Cold wave

“ In the last chapter we studied the progression of the cold wave of low temperatures in an easterly direction across the United States. Notice now the relation of the winds on the successive maps of our series to the movement of the cold wave. Place your wind charts and isothermal charts for the six days side by side, and study them together. The temperature distribution on the second day differs from that on the first. What are the chief differences? Examine the wind charts for these two days. Do you detect any differences in the wind directions or systems on these days? ”

“ The immediate contact of a cold current above a warm damp one is equally unlikely, unless the general atmospheric condition were greatly disturbed, which is the same thing as saying that wave clouds would not occur. ”

“ No matter how fiercely the sun might shine, life on the earth would be entirely destroyed by cold.
When water vapor, clouds, or dust motes intercept certain portions of the sun’s rays, they change them from vibrations in ether to the motions of molecules, and the motions of these molecules are expressed in a rise in temperature in the vapor, cloud, or dust. Earth radiations of heat, having longer and slower wave lengths than those that come from the sun, are more readily absorbed by the atmosphere. ”

“ In this illustration, colder air is north of warmer air. In Figures 3510a–3510d isobars are drawn at 4-hectopascal intervals. The wave tends to travel in the direction of the general circulation, which in the temperate latitudes is usually in an easterly and slightly poleward direction. Along the leading edge of the wave, warmer air is replacing colder air. This is called the warm front. The trailing edge is the cold front, where colder air is underrunning and displacing warmer air.
The warm air, being less dense, tends to ride up greatly over the colder air it is replacing. ”

“ Storms and Cold Waves Simply Great Eddies in the Atmosphere. Now picture in your mind that all the air inside the 30.2 isobar, as it flows inward, is rotating about the Low in a direction contrary to the movements of the hands of a watch, and you have a fair conception of an immense atmospheric eddy. ”

“ The prevalence of a stiff wind, especially the northwest wind of cold waves, equalizes temperatures to a remarkable extent; the minima of stations covering considerable areas rarely vary more than 1 or 2 degrees. ”

“ Save for the musical twang of splitting ice, now and then, along the river, a measureless silence descends upon the world. As the cold strengthens, in the northern heavens the pale aurora lifts its quivering arch.
The extreme cold is felt always in still weather. As the wind rises, so does the temperature. When sixty-eight below zero of Fahrenheit implies a calm, a rise of thirty-eight degrees is probable as the wind rises. ”

“ Fig. 714.—High tide and storm on the coast of Schleswig.
Heat, we know, is the effects of the rapid motion of small particles of matter, and is radiated from our bodies—so we feel cold; it reaches our bodies, and we feel warm. So air is heated or cooled by the sun, not in its absence, except when the earth and air have been so warmed during the day that the heat is given out by them long after sunset. We have read of the pressure of the atmosphere in the Physics section, and that warm air is lighter than cold air, as shown in the ascension of the Montgolfier balloon. ”

“ It is absorbed into the dry atmosphere. But when the day is “damp” we find that the air has nearly as much moisture as it can carry, and the steam is condensed, a portion falling in tiny drops like rain. This is proved every day in cold weather when ice is found in the windows—the cold air has condensed and frozen the water breathed out from our lungs, and snow has been known to fall in a ball-room when a cold current of air was admitted. ”

“ The intense and constant action of the sun’s rays in the torrid zone produces great heat, while the less powerful and frequently interrupted influence of his rays in the frigid zones induces extreme cold. Hence we have in one region heated air, in another cool air. Now, the effect of heat upon air is to expand it, make it light, and cause it to rise. The moment it does so, the cold air rushes in to supply its place; and this rushing in of the cold air is what we call wind. ”

“ The formation of a cloud tells us not only that vapor is being condensed in the air, but that warm and cool currents have encountered each other.
In the horizontal movement, the cold and warm currents overlap each other, the vapor-laden warm air from the equator rising over the colder current. A consequence is, the warm air ascends until its waves reach an elevation where condensation takes place along their crests, producing flecks and bars of cloud-caps of the aerial waves. ”

“ You will then perceive, as the weather grows warmer or colder, that the air contracts itself into a narrower space in cold weather and dilates in the warm, which will be exhibited by the rising of the water as the air contracts itself, and its depression as the air dilates. The sensibility of the air with regard to heat or cold is so delicate and exquisite, that it far exceeds the human touch, so that a ray of sunshine, the heat of the breath, and much more, that of the hand placed on the top of the tube, immediately causes an evident depression of the water. ”

“ Wind blowing from a large body of water is always heavily laden with moisture, which decreases the rate of radiation both day and night, but especially during the period of cold in the early morning when frost is liable to occur. Such winds, largely affected by the temperature of the water over which they have passed, modify the temperatures of both day and night. ”

“ The heated air charged with moisture rises over the sunward hemisphere, and flows off above, on all sides, toward the night side, while from the latter cold air flows in beneath to take its place. Along the junction of the two hemispheres the clouds and moisture are condensed by the intense cold, and fall in ceaseless snowstorms. ”

“ In England, where the action of such isolated clouds is less intense, the different electricities in different portions of the cloud, whose opposite and changing action produce all the phenomena, the condensation, the cold and congelation, the currents, etc., have been accurately ascertained. We can not get into the situation occupied by Mr. Wise. But every [Pg 390] man may observe these intestine motions occasionally, in the advance condensation of an isolated thunder-shower, in front of, but near the smooth line of falling rain. ”

“ When we perceive, even under the equator, certain mountains covered with eternal snow, upon observing the rapid diminution of temperature which the strata of the atmosphere undergo during ascents in balloons, meteorologists have supposed, that in the regions wherein the extreme rarity of the air will always exclude the presence of mankind, and that especially beyond the limits of the atmosphere, there ought to prevail a prodigious intensity of cold. ”

“ This suppression is, as I have said, occasioned by the cold winds, which fall from the air, bind the earth, freeze the waters, and shut up the emanations of the terrestrial heat during the time the frosts remain; so that it is not at all surprising that the cold in winter is in fact so much the greater as we advance further towards the climates where the mass of air, receiving the rays [321] of the sun more obliquely is for that reason colder. ”

“ Once forced from their anchorage, the first storm that arises drifts them to sea, where the beautiful law which renders ice lighter than the warmest water, enables it to float, and drifts southward a vast magazine of cold to cool the tepid water which bears it along—the evaporation at the equator causing a deficit, the melting and accumulation of the ice in the frigid zone giving rise to an excess of accumulation, which tends, along with the action of the air and other causes, to institute and maintain the transporting current. ”

“ The condensed aqueous vapors raised in the atmosphere by the sun and wind, converted into clouds, which fall in rain, snow, hail, or mist: their falling is occasioned by their own weight in a collision produced by contrary currents of wind, from the clouds passing into a colder part of the air, or by electricity. If the vapors are more copious, and rise a little higher, they form a mist or fog, which is visible to the eye; higher still they produce rain. Hence we may account for the changes of the weather: why a cold summer is always a wet one—a warm, a dry one. ”

“ Consider the case of a loud sound made near the surface of the earth. If the air were all at rest, and everywhere at the same temperature, the sound waves should spread out in hemispherical form. But if, as is generally the case, the temperature near the ground is higher than it is up above, then the part of the wave near the earth travels more quickly than that in the higher regions of the air. ”

“ On the other hand, the local contraction by cold during night is greatest over land, where the air is clear, dry, and calm, or nearly so, and least over the ocean, where the air is clouded, and loaded with moisture. As familiar illustrations of atmospheric movements result ing from local expansions by heat and contractions by cold, we may refer to the land and sea breezes, and what de pend upon exactly the same principle, the dry and rainy monsoons in different parts of the globe. ”

“ Such clouds reflect the undulations of lee waves formed in the atmosphere when stable currents of air flow over obstacles such as hills or mountains. An up-and-down wave motion may be impressed upon the air, provided that temperature and wind conditions are suitable. As the air describes its wavelike path, it alternately warms and cools, the warming taking place as it sinks into the wave trough and the cooling as it ascends to the wave crest. ”

“ Although the wind was no more than a good breeze, and the ocean was but little disturbed, there were those symptoms in the atmosphere and in the long ground-swells that came rolling in from the southwest, that taught the mariner the cold lessons of caution. We believe that heavier gales of wind at sea are encountered in the warm than in the cold months; but there is something so genial in the air of the ocean during summer, and something so chilling and repulsive in the rival season, that most of us fancy that the currents of air correspond in strength with the fall of the mercury. ”

“ You know a great many times when you go out into the wind how cold it feels, and yet if the wind would actually stop, you would think it warm. It is the wind that causes the rapid evaporation and makes the surface of the skin feel cold. As it is true that the moisture in the air acts as a blanket to us in our homes, it is likewise as true that the vapor in its natural form outside of the house acts as a blanket for the earth. ”

“ When air is comparatively warm, it will expand, and this air, which is heavily saturated is brought up by breezes onto the mountain range, which is cold, causing the air to lose its heat and contract and really force the water out of the air. The same principle applies to sea breezes bringing rain.
WINDS Winds are caused as a result of differences in temperature between the various layers of the atmosphere. A certain amount of air becomes heated and rises, and as explained before, expands. As the air expands, it becomes lighter, and because it is light it goes upward toward higher regions. ”

“ I then proceeded to account for the equable heat in the internal world, and the extreme cold at the icy hoop, upon principles which appeared to me to be very obvious.
In the first place, the sun’s direct influence is exerted, on an equal portion of the globe at all times; which influence is felt, on the external surface, only where it is directly exerted. In such places it is felt intensely, but from the free action of the external atmosphere, so soon as that influence is withdrawn the heat escapes and flies off rapidly, generating cold in its passage, or by evaporation as we express it. ”

“ Does there seem to you to be any definite system, of any kind, in our changes of temperature? In what ways are people in general affected by hot weather? By cold weather? What difference does a very hot or a very cold day make in your own case?
Wind Direction and Velocity.—Wind is an important meteorological element because it has many close relations to human life. It affects very markedly our bodily sensations of heat or cold. A cold, calm day is pleasanter than a cold, windy day. On the other hand, a hot, calm day is usually much more uncomfortable than a hot, windy day. ”

“ The cold air descending from above, as it penetrates our warm region full of watry particles, condenses them, renders them visible, forms a cloud thick and dark, overcasting sometimes, at once, large and extensive; sometimes, when seen at a distance, small at first, gradually increasing; the cold edge, or surface of the cloud, condensing the vapours next it, which form smaller clouds that join it, increase its bulk, it descends with the wind and its acquired weight, draws nearer the earth, grows denser with continual additions of water, and discharges heavy showers. ”

“ Frost, Ice, Snow and Hail, do not proceed from the coldness of the air, but rather the coldness of the air proceeds from them; for Ice, Snow, and Hail, proceed from cold contraction and condensation of a vaporous or watery substance; and, as Frost and Snow cause air to be cold, so Thunder and Lightning cause it to be hot, so long as they last. ”

“ Cold air comes from the side to take the place of hot air that rises.
When the rays of the sun heat an area of the earth, the air over such a place expands and becomes lighter, naturally rising, and the result of this is that the winds are produced by cool air moving in to take the place of the heated air. This cool air moves in from all directions. When such a thing happens at any point on the earth’s surface, it is known as a storm center, an area of low pressure. ”