Insolation and the Greenhouse Effect

Energy in Earth’s Atmosphere

Insolation: Incoming Solar Radiation

The Sun’s strength or intensity depends on three factors:

1. Angle of insolation

2. Duration of insolation

3. Type of surface it strikes

Angle of Insolation

Where are we and how much are we getting right now?

Autumnal equinox

Fall in the northern hemisphere

Winter solstice

Winter in the northern hemisphere

Vernal Equinox

Spring in the northern hemisphere

Summer solstice

Summer in the northern hemisphere

Duration of Insolation

Length of time the sun is up.

Relationship: longer duration of insolation, higher the temperature (more intense)

Varies with latitude

Absorption of Insolation

Only 50% of the sun’s energy is absorbed by Earth’s surface.

Rest is reflected, scattered or absorbed by the atmosphere.

The absorption of heat energy from the sun depends on the specific heat of the substance.

Land has a lower specific heat, so takes less time to heat up, while water has a higher specific heat, thus taking more time to heat up.

Four Reasons water and land temperature differ:

Water has a higher specific heat.

Water reflects low angle insolation better.

Water is transparent insolation penetrates more deeply, more quickly.

Convection currents carry heat energy into hydrosphere land heats faster than water and land cools faster than water. GOOD ABSORBERS ARE GOOD RADIATORS

Color or structure of surface also determines if heat will be absorbed or reflected

In general, light colored surfaces reflect

While dark colored surfaces absorb

Incoming energy from the sun: UV, visible and infrared

Outgoing energy from Earth: terrestrial radiation – infrared.

INSOLATION WRAP-UP

Angle of insolation = how high sun is in sky.

Measured from the horizon (position of the sun) greatest angle = 90⁰

Changes with the seasons – in Northern Hemisphere: Lowest noontime angle =December 21, winter solstice

Highest angle =June 21, summer solstice

As angle of insolation increases and duration of insolation increases- temperature increases.

Most energy gets to Earth’s surface as visible light.

Ozone absorbs high energy radiation

Infrared radiation is absorbed by water and carbon dioxide.

A substances reflectivity = albedo

Insolation – Temperature Lag

A time lag exists between time of greatest intensity and time of highest air temperature. WHY?

Ex: June at noon – Earth receives most solar energy but highest temperature is later.

Because temperature depends on the balance between incoming energy and energy lost.

Even after maximum insolation, Earth continues to receive more energy than lost temperature continues to rise during this ‘lag’ period.

Following balance , energy lost > energy gained therefore about mid afternoon temperature drops.

What is the Greenhouse Effect?

http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/

Natural effect

Keeps our planet inhabitable

Other greenhouse planets- Venus

Comparing the Earth to a greenhouse

The glass=the earth’s atmosphere

Inside the greenhouse=conditions here on earth’s surface

Which type of ray is incoming?

Which type of ray is outgoing?

Terrestrial Radiation The form of energy the

earth gives off

Infrared=outgoing

Visible light=incoming

Greenhouse gases

What is global warming the result of?

Addition of more greenhouse gases to the atmosphere

Greenhouse gases are added naturally and by human activities

What are the effects of global warming?

Warmer temperatures globally

Melting of polar ice cap and glaciers

Sea level rise

Climate change

More severe weather?

What can you do?Lower your energy consumption (burning of

fossil fuels)

Recycle

Lower your carbon footprint