What defines an air mass?

An air mass is defined as a large body of air that has relatively uniform temperature and moisture characteristics over a horizontal plane. This uniformity can be quite extensive, often covering hundreds or thousands of square miles. The properties of an air mass are influenced by the surface over which it forms, such as land or water, and therefore can be classified based on temperature (warm or cold) and humidity (moist or dry).

The significance of an air mass lies in its ability to influence weather patterns as it moves. For instance, when a warm, moist air mass moves into a cooler area, it can result in precipitation. The classification helps meteorologists predict weather by understanding how air masses interact with one another and the regions they traverse.

In contrast, the other choices describe different phenomena or characteristics that do not align with the definition of an air mass. A small region of air with varying temperature and humidity does not meet the criteria for uniformity characteristic of an air mass. A mass of air moving in one direction at high speed describes wind rather than the defining qualities of an air mass. Lastly, a layer of air above the earth's surface refers to the atmosphere in general and does not capture the specific criteria of uniformity and distinct characteristics associated with an air