Download Introducing global ecosystems

Distribution of global ecosystems
Introducing global ecosystems
Your goals for this lesson is to understand
1) how climate explains the distribution and
characteristics of global ecosystems
2) The impacts of global atmospheric
circulation on global ecosystems
3) The impacts of altitude, relief and ocean
currents
Global ecosystems
• Are defined mainly by the dominant type of
vegetation that grows in the region, such as
tropical rainforest or tundra.
• Form broad belts across the world from west to
east, parallel to the lines of latitude.
• Their climate and characteristics are determined
by global atmospheric circulation
• Variations in these west-to-east belts of
vegetation are due to factors such as ocean
currents and mountain ranges.
Factors which affect global
ecosystems
1- Global atmospheric
circulation pages 22/23
Watch (to seasons)
Stable, clear skies occur here, with few clouds. It is
dry because most water vapour was dropped as
convection rainfall near the equator. This creates
regions known as sub-tropical anticyclones.
Global atmospheric
circulation
Cooling makes the
air denser, and
much of this
denser air sinks
back towards the
earth and 30˚
north or south of
the equator.
(Descending limb
of the Hadley Cell.)
The ITCZ - Inter Tropical Convergence Zone
- is an area of low atmospheric pressure that
forms where the Northeast Trade Winds meet
the Southeast Trade Winds near (actually just
north of) the earth's equator.
The air that has risen in the convection currents stops when
it reaches a layer in the atmosphere called the tropopause.
It cannot continue to rise, so is forced to flow Pole wards.
As air flows away from its
main heat source, the
equator, it sinks.
This causes thick
clouds and
torrential rain.
(Rising limb of the
Hadley Cell.)
The hot air contains large
amounts of water vapour,
evaporated from the
ground or transpired from
vegetation. This heated air
rises in the form of
convection currents and
then cools, creating an
area of low pressure
known as the ITCZ.
The sun’s rays are most concentrated here – leading to the
heating of the air lying above the ground surface.
Jet streams
Jet streams are fast flowing, relatively narrow air currents found in the
atmosphere around 10 kilometers above the surface of the Earth. They form at
the boundaries of adjacent air masses with significant differences in
temperature, such as the polar region and the warmer air to the south.
Watch
The polar jet stream can travel at speeds greater than 100 miles per hour
(160 km/h). Here, the fastest winds are coloured red; slower winds are
blue.
Read, label, annotate
• Read the handout on characteristics of global
ecosystems.
• Label the Figure of the atmospheric circulation
in the northern hemisphere with the name of
the ecosystems. Draw an arrow to show their
location. Annotate the Figure with the link
between the characteristics of the ecosystems
and the global atmospheric circulation
Relief
Some very dry areas lie in the rain shadow of
high mountains ranges. As the prevailing winds
in the sub-tropics are the trade winds, blowing
from the north-east in the northern hemisphere
and the south-east in the southern hemisphere,
then any barrier, such as the Andes, prevent
moisture from reaching the western slope.
Watch
Impact of
Altitude on
temperatures
and vegetation
Ocean currents
Watch
Cold currents
In some places cold ocean currents run along the
coastline.
Wind is cooled as it travels over the cold water and
its ability to hold moisture is reduced.
Moisture that’s stored in the atmosphere is
released as precipitation over the ocean before
reaching the land.
So when the wind reaches the land there’s very
little moisture left so very little rainfall falls.
For example, the Namib Desert in Africa exists
because of the Benguela Current, a cold ocean
current that rubs up the west coast of Africa.
Atacama DesertRain shadow and
cold current
Explain how the cold ocean current
and the mountains are responsible for
aridity in the Atacama desert. (4)