Download APES * Earth*s Heat Engine

APES – Earth’s Heat Engine
How heat is transported through
Earth’s atmosphere and oceans
Lecture Overview
• How is heat redistributed around our planet?
• What creates distinct patterns of rainforests
and deserts?
Answer:
• The sun!
• Well… it’s not quite that
simple.
Where do winds come from?
• What happens when you heat molecules?
• Heated fluids and gases become less dense and rise
• Cooled fluid/gases become more dense and sink
Air moves because at one place
less dense air rises, while in
another place denser air sinks
toward Earth
A convection cell is formed in
the atmosphere when air is
warmed at one location and
cooled at another
cooling
Less dense
fluid rises
More dense
fluid sinks
heat
Where do winds come from?
• Idealized Earth with no
rotation, no land
air cools
and sinks
– Unequal heating like
real Earth
• Around equator, the air
warmed from below
rises
• Flows toward poles,
where it is cooled and
sinks back toward the
equator
• Go to Moving Heat
Animation
air rise
Fig. 7.16
What factors determine the density of
air?
• Heating and cooling of air and gains and losses of water
vapor in the air are related to:
– Unequal distribution solar energy over Earth’s surface
– Presence or absence of water
– Variation in temperature of earth’s surface materials in
response to heating
• These act to affect the density of air
– Temperature - warmer air, less dense
– Water vapor – moist air less dense (water has lower
molecular weight than dry air)
– Altitude – less dense with increasing altitude
• Warm moist air is less dense than cool, dry air
What is atmospheric pressure?
• Atmospheric pressure is the
force of a column of air on
an area of earth’s surface
• High pressure – density of air
is more dense than average
• Low pressure – density of air
is less dense than average
• Winds blow from high to low
pressure
• Winds named from direction
they come from
N
low pressure
Is this a North
or South
wind?
high pressure
S
How are vegetation patterns related to
atmospheric circulation?
http://www.esa.int/Our_Activities/Observing_the_Earth/ESA_global_land_cover_map_available_online
Comment: Better legend for
previous map
The water cycle is driven by solar
energy too
• We often think of
the water cycle as a
local phenomenon
• Important globally
• Return to Moving
Heat Animation
How can disrupting the water cycle,
change climate?
How can disrupting the water cycle,
change climate?
• The rainforests (and all
forests) ‘make’ their
own clouds
• Transpiration video
• Transpiration in Amazon
creates rainfall in:
–
–
–
–
–
Peru
Bolivia
Argentina
Uraguay
Paraguay and S. Brazil
http://www.guardian.co.uk/environment/2009/apr/01/prince-charles-rainforest-funding
Energy in Evaporation and
Condensation
• Energy is
transported through
atmosphere with the
molecules, especially
water!
• The transfer of
energy from surface
to atmosphere
disrupted.
Summarize so far…
• How are the water cycle and atmospheric
circulation related?
• What impacts does deforestation have to both
cycles?
Tomorrow
• Examine the atmosphere in more detail
– Normal function of greenhouse gases
– Heat trapping properties of certain gases