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September-October 2011

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Beautifying Altostratus

Caption: Stratus pouring from the Pacific Ocean over the Coast Range between Half Moon Bay and San Mateo.

Caption: Stratus pouring from the Pacific Ocean over the Coast Range between Half Moon Bay and San Mateo.

It was a seminal moment in the history of science when Luke Howard first gave names to clouds in the winter of 1802–1803. But just as in Charles Perrault's fairy tale Sleeping Beauty, where seven good fairies were invited to Beauty's christening feast, but one ugly fairy was forgotten, Howard named seven beautiful cloud genera, but he failed to name the form that might just be the ugliest—the altostratus.

The Nature of Beauty

What is it that makes a cloud beautiful or ugly? This brings up the difficult question of the nature of beauty. By definition, beauty—“the perfect combination of characteristics pleasurable to see”—is in the eyes of the beholder. For although when we humans view a fly under a microscope, it almost universally causes us strong feelings of revulsion and disgust, that fly may appear beautiful or at least alluring to another fly. The case of the fly suggests that there may well be some standards for our feelings of beauty and ugliness, and people who study beauty do find certain common characteristics in the objects we judge to be beautiful or ugly.

Regarding beauty in humans, there is beauty in youth, partly because of fine skin tone and lithe form. We also tend to find beauty when there is near symmetry. And perhaps surprisingly, we find beauty in what is the human average, for example, a face that is neither too long nor too round, but “just right.” Many scholars argue that Leonardo da Vinci sought this average in painting the Mona Lisa. Other factors such as motion and color are part of our assessment of beauty. A still photograph may fail to show a sense of dynamism that can transform the mundane into the beautiful. And, with our gift of color vision, it is natural that we attempt to add to our personal beauty by adorning, painting, and dying ourselves in a range of colors. Colors also appear more vibrant when they appear in certain combinations, rather than singly. This makes a spectrum more beautiful to most of us than a patch of any single color.

Caption: Altostratus over Millenium Park, Chicago, reflected in the Cloud Gate sculpture.

Caption: Altostratus over Millenium Park, Chicago, reflected in the Cloud Gate sculpture.

Criteria applied to human beauty extend to beauty of the sky and its clouds. Young, growing cumulus with sharp cauliflower edges appear far more beautiful to most of us than old, dissipating cumulus with indistinct edges. Color and lighting contrasts also add to the beauty of clouds. Thus young cumulus are even more strikingly beautiful when they stand out against a deep blue background sky, while cumulus that are immersed in hazy air are far less aesthetically pleasing, although they may be far more mysterious. Clouds can also assume a spectacular mantle of almost spectral sunrise and sunset colors that we invariably find to be stunningly beautiful. Symmetry and regularity make clouds beautiful, as when altocumulus takes the form of regular hexagonal cells or perfect sinusoidal wave trains.

In almost all cases, these very criteria that characterize beauty disqualify a beautiful cloud from being called altostratus. But before turning back to clouds, perhaps there is one more feature we have neglected in our consideration of beauty. For that, I turn to Abraham Lincoln, a man who was thought by most of his contemporaries to be ugly.

An anonymous British journalist once wrote of Lincoln, “To say that he is ugly is nothing; to add that his figure is grotesque, is to convey no adequate impression.… Add to all of this an air of strength, physical as well as moral, and a strange look of dignity coupled with all this grotesqueness, and you will have the impression left upon me by Abraham Lincoln.” Another contemporary wrote, “His large bony face when in repose was unspeakably sad and as unreadable as that of a sphinx, his eyes were as expressionless as those of a dead fish; but when he smiled or laughed at one of his own stories or of that of another then everything about him changed; his figure became alert, a lightning change came over his countenance, his eyes scintillated and I thought he had the most expressive features I had ever seen on the face of a man.” The poet, Walt Whitman, who idolized Lincoln said, “He has a face…so awful ugly it becomes beautiful with its strange mouth, its deep cut, criss-cross lines, and its doughnut complexion.” Lincoln concurred with these judgments, thinking himself very ugly, indeed. But always his sense of humor and humility emerged. Once, when accused of being two-faced, he replied, “If I were two-faced, would I be wearing this one?” Yet, if we hear the words of Lincoln that inspired so many and see his soul through his words and deeds, we can not avoid thinking of him as one of the most beautiful of men who ever lived.

Is there a similar beauty that we can see in the soul of altostratus? We will seek so that we may find. Perhaps when we are finished looking, we will have found that the “ugly old witch” of a cloud is not so ugly after all. So, as a first step, let us consider why the naming of clouds was such a momentous occasion, why altostratus was omitted, and why it is so important to include altostratus in any cloud classification.

Creating a System

What was so momentous about naming clouds? Johann Wolfgang von Goethe, scientist, philosopher, and poet, recognized the great significance of Howard's achievement. In the prelude to a series of poems about clouds, Goethe noted that Howard was “the first to hold fast conceptually the airy and always changing forms of clouds, to limit and fasten down the indefinite, the intangible and unattainable, and give them appropriate names.” Before Howard named clouds, no one could even talk about them intelligibly.

Caption: Wavy altostratus over the Sierra Nevada Range, seen from Granada, Spain.

Caption: Wavy altostratus over the Sierra Nevada Range, seen from Granada, Spain.

Howard was a naturalist by calling and a pharmacist by profession. He was highly sensitive to the weather and moods of the sky, and he was also trained in the revolutionary classification systems of plants and animals developed half a century earlier by Linnaeus. It made sense for him to apply that system to the clouds. And his achievement was momentous because science, like heaven and earth, begins by classifying or giving form to what we observe.

1. In the Beginning God created the heaven and the earth. 2. And the earth was without form…

King James Bible, Genesis, Chapter 1

Almost all human creations build upon foundations laid by predecessors. Isaac Newton did not dream up his founding work on physics and higher mathermatics, the Principia Mathematica, out of thin air, but built on a long tradition which began with classifying heavenly objects into categories that included stars, planets (wanderers), satellites, and comets, and then determining their properties, which included their motions. Newton acknowledged that in his work, he had “stood upon the shoulders of giants.”

As with any discovery, Luke Howard felt compelled to seek a practical value for his cloud system. He noted that cloud identification made it possible to improve weather forecasting and gave examples of how clouds of one form often morph or evolve into other forms that were associated with different weather. Ironically, while Howard stressed the evolution of clouds into other forms, Linnaeus and more than a century of his followers either denied the existence or remained ignorant of the mechanism of the evolution of plants and animals by following a system that enforced rigid compartmentalization. Nevertheless, it was the very success and strength of Linnaeus' system that helped Darwin formulate his theory of evolution and pen his master work On the Origin of Species. And perhaps Howard's morphing clouds helped to pave the way for Darwin by literally putting the notion of evolution in the air.

Why was it that Howard named only seven of the 10 cloud genera we recognize today, and why did he omit altostratus? The first and most obvious reason was that Howard did not divide the sky into three layers—low, middle, and high. I personally don't see much difference between altocumulus and cirrocumulus other than this tripartite division. The cloud elements (cells or ripples) of altocumulus are merely larger—they occupy between 1° and 5° of our visual field, while cirrocumulus cells or ripples occupy less than 1°. When the sky was stratified, some 75 years after Howard (in 1877) by Émilien Renou (who, like Howard, was a founder of urban climatology), altostratus and altocumulus naturally filled the middle layer. But a more subtle and fundamental reason for not identifying altostratus as a cloud form was that, in most cases, it has little or no apparent form. A closer look at Luke Howard's original classification scheme provides evidence for this assertion.

Caption: Wanderer Above the Sea of Mist 1818, by Kunsthalle Hamburg.

Caption: Wanderer Above the Sea of Mist 1818, by Kunsthalle Hamburg.

Howard began by identifying the three most fundamental cloud genera—cirrus, cumulus, and stratus: cirrus from the Latin for a lock, tendril, curl, or ringlet of hair, Howard described as “Parallel, flexuous fibres extensible by increase in any or all directions”; cumulus, Latin for a heap, pile, mass, or surplus, was in Howard's words “Convex or conical heaps, increasing upward from a horizontal base,”; and stratus, Latin for a spreading, was described as “A widely extended horizontal sheet, increasing from below.” The expressions “increasing upward” or “increasing from below” are confusing, but on page 22 of his book, The Climate of London, Howard described how stratus often forms as fog that begins in the valleys and ultimately extends upward to the hilltops until it covers the sky. Then Howard noted that in the mornings, the stratus regains some semblance of form when the sun breaks it into cloud elements that resemble smooth cumulus, but then gradually shred and dissolve until they evaporate completely.

Caption: Stratus pouring through a gap in the Alps near Mt. Blanc.

Caption: Stratus pouring through a gap in the Alps near Mt. Blanc.

A Cloud of Many Shapes

So, Luke Howard's stratus may be mostly amorphous, but it starts and ends life with a definite form that can offer gorgeous vistas. While most of us cower fogbound in the valleys, an adventurer on a hilltop can gaze down on seas of sunlit stratus that gleam white or glow with all the hues of sunrise, and the emergent parts of the landscape appear almost incandescent. Caspar David Friedrich captured some of the magic of this kind of scene in his painting Wanderer over the Sea of Fog, and he was part of a long tradition of painters beginning with the Chinese and now including photographers who have revealed even more. Sometimes, iridescent rings of glories or a bright cloud bow circle the observer's shadow on the cloud top. At other times, the stratus possesses a dynamism as it gathers into a tsunami that breaks and pours over the hills but dissolves harmlessly as it descends sunlit slopes. The sight can be both beautiful and awesome in its silent grandeur. But since altostratus cannot be surmounted this way covers all highlands, it is forbidden all these magnificent spectacles.

Both Howard's descriptions and drawings strongly suggest that all his cloud modifications possess distinct features and outlines, at least when they are first taking shape. Even the nimbus, or shower cloud, is shown from a distance with fall streaks extending down to the ground. Howard defined Cirrocumulus as “Small, well defined, roundish masses increasing from below,” and his drawings show that he meant both cirrocumulus and altocumulus. Howard defined cirrostratus as “Horizontal or slightly inclined masses, attenuated towards a part or the whole of their circumference, bent downward or undulated, separate, or in groups, or consisting of small clouds having these characters.” This sounds more like a species or variety of altocumulus or cirrocumulus than the veil-like cirrostratus we identify today, although Howard does stress that cirrostratus often appears as cirrus clouds thicken and is the cloud most likely to support halos. And his drawings of cirrostratus include what we would call both extended anvils and lenticular clouds. In fact, based on the sketches, the main difference between his cirrocumulus and cirrostratus is that his cirrocumulus cloud elements have corrugated and turbulent cloud outlines, while his cirrostratus cloud elements have smooth, laminar outlines.

Caption: Cirrostratus showing an extremely large halo.

Caption: Cirrostratus showing an extremely large halo.

Finally there was cumulostratus, a cloud genus we no longer recognize, but that Howard described as “the cirro-stratus blended with the cumulus, and either appearing intermixed with the heaps of the latter, or super-adding a widespread structure to its base.” His drawings all look like cumulus cloud streets or clusters.

The Woeful Countenance of Altostratus

Altostratus offers no such vistas. It is the only cloud that is invariably surrounded by others. Most often, altostratus is the intermediate sheet in the extensive cloud cover of extratropical cyclones, where it is hemmed in by cirrostratus on the poleward side and nimbostratus on the tropical side. It can also occupy a similar intermediate position in the cloud cover of hurricanes and the extended anvils of thunderstorm complexes.

So, before we attempt to beautify altostratus (a difficult task), we must honestly acknowledge that altostratus is usually ugly and depressing. When are you most likely to see altostatus? First, with an approaching winter cyclone. Here is the typical scenario. Graceful white wisps of cirrus are first to cross a deep blue sky. The cirrus congeal into cirrostratus, and a range of sometimes spectacular halos may form around the sun. But as the cloud veil thickens, the sky grows duller and grayer, and all halos and shadows fade away. It is at this point that the altostratus makes its appearance, often attended by other clouds both below and above the main cloud layer. A watery sun or moon may grace the scene, or the cloud base may display interesting structure amid the overall dullness, but these features soon descend into blurry darkness. Then the rain or snow begins.

Caption: Altostratus of an approaching storm. Here lower cloud elements that herald a moistening atmosphere blacken the sky while cirrus above cast fibrous shadows and may seed the altostratus. The classically dimmed and distorted watery sun pierces the altostratus (Cliffside Park, NJ).

Caption: Altostratus of an approaching storm. Here lower cloud elements that herald a moistening atmosphere blacken the sky while cirrus above cast fibrous shadows and may seed the altostratus. The classically dimmed and distorted watery sun pierces the altostratus (Cliffside Park, NJ).

Altostratus sometimes returns after many hours, or even several days, of rain or snow as the storm begins to depart. Precipitation becomes more sporadic and spotty, and the stratiform cloud curtain slowly rises so that the sky may brighten imperceptibly. Temperature may fall, and the wind often picks up. Shreds of low cloud generated over the wet ground and tilted by the wind race across the sky below the altostratus base. These cloud elements may be very dark or very light, depending on how light falls on them after penetrating the altostratus. Ironically, despite the fact that this scene presages the end of the storm, it tends to impose a deep sense of gloom and foreboding.

Caption: Wheat Field Under Clouded Sky painted in July 1890, by Vincent Van Gogh.

Caption: Wheat Field Under Clouded Sky painted in July 1890, by Vincent Van Gogh.

Vincent van Gogh portrayed that gloomy meteorological moment in several paintings in the final weeks of his life. In May 1890, van Gogh had moved from Saint-Rémy, with its sunny Mediterranean sky, to Auvers-sur-Oise, a suburb northwest of Paris. Here, his painted skies darkened in response to some inner calling provoked by the dismal weather. June 1890 was cloudier and colder than average, but then July turned truly miserable. Rain fell every day from June 30 to July 11, during which time it remained almost continuously overcast and much colder than normal. Under these woeful conditions, around July 10, Vincent wrote he had painted three “vast fields of wheat under troubled skies,” and added, “I did not need to go out of my way to express sadness and extreme loneliness.”

The Wheat Field Under Clouded Sky is probably one of these, and all the signs (aside from the cobalt blue) indicate that van Gogh was representing the sky as it appears at the end of a winter storm, like the one shown in the photograph of a departing storm in Cliffside Park, New Jersey. The sky darkens toward the horizon, as it can only when it is overcast. White fractocumulus appear below the general cloud cover, while scud hugs the ground as it does when cooler air comes in contact with warmer, rain-soaked ground. The air has been swept so clean by days of rain that every feature of the field can be seen distinctly out to the horizon, where the cloud cover drops like a curtain to terminate the view.

Caption: Altostratus of a departing storm with shredded cloud elements called fractostratus below (Cliffside Park, NJ). Within a few hours the sky cleared but the scene was gloomy.

Caption: Altostratus of a departing storm with shredded cloud elements called fractostratus below (Cliffside Park, NJ). Within a few hours the sky cleared but the scene was gloomy.

I do not think any feelings of ugliness or beauty accompany the sense of gloom and foreboding of the appearance of altostratus that marks the incipient departure of a winter storm. There are other times when the sky imparts feelings of awe or terror, or a sense of the sublime or monumental that we do not associate with beauty or ugliness. For example, it was an altostratus that constituted one of the most breathtaking skies I have ever seen. It occurred right around sunset. I glanced out the window of my Ivory Tower Office just before heading off to teach an evening class at City College and saw a layer of deep gray altostratus that had been roiled into a monumental wave.

What gave rise to such an awesome sight? The base of altostratus often rests on a warm frontal surface, just above a cold air mass. The frontal surface is a zone of pronounced vertical wind shear, and shear on an interface produces waves via the Kelvin–Helmholtz Instability. The quality of the base also reflects the nature of the air flow. If the flow is turbulent, the cloud base will appear rough and mottled, but if the flow is laminar, the cloud base will appear smooth, and if it is wavy it could be called lenticularis or possibly asperatus. The base and its fine structure can be seen distinctly whenever the air below the frontal surface is dry. Once raindrops or snowflakes begin falling through cloud base, they blur the detailed structure, and rain or snow often reaches the ground in 10 to 20 minutes. Less than half an hour after the photograph, the cloud base blurred. A few minutes later, light rain began to fall, which lasted only a few minutes. The cosmic scene fizzed out innocuously.

Caption: Altostratus over Shepard Hall, City College of New York.

Caption: Altostratus over Shepard Hall, City College of New York.

Now that the cosmic failed, we will settle for beauty. Even though the very definition of altostratus eviscerates almost anything that can be alluring, we will find the loopholes. According to the Glossary of Meteorology, altostratus is

a gray or bluish (never white) sheet or layer of striated, fibrous, or uniform appearance without rounded cloud masses … if gaps and rifts appear, they are irregularly shaped and spaced.… It may obscure the sun at its thickest parts, or impose a “ground-glass” effect upon the sun's image, so as to prevent sharply outlined shadows from being cast by terrestrial objects. Halo phenomena do not occur. Altostratus is a precipitating cloud and therefore often is accompanied by virga and mamma. Rain, snow, ice pellets, etc., are present in the cloud and under its base, frequently rendering the base quite indistinct, particularly when the precipitation does not reach the ground.

There is little hint of potential for beauty here. The fibrous appearance of altostratus is no more than a congealed remnant or shadow of the beautiful fibers of cirrus or cirrostratus, and unlike these ice crystal clouds, altostratus is optically too thick and its ice crystals too clustered or contaminated by droplets to be adorned by halos. Unlike stratus, altostratus is too high to allow panoramic views from the hilltops. Unlike altocumulus, altostratus never shows organized waves or cellular structure.

Altostratus Beautified

But we have already seen the classical signature of altostratus that can give rise to beauty—the watery sun or moon. When the thickness of altostratus varies, the watery sun or moon alternately appears and disappears. This alternation between vagueness and invisibility has made altostratus an ideal companion cloud for classical horror movies. It imparts a sense of mystery and suspense, but is not likely to be seen as beautiful. Sometimes, however, a pale orange ring surrounds the watery sun or moon. This is a visage of a faint corona. Coronas are both awesome and beautiful when they consist of multiple rings of colored light. The most spectacular coronas form when seen through a cloud that is not too thick and that consists of droplets that are all nearly identical in size. Because of these strict requirements, the most striking coronas are seen in wave clouds (altocumulus) but on rare, rare occasion, they can form in altostratus. So here, altostratus has its first chance at beauty, but if more than a hint of organized waves appears in the cloud, it must be called altocumulus.

Caption: Altostratus remnants of showers over Boynton Beach, Florida.

Caption: Altostratus remnants of showers over Boynton Beach, Florida.

Altostratus can also be beautified when light from the rising or setting sun passes under the edge of the cloud sheet and illuminates its base. The resulting glow can extend to the zenith and impose a hauntingly lurid beauty, particularly when it follows a long reign of somber darkness.

So what can we say in way of conclusion? An ugly, nondescript cloud such as altostratus should not expect or even hope to be thought of as beautiful. The cloud should be satisfied if it can inspire awe or terror, or arouse other strong emotions such as depression, foreboding, gloom, and loneliness. But every cloud, like every person, does deserve its moment in the sun when it shines with a beauty that is all the greater for being totally unexpected.

STANLEY GEDZELMAN is a professor in the department of Earth & Atmospheric Science at the City College of New York.

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