AN important application of the science of Meteorology to Aviation is inconnection with the provision of accurate data for navigation This aspect of thesubject involves a knowledge of what may be termed “windstructure,” that is, the horizontal variation of wind with place andtime, and the variation with height within the atmospheric layer in which flyingnormally takes place

In discussing the variation of wind with height it is desirable first to assume astandard of reference The wind near the surface of the ground is of little usein this respect since it is subject to many local variations The most convenientstandard is the undisturbed wind in the lowest layer which is free fromfluctuations caused by the upward propagation of disturbances from the surfaceof the earth