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Clouds: Magical and Mysterious
Down through the ages, humans have pondered the lives of clouds.

When Crystal-Face scientists (see story) plumbed the violent and complex depths of cumulonimbus clouds, they were, some would say, just continuing humankind’s exploration of these ethereal phenomena. For millennia, people have ascribed all kinds of meaning to clouds, as they have tried to understand clouds’ mysterious characters.

“When a cloud grows dark in heaven,” noted an anonymous Chaldean weather man, “a wind will blow.” Judging from the enthusiasm of Anthony Del Genio and his colleagues, it seems our capacity for wonder over the true nature of the ethereal phantoms of the sky is still tormenting the earthbound limits of our terrestrial imaginations. More than ever.

Unbeknownst to that Chaldean weather man, his contemporaries in the Shang Dynasty, in China, were observing the same parade of clouds across the heavens. Chinese scholars theorized that careful observations and quantifiable data would enable them to deconstruct weather into knowable, measurable, parts. In fact, they were the first “scientists” to use charcoal to gauge the relative humidity of air, an achievement that predates Pericles and the Golden Age of Greece by two millennia. Centuries later, Taoists anticipated discoveries by modern meteorologists when they established a Ministry of Thunder and a God of Clouds, but it wasn’t until Aristotle cast his eyes skyward and composed his extraordinary treatise, “Meteorologicia,” that clouds found a permanent home in science. Parting company with his Asian predecessors, the great Hellenic metaphysician described clouds as a mixing of vapors that were drawn from both the upper atmosphere and terra firma, a great rising and falling and commingling of moisture trapped in perpetual motion by the attraction of the earth and the repulsing power of stars. His insightful musings framed the debate about clouds for nearly 2,000 years, when scientific advancements in the Age of Enlightenment, combined with the theoretical genius of Rene Descartes, set the science of clouds on the course where we find it today. 

Remarkably, Descartes speculated that clouds were made up of tiny water droplets and particles of ice formed by compressed vapor. This vapor, he reasoned, escapes from the ground and bodies of water to form these lighter-than-air heaps in the sky that we call clouds. But just how these processes worked in the atmosphere to influence our climate would remain a mystery for another two centuries, when19th century scientists, armed with newfangled tools such as thermometers and barometers, took their questions into the sky in hot air balloons.  Even as they ascended to dizzying heights above Paris and London, it never occurred to these intrepid aerialists that clouds should have names.

That taxonomic threshold would be crossed in 1802 by an unassuming young English chemist named Luke Howard. On a rainy December evening, Howard stood before a small gathering at Plough Court, in London, and uttered a new family of words derived from Latin: cirrus, stratus, cumulus. Howard used these terms to describe three basic formations of clouds, with four divisions within each group. These cloud forms, he argued, were as distinct from each other as chickens are distinct from trees. Cirrus were clouds shaped like wisps of hair; cumulus clouds build into piles and heaps, and finally, stratus clouds are layered in sheets. Each member of the cloud family is shaped by distinct climatic phenomena.  

Howard’s prosaic title, “On the Modifications of Clouds,” belied a daring proposal that would forever alter the way scientists look at the sky. By the time meteorologists added nimbostratus a century later, Howard’s taxonomy had become a universal fixture of everyday language. Today clouds arrive in our midst with the names of Roman gods—undulatus, cumulonimbus incus, fibratus, and lenticularis, among numerous others—arriving as shadows drifting across a field of ripe grain or accompanied by stinging hail or deadly winds. Howard’s achievement set the stage for the next great leap forward, but the adventure commenced by the Chaldeans and Chinese would have to wait until 20th century rocket technology punched a hole in the sky. Then the intellectual descendants of Aristotle could reframe questions in the 21st century that puzzled their ancient ancestors in Babylon.


Stratus clouds

Stratus clouds are made up of low, sheetlike layers that usually cover the whole sky, blotting out the sun. They bring gray, overcast days. When rain falls from them, they’re called nimbostratus clouds. (The word nimbus identifies clouds that bring rain.)
Courtesy of University of Illinois Cloud Category and NASA



Cumulus (meaning “heap”) clouds are the large clouds often described as looking like huge puffs of cotton. When cumulus clouds get dark gray and produce rain or hail, they are then called cumulonimbus clouds. They often produce lightning and thunder.
Courtesy of University of Illinois Cloud Category and NASA



Cirrus (meaning “curl”) clouds are very high, wispy, featherlike clouds. They’re made of ice, even in the summer, because they are high-altitude clouds.
Courtesy of University of Illinois Cloud Category and NASA



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