Transcript Importance of Photochemical Processes in the Sea

Earth Rotation
• Earth’s rotation gives rise to a fictitious force
called the Coriolis force
• It accounts for the apparent deflection of
motions viewed in our rotating frame
• Analogies
– throwing a ball from a merry-go-round
– sending a ball to the sun
Earth Rotation
• Earth rotates about its axis wrt sun (2p rad/day)
• Earth rotates about the sun (2p rad/365.25 day)
• Relative to the “distant stars” (2p rad/86164 s)
– Sidereal day = 86164 sec (Note: 24 h = 86400 sec)
• Defines the Earth’s rotation frequency, W
W = 7.29 x 10-5 s-1 (radians per sec)
Earth Rotation
• Velocity of Earth surface
• Ve(Eq) = Re W
Re = radius Earth (6371 km)
Ve(Eq) = 464 m/s
• As latitude, f, increases,
Ve(f) will decrease
• Ve(f) = W Re cos(f)
W
Ve Decreases with Latitude
500
450
400
300
250
V
earth
(m/s)
350
200
150
Ve(f) = W Re cos(f)
100
50
0
-80
-60
-40
-20
0
20
latitude (N)
40
60
80
Earth Rotation
• Moving objects on Earth move with the
rotating frame (Ve(f)) & relative to it (vrel)
• The absolute velocity is vabs = vrel + Ve(f)
• Objects moving north from Equator will
have a larger Ve than that under them
• If “real” forces sum to 0, vabs will not
change, but the Ve(f) at that latitude will
Rotation, cont.
• Frictionless object moving north
vabs = const., but Ve(f) is decreasing
vrel must increase (pushing the object east)
• When viewed in the rotating frame, moving
objects appear deflected to right (left SH)
• Coriolis force accounts for this by proving a
“force” acting to the right of motion
Earth Rotation
• Motions in a rotating frame will appear to
deflect to the right (NH)
• Deflection will be to the right in the northern
hemisphere & to left in southern hemisphere
• No apparent deflection right on the equator
an object with an
initial east-west
velocity will
maintain that
velocity, even as it
passes over
surfaces with
different velocities.
Coriolis Force
As a result, it
appears to be
deflected over that
surface (right in NH,
left in SH)
Coriolis Force and Deflection of Flight Path
• Show Coriolis movie