phy392_lecture02_web_2011

phy392_lecture02_web_2011 - PHY392S Physics of Climate...

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PHY392 - Physics of Climate Lecture 2, Page 1 PHY392S Physics of Climate Lecture 2 - Complete Notes Radiation - An Introduction Radiation and its physical basis The concepts of radiation intensity and flux Blackbody radiation
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PHY392 - Physics of Climate λ = 284Å = 304Å = 171Å = 195Å Sun – SOHO observations 07/01/03, from http://sohowww.nascom.nasa.gov/ Radiation The primary source of energy that drives the Earth’s climate system is the Sun. The Sun’s energy comes to us mostly in the form of electromagnetic radiation. Understanding climate requires understanding the nature of electromagnetic radiation and how it interacts with a planetary atmosphere and surface.
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λ Electromagnetic wave Magnetic field Electric field Defined by the solutions of Maxwell’s equations. As they move, photons carry electric and magnetic fields that oscillate at a certain frequency, giving rise to an electromagnetic wave. Can be thought of as particles (photons) that carry energy at speed c (c = 2.998 x 10 8 m/s - vacuum). The term electromagnetic radiation refers to a phenomenon that moves energy from one place to another, and carries with it an electric and a magnetic field. Electromagnetic Radiation EM waves are usually specified by: E H direction of propagation Wavelength ( λ ) = distance between crests Frequency (f or ν ) = number of oscillations per second = c/ λ Wavenumber ( ν or ν ) = number of crests per unit length = 1/ λ PHY392 - Physics of Climate Lecture 2, Page 3
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Radiation as Wave Motion - 1 An EM wave with a single frequency f will have a sinusoidal form: where we have defined wave vector angular frequency The minus sign is due to the direction of propagation, from x = 0 to . The energy transferred by the wave is the same for all x and t. ( ) t kx sin a ft 2 x 2 sin a ) t , x ( A ω = π λ π = ν π = λ π = 2 / 2 k f 2 π = ω PHY392 - Physics of Climate Lecture 2, Page 4 ( ) 2 o 2 o E ) t , x ( E t kx sin E ) t , x ( E = ω =
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Radiation as Wave Motion - 2 The energy per unit area per unit time flowing perpendicularly into a surface is given by the Poynting vector : units of W/m 2 where = vacuum permittivity = electric field = magnetic field The energy transport is
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phy392_lecture02_web_2011 - PHY392S Physics of Climate...

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