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Particle
Rain, raindrop, rainfall
Rain, raindrop, rainfall
Small droplets of water that surround a fine particle of dust, crystal of salt, or some other solid object. Raindrops fall through the air when they are heavy enough
to fall against the rising air that
is inside a cloud. When the air is rising slowly, as in the clouds at the warm front of a depression, the raindrops only need to be of modest size (1mm diameter or less) to fall out to the ground. Such
fine rain is called drizzle. As the rising air gets more powerful, the droplets have to be larger before they can fall. In a thundercloud (see: Thunderstorm) the rising air currents are strong, so that drops
 Rainfall – Rain is falling from the centre of this isolated cumulonimbus cloud. The streaks of rain, called virga, are clearly seen, although the rain never reaches the ground because the air below is so dry that the droplets evaporate as they fall.
have to be very large to fall out
– often several millimetres across. That is why raindrops from large cumulus thunderclouds are bigger than those from layer clouds.
Many raindrops begin life
as ice crystals. That is because clouds are very cold and ice forms in their highest levels. As ice crystals lock together, they form large shapes called snowflakes. As the snowflakes fall, they begin
 Rain – Raindrops begin as small droplets of water that condense on particles of dust or, in the case of cold clouds, on ice crystals.
to melt and eventually turn into raindrops. This is probably the most common way for raindrops
to form in layer clouds. In cumulus clouds raindrops are swept together in the powerful air currents until they become big enough to fall from the sky.
As raindrops fall from the sky, they change shape. They begin
as spheres; but as they fall, air resistance makes them flatten and then become ‘doughnut shaped’. No raindrops are ever teardrop shaped, as mistakenly shown in some diagrams.
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