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. 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) • Total radiation emitted is equal to the sum over all wavelengths above

25. Radiation Laws • Stefan-Boltzmann Law – the total amount of blackbody radiation emitted (I) is related to temperature: I = σT4

26. Radiation Laws • Stefan-Boltzmann Law – the total amount of blackbody radiation emitted (I) is related to temperature: I = σT4 • For a graybody, this becomes: I = εσT4 where ε is the emissivity

27. Radiation Laws • Wien’s Law – the wavelength of maximum blackbody emission is related to temperature: ʎmax = 2900/T

28. Radiation Laws • Wien’s Law – the wavelength of maximum blackbody emission is related to temperature: ʎmax = 2900/T Sun is HOT (~6000K) Earth is NOT (~290 K)

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

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

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

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

33. 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)

34. 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)

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

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

37. Period of Daylight Vernal and autumnal equinox

38. Period of Daylight Summer solstice

39. Period of Daylight Winter solstice

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

41. Solar Angle

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

43. Beam Depletion

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

45. 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!

46. 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