Rain
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Rain is droplets of water falling down from clouds in the sky. Droplets of water with a diameter larger than 0.5 mm are rain. Those with a diameter of about 0.2-0.5 mm are drizzle.
Rain is part of the water cycle. Rain is a form of precipitation.
[edit] Types of rain
[edit] Convection rain
Convection rain is commonly found in hot wet places of the world. Sometimes it is also found in tropical deserts and inland areas during summer, when temperatures are high. During daytime, the sun makes the ground very hot. Lower layer of air near the ground surface is heated by conduction. It then expands and rises, forming strong vertical air currents. When temperature of the rising air falls to dew point, water vapour condenses into thick cloud and forms convection rain.
[edit] Relief rain
Relief rain usually occurs along coastal areas where a line of hills runs parallel to the coast, and at right angle to the direction of prevailing onshore winds. When wet onshore winds from the sea meet a mountain barrier, it is forced to rise along the slope and cools. When the air temperature falls to its dew point, water vapour condenses to form clouds. When the clouds can no longer hold the water droplets, relief rain begins to fall on the windward slope of the mountain. On the leeward slope, air sinks, it is warmed and further dried by compression. Therefore, the leeward slope is known as the rain shadow.
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