Rita D. Haberlin
Characteristics of the Sun
What is it?
An ordinary star A mass of incandescent gases A thermonuclear fusion engine Hydrogen fuses into helium A rotating, revolving body
Electromagnetic radiation travels through space without requiring a medium
Nature of Solar Radiation
Hot bodies emit short wave radiation Solar radiation is shortwave radiation
Visible Light 41%
Ultraviolet, X, and gamma 9% Infrared Visible Light Ultraviolet,X, gamma
Short-wave 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?
Two Factors Affect the Intensity of Solar Radiation
Sun spots and solar flares
Earth’s changing distance from the sun
The Solar Constant
The “SOLAR CONSTANT” is the amount of energy received by an imaginary surface perpendicular to the sun’s rays outside the earth’s atmosphere. The value of the solar constant is about 1400 watts of radiation per square meter.
Does anywhere on earth receive 1400 watts radiation per square meter?
Scientists use the word Insolation not sunshine to refer to the amount of 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 varies with
– – –
Latitude Season Time of day
Interception of energy passing through the atmosphere
Length of Daylight at 40 Latitude N
Solar Constant Versus Insolation
Over 50% of solar radiation is intercepted as it passes through the atmosphere
Atmosphere Solar Constant
What happens to solar radiation as it passes through the atmosphere?
100 units solar energy
Reflection off clouds 20%
Reflection off earth 5% Only 50% of solar energy warms the earth’s surface
Mechanisms of heat transfer
How is the atmosphere heated?
Absorption Convection Conduction Longwave radiation
The sun heats the earth and the earth heats the atmosphere
The Greenhouse Effect
• Greenhouse windows act like carbon dioxide in the atmosphere.
• Shortwave solar radiation penetrates the glass but traps longwave radiation inside.
Is This Heat Trapped Forever?
Outgoing earth radiation must equal incoming solar radiation
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?
Poleward Heat Transport
In what ways 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.