Discuss the mode of occurence of orographic and convectional rainfall
Answers
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. So after the condensation of water vapour, the release of moisture is known as precipitation. This may take place in liquid or solid form.
Precipitation in the form of drops of water is called rainfall, when the drop size is more than 5 mm.
It is called virage when raindrops evaporate before reaching the earth while passing through dry air.
Drizzle is light rainfall with drop size being less than 0.5 mm, and when evaporation occurs before reaching the ground, it is referred to as
When the temperature is lower than the 0° C, precipitation takes place in the form of fine flakes of snow and is called snowfall. Moisture is released in the form of hexagonal crystals. These crystals form flakes of snow. Besides rain and snow, other forms of precipitation are sleet and hail (more about hail while studying thunderstorms), though the latter are limited in occurrence and are sporadic in both time and space.
Sleet is frozen raindrops and refrozen melted snow-water. When a layer of air with the temperature above freezing point overlies a subfreezing layer near the ground, precipitation takes place in the form of sleet.
Raindrops, which leave the warmer air, encounter the colder air below. As a result, they solidify and reach the ground as small pellets of ice not bigger than the raindrops from which they are formed. Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones. These are formed by the rainwater passing through the colder layers. Hailstones have several concentric layers of ice one over the other.
Rainfall: drop size more than 0.5 mm.
Virage: raindrops evaporate before reaching the earth.
Drizzle: light rainfall; drop size less than 0.5 mm.
Mist: evaporation occurs before reaching the ground leading to foggy weather.
Snowfall: fine flakes of snow fall when the temperature is less than 0°C.
Sleet: frozen raindrops and refrozen melted snow; mixture of snow and rain or merely partially melted snow.
Hail: precipitation in the form of hard rounded pellets is known as hail; 5 mm and 50 mm.