Transcript The Coriolis Force and Weather

The Coriolis Force and Weather
By Jing Jin
February 23, 2006
Gaspard-Gustave Coriolis
• May 21, 1792September 19, 1843
• French mathematician,
mechanical engineer,
and scientist
• kinetic energy and work
to rotating systems like
waterwheels
The Coriolis Force Defined
• Arises from a noninertial
frame (accelerated or
rotating frame of
reference)
• Causes deflection of a
moving object from a
straight line
• Fictitious force
(~gravity, centrifugal
force)
A fluid assuming a parabolic
shape as it is rotating
Measuring the Coriolis Force
• The Foucault pendulum
consists of a heavy bob
suspended from a bearing
that allows it to turn in any
direction as deflected by the
Coriolis force  it appears to
rotate.
• The precise rate of rotation
depends on the latitude on
the Earth where the bob is
located.
Measuring the Coriolis Force
•
•
The formula for the Coriolis
acceleration is -2w x v,
where v is the velocity of the
particle in the rotating system
and w is the angular velocity
vector (which has magnitude
equal to the rotation rate and
points in the direction of the
axis of rotation) of the rotating
system.
This is vector multiplications 
magnitude of the Coriolis
acceleration of the object will be
proportional to the velocity of
the object and also to the sine
of the angle between the
direction of movement of the
object and the axis of rotation.
The formula implies that the Coriolis
acceleration is perpendicular both to the
direction of the velocity of the moving
mass and to the rotation axis. So in
particular:
 if the velocity (as always, in the
rotating system) is zero, the Coriolis
acceleration is zero
 if the velocity is parallel to the
rotation axis, the Coriolis
acceleration is zero
 if the velocity is straight
(perpendicularly) inward to the axis,
the acceleration will follow the
direction of rotation
 if the velocity is following the
rotation, the acceleration will be
(perpendicularly) outward from the
axis
Effects on Weather Patterns
Cyclonic flow around a low pressure area.
The blue arrows represent the pressure
gradient force, the red arrows represent
the Coriolis force.
• meteorology and
oceanography
• storms develop into
cyclones: the Coriolis force
deflects air parcels moving
toward a center of lower
pressure and causes them to
swirl around the center of
low pressure
• Induced rotation is clockwise
in Southern Hemisphere and
counterclockwise in Northern
Hemisphere
Trajectory of Long-Distance
Artillery Shells
• British naval gunners used
Northern Hemisphere
measurements of the Coriolis
force for targeting in a
conflict in the Southern
Hemisphere
• But the Coriolis force acts in
the opposite direction in the
Southern Hemisphere
• Thus, the long-range shells
were incorrectly aimed and
missed their targets by
miles.
Another Application
• A hypothetical situation:
The circles are inertia
circles. Air mass that is
in motion would, if no
other forces are
present, turn full circle.
Works Cited
• Hawley, John F. and Katherine A. Holcomb.
Foundations of Modern Cosmology. 2nd ed. New York:
Oxford University Press, 2005.
• “Coriolis Force.” Wikipedia. 23 February 2006
<http://en.wikipedia.org/wiki/Coriolis_force>.