Term | Definition |
latent heat | the heat energy that is absorbed or released by a substance during a phase change |
sublimation | the process in which a solid changes directly into a gas (the term is sometimes also used for the reverse process) |
dew point | at constant pressure and water vapor content, the temperature at which the rate of condensation equals the rate of evaporation |
absolute humidity | the mass of water vapor per unit volume of air that contains the water vapor; usually expressed as grams of water vapor per cubic meter of air |
relative humidity | the ratio of the amount of water vapor in the air to the amount of water vapor needed to reach saturation at a given temperature |
cloud | collection of small water droplets or ice crystals suspended in the air, which forms when the air is cooled and condensation occurs |
condensation nucleus | a solid particle in the atmosphere that provides the surface on which water vapor condenses |
adiabatic cooling | the process by which the temperature of an air mass decreases as the air mass rises and expands |
advective cooling | the process by which the temperature of an air mass decreases as the air mass moves over a cold surface |
stratus cloud | a gray cloud that has a flat, uniform base and that commonly forms at very low altitudes |
cumulus cloud | a low-level, billowy cloud that commonly has a top that resembles cotton balls and a dark bottom |
cirrus cloud | a feathery cloud that is composed of ice crystals and that has the highest altitude of any cloud in the sky |
fog | water vapor that has condensed very near the surface of Earth because air close to the ground has cooled |
precipitation | any form of water that falls to Earth's surface from the clouds; includes rain, snow, sleet, and hail |
coalescence | the formation of a larger droplet by the combination of smaller droplets |
supercooling | a condition in which a substance is cooled below its freezing point, condensation point, or sublimation point without going through a change of state |
cloud seeding | the process of introducing freezing nuclei or condensation nuclei into a cloud in order to cause rain to fall |