Gyres and Currents

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Made by Michael Kramer
Coriolis Effect
 Apparent deflection of the path of an object that moves
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within a rotating coordinate system
Object doesn’t deviate from path, but appears it does
Most apparent in path of an object moving longitudinal
An object moving along North-South path will undergo
deflection to its right in Northern Hemisphere and to its
left in Southern Hemisphere
This caused by Earth rotating eastward and tangential
velocity of a point on Earth is a function of latitude
(Velocity is zero at poles and max value is at Equator)
Deflection is related to motion of object, Earth, and
latitude. Magnitude is given by 2Sin.
Coriolis Effect Animations and
Videos
 Coriolis Effect Animation
 Coriolis Effect Youtube Video
El Niño
 Defined by prolonged differences in Pacific Ocean surface
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temperatures when compared with average value.
Caused by the Coriolis Effect
Occurs at irregular intervals of 2-7 years and last 9 months to 2
years
When warming/cooling occurs for 7-9 months, it is classified as
El Niño conditions. When it occurs for more than 9 months, it is
classified as El Niño episodes.
First signs are: rise in surface pressure, fall in air pressure, trade
winds, warm air rises near Peru, and warm water spreads from
West Pacific and Indian Ocean to East Pacific.
La Niña is the opposite of El Niño, and happens where it
corresponds to a lower surface temperature.
Pictures of El Niño
Gyres
 Large system of rotating ocean currents, generally
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those involved with large wind movement
Caused by Coriolis Effect
Large mounds of water and flow around them are
Gyres and they produce circular currents in all of the
ocean basins
Five most common gyres are: Indian Ocean Gyre,
North Atlantic Gyre, North Pacific Gyre, South
Atlantic Gyre, and South Pacific Gyre
Other gyres include tropical, subtropical, and subpolar
Map of Gyres
Picture of Gyre
Cool Facts about Gyres
 Another name for “swirling vortex”
 There is a small gyre in the Arctic Ocean known as the
Beaufort Gyre, which is being studied by scientists due
to the high amount of freshwater in it
 North Pacific Gyre is home to the Great Pacific
Garbage Patch that contains about 3 million tons of
plastic litter
 South Pacific Gyre is Earth’s largest system of rotating
ocean currents and center of the gyre is regarded as
Earth’s largest oceanic desert
 The Southern ocean has two gyres: Weddel and Ross
Currents
 Ocean current is a continuous and directed movement
of ocean water generated by a variety of forces
 These forces include breaking waves, wind,
temperature, salinity, tides, and the Coriolis Effect
 These currents can flow for vast distances and create
the great flow of the global conveyor belt that
determines the climate of many regions
 Two examples are the Gulf Stream and the California
Current
Currents
 The balance met between the Coriolis Effect and gravity creates a
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flow known as a Geostrophic current
Boundary Currents are the main geostrophic currents around the
gyre
Difference between Western and Eastern boundary currents is
the strength because of rotating of the Earth that moves down
the hill of water to western sides of ocean basins
Western boundary currents include: Gulf Stream, Kuroshio
Current, Labrador Current, Oyashio Current, Agulhas Current,
Brazil Current, and East Australia Current
Eastern boundary currents include: California Current, Canary
Current, Peru Current, and Benguela Current
Currents Continued
 There are two types of Currents: Surface and Deep Water
 Surface Currents make up about 10% of all water in the
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ocean and are the upper 400 meters of the ocean
Deep Water Currents make up other 90% of the ocean and
move around ocean basins by density driven forces and
gravity
Currents are influenced by two types of forces: Primary and
Secondary
Primary forces start the water moving and are solar
heating, winds, gravity, and the Coriolis effect
Secondary Forces influence where the currents flow
Surface Circulation
 Solar heating causes the water to expand
 The water is about 8 cm higher near the equator than in
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middle latitudes and this causes a slope that water wants to
flow down
Winds blow on the surface of the ocean and push the water
Friction occurs between the wind and water’s surface
A wind blowing for 10 hours across the ocean will cause
surface waters to flow at roughly 2% of wind speed
Gravity will pull the water down the pile of water against
the pressure gradient
The Coriolis Effect then intervenes and causes the water to
move to the right around the mound of water
Pictures
Ekman Transport
 Term given for 90 degree net transport of surface layer due
to wind forcings
 This was found by Fridtjof Nansen who found ice transport
to occur at an angle to the wind direction during his arctic
expedition
 Direction is dependent on hemisphere. If angle is to the
right of the direction of the wind, it is in the Northern
Hemisphere. If angle is to the left, it is in the Southern
Hemisphere.
 The Ekman Transport is the average of the Ekman spiral,
which is the spiral created by ocean water at the surface
moved by an angle of wind as it turns against the water
under the surface.
Ekman Transport Pictures
Upwelling and Downwelling
 Upwelling along coast is
caused by Ekman
transport of waters.
These waters are moved
offshore and replaced by
waters from below. This
brings cold and rich
water to the surface.
 Downwelling is caused
by the Ekman transport
on shore.
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