Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (1 of 9) Further Reading: Chapter 04 of the text book Outline - matter and energy - radiation laws - solar and terrestrial radiation

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (2 of 9) Introduction Discussed how energy from the sun reaches the earth and how the orbit of the earth affects how much energy hits a certain point on the surface Now we want to discuss what this energy does once it reaches the earth: Need to understand how energy interacts with matter So, what is matter? And, what is energy?

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (3 of 9) Matter Substance that occupies space and has mass Composed of atoms and molecules Gas: Atoms/molecules are spread very far apart Exhibit random motion relative to their neighbors Gases expand and compress easily Liquid: Atoms/molecules exhibit random motion relative to their neighbors Interactions with one another Liquids do not expand and compress easily: allows the travel of waves Maintains a closed surface even without a container Solid: Atoms/molecules in fixed arrangement to one another Solids do not compress Bonds can be broken given sufficient energy State of material depends upon the amount of internal energy in the material Changing the energy can change its state

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (4 of 9) Energy “Ability to do work” Electromagnetic radiation: Energy which travels in waveform Does not require a medium Mechanical Energy: Kinetic Energy - Energy associated with bodies (or atoms) in motion Potential Energy - Energy associated with the position of a body (or atom) Atmosphere and oceans have both kinetic energy (due to their motions) and potential energy (due to their location) Sensible heat: Energy associated with motions of atoms/molecules within a larger body Also called internal kinetic energy When we measure “temperature” we are actually measuring the internal kinetic energy: as energy increases -> molecules move faster-> temperature increases Latent Heat: Energy associated with the change of phase (or state) of a body Also related to the energy of the atoms in a larger body (i.e. kinetic energy): as energy increases -> molecules move faster -> phase changes Does not result to change in temperature

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (5 of 9) Latent Heat The Movie Solid -> liquid -> Gas Internal Kinetic energy increases Requires input of energy Conversion of any kind of energy into latent heat Gas -> Liquid -> Solid Internal kinetic energy decreases Releases energy Conversion of latent heat into energy (typically sensible heat) Or loss of energy (i.e. loss of energy from water to environment produces ice) Conversion of one form of water to another is a critical mechanism for transferring heat with the atmosphere

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (6 of 9) Radiation Energy Animation: EM-Wave Key Properties: All matter emits radiation (as long as it has a temperature and all matter has a temperature) Travels in waveform Characteristics of the waveform determines how much energy the radiation has Energy can travel through vacuum Wavelength is the distance between two successive peaks or lows (frequency is inverse of wavelength) Short wavelengths = higher energy Long wavelengths = lower energy

Natural Environments: The Atmosphere GG 101 – Spring 2005 Example Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (7 of 9) Stefan-Boltzmann Law (Visualization) Relates the total flux of energy per unit area emitted by a body to its temperature (the higher the temperature, the more the energy emitted) Energy flux: W/m2 Stefan-Boltzmann constant (5.67 x 10-8 W/m2/K4) Temperature K (kelvin) Example Sun: T = 6000 K  m = 70,000,000 W/m2 Earth: T = 300 K  m = 450 W/m2

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (8 of 9) Wein’s Law Computes the wavelength of the most intense radiation as a function of temperature (the higher the temperature, the shorter the wavelength of maximum emission) Wavelength: (micrometers) Temperature (K) Example Sun: T = 6000 K  l = 0.48 mm (0.00000048 m) Earth: T = 300 K  l = 9.6 mm (0.0000096 m)

Natural Environments: The Atmosphere GG 101 – Spring 2005 Boston University Myneni Lecture 05: Energy and Radiation Jan-31-05 (9 of 9) Short and Longwave Radiation Bodies with higher temperature emit: More energy Shorter wavelengths More specifically: a body emits energy at many wavelengths; how much energy at each wavelength depends on the temperature of the body Sun (Solar Radiation): higher peak -> more intense radiation shortwave (0.2-4 micrometers) ultra-violet (0.2-0.4 mm) visible (0.4-0.7 mm) and shortwave infrared (0.7-4.0 mm) Earth (Terrestrial Radiation): low peak -> less intense radiation longwave (4-50 micrometers) thermal