What is an air mass?

An air mass is defined as a large body of air that has uniform characteristics in terms of temperature and moisture content throughout its extent. This uniformity is crucial as these properties can affect weather patterns significantly. Air masses typically form over large regions of the Earth’s surface where the air remains relatively undisturbed. They can absorb characteristics of the surface beneath them, which can include influences from oceans, landmasses, and vegetation.

For instance, if an air mass forms over a tropical ocean, it will likely be warm and humid, whereas an air mass over a polar region will be cold and dry. These characteristics are critical when studying meteorology because the movement and interaction of different air masses often lead to various weather phenomena, including storms, calm weather, and temperature changes.

The other options relate to aspects of atmospheric science, but they do not completely define what an air mass is. A mass of humid air only describes a specific type of air mass without acknowledging the temperature component. A collection of clouds does not account for the broader concept of air properties, and a system of weather systems implies a more complex interaction of various phenomena rather than focusing solely on the characteristics of a single air mass. Therefore, the first option encapsulates the definition of an air mass