A system of air formed by cooling air that becomes denser and heavier and then sinks to form an area of high pressure.

• A. Low-pressure system
• B. Air mass
• C. Wind
• D. High-pressure system

Answer: (D)

Cooling air becomes denser and heavier, so it sinks toward the surface. As air parcels descend, they compress and increase the weight of air at the ground, raising the surface pressure and forming a high-pressure region. Descending air also stabilizes the atmosphere and tends to suppress cloud formation, leading to clear, calmer weather. This combination of sinking air and rising surface pressure is the hallmark of a high-pressure system. In contrast, low-pressure systems form when air rises, air masses are just a body of air with uniform properties, and wind describes horizontal movement rather than the vertical sinking process described.