Chapter 2 – Solar Radiation and the Seasons

1. Chapter 2 – Solar Radiation and the Seasons

2. Energy • Energy is defined as the ability to do work

3. Energy • Energy is defined as the ability to do work • Kinetic energy – the energy of motion

4. Energy • Energy is defined as the ability to do work • Kinetic energy – the energy of motion • Potential energy – energy that can be used

5. Energy • Energy is defined as the ability to do work • Kinetic energy – the energy of motion • Potential energy – energy that can be used • Energy is conserved! (1st law of thermodynamics)

6. Energy Transfer • Although energy is conserved, it can move through the following mechanisms: 1) Conduction – heat transfer by physical contact, from higher to lower temperature

7. Conduction in the Atmosphere • Occurs at the atmosphere/surface interface • Partly responsible for daytime heating/nighttime cooling! (The diurnal cycle)

8. Energy Transfer • Although energy is conserved, it can move through the following mechanisms: 2) Convection – heat transfer by movement

9. Convection in the Atmosphere • Vertical transport of heat

10. Convection in the Atmosphere • Vertical transport of heat • Horizontal transport of heat = advection

11. Convection in the Atmosphere Courtesy maltaweather.info

12. Energy Transfer • Although energy is conserved, it can move through the following mechanisms: 3) Radiation - transfer of energy by electromagnetic radiation (no medium required!)

13. Radiation Characteristics of radiation 1) Wavelength – the distance between wave crests

14. Radiation Characteristics of radiation 1) Wavelength – the distance between wave crests 2) Amplitude – the height of the wave

15. Radiation Characteristics of radiation 1) Wavelength – the distance between wave crests 2) Amplitude – the height of the wave 3) Wave speed – constant! (speed of light - 186,000 miles/second)

16. Radiation • The wavelength of radiation determines its type

17. Radiation • The wavelength of radiation determines its type • The amplitude determines the intensity

18. Radiation • What emits radiation?

19. Radiation • What emits radiation? EVERYTHING!!

20. Radiation • The types (wavelengths) and intensity (amplitudes) of radiation depend on temperature

21. Radiation • The types (wavelengths) and intensity (amplitudes) of radiation depend on temperature Sun is HOT (~10,000oF) Earth is NOT (~59oF) Shortwave radiation Longwave radiation

22. Radiation • Blackbody – an object that absorbs all radiation and emits the maximum amount of radiation at every wavelength (not realistic)

23. Radiation • Blackbody – an object that absorbs all radiation and emits the maximum amount of radiation at every wavelength (not realistic) • Graybody – an object that emits a fraction (emissivity) of blackbody radiation (more realistic)

24. Practical use of Radiation Properties • Visible satellite imagery doesn’t work in the dark

25. Practical use of Radiation Properties • Visible satellite imagery doesn’t work in the dark • Infrared (longwave) radiation occurs always – use infrared satellite imagery!

26. Solar Radiation and the Earth • The solar constant – the amount of solar radiation hitting the earth

27. Solar Radiation and the Earth Earth – 1367 W/m2 Mars – 445 W/m2

28. The Sun’s Energy

29. Solar Radiation and the Earth • Earth orbits the sun eliptically (once per 365.25) days Farthest point (aphelion, Jul 4) Closest point (perihelion, Jan 4)

30. Solar Radiation and the Earth • Earth gets ~7% more radiation in winter (not enough to cause the seasons!) What does? Farthest point (aphelion, Jul 4) Closest point (perihelion, Jan 4)

31. Solar Radiation and the Earth • Earth’s tilt is the true cause of the seasons! • Earth’s axis is tilted 23.5o

32. Solar Radiation and the Earth • 3 factors contribute to the amount of incoming solar radiation (insolation): 1) Period of daylight

33. Period of Daylight Vernal and autumnal equinox

34. Period of Daylight Summer solstice

35. Period of Daylight Winter solstice

36. Solar Radiation and the Earth • 3 factors contribute to the amount of incoming solar radiation (insolation): 2) Solar angle

37. Solar Angle

38. Solar Radiation and the Earth • 3 factors contribute to the amount of incoming solar radiation (insolation): 3) Beam depletion

39. Beam Depletion

40. Solar Radiation and the Earth • What’s the end result of these 3 mechanisms and the tilt of the earth?

41. Solar Radiation and the Earth • What’s the end result of these 3 mechanisms and the tilt of the earth? - Weather as we know it!

42. Solar Radiation and the Earth • What’s the end result of these 3 mechanisms and the tilt of the earth? - Weather as we know it! Jet stream… Mid-latitude cylcones…fronts… Thunderstorms…winds

43. Albedo • the proportion of the incident light or radiation that is reflected by a surface, typically that of a planet or moon.

44. What impacts Albedo? • Clouds Depending on their altitude and optical properties, clouds either cool or warm the earth.  • Surface albedo: Just as some clouds reflect solar energy into space, so do light-colored land surfaces.  • Oceans: From space, oceans look much different than adjacent land areas - they often appear darker, suggesting that they should be absorbing far more sunlight

45. What impacts albedo? • Forested areas: Like the oceans, the interaction of forests and sunlight is complex. The amount of solar radiation absorbed by forest vegetation depends upon the type and color of vegetation, the time of year, and how well watered and healthy the plants are.