Divergence and Vertical Motion Questions and Answers

Answer: C

With horizontal temperature gradients unable to persist, the thermodynamic equation reduces to a balance between diabatic heating and adiabatic cooling by ascent, so the vertical motion is set directly by the heating rate. This diagnostic relation is the basis of much tropical modelling. Horizontal advection is negligible precisely because the gradients are weak, and radiative adjustment is far too slow to balance convective heating. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

Gill's solution shows a Kelvin wave response extending eastward and a pair of Rossby gyres to the west and poleward of the heating, which is the standard model of the atmospheric response to tropical convection. The asymmetry arises because Kelvin waves travel east and Rossby waves west. This pattern explains the observed circulation associated with the Madden-Julian Oscillation and with El Nino heating anomalies. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

Equatorial Kelvin waves propagate only eastward, so the Kelvin response appears downstream to the east while the Rossby gyres sit to the west. That asymmetry is one of the most recognisable features of tropical circulation charts. The Rossby response is both westward and slightly poleward, giving the characteristic pair of off-equatorial cyclonic centres seen in the Gill solution.

Answer: B

Upper level velocity potential responds directly to the divergent outflow above deep convection and shows the planetary scale pattern clearly, which is why it is the standard field for monitoring tropical intraseasonal variability. Tropical sea level pressure anomalies are only a hectopascal or two and easily lost in the noise, and 500 hectopascal height contains little tropical signal because the temperature gradients are so weak. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: C

Equatorial Kelvin waves cross an ocean basin in a few days, so the atmospheric circulation adjusts to a change in the heating on that timescale. This is far faster than the ocean responds, which is why the atmosphere is usually treated as being in equilibrium with the sea surface temperature on seasonal timescales. Minutes belong to individual convective cells and years to stratospheric oscillations. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

Because the atmosphere reaches equilibrium with the sea surface temperature within days, its own initial state is forgotten long before the season ends, and predictability comes from the slowly evolving ocean instead. This is why seasonal forecasting requires coupled models and why El Nino prediction is central to it. The ocean evolves substantially over a season and cannot be held fixed. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: A

Deep convection draws air in near the surface and expels it near the tropopause, giving the familiar pattern of low level convergence and upper level divergence with a level of non-divergence in between. The upper outflow is what the velocity potential field displays. The reverse pattern occurs over regions of large-scale subsidence such as the eastern subtropical oceans.

Answer: B

The convergence zone is a band of deep convection near the thermal equator where the trade winds of the two hemispheres meet, and its ascent forms the rising branch of both Hadley cells. The subtropical highs mark the descending branches, the polar front belongs to the mid-latitude circulation, and the trade wind inversion is a feature of the subsiding air on the equatorward flank of the highs. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: C

The zone migrates into the summer hemisphere, reaching well north of the equator over land in July and south in January, with a lag reflecting the thermal inertia of the surface. Its movement over land is much larger than over ocean because the sea responds slowly. The forty to fifty day eastward propagation describes the Madden-Julian Oscillation, which is a separate intraseasonal phenomenon. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: D

Persistent subsidence near thirty degrees latitude warms and dries the air, suppressing cloud and producing the great deserts of both hemispheres. The distribution of the world's arid zones is thus a direct consequence of the general circulation. Equatorial rain forests lie beneath the ascending branch, and the storm track belongs to the baroclinic mid-latitudes rather than to the Hadley circulation. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.