Slide 8 of 26
Notes:
To understand the Earth heat budget, we also need some basics on electromagnetic radiation. This is an oscillating wave, like the waves we see on the surface of water, but consisting of fluctuating electric and magnetic fields, moving at the speed of light with linked temporal frequency and spatial wavelength.
How become aware of such radiation depends strongly upon its wavelength. For visible light this would be in the range 0.3 - 0.6 microns, implying about 2 million wavelengths in a meter. We never see the individual waves, but our eyes are sensitive to the intensity (flow of energy per unit area) from much larger objects. We feel on our skin the radiant heat in the near infra red from bodies that are significantly warmer than our typical surroundings, e.g. from the element on an electric stovetop. Ultra violet radiation from the sun at wavelengths less than 0.3 microns is invisible but causes sunburn and skin cancer. X-rays and gamma rays from nuclear reactions have much shorter wavelengths still and penetrate deeply into tissue, damaging the DNA in cells. At the other extreme, microwave radiation has wavelengths measured in centimeters and meters, does no known damage to cells except from excessive heating, and is used in microwave ovens, radar, and TV transmissions.
For this class we will focus on the light from the sun, mostly in the visible band, and on heat leaving the earth by radiation in the infra red band.