 # MET 61 1 MET 61 Introduction to Meteorology MET 61 Introduction to Meteorology - Lecture 7 “Warming the Earth and Atmosphere” Dr. Eugene Cordero San Jose.

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MET 61 1 MET 61 Introduction to Meteorology 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)

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

While there are four forms of energy in the atmosphere, there are only three modes of energy transmission By Radiation By Conduction or the By Convection or the

While there are four forms of energy in the atmosphere, there are only three modes of energy transmission By Radiation of electromagnetic waves propagated through space By Conduction or 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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Energy flow through a simple climate system First Law of Thermodynamics states that energy can neither be created nor destroyed. This leaves only two possibilities; either Energy Input Energy Output Climate System

Energy flow through a simple climate system First Law of Thermodynamics states that energy can neither be created nor destroyed. This leaves only two possibilities; either Energy input = energy output, or Energy input = energy output +/- energy storage change Energy Input Energy Output Climate System

Electromagnetic radiation 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=3.0x10 8 m/s Wavenumber is defined as # waves/unit of measure.  =1/ (m -1 )

Electromagnetic radiation 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=3.0x10 8 m/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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MET 61 14 MET 61 Introduction to Meteorology The Earth-Sun relationship 4 x 10 26 Watts Mean d = 149.5 x 10 6 km

What emits electromagnetic radiation? All bodies that possess energy Efficiency of emission is dependent on its: Where a body emits the maximum radiation for its temperature it is called a: Less efficient radiators have  varying between 0 and 1.

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.

MET 61 17 MET 61 Introduction to Meteorology 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: – Absorption and emission properties are described in terms of –

MET 61 18 MET 61 Introduction to Meteorology 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’.

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MET 61 20 MET 61 Introduction to Meteorology Absorption spectra for CO 2

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MET 61 22 MET 61 Introduction to Meteorology Absorption spectra for H 2 O

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MET 61 24 MET 61 Introduction to Meteorology Absorption spectra for O 2 and O 3

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MET 61 26 MET 61 Introduction to Meteorology Total Atmospheric Absorption Spectra CO 2 +H 2 O+O 3 etc.

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

Two fundamental facts about e-m radiation The higher the temperature of the object emitting radiation: – – These relationships are defined by the Planck and Stefan-Boltzmann Law

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

MET 61 30 MET 61 Introduction to Meteorology 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: c 1 =3.74x10 -16 W m 2 ; c 2 =1.44x10 -2 m ºK

MET 61 31 MET 61 Introduction to Meteorology 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: c 1 =3.74x10 -16 W m 2 ; c 2 =1.44x10 -2 m ºK

MET 61 32 MET 61 Introduction to Meteorology 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 33 MET 61 Introduction to Meteorology Stefan-Boltzmann law Relates the blackbody irradiance to the temperature. Integrates the monochromatic irradiance over all wavelengths  is Stefan-Boltzmann constant: 5.67x10 -8 W m -2 deg -4. For non-black bodies a value (between 0 - unity) for emissivity must be included, e.g. E =  T 4

MET 61 34 MET 61 Introduction to Meteorology 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 =  T 4

MET 61 35 MET 61 Introduction to Meteorology 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 36 MET 61 Introduction to Meteorology 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 37 MET 61 Introduction to Meteorology Solar Energy Radiant Flux of solar energy is ~ 3.9x10 26 W Irradiance (E * ) : energy/m 2 The Sun’s irradiance at the outer portion of solar disk is (radius=7x10 8 ) is:

MET 61 38 MET 61 Introduction to Meteorology Solar Energy Radiant Flux of solar energy is ~ 3.9x10 26 W Irradiance (E * ) : energy/m 2 The Sun’s irradiance at the outer portion of solar disk is (radius=7x10 8 ) is:

MET 61 39 MET 61 Introduction to Meteorology Solar Energy (2) The average temperature of the sun is about: –5780°K From the Stefan-Boltzmann relationship: Irradiance is: This is another way to calculate the Sun’s irradiance at the outer portion of the solar disk

MET 61 40 MET 61 Introduction to Meteorology Solar Energy (2) The average temperature of the sun is about: –5780°K From the Stefan-Boltzmann relationship: Irradiance is: F =  T 4 = (5.67x10 -8 W m -2 K -4 ) (5780) 4 F= 6.33 x 10 7 W/m 2 This is another way to calculate the Sun’s irradiance at the outer portion of the solar disk

MET 61 41 MET 61 Introduction to Meteorology 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 43 MET 61 Introduction to Meteorology 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 44 MET 61 Introduction to Meteorology Solution B) Use below

MET 61 45 MET 61 Introduction to Meteorology 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.

MET 61 46 MET 61 Introduction to Meteorology 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 47 MET 61 Introduction to Meteorology Geopotential Defined as the potential energy of a unit mass relative to sea level. Which is equal to the work (W=Fd) done by raising this mass from sea level to the altitude z.

MET 61 48 MET 61 Introduction to Meteorology Geopotential Height Is defined to include the decrease in gravity, g, with increasing altitude. Where R 0 = 6356.7km and g=9.8m/s 2 Or sometimes called, Z. What is H at z=5km. Explain why they are different.

MET 61 49 MET 61 Introduction to Meteorology Solar Energy Radiant Flux of solar energy is ~ 3.9x10 26 W Irradiance (E * ) : energy/m 2 Derive the solar constant (the irradiance at the top of the earth’s atmosphere): S

MET 61 50 MET 61 Introduction to Meteorology Activity 6 (Due March 14 th ) 1.Red light has a wavelength of 0.7  m. Find the corresponding frequency and wavenumber. 2.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…)? 3.Calculate and plot out (using a computer) the blackbody irradiance for the sun and earth. 4.4.12 5. 4.14

MET 61 51 MET 61 Introduction to Meteorology Assigned Reading: Jan 30- Feb 4: Ahrens Ch 2:Ahrens Ch 2: Stull Ch 2: Pages 29-38Stull Ch 2: Pages 29-38 Activity #2 question:Activity #2 question: Stull: N14 (a, e, g) Stull: N14 (a, e, g)

Simplified radiative energy cascade for the Earth-atmosphere climate system Energy Input Energy Output E-A Climate System Extraterrestrial Short Wave Radiation Reflected Extraterrestrial Short Wave Radiation Terrestrial Long Wave Radiation Planetary Albedo Solar Temperature Planetary Temperature

MET 61 54 MET 61 Introduction to Meteorology Some relationships…  = 5.57x10-8 W m -2 ºK -4. c 1 =3.74x10 -16 W m 2 ; c 2 =1.44x10 -2 m ºK

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