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

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

15. 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 I = σT4 I = εσT4 where ε is the emissivity
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 ) 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