Heat haze

“ The steam heat was so great that one saw everything in a haze, and one felt one's own pores expand and one's clothes get quite wet with the absorbed damp in the atmosphere over-saturated with moisture. ”

“ They parry the sunshaft, break and color the light, increase the density of the envelope. Dust is always present in the desert air in some degree, and when it is at its maximum with the heat and winds of July, we see the air as a blue, yellow, or pink haze. This haze is not seen so well at noonday as at evening when the sun’s rays are streaming through canyons, or at dawn when it lies in the mountain shadows and reflects the blue sky. ”

“ A covering of cloud, fog, or dense haze may not only screen off the heat of day, but greatly retard the lowering of temperature at night by reflecting and radiating back to the ground much of the heat that it has lost. ”

“ These observations indicate that moisture is deposited on the dust-particles from air, which is not saturated, and that the condensation takes place while the air is comparatively dry, before the temperature is lowered to the dew-point. There is, then, no definite demarcation between what seems to us clear air and thick haze. The clearest air has some haze, and, as the humidity increases, the thickness of the air increases. ”

“ A VERY FISHY FARM. ONE OF THE OLD SAILOR'S YARNS. BY W. J. HENDERSON.
It was a sultry summer morning. The rays of the sun beat down with merciless power through an atmosphere which was saturated with humidity. The sea, flashing in long slanting lines of dazzling silver, melted away in the distance into a cloud of thick yellowish haze. There was no horizon-line, for this haze hung downward from the sky like a veil. It seemed to grow thicker and more dingy in appearance from hour to hour, and as it did so the atmosphere became more and more oppressive. ”

“ A haze lies about the Downs and softens their smooth outline as in summer, if you can but face the bleak wind which never rests up there. The outline starts on the left hand fairly distinguished against the sky. As it sweeps round, it sinks, and is lost in the bluish haze; gradually it rises again, and is visible on the right, where the woods stand leafless on the ridge. Or the vapour settles down thicker, and the vast expanse becomes gloomy in broad day. ”

“ When present as vapor the air is much more transparent, and it is a common expression to use, that when distant hills look "so close" rain may be expected shortly to follow, since the water is present in a state to precipitate in larger particles. But when present as small particles of water the hills look very distant, owing to what we may call the haze between us and them. In recent weeks every one has been able to see very multiplied effects of such haze. ”

“ After sundown the temperature of exposed objects falls, of some faster than others, depending on their capacities for radiation. Vegetation radiates freely and often falls to the dew point of the air, at which [90] time dew begins to form on it and continues to be deposited as long as the temperature remains above freezing. Now, here carefully note that if the dew point is above 32° the condensation of water vapor in the form of dew liberates latent heat, which usually will be sufficient to check the fall of temperature and prevent the formation of frost. ”

“ I suppose the thick air, as well as the transparent, is in both cases saturated with aqueous vapor;—but also in both, observe, vapor that floats everywhere, as if you mixed mud with the sea; and it takes no shape anywhere: you may have it with calm, or with wind, it makes no difference to it. You have a nasty haze with a bitter east wind, or a nasty haze with not a leaf stirring, and you may have the clear blue vapor with a fresh rainy breeze, or the clear blue vapor as still as the sky above. ”

“ But it is especially in the polar regions, where the eternal ice that reigns there constantly condenses the aqueous vapors under the form of haze, that this recomposition must be brought about; the more so, as the positive vapors are carried thither and accumulated by the tropical current, which, setting out from the equatorial regions, where it occupies the most elevated regions of the atmosphere, descends as it advances towards the higher latitudes, until it comes in contact with the earth in the neighborhood of the poles. ”

“ The ground and other solid materials are better radiators than air, and lose heat more rapidly, especially dark-colored materials. Consequently, the solid materials become colder than the surrounding air. This is why frost may form on exposed surfaces, particularly dark ones, when the air temperature remains above freezing. ”

“ A thick haze may be occasioned by an increased number of dust-particles with little moisture, or of a diminished number of dust-particles with much moisture, above the point of saturation. The haze is cleared by this temperature rising, so as to allow the moisture to evaporate from the dust-particles.
Whenever the air is dry and hazy, much dust is found in it; as the dust decreases the haze also decreases. For example, Dr. Aitken, at Kingairloch, in one of the clearest districts of Argyleshire, on a clear July afternoon, counted 4000 dust-particles in a cubic inch of the air ”

“ The exhalation and evaporation of the juices of trees, by whatever process effected, take up atmospheric heat and produce a proportional refrigeration. This effect is not less real, though to common observation less sensible, in the forest than in meadow or pasture land, and it cannot be doubted that the local temperature is considerably affected by it. But the evaporation that cools the air diffuses through it, at the same time, a medium which powerfully resists the escape of heat from the earth by radiation. ”

“ In all haze the temperature is above the dew-point. The dust-particles have only condensed a very small amount of the moisture so as to form haze, before the fuller condensation takes place at the dew-point.
At the Italian lakes, on many occasions when the air is damp and still, every stage of condensation [Pg 46] may be observed in close proximity, not separated by a hard and fast line, but when no one could determine where the clear air ended and the cloud began. Sometimes in the sky overhead a gradual change can be observed from perfect clearness to thick air, and then the cloud. ”

“ By heating water over a fire, bubbles rise from the bottom of the vessel, adhere awhile to the sides of it, and then ascend to the surface, and burst and go off in visible vapor, or, in other words, by evaporation. Water is evaporated by the heat of the sun merely, and even without this heat, in the open air. It is evaporated at very low temperatures, when fully exposed to the air. Even ice evaporates in the open air. We often observe in Winter, that a thin covering of ice or snow disappears from our roads, although there has been no thawing weather. ”

“ During winter the scene may at first sight appear nearly similar; the warm and flickering haze is changed for a light that can be seen into; the noise of the surge comes deeper through the clear air of frost, and with it at intervals hoarse sounds and shrill whistles, to which the ear is unaccustomed; acres of dark masses are seen, which may be taken for low rocks or scalps, and the line of the sea in the bays contains something which rises and falls, and seems as if it were about to be cast on shore with every coming swell. ”

“ Now evaporation takes place from animals as well as from vegetables, and the consequent cold is more than balanced by the heat of what may be termed the vital fire, which, like most other fires, burns brightest on exposure to a current of atmospheric air, being increased either by the result of the new chemical combinations having less capacity for heat, or by the stimulus of the fresh moving air exciting the vital action. Of the general influence of close forest on temperature, we are also not very well assured ”

“ In turn, relative humidity in a given air mass is controlled almost entirely by air temperature, and decreases as the temperature rises and increases as the temperature goes down. Because of the strong tie between air temperature and relative humidity, and between air temperature and solar radiation intensity, we can expect that whatever affects radiation intensity will also affect fuel moisture. Thus, the moisture content of dead fuel is normally higher at night than during the day, and greater in the shade than in the open. ”

“ It was found that the air from the thinly inhabited parts, that is, the north-west quadrant, was nine times clearer than the air from other directions with the same wet-bulb depression, and that the density of the haze was directly proportional to the density of the population of the area from which the wind blew. ”

“ The haze varies with the temperature and humidity of the atmosphere. At certain times and places it is almost as blue as the sky itself; but to see its colour, the attention must be withdrawn from the mountains and from the trees which cover them. In point of fact, the haze is a piece of more or less perfect sky; it is produced in the same manner, and is subject to the same laws, as the firmament itself. We live in the sky, not under it.
These points were further elucidated by the deportment of the selenite, plate, with which the readers of the foregoing pages are so well acquainted. ”

“ Under similar conditions, the heat capacity of dry soil and rock is 19 to 20 Btu/ft3/°F, and that of water is about 62 Btu/ ft3/°F. The high heat capacity of water is one of the reasons why the climate near oceans and large lakes is often more moderate than that of the climate further inland. The water absorbs and stores large quantities of heat during the summer without much change in temperature, and this tends to keep the air over the adjacent land relatively cool. In the winter the stored heat is released and warms the air over nearby land areas. ”

“ The general deductions which he made from his numerous observations during these two years are that (1) air coming from inhabited districts is always impure; (2) dust is carried by the wind to enormous distances; (3) dust rises to the tops of mountains during the day; (4) with much dust there is much haze; (5) high humidity causes great thickness of the atmosphere, if accompanied by a great amount of dust, whereas there is no evidence that humidity alone has any effect in producing thickness ”

“ If we wish to avert heavy rain or hail we must either cut off the supply of moisture, or else prevent the rapid expansion, or else throw dust upward into the air to cause cloudy condensation instead of rain. Apparently this latter process is carried out for us in nature when great forest fires afford enough particles of smoke to provide for the cloudy condensation of the free moisture. From the great clouds of smoke that attend these forest fires we get no rain until after a long time the heat that is in the cloud is lost by radiation, or until larger drops are formed by further expansion. ”

“ Without atmospheric dust, we should not have the glorious cloud scenery which we at present enjoy. We should have no haze in the atmosphere, we should have no twilight. Darkness would come as soon as the sun passed below the horizon.
The relative humidity of the air has a great effect on the dust by increasing the size of the particles of water vapor and so increasing the haze. The number of dust particles rapidly decreases with the amount of moisture present. ”

“ If the vapors arising from this enormous evaporation should all be condensed into clouds and converted into rain it would create a rainy season that would last throughout the year.
The humidity caused by an abundant rainfall in any low, hot country is usually enough to unfit it for human habitation. The combined effect of heat and moisture upon a fertile soil causes an excess of both growing and decaying vegetation that fills the atmosphere with noxious vapors and disease producing germs. The sultry air is so oppressive that it is more than physical endurance can bear. ”

“ Also, according to Captain Nash, there was probably some unstable air, which in itself indicates inequalities of temperature and/or humidity.
A thorough study of the situation showed that inversions of both temperature and humidity must have been present. In the summer of 1952 all the eastern states were suffering from an intense heat wave and drought, and the ground cooled rapidly after sunset, because of the lack of cloud cover during the day. In a period of heat and drought, the nightly cooling produces marked inversions favorable to extreme refraction or reflection. ”

“ Q. Why is hoar-frost seen only after a very clear night?
A. Unless the night has been very clear indeed, the earth will not have thrown off heat enough by radiation, to freeze the vapour condensed upon its surface.
Q. Why does hoar-frost very often cover the ground and trees, when the water of rivers is not frozen?
A. Hoar-frost is not the effect of cold in the air, but the cold of the earth (produced by excessive radiation) ; in consequence of which, the dew (condensed upon it) is frozen.
Q. Why is the hoar-frost upon grass and vegetables much thicker than that upon lofty trees? ”

“ Similarly in the day-time; the prevalence of vapour obstructs the passage of the solar rays, and the temperature rises slowly; but the absence of vapour causes a rapid rise.
The comparative absence of aqueous vapours in mountainous districts, facilitating radiation both solar and terrestrial, causes the heat of the sun to fall upon tourists with scorching effect.
When the air is what we call sultry, it is saturated with moisture, and evaporation from our bodies proceeds sluggishly. Hence the well-known oppressive sensation often felt in the summer months, especially in July. ”