Currents and Wind
The Earth is Spinning…
 Because
Earth spins,
winds and
water
appear to be
deflected in
a curved
motion
 This is called
the Coriolis
Effect
DON’T FORGET WE’RE TALKING ABOUT THE DEFLECTION FROM THE
PERSPECTIVE OF WHERE THE OBJECT IS MOVING FROM! Look at this
picture and see that in the north, the arrows curve to the right from the point of
origin and to the left in the south.
 Which way do things
not connected to
Earth get deflected
in the northern
hemisphere?
RIGHT!
 In the southern
hemisphere?
LEFT!
Wind
 Winds drive ocean surface currents.
 Because wind is not connected to Earth, it is effected
by the
Coriolis Effect
What is wind?
 When the sun heats the surface of Earth, the air closest
to the ground also gets heated.
 When air is
heated it
becomes
less dense
and begins
to rise.
 Cooler air
moves into its
place.
 This is wind.
Earth’s Major Wind Patterns
Most winds are named by what
direction they come from.
How do you
think the trade winds
got their name?
Polar Easterlies
Westerlies
Trade Winds
Trade Winds
These helped
develop trade
Routes centuries
ago.
Westerlies
Polar Easterlies
Doldrums and Horse Latitudes
 Doldrums
is defined
as a boring and
monotonous time.
 The area along the
equator doesn’t
have much wind,
so it is called the
doldrums.
 Sailing vessels
often got stuck
here for weeks
because of lack of
wind.
Doldrums and Horse Latitudes
 Another area of
calm air with little
wind occurs along
the 30 degree
latitudes.
 Supposedly,
sailing ships that
got stuck here
would throw
horses overboard
to make the ship
lighter in hopes of
sailing out of this
calm area.
Surface Currents
 A current is a moving fluid (liquid or gas)
 Winds produce currents in the ocean when they blow
from the same direction for a long period of time.
Ekman Transport
 When wind moves across
water, the water moves at a
20-45° angle to the wind.
 That water causes the water
around to move at angle to
itself, and so on and so on.
 Eventually, there is water
flowing in the opposite
direction of the wind, but it is
much deeper under water.
 On average, the water moves
at a 90° angle to the wind. (To
the right in the North and to
the left in the south.)
Gyre
 A gyre is a circular current formed by a combination of
the rotation of the earth, prevailing winds, and land
masses that interfere with the movement of water
currents.
Major Gyres
 Warm water
is deflected
away from
the equator
by wind.
 Cool water is
deflected
from the
poles toward
the equator
by winds.
Thermohaline Circulation
 Thermo- means heat and -haline means salt
 At the poles, water is very cold
 When the water freezes to form ice, it excludes salt, so the ice is
all freshwater
 The water left behind is extremely salty and cold
 This combination makes the water very dense, so it sinks.
 It slowly travels along the floor of the ocean toward the equator,
and warmer, less salty water flows in to replace it.
 This is a VERY slow process. Surface currents average 6 mph, but
it is estimated that it takes 600-800 years for the entire
thermohaline cycle to complete itself.