Tephigrams and surface charts serve other purposes, and water vapour imagery shows upper level structure that may be suggestive but is not a turbulence forecast in itself.

Answer: B

The divergence of the Eliassen-Palm vector gives the eddy forcing of the zonal mean flow, combining the effects of the eddy heat and momentum fluxes into a single quantity. Convergence of the flux decelerates the mean flow. This is the standard framework for wave-mean flow interaction studies in both the troposphere and the middle atmosphere.

Answer: C

The transformed Eulerian mean circulation approximates the mean Lagrangian motion of air parcels by combining the Eulerian mean with the eddy induced Stokes drift. In the conventional Eulerian mean the eddy fluxes and the mean advection largely cancel, obscuring the net transport. The transformed framework makes the Brewer-Dobson circulation visible as a single meridional cell. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: D

The Brewer Dobson circulation rises in the tropics, moves poleward and descends at high latitudes, transporting ozone from its tropical source region towards the poles. It is driven by wave breaking rather than by heating and appears clearly only in the transformed framework. The Hadley and Walker circulations are tropospheric, and the polar vortex is a zonal flow.

Answer: A

The extratropical wave drag acts as a pump, drawing air upward in the tropics and poleward aloft, which is why the circulation is often described as wave driven rather than thermally driven. Radiative heating alone would not produce the observed transport. The circulation explains why stratospheric air is older at high latitudes and why ozone concentrations peak far from the tropical source region. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: B

Ozone is produced photochemically in the tropical upper stratosphere yet its column abundance is greatest at middle and high latitudes, which can only be explained by poleward transport. Dobson noticed this apparent paradox and it led directly to the proposal of the circulation. Age of air measurements using long lived tracers have since confirmed the picture quantitatively. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.