Precipitation
The process of continuous condensation in free air helps the condensed particles to grow in size. When the resistance of the air fails to hold them against the force of gravity, they fall on to the earth’s surface. This release of moisture is known as precipitation.
Forms of Precipitation
- Precipitation can occur in solid or liquid forms:
Rainfall:
- Precipitation in the form of water is called rainfall.
Snowfall:
- In higher altitudes or latitudes, the condensation of water vapor may take place below the freezing point and the precipitation takes place in the form of fi ne flakes of snow.
Sleet:
- Sleet is frozen raindrops and refrozen melted snow-water. If a warmer layer of air overlies a colder layer, the raindrops solidify on encountering the lower colder layer and fall as small pellets of ice.
- For sleet formation, the surface temperature should be less. Hence it is a cold-weather phenomenon.
Hailstones:
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If the moist air ascends rapidly to the cooler layers of the atmosphere the water droplets freeze into small rounded solid pieces of ice and reach the surface as hailstones. Hailstones have several concentric layers of ice one over the other. Hail requires strong convective currents (upward motion of air) to carry the moist air to greater heights. Hence, cool surface temperatures greatly inhibit hail formation.