2. The Earth’s Energy Budget Chapter 3

3. Objectives Trace the flow of energy through the atmosphere

4. A budget Income = outgo

5. Energy Income Insolation – incoming solar radiation Predominantly short wave radiation (0.4 – 0.7mm) Varies locally with season, latitude Total annual global insolation should remain constant

6. When energy enters the atmosphere it can be …. AbsorbedReflectedScatteredTransmitted

7. Absorbed Energy is absorbed by gasses, particulates, droplets Different wavelengths are absorbed differently. Ex. Most UV is absorbed by ozone, but most visible light is not absorbed CO 2 and H 2 O are better at absorbing IR than N 2 or O 2

8. Absorbed Result Absorber warms Amount of solar energy reaching the surface is reduced

9. Reflected Specular reflection – a beam is reflected with equal intensity Diffuse radiation – a beam is split into many smaller, less intense beams = scattering

10. Rayleigh scattering Caused by individual gas molecules Scatters shorter wavelengths (blue) more than longer wavelengths Redirects the scattered waves in every direction (and thus toward any direction), therefore, the sky looks blue

11. Rayleigh scattering Responsible for red sunsets

12. Mie scattering Caused by aerosols Tend to scatter all wavelengths Tends to scatter energy forward (toward the surface of the earth) Pollution causes the sky to look gray

13. Rayleigh and Mie scattering

14. Nonselective scattering Water droplets act like little lenses – create rainbows Masses of water droplets (clouds) reflect all wavelengths equally, thus they appear white or gray

15. Nonselective scattering

16. Transmitted Some amount of solar energy passes unobstructed to the surface of the earth Amount depends on atmospheric conditions

17. Overall annual amounts

18. When solar energy reaches the surface of the earth it can be… Reflected Absorbed

19. Reflected Albedo – reflectivity. Percent of energy reflected by a material. Snow has a higher albedo than dirt Overall the albedo of the earth is about 30%

20. If solar energy is absorbed by the surface it will eventually be removed by … Radiation Conduction Convection

21. Radiation The surface emits longwave radiation ONE TO 10  m Of this radiation some passes out into space, some is absorbed by the atmosphere and then reemitted in all directions

22. Conduction Can warm the earth below Can warm the laminar boundary layer (very thin layer of air in contact with the surface)

23. Convection Energy is transferred by movement of material in a fluid Warm air rises Cool air sinks In the process mixing occurs

24. Free convection

25. Forced convection

26. Convection Sensible heat – heat that you can sense (feel) i.e. warm air Latent heat – energy used to change the phase of water Latent heat of fusion – heat required to melt ice Latent heat of evaporation

27. Even though the energy budget of the atmosphere remains balanced there are latitudinal variations 0 0 to 40 0 net surplus40 0 to 90 0 net deficit

28. Budget is balanced by advection – horizontal movements of energy Global wind currentsOcean currents

29. Energy Balance and Temperature Chapter 3

30. Measurement of temperature - statistics Daily mean = mean of daily high and low temp. Monthly mean = mean of daily means for a month Yearly mean = mean of monthly means for a year

31. Temperature controls Land and waterOcean currentsAltitudeGeographic positionCloud cover and albedo

32. Land and Water Land exchanges heat more readily than water Water moves and thus mixes Light can penetrate into the water water has a high specific heat

33. Ocean currents Ocean currents transfer heat

34. Altitude Air is heated by the surface The farther away from the surface the cooler Mean environmental lapse rate = 6.5 0 C/km

35. Geographic Position Coast vs. inland Windward vs. leeward side of mountains

36. Cloud Cover and Albedo Cloud cover tends to reduce temperature variation (cooler days and warmer nights) High albedo reduces warming

37. Measurement of temperature - tools Maximum thermometer Minimum thermometer Thermograph Thermisor Instrument shelter

38. Temperature and human comfort – wind chill

39. Temperature and human comfort – heat index

40. Application of Temperature Data Heating Degree-days Number of degrees (F) below 65 0 on any day Cooling Degree-days Number of degrees (F) above 65 0 on any day

41. Have a great day!