Pageviews past week

Saturday, July 9, 2011



from The Song of the Sky by Guy Murchie Jr. being an excerpt from pages 143-157 from the first edition of his book published in 1954 by The Riverside Press, Cambridge, Ma.

Devastating as is the hurricane in its vast strength, however, it is far behind the tiny tornado in concentrated velocity. Named from the Latin tornare, “to turn”, and variously described by Pliny the Elder, Seneca, and Lucretius, this frenzied whirlwind plays hornet to the hurricane’s elephant. It has its corresponding local names from the tourbillomn of France to the piao of China, its waterspout variants from the dancing trompa of the black Sea to the descriptive skypompe of the baltic.

While the hurricane, cutting a swath two or three hundred miles wide and sometimes ten thousand miles long during its fortnight to a month of rampage, blows with a velocity known to have exceeded 200 m.p.h. at its highest fury, the little tornado’s path is rarely as much as half a mile wide, usually less than a couple of dozen miles long, and it seldom outlives the hour. Yet the air whizzing around the tornado’s vacuous center moves with a speed estimated at from 200 to 800 m.p.h. More accurate determination of tornado velocity has not been made at this writing, for the good reason that on rare occasions when anemometers have happened to be in its path, they have been wrecked by the wind itself-committing a kind of meteorological suicide.

Like the hurricane, the tornado is conceived in heat and turmoil. It may appear in almost any country, and has been reported in every one of the United States. statistically, the most like;y place in the world to meet one is in eastern Kansas late in the afternoon of a sultry day around the end of May, and thye are fairly common any place east of the Rocky mountains, where the cold dry winds from the north or west meet the warm moist airs from the Gulf.

Thunderstorm weather is ideal for tornado breeding, with violent heat rivers bearing the air upward like a giant drain in reverse, the black thunderheads serving as the inverted bottom of the tropospheric bathtub out of which the air is being sucked aloft in a swirling effusion.

The dynamics of it is not really so simple, however, and W. J. Humphreys, authority on physics of the air, has listed “twenty-six conditions normally associated wit the occurrence of tornadoes.” Although there is always open season on interpretation of tornado statistics, the checking of which in the field is usually as haphazard as it is hair-raising, meteorologists are largely agreed on the basic nature of the wind gone wild.

In general terms, the consider the tornado as a small focal point in a large turbulence- and eddy stirred by the clash and mixing of two opposite kinds of air: (1) warm, buoyant, expanded, humid air that tries to rise up from the lower levels and (2) cool, heavy, dry air that prefers to sink down from the shifting heights. When a polar air mass is drifting along from the northwest, for instance, tornadoes sometimes appear from fifty to a hundred miles ahead of it while the lower wind is still blowing warmly from the southwest, because the over-reaching “upper cold front” of advance dry air creates top-heaviness, manifesting itself usually as a squall line of thunderstorms where the hot lower air tries to chimney its way up through the unstable roof-where any persistent updraft may be caught (like the baby hurricane) between conflicting winds and set whirling before the lash law of angular momentum.

Of course this is by no means the only birthway of the tornado, which can sprout directly from a giant typhoon or grow out of the updraft of a man-made fire. The hot black smoke from a burning oil field in California in 1923 generated ‘hundreds of whirlwinds, one of which was violent enough to kill two people and wreck a house,” and during that same year in japan four full-fledged tornadoes were reported to have emerged like phoenixes out of the fires that followed the great Tokyo earthquake on September first.

While small in horizontal area as compared to a hurricane, the tornado can be just as tall, and the great twister that smashed through Worcester, Massachusetts, in 1953 was fourteen miles high at the cirrus top of its overriding thunderhead. The relationship between these two classic forms of cyclonic wind is shown more particularly by the fact that the tornado has an eye at its center also, and some meteorologists think there is a proportionate downdraft of relatively warm air in the eye’s middle (although none has yet aspired to prove it. In a few cases cool-headed observers have noticed the momentary calm and the clear air inside a large tornado eye (sometimes more than a mile in diameter), and several have remarked on the chill (not entirely psychological) felt during its passing. The coolth at the base of the vortex seems to be a generally accepted fact and is in accord with the well-known cooling effect of expansion (as in air released from a tire). Outside the vacuous vortex, conversely, the air is denser, warmer and there has been observed a surrounding downdraft that spirals inward near the ground just as definitely as the ferocious updraft spirals outward into the sky, like two forming, counterbalancing parts of an integral circulation as in the hurricane, in hot and cold currents of the sea, even as in the two-way flow of our human blood.

A glider pilot flying near a huge dust devil over a desert recently proved this to his own satisfaction, clocking the pouter downdraft at 1800 feet a minute, the air getting warmer (by adiabatic compression) as it descended. Near the ground a few hundred feet outside another whirlwind some ardent weather scout felt “hot puffs” of air moving inward toward the twister and measured them with his pocket thermometer at “about 20 degrees F. warmer than the prevailing air.

That sort of evidence is almost all that Science has to go on with tornadoes, but by putting together hundreds of hits into the meteorological mosaic, the weathermen have learned a good part of the over-all picture. They know that tornadoes need not be expected until there are signs of thunder about, for the pendant funnel always hangs down from a towering cumulo-nimbus cloud-bank, often one showing turbulence all over its under surface in the form of drooping eddy pouched called mammatus because they resemble breasts. but it is not the funnel itself that is to be feared. Rather it is the fast wind whirling around its base, the tornado’s outer collar that is usually black with raised dust and in which debris is continuously being sucked aloft, then inevitably hurled outward again in a wild fountain of nigritude.

So powerful is the terrific updraft that it has been known to lift tons of steel in its overwhelming spiral that at times must develop a vertical velocity of several hundred miles an hour! Although a tornado’s base is normally dragged along behind its more dynamic top, like a vacuum-cleaner hose behind its motor, Meteorologist Edward M. Brooks of St. Louis University cites one over eager twister that somehow ran ahead of its thundercloud, then immediately created a new one that shot up to “35,000 feet in one minute.

Sometimes the dark funnel grows so fat in its upper turbination it has been described as balloon-shaped. Sometimes it is thicker at the bottom than the top, like a tree, or it may become wasp-waisted with the narrowest part halfway up the trunk, a virago in pirouette. At other times it dwindles to a snakelike thinness, now black as tar, now fading into ghostlike transparency.

There is something weird about an invisible tornado descending upon a town, like the unseen angel of death, but exactly that has been known to happen when the vortex was passing through unusually dry air- too dry for condensation. sometimes the clouds above the tornado show a faint greenish or yellowish reflection from the earth, and when the funnel is well of the ground it usually remains a steamy gray, now and then turning almost as pale as milk. On rare occasions, in winter, it may dip low and become suddenly pure white, as the time a tornado passed over a snow field on the east slope of the Wasatch Mountains in plain sight of Salt Lake City airport, sucking tones of snow up into its maw like some kind of rotary snowplow, releasing an intense miniature blizzard in its wake.

Most witnesses of tornadoes do not remember them as having any particular smell other than that of the raised dust, yet a few reliable and sensitive observers have reported a distinct odor or sulphur and ozone-perhaps the chemical consequences of vacuous air and electrical discharge. Certainly tornadoes are associated with a special lightning of very delicate lace-like texture and of almost continuous flickering frequency. Pilots flying blind through thunderstorms have been known to take evasive action after recognizing this tornadic trademark, usually climbing above 15,000 feet to avoid the risk of running into a hidden vortex at its level of greatest frenzy.

What can happen in a blind collision between and airliner and a tornado ambushed in a cloud is suggested by the fate of the DC-6 that is thought to have run into a ‘stormspout” off mobile, Alabama, on February 14, 1953. All that is definitely known is that the bog plane was suddenly and mysteriously thrown out of control and spun or dove into the gulf, killing all forty-six persons aboard.

As to the sound of a tornado, the memories of all witnesses are usually quite definite. It has the roar of a thousand trains passing in the night. If more distant, the prolonged whine of a swarm of bees. Even from twenty-five miles away, the persistent bellow of a mature tornado has been noticed, and for as long as an hour before the storm’s arrival, keen ears have warned a population of the danger. The final roar is frequently augmented by nearly continuous thunder and often as not by a rattling obbligato of large hail mixed with shingles, nails, and assorted splintering boards.

The average recorded duration of the tornado’s passage over one spot is but 15 seconds, and its average total endurance along the ground about eight minutes. But many tornadoes are far from average. One midwestern twister was recorded as dawdling along in a continuous path for “seven hours.” Although the average swath cut by tornadoes, according to statistics, is thirteen miles long, this amazing storm started in missouri at noon and meandered eastward across the middle of illinois and southern Indiana, stopping only at sunset close to the Ohio border, having traveled 293 miles, “the longest continuous path of a tornado of which there is any authentic record.” An unusual but not unique feature of this one also was that no funnel of any sort was visible after the first hour, but just “a boiling mass of clouds” in which individual clouds “seemed to roll towards each other and downward, like the meshing of a pair of huge cog wheels,” no doubt sucked inward by the central vortex hidden somewhere in the very low cumulo-nimbus confusion.

In general, tornadoes last their longest over flat open country and travel fairly steadily in a northeasterly direction. Rough terrain, large buildings, or high hills are apt to change their course or bounce them back into the sky, but such wind barriers also have been known to spawn entirely new twisters. You might think that houses on hilltops or windward slopes would be more vulnerable to tornadoes than those in secluded valleys, but statistics do not bear this out. Instead, the record indicates that leeward slopes actually have suffered more destruction than windward ones, and that tornadoes have almost a great propensity for dipping into valleys as an elephant has for groping into peanut bags.

A Kansas whirler on June 5, 1917, after barreling over the wheatfields for thirty-five miles, “swept down the face of a a steep bluff sheltering the town of Elmont and demolished every house but one.” Others frequently have bored deep enough into river beds to suck them completely dry. One extracted all the water from a well thirty-six feet deep.

Tornadoes can be indecisive to the point of uncanniness too, and a few have been known to move in circles, make U-turns, figure-eights, and even stand spinning in one spot for nearly twenty minutes.

The best account of a close look at a tornado I have run across is the account of Will Keller, a Kansas farmer, who told it thus to Alonzo A. justice of the Dodge City Weather Bureau:

On the afternoon of June 22, 1928, between three and four o’clock I noticed an umbrella-shaped cloud in the west and southwest and from its appearance suspected there was a tornado in it. The air had that peculiar oppressiveness which nearly always precedes a tornado.

I saw at once my suspicions were correct. Hanging from the greenish black base of the cloud were three tornadoes. One was perilously near and apparently headed directly for my place. I lost no time hurrying with my family to our cyclone cellar.

The family had entered the cellar and I was in the doorway just about to enter and close the door when i decided I would take a last look at the approaching cloud. I have seen a number of these and did not lose my head, though the approaching tornado was an impressive sight.

The surrounding country is level and there was nothing to obscure the view. There was little or no rain falling from the cloud.

Two of the tornadoes were some distance away and looked like great ropes dangling from the parent cloud, but the one nearest was shaped more like a funnel, with ragged clouds surrounding it. It appeared larger than the others and occupied the central position, with he great cumulus dome directly over it.

Steadily the cloud came on, the end gradually rising above the ground. I probably stood there only a few seconds, but was so impressed with the sight it seemed like a long time. At last the great shaggy end of the funnel hung directly overhead. Everything was as still as death. There was a strong, gassy odor, and it seemed as though I could not breathe. There was a screaming, hissing sound coming directly from the end of the funnel. I looked up, and to my astonishment I saw right into the heart of the tornado. There was a circular opening in the center of the funnel, about fifty to one hundred feet in diameter and extending straight upward for a distance of at least half a mile, as best I could judge under the circumstances. the walls of this opening were rotating clouds and the whole was brilliantly lighted with constant flashes of lightening, which zig-zagged from side to side. Had it not been for the lightning, I could not have seen the opening, or any distance into it.

Around the rim of the great vortex small tornadoes were constantly forming and breaking away. These looked like tails as they writhed their way around the funnel. It was these that made the hissing sound. I noticed the rotation of the great whirl was anti-clockwise, but some of the small twisters rotated clockwise. The opening was entirely hollow, except for something I could not exactly make out but suppose it was a detached wind cloud (perhaps the tornadic counterpart of the hurricane’s eyelid.) This thing kept moving up and down. The tornado was not traveling at great speed. I had plenty of time to get a good view of the whole thing, inside and out.

Although the spinning speed of the vortex in such a storm has never been measured, plenty of indirect evidence has accumulated: the3 burnt look of trees stripped bare in the tornado’s wake, the imbedding of grass stems in wooden fence posts, even a case of a bean discovered “one inch deep in an egg without having cracked the shell.” The element of personal whimsy is of course proverbial with tornadoes, in the way they will pick out a one house yet leave the next untouched; or whisk one member of a family into the sky like magic; perhaps carry a cupboard full of crockery for a quarter of a mile and set it down without breaking a dish.

One twister whooshed a horse into the air among debris, horse flies, horse shoes and barn, allowing the terrified animal to alight unharmed half a mile distant. In another case a woman milking a cow saw the cow swept into a black funnel, leaving her sitting with a pail - but no cow. At Harleyville, Kansas, a whirler passing close to a farmhouse sucked the bedding and mattress from under a sleeping boy without so much as giving him a scratch. Another blew a lighted kerosene lamp for several hundred yards, leaving it still burning and undamaged though with a smoky chimney.

An exceptional account of tornadic violence as viewed from the sky is the report of an Air Force lieutenant who happened to be flying over Waco, Texas, when that city of 90,000 people was struck on May 11, 1953. As the twister bore down down Main Street, he saw plate-glass windows on both sides burst outward into the street in progressive waves, then opposing brick walls met each other as they crashed on top of the lanes of slow-moving cars, roofs falling into the wall-less interiors of the stores. A theater and a six-story furniture mart burst at the seams like slow bombs, both immediately collapsing into twisted heaps of wreckage.

The explosive tendency of an enclosed building when enveloped in a tornado vortex is obviously the result of the sudden decrease in pressure outside the building relative to its normal interior atmosphere of about fifteen pounds per square inch. When the barometer drops to twenty-three inches, as was unofficially recorded for the U>S: Weather Bureau in the eye of a tornado at Minneapolis on August 20, 1904, the pressure inside a closed house suddenly finds itself almost four pounds per square inch higher than outside. That means that the force of a ton is immediately exerted against every section of wall two feet square, several tons upon an average window, and nearly a thousand tons throughout the typical small house.

One of the statistics about tornado damage that used to puzzle the pious was the fact that so many churches were completely blasted, while the more numerous barrooms and taverns rarely suffered even minor damage. Only recently have church dignitaries come to realize the meteorological importance of the swinging door as a safety valve of pressure distribution. In the midwest, I hear, a few of the more enlightened ministers, sensing the moral of this tornadic bias for Bacchus, are taking to opening up their churches to the air and incidentally to the people all week long, day and night. This kind of church, to my weather eye, is likely to live longer not only in the secular gales but in some of the even less measurable flowings of the human heart.

If explosive air pressures can blow up buildings, of course, the same principle must apply proportionally to air and gas encased in living bodies, and it is known that persons killed by tornadoes are sometimes so swollen they look “like pigs” just after the passage of the vortex. This naturally applies to farm animals as well, and it is a common sight to see chickens not only blown up but plucked clean by a tornado. The fact that their feathers come off so readily even when the bird is unharmed had led some meteorologists to speculate that the air sealed into the feather quills actually explodes under the sudden provocation of the vacuum.

How significant the whirlwind is in the world, is hard to comprehend without checking its incidence in places near and far, looking at its lesser cousins, even perhaps glancing back from the perspective of time. Did you know that Washington D.C., has seen four tornadoes, all since Calvin Coolidge took the presidential oath? And that a dozen American cities have been struck at least five times each: Chicago, Cincinnati, Fort Smith, Indianapolis, little rock, Minneapolis, Oklahoma city, New Orleans, St. Louis, Terre Haute, Topeka, and Wichita?

England has had its share of tornadoes too, including one that romped through the very heart of London from Victoria Station to Euston on October 26, 1928, hurling chimney pots and cornices into the streets by the hundred. Others have struck such unlikely places as Moscow, Naples, Naples, Bourges, Delhi, the outskirts of of Tienstsin, Bermuda, many parts of Australia, even the Fiji Islands.

Although a good deal has been discovered recently about tornadoes, man has not learned how to outwit them. In fact their nature seems to have the curious effect of making them increasingly dangerous and destructive as populations grow. This seems to be because cities are a tornado’s natural prey, and effective warning systems very difficult to organize. People who would telephone an alarm of fire forgot to give the most important (and more unselfish) alarm of tornado, and the storm wreaks its worst havoc in cities where anyone caught in the streets is in mortal danger of being buried under flying debris. This is in striking contrast with hurricanes, which are mainly maritime, are progressively being disarmed through systems of warnings several days ahead (including a new balloon that automatically floats in a hurricane’s eye and continuously broadcasts its position), and which in any case seldom develop the wind force for collapsing buildings more substantial than cheap hangers, barns, and cottages.

The dust devil can be distinguished from the tornado mainly by its smaller size and the fact that it is dancing upon the earth rather than hanging from a cloud. To a meteorologist it is the trunk without the elephant.

Nonetheless, these small vortexes of sand are a common sight on the desert, and derive their power from updrafts of sun-baked air caught in natural eddies of the wind. Their average height has been estimated as 600 feet, maximum diameter about 100 feet, and they seldom last an hour. The biggest one on record was seen on the Egyptian desert near Cairo. It stood a mile high, and spun along for five and a half hours, obeying the general rule of thumb that a dust devil will stay alive as many hours as it has thousands of feet in altitude.

The centrifugal action of the devil’s vortex has the interesting effect of keeping the larger grains of dust or sand to the outside, making a gradation of progressively smaller particles toward the center where there is a suggestion of an eye of calmness, a fitful navel of cousinship with all the greater vortex storms of the world. Although the c updraft has been conservatively estimated to exceed thirty miles an hour vertically, the circumferential swirl must sometimes attain several times that speed in horizontal component. And the spinning devil has a curious predilection for higher ground - so much so that it will work its way uphill even if this means bucking a 3 m.p.h. prevailing down-slope breeze.

When the surrounding wind fields are turbulent, dust devils often contort themselves into curves of brown wind dervishes that lay nearly horizontal, steamrolling across the Mexican desert, now bounding over the hillocks, now tilting vertically to rise a thousand feet, now leaning downward again before the dry hot wind.

It is rare for a dust devil to grow into a real tornado, but it has been known to happen “in special cases” (according to Edward N. Brooks), and this sun-heated desert vortex still holds its reputation for mystery dating from ancient times.

The most epic whirlwind in history, I believe, was the one that miraculously arose during Mohammed’s first battle in the little valley of Badr near Medina in A.D. 624. Awakening from a brief spiritual trance just at the critical turn of the fighting, mohammed impulsively picked up a handful of dirt and flung it toward his enemies with a holy curse. Whether or not he intended literal fulfillment of the ancient prophecy that he who sows the wind shall reap the whirlwind, he mounted a horse and charged like a madman into the midst of the fray, followed by a very small dust devil that had curiously sprung to life from his cast handful of earth. As the wrathful prophet dashed forward it is said that the whirling spiral of dust behind him grew rapidly in size and speed until it drew abreast of Mohammed and swept with full fury into the masses of Koreishite swordsmen opposing him. In a few minutes the enemy were so blinded and confused by the unexpected storm that most of them turned in headlong retreat and the first Moslem victory was assured.

Waterspouts are basically similar to tornadoes and dust devils yet have a cleaner, smoother look because of the dearth of dust at sea and the seascape’s relative lack of friction. They also depend proportionately more on humidity for power, less on heat.

The commonest kind are what weather men call “storm spouts” or miniature tornadoes which, like all tornadoes, have their roots in cumulo-nimbus clouds. They often come in flocks. One ship saw thirty big ones in one day. The Gulf knows many of them in summer and they appear on the Great Lakes and most of the tropic and not-too-temperate seas. They often turn out when the sky is sultry and sullen, when there may be a bluish haze and surface suggestions of the moonier air currents. Suddenly a dark elephantine cloud with a hanging trunk in noticed, usually lengthening rapidly from the stubby tornadic funnel to the scrawnier, snake-like stem of the typical waterspout. As the winds carry it along, the thin whirling stalk may bow forward ahead of the cloud, dragging its spinning base after it willy-nilly, like a celestial vine goddess borne by her torso.

In most cases you can look right through the transparent bole of the vortex as it dips down to draw up what superheated air and spray it can collect just over the water. But it has enough condensed moisture to be not invisible, and occasionally even appears with an outer cylinder of falling mist descending around it like a fountain after being lifted in the inner whirl.

Although the amount of suction, of inward and upward flow, is not so great in a full, sea-going waterspout, the basic tornado nature of this wind is obvious from the fact that in many cases it starts as a land whirler, and may change from a waterspout to a tornado and back several times in crossing isthmuses, gulfs, capes, and straits, impartially demolishing houses one minute and boats the next. Few of them last long enough in one spot to be reliably measured, but a spout destined for particular renown happened to appear one day in August 1896 between Marta’s Vineyard and the Massachusetts mainland just as summer boarders were relaxing from lunch. As there were many trained observers on hand and the spectacle lasted thirty-five minutes, it became perhaps the best photographed and documented waterspout in history. It turned out to be “3600 feet high, 840 ft. in diameter at the top, 140 ft. in the middle, 240 ft. at the base.” Its “cascade” was “420 ft. high” and showered spray outward “to a diameter of 720 ft.”

The maritime equivalent of the dust devil is the “fair-weather waterspout,” which depends on a spontaneous local updraft of hot air over water strong enough to develop a durable and recognizable vortex - something that does not happen easily. however, in tropical sultry seas these spray devils, as they might be called, have been known to appear in impressive numbers - dancing over the shining waves like the colts of Erichthonios, lifting a salty mist many hundreds of feet into the sky, often assuming the forms of great dragons of the nether rainbow, or birds with fluttering winds. I read of one seen off the coast of New South Wales which became “very long, swaying and coiling like a serpent,” until “all at once it made a complete coil and vanished.”

The smaller ones, like picture - book houris, more fascinating than dangerous, and I have not known any modern ocean ship to suffer serious damage in encountering them - though flags have been torn, barrels and light gear whipped around, and fresh spray lashed against the captain’s door (indicating most water in a waterspout is condensed aloft rather than picked up below).

1 comment:

  1. Last photo isn't a tornado but a dust devil.