Geoscience Reference
In-Depth Information
www.wiley.com/college/arbogast
Fluctuations in the Pressure Gradient
In order to better understand how the pressure gradient force
influences airflow, go to the Geo Media Library and select
Fluctuations in the Pressure Gradient . This simulation is
based on Figure 6.10, which shows a hypothetical pressure
gradient between Oklahoma City, Oklahoma, and Nashville,
Tennessee. You can adjust the atmospheric pressure between
the two places to see how these changes impact the flow of
air between them. As you make these adjustments, notice the
impact that they have on wind speed and the overall direc-
tion of the winds. After you complete the simulation, answer
the questions at the end to test your understanding of this
concept.
flight, the rocket follows the 74° W meridian as it flies toward
the target. As it continues southward, however, it would appear
to begin curving to the right (or west) relative to the target from
your vantage point. Why? It is not because the rocket's direction
actually varies from its original destination. Instead, it appears
to curve because the Earth rotates under (or eastward of) the
rocket while it is in the air. In this fashion, the rocket would land
somewhere to the west of New York City unless the initial course
was corrected in some way to account for the Earth's rotation.
Figure 6.11 also shows the apparent path of a rocket fired from
the South Pole (90° S) toward the Equator. Note that this rocket
is deflected to the west as well, but this time from right to left rel-
ative to the path of initial motion as viewed from the South Pole.
Although we can observe how a rocket's path might be al-
tered by the Earth's rotation, how does the Coriolis force influ-
ence the wind? Remember that at ground level the direction of
airflow is influenced by the pressure gradient force and results
in airflow that is perpendicular to the isobars (as in Figure 6.10).
Once the air rises into the upper troposphere, however, its speed
increases because it flows freely without obstruction. Once this
altitude is reached, the air is influenced most directly by the
Coriolis force, which causes winds to spiral to the right in the
Northern Hemisphere and to the left in the Southern Hemisphere.
In this context, remember that convection loops consist of spi-
raling masses of descending or rising air that are linked horizon-
tally by advection (Figure 6.12). This process is most pronounced
What you see on a weather map
H
L
What is happening in the atmosphere
1
Converging winds
6
Diverging winds
Air moves parallel to
isobars at high altitudes
5
Rising warm air that cools
2
Descending cool
air that warms
High
Low
Cyclone at surface
Anticyclone at surface
Air moves perpendicular to
isobars at Earth's surface
3
Diverging winds
4
Converging winds
Figure 6.12 A dynamic convection loop. Cyclones and anticyclones are linked together in a convection
loop consisting of air masses that spiral due to the Coriolis force. Note how the air masses move vertically
within the high- and low-pressure systems and horizontally between them.
 
 
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