General Circulation of the Atmosphere Questions and Answers

Answer: A

The surface influence of a stratospheric event persists for several weeks, filling exactly the gap between the limit of deterministic weather forecasting and the beginning of seasonal predictability. That subseasonal range had long been described as a desert of predictability. The stratosphere is one of the few identified sources of skill within it, alongside the Madden-Julian Oscillation.

Answer: B

The eastward propagating envelope of tropical convection forces Rossby wave trains into mid-latitudes with a lag of one to two weeks, which is exploited for subseasonal prediction. Tracking its phase and amplitude is now routine at forecasting centres. ENSO and multidecadal variability operate on much longer timescales, and the quasi-biennial oscillation modulates rather than forces the subseasonal signal.

Answer: C

The Wheeler and Hendon diagram plots the two leading principal components of combined circulation and convection fields, so the state appears as a point moving anticlockwise through eight numbered phases. Amplitude and phase together summarise the oscillation compactly. Hovmoller diagrams are also used to display the propagation but the phase space plot is the standard operational index.

Answer: A

The order is Hadley \(\gt\) Ferrel \(\gt\) Polar.

Each cell is capped by the tropopause over its latitudes, and the tropopause is highest over the tropics. The Hadley cell, rising in the deep convection near the equator, reaches about 15 to 18 km. The Ferrel cell in mid-latitudes extends to roughly 10 to 12 km, and the polar cell, under the low, cold polar tropopause, only to about 8 km.

The other orders put the shallow polar cell above one of the others, which is the opposite of how the tropopause slopes from equator to pole.

Answer: B

The main carrier of poleward energy is baroclinic waves.

In the midlatitudes the strong north-south temperature gradient makes the westerlies baroclinically unstable. The resulting waves, the travelling cyclones and anticyclones of the weather map, move warm air poleward and cold air equatorward and carry most of the atmosphere's poleward heat transport there.

Atmospheric tides are small, regular oscillations, gravity waves mainly transport momentum vertically, and boundary-layer turbulence moves heat up from the surface rather than towards the poles.