A nimbus cloud is usually called a rain cloud. There are two types of nimbus clouds that may appear before dumping precipitation in many forms: nimbostratus and cumulonimbus. Each is described below.
Nimbostratus clouds in West Virginia
A nimbostratus rain cloud tends to bring constant precipitation and low visibility. The rainfall is typically modetrate to heavy in nature. This cloud type normally forms above 1,981 m from altostratus cloud but can thicken into the lower levels during precipitation. Nimbostratus will occur along warm fronts where the slowly rising warm air mass creates nimbostratus and stratus clouds. These clouds are usually preceded by cirrostratus or altostratus clouds. Frequently, an altostratus cloud thickens and descends into lower altitudes, and will become a nimbostratus.
Cumulonimbus Cloud over Africa
A cumulonimbus rain cloud is tall, dense, and related to thunderstorms and other, more intense, weather. These clouds are a result of instability in the atmosphere. They can form alone, in clusters, or, when along a cold front, in a squall line. There is usually quite a bit of lightning through the heart of the cloud. Cumulonimbus clouds form from cumulus congestus clouds and can develop into a supercell(a thunderstorm that can give rise to tornadoes).
Whatever type it is, a rain cloud is made up of condensed water or ice. These clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules “clump together” faster than they are torn apart by their thermal energy. Some of that water vapor condenses to form cloud droplets or ice crystals. Despite their potentially ominous meaning, clouds are some of the most beautiful weather phenomena on this planet and others.
We have written many articles about rain clouds for Universe Today. Here’s an article about the types of clouds, and here’s an article about cloud seeding.
If you’d like more info on rain clouds, check out the Homepage for the National Oceanic and Atmospheric Administration. And here’s a link to NASA’s Earth Observatory.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.
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