Explain the connections among air pressure, temperature, humidity, and fronts.

Air mass is a large body of air that exhibits uniform temperature and moisture characteristics and helps to determine the weather within an area. Warm air masses tend to form over oceans in warm-temperature regions of the tropics and sub-tropics, while cold air masses tend to form over land in cold-weather regions nearer the poles. The cold air masses that form at the poles move toward the equator, while the warm air masses that form at the equator move toward the poles. These air masses can undergo gradual, but significant, changes as they pass over warmer or colder land surfaces encountering different types of air. These boundary lines are called fronts.

81 is a composite number