Download 13.6 Wind and Ocean Currents

Wind and Ocean
Currents
SCIENCE 10
A Little Background …
 Atmospheric Pressure is the pressure the air exerts
as gravity pulls it towards 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.
Neat Fact
 The weight of the air that is pushing down on your
shoulders at any given time is equivalent to 1 ton, or
about the weight of a fully grown rhino.
What is Wind?
 Wind is a movement of air in the atmosphere.
How Wind Develops
 Wind is 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
 Localized winds are winds affect only small areas.
 Types of Local Winds
 Sea Breezes- from sea to land
 Land Breezes- from land to sea
 Prevailing winds are winds that affect large areas.
- They affect weather around the globe.
Causes of Prevailing Winds
 Prevailing Winds are caused by a combination of
convection currents and the Earth’s eastward rotation.
 Air at the equator is warmed and rises, forming a
convection current called the equatorial convection
current. This wind moves northward and begins to
cool.
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.
 video
 Video2
Coriolis cont…
 This is 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.
 Prevailing winds 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
Class Work
• Read pages 516 to 519 to review winds. Pay close
attention to the Figures 1 and 2 on page 516 and
517.
• Complete questions:
 1 and 2 on page 519 to reinforce what you have
learned about wind.
Ocean Currents
Ocean Currents
 Ocean Currents are a mass movement or flow of
ocean water.
 Currents are like a river within the ocean.
 The reason Norway and Iceland have mild
winters is due to ocean currents.
 Two types
 Surface and Deep
Surface Current
 Surface Currents are 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


•
•
Red current = warm current
Blue current = cold current
Surface currents flow in a circular pattern
– 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:
1.
2.
3.
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
 Deep Currents are a stream-like movement of
ocean water far below the surface.
 Caused by changes in density
 This
change in density is the result of
changing temperature and salinity(saltiness)
Causes, in-depth ;)
 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 to move and to be replaced (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…