Jacques Wardlaw Redway

“ Usually the planes of contact between adjacent layers are indicated by clouds.
The air of adjacent layers, or strata, does not readily mix one with the other. Smoke, dust, and cloud matter, rising to the top, or sinking to the bottom of a layer does not always penetrate the adjacent layer. In the absence of strong winds such matter is apt to spread out laterally. Moreover, the aviator, in passing from one layer to another, is apt to receive a sharp bump at the plane of contact. In meteorology the plane of contact is commonly known as a ceiling or lid. ”

“ Sounding balloons do not find the decrease of temperature with increasing altitude to be regular; on the contrary, they encounter layers of air throughout which the temperature is practically unchanged. They also encounter other layers in which an inversion occurs—that is, the temperature rises with increasing altitude. In other words, instead of a uniform temperature gradient from ground level to stratosphere, the air consists of a succession of layers, differing in temperature, humidity and horizontal velocity of movement. ”

“ In flying from an adverse wind into a wind blowing in the direction in which the plane is moving, the drop is real but the downdraught is apparent merely.
There are actual downdraughts, however, which the airman is certain to encounter—because air going up must be balanced by air coming down. Just as water pours over a perpendicular ledge, forming thereby a cataract, so air is usually pouring over a steep scarp in a similar manner. The air over a plateau is apt to be colder than that several hundred feet below. More certainly it will be colder if it has traversed great fields of snow. ”

“ In Montana, Idaho and Alberta, the Chinook wind is far-reaching in its climatic effects. Both grazing and wheat-growing are made possible in regions that otherwise would be unproductive. The Chinook wind does not differ from the Foehn wind of Europe with which it is classed. In each case moist air drawn into a cyclone and pushed over a range, descends on the other side as a warm, dry wind. ”

“ The succeeding land breeze which sets in is apt to be a much stronger wind.
Mountain Valley Winds are common in all mountain regions. During the day, when the air is growing warmer, the wind blows up the valley; at night, when it is losing its heat the flow is down the valley. ”

“ 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 ”

“ Measurements have shown that ordinary updraughts may have a velocity of 10 feet per second; under a cumulus cloud of the thunderhead type the velocity may be as high as 40 feet per second. The updraughts that produce clouds give visible signs of their existence. Those caused during clear days by bosses of rock or by bare ground are not so easily detected. They are not apt to begin existence until the sun is high enough to heat the areas producing them; they rarely form during cloudy days. ”

“ The long downward slope over a smooth surface adds to the velocity of westerly winds. During winter months the cold-wave winds from Canada contribute a mass of air which, moving eastward, gives added velocity to the winds of this region.
The latitude of strongest winds in the United States is approximately along the forty-fifth parallel in the summer and a few degrees lower in winter. Winter months are the season of the strongest winds. ”

“ The Chinook begins as a moist wind on the windward side of a high range. As it is pushed upward along the mountain slope it is chilled by expansion below the dew-point, and condensation takes place. This liberates a great deal of latent heat, materially warming the air. The air is warmed still further by compression as it rolls down the leeward slope of the range. ”

“ The Blizzard is nominally a cold-wave wind which is sufficiently vigorous to pick up and carry loose snow; it is a northwesterly wind. Popular usage applies the name to any wind of gale force that accompanies a snowstorm. ”

“ Sounding balloons and kites furnished with recording apparatus are beginning to supply humanity with much-needed information concerning horizontal movements of the upper air; the airmen are furnishing knowledge of vertical movements.
Research in recent years shows that the updraught in equatorial regions is not uniform in force nor continuous at all times. Neither is the overflow of rising air toward polar regions uniform or regular. Sounding balloons occasionally have been carried toward the equator instead of away from it. ”

“ The Calms of Cancer and of Capricorn separate the belts of prevailing westerly winds from the Trade Wind belt. They are regions of high pressure and usually of cloudless skies. Vessels from ports of Europe and the United States crossed the Calms of Cancer when making West Indian ports. These calms were therefore a great drawback to commerce. Steam navigation has eliminated the waste of time and the loss of jettisoned cargoes; [2] but conditions more or less detrimental, which humanity cannot overcome, still exist. Much of the southwestern ”

“ To the airman, on the other hand, the horizontal air movements are usually less of consequence than the vertical movements. Good air for flying must be free from holes and bumps.
An air hole is not a vacuous space, nor is it one in which the density of the air is abnormally low. Sometimes it is a downdraught; quite often it is convectionally still air. If the airman has been flying over hot, bare ground, where the updraught is strong, his plane takes a drop when he passes over a patch of greensward, where the updraught ceases ”

“ Along coasts, the sea breeze and the alternating land breeze are the rule rather than the exception during a considerable part of the year. As a rule, the sea breeze extends rarely higher than 3000 feet. ”

“ West of the Mississippi River to the Rocky Mountains, the winds vary from southwesterly to northwesterly. They are steadier and stronger than those east of the Mississippi River. Southwesterly winds prevail much of the time. ”

“ The southeast winds are materially stronger than the northeast winds. The easterly component is the important commercial factor—hence the popular name. For the year their average is from 11 to 14 miles per hour, or from 2 to 3, Beaufort scale. [1] On the Pacific Ocean the Trade Winds are neither so strong nor so regular as in the Atlantic; on the Indian Ocean only the southern part of the belt is observable. ”