1. Solar Energy on Earth

2. The Electromagnetic Spectrum
Energy travel as waves and particles called photons
Energy is the capacity to do work
E=MC2
Where E is energy, M is mass and C is the speed of light (300,000km/sec)
Energy has electrical AND magnetic properties
ALL objects ABSORB and EMIT EM radiation

4. EM Radiation Described in terms of Wavelength or Frequency
Wavelength distance between successive crests or troughs in km, m, mm, mm
Frequency # wave crest/time (1sec) cycles/sec or Hertz (Hz)
The longer the Wavelength (l) the lower the frequency
Frequency is inversely proportional to l, so the higher the frequency the shorter the l

5. There is a simple relationship between the wavelength (l), frequency (n), and velocity (c). If you know any 2 of them then you can compute the 3rd using
  c = l n
or, velocity (c) equals wavelength (l) times frequency (n).

6. EM Radiation Travel through space
In a vacuum travel at the speed of light
Pass through liquids, solids, gases
EM radiation can be reflected, refracted, transmitted as well as absorbed
Solar radiation arrives on Earth primarily as visible ( mm) and Ultra-violet and is reflected and absorb and re-radiated to space as visible and Infra-red (heat)

8. Interactions with the Atmosphere
Scattering
Refraction
Absorption

9. Scattering
The redirection of EM energy by particles suspended in the atmosphere or large molecules of atmospheric gases

10. Refraction
The bending of light rays at the contact between two media that transmit light but with different density; when light enters the denser medium, it is defracted toward surface normal

11. Absorption
The atmosphere prevents, or strongly attenuates, transmission of radiation through the atmosphere
Three gases: - Ozone (O3): absorbs ultraviolet radiation high in
atmosphere - Carbon-dioxide (CO2): absorbs mid and far
infrared ( microm) in lower atmosphere - Water vapor (H2O): absorbs mid-far infrared
( , >27microm) in lower atmosphere

12. Interactions with Surface
 All EM energy reaches earth's surface must be reflected, absorbed, or transmitted
Their rate depends on: type of features, wavelength, angle of illumination
Reflection
Absorption
Transmission

13. What other features impact Solar Energy?

14. Vegetation
Chlorophyll absorbs blue and red, reflects green (visible light spectrum)
The spongy mesophyll cells reflect near infrared light that is related to vegetation biomass because the intercellular air space of spongy mesophyll layer is where photosynthesis and respiration occur
Vegetation moisture content absorbs mid infrared energy
From

15. Soils Soil moisture decreases reflectance
Coarse soil (dry) has relatively high reflectance
Surface roughness, organic matter, iron oxide affect reflectance

16. Water Transmission and Absorption
Water surface, suspended material, and bottom of water body can affect the spectral response

17. Solar Altitude Intensity of solar radiation varies with latitude
Intensity of solar radiation varies with time of day
Intensity of solar radiation varies with path through atmosphere gases

18. TEMPERATE
POLAR
TROPIC

20. Solar Radiation & The Atmosphere
Solar radiation interacts with gases and aerosols
Scattering & reflection (albedo), absorption (absorptivity) or transmissivity (amount that reaches earth’s surface) of solar radiation must equal 100%
In scattering a particle disperses solar radiation in all directions
Scattering by molecules is wavelength dependent and preferential scattering of blue-violet light by N2 and O2 is the reason for the daytime sky
Water and ice scatter visible light equally at all wavelengths so that clouds appear white

21. Albedo Fraction of total radiation reflected by an object (surface).
Varies according to:
Cloud cover.
Particles in air.
Angle of sun’s rays.
Types of surface.

23. Stratospheric Ozone Ozone is a gas made up of three oxygen atoms (O3).
Ozone is destroyed when it reacts with molecules containing nitrogen, hydrogen, chlorine, or bromine. (CFCs)
Ozone protects life on Earth from the Sun’s ultraviolet (UV) radiation.
Ozone screens all of the most energetic, UV-c, radiation, and most of the UV-b radiation.
Ozone only screens about half of the UV-a radiation. Excessive UV-b and UV-a radiation can cause sunburn and can lead to skin cancer and eye damage.
In the lower atmosphere (the troposphere) near the Earth’s surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions.
At ground level, high concentrations of ozone are toxic to people and plants.

25. Intensity of solar radiation
The Earth receives solar radiation unequally over its surface
The intensity per unit area of surface is greatest at the equator
Intermediate in the middle latitudes
The lowest intensity is at the polar regions

27. Global Solar Radiation Budget
Reflected 31%
Absorbed by atmosphere 20%
Absorbed by Earth’s surface 49%
Earth’s climate is controlled by a Greenhouse Effect
Gases in the atmosphere control this effect
H2Ovapor, CO2, O3, CH4, N2O
The percent of IR radiation absorbed varies with l
An Atmospheric Window is a range of l over which little or no radiation is absorbed
A visible window extends mm and major IR 8-13 mm, the peak IR emission of the planet is at 10mm

28. Absorptivity is very low or near zero in atmospheric window

29. Greenhouse Gases
CO2 is stored in four reservoirs: three that are active and one inactive reservoir including
the atmosphere,
the oceans,
the terrestrial system
Earth’s crust
Most CO2 is stored in the oceans while the smallest amount is found in the atmosphere.
Short-wavelength incoming radiation is not blocked by CO2, but re-radiated long-wavelength energy is, and this warms the atmosphere causing the greenhouse effect