Wind speed

“ In Paris, the wind speed exceeds thirty-four miles per hour on only sixty-eight days in the average year, and exceeds fifty-four miles on only fifteen days. Observations at Boston show that the velocity of the wind exceeds twenty miles per hour on half the days in winter and on only one-sixth the days in summer. ”

“ The force of the wind on a surface placed squarely across the flow of air increases roughly with the square of the wind speed. For this reason, it is a good approximation to say that an eighty-mile wind is four times as destructive as a forty-mile wind. ”

“ Further, that the greater the speed the greater the fluctuations, so that a high wind has to be regarded as "air moving in a tumultuous mass," the velocity at one moment perhaps forty miles an hour, then diminishing to an almost instantaneous calm, and then resuming. "In fact, in the very nature of the case, wind is not the result of one simple cause, but of an infinite number of impulses and changes, perhaps long passed, which are preserved in it, and which die only slowly away." ”

“ The velocity with which the wind moves from the High toward the Low depends on differences in air pressure, modified in the lower stratum by the friction offered in passing over surfaces of varying degrees of roughness, the speed being greater over a water surface with the same difference in air pressure than over a level unwooded prairie, and greater over the open prairie than over an irregular wooded area. ”

“ If there is so much uncertainty in forecasting the path of a disturbance at sea, how much more uncertain must it be on land? Elaborate statistics of the average daily movement of various types of storms have been officially published. The average speed of storms [Pg 43] (not wind speeds) across the United States is 11 metres per second or 25 miles an hour. Storms travel more rapidly in winter than in summer, about half again as fast ”

“ In the case of winds, the inertia of the moving mass becomes what is commonly termed “wind pressure” against any object not moving with it at an equal speed. The following table gives the measurements of wind pressure, as recorded at the station on the Eiffel Tower, for differing velocities of wind:
In applying this table, the velocity to be considered is the net velocity of the movements of the airship 32 and of the wind. ”

“ By movement we do not refer to the direction of the wind at any particular point, but the onward movement of the whole cyclonic system, which is usually from twenty-five to thirty miles an hour, but in some cases the speed is much greater. ”

“ Where, for example, the speed of the air is increased along any level of an air stream, the pressure is lessened, and conversely. Thus, if the wind blows squarely against the front of an isolated house, the speed will be greatly checked at the center front, 372and accelerated at both sides and over the roof, thereby increasing the apparent barometric pressure on the front, and lessening it on the sides and over the top. A similar effect may be observed when the air flows round the hull and framing of air craft. ”

“ Between two seas the sea-bird's wing makes halt,
Wind-weary; while with lifting head he waits
For breath to reinspire him from the gates
That open still toward sunrise on the vault
High-domed of morning, and in flight's default
With spreading sense of spirit anticipates
What new sea now may lure beyond the straits
His wings exulting that her winds exalt
And fill them full as sails to seaward spread,
Fulfilled with fair speed's promise. ”

“ There are many observations which an intelligent traveler can make, even from a car-window, although a slower method of progression is, of course, to be preferred in such a study. "Wind velocity may be reasonably accurately estimated, after a little practise, by noting the effect of the wind in blowing trees, or in producing waves of different sizes in lakes or on rivers. The prevailing wind direction can often be very accurately determined by observing the slant of wind-blown trees, or again, by taking note of the effects of wave action on the leeward side of a lake or pond. ”

“ The greater velocity of the westerly winds than the easterly ones is well known I believe in every climate of the world; which may be thus explained from the theory above delivered. 1. When the air is still, the higher parts of the atmosphere move quicker than those parts which touch the earth, because they are at a greater distance from the axis of motion. 2. The part of the atmosphere where the north or south wind comes from is higher than the part of it where it comes to, hence the more elevated parts of the atmosphere continue to descend towards the earth as either of those winds approach. ”

“ Certainly the wind had wiped away all traces of the emotional storm from Douglas’s countenance. The young man by her side could but admire the pure profile presented to him, with its soft, girlish lines but withal a look of strength and determination. ”

“ The rotation of the earth deflects the movement of the air, giving a westerly motion to the winds. Their force and direction are best studied from the monthly pilot charts published by the United States Hydrographic Office. Although the pilot charts refer specifically to ocean winds, the general information published, so far as wind direction is concerned, applies to land winds also.
The strength of the Trade Winds varies according to latitude and also according to season. The velocity is highest near the edges of the belt and lowest at its center ”

“ A current of air increases in velocity where the space of its passage is straitened: the same wind which was moderate in an open plain becomes violent in passing through a narrow passage in a mountain, or between two [100] lofty buildings; and its most violent action is at the top of these structures or mountains, for air being compressed by these obstacles, its density and mass becomes increased, and as the velocity remains, the force or momentum of the wind naturally becomes much stronger. ”

“ Moreover, the weather map does not indicate the true flow of the air, for observations of the wind made at the [Pg 28] ground tell only a part of the story of the balance which the flowing air must maintain under the action of various forces, such as gravitation, rotational deflection, centrifugal tendency, and the various expansion and compression forces.
The winds near the ground are modified both in velocity and direction by friction. The free flow is often interfered with by topography. ”

“ The calculations performed by me show, further, that for the observed velocities of the wind there may be formed in the atmosphere not only small waves, but also those whose wave lengths are many kilometers which, when they approach the earth’s surface to within an altitude of one or several kilometers, set the lower strata of air into violent motion and must bring about the so-called gusty weather. ”

“ Being expanded and puffed out above the general atmospherical level, but retaining its velocity—for the supposition is that it moves without friction—and returning through the upper regions, it would flow back as it went, viz., as a westerly wind, and arrive at its null belt in the direction of the meridian. But the wind has friction, and is resisted in every movement; the atmosphere partakes of the spheroidal form, which has been impressed upon the earth itself by its axial rotation. ”

“ Convection currents between upper and lower air strata, it is suggested by Koppen, explain diurnal variations in wind velocity and direction. At low stations the maximum velocity occurs at the time of the highest temperature, while at high stations the reverse obtains. ”

“ It is awfully hot down here but just when it is so hot that you feel you must turn over on the other side to keep from burning and to brown evenly, why a wind comes up they call “a norther” and you sizzle like a red hot poker stuck into cold water. A norther is about the coldest and most penetrating thing I have ever struck. We never seem to catch cold, however. The norther blows all the germs off of one, I fancy. ”

“ The lower atmospheric strata are retarded by friction against the earth, and the upper ones by those immediately below them; the velocity of translation, therefore, in the case of wind, increases from the ground upward. This difference of velocity tilts the sound-wave upward in a direction opposed to, and downward in a direction coincident with, the wind. ”

“ Hence, what would simply be a north or south wind but for the earth’s rotatory motion, becomes a north-east and south-east wind as it approaches those regions where, the velocity of the globe being so much greater than where it originated, it lags behind it in its easterly course. ”

“ It is not enough that we have the evaporation of moisture that will ascend into the higher regions of the air and there be condensed into cloud and possibly rain, but we must have the means for distributing these conditions over a large area, and for this purpose we have the phenomenon of wind. Why the winds blow can be accounted for to a certain extent,—we might say to a large extent,—but there yet remain many unsolved problems relating to wind and weather. Of the phenomena of wind we will speak more fully in a future chapter. ”

“ The velocity of these vapors, though not necessarily in reality greater than that of the central clouds, appears greater, owing to their proximity, and, of course, also to the usual presence of a more violent wind. They are also apparently much more in the power of § 4. They are subject to precisely the same great laws.the wind, having less elastic force in themselves; but they are precisely subject to the same great laws of form which regulate the upper clouds. They are not solid bodies borne about with the wind, but they carry the wind with them, and cause it. ”

“ By painstaking experiment with delicate instruments, specially constructed, the Professor shows that wind in general, so far from being, as was commonly assumed, mere air put in motion with an approximately uniform velocity in the same strata, is, in reality, variable and irregular in its movements beyond anything which had been anticipated, being made up, in fact, of a succession of brief pulsations in different directions, and of great complexity. ”

“ With a temperature of 75° and wind velocity thirty-two miles an hour on the ground, the temperature was 38° and the wind velocity thirty-two miles an hour at the highest point reached, while the highest wind velocity recorded was forty miles an hour at 11,000 feet. ”

“ Generally speaking, the atmosphere is always in motion, and moving air is called wind. Our meteorologists first studied winds near the surface of the ground: it is only of late years that high altitude measurements have been considered practically desirable. Now, records are obtained by the aid of kites up to a height of nearly four miles: estimates of cloud movements have given data on wind velocities at heights above six miles: and much greater heights have been obtained by free balloons equipped with instruments for recording temperatures, pressures, altitude, time, and other data. ”

“ If winds are due to such a simple mechanical causation as the production by the sun, of a rarefied atmosphere, the colder air rushing in from all sides into the empty spaces, we should hardly expect to find any definite currents bounded by well-defined limits; much less should we look for transverse and opposite currents going like messengers at varying rates of speed, some slow, and others exceedingly swift. ”

“ The principal one is obvious; that you can only go just where the wind will take you; but there is an advantage corresponding to this in the quietness and steadiness of the motion, and it is not at all improbable that, with the rapid advances which are being made continually in the science of meteorology, the laws of winds will be ascertained sufficiently to enable the aeronaut to find one which will carry him in the general direction in which he wants to go, on most occasions, by choosing a proper elevation. ”

“ To state the fact more accurately: such wind-velocities as prevail at sea-level in Adelie Land are known in other parts of the world only at great elevations in the atmosphere. The average wind-velocity for our first year proved to be approximately fifty miles per hour. The bare figures convey more when they are compared with the following average annual wind-velocities quoted from a book of reference: Europe, 10.3 miles per hour; United States, 9.5 miles per hour; Southern Asia, 6.5 miles per hour; West Indies, 6.2 miles per hour. ”