Variations in wind velocity near the ground

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Abstract
Information about wind velocity is generally obtainable in the form of mean hourly velocity and highest velocity in a gust at the level of the recording anemometer which, where possible, has an effective height (judged by the quality of exposure) approaching an agreed standard of 10 m. (33 ft.). For various purposes, estimates of both mean velocity and gustiness at other heights and in other exposures are often required. A summary is given here of relevant literature, in preparation of which I am much indebted to Dr. C. E. P. Brooks, both for his wide selection of works on the subject and for his helpful discussion and criticism.The article deals first with variations in mean velocity with increase of height above the ground, and then with gustiness and its relation to change of mean velocity and height. Next, seasonal and diurnal variations in gustiness are considered and the effect of changes in direction of the mean wind. A general approximate law for variation of wind velocity with height is suggested and tables are given for estimation of velocities at other than the height of observation; the article concludes with a paragraph on range of wind velocity.The wind velocities here considered are those in the lowest layers of the atmosphere, extending from ground level to a height of about 500 m. Where possible measurements of height are given in metres, velocity in metres per second, and temperature gradient in degrees Fahrenheit per metre (an upward increase is regarded as positive), these units being those of most frequent occurrence in the literature examined.

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