. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. Chapter 13 —CIRCULATION OF THE ATMOSPHERE M*. fci^gfc LOW WIND SPEED (BELOW 20 MPH) HIGH WIND SPEED (ABOVE 20 MPH) Figure 13-15.— Eddy currents formed when wind flows over uneven ground or obstructions. "gustiness" is usually used in conjunction with sudden intermittent increases in the wind speed near the surface levels, and turbulence is used with reference to levels above the surface. Gustiness can be measured by wind instruments, whereas turbulence, unless encountered by air- craft equipped wit
. Aerographer's Mate 3 & 2. United States. Navy; Meteorology; Oceanography. Chapter 13 —CIRCULATION OF THE ATMOSPHERE M*. fci^gfc LOW WIND SPEED (BELOW 20 MPH) HIGH WIND SPEED (ABOVE 20 MPH) Figure 13-15.— Eddy currents formed when wind flows over uneven ground or obstructions. "gustiness" is usually used in conjunction with sudden intermittent increases in the wind speed near the surface levels, and turbulence is used with reference to levels above the surface. Gustiness can be measured by wind instruments, whereas turbulence, unless encountered by air- craft equipped with a gust probe or an acceler- ometer, is usually estimated. An eddy is the more or less circular motion of the wind produced by an obstruction in its Figure 3-16.— Effect of windflow over mountains. path, such as irregularities on the earth's sur- face (hills and mountains), trees, and buildings. The length of an obstacle and the stability of the air are the factors which determine whether the air will flow around or across the object. Turbulence caused by large objects, such as buildings, is usually a combination of horizontal and vertical eddies. (See fig. 13-15.) There may be a stationary eddy on the wind- ward side of a mountain if the windward side has a steep slope. The leeward side of mountains has the most pronounced eddy activity, and in most cases violent downdrafts exist. The downdrafts are extremely dangerous to aircraft, and instances are recorded of their having caused aircraft to crash into mountain sides. (See fig. 13-16.) 311. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Naval Education and Training Program Development Center; United States. Bureau of Naval Personnel. Washington : U. S. Dept. of Defense, Navy Dept. , Naval Education and Training Support Command
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