Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK 6.2
Atmospheric pressure systems are often
easy to see on satellite images. This par-
ticular image focuses on Europe in Octo-
ber 2001, with Spain in the lower left part of
the image and clouds showing up in bright
white. Given your understanding of pressure
systems, where is the high-pressure system
in this image? Where is the approximate
center of the high? In what direction is this
system spinning and where are the southerly
and northerly winds in the system?
winds to be light, because air flowing into that region would be
moving slowly. As you approach the center of the low, however,
the isobars become closer together. Given that isobars represent
locations of equal atmospheric pressure, this close spacing can
only mean that a rapid change in surface pressure occurs over a
relatively small geographical space—for example, from Mem-
phis to Nashville. In other words, this part of the circulatory
system has a steep pressure gradient and the air flows faster as it
moves toward the center of the low, to fill the relative void cre-
ated by the less dense air at the surface. If you happened to be in
this area on this particular day, you would notice strong winds.
launched at the North Pole (90° N) toward New York City (about
40° N). Look at Figure 6.11 as you work through this discussion.
Imagine that you are standing at the pole and are able to view
the rocket's path as it flies south. During the initial period of
North Pole
North Pole
Intended
fli g ht path
I
In tend ed
e d
Actual
flight path
Coriolis Force
In addition to the pressure gradient force, another factor that
strongly influences the process of airflow in the atmosphere is the
Coriolis force . In contrast to the pressure gradient force, which
develops because of differences in atmospheric pressure between
regions, the Coriolis force is related to the rotation of the Earth
on its axis. Given this rotation, objects in the atmosphere, includ-
ing air, appear to be deflected or pulled sideways as Earth rotates
under them. In the Northern Hemisphere, the direction of deflec-
tion for an object moving toward the Equator is to the right when
viewed from above the North Pole. In the Southern Hemisphere,
the deflection of an object moving toward the Equator is to the
left when viewed from below the South Pole.
A good way to visualize the Coriolis force is to examine
the apparent path a hypothetical rocket would take if it was
i g
h t p ath
h
t p
h
g
p
a
New York City
74 ° W
Rotation
Intended
flight path
(from South
Pole)
Actual flight
path (from
South Pole)
Figure 6.11 The Coriolis force. The Coriolis force influ-
ences the path of a rocket traveling from the North Pole to
New York City, deflecting it to the west. Notice the direction of
the Earth's rotation and how the rocket path is diverted more
as it approaches the Equator. Also note that a rocket traveling
from the South Pole to the Equator is deflected west as well.
Coriolis force The force created by the Earth's rotation that
causes winds to be deflected to the right in the Northern Hemi-
sphere and to the left in the Southern Hemisphere.
 
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