Turbulence

“ It is clear that the wind gusts, swirls, and turbulences exist in the air, for they are quite evident when we watch a snowstorm and can see the snowflakes as they float, impelled now in one direction, now another, or as we see dry leaves carried about by a sudden gust of wind, or, even more clearly when over sandy plains we can see the great columns of dust ascending in the center of whirlwinds for hundreds of feet, carrying heavy particles to great heights. ”

“ Pilots quite frequently have reported that when a flash of lightning has passed near their planes they have felt a slight "bump." This would be a result of the pressure wave, but all available data indicate that there never have been any serious effects upon the stability and flight path of an airplane from this cause. We do not believe that lightning itself produced such severe turbulence as to have caused or contributed to this accident. ”

“ The water at the head of a weir is passing every instant from slower into quicker motion; but (until broken in the air) the fast flowing water is just as dense as the slowly flowing water. But a fan alternately compresses and rarefies the air between it and the cheek, and the violence of a destructive gust in a gale of wind means a momentary increase in velocity and density of which I cannot myself in the least explain,—and find in no book on dynamics explained,—the mechanical causation. ”

“ We hear the thunder, which discharged is
At same time with the fire and by same cause,
Born of the same collision.
In following wise
The clouds suffuse with leaping light the lands,
And the storm flashes with tremulous elan:
When the wind hath invaded a cloud, and, whirling there,
Hath wrought (as I have shown above) the cloud
Into a hollow with a thickened crust,
It becomes hot of own velocity:
Just as thou seest how motion will o'erheat
And set ablaze all objects,--verily
A leaden ball, hurtling through length of space,
Even melts. ”

“ The wind at a' a' a', continuing on with a circular motion, is represented thenceforward in its course by the curved arrows a e, a' e'. The wind coming from the east and the west has no direct impulse from diurnal rotation, but the wind on either side of it has, and hence the prime vertical wind is carried around with the rest. If, now, we imagine the disc C to be put in motion, and the storm to become a travelling one, we shall have to consider the composition and resolution of other forces also, such as those of traction, aberration, and the like, before we can resolve the whirlwind. ”

“ When the wind blows violently over the sea or land, it removes and carries off with it every thing that is not firmly fixed to the general mass. The clouds must appear straggling [Pg 76] and broken, carried according to the direction and the force of the wind, and blended with clouds of dust raised from the sandy shore. Branches and leaves of trees must be represented as carried along by the violence of the storm, and, together with numberless other light substances, scattered in the air. Trees and grass must be bent to the ground, as if yielding to the course of the wind. ”

“ It is a mixture of fog and storm; and even in our own day we cannot well account for the phenomenon. Hence many disasters.
We try to explain all things by the action of wind and wave; yet in the air there is a force which is not the wind, and in the waters a force which is not the wave. That force, both in the air and in the water, is effluvium. Air and water are two nearly identical liquid masses, entering into the composition of each other by condensation and dilatation, so that to breathe is to drink. Effluvium alone is fluid. The wind and the wave are only impulses ”

“ A violent storm of wind will make us tremble with fear, even in a strong well-built house, and in the midst of a populous city; yet we have seldom or never either seen or experienced the vast power of the enraged waves, when beat about by the winds, and dashed against each other till they seem transformed into froth and vapour, and the whole surface of the ocean presents to the eye a confused scene of immense watery mountains and bottomless precipices ”

“ If we should be in the track of a moving storm so that its center passed over us the winds at the beginning would blow in one direction and then there would come a subsidence until it had moved forward through the quiet zone, when we should feel the wind in the opposite direction until the area of low pressure had moved forward into the region of high pressure. The velocity of the wind will be determined by the difference of pressure between [Pg 96] the areas and by the distance that the areas of high and low pressure are apart. The steeper the grade the more rapidly the fluid will flow. ”

“ From steadfast Wind-belts, giving birth to steadfast Ocean-streams, we pass naturally to those fitful storms which lash the ocean into passing passions, and to the uncertain breezes of temperate climes.
There are currents and counter-currents, breezes and contrary breezes, winds from north and south and east and west, over the whole earth. Each separate movement of air helps to stir the waters of the sea into renewed restlessness. ”

“ North-westerly gusts of wind raised clouds of dust, and drove it in eddying drifts across the plain, till a thunderstorm with a smart fall of rain cleared the atmosphere, and allowed the sun to shine out a while before setting for the day. ”

“ That jumpy wind is an ugly sign. And look!—over there in the East—see that black line, low down? If that isn't a storm I'm a land-lubber. The gales round here are fierce, when they do blow—tear your canvas out like paper. You take the wheel, Doctor: it'll need a strong arm if it's a real storm. ”

“ This air, driving the vapour everywhere as it rushes along, produces gales and constantly increasing currents by its mighty blasts. Wherever the winds carry the vapour which rolls in masses from springs, rivers, marshes, and the sea, it is brought together by the heat of the sun, drawn off, and carried upward in the form of clouds; then these clouds are supported by the current of air until they come to mountains, where they are broken up from the shock of the collision and the gales, turn into water on account of their own fulness and weight, and in that form are dispersed upon the earth. ”

“ Among these are the real causes of different kinds of storms and how they originate; why they move forward and backward, carrying the lines and areas of high and low barometer, of isobars and gradients, with them, and why they cease; why the barometer indicates the approach of some storms in advance, but is useless in others; why it falls in some storms but rises in others; why a progressive storm travels against the prevailing wind, and why the wind changes during its progress; why there is a region of calm, and why the wind is stronger around this region of calm. ”

“ In summer, this falling of the upper layers in front of the storm is so apparent, that every part is seen to expand under the eye by perspective,—swelling, and curling, and writhing, like the surface of water or oil when just commenced boiling. ”

“ All winds are caused by the disturbances of indifferent equilibrium, and the motion of the air is to restore equilibrium.
2. These disturbances are caused through overheating of the layers of air near the surface of the earth by insolation, through unsymmetrical cooling of the higher layers by radiation, and through the heaping up of air masses caused by obstructions.
3. The disturbances are adjusted by ascending currents, wherein the particular species of acceleration occurs in which the increase of velocity is proportioned to the diminution of pressure. ”

“ Storms are a sort of violent readjustment in some polarized flow. You have a polarized circuit, a circuit of unstable equilibrium. The instability increases till there is a crash. Everything seems to break down. Thunder roars, lightning flashes. The master roars, the whip whizzes. The sky sends down sweet rain. The ship knows a new strange stillness, a readjustment, a refinding of equilibrium. ”

“ For here the wind not only has free scope, but it also finds another element, fluid but incompressible, to obey its impulse and follow in the course which it takes. If the WIND be like a wild spirit, the WATER is a mighty, irresistible body, endowed with motion by the other, and capable of any work, from the drowning of a sea-gull to the wrecking of a stately ship. ”

“ Hurricane-like gusts of wind sweep all around. The air is filled with continuous froth. The water no longer falls in drops, but in cascades—walls of water pour down, lashing our faces and hands painfully. ”

“ On a fine day evaporation produces a beautiful, quiet, and peaceable looking cloud, while the rolling eddies in front of a thunderstorm produce wild-looking masses of extraordinary shape, whose terrifying effect is enhanced by their inky look and by the ominous calm which precede an impending storm. ”

“ The little eddies of wind, which on a fine summer morning may be seen whirling up the dust and dry leaves in circles on a road, are exactly on the same principle as those mighty phenomena which become tornadoes, cyclones, and water-spouts, when they reach the ocean, where they may easily dismast and perhaps sink the largest line-of-battle ship. ”

“ The whole experiment serves to demonstrate that such an active gyration as we have ascribed to storms, and have proved, as we [Pg 275] deem, to appertain to some, at least, of the more violent class; must necessarily expand and spread out, by its centrifugal action, the stratum of atmosphere subject to its influence, and which must, consequently, become flattened or depressed by this lateral movement, particularly toward the vortex or center of the storm; lessening thereby the weight of the incumbent fluid, and producing a consequent fall of the mercury in the barometrical tube. ”

“ Heat and cold are thus combined; the equilibrium is distributed by a shock, the wave of wind issues forth and is distended, scattered and broken up in every direction in fierce streams. The dispersion of the gusts shakes the streaming locks of the wind upon the four corners of the horizon. ”

“ The arrows fly with the wind, and, as will be seen, almost without exception are moving towards the Low, or storm center, clearly demonstrating the effect of gravity in causing the air to flow from the several regions marked “High”, where the air is abnormally heavy, toward the Low, where the air is lighter. ”

“ At the rare spot, agitated as it is by winds from all directions, turbulent and boisterous weather, whirlwinds, hurricanes, rain, thunder and lightning, prevail. This kind of weather occurs most frequently in the torrid zone, where the heat is greatest. ”

“ If clouds look as if scratched by a hen
Get ready to reef your topsails then.
Mackerel sky and mare’s tails,
Make lofty ships carry low sails. The shift of the wind is different in the right-hand portion of the depression to what it is in the left-hand portion. In the former, on its first approach, the wind backs to south and falls very light to an almost ominous calm. The first puffs or “paws” of wind give rise to a noise in tree tops without much wind, and little eddies of dust, or to a whistling of the wind indoors, which are all well-known signs of rain. ”

“ Then this calm place will become stationary, and so remain, until, from some cause, one or the other of the meeting winds gains strength or loses force; then the stronger will press upon the weaker, and the calm belt will change place and adjust itself to the new forces. The changes that are continually going on in the strength of the winds keep the calm belt in a trembling state, moving now to the north, now to the south, and always shifting its breadth or its place under the restless conditions of our atmosphere. ”

“ This haps when sometimes wind's aroused force Can't burst the cloud it tries to, but down-weighs That cloud, until 'tis like a column from sky Upon the seas pushed downward—gradually, As if a Somewhat from on high were shoved By fist and nether thrust of arm, and lengthened Far to the waves. And when the force of wind Hath rived this cloud, from out the cloud it rushes Down on the seas, and starts among the waves A wondrous seething, for the eddying whirl Descends and downward draws along with it That cloud of ductile body. ”

“ A study of cyclones and tornadoes, or even of the little air-whirls which in hot weather lift the dust of our streets, shows that the particles of the atmosphere in rushing in toward the centre of upward movement take on the same whirling motion as do the molecules of water in the basin—in fact, the two actions are perfectly comparable in all essential regards, except that the fluid is moving downward, while the air flows upward. ”

“ From morn till night the silent footfalls of the ponderous vapours travel overhead, no sound, no creaking of the wheels and rattling of the chains; it is calm at the earth, but the wind labours without an effort above, with such case, with such power. ”

“ Another theory of storm-motion, strongly held by those who attribute all our storms to condensation of vapor, is that the track of the depression is always directed toward the region where the air is dampest. ”

“ You have, no doubt, frequently observed a single cloud pass, from which a violent gust of wind issues, but of no great extent. I have observed such a gust make a lane through the woods, of some miles in length, by laying the trees flat to the ground, and not above eight or ten chains in breadth. Though the violence of the wind be in the same direction in which the cloud moves and precedes it, yet wind issues from all sides of it; so that supposing the cloud moves south-easterly, those on the north-east side of it feel a south-west wind, and others on the south-west side, a north-east. ”

“ The wind blows in tempestuous gusts, and the seas are running higher than I have ever before seen them. The sky is covered with clouds, from which we receive frequent showers of rain, accompanied in a single instance, with thunder and lightning. ”