Visualizing Environmental Science

PROCESS DIAGRAM

The Atmosphere 195

In addition to these global circulation patterns,
the atmosphere features smaller-scale horizontal move-
ments, or winds. The motion of wind, with its eddies,
lulls, and turbulent gusts, is difficult to predict. It results
partly from fluctuations in atmospheric pressure and
partly from the planet’s rotation.
The gases that constitute the atmosphere have weight and
exert a pressure—about 1013 millibars (14.7 lb per in^2 ) at sea
level. Air pressure is variable, depending on altitude, tempera-
ture, and humidity. Winds tend to blow from areas of high at-
mospheric pressure to areas of low pressure, and the greater
the difference between the high- and low-pressure areas, the
stronger the wind.
As a result of the Coriolis
e ffect, Earth’s rotation from west
to east also influences the direction
of wind. To visualize the Coriolis
effect, imagine that a rocket is
launched from the North Pole
toward New York ( Figure 8.5).

The atmosphere has three prevailing winds—major

surface winds that blow more or less continually (see

Figure 8.4). Prevailing winds from the northeast near the

North Pole, or from the southeast near the South Pole,

are called polar easterlies. Winds that blow in the middle

latitudes from the southwest in the Northern Hemisphere

or from the northwest in the Southern Hemisphere are

called westerlies. Tropical winds from the northeast in

the Northern Hemisphere or from the southeast in the

Southern Hemisphere are called trade winds.

1. What gases make up the atmosphere?


2. What two layers of the atmosphere are closest
   to Earth’s surface? How do they differ from one
   another?


3. What factors cause wind, and how do they
   relate to the Coriolis effect?

Coriolis effect The

tendency of moving

air or water to be

deflected from its path

and swerve to the

right in the Northern

Hemisphere and to

the left in the Southern

Hemisphere.

The Coriolis effectÊUÊFigure 8.5

✓✓THE PLANNER

North Pole

Rotation

Actual

flight path

New York City

74 ° W

40 °

N

Intended

flight path

North Pole

Actual flight path

(from South Pole)

Intended flight path

(from South Pole)

Equator

Rocket is launched from the

North Pole toward New York

(along 74°W longitude).

1

As the rocket travels to New

York, Earth’s rotation causes

the rocket to head west of its

intended flight path.

3

Notice the

direction of

Earth’s rotation.

2

Similarly, a rocket launched

from the South Pole toward

New York would head west

of its intended flight path.

4

Adapted from Figure 6.11 in A. F. ArbogastDiscovering Physical Geography

, Hoboken, NJ:

John Wiley and Sons, Inc. (2007)

Viewed from the
North Pole, the
Coriolis effect
appears to deflect
ocean currents and
winds to the right.
From the South Pole,
the deflection
appears to be to
the left.

Would you expect the

Coriolis effect to lead to greater wind

speeds near the poles or near the equator?

Explain.

Think Critically