What is humidity defined as?

Humidity is defined as the amount of water vapor present in the air. This measurement is crucial in various fields, particularly in meteorology and aviation, because it directly affects weather patterns, aircraft performance, and passenger comfort. High humidity can lead to a sensation of increased temperature, affect the lift of aircraft, and influence decisions made during flight operations. Understanding humidity helps pilots and meteorologists predict conditions such as fog, thunderstorms, and other weather phenomena.

The other options, while related to atmospheric conditions, do not accurately describe humidity. The weight of dry air pertains to its density but does not account for moisture levels. The pressure exerted by air relates to atmospheric pressure, which is a separate concept from humidity. Temperature of the atmosphere is a measure of warmth but does not provide any information about moisture content. Thus, defining humidity as the amount of water vapor in the air is essential for grasping its importance in aviation studies.