Section 1- Ch 2: Solar Radiation and the Seasons
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CHAPTER TWO OBJECTIVES
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Greetings Weather Enthusiasts!
In lecture class during Week 3, we covered the Geographic Grid, Earth-Sun Relationships, Energy, Power, and the different forms of Energy Transfer - Radiation, Conduction, and Convection.
In lecture class during Week 3, we covered the Geographic Grid, Earth-Sun Relationships, Energy, Power, and the different forms of Energy Transfer - Radiation, Conduction, and Convection.
RADIATION CHARACTERISTICS
The Electromagnetic Spectrum
Radiation is the transfer of energy requiring no physical medium (can occur through empty space). Radiation is continually emitted by all substances. When you snuggle up with a loved one (human or animal) you can feel their radiating heat. We get the bulk of our energy from the Sun’s radiation, and it is this reception of radiation that is THE DRIVING FORCE for virtually all processes we will discuss in this course.
Radiation comes in the form of ELECTROMAGNETIC WAVES, because the radiation is composed of bpth electric and magnetic waves. Two properties of waves are their amplitude and wavelength.
There’s an infinite # of wavelengths…
Radiation comes in the form of ELECTROMAGNETIC WAVES, because the radiation is composed of bpth electric and magnetic waves. Two properties of waves are their amplitude and wavelength.
- Amplitude refers to the height of the wave crest. Radiation quantity refers to amount of energy transferred, and is associated with wave amplitude. Everything else being equal, the amount of energy being transferred is directly proportional to wave amplitude
- Wavelength is the distance from crest to crest (or trough to trough). Radiation wavelength relates to radiation quality:
- Wavelength identifies the type of radiant energy (X-ray, Gamma, Microwave, etc.)
- All electromagnetic radiation travels at the speed of light (300K km/s or 186K mi/s . It takes about 8 minutes for the Sun’s energy to reach us. For the next nearest star, it's about 4.3 years!
There’s an infinite # of wavelengths…
- Just like the Sun (video), All objects radiate energy in a # of wavelengths
- We are concerned with wavelengths on the magnitude of MICROMETERS = 1 millionth of a meter
The Electromagnetic Spectrum
There are Physical laws defining amount and wavelength of emitted energy and they apply to hypothetical perfect emitters of radiation known as blackbodies. The Earth and Sun are similar to blackbodies.There are TWO LAWS you should be familiar with:
- (Stefan-Boltzmann law) The intensity of radiation depends on the temperature raised to the fourth power; and
- Wien’s law For any radiating body, the wavelength of peak emission (in micrometers) is given by Wien’s law.
- The MAIN POINTS to gather from these laws is the following:
- The Sun emits high intensity short-wave radiation: < 4um = shortwave
- The Earth emits low intensity long-wave radiation: > 4 um = longwave
SOLAR CONSTANTHow much solar energy reaches the Earth? We know this amount, it’s called the Solar Constant. The Solar Constant is the average amount of solar energy received at the top of Earth’s atmosphere: 1367 W/m3.
Remember Perihelion and Aphelion? When the Earth is closest to the Sun in its orbit, it receives more energy, and when it is further away, less. It’s not that a beam of energy loses intensity as it moves through space, it’s that the same beam of energy is distributed over a larger and larger area, making it less effective at warming or illuminating. |
Reduction of Energy Received Due to Distance
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TERMS
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PREPARE FOR YOUR QUIZTo check for understanding, you will take a short quiz on Chapter 2. You will have two chances to take the quiz on Moodle, and I will record your highest score. Review the following to prepare for the quiz:
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