Clouds have a way of capturing our attention. They can tower majestically over a crimson sunset, pack millions of gallons of water in a foreboding gray mass, or even resemble cute animals. But aside from their aesthetic appeal, clouds serve important functions in nature, acting as barriers for heat moving in and out of Earth’s atmosphere and regulating the planet’s climate. Here are six fascinating facts about clouds that will hopefully leave you feeling lighter than air.
There Are 10 Basic Types of Clouds
Clouds are composed of water droplets or ice crystals, but not all clouds are created equal. According to the World Meteorological Organization's International Cloud Atlas, there are 10 major cloud types, grouped by their distance from the Earth’s surface, which affects their appearance and composition. Low-level clouds — which are less than 6,500 feet from the ground and mainly composed of liquid water droplets — include cumulus, cumulonimbus, stratus, and stratocumulus clouds. The mid-level (6,500 to 23,000 feet) group — often composed of a mix of water droplets and ice crystals — includes altocumulus, altostratus, and nimbostratus clouds. Finally, high-altitude (16,500 to 45,000 feet) clouds are composed entirely of ice crystals and take on a feathery or wispy appearance; this group includes cirrus, cirrocumulus, and cirrostratus clouds. Additionally, clouds are grouped into 15 different species, classified by shape and structure, with those species further subclassified according to variety and supplementary features.
Clouds Are Much Heavier Than They Look
Although clouds can resemble big, buoyant puffs of cotton, looks can be deceiving. For example, a cumulus cloud measuring 1 cubic kilometer contains approximately 500 million grams of water droplets, equaling 1.1 million pounds — or about the weight of 100 elephants. So how exactly are these massive water containers able to “float” in the sky? It helps that moist air is actually lighter than the surrounding dry air. And while a cloud’s heavier droplets will fall to the ground, most droplets are too minuscule to be affected by gravity. Instead, these droplets are pushed farther away from the ground by a process known as atmospheric updrafts.
Some Clouds Are Human-Made
We’ve all looked up to the sky at some point and seen contrails, the streams left in the wake of high-flying aircraft. These line-shaped clouds consist of water vapor from aircraft engine exhaust that has condensed into ice crystals, essentially turning them into a temporary batch of artificially-made cirrus clouds. According to the Federal Aviation Administration, research has shown that, while contrails are not dangerous to humans, these high-altitude trails trap heat and impact the climate significantly.
Clouds Are Found on Other Planets
Clouds are not solely an Earthly phenomenon. The basic physics behind cloud formation — atmospheric gases cooling into a solid form and sustained in droplets — also apply to other planets within our solar system and beyond. However, these extraterrestrial floaters often have entirely different (and dangerous) compositions than the clouds on Earth. The thick clouds of Venus, for example, are composed of sulfuric acid, while those of the gas giant Jupiter can be bursting with ammonia compounds.
Americans Weaponized Clouds During the Vietnam War
During the Vietnam War, U.S. forces engaged in “cloud seeding” to increase rainfall and dampen the enemy’s ground efforts in a project dubbed Operation Popeye. Introduced in 1967, Operation Popeye was a five-year campaign that called for plane crews to ignite canisters of silver and lead iodide and direct the smoke into ongoing storms above Vietnam. It’s unclear how much cloud seeding aided the American cause, but after the extent of the top-secret campaign became public, the Senate Foreign Relations Committee convened to discuss the matter in 1974. Later, an international treaty was introduced to ban future weather manipulation by military forces.
Clouds Are a Symbol of Good Luck in China
As the saying goes, no one wants a cloud to rain on their parade, but in Chinese culture, the presence of “auspicious” clouds is an omen of good fortune. In Chinese mythology, clouds serve as a means of transport for divine figures, and also represent a physical barrier between their world and those of mortals. As such, these motifs were frequently depicted in traditional art, while writings of the Ming Dynasty (1368 to 1644) and Qing Dynasty (1636 to 1912) were filled with references to auspicious clouds. The significance of these symbols remains strong in modern times, with lucky clouds prominently featured on the uniforms of Chinese athletes for the 2008 Beijing Olympics.