Page 313 - Fundamentals of Air Pollution

V. General Circulation 269

Fig. 17-24. Meridional single-cell circulation (on the sunny side of a nonrotating earth).

torward near the earth's surface. However, since the earth's rotation causes
the apparent deflection due to the coriolis force, meridional motions are
deflected to become zonal (along latitude bands) before moving more than
30°. Therefore, instead of the single cell consisting of dominantly meridional
motion (Fig. 17-24), meridional transport is accomplished by three cells
between the equator and the pole (Fig. 17-25). This circulation results in
subsidence inversions and high pressure where there is sinking toward
the earth's surface and low pressure where there is upward motion.

A. Tropics

Associated with the cell nearest the equator are surface winds moving
toward the equator which are deflected toward the west. In the standard

Fig. 17-25. Meridional three-cell circulation (rotating earth).