Discover Rare Ocean Wave Clouds: Kelvin-Helmholtz Clouds, Asperitas, and More!

Written by Sanaphay Rattanavong
Updated: August 14, 2023
Share on:


Imagine looking up at the sky and seeing it ripple like ocean waves. A sight so surreal it feels like a glitch in the Matrix. But rest assured, this is no glitch. It’s a rare and mesmerizing meteorological phenomenon, rare cloud formations in particular. From the turbulent beauty of Kelvin-Helmholtz clouds to the surging majesty of tidal wave clouds and the mesmerizing novelty of asperitas formations, join us as we explore these atmospheric enigmas.

Regardless of Rarity or Commonness, What Are Clouds Anyway?

Clouds, those puffs of icy water droplets in our atmosphere, are the unsung heroes of Earth’s weather and climate. They paint our skies with breathtaking canvases, influence temperatures, and orchestrate precipitation patterns. They do the actual rain dancing. Understanding them is like learning the grammar of our atmosphere. They offer us invaluable insights into current weather patterns, and clues about future ones. They tell us how healthy Mother Earth is.

Water Cycle in nature stock illustration

During the water cycle, water can and will change between the different states of matter.


Rare Oceanic Cloud Formations: The Skyward Surf

By looking up, we sometimes find complex, beautiful cloud formations. Such sky surfers mirror the diversity of ocean waves. They retain exotic names like Kelvin-Helmholtz clouds, tidal wave clouds, and asperitas formations. But most poignantly, they inspire awe and a sense of the uncanny with their resemblance to still-framed ocean waves.

Atmospheric scientists investigate these enigmas to better comprehend cloud development, cloud architecture, and the effects of clouds on the weather. Wave clouds feature distinctive patterns of alternating clouded and clear bands. They’re of particular interest when stable air flows over elevated land features. Unsurprisingly, glider pilots are drawn to the steep streamlines of these clouds. They are of particular value because of their impact on Earth’s radiation budget and climate models.

Ice crystals, formed via homogeneous nucleation (the process by which new droplets are created), are the primary form of precipitation. Thus, studying the ice composition within these clouds is also important. Like the sea, wave clouds can take on a variety of smooth or choppy shapes. Notably, multi-level mountain wave clouds form whenever there are different levels of moisture present above a mountain. This is not unlike the varying depths of the ocean.

Understanding the ocean and the sky and their mutual dependence is essential for making sense of these strange yet natural phenomena.

Kelvin-Helmholtz Clouds: A Skyward Mirror of Oceanic Beauty

When Kelvin-Helmholtz clouds form, it is like watching the ocean’s waves dance above us. These fleeting shapes are a reflection of the ocean in the sky. Literally, since they’re the product of fluid dynamics at work. Kelvin-Helmholtz clouds take their names from two pioneers in the field of fluid dynamics, Lord Kelvin and Hermann von Helmholtz. They form when there is a speed disparity between two layers of air.

Yes, these are Earth clouds. Marin County, California, recorded by Jim Collier, to be precise.

These elusive clouds are rare, short-lived, and typically form at high altitudes, making their sighting a prized event. Despite their ethereal nature, the phenomenon that governs their formation, the Kelvin-Helmholtz instability, can occur in any fluid system. Humbled, if a bit freaked out, we’re reminded of the universality of physical laws.

Also known as billow or shear-gravity clouds, the Kelvin-Helmholtz wave clouds are understandably breathtaking.

Asperitas: The New Kid on the Stormy Seas of Rare Clouds

Asperitas clouds (undulatus asperitas) are fascinating because they look like crashing waves during a storm. (The name derives from the Latin for “harshness” or “roughness.”) This is proof of the turbulence that atmospheric processes can produce formations. Gavin Pretor-Pinney’s advocacy led to the recognition of these clouds as a distinct formation in 2009. They have a rippling base that may be smooth or dappled.

Recorded in Lincoln, NE, in 2014, by Alex Schueth, asperitas weren’t even officially classified at the time of capture.

Unlike lofty Kelvin-Helmholtz clouds, asperitas formations stay low. Their allure lies in their wave-like structure and dramatic visual effects due to variable illumination and thickness. These unusual formations, mirroring the turbulence of a stormy sea, received official classification from the World Meteorological Organization in 2017. They offer a rather striking demonstration of atmospheric fluid dynamics.

The Oncoming Tide: Tidal Wave Clouds

Tidal wave clouds demand attention with their remarkable resemblance to an impending rush. They are not unlike the massive tidal waves surging over the ocean surface. When an air mass collides with a mountain range, these clouds are most frequently formed by atmospheric oscillations. The air generates a gravity wave pattern as it ascends the mountains and then falls to the other side. This results in towering, tide-like cloud formations. These clouds appear to convey the rhythmic motion of the water right into the sky, which is a magnificent sight to behold.

Even from a short video, we can easily imagine how intense being under such tidal wave clouds might be.

The Subtle Waves: Stratocumulus Clouds

Stratocumulus clouds bring the imagery of gentle ocean waves right into the heart of our skies. These low-level, lumpy cloud layers stretch across the sky, forming a blanket that often obscures the blue beyond. From a distance, these formations might seem like a calm “sea of clouds,” their undulating pattern mirroring the rhythmic swells of the ocean, inviting a moment of serene contemplation.

The “sea of clouds” has everything to do with the actual oceans and seas, which makes up over 70 percent of Earth’s surface.

Harbingers of the Storm: Mammatus Clouds

Mammatus clouds are nature’s warning of an impending storm. Also known as “mamma clouds” within meteorologist circles, their distinct pouch-like features, which might appear menacing, are frequently associated with severe weather conditions. These clouds, like whitecaps on a windy sea, are born of great turbulence. They occur most often in sinking air as opposed to most cloud forms, which form in rising air.

When the sun is low, the “udders” or “breasts” or the mammatus clouds are set in dramatic spectral relief.

Arcus Clouds: The Forerunners of Thunderstorms

Large, horizontal, low-lying cloud formations known as arcus clouds are often seen in the hours before a storm or cold front makes landfall. Sky displays like this are common along the leading edge of a gust front or the boundary of a storm’s outflow. There are two main categories for these clouds: shelf clouds and roll clouds.

Most arcus clouds are shelf clouds, which are also the most common. They look like they’re dangling from the bottom of a parent cloud, usually a thunderstorm or cumulonimbus, and have a wedge shape. Shelf clouds frequently accompany tornadoes, heavy downpours, and loud noises. When the downdraft of a thunderstorm spreads out, it brings cooler, denser air with it, forcing the warmer, more humid air below it to rise. The distinctive shelf cloud is formed when rising air cools and condenses.

Usually attached to a thunderstorm, shelf clouds bid us to take cover.

Unlike the more common arcus clouds, roll clouds are relatively rare. They look like skinny cylinders rolling along the ground horizontally. In contrast to shelf clouds, roll clouds have a distinct “tube” or “roll” appearance because they have become completely separated from their parent cloud. Like shelf clouds, downdraft clouds form when there is a large moisture or temperature disparity between the storm’s downdraft and the surrounding air.

The two types of arcus clouds are shelf and rolling. Both indicate severe weather.

The dramatic and imposing appearance of arcus clouds is often a precursor to severe weather events. They often herald thunderstorms, squalls, and even tornadoes. Therefore, their presence can serve as an important warning to meteorologists in weather forecasting and warning systems, helping them to do their jobs more effectively.

The Sea of the Sky: Altocumulus Clouds

Altocumulus clouds often form a spectacular “sea of clouds” in the mid-level of the troposphere. Their wave-like patterns are mesmerizing to watch, especially when wind shear disturbs the cloud layer. The broken, puffy appearance of these clouds, combined with the effect of the setting or rising sun, can make one feel as if they are gazing upon a sun-kissed ocean from high above. Or a shimmering sky from far below.

Altocumulus clouds don’t produce rain and have been known to look like puffy jellyfish.

It’s important to keep in mind that a number of factors, such as the speed and direction of the wind, the temperature, the humidity, and even the presence of dust or other particles in the air, all interact to produce the amazing variety of cloud forms. These ephemeral occurrences in the sky add beauty and mystery to the sky. But beyond aesthetics, they also communicate stories about the ever-shifting moods and motions of the atmosphere.

Navigating the Waves: Hazards to Aviation

Turbulence and weather conditions associated with various cloud formations pose risks to aviation. For example, Kelvin-Helmholtz clouds can cause turbulence due to wind shear. Asperitas clouds and tidal wave clouds indicate atmospheric instability. Stratocumulus clouds lead to poor visibility. Mammatus clouds are often associated with severe weather, and cirrus clouds can cause icing conditions for aircraft. Finally, altocumulus clouds may indicate a warm front, leading to weather changes that can affect flight operations.

Clouds and Culture

Clouds have been integral to folklore, mythology, and artistic expression across civilizations. Greek mythology associated cloud nymphs with weather phenomena, while in Hindu mythology, the deity Indra controlled the weather. In Norse and Japanese mythologies, gods associated with thunder and storms were prominent. Similarly, Native American mythologies often associated weather phenomena with specific deities.

Spectacular view of Mount Popa over the clouds. Mt.Popa is the home of "Nat" the Burmese mythology ghost. This place is the old volcano in Myanmar.

Mt. Popa is the home of “Nat” the


mythology ghost. This place is the old volcano in Myanmar. Similar to Mount Olympus of Greek Mythology, this peak sits at the “heavenly threshold.”


 Navigating the Cumulus of Cloud Idioms

Clouds, with their diverse forms and appearances, inspire numerous idioms across cultures. From the hopeful “Every cloud has a silver lining,” implying optimism in adversity, to the ominous “A cloud hangs over someone,” denoting impending doom or suspicion. Expressions such as “on cloud nine” depict immense joy, while “living in cloud-cuckoo land” indicates unrealistic aspirations. Idioms like “to cloud the issue” suggest confusion, while “let (something) cloud (one’s) judgment” warns against harmful influences. “Blue skies,” on the other hand, offer a positive, carefree outlook.

These idioms form just a part of the many cloud-related phrases enriching our language. They reflect the importance of clouds in our cultural narratives.

Cloud idioms also exist in other languages. Both French’s “Avoir la tête dans les nuages” and Spanish’s “Estar en las nubes” resemble English’s “head in the clouds,” meaning to daydream. The German phrase “Auf Wolke sieben schweben” mirrors “on cloud nine,” indicating joy or love. (No shadenfreude here!)

The idiom “on cloud nine” has variants like Italian’s “Al settimo cielo” (in the seventh heaven) and Chinese’s “在九霄云外” (beyond the clouds). The theme of “seventh heaven” in translations often ties back to religious cosmologies, signifying ultimate bliss.

Interestingly, the Kurdish phrase “Di behra sêyem de” (in the third sea) uses the number three. This may symbolize completeness in many cultures. Additionally, “sea,” a metaphor for vastness, perhaps suggests total immersion in an experience or extreme joy.

These cloud idioms contribute to the rich and diverse linguistic tapestry they create, resonating with various emotions and scenarios. Their prevalence underscores the cultural and symbolic importance of clouds in language, mirroring the ever-changing sky.

Digital Media and the Internet

Digital media and the internet have profoundly changed our interaction with the world. The concept of clouds, as metaphor and model, plays a major part in this digital realm. Cloud-based apps and games leverage cloud computing to offer dynamic experiences. Such things also extend to business solutions, allowing companies to scale their operations like never before. Yet, there’s a foreboding sense of what may come when life is nearly wholly uploaded “to the cloud.”

Spotlight on Rare Cloud Formations

We would be remiss to not mention a few other notable rare cloud formations. We take a look at the unusual suspects, highlighting the key characteristics, causes, and consequences of each.

1. Noctilucent Clouds

Noctilucent clouds, also known as “night-shining” clouds or polar mesospheric clouds, are the highest, coldest, and rarest clouds on Earth. They appear in the mesosphere, just below the boundary of outer space, and form when water vapor freezes into ice crystals that reflect sunlight. Observations of these clouds are most common during the summer months, particularly in the Northern Hemisphere’s northern skies. Sightings have become more frequent in recent years, possibly because of climate change, making it more likely to witness these spectacular sky sights.

Noctilucent clouds became brighter and appeared more frequently during Industrial Revolution, and continue to do so.

2. Lenticular and Cap Clouds

Rare formations made by orographic lifting include lenticular and cap clouds. Despite their potential to cause airplane turbulence, these clouds frequently cap mountaintops and are attractive to paragliders.

Mount Rainier with lenticular clouds in black and white, Washington, USA

Often forming over mountains, such as Mount Rainier here, most people remain unaware of their existence.

©Mark A Lee/

3. Polar Stratospheric Clouds (Nacreous Clouds)

Polar stratospheric clouds, or nacreous clouds, form in the winter polar stratosphere at altitudes of 49,000 to 82,000 feet. They are wave clouds often found downwind of mountain ranges, which can induce gravity waves in the lower stratosphere. These clouds play a significant role in Antarctic ozone destruction, raising environmental concerns because of their contribution to ozone depletion.

Mother-of-pearl cloud in Norway 245

Polar stratospheric clouds, also known as nacreous clouds, are known in common parlance as mother-of-pearl clouds.

©Uwe Michael Neumann/

4. Morning Glory Clouds

A rare meteorological marvel, the Morning Glory Cloud primarily graces the southern skies of the Gulf of Carpentaria in Northern Australia. Its sudden wind squalls and intense low-level wind shear generate a low-level atmospheric solitary wave. Remarkably, this wave often races between 32 and 65 feet per second, crafting magnificent bands of roll clouds.

Medium-sized circulations or mesoscale circulations, sea breezes, and certain temperature inversions all play crucial roles in the formation of these striking Morning Glory clouds. Indigenous to the region, the Gangalidda people attach significant cultural importance to this phenomenon. It has also caught the fancy of glider pilots, prompting a biennial festival in Burketown that celebrates this natural spectacle.

A type of roll cloud, Morning Glory clouds are distinguished for their spaced out lines or rolls.

From the ethereal noctilucent clouds to the intriguing Morning Glory formations, these skyward phenomena do more than just captivate us with their beauty and mystique. They are integral to various atmospheric and ecological processes. Our understanding of these unique clouds can help unravel the complex web of our planet’s atmospheric systems. Furthermore, it can shed light on the possible implications of human activities on these delicate balances.

Implications of Rare Cloud Formations

From noctilucent clouds to arcus formations, the spectacle of rare clouds in the sky is undeniably fascinating. However, their importance extends beyond their visual appeal; they are key indicators of climate change, weather patterns, and intricate atmospheric processes.

Consider the elusive noctilucent clouds, the loftiest inhabitants of our atmosphere at an altitude of approximately 50 miles. These “night-shining” formations are typically invisible during the day, only revealing themselves when illuminated by sunlight from below the horizon, while the lower atmosphere lies in Earth’s shadow. Mainly visible during summer months at high latitudes, their presence and frequency are influenced by changes in atmospheric temperature and water vapor content. Therefore, a rise in sightings of noctilucent clouds might suggest climate change-induced alterations in the upper atmosphere.

Then, there are the nacreous or polar stratospheric clouds, present in the winter polar stratosphere at elevations spanning 49,000 to 82,000 feet. Their twilight dance is not just mesmerizing but also revealing. Composed of ice crystals, these clouds host chemical reactions involving chlorine and bromine. These reactions can eventually lead to ozone layer depletion when sunlight re-emerges in the polar spring, making nacreous clouds significant actors in the process.

Arcus clouds are another stunning yet instructive formation. These extensive, low-lying clouds often precede the front line of thunderstorm outflows. Divided into shelf clouds, characterized by their expansive, wedge-shaped appearance, and roll clouds, resembling horizontal tubes, their presence often hints at incoming severe weather. Meteorologists, therefore, view arcus clouds as a harbinger of extreme conditions, aiding in weather predictions and warnings.

These intriguing cloud formations serve a dual purpose. Not only do they add to the beauty of our skies, but they also contribute to our understanding of the Earth’s complex climate system. They aid in monitoring climate change, decoding atmospheric chemistry, and forecasting severe weather events. This highlights the significance of studying and preserving these atmospheric phenomena.

In the Eye of the Beholder: How to Spot Rare Clouds

First, be lucky. Second, be incredibly lucky. But it also doesn’t hurt to be knowledgeable. Here are some tips for increasing your odds of spotting these atmospheric unicorns:

Noctilucent Clouds

These can be spotted during the summer months, typically after sunset or before sunrise. Look up towards the horizon, where the sun has just set or is about to rise.

Nacreous Clouds

These are commonly seen in high-latitude regions during the winter. Best viewed in the hours immediately following sunset or preceding sunrise.

Arcus Clouds

These form at the leading edge of a gust front or outflow boundary from a thunderstorm or cold front. Watch out for these when a storm is approaching.

Asperitas Clouds

Usually found under the base of a cloud layer, often preceding thunderstorms. If you notice wavy, rough, sea-like patterns in the sky before a storm, you might be looking at asperitas clouds.


Clouds do more than just accessorize our skies. They tell stories about our weather, climate, and atmosphere. The next time you spot oceans forming in the sky, you’ll know it’s not a glitch in the holographic meta-reality, but a rare and fascinating phenomenon that perfectly captures the dynamic and interconnected nature of our planet.

The photo featured at the top of this post is © SubstanceTproductions/

Share on:
About the Author

Embracing the interplay between the arts, nature, and technology, Sanaphay Rattanavong sculpts narratives through both data and human/animal-focused lenses at A-Z Animals, primarily in the realms of weather, culture, cleantech, and climate resilience. His specializations also include creativity and animal intelligence. And cats. He holds an MFA in Creative Writing from Bennington College and has labored for more than 10 years in the trenches of journalistic, blog, magazine, and fiction writing. An outdoor enthusiast who also enjoys the finer things in culture, Sanaphay resides in Minneapolis, Minnesota, with stints in Toronto, Ontario.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.