Which global pressure belt lies around 30° North and South latitudes and is…
2026
Which global pressure belt lies around 30° North and South latitudes and is associated with dry climates?
Answer: D. Sub-tropical high — Concept — A pressure belt is a zone in which the vertical motion of air fixes the surface pressure: where air rises the surface pressure falls, and where air…
- A.
Equatorial low
- B.
Sub-polar low
- C.
Polar high
- D.
Sub-tropical high
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Show answer & explanation
Correct answer: D
Concept — A pressure belt is a zone in which the vertical motion of air fixes the surface pressure: where air rises the surface pressure falls, and where air sinks the surface pressure builds up. Ascending air expands, cools and condenses its moisture, so a low-pressure belt is a wet belt; descending air is compressed, warms adiabatically and its relative humidity drops, so a high-pressure belt is a dry belt. Two of the belts are thermal, produced directly by heating or cooling of the surface, and two are dynamic, produced by convergence or divergence in the upper-air circulation.
Application — In the Hadley circulation air rises over the equator, travels poleward at high altitude, cools and sheds its moisture on the way, and is turned almost due east by the Coriolis force near 30°. Unable to continue poleward aloft, this air piles up and subsides between about 25° and 35° in both hemispheres. The subsidence is dynamic in origin: the sinking air is compressed, warms and dries, and cloud formation is suppressed. That descending limb is the sub-tropical high pressure belt, the calm horse latitudes along which the world's great hot deserts — the Sahara, Arabian, Thar, Kalahari, Atacama and Australian deserts — are strung.
Cross-check — Set the four belts side by side by latitude and by the direction of vertical air motion:
Pressure belt | Approximate latitude | Vertical air motion | Weather character |
|---|---|---|---|
Equatorial low | 0°–5° N and S | Ascending (thermal) | ITCZ and doldrums, heavy convectional rain |
Sub-tropical high | About 30° N and S | Descending (dynamic) | Clear skies, hot deserts, calm horse latitudes |
Sub-polar low | About 60° N and S | Ascending (dynamic) | Polar front, travelling cyclones, frontal rain and snow |
Polar high | About 90° N and S | Descending (thermal) | Bitterly cold air, very little precipitation |
Conclusion — The belt that girdles roughly 30° North and South and owes its dryness to subsiding, warming air is the sub-tropical high.