MET 61 Introduction to Meteorology - Lecture 7

1. MET 61 Introduction to Meteorology - Lecture 7 “Warming the Earth and Atmosphere” Dr. Eugene Cordero San Jose State University W&H: pg 113-122 Stull: Chapter 2 Ahrens:  Chapter 2 Class Outline: Nature of energy Radiation in the atmosphere Radiation laws (relationships) MET 61 Introduction to Meteorology

2. The Nature of Energy in the Atmosphere • Radiant Energy is energy associated with electromagnetic waves propagating through space • Thermal Energy is energy associated with the ability of one body or substance to raise the temperature of a cooler one • Potential Energy is energy due to position, e.g. moisture in a cloud about to fall as rain • Kinetic Energy is energy due to motion, e.g. air in motion

3. While there are four forms of energy in the atmosphere, there are only three modes of energy transmission • ByRadiation • ByConductionor the • By Convection or the

4. While there are four forms of energy in the atmosphere, there are only three modes of energy transmission • ByRadiation of electromagnetic waves propagated through space • ByConductionor the transfer of energy in a substance by means of molecular excitation without any net external motion • By Convection or the transfer of energy by mass motions within a fluid or gas, resulting in actual transport of energy.

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7. Energy flow through a simple climate system Energy Input Energy Output Climate System First Law of Thermodynamicsstates that energy can neither be created nor destroyed. This leaves only two possibilities; either

8. Basic Radiation Concepts

9. Electromagnetic radiation l • Radiation is the transfer of energy by rapid oscillations of electromagnetic fields. • The most important general characteristic is its wavelength (), ____________________________. • Frequency,  and wave speed, c are related as: =c/; c=3.0x108m/s • Wavenumber is defined as # waves/unit of measure. =1/ (m-1) ; note difference in book notation Defined as the crest-to-crest distance

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11. Spectrum of electromagnetic radiation

12. The Earth-Sun relationship Mean d = 149.5 x 106 km 4 x 1026 Watts MET 61 Introduction to Meteorology

13. What emits electromagnetic radiation? • All bodies that possess energy [i.e. whose temperatures are > 0 Kelvin (-273.2 C)] emit radiation • Efficiency of emission is dependent on its emissivity ( • Where a body emits the maximum radiation for its temperature it is called a black body • Less efficient radiators have  varying between 0 and 1.

14. Energy absorption and emission • Molecules can absorb and emit discrete amounts of energy (photons). • These discrete amounts of energy are associated with electron orbits, rotational changes and vibrational rates. • Certain objects are selective absorbers: • They absorb (and emit) only certain wavelengths. • Absorption and emission properties are described in terms of • ‘line spectrum’. MET 61 Introduction to Meteorology

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16. Absorption spectra for CO2 MET 61 Introduction to Meteorology

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18. Absorption spectra for H2O MET 61 Introduction to Meteorology

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20. Absorption spectra for O2and O3 MET 61 Introduction to Meteorology

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22. Total Atmospheric Absorption Spectra CO2+H2O+O3 etc. MET 61 Introduction to Meteorology

23. Wavenumber Go to the 200 mb height/Isotach (GFS) and identify the approximate wavenumber for the jet stream using the analysis field.

24. Two fundamental facts about e-m radiation • The higher the temperature of the object emitting radiation: • the shorter the wavelength of radiation emitted • the greater the amount of radiation emitted • These relationships are defined by the Planck and Stefan-Boltzmann Law

25. Blackbody Radiation • A blackbody emits it’s maximum possible radiation for that temperature. • A blackbody is a theoretical concept. • Plank’s law states that the irradiance of monochromatic (at one wavelength) radiation emitted by a blackbody at temperature T is: c1=3.74x10-16 W m2; c2=1.44x10-2 m ºK MET 61 Introduction to Meteorology

26. Planck’s Curve Top Diagram • 300 K object top and right hand axes, 6000 K object left and bottom axes • Note massive increase in energy and decrease in wavelength for the hotter object Lower Diagram • Generalised curves showing changes in wavelength and energy emission with temperature MET 61 Introduction to Meteorology

27. Stefan-Boltzmann law • Relates the blackbody irradiance to the temperature. • Integrates the monochromatic irradiance over all wavelengths  is Stefan-Boltzmann constant: 5.57x10-8 W m-2 deg-4. For non-black bodies a value (between 0 - unity) for emissivity must be included, e.g.F = T4 MET 61 Introduction to Meteorology

28. Wien’s Displacement Law • Relates the wavelength of peak emission for a blackbody at temperature T. where  is in m and T in K MET 61 Introduction to Meteorology

29. Solar Energy • Radiant Flux of solar energy is ~ 3.9x1026 W • Irradiance (E*) : energy/m2 • The Sun’s irradiance at the outer portion of solar disk is (radius=7x108) is: MET 61 Introduction to Meteorology

30. Solar Energy (2) • The average temperature of the sun is about: • 5780°K • From the Stefan-Boltzmann relationship: Irradiance is: F =T4 = (5.67x10-8 W m-2 K-4) (5780)4 F= 6.33 x 107 W/m2 • This is another way to calculate the Sun’s irradiance at the outer portion of the solar disk MET 61 Introduction to Meteorology

31. In Class Questions • In the following diagram the profile of radiation intensity is given for the Sun and the Earth. Using the previously discussed radiation laws, calculate • a) the approximate values of the wavelengths of maximum emissions for the sun and earth • b) The maximum radiation intensity for both the sun and the earth. MET 61 Introduction to Meteorology

33. Solution • Calculate the wavelength of maximum radiation for the sun and the earth? • For the Sun (max) = 2897/6000 = 0.483 m • For the Earth (max) = 2897/288 = 10.01 m MET 61 Introduction to Meteorology

34. Solution B) Use below MET 61 Introduction to Meteorology

35. Short and longwave radiation • All objects emit radiation: • Sun emits radiation mostly at shorter wavelengths; ultraviolet (UV) and visible: • Earth emits radiation mostly at longer wavelengths; infrared (IR) • Difference based on temperature of emitting body. • (shortwave or solar radiation) • (Longwave or terrestrial radiation) MET 61 Introduction to Meteorology

36. Solar Energy • Radiant Flux of solar energy is ~ 3.9x1026 W • Irradiance (E*) : energy/m2 • Derive the solar constant (the irradiance at the top of the earth’s atmosphere): S MET 61 Introduction to Meteorology

37. Activity 6 (Due March 14th) • Red light has a wavelength of 0.7 m. Find the corresponding frequency and wavenumber. • If you were trying to identify changes in the Earth’s surface temperature, what clues would you look for from a space-based observing system (hint radiation…)? • Calculate and plot out (using a computer) the blackbody irradiance for the sun and earth. • 4.12 • 5. 4.14 MET 61 Introduction to Meteorology

39. Some relationships…  = 5.57x10-8 W m-2 ºK -4. c1=3.74x10-16 W m2; c2=1.44x10-2 m ºK MET 61 Introduction to Meteorology