Which term describes a large volume of air with relatively uniform temperature and humidity?

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

Answer: (C)

An air mass is a large volume of air with relatively uniform temperature and humidity. This uniformity comes from forming over a large, relatively uniform surface (like a vast stretch of land or ocean) where the air sits long enough to take on the surface's characteristics. Once formed, the air mass covers hundreds to thousands of kilometers and tends to keep those properties as it moves, until it meets different surface conditions or is altered by mixing.

Weather describes the short-term atmospheric conditions at a location, which can change quickly and vary across a region, even within or between air masses. A high-pressure system is a pattern of sinking air associated with typically clear conditions, but it’s about atmospheric pressure patterns rather than describing a single body of air with uniform properties. Wind is the horizontal movement of air driven by pressure differences, not a name for a large, uniform body of air.

A maritime tropical air mass, for example, forms over warm oceans and brings warm, humid air; a continental polar air mass forms over cold land and brings cold, dry air. These examples show how air masses carry distinct, relatively uniform properties over large areas and influence weather as they move or interact with other air masses.