13.6 Wind and
Ocean
Currents
Science 10
A Little Background …
• Atmospheric Pressure is the
force of the air pressing down
on the earth’s surface
– Atmospheric pressure is
measured using a barometer.
– Since air molecules are so spread
out (lots of empty space), we
don’t feel the pressure that they
exert
• Differences in air pressure help
cause winds and affect air
masses. They are also factors
in the formation of storms such
as thunderstorms, tornadoes
and hurricanes.
What is Wind?
• Wind is a movement of air in the
atmosphere
How Wind Develops
• Caused by a difference in air pressure
due to unequal heating of the
atmosphere.
Question: Where on the planet does the
surface get heated more than other
areas?...
• At the Earth’s surface, wind always
blows from areas of high pressure to
areas of low pressure
How are Winds Created?
Winds are created by….
1. Heating the air, decreases pressure (warm air
rises creating a low pressure)
↓
2. Cool air rushes into replace the warm air (cooler
dense air, produces high pressure)
↓
3. As air goes from high to low pressure winds
form
This is a CONVECTION style… Convection
Current Demo Time!!
http://www.youtube.com/watch?v=7xWWowXtuvA
Classifying Winds
I. Localized
- affect only small areas
Types of Local Winds
• Sea Breezes- from sea to land
• Land Breezes- from land to sea
II. Prevailing winds
- affect large areas,
- types to follow after we look at
what causes prevailing winds
Causes of Prevailing
Winds
• Due to a combination of
convection currents and
coriolis effect
• air at the equator is warmed
and rises, forming a
convection current called the
equatorial convection current
The Coriolis Effect
• Earth’s rotation causes
anything that moves LONG
DISTANCES, such as
prevailing winds, to APPEAR
to change directions.
• The apparent change in
direction of a moving object
in a rotating system is called
the CORIOLIS EFFECT.
Demo Video
http://www.youtube.com/watch?v=mcPs_OdQOYU
Coriolis cont…
• Evident on the earth because as
Earth rotates eastward, an object
travelling from north to south will
appear to move to the right
• In the southern hemisphere
objects moving from the pole
appear to move to the left
• The Coriolis effect is more
predominant closer to the poles
Prevailing Wind
Terms:
• Polar easterlies – occur
between 60 degrees latitude and
the poles and moves east to west
• Mid-latitude westerlies – occurs
between 30 degrees and 60
degrees latitude and move from
west to east
• Northeast trade winds – occur
just north of the equator and
move east to west
• Southeast trade winds – occur
just south of the equator and
move east to west
Effects of Prevailing
Winds
• Help distribute large amounts
of solar energy from the
equator to the colder parts of
the world.
• Also carry moisture, causing
a variety of precipitation
(snow, rain, etc…)
Wind terms cont…
• Gusts – occur because of a
rapid air pressure change
and move in no fixed
direction
• Squalls – gusts accompanied
by rain
• Wind speed indicator –
anemometer/weather vane
Sooooooo… Do you
think the Coriolis Effect
and Wind effect how
water moves in the
ocean?
Ocean Currents
Ocean Currents
• Mass movement or
flow of ocean water
• River within the
ocean
• Two types
–Surface and Deep
Surface Current
• Horizontal, stream-like
movements of water that
occur at or near the
surface of the ocean
• Can reach depths of
several hundred meters
Surface Current Animation
•
•
•
Surface currents flow in a circular pattern
–
–
–
•
Red current = warm current
Blue current = cold current
Northern Hemisphere flows clockwise
Southern Hemisphere flows counter-clockwise
Poles flow in opposite direction
Notice that the warm currents flow from the equator
Surface
Currents
• Controlled by three factors
– Prevailing winds = Cause
surface currents to flow in
the direction the wind is
blowing (top 400 m)
– Coriolis Effect
– Continental Deflections =
shape of the land it flows
up against
Deep Currents
• Stream like movement of
ocean water far below the
surface. THIS IS WAY DOWN
THERE!
• Caused by changes in density
– This change in density is the
result of changing
temperature and salinity
Causes, broken down…
•
Change in temperature
– Decreasing the temperature (it’s colder) of
water increases density (water sinks)
•
Change in salinity
– Increasing the salinity of water increases
density (again, making water sink)
– Salinity increases because when water at the
poles freezes, the salt doesn’t freeze so it’s
left behind and sinks to the ocean floor and is
replaced by new water (hence the current)
Both TEMPERATURE AND SALINITY causes
warmer less dense water from the equator
moves to replace it (water will always want to
be level and that is why the water that leaves
gets replaced)
The Pic on the next page does a good job
explaining this phenomena…