Figure 2-4 Pressure Gradient Force
Atmospheric circulation moves air in mainly two ways: ascending and descending currents.
When the air descends, the downward force against the Earth creates a high-pressure system on
the surface. The air then can only spread out and diverge, moving across the surface of the
Earth, producing the horizontal flow of air known as wind. Likewise, air moving upward away
from the Earth, results in a low at the surface and tries to converge toward the center of the low,
also producing wind.
However, the wind cannot and does not blow straight out of a high into a low. These motions
are the result of the pressure gradient force (Figure 2-5).
Figure 2-5 Pressure Gradient Force
Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability