Solar Energy to Earth and Seasons Current News and Weather Electromagnetic Spectrum   Insolation (Short-Wave Energy) Terrestrial Radiation (Long-Wave Energy) Greenhouse Effect For Next Class: Read Ch. 3

Dimensions and Distances Earth’s orbit Average distance from Earth to the Sun is 150,000,000 km (93,000,000 mi) Perihelion – closest at January 3 147,255,000 km (91,500,000 mi) Aphelion – farthest at July 4 152,083,000 km (94,500,000 mi) Earth is 8 minutes 20 seconds from the Sun Plane of Earth’s orbit is the plane of the ecliptic

Our Solar System Figure 2.1

Discussion Questions 1. What is the electromagnetic spectrum and why is it important?

The Electromagnetic Spectrum Figure 2.6

Wavelength and Frequency Figure 2.5

Wave Model of Electromagnetic Energy The relationship between the wavelength, , and frequency, , of electromagnetic radiation is based on the following formula, where c is the speed of light: Note that frequency,  is inversely proportional to wavelength,  The longer the wavelength, the lower the frequency, and vice-versa.

Stephan Boltzmann Law The total emitted radiation (Ml) from an objet is proportional to the fourth power of its absolute temperature. This is known as the Stephan-Boltzmann law and is expressed as: where s is the Stephan-Boltzmann constant, 5.6697 x 10 -8 W m-2 K -4. Thus, the amount of energy emitted by an object such as the Sun or the Earth is a function of its temperature.

Wein’s Displacement Law In addition to computing the total amount of energy exiting an object such as the Sun, we can determine its dominant wavelength (lmax) based on Wein's displacement law: where k is a constant equaling 2898 mm K, and T is the absolute temperature in kelvin. Therefore, as the Sun approximates a 6000 K blackbody, its dominant wavelength (lmax ) is 0.48 mm:

Sources of Electromagnetic Energy Jensen 2005 The 5770 – 6000 Kelvin (K) temperature of thermonuclear fusion on the sun produces a large amount of relatively short wavelength energy that travels through the vacuum of space at the speed of light. Some of this energy is intercepted by the Earth, where it interacts with the atmosphere and surface materials. The Earth reflects some of the energy directly back out to space or it may absorb the short wavelength energy and then emit it at a longer wavelength.

Discussion Questions 1. What is the electromagnetic spectrum and why is it important? 2. What is the difference between solar and terrestrial radiation?

Solar vs. Terrestrial Radiation Solar Radiation (Insolation): Short-wave, high intensity, mostly in the visible portion of the EM spectrum. Source is the Sun. Terrestrial Radiation: Long-wave, lower intensity. Source is the Earth and Atmosphere (or Earth-Atmosphere System)

Solar and Terrestrial Energy Figure 2.7

Discussion Questions 1. What is the electromagnetic spectrum and why is it important? 2. What is the difference between solar and terrestrial radiation? 3. How does latitude influence incoming solar radiation and temperature?

Figure 2.9

Seasonality Two important seasonal changes Sun’s altitude – angle above horizon or Solar Elevation at Noon (SEN) Day length

Chapter 2, Table 2.2 Labeled

Annual March of the Seasons Winter solstice – December 21 or 22 Subsolar point Tropic of Capricorn Spring equinox – March 20 or 21 Subsolar point Equator Summer solstice – June 20 or 21 Subsolar point Tropic of Cancer Fall equinox – September 22 or 23

Discussion Questions 1. What is the electromagnetic spectrum and why is it important? 2. What is the difference between solar and terrestrial radiation? 3. How does latitude influence incoming solar radiation and temperature? 4. Where on Earth would 24 hours of sunlight be observed on or around June 21? Why?

Chapter 2, Unnumbered Figure 1, Page 50 Labeled

Chapter 2, Unnumbered Figure 1, Page 51 Labeled

11:30 P.M. in the Antarctic Figure 2.16

Insolation at Top of Atmosphere Figure 2.10

Discussion Questions 1. What is the electromagnetic spectrum and why is it important? 2. What is the difference between solar and terrestrial radiation? 3. How does latitude influence incoming solar radiation and temperature? 4. Where on Earth would 24 hours of sunlight be observed on or around June 21? Why? 5. What is the greenhouse effect and why is it important?

Solar Elevation at Noon (SEN)

Solar Elevation at Noon (SEN) SEN is the angle of the noon sun above the horizon SEN = 90˚ - ArcDistance ArcDistance = number of degrees of latitude between location of interest and sun’s noontime vertical rays If the latitude of location of interest and sun are in opposite hemispheres, add to get ArcDistance If they are in the same hemisphere, subtract from the larger of the two values

SEN Example What is the SEN on June 21 for Boone (36 N) SEN = 90 – ArcDistance Where are the sun’s noontime vertical rays? ArcDistance = 36 – 23.5 ArcDistance = 12.5 SEN = 90 – 12.5 SEN = 77.5˚

SEN Exercises What is SEN in Punta Arenas (53º S) on June 21? December 21? What is SEN in Cayembe, Ecuador (0º) on June 21? March 21? What is SEN in Barrow, Alaska (71º N) on June 21? December 21?

Terrestrial Radiation Greenhouse Effect Heating of Earth’s surface and lower atmosphere caused by strong absorption and emission of infrared radiation (IR) by certain atmospheric gases known as greenhouse gases Similarity in radiational properties between atmospheric gases and the glass or plastic glazing of a greenhouse is the origin of the term greenhouse effect © AMS

Terrestrial Radiation Greenhouse Effect Responsible for considerable warming of Earth’s surface and lower atmosphere Earth would be too cold without it to support most forms of plant and animal life © AMS

How Greenhouse Effect Works https://www.youtube.com/watch?v=sTvqIijqvTg © AMS

Terrestrial Radiation Greenhouse Gases Water Vapor is the principal greenhouse gas Clear-sky contribution of 60% Other contributing gases: carbon dioxide (26%) ozone (8%) methane plus nitrous oxide (6%) © AMS

Terrestrial Radiation Greenhouse Gases Atmospheric window: range of wavelengths over which little or no radiation is absorbed Visible atmospheric window extends from about 0.3 to 0.7 micrometers Infrared atmospheric window from about 8 to 13 micrometers © AMS

Terrestrial Radiation Greenhouse Effect Heating of Earth’s surface and lower atmosphere caused by strong absorption and emission of infrared radiation (IR) by certain atmospheric gases known as greenhouse gases Similarity in radiational properties between atmospheric gases and the glass or plastic glazing of a greenhouse is the origin of the term greenhouse effect © AMS

Terrestrial Radiation Greenhouse Effect Responsible for considerable warming of Earth’s surface and lower atmosphere Earth would be too cold without it to support most forms of plant and animal life © AMS

Terrestrial Radiation Greenhouse Gases Water Vapor is the principal greenhouse gas Clear-sky contribution of 60% Other contributing gases: carbon dioxide (26%) ozone (8%) methane plus nitrous oxide (6%) © AMS

Terrestrial Radiation Greenhouse Gases Atmospheric window: range of wavelengths over which little or no radiation is absorbed Visible atmospheric window extends from about 0.3 to 0.7 micrometers Infrared atmospheric window from about 8 to 13 micrometers © AMS

Terrestrial Radiation Greenhouse Gases Water vapor strongly absorbs outgoing IR and emits IR back towards Earth’s surface Does not instigate warming or cooling trends in climate Role in climate change is to amplify rather than to trigger temperature trends Clouds affect climate in two ways: Warm Earth’s surface by absorbing and emitting IR Cool Earth’s surface by reflecting solar radiation © AMS