Refer to figures.
At latitudes around 30°N and 30°S, we find the subtropical high-pressure belts. These form due to sinking air in the global atmospheric circulation system, specifically from the Hadley cell, one of the three major circulation cells in each hemisphere:

1. Hadley Cell (tropical)
2. Ferrel Cell (mid-latitudes)
3. Polar Cell (high latitudes)

Warm air rises near the Equator due to intense solar heating, particularly in the Intertropical Convergence Zone (ITCZ). As this air ascends, it reaches the upper levels of the troposphere where it begins to spread out toward the poles. During this movement, the air gradually cools. By the time it reaches latitudes around 30°, it has cooled enough to become denser, causing it to sink back down toward the surface. This descent of air, known as subsidence, creates convergence in the upper atmosphere and results in increased surface pressure. The outcome is the formation of the subtropical high-pressure belt, a region characterized by dry, stable, and often desert-like conditions.

• “Subtropical low-pressure belt” --> INCORRECT. At around 30°N and 30°S, the air is actually sinking, not rising. Sinking air leads to high pressure at the surface, not low pressure. Low-pressure zones form in regions where air is rising, such as near the Equator (in the Intertropical Convergence Zone) or around 60° latitude, where warm and cold air masses meet at the polar front. Therefore, there is no persistent "subtropical low"; rather, these latitudes are characterized by stable, descending air that forms the subtropical high-pressure zones.

"Polar-air outbreaks" --> INCORRECT. These are specific weather events in which cold air from polar regions pushes down into the mid-latitudes. They are not permanent or typical features at 30° latitude. Instead, they are transient.

"Intertropical Convergence Zone (ITCZ)" --> INCORRECT. ITCZ is not found at 30° latitude either. It lies near the Equator, typically between 0° and 10° latitude. The ITCZ is a region of persistent low pressure formed by the convergence of the northeast and southeast trade winds.