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

heat

Less dense fluid rises

More dense fluid sinks

coolingAir 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

Where do winds come from?

• Idealized Earth with no rotation, no land– 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

Fig. 7.16

air rises

air cools and sinks

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

low pressure

high pressure

Is this a North or South wind?

N

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