water-saturation percentage {aridity}|.
Air water decreases with humidity and increases with temperature and wind speed {evaporation}|. Latitudes from 10 to 40 degrees have more evaporation than precipitation, and lose heat. Other latitudes have more precipitation than evaporation, and gain heat. Oceans have more evaporation than precipitation. Land has more precipitation than evaporation.
Air can hold variable water amounts {humidity}|. Water in air is 0% to 4%.
measurement
Humidity can be water mass in air mass {specific humidity}. It can be water mass in air volume {absolute humidity}. It can be water vapor mass compared to maximum amount possible at that temperature and pressure, expressed in percent {relative humidity}.
levels
Relative humidity is most comfortable at 50%. High humidity makes cold air feel colder and warm air feel warmer. High temperatures feel cooler if humidity is lower. Higher humidity makes temperature feel higher or lower, because water does not evaporate from skin as easily.
altitude
Humidity is highest at surface and decreases greatly with altitude.
latitude
Humidity is highest at equator and decreases toward poles.
time of day
Humidity increases at night as air cools. Humid air can cool to dew point.
air pressure
More water in air makes lower air pressure, because water molecules weigh less than average air molecule. Wet days have low air pressure. Dry days have high air pressure.
Human-hair-length change {hygrometer}| can measure humidity.
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Date Modified: 2022.0225