Agenda - WHAT YOU LEARN

• The Importance of the Sun
• The Characteristics of the Sun
• The Nature of Solar Radiation
• What Happens to Solar Radiation as it Passes Through the Atmosphere
• How the Atmosphere is Heated
• How the Global Energy Budget Stays in Balance
• Key Points

How are our lives connected to this giant sphere of incandescent gases?
• Powers the complex circulation of the atmosphere (drives winds)
• Brews hurricanes and tornadoes
• Sets the hydrologic cycle in motion
• Is the basis for life on earth
• Helps to break rocks apart
• Influences geophysical events
• Makes us happy
• Causes skin cancer

What is it?
• An ordinary star
• A mass of incandescent gases
• A thermonuclear fusion engine
• An output of electromagnetic radiation
• A rotating, revolving body
• Electromagnetic radiation travels through space without requiring a medium

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NATURE OF SOLAR RADIATION

• Solar radiation takes several forms
• Visible light
• Infra red
• Ultraviolet, X, and gamma rays
• Solar radiation is shortwave radiation
• Shortwave radiation does not readily heat most gases.

Is solar radiation constant?

• Is the sun like a gigantic electric light bulb in the sky?
• Does it always emit the same intensity of energy?

The term Solar Constant describes the amount of energy received by a surface perpendicular to the sun's rays and outside the earth's atmosphere.
Value = 1400 watts radiation per square meter

Does anywhere on earth receive 1400 watts radiation per square meter?

• No.
• Scientists use the word Insolation not sunshine to refer to the amount of incoming solar radiation that reaches the earth’s surface.
• Insolation at the earth's surface is always less than the solar constant.
• Why?

Two sets of variables determine the amount of insolation:

• The angle of the sun
• Latitude
• Season
• Time of day
• Losses of energy passing through the atmosphere

Solar Radiation Versus Insolation
Over 50% of solar radiation is lost as it passes through the earth's atmosphere

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WHAT HAPPENS TO SOLAR RADIATION AS IT PASSES THROUGH THE ATMOSPHERE?

• Counterradiation
• Earth's longwave radiation is not all lost to space.
• Carbon dioxide and water vapor absorbs earth's radiation and reradiates it toward the earth.
• Clouds also keep us warm at night by radiating longwave radiation to earth.
• The Greenhouse Effect
• Greenhouse windows act like carbon dioxide in the atmosphere.
• Shortwave solar radiation penetrates glass but traps longwave radiation inside.

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HOW THE GLOBAL ENERGY BUDGET STAYS IN BALANCE

Is This Heat Trapped Forever?
Outgoing earth radiation must equal incoming solar radiation (insolation).
Is there a radiation balance at every latitude?

Annual Net Radiation Balance

• High latitudes (40º to the poles) emit more radiation than they receive (deficit).
• Low latitudes receive more insolation than than they emit (surplus).
• How is this possible?

The Latitudinal Radiation Imbalance

• The surplus heat of the low latitude tropics must move toward the poles to balance the heat deficit in the high latitudes.

How does surplus heat move from low latitudes to high latitudes?

• Oceanic circulation in the form of ocean currents.
• Atmospheric circulation in the form of winds.
• Latent heat absorbed in the low latitudes but released in the high latitudes.

• Solar power is electromagnetic radiation that is a potential source of energy.
• Shortwave radiation from the sun is intercepted as it travels through the atmosphere to heat the earth.
• The atmosphere is heated by longwave radiation, sensible heat, and latent heat.
• Energy is moved from low latitudes to high latitudes by winds, ocean currents, and in the form of latent heat.

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