What is an air mass defined as?

An air mass is defined as a large body of air that has relatively uniform temperature and moisture content in its horizontal dimensions. This uniformity occurs as the air mass travels across a large area, allowing it to develop characteristics specific to its source region, which could be over the ocean or continental land. For instance, an air mass originating over a warm ocean will be warm and moist, while one from a polar region will be cold and dry. The characteristics of an air mass influence local weather patterns significantly, as they interact with other air masses and geographical features. Understanding air masses is crucial for predicting weather changes and understanding atmospheric behavior.

The other options do not accurately describe the definition of an air mass. Small pockets of air pertain more to localized weather effects rather than the expansive nature of air masses. Similarly, while some air masses can be humid, not all are; the defining feature is uniformity in temperature and moisture, not a guarantee of humidity. Finally, while cool air masses can bring storms, this is not a defining characteristic of air masses in general, as their impact on weather varies greatly depending on their characteristics and interactions.