Radiation balance

Any object in the Universe which has a temperature above the temperature "absolute zero" (-459.67 degrees Fahrenheit or -273.15 degrees Celsius or zero degrees Kelvin) has radiation.

• Explain the differences between short and longwave radiation and how they heat the Earth • Define and describe radiation cooling • Define and describe counter-radiation warming • Explain why the naturally occurring concentrations of greenhouse gases in our atmosphere

are necessary• Explain the concept of a stable state and a dynamic equilibrium and how it relates to the

radiation budget and temperature of the atmosphere • Explain albedo and contrast a dark and a light surface in terms of their reflectivity and

absorption of insolation• Trace the path of 100 units of incoming solar radiation• Give an example of positive feedback effects associate with increased global warming and

decreased ice cover in the Arctic• Explain why the coldest temperatures occur on clear nights • Differentiate between heat and temperature • Differentiate between sensible and latent heat • Define and describe convection currents • Explain how evaporation and condensation of water can transport heat • Given a phase change for water, state if heat or energy is absorbed or released into the

environment • Define evaporative cooling and condensation warning• List and explain factors that determine the heat energy balance and temperature• Define/describe advection

Radiation

All objects emit radiation

Radiation can pass through objects unaffected, travel thru a vacuum, or be absorbed and reemitted.

Radiation

The sun emits radiation composed of high energy infrared radiation, visible light, and ultraviolet radiation collectively known as shortwave radiation (SW)

The earth emits radiation composed of lower energy infrared radiation collectively known as longwave radiation (LW)

Sun Earth

Sun: shortwave radiation

Earth: longwave radiation

How does solar radiation heat Earth?

Through counter-radiation warming, in which the atmosphere is heated from below by longwave radiation.

Analogy: parked car with the windows rolled up

Radiation cooling

When are our nights coldest, when it is cloudy or when it is clear?

Why is the desert so cold at night?

Nighttime longwave radiation emission, April

Smudge PotsFruit growers will sometimes use smudge pots to try to protect their crops from a possible killing frost, particularly on clear, cold nights. A smudge pot is a portable heater/burner which produces thick heavy smoke. Fruit growers place a number of these around the orchard in the evening to prevent the crop from freezing at night. Do smudge pots actually work? Why?

A. Yes. They work simply by heating the air in the orchard to keep it above freezing.

B. No. They don't work. They can not supply enough heat to keep the orchard from freezing.

C. Yes. They work by producing a heavy smoke layer over the orchard which prevents heat loss by radiation to the night sky

D. I think someone should notify the Pollution Control Agency.

http://www.aqmd.gov/news1/Archives/History/smudge.html

Path of incoming solar radiation (100 units)

Only 50% of insolation absorbed at surface

20% of insolation absorbed by atm

30% of insolation lost to space

Radiation balance

SW in and LW out to maintain temperature at steady state (water level does not fluctuate)

Dynamic equilibrium: changes in the amount of incoming or outgoing radiation (water level has up and down trends)

How would increased atmospheric concentrations of these substances alter the water level of thebucket (temperature)?:

Aerosol air pollution?Carbon dioxide?

Radiation budgets

Net radiation

Which plot is our summer? Our winter? Annual radiation balance?

Albedo: a measure of how well a surface reflects insolation.

Reflected shortwave radiation, May

Albedo measures (% reflected)

• Fresh snow 80-95 %• Forests 10-20 %• Asphalt 5 to 10 % • Water bodies 10 to 60 % (depending on

sun angle)• Light roof 35 to 50 %• Dark roof 8 to 18 %

Example of albedo-related feedbacks

Heat Transfer

1. Energy is not created or destroyed but converted from one form to another

2. Radiation is converted to heat energy The first commercial microwaves (1947) were actually

gigantic and enormously expensive, standing 5 1/2 feet tall, weighing over 750 pounds, and costing about $5000 each. They had to be water-cooled, so plumbing installations were also required.

Heat versus temperature

3. Heat is the measure of the total amount of motion of molecules.

Temperature is a measure of the average speed of the molecules.

A unit volume of ocean has more heat but a lower temperature than the samevolume air in the thermosphere (low heat but high temperature).

4. Heat energy flows from warm to cold

5. Two kinds of heat: sensible and latent

6. Sensible heat can be sensed and measured.

7. Sensible heat can be transferred three ways: radiation, conduction, convection

Radiation Conduction Convection

But what is latent heat?

8. Latent heat is heat that is tied up in the phase changes of water

Remember: Evaporation cools the environment; condensation warms it.

Latent heat flux

Latent heat flux is the amount of energy moving from the surface to the air due to evaporation.

Latent heat fluxflux

Latent heat flux is the amount of energy moving from the surface to the air due to evaporation. Why is latent heat flux less in the cities? What are the implications for temperature?

9. Temperature at any one point is determined by the net balance between net radiation, sensible heat content, latent heat transfer, advective heat transport (wind-driven), and moisture availability

What determines the tempon the roof of this car?

10. Heat is continually redistributed in the Earth’s atmosphere via evaporation and condensation.

11. Ocean currents also redistribute heat