Precipitation is water droplets or ice crystals (in the case of hail), which, after being formed by condensation in clouds, become too heavy to remain suspended in the air. These water particles can fall directly, or evaporate into the air before reaching the ground.
More generally, precipitation can be characterized as all meteoric water falling on the surface of the earth, in liquid form (drizzle, rain or showers), or in solid form (snow, sleet, hail).
The formation of precipitation includes different stages:
- Condensation and supersaturation of the air - Development of hydrometeors - Falling of hydrometeors in different forms
Precipitation occurs when the local air becomes saturated with water vapour and can no longer maintain this vapour level in gaseous form. This occurs when the moist air, which is less dense, cools; usually when an air mass increases in the atmosphere.
Hydrometeors, like all airborne particles, are subject to both their own weight and friction with the surrounding air. In the absence of air movement, all hydrometeors fall, more or less quickly, depending on their size, shape and density.
There are mainly two types of precipitation:
Stratiform precipitation: they are of low intensity but with a long duration, related to the large surface covered by the cloud. They generally occur during the passage of depressions associated with stratus clouds.
Convective precipitations (or showers): they are of short duration, but of a strong intensity. They are produced by the convective instability of the air associated with the formation of cumulus or cumulonimbus clouds (so-called thunderstorm clouds).
In addition, precipitation can fall in three forms depending on the air temperature:
Indeed, depending on the atmospheric conditions, we find :
Rain: it is formed by droplets or ice crystals, not being subjected to temperatures below the freezing point. Their size is variable, we speak of drizzle, when they are less than 1.5 mm, otherwise we speak of rain.
Freezing rain: this type of precipitation appears when the pressure and temperature conditions on the ground are below freezing.
Sleet: unlike hail, it is formed of rain completely frozen after passing through a thick layer of air under 0 ° C. The size of the grains does not generally exceed 5 mm.
Hail: composed of ice balls, which can fall at a speed of 160 km/h, whose size is variable, sometimes impressive. We talk about it in this article.
Snow: it can be defined as frozen water in the upper regions of the atmosphere, falling in white and light flakes.
Did you know that India is the rainiest country in the world? More precisely, the annual rainfall record is held in Mawsynram, in the north of Bangladesh. Each year, 12 meters of water fall in this city!
The record for snowfall is held in the United States, at Mount Rainier, where 31.10 m of snow fell during the winter of 1971/1972.
The record for the heaviest hailstone in France is 978 grams, a hailstone that fell on August 11, 1958 in Alsace.