Environmental Engineering FOURTH EDITION

354 ENVIRONMENTALENGINEERING

m Wind circulation

A. If the earth dld not turn, the air would circulate in a fixed pattern

easterlies

Prevailing

Westerlies

Northeast

trades

,Southeast

trades

Prevailing

westerlies

' easterlies

B.The earth turns, creating variable wind patterns

Figure 18-4. Global wind patterns. (Courtesy of the American Lung Association.)

Figure 18-5. Heat island formed over a city.

from the southwest. The three features of a wind rose are:

the orientation of each segment, which shows the direction from which the wind

the width of each segment, which is proportional to the wind speed, and

the length of each segment, which is proportional to the percent of time that wind

came,

at that particular speed was coming from that particular direction.

Air pollution enforcement engineers sometimes use apollution rose, a variation of

a wind rose in which winds are plotted only on days when the air contamination level