Heat Heat Transfer

The Natural The Natural Greenhouse EffectGreenhouse Effect

Trapping Heat

In an artificial greenhouse sunlight (solar radiation) passes through the glass

Some of the solar radiation reflects off of the objects inside and escapes back through the window

Some of the solar radiation is absorbed by the objects which become warm

Trapping Heat (continued)

The heat in the objects heat the air in the greenhouse The hot air cannot escape so the greenhouse gets

warmer and warmer Glass lets the sunlight in, but not the warm air out Greenhouses have devices to cool the air down if

necessary

Insolation Insolation is the

amount of solar radiation received by a region of the Earth’s surface

Insolation depends on: latitude Specific

characteristics of the lithosphere, atmosphere, and hydrosphere

The Natural Greenhouse Effect

Some of the solar radiation that is absorbed by the Earth’s surface is re-emitted into the atmosphere as infrared radiation

Most of this radiation is absorbed as thermal energy in the atmosphere by clouds and gases such as water vapour, CO2, and CH4

The absorption of thermal energy by the atmosphere is known as the natural greenhouse effect

Greenhouse Gases http://www.koshland-science-museum.org/exhibitgcc/images/causes02.jpg

The Earth would be significantly cooler without the trapped thermal energy

The natural greenhouse effect keeps our planet in the temperature range that supports life

Water vapour, CO2, NO and CH4 are greenhouse gases

Water vapour is the main contributor to the natural greenhouse effect

The Sun Emits Many Kinds of Energy

The Net Radiation Budget

The Net Radiation Budget(continued)

The net radiation budget is the difference between the amount of incoming radiation and the amount of outgoing radiation

The Earth receives 342W/m2 per year of solar radiation (W = watts – units of energy per second)

31% is immediately reflected back into space by clouds,the atmosphere and land surfaces

Approximately 30% is absorbed by the atmosphere The rest warms the Earth’s surface, which returns that

heat to the atmosphere as infrared radiation, thermal energy and water vapour

The atmosphere emits this radiation both up and down Less than 1% of incoming solar radiation is transformed

(by photosynthesis) into chemical energy

Balancing the Radiation Budget

Net Radiation Budget = Incoming Radiation – outgoing radiation = Zero

On average the amount of incoming radiation is equal to the outgoing radiation for all planet Earth

If this balance were to change, then the average global temperature would either increase or decrease

Although the net radiation is balanced, some regions have an unbalanced net radiation budget (polar regions tend to have less incoming than outgoing and the reverse for the tropics)

Albedo http://engineering.dartmouth.edu/dartsat/albedo.jpg&imgrefurl

Albedo is the percent of incoming solar radiation that is reflected from Earth’s surface.

The albedo of Earth is about 30% Light-coloured, shiny surfaces reflect more solar radiation Darker, duller surfaces reflect less solar radiation Albedo varies with the seasons

Thermal Energy Transferhttp://www.g9toengineering.com/resources/heattransfer.jpg

Thermal energy transfer from an area of high temperature to low temperature

Thermal energy can occur by radiation, conduction or convection

Thermal Energy Transfer2

Radiation http://rst.gsfc.nasa.gov/Sect16/ev151_CERES_fiemit.jpg

Radiation is the emission of energy as waves

When radiant energy encounters particles of matter it may be reflected or absorbed

Absorbed energy increases the movement of the particles

Any substance at a higher temperature than its surroundings will emit radiant energy usually as infrared radiation

Thermal Energy Transfer3

Radiation http://www.metoffice.gov.uk/science/creating/first_steps/images/fs_atmos_rad_tran.gif

Ex. the sun radiates solar radiation

When it reaches Earth some is absorbed

The warmer matter has molecules that are higher in energy

The matter transfers some of its thermal energy to substances at a lower temperature or re-emits it as infrared radiation

Thermal Energy Transfer4

Conduction Conduction is the

transfer of thermal energy through direct contact

This usually takes place between solids

Thermal Energy Transfer5

Convection Convection is transfer of

thermal energy through the movement of particles from one location to another

This usually happens in fluids (liquids/gases)

Water has a higher heat capacity than air has

Water has a large effect on Earth’s climate

Thermal Energy Transfer6

on Earth http://rst.gsfc.nasa.gov/Sect16/full-20earth2.jpg

Although the Earth receives insolation from the sun, different parts receive different amounts

Thermal energy is transferred throughout the atmosphere and hydrosphere

Thermal Energy Transfer in the Atmosphere &

Hydrosphere

Some Key Terms

Windhttp://www.weatherquestions.com/wind.jpg

Heated atmospheric gases expand and rise (lower atmospheric pressure)

Cooled atmospheric gases contract and fall (higher atmospheric pressure)

Wind is the movement of air from areas of high to low pressure

The Coriolis Effect Air tends to move from

the poles directly south or north

Because the Earth is rotating on its axis the winds are deflected either left (southern hemisphere) or right (northern hemisphere)

This is the coriolis effect

Global Wind Patterns The convection

currents cause by rising and falling warm and cold air and the coriolis effect result in the global wind patterns

Jet Streams A jet stream is a

band of fast-moving air in the stratosphere

The Earth has several jet streams

Jet streams affect the formation of severe weather

Thermal Energy Transfer in the Oceans

Vertical Transferencehttp://www.kidsgeo.com/images/ocean-current.jpg

Thermal energy is transferred vertically in water through convection currents

Warm water tends to rise

Cool water tends to sink

Currentshttp://www.hickerphoto.com/data/media/171/ocean_currents_t1384.jpg

As global winds blow on the ocean surface they push the water driving the surface currents in the ocean

The End Do learning checkpoint questions pg 278 Do key concept review pg 289 # 1 – 3, 5 –

8, 11 – 13 Do chapter 7 vocabulary