Precipitation is the mechanism for transporting water from the atmosphere to the surface of the earth. In other words, precipitation is the product of the condensation of atmospheric water vapour that falls under gravity. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapour, so that the water condenses and "precipitates".
Forms of Precipitation
- There are several forms of precipitation, the most common of them is rain. Other forms of precipitation include; drizzle, sleet, snow, graupel hail, and freezing rain.
- Fog and mist cannot be categorized as precipitation but suspensions because the water vapour does not condense in enough quantity to precipitate.
Process of Precipitation
- There are two major processes, which while acting together lead to the formation of saturated air, that is, 1) cooling the air or 2) adding water vapour to the air.
- Generally, precipitation falls to the surface and forms as smaller droplets. It combines and collides with other rain drops or ice crystals within a cloud. Rain drops range in size from oblate, pancake-like shapes for larger drops, to small spheres for smaller drops.
- Raindrops can be up to 6 mm in diameter, but anything less than 0.5 mm in diameter is classed as drizzle. Drizzle consists of very small droplets of water falling from low level stratus clouds.
- Freezing rain is rain droplets which fall in super-cooled liquid form, but freeze on impact with the ground or another object to form clear ice - also known Hail is solid precipitation in the form of balls or pieces of ice known as hailstones.
Formation of Hail
- Hail only forms in cumulonimbus clouds - more commonly known as thunder clouds. They get larger and larger by becoming coated with more and more ice. When they get really big, the cloud cannot hold them up anymore and they fall to earth, and by this time they are big balls of ice, and so don't have time to melt before they arrive at the ground.
- Snow is tiny ice crystals stuck together to become snowflakes. If enough ice crystals stick together, they'll become heavy enough to fall to the ground.
Sleet is "rain and snow mixed". Sleet or pellets, is snow which starts melting before it reaches the ground.