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Wind and Ocean Circulation
http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/media/ocean_and_wind_
currents.swf
Why Are Air and Ocean Currents
Important?
• Oceans are important to the earth’s
climate
– They redistribute heat around the globe
– They absorb heat, helping to regulate the
earth’s temperature
– Air and Ocean currents work hand-in-hand
Ocean Currents are influenced by
two types of forces
1. Primary Forces--start the water moving
The primary forces are:
1. Solar Heating- cause water to expand
2. Winds- blows on surface, push water
3. Gravity- pull water down “hill”
4. Coriolis- intervenes and causes water to move to
the right, around mound of water
2. Secondary Forces--influence where the currents flow
1. Surface Circulation: tied to the prevailing wind
circulation of the atmosphere; general pattern of these surface
currents is a nearly closed system of currents, called gyres
Winds
• Unequal heating by the sun causes
differences in air pressures.
• Cold air drops while warm air rises.
• Warm air expands = low pressure because
it is spread out and less dense
• Cold air sinks = high pressure because it is
compact and more dense
Winds and Coriolis Effect
• This causes a circulation
of air to occur in a
north-to-south direction
• However, the Coriolis
effect deflects these
winds, so wind patterns
are a bit more
complicated
What is the Coriolis Effect?
• On the earth, the effect tends to deflect
moving objects to the right in the northern
hemisphere and to the left in the southern and
is important in the formation of cyclonic
weather systems
• The curvature of things moving across the
earth as it rotates
• Click here for videoWelcome to Discovery
Education Player
Atmospheric Cell Loops
• There are 3 atmospheric cell
loops that exist:
– Hadley Cells
• Warm air rises near the
equator, cools, falls in the
subtropics, then goes back
to the equator
– Ferrel Cells
• Air rises in sub-polar
regions, cools and falls in
the sub-tropics, then
moves toward the poles
– Polar Cells
• Air descends at the poles
and moves toward the
equator
What are Prevailing Winds?
Prevailing Winds are winds that affect large areas, therefore
affecting weather around the whole world.
• Due to the Earth rotating, the direction of prevailing winds form a
unique pattern.
• Three main prevailing winds:
– Trade winds – blow surface
water westward
– Westerly winds – blow
surface water back towards
the east
– Polar winds- the dry, cold
prevailing winds that blow from the
high-pressure areas of the polar
highs at the north and south poles
towards low-pressure areas within
the Westerlies at high latitudes
Prevailing Winds
• Polar Easterlies
Latitude/Wind Direction
Between 60° latitude and the
poles; From East to West
• Mid-latitude
Westerlies
Between 30° and 60° latitude;
From West to East
• Northeast Trade
Winds
Near 0°, North of the Equator to
30°N; From Northeast to West
• Southeast Trade
Winds
Near 0°, South of the Equator
to 30° ;From Southeast to West
The Coriolis Effect on
Prevailing Winds
As the Earth rotates, the path of prevailing winds is
deflected.
Since the Earth rotates to the East . . .
• In the Northern hemisphere, the Earth is rotating
counterclockwise, so the prevailing wind is deflected
to the right.
• In the Southern hemisphere, the Earth is rotating
clockwise, so the prevailing wind is deflected to the
left.
Cyclones and Anticyclones
• Anticyclones occur where cooler
air sinks and a zone of high
atmospheric pressure develops
– These form at subtropical
latitudes
• Cyclones occur where warm air
rises, and areas of low pressure
develops
– These form at the equator and at
sub-polar latitudes
How are winds and oceans linked?
• Cyclones and anticyclones create linked, circulating wind
patterns which continually move and change.
• The Coriolis effect causes them to spin, either clockwise
or counterclockwise, depending on the hemisphere they
occur in.
• These winds move over the ocean surfaces and cause
ocean surface currents
Coastal Breezes
Land heats up
faster than water.
Warm air rises over
land, and moves
toward the sea.
Cooler air from the
sea is lower, and
moves over the
land. This causes
Onshore breezes blow from the land
coastal breezes.
Offshore breezes blow from the sea
Ocean Currents
• There are two
types of ocean
currents:
– Surface currents,
which are caused
by winds
– Deeper ocean
currents, which
are caused by
changes in density
as a result of
changing
temperature and
salinity
Surface Currents (Surface Circulation)
• These waters make up about 10% of all
the water in the ocean.
• Are the upper 400 meters of the ocean.
• Important to climate of the earth
– Transport heat energy from tropics to cooler
parts of the globe
– Impact shipping and fishing industries as well
How do surface currents work?
The Ekman Spiral
• As the wind blows,
•
the molecules on the
very surface of the
ocean are moved at
an angle (not in the
same direction as the
wind)
The frictional drag on
molecules below
move the rest of the
water at right angles
to the wind direction
GYRES
• A gyre in oceanography is any large system of
•
rotating ocean currents, particularly those involved
with large wind movements.
Gyres are caused by the Coriolis Effect
– planetary vorticity along with horizontal and vertical
friction, which determine the circulation patterns from the
wind curl (torque).
• The term gyre can be used to refer to any type of
vortex in the air or the sea, even one that is manmade, but it is most commonly used in
oceanography to refer to the major ocean systems.
5 OCEAN GYRES: places where currents
meet
Ocean Gyres:
large mounds of water and
the flow around them. They produce large circular
currents in all the ocean basins.
Gyres
Deep Water Circulation
(Thermohaline Circulation)
• These waters make up the other 90% of the ocean
• Move around the ocean basins by density driven forces and
•
gravity.
driven by changes in density
– The density difference is a function of different temperatures and salinity
– They sink into the deep ocean basins at high latitudes where the
temperatures are cold enough to cause the density to increase.
•
•
– A result of thermohaline processes (changes in
temperature or salinity)
Some are vertical, moving water upward and downward to and
from the surface (upwelling and downwelling)
Surface and deep-water currents are all linked in a global
pattern of circulation.
The effect of winds on the
vertical movement of water
• Upwelling along the coast caused by
Ekman transport of waters (waters move
to the right of the wind).
– The waters moved offshore are replaced by
waters from below. This brings cold, nutrient
rich waters to the surface
• Downwelling caused by Ekman transport
onshore (movement of water to the right
of the wind direction).
What is Downwelling?
• When the density of water increases, it
sinks below less dense layers of water
– (remember that density increases as
temperature and salinity increases?)
Downwelling
• Caused or occurs as
a result of 3
situations:
– thermohaline
processes
– Also caused when a
current hits a coast
– Also occurs beneath
mounds of water that
form in the middle of
anticyclones and
gyres
– Click here for
animation
Upwelling
• Occurs as a result of the same conditions
that cause downwelling
• Where downwelling occurs, water must
rise to replace it
• When the wind blows surface water
(parallel to the coastline) away from a
coastline, water upwells to replace the
water that left
• Click here for animation
Why are downwelling and
upwelling important?
• They are needed to revitalize the nutrient
and oxygen content in the oceans of the
earth
• Nutrients and oxygen are brought up from
deeper parts of the oceans with cooler
water
• Warmer water sinks, and picks up more
oxygen and nutrients as it cools
Global Conveyor
• Colder water at the poles sinks, and moves
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•
•
•
•
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toward the equator.
As the water warms, it becomes less dense, and
rises at the equator (upwelling)
Water from the equator continues to move
toward the poles
As water cools near the poles, it becomes more
dense and sinks (downwelling)
It takes 1000 years for water to make one loop
around the planet
Click here for simulation
Click here for animation
The Great Pacific Garbage Patch
What is it?
• Island of Floating Plastic; thought to be twice the size of Texas.. But size is
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still debated
made up of widely dispersed, broken-down plastic waste particles
When plastic bottles, cups and bags are dropped in the street, rain washes
them into storm sewers, rivers and eventually the ocean
Stuck in the North Pacific gyre, circulating
it swirls around until sunlight and salt water break it down into small
plastic chips. With millions of tons of such trash in the North Pacific Gyre,
the water now resembles “plastic soup,”
Fish and birds mistake the plastic bits for food, resulting in death by
poisoning or digestive blockage. Plastic also absorbs pollutants like banned
PCBs, or polychlorinated biphenyls, once widely used in electrical
equipment. When we eat contaminated fish, we ingest these harmful
chemicals
• http://education.nationalgeographic.com/education/encyclopedia/great-pacificgarbage-patch/?ar_a=1
Ocean Currents
• http://www.youtube.com/watch?v=Hu_Ga
0JYFNg