HOW WIND PRODUCES WAVES.

New Zealand Herald, Volume XLVI, Issue 14157, 4 September 1909, Page 5 (Supplement)

HOW WIND PRODUCES WAVES.

WAVE MOVEMENTS IX WATER, SAND, AND SNOW. There are wind waves in water, sand, and snow. The great sea waves are produced at that part of a cyclone where the direction of the wind coincides with the direction of advance or the depression. Along this line of advance the waves in their progress are accompanied by a strong wind blowing across their ridges as long as the atmospheric depression is maintained. So the waves are developed until they become steep. The average height in feet is about half the velocity of the wind in miles. A wind of 52 miles an hour gives waves of an average height of 26 feet, although individual waves will attain a height ot 40 feet. The prevailing wind in all longitudes is westerly, so wherever a westerly wind springs up it finds a long westerly swell, the effect of a previous wind, still running, and the principal effect of the newly-born wind is to increase the steepness of the already running long sweil so as to form majestic storm-waves, which sometimes attain a length of 1200 ft from crest to crest. The longest swells due to wind are almost invisible during storms, for they are masked by the shorter and steeper waves, hut they emerge into view after or bevond the storm.

The. action of the wind to drift dry sand in a procession of waves is seen in the deserts. As the sand waves cannot travel by gravitation, their movements are entirely controlled by the wind, and they are therefore much simpler and more regular in form and movement than ocean waves. In their greatest heights of several hundred feet the former become more complex, owing to the partial consolidation of the lower layers of sand by pressure, but they still have the characteristic wave features.

In the Winnipeg prairies of Canada freshly-fallen snow is drifted by wind in ■u. procession of regular waves progressing with a visible and ghost-'iike motion. They are similar to desert -waves, but less than half as sleep, the wave length being 50 times as great as the height. .Tito flatness of the wind-formed snow-waves affords a, valuable indication of the great distance to which hills shelter from the wind.