Geoscience Reference
In-Depth Information
The Coriolis Force
To see how the Coriolis force looks in animation, go to the
Geo Media Library
and select
The Coriolis Force
. This
animation examines how the Coriolis force influences at-
mospheric circulation. Be sure to watch how the rotation of
Earth on its axis impacts the way air flows on the planet.
After you finish watching the animation, be sure to answer
the questions at the end to test your understanding of this
concept.
at higher latitudes and generally results in westerly airflow from
the subtropics to the poles. Once again, you might be inclined
to think that the air is flowing toward the west; instead, westerly
winds are those that flow from west to east. At this point the
Coriolis force and the pressure gradient force effectively balance
each other, resulting in upper airflow that is
parallel
to the isobars
rather than perpendicular, as seen at the surface. The net result of
this flow pattern is that air moves
around
pressure systems in the
upper atmosphere. Such winds are called
geostrophic winds
.
force of friction and occurs because of the drag and impedi-
ments created by features on the surface of Earth, such as
mountains, trees, and even buildings. As you can imagine,
these features cause winds to slow down and move in irregu-
lar ways (Figure 6.13). The force of friction results in air-
flow that is somewhere between the flow driven by the pres-
sure gradient (i.e., perpendicular to isobars) and the Coriolis
force (which is parallel to isobars). As a general rule, the
effect of friction is strongest at the surface and diminishes
progressively to an altitude of about 1500 m (approximately
5000 ft). In response to this variability, the wind flows at an
Frictional Forces
In addition to the pressure gradient and Coriolis forces,
yet a third force influences the process of airflow in the
atmosphere, one that occurs at ground level and that oper-
ates in direct opposition to the winds. This variable is the
Geostrophic winds
Airflow that moves parallel to isobars
because of the combined effect of the pressure gradient force
and Coriolis force.
2400
8000
Smooth airflow at high altitudes
1800
6000
1200
4000
Turbulent airflow near Earth's surface
600
2000
Sea
level
Sea
level
Figure 6.13 The effect of friction on wind flow near the Earth's surface.
Compared to
winds at higher altitudes, the flow of surface air is significantly modified by features on the
Earth's surface.
