# Currents Powerpoint - Mr. Wieners 8th Grade Science

```The TEKS
Know that climatic interactions exist among
Earth, ocean, and weather systems.
• 8.10 (A) recognize that the Sun provides the
energy that drives convection within the
atmosphere and oceans, producing winds and
ocean currents;
CONVECTION
Transfer of heat by the movement of
warmed fluid (air or liquid)
Warm fluid rises (less dense)
Cool fluid sinks (more dense)
CONVECTION
CONVECTION
CONVECTION
Moves air in the atmosphere!
Moving Air = Winds
Convection in the atmosphere
is the main cause of the wind.
Where does the Energy for
Convection come from on
Earth?
THE SUN!!!
CONVECTION
CONVECTION
causes deep ocean currents!
CONVECTION
Wind over the
shore changes
direction
because of
EARTH’S
UNEVEN
WARMING &
COOLING!
Hot Air is Less Dense!
Atmospheric Density
How high is the atmosphere?
99% is within 30 km / 18
miles of the surface of the
Earth
Half the atmosphere is 5 km /
3.5 miles above the surface of
the Earth
Air Pressure – the weight of the air pressing on the
surface at a give location
What is most
dense
SINKS!
Atmospheric Movement
MOSTLY CAUSED BY:
- Temperature differences
- Pressure differences
- Coriolis Effect (due to Earth’s rotation)
Air Movement
Gas molecules move from high density to lower density
The TEKS
Know that climatic interactions exist among
Earth, ocean, and weather systems.
• 8.10 (B) identify how global patterns of
atmospheric movement influence local
weather using weather maps that show high and
low pressures and fronts;
We would
expect…
Coriolis Effect breaks up
Global Circulation
• On Earth the large
circulation cell breaks up
into 3 smaller ones,
moving diagonally
• Other worlds have more
or fewer circulation cells
depending on their
rotation rate
The Coriolis effect
• The Coriolis effect
– Is a result of Earth’s rotation
– Causes moving objects to follow curved paths:
• In Northern Hemisphere, curvature is to right
• In Southern Hemisphere, curvature is to left
– Changes with latitude:
• No Coriolis effect at Equator
• Maximum Coriolis effect at poles
The Coriolis effect on Earth
• As Earth rotates,
different latitudes
travel at different
speeds
• The change in speed
with latitude causes
the Coriolis effect
Figure 6-9a
Global Winds - winds that blow steadily
in paths for thousands of kilometers
Total Atmosphere Circulation
Role of the Ocean
• Slowly absorbs and slowly releases heat
energy helping keep Earth’s temperatures
relatively stable
• Oceans heat or cool the air above them and
transport heat around the globe in currents.
• Hurricanes form over warm ocean water,
drawing their energy from the water’s heat.
Ocean Currents
Currents
•
large scale water movements
– occur everywhere in ocean
– both surface and deep
•
2 main types: surface currents (10%) and subsurface currents (90%)
– surface currents are primarily wind driven
– deep currents are density driven
– other forces affecting currents
Coriolis effect
friction
gravity
thermal expansion
geologic shape of ocean basin
Major oceanic circulation systems
Current Gyres
Gyres are large circular-moving loops of water
Five main gyres (one in each ocean
basin):
• North Pacific
• South Pacific
• North Atlantic
• South Atlantic
• Indian
• Generally 4 currents in each gyre
• Centered about 30o north or south
latitude
Wind-driven surface currents
Lost at Sea
Duckie Progress
•January 1992 - shipwrecked in the Pacific Ocean, off the coast of
China
•November 1992 - half had drifted north to the Bering Sea and
Alaska; the other half went south to Indonesia and Australia
•1995 to 2000 - spent five years in the Arctic ice floes, slowly
working their way through the glaciers
•2001 - the duckies bobbed over the place where the Titanic had
sunk
•2003 - they were predicted to begin washing up onshore in New
England, but only one was spotted in Maine
•2007 - a couple duckies and frogs were found on the beaches of
Scotland and southwest England.
Other Effects of Wind on Water Movement
Downwelling –a wind-driven surface current collides
with a land mass, forces the surface water into the
deep ocean bringing dissolved oxygen from the
surface to the deep.
two surface currents colliding
surface current colliding with land mass
Upwelling - when a wind-driven surface current
moves away from a land mass, pulls deep ocean
water to the surface bring nutrients from the
deep ocean to the surface.
two surface currents pushed in opposite directions
surface current pushed away from land mass
Surface and Deep-Sea Current
Interactions
Unifying concept: “Global Ocean Conveyor Belt”
http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
Atmospheric Movement
MOSTLY CAUSED BY:
- Temperature differences
- Pressure differences
- Coriolis Effect (due to Earth’s rotation)
Global Winds - winds that blow steadily
in paths for thousands of kilometers
Types of Global Winds
• Polar Easterlies -Formed from cold sinking air moving
from the poles creating cold temperatures, extend from
the poles to 60° latitude
• Westerlies - Flow towards the poles from west to east
carrying moist air over the Unites States, found between
30° and 60° latitude
use by early sailors, blow from 30° almost to the equator
• Doldrums - Located along the equator where no winds
blow because the warm rising air creates and area of low
pressure
Jet Streams
• Jet Streams function as steering currents
for air masses and as zonal boundaries for
sharp differences in temperature. Jets are
something like "rivers of air" found at high
altitudes and noted for their high speeds.
Typical positions of two jet streams are
shown in this diagram
• The jet streams are narrow belts of high speed
winds that blow in the upper troposphere and
lower stratosphere
• Separates warm air from cold air
Local Winds
Seabreeze (during
the day, onshore)
Land Breeze (at
night, off-shore)
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