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  Luke Howard’s personal life, a marriage and various apprenticeships as a chemist, had slowed his meteorological investigations, and it wasn’t until fate relocated him to Plaistow, a suburb on the outskirts of London, that he was again able to resume, as he later wrote, “the observations I had long been making on the face of the sky.” With no more equipment than a good eye and a crick in his neck, Howard set out to classify the unclassifiable: the ineffable, vaporous, ever-changing clouds. He could see an order to them, one that after a few more years of keen observation and note-taking, was robust enough to publish as a scientific paper. So in December 1802, Luke Howard, a member in good standing, read his paper entitled On the Modifications of Clouds to the Askesian Society. It changed meteorology forever.

  Howard set out three basic cloud types: cumulus, stratus and cirrus. But there were combinations of these, which added up to 10 types: cirrus, cirro-cumulus, cirro-stratus, alto-cumulus, alto-stratus, cumulus, strato-cumulus, nimbo-stratus, stratus and cumulo-nimbus. It was breathtakingly simple yet completely inclusive. He had pulled off a Linnaean coup for clouds. Shortly after his paper was delivered, he became a scientific celebrity across Europe. Even Goethe was impressed, writing, years later in 1817, this short appreciative doggerel:

  But Howard gives us with his clearer mind

  The gain of lessons new to all mankind;

  That which no hand can reach, no hand can clasp

  He first has gained, first held with mental grasp.

  Defin’d the doubtful, fix’d its limit-line,

  And named it fitly. — Be the honour thine!

  As clouds ascend, are folded, scatter, fall,

  Let the world think of thee who taught it all.

  Cloud Watching

  In 1887, the first International Cloud Atlas was published. It was replete with illustrations of Howard’s cloud types and some of the first published color photographs. We know today that these various types of clouds, almost like separate species, inhabit different altitudes, and any of us who have flown through and above them are cloud explorers. We have felt the turbulence of updrafts within cumulus clouds and seen panoramas no earthbound observer has ever witnessed. For a cloud-gazer like me, a nephological aficionado, the wonder of clouds outside an airplane window never fails to astonish and inspire.

  A descending airliner samples Howard’s cloud almost in the same order as the International Cloud Atlas, starting with cirrus clouds (Latin for “lock of hair”), which hover at altitudes of 16,500 to 50,000 feet (3 to 9 miles) above the ground. These lofty clouds have the most subspecies, 13 in all, including cirrus incinus (“mares’ tails”) and cirrocumulus stratiformes (the “mackerel sky” that often spreads from horizon to horizon). Every one of the 13 are entirely composed of ice crystals. Often cirrus clouds have the look of brushstrokes or tufts of hair. I have raced by cirrus incinus on airplane flights near cruising altitude, their wispy tails flickering so close I could have reached out to touch them.

  Stratus clouds (Latin for “layer”) can be as high as cirrus clouds or as low as cumulus clouds. They occur at the boundaries of different air temperatures and are flat and layered, because no vertical convection columns puff them up. They have seven subspecies among which is altostratus, forming just below cirrus altitude. Altostratus are often semitransparent, so you can see the disc of the sun through them. I remember one flight where, as we began our descent, we appeared to be landing on a vast field of stratiform clouds that rose up over the sides of the airplane like mist over a lake, a cotton fog we sank into. The blue daylight dimmed until, deep inside the cloud, the windows were a dark pearl gray, as if they’d all been painted. Then suddenly, the windows brightened, and we came out of the bottom of the stratus layer into a gray, twilight world sandwiched between two layers of clouds — altostratus above and nimbostratus below. (Nimbus is the Latin word for rain.) It was a parallel universe in which somber cloud vistas devised strange landforms to the horizon — low gray mountains and great plains. Then our flight sank into this nacreous landscape without a tremor, submerging again into the pearly darkness.

  Classic cumulus clouds (Latin for “heaped”) are generally low clouds, and their bases often hover less than 6,500 feet above the ground. From above, cumulous clouds seem like puffy mountains with no features, no rivers or forests, only snow-white landscapes. The unbroken whiteness makes them seem heavenly, like celestial terrain transformed, purified.

  Cumuli are the mascots of the empyrean vault of heaven, endless form seemingly without purpose or function, sheer natural invention. Stratus clouds enclose relatively little turbulence, but cumulous clouds always contain updrafts and so the ride through is usually a little bumpy. Being a bit of a backseat pilot, I’ve always felt a sense of relief as my flight passes out of a cumulus cloud.

  The 1896 edition of the International Cloud Atlas stood for more than 50 years; the edition that meteorologists use today was published in 1951. This atlas used what was referred to as the C code and started at 0 instead of 1. It also did away with the cumbersome hyphens. The order of the cloud types is now as follows: 0. cirrus, 1. cirrostratus, 2. cirrocumulus, 3. altocumulus, 4. altostratus, 5. nimbostratus, 6. stratocumulus, 7. stratus, 8. cumulus, 9. cumulonimbus. Here, finally, is the origin of the term “cloud nine.”

  The tallest, grandest cloud of all — in extreme cases reaching heights of 12 to 15 miles, more than twice the height of Mount Everest — closes out the list of cloud types, and of all the clouds it has the most complex and dynamic inner life. When one of these monster cumulonimbus clouds rises until it hits the top of the troposphere, it acquires the classic anvil shape and now takes on one final Latin moniker: cumulonimbus incus. It is a weather system unto itself. No one has explored the interior of one of these clouds by balloon or purposely by airplane; they are just too dangerous. But one American became a pioneer through circumstances beyond his control.

  During the late afternoon of July 26, 1959, U.S. Marine Corps Lieutenant Colonel William Rankin and his wingman, Lieutenant Herbert Nolan, were piloting a pair of F-8 Crusader fighter jets to a base in Beaufort, North Carolina. They were flying at an altitude of 47,000 feet (9 miles) to avoid turbulent weather beneath them. Just before they began their descent, Rankin heard grinding noises coming from his engine. Then his instrument lights went out, and when he pulled the emergency auxiliary power lever, it broke off in his hand. He radioed Nolan and told him he was ejecting.

  At this altitude, the ambient temperature is -50˚C. There is next to no oxygen and the air pressure is less than a third of that at the surface. Rankin wasn’t wearing a pressure suit. As soon as his canopy blew off and his chair rocketed out of the aircraft, his body began to decompress. His ears, nose and mouth started bleeding and his stomach became dangerously distended. His glove had been ripped off and he could feel frostbite instantly numbing his hand. Fortunately, he had an oxygen canister attached to his helmet, so he remained conscious.

  His descent — from ejection to touchdown — should have taken about eight minutes, a 3.5-minute freefall to 10,000 feet where his parachute would automatically deploy. But he had bailed out over a thunderstorm. Violent updrafts within the cumulonimbus cloud held him in their grip for almost 40 minutes.

  I was blown up and down as much as 6,000 feet at a time. It went on for a long time, like being on a very fast elevator, with strong blasts of compressed air hitting you. Once when a violent blast of air sent me careening up into the chute I could feel the cold, wet nylon collapsing about me. I was sure the chute would never blossom again. But, by some miracle I fell back and the chute did recover its billow.

  The first clap of thunder came as a deafening explosion that literally shook my teeth. I didn’t hear the thunder, I actually felt it — an almost unbearable physical experience. If it had not been for my helmet, the explosions might have shattered my eardrums.

  I saw lightning all around me in every shape imaginable. W
hen very close, it appeared mainly as a huge, bluish sheet several feet thick. It was raining so torrentially that I thought I would drown in midair. Several times I held my breath, fearing that otherwise I might inhale quarts of water.

  Rankin eventually landed in a forest and made his way to a road where he flagged down a passing motorist. Later, in hospital, he was treated for bruises, frostbite and severe decompression.

  This is why airliners avoid flying through active cumulonimbus clouds. Lightning is scary up close but it seldom strikes an airplane, and heavy rain just blows through the fans of jet engines. It’s those updrafts and downdrafts — particularly if they’re side by side. They can, and have, torn airliners apart. So cloud nine is hardly the bucolic, tranquil paradise it has been made out to be. Just ask William Rankin.

  4

  The Poem of Earth

  Rain

  “I feel sorry for short people, you know.

  When it rains, they’re the last to know.”

  Rodney Dangerfield

  A cloud is a galaxy of microscopic water droplets. Immune to gravity, the droplets float suspended in the air like bubbles in syrup. In most clouds, this weightless multitude exists in a steady state, but if the cloud is large and there are other forces acting on the droplets — thermal convection updrafts and downdrafts for one, or a change in altitude as a cloud is pushed up and over a mountain — then some of the droplets collide and combine into larger droplets. If they keep coalescing, they eventually get so large that gravity begins to pull them downward, collecting even more droplets until they become raindrops. When vapor coalesces higher in a cloud, as growing crystals of snow, these too will begin to fall, but they’ll melt into rain if the temperature at the base of the cloud is above freezing.

  If we follow one raindrop as it falls from the cloudy heights, we’d have to keep quickening our pace because as it falls it picks up speed. To a point. In a vacuum, the raindrop’s acceleration would continue indefinitely, but air resistance slows its fall. When the forces of gravity and air resistance balance each other, the drop ceases to accelerate and reaches its terminal velocity. Of course, the size and weight of the raindrop decides what the velocity will be: the heavier, the faster. Not that rain contradicts Galileo’s rule — large objects accelerate at exactly the same rate as small objects — it’s just that smaller drops of rain encounter more air resistance as a ratio of their size to mass. It’s the same reason a feather falls more slowly than a pebble. Drops of drizzle, which are less than 0.5 millimeters across (salt-grain size), have a terminal velocity of 4.5 miles per hour, while a large raindrop about five millimeters across (house-fly size) falls at the rate of 20 miles per hour. By comparison, a falling human being hurtles to the ground at a terminal velocity of about 125 miles per hour.

  Raindrops are not teardrop shaped. The smallest, like those that make up drizzle or Scotch mist, are almost perfectly spherical. As they get larger, into the five millimeter range, their bottoms flatten out with air resistance and they assume a sort of bun-like profile. Raindrops larger than five millimeters get a dimple indent in the bottom of their buns and begin to look more and more like mushroom caps or fat parachutes. Nine millimeters is the upper limit for raindrop size. Any larger than that and they break up into smaller drops because, at higher terminal speeds, air resistance increases by the square of the velocity.

  Another factor affecting the speed of the fall is the density of the atmosphere. A raindrop on Mars would fall faster than one on Earth, even with lower gravity, because there is very little air resistance. Our own planet has probably had variations in the density of its atmosphere over the millennia, but we have had no way of measuring those fluctuations until recently, when fossils of raindrop impressions were discovered on a farm near Prieska, South Africa. A layer of fresh ash from a volcano preserved these traces as the ash transformed into rock. When the rock was dated, it turned out that this passing shower occurred 2.7 billion years ago. Scientists analyzing the tiny impact craters realized that they were more than a time capsule, they were a snapshot of the thickness of atmosphere during the Great Oxygenation Event. They estimated that the ancient raindrops measured 3.8 to 5.3 millimeters across and that, given the radius of the splashes, the atmospheric density was not that much different from today. So the wind on our time traveler’s face would feel the same as any wind on Earth today.

  Aphoristic Showers

  “Moods light up the world.”

  Martin Heidegger

  “Lovely day, isn’t it?” my neighbor said this morning. I had to agree — sunny, warm, with just the hint of a breeze. She gestured at the sky. I looked up and noticed that, except for a few irregular shreds of cumulus fractus clouds, which are barely clouds at all, the autumn sky was unbroken blue. She was smiling, and I have to admit my own mood was so buoyant that finding a utility bill in my mailbox didn’t phase me at all. A sunny day lifts everyone’s spirits. As Marcel Proust wrote in Remembrance of Things Past, “A change in the weather is sufficient to recreate the world and ourselves.”

  The intimate relationship between weather and mood plays out in common sayings. To comfort someone who is under the weather, we offer them a ray of hope and reassure them that every cloud has a silver lining. An easy task is a breeze, but you can be snowed under by a difficult one. Furthermore, it seems we all contain our own internal weather. An optimist has a sunny disposition; a dreamer walks with her head in the clouds. Someone with anger management problems has a stormy temperament, and a fair-weather friend is fickle, definitely not right as rain. A lull before a conflict is the calm before the storm. Rainy days can bring on the blues: “Rainy day go away, come again some other day.”

  It’s hard to tell sometimes whether the weather is getting you down or if you’re just down. Seasonal affective disorder is definitely a case of the former, where the sufferer’s mood declines with the waning daylight hours of northern latitudes. People afflicted with migraines report that rainy, low-pressure systems bring on their worst headaches. But can the reverse be true also? Can our inner moods, by some subtle telekinesis, affect the weather? Being vainglorious creatures we sometimes think the weather is mirroring our emotions. In literature, this is called pathetic fallacy — the wind is angry, those gray clouds are sullen.

  Literary Rain

  Writers tease out the intimate implications of weather as experienced by emotional, sentient beings. In the sensorium of experience, the greatest writers have always been masters of inflection and analogy. Their summaries of phenomena are as precise, in their way, as the most detailed observations of science. And literature is replete with rainy days.

  It’s safe to say that gray, rainy days are moody or somber, but rainy nights can be gloomier still. Regrets and lost loves can haunt a poet like Edna St. Vincent Millay on a rainy night. Consider the beginning of her “Sonnet XLIII.”

  What lips my lips have kissed, and where, and why,

  I have forgotten, and what arms have lain

  Under my head till morning; but the rain

  Is full of ghosts tonight, that tap and sigh

  Upon the glass and listen for reply,

  And in my heart there stirs a quiet pain

  For unremembered lads that not again

  Will turn to me at midnight with a cry.

  Ray Bradbury wrote perhaps the bleakest passage about nocturnal rain in his novel Green Shadows, White Whale: “I went to bed and woke up in the middle of the night thinking I heard someone cry, thinking I myself was weeping, and I felt my face and it was dry. Then I looked at the window and thought: Why, yes, it’s just the rain, the rain, always the rain, and turned over, sadder still, and fumbled about for my dripping sleep and tried to slip it back on.” Bradbury was writing about a rainy night in Ireland, which has almost as much rain as England. Talk about dismal. If his character had lived in London, England, during the late Victorian era, his mood might have been even worse. For the entire m
onth of December 1890, the London weather bureau didn’t register a single minute of sunlight.

  Thomas Merton wrote about a mystical experience he had listening to the rain in darkness: “What a thing it is to sit absolutely alone, in the forest, at night, cherished by this wonderful, unintelligible, perfectly innocent speech, the most comforting speech in the world, the talk that rain makes by itself all over the ridges, and the talk of the watercourses everywhere in the hollows!”

  That’s more like it. Now we are in the poetic realm of the sublime and mysterious, and Merton is far from being the only writer to hear voices in the rain. In his novel Still Life with Woodpecker, Tom Robbins described the West Coast rain falling over an hallucinogenic landscape in Seattle: “The thin, gray rain that toadstools love. The persistent rain that knows every hidden entrance into collar and shopping bag. The quiet rain that can rust a tin roof without the tin roof making a sound in protest. The shamanic rain that feeds the imagination. The rain that seems actually a secret language, whispering, like the ecstasy of primitives, of the essence of things.”