General Circulation of the Atmosphere Questions and Answers

Answer: A

The tropics absorb more solar radiation than they emit as infrared, while the polar regions emit more than they absorb, and the atmosphere and ocean together transport the difference poleward. That transport requirement is what the general circulation exists to satisfy. Rotation shapes the resulting circulation profoundly but supplies no energy, and the land-sea distribution modifies the pattern regionally without creating the fundamental imbalance that drives the whole system.

Answer: B

The net radiation at the top of the atmosphere changes sign near 38 degrees in each hemisphere, so poleward heat transport must reach its maximum near that latitude. The observed maximum transport of about 5.5 petawatts does occur there. The tropics of Cancer and Capricorn mark the limits of overhead sun rather than the radiation balance, and 60 degrees lies well within the deficit region. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

Satellite measurements of the radiation balance require a combined atmospheric and oceanic transport of roughly \( 5.5 \times 10^{15} \) watts across 38 degrees. The atmosphere carries the larger share outside the tropics and the ocean the larger share within them. The magnitude is worth remembering because it puts every other energy flow in the climate system into proportion. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: D

Travelling cyclones and anticyclones carry warm air poleward and cold air equatorward, accounting for the bulk of the mid-latitude transport. The mean meridional circulation dominates within the tropics through the Hadley cell, and the ocean carries a substantial share at low latitudes. Radiative transfer moves energy vertically far more effectively than horizontally. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: A

The Hadley cell rises near the thermal equator, moves poleward aloft and descends near thirty degrees, carrying heat poleward in its upper branch. It is thermally direct and drives itself. The Ferrel cell is indirect and eddy driven, the polar cell is weak, and the Walker circulation is zonal rather than meridional and transports no net heat polewards. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

Air moving poleward aloft conserves angular momentum and is deflected eastward by the Coriolis force, so by about 30 degrees the flow is almost entirely zonal and can carry heat no further. The cell therefore closes and descends there, creating the subtropical highs and the desert belt. The edge migrates seasonally and has been observed to shift poleward in recent decades. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: C

Subsidence near 30 degrees produces the semi-permanent anticyclones of the subtropical oceans and the great deserts of both hemispheres. The convergence zone and equatorial trough lie beneath the ascending branch and the polar front belongs to the mid-latitude baroclinic zone. The distribution of the world's arid regions is thus a direct consequence of the general circulation. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: D

Air returning equatorward at low levels is deflected westward by the Coriolis force, giving the northeast and southeast trades of the two hemispheres. Their remarkable steadiness made them essential to sailing routes. The westerlies belong to mid-latitudes, the polar easterlies to the polar cell, and the monsoons to the seasonal migration of the whole system over the continents. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: A

With no torque acting, the sum of the planetary and relative contributions to the angular momentum is conserved, so the relative zonal velocity must increase as the distance from the axis shrinks. This is why the subtropical jet exists. Potential vorticity is also conserved but does not give the jet directly, and the relative zonal velocity is precisely what changes. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: B

Starting from rest at the equator, conservation gives a zonal wind of \( \Omega a \sin^{2}\phi / \cos\phi \), which at 30 degrees works out at roughly 130 metres per second. The observed subtropical jet reaches only about a third of this, showing that eddies and friction remove momentum along the way. The disagreement is more instructive than agreement would have been. The shared properties explain why these belong to one family, and the differences explain why more than one exists.