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The incoming solar energy

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Title: Chapter 2: Solar Radiation and the Seasons Last modified by: Jialin Lin Document presentation format: On-screen Show (4:3) Other titles: Times New Roman MS P ... – PowerPoint PPT presentation

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Title: The incoming solar energy


1
The incoming solar energy
2
Review of last lecture
  • Ice age a long time (millions to tens of
    millions of years) of cold temperatures and
    extended ice cover. gt5 in earths history
    (including now). Develop slowly, but end more
    abruptly.
  • Glacial cycle has a 100,000 year oscillation
    period
  • Past abrupt climate change
  • Tipping points

3
Energy basics
  • Energy the ability to do work
  • Many forms electrical, mechanical, thermal,
    chemical, nuclear,
  • Joule (J) standard unit of energy (1 J 0.239
    calories)
  • Watt (W) rate of energy flow (W 1 J/s)

4
Methods of Energy Transfer
  • Conduction
  • Molecule to molecule transfer
  • Heat flow warm to cold
  • e.g. leather seats in a car
  • Convection
  • transferred by vertical movement
  • physical mixing
  • e.g. boiling water
  • Radiation
  • propagated without medium (i.e. vacuum)
  • solar radiation provides nearly all energy
  • The rest of this chapter deals with radiation

5
Radiation
  • Everything continually emits radiation
  • Transfers energy in waves
  • Waves are both electrical and magnetic, hence
    electromagnetic radiation
  • Travels at the speed of light (300,000 km/s). It
    takes 8 minutes for light from the Sun to reach
    Earth, and 4.3 years for light from the next
    nearest star, Proxima Centauri to reach us.

6
Radiation Quantity and Quality
  • Quantity how much? ?
  • Wave height (Intensity).
  • Quality what kind? ?
  • Wavelength distance between crest and crest
    (or trough and trough). generally reported in µm
    (microns)- one millionth of a meter.

7
The Electromagnetic Spectrum
The limitations of the human eye!
8
A man detected by different instruments
Infred device
Bare eyes
X-ray
Microscope
9
Physical Representation of Radiation
  • Blackbodies purely hypothetical bodies that
    absorb and emit the maximum radiation at all
    wavelengths
  • The Earth and the sun are close to blackbodies.

10
What determines the quantity (intensity)? The
Stefan-Boltzmann Law
  • States that the intensity of radiation emitted
    from a blackbody is a function ONLY of
    temperature
  • I?T4
  • where I is the intensity of the radiation, T
    is the temperature in K, and ? is the
    Stefan-Boltzmann constant, 5.67 x 10-8 W m-2 K-4)
  • So, hotter bodies emit more energy than colder
    bodies (double T, 16x more radiation)
  • Earth (290K) I 401 Wm-2
  • Sun (6000K) I 7.3 x 106 Wm-2.
  • So ISun gtgt Iearth

11
What determines the quality (wavelength)? The
Weins Law
  • States that the peak wavelength of radiation
    emitted from a blackbody is a function ONLY of
    temperature
  • ?max b/T
  • where ?max is the peak wavelength of the
    radiation, T is the temperature in K, and b is
    the Weins displacement constant (2.90 x 10-3 m
    K)
  • So, hotter bodies emit at shorter wavelengths
  • Double T, half wavelength
  • Earth (290K) ?max 10 µm
  • Sun (6000K) ?max 0.5 µm

12
Wavelength of Sun and Earth Radiation
Sun shortwave (0.4-0.7 µm) Peak 0.5 µm
(green)
Sun
Earth longwave (4-100 µm) Peak 10 µm
(infrared)
13
Composition of sunlight
14
The rainbows
15
The Sun also emits high energy particles
Northern light (Aurora)
  • Caused by electrons and protons
  • They can only penetrate into the atmosphere from
    the magnetic north pole and south pole
  • They collide with the atmospheric molecules to
    generate the aurora

16
Video The solar cycle
  • http//www.youtube.com/watch?vsASbVkK-p0wplaynex
    t1listPL8EDAE089117E3D77featureresults_main

17
The sunspot number - A good index for solar
activity
  • Sunspots are temporary phenomena on the surface
    of the sun that appear visibly as dark spots
  • Caused by intense magnetic activity
  • The number of sunspots changes significantly
    between solar maximum and solar minimum

18
The solar cycle
  • is the periodic change in the sun's activity
    (including changes in the levels of solar
    radiation and ejection of solar material) and
    appearance (visible in changes in the number of
    sunspots, flares, and other visible
    manifestations).
  • has a duration of about 11 years.
  • has been observed (by changes in the sun's
    appearance and by changes seen on Earth, such as
    auroras) for hundreds of years.

19
The solar cycle and earths climate
  • Change of precipitation associated with solar
    maximum
  • Red-Increase, Blue-decrease (from Meehl et al.
    1999, Science)

20
Solar cycle and US air temperature
21
Solar cycle and grape production in France
22
Summary
  • What is energy? 3 methods of energy transfer
  • The names of the 6 wavelength categories in the
    electromagnetic radiation spectrum
  • Intensity of radiation (Stefan-Boltzman law)
    I?T4
  • Wavelength of radiation (Weins law)
    ?max b/T
  • The wavelength range of Sun (shortwave) and Earth
    (longwave) radition
  • The 11-year solar cycle
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