Popular Science Monthly/Volume 85/September 1914/The Paradox of the East Wind
|THE PARADOX OF THE EAST WIND|
By Professor ALEXANDER McADIE
BLUB HILL METEOROLOGICAL OBSERVATORY
ABOUT ten miles south of Boston, on the highest land within sight of the sea from Maine to Florida, is a well-known meteorological observatory, founded some thirty years ago by a young graduate of the Massachusetts Institute of Technology. The founder, Lawrence Botch, became in time the pioneer explorer of the upper air, contributing much to our knowledge of air motion at different levels. In collaboration with Teisserenc de Bort, he may be credited with inaugurating the campaign which resulted in the important discovery of the double character of our atmosphere, as shown by the two great divisions of the stratosphere and the troposphere.
A few years before his death, Botch, who was then professor of meteorology at Harvard, remodeled the Blue Hill Observatory and on the walls of the new library placed eight symbolized figures of the winds. These were copies in relief of the winged human figures on the frieze of the not-too-well-known Tower of the Winds, which has stood for twenty-odd centuries at the base of the hill crowned by the Acropolis.
The Greek was a past-master in the art of personifying natural phenomena and these figures of the winds are ornamented, clothed and posed so as to suggest the characteristic feature of the particular direction represented. Boreas, an old friend, representing the north wind, is a determined-looking fellow, warmly clad but active in spite of his many wraps and heavy buskins. He carries a conch shell and has been blowing it. The sculptor meant, of course, to represent the boisterous roaring of the north wind, especially noticeable where the air in its passage comes over some range or group of hills. Of all the winds, Boreas is the noisiest. But it is not so much with Boreas, or his companion on the left and fellow noise-maker, the ruffian Skiron, warder of the northwest winds, that we are concerned, as with the east wind, the hopeful, open-faced Apheliotes. Apheliotes Nov. Ang. is perhaps an unfamiliar phrase yet it is only the classical rendering of a very familiar expression, namely, the east wind of New England. And many speak of the east wind as if it belonged to New England alone, associating this stream of surface air, a very shallow current, as we shall show later, with the coast north of Cape Cod, although it prevails along the entire Atlantic seaboard.
It is a wind from the sea, and whether it comes as the gentle, welcome sea-breeze of summer or as the sea-turn due to the advancing cyclone from the west, it is still a recognizable ocean wind. Such winds are regarded in most lands with favor. Why then, do we, of the eastern states, hold it in ill repute? At Athens, the east wind, the wind from the sea—the Apheliotes of the Tower—is typified by a young man with hair flowing in every direction. The youth has a fine open countenance and holds with both hands the skirts of his mantle which is filled with fruits and flowers. Along the shores of the Ægean, tillers of the soil, prone to take the weather an-cha-Allah (as Allah wills), bow when the east wind blows, echoing the words of one Dervish Mustapha in his greeting
This is a divine wind, for it wafts the blessings of Allah to us from Mecca.
On the Atlantic coast, as elsewhere in the United States, the prevailing winds are westerly. In fact the general movement of the surface air in temperate northern latitudes is from west to east. It is interesting and perhaps worth while to speculate on the climatic changes which would occur if the prevailing flow of air were reversed and the surface current moved from east to west. Then the east wind, the Apheliotes Nov. Ang. would become the prevalent wind. It would not be as now, a shallow intermittent current, but would extend to some height. The Atlantic states would have a balmy, equable climate, with occasional storms from the sea preceded by west winds, rather dry, and followed by moderate east winds and showers. The climate would be like that of Bermuda. East of the Mississippi there would be fewer hot spells, likewise fewer freezes. The cold wave which now follows the "low" would be unknown. The climate of the country west of the Rocky Mountains, however, would be rigorous. Temperature changes would be pronounced on the Pacific coast.
Let us examine now the records of the flow of the air from sea to land and from land to sea, at different levels, as shown by the Blue Hill records. Owing to the sensitiveness of the instruments and the open character of the scales employed, also because there has been no change in exposure or methods, the data are thoroughly comparable and in themselves constitute a unique and valuable contribution to American ærology. It is doubtful if at any other station in our country records of wind direction and velocity are so detailed and complete. Checked by numerous experiments with kites and balloons, the records show that there is twice as much wind from the west as from the east. This will surprise many, for the impression is widespread that the climate of the Atlantic seaboard, is determined primarily by the east wind. On the contrary, west winds dominate and control both by duration and velocity. The indictment may seem somewhat sweeping; but so far as we can at present determine, the west and northwest winds are responsible for the severity of our winter; and the southwest wind for the heat of summer. Counting the actual hours of flow of air in different directions, it appears that the west prevails one fifth of the time, the northwest, nearly as long, and the southwest, one sixth of the whole period. In a year, the west wind blows 1,739 hours, the northwest 1,609 and the southwest 1,412. The total duration of all winds from easterly points of the compass is but 1,950; and the ratio of east to west is as four to ten. The east wind by itself prevails only six hours in a hundred and so can hardly be a controlling factor of the climate. But some one may say: "Granting that the east wind does not blow as long as the winds from other quarters, possibly it blows harder?"
No, just the opposite is the case. The mean velocities in meters per second from sea-level up to a mile, are NW. 12, W. 12, SW. 11, N. 11, S. 10, NE. 9, SE. 9 and E. 6. This proves that the east wind is the feeblest of all the winds. Moreover easterly winds blow more frequently in summer than in winter. The east wind is also the current of most uniform velocity, i.e., the least gusty, while our friends Boreas and Skiron true to their reputations are genuine gust makers. The period of greatest gustiness or instability, is the afternoon. All the winds increase in velocity with elevation up to a certain height; but the east and northeast winds are not deep and at an elevation of two kilometers (6,562 feet) these winds rarely occur. There are two kinds of east wind, the cyclonic wind which is moderately strong; and the sea-breeze which is only a few hundred feet in depth. The latter occurs on clear, warm, quiet days and never when the pressure distribution is favorable for turbulent conditions. It does not originate on land but comes in from the sea and seems to push away slowly the quiet, stagnant air in front. The ripples on the water as the breeze works its way landward look like schools of mackerel. On very quiet warm mornings the breeze may arrive as early as ten o'clock. It veers slightly as the sun gets half-way down and dies away as gently as it began. It does not penetrate far inland and its effect in lowering the temperature is limited to a few miles back from the shore. It comes too at a season when the air-gods seemingly are willing to rest, when the storm frequency is a minimum, when the Atlantic and the land have respite from the strenuous succession of storms. Then ceases for a while the rapid alternation of "high" and "low," the alternation which causes the characteristic changeableness for which the east wind is made scapegoat.
Truly men have much to learn about the medium in which they live, the very air they breathe. Paradoxically the orchardist blames the frost, as he sees it, for the damage to his crop, whereas the congealed water in the process of solidifying retards the fall in temperature, giving out in the unequal fight its own latent heat of fusion, some 80 calories per gram of ice, plus the latent heat of condensation, some 596 calories per gram of water. Similarly men blame the breath of old ocean, the invisible vapor brought in by the east wind, calling it chilly, damp and disagreeable; forgetting that the cold has been caused primarily by the wide-sweeping western winds. Certainly Apheliotes is a water-bearer; he bears and pours, ministering to the desiccate air even as the garden lover bears and pours upon the parched and thirsty beds. For the service rendered, this wind from the water gets small praise, while noisy Boreas and blustering Skiron driving all warmth and moisture before them pass approved of men as health givers.