In meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric water vapour that is deposited on the earth's surface.[1] It occurs when the atmosphere, a large gaseous solution, becomes saturated with water vapour and the water condenses and falls out of solution (i.e., precipitates).[2] Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air.

Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, drizzle, snow, ice pellets, and hail. Virga is precipitation that begins falling to the earth but evaporates before reaching the surface. Precipitation is a major component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the oceans.[3] Given the Earth's surface area, that means the globally-averaged annual precipitation is about 1 m (39 in), and the average annual precipitation over oceans is about 1.1 m (43 in).

The phenomenon may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most likely takes the form of frost, rather than rain or snow.[4]

Sources and CitationsEdit

  1. AMS Glossary entry for Precipitation American Meteorological Society
  2. Precipitation: hail, rain, freezing rain, sleet and snow - University of Illinois
  3. Dr. Chowdhury's Guide to Planet Earth. The Water Cycle. Retrieved on 2006-10-24.