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Write about this….
Have you ever experienced a very
strong wind gust? What
happened? Have you ever felt a
gentle breeze? What did it feel like?
How wind works
• Winds flow on earth based on differences in
pressures, everything flows high to low!
• The prevailing winds on Earth flow from
areas of high pressure to areas of low
pressure
• 14.7 lb/in2 is standard atmospheric pressure
What the heck is air pressure…
• A column of air 1
square inch that
extends all of the
way to the end of
the atmosphere
exerts weight 14.7
lbs.
• What does psi
mean?
Warm and cold air pressures
• Warmer air is typically less dense and
higher in water vapor content
– (low pressure zone)
• Colder air is typically higher in density
and lower in water vapor content
– (high pressure zone)
The climates on Earth…what should this do for winds?
How about this…..
• Warm less dense air rises at the equator
• Cold dense air falls at the poles
Why does wind speed change?
• Pressure gradient :
Horizontal difference
between high and low
pressure zones
– Steep gradient
makes high wind
– Shallow gradient
makes low wind
So why do wind patterns not flow
due North or South?
• The Coriolis effect:
–Caused by the rotation of the
earth on its axis
–Coriolis deflection Causes these
simple flow patterns to be broken
up and cause different wind
patterns across earth’s latitudes
Naming winds
• Winds are named for where they come
from
• A person born in New York may call
themselves a New Yorker or a person
from Puerto Rico may call themselves
Puerto Rican
• Winds born in the:
North = Northerlies
East = Easterlies
South = Southerlies
West = Westerlies
Winds are also named for what they do!
• Trade winds – used by mariners, to help their
ships move faster or in the proper direction
• Horse latitudes - low wind area throw off the
horses save food and water for us
• Doldroms – slow and lethargic winds
• Roaring forties – areas with many wild winds
Sailing in the
Doldrums
Artist’s rendering of the roaring
forties
Sailing in the
trade winds
Why is Ocean Circulation
Important?
• Transport ~ 20% of
latitudinal heat
– Equator to poles
• Transport nutrients and
organisms
• Influences weather and
climate
• Influences commerce
Currents
• An ocean current is a continuous, directed
movement of ocean water generated by
the forces acting upon this mean flow,
such as breaking waves, wind, Coriolis
effect, temperature and salinity differences
and tides caused by the gravitational pull
of the Moon and the Sun. Depth contours,
shoreline configurations and interaction
with other currents influence a current's
direction and strength.
There are two types of currents
• Wind driven currents make up
approximately 10% of oceanic water
flow
• Density driven currents make up
approximately 90% of oceanic water
flow
– Based on these factors
• Temperature
• Salinity
• Pressure
Surface currents
• Surface currents are created by
wind drag on the surface of the
water
• The area of contact between the
wind and water is called the Fetch.
• The bigger the fetch the more
energy that can be transferred
Power from wind
• 10 % oceanic water movement is
powered by the wind
• Faster traveling air has more
energy to transmit to the water
beneath it
• The transfer of energy is not very
efficient
• Water typically travels 3-4 % the
speed of the wind above it
Example:
wind speed = 50 kph
Equation:
50 X .3 -.4 = 1.5 - 2.0 kph
water current speed:
1.5 – 2.0 kph
wind patterns + Coriolis equals
• Zonal wind Flow = movement of winds
that is parallel to the lines of latitude
The currents are deflected by
continents creating
• Circulation Gyres = large looping
currents caused by a current being
bent back on its self causing a
loop of water
10% of ocean circulation is driven by
wind
Currents in the ―Real‖ Ocean
Currents rarely behave exactly as
predicted by these theoretical
explanations due to factors such as
• Depth—shallow water does not permit
full development of the Ekman spiral
• Density—deeper currents moving in
different directions influence the
overlying surface movement
What do Nike shoes,
rubber ducks, and
hockey gloves have to
do with 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.
North Pacific Subtropical Gyre
Upwelling and downwelling
Vertical movement of water ( )
– Upwelling = movement of deep water to
surface
• Hoists cold, nutrient-rich water to surface
• Produces high productivities and abundant
marine life
– Downwelling = movement of surface water
down
• Moves warm, nutrient-depleted surface water
down
• Not associated with high productivities or
abundant marine life
Surface and Deep-Sea Current
Interactions
Unifying concept: ―Global Ocean Conveyor Belt‖
http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
Heat Transport by Currents
• Surface currents play significant roles in
transport heat energy from equatorial
waters towards the poles
• May serve as ―heat sources‖ to cooler
overlying air, ―heat sinks‖ from warmer
• Evaporation and condensation
participate in latent heat exchanges
Matter Transport and
Surface Currents
• Currents also involved with gas
exchanges, especially O2 and CO2
• Nutrient exchanges important within
surface waters (including outflow from
continents) and deeper waters
(upwelling and downwelling)
• Pollution dispersal
• Impact on fisheries and other resources
Global ocean circulation that is driven by differences in the density of the
sea water which is controlled by temperature and salinity.
White sections represent warm surface currents.
Purple sections represent deep cold currents