Evening Republican, Volume 16, Number 189, Rensselaer, Jasper County, 8 August 1912 — Rivers In the Air [ARTICLE]

Rivers In the Air

Did you know there are air-falls In the atmosphere just as real and apparent as are the waterfalls you have so often viewed with admiration and delight because of their natural beauty? In the famed Yosemite valley the most interesting feature is, to the scientist perhans, its winds. The winds there are seldom more than light zephyrs, moody and capricious to the ordinary tourist, but when rightly understood, one of the wonders of the valley. These Interesting facts are told by Prof. P. E. Matthes of the United States geological survey in the Sierra Club Bulletin. In no other place in the entire world, perhaps, are ( the air currents more systematic and regular than in the Yosemite valley, he says. In the first place, the sun naturally heats the ground more rapidly than it does the air. Thus every hillside basking in the sun becomes a heat radiator and gradually warms the air above it, so that the air, becoming lighter, begins to rise. But under those conditions the air does not rise vertically because the air directly over it is still cool and Is pressing downward. Therefore, up the sides of the warm slope the heated air makes its way. That is why the tourist making his way up the mountain slope with the sun on his back finds his own dust traveling upward with him in a choking cloud. But on coming down the same trail when the face of the slope Is in the shadow the dust ever descends with the traveler In the same irritating cloud. When the face of the mountain is in the shade the air is cooling from the face of the slope and is pressing its way down into the valley. Just as soon as the sun leaves the slope of the mountain, the earth begins to lose its beat by radiation, and in a very short time Is really cooler than the air. The layer of air next the face of the hillside chills by contact with the earth, and becoming heavier as It condenses, begins to press down along the slope. Thus there is, normally, the warm updraft on the sunny slope and the cold downdraft on the side in the shadow. In a windlesa region like the Yosomlte, with its bold' cliff topography, these upward and downward air currents are somewhat interrupted. On every sunny slim* bold cliffs create shadows and consequently there are downward air currents of local breezes dally at regular hours, as the shadows coffie and go. Glacier Point is one place in partioular in which Professor Matthes saya this shadowy effect on the air currents may readily he tested by casting small bits of paper into the air. As the afternoon wears on and the shadows in the valley gather, the chid draft in the hills pours downward, forming the valley like a great river, and flowing on to the plains below. Every side canyon and valley sends Its reinforcements, like the tributaries of. a great river, to this general air current flowing onward to the plain. With the return of the morning sun, the earth at the tops of the hills la warmed and the downward current in the air is suspended. The updraft soon . begins as the sun shines into the valleys. The air currents are so regularthat they may almost be timed. Few realize, says the author of the paper, that it is on these reversing air currents that one of the chief attractions of the Yosemite depends. Mirror lake, to be viewed at its best, must be seen in the darly dawn, when the reflections are most perfect The lake Is stillest and Its surface most mirror-like when the cold night currents have ceased and the uprising day currents of air have not yet begun. Yet unless one is punctual he will miss the chief beauty of the place, for this perfect stillness Is as brief as the turn of the tide. In the evening and during the night, when the downdraft of air from the mountain sides is strong, the stream of cool air pressing down the slope plui* ges over cliffs just as water is seen to fan from similar heights. On either the Yosemite falls or the Nevada falls trails, this alr-faU cariosity Is readily encountered in the evening. During the daytimg, on the other hand, the air rises vertically along the cliffs and up Into the hanging valleys, taking part of the spray from the falls along with it A pretty example of the air carrying the spray from the fall upward may be seen at Bridal Veil falls, where two little combs of spray, one on each side of the stream, steadily curve upward over the brink. As soon as the sun Is off the cliff the spray combs cease to exist