Chapter 2 Heating Earth’s Surface and Atmosphere The Atmosphere 9e Lutgens & Tarbuck Power Point by Michael C. LoPr

1. Chapter 2Heating Earth’s Surface and AtmosphereThe Atmosphere 9eLutgens & TarbuckPower Point by Michael C. LoPresto

2. Earth’s Motions • Earth has two principle motions • Rotation – the spinning of Earth about its axis • Revolution – the movement in orbit around the sun

3. Distance between Earth and Sun averages 150 million km. • Distance varies during the year • Perihelion: point in orbit of a planet closet to the sun. • Aphelion: point in orbit of a planet farthest from the sun.

4. The Seasons • Earth’s Orientation-Inclination of the Axis

5. The Seasons • The gradual change in day length accounts for some of the difference between winter and summer • The seasonal changes in the angle of the Sun above the horizon accounts for most of the difference • When the sun is directly above, the rays are more concentrated • When the sun is at an angle, the rays are spread out over a larger area

7. Earth-Sun Relations

8. The four days each year given special significance based on the annual migration of the direct rays of the Sun and its importance to the yearly cycle of weather are:

9. Solstices and Equinoxes

13. Solstices and Equinoxes • Winter Solstice – shortest day, first day of winter (December 21 or 22) • when the vertical rays of the Sun are striking 23.5° south latitude (Tropic of Capricorn

14. Summer Solstice – longest day, “official” first day of summer (June 21 or 22) • when the vertical rays of the Sun are striking 23.5° north latitude (Tropic of Cancer)

15. Equinoxes – Half way between the solstices, equal days and nights • Autumnal equinox – Sept. 22 or 23 • Vernal (spring) equinox – March 21 or 22 • when the vertical rays of the Sun strike the equator

17. Energy and Temperature • Energy – the capacity to do work • Kinetic Energy – energy associated with and object by virtue of its motion (swinging a hammer) • Potential Energy – has the potential to do work (food, hail suspended in a storm) • Temperature – how warm or cold an object is OR a measure of the average (not total) kinetic energy of the atoms or molecules in a substance

18. Heat • Heat – the transfer of energy into or out of an object and its surroundings. • Flows from region of higher temperature to one of lower temperature. • Once equal, flow stops.

19. Mechanisms of Energy Transfer

20. Mechanisms of Heat Transfer • Conduction – transfer of heat from one object to another through electron and molecular collisions (ex. Metals) • Convection – heat transfer that involves the actual movement or circulation of a substance • Thermals – examples of convection that involve upward movement of warm, less dense air - advection – the horizontal component of convection, common name “wind”

21. Radiation – does not need a medium, can travel through the vacuum of space • The sun is the ultimate source of energy that drives the weather • Electromagnetic Spectrum • Gamma, X-ray, UV, Visible Spectrum, IR, Micro, Radio • All electromagnetic waves travel at 300,000 km/s • It is the wavelength that changes • Most of the sun’s waves is concentrated in the visible to near visible range (43%), IR (49%), and <1% x-ray, gamma, and radio

22. Electromagnetic Radiation Electromagnetic Spectrum

23. Laws of Radiation • 1. all objects emit radiant energy • 2. hotter objects radiate more total energy per unit area than colder objects • 3. the hotter the radiating body, the shorter is the wavelength of maximum radiation • 4. objects that are good absorbers of radiation are also good emitters

24. Radiation from Sun & Earth

25. Incoming Solar Radiation • Some energy absorbed • Object gets warmer • Some energy transmitted • Object transparent to certain wavelengths • Some radiation bounces off object • Reflection: bounces back @ same angle and intensity • Scattered: larger # of weaker rays in many directions

26. Reflection Scattering

27. Incoming Solar Radiation • About 50% of the solar energy hits the Earth’s surface • 30% is reflected back to space • The remaining 20% is absorbed by clouds and atmospheric gases • Albedo – the fraction of radiation reflected by a surface

28. What Happens to Radiation?

29. Radiation Emitted by Earth Atmospheric Window

30. Radiation Emitted by Earth • Radiant energy absorbed is eventually reradiated skyward • This radiation is in the form of long wave infrared radiation • Because atmospheric gases are more efficient absorbers of long wave radiation, the atmosphere is heated from the ground up

31. The general drop in temperature with increased altitude in the troposphere (about 6.5°C/kilometer, a figure called the normal lapse rate) supports the fact that the atmosphere is heated from below.

32. Heat Budget

33. Heat Budget • The annual balance that exists between incoming and outgoing radiation is called the heat budget. • Earth’s average temperature remains relatively constant despite seasonal cold spells and heat waves. • This holds for the entire planet but not at each latitude.

34. Sun Angles at Different Latitudes

35. Latitudinal Heat Balance

36. Averaged over the year, a zone between 38°N and 38°S receives more solar radiation than is lost to space. • The opposite is true for higher latitudes, where more heat is lost through radiation than is received. • It is this energy imbalance between the low and high latitudes that drives the global winds and ocean currents, which transfers surplus heat from the tropics poleward.

37. Also, the radiation balance of a given place fluctuates with changes in cloud cover, atmospheric composition, and most important, Sun angle and length of daylight. • Thus, areas of radiation surplus and deficit migrate seasonally as the Sun angle and length of daylightchange.

38. Temperature Data at Different Latitudes

39. Calculating Sun Angles

40. Chapter 2 END

41. The Greenhouse Effect

42. Reflection and Earth’s Albedo