Warming Earth and its Atmosphere The Diurnal and Seasonal Cycles

Transcription

1 Warming Earth and its Atmosphere The Diurnal and Seasonal Cycles

2 Or, what happens to the energy received from the sun?

3 First We Need to Understand The Ways in Which Heat Can be Transferred in the Atmosphere Latent heat Conduction Convection Advection Radiation

4 1. Convection Heat transfer in the vertical through buoyant motion

5 Buoyancy When something is less dense than the fluid (gas) that it displaces, it will rise. (and visa versa)

6 Atmospheric convection Cumulus Cloud Upward Heat Transfer

7 Evidence of Buoyant Motion in the Atmosphere Hot air balloon, helium balloon, blimp Birds soaring in circles, without flapping their wings Sail planes Shimmering of air over roads and parking lots in summer Cumulus clouds Smoke rising over fire

8 2. Latent heat the concept

9 Personal Experiences Latent Heat Consumption by Evaporation Chill stepping out of a shower evaporation consumes heat Use of swamp coolers instead of air conditioners in dry climates It is cooler over green grass than over a stone surface evaporation from leaves Cool breeze with thunderstorms in vicinity evaporation of rain below the cloud

10 Personal Experiences Latent Heat Release by Condensation or Freezing Spraying fruit trees with water when frost damage is possible freezing of water releases heat The bubbly appearance of cumulus clouds released latent heat in cloud makes them buoyant

11 Bubbly Cumulus Clouds

12 The Transport of Latent Heat Condensation Water Vapor ***** ***** Air Moves Vapor to Cloud Droplets Evaporation Heat Taken From Ocean Heat Released In Cloud

13 3. Conduction Transfer of heat from molecule to molecule Think of heat in terms of how fast the molecules are moving Fast moving molecules where something is hot collide with adjacent slow moving molecules where it is cooler, causing the slower molecules to speed (heat) up.

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15 Heat conductivity ability of material to conduct heat Air -.02 (Watts per meter per o C) Wood -.08 Water -.60 Wet soil Stone Iron - 80.

16 Thus, Air is a Poor Conductor of Heat (ever think about why thermopane windows work?)

17 4. Advection Warm air Wind direction X Cold air YOU ARE HERE (Temperature will increase)

18 5. Radiation Has nothing to do with nuclear radiation this is called electromagnetic radiation Different names are used for different wavelengths of electromagnetic radiation.

19 Everything with a Temperature above absolute zero emits EMR

20 Millimeters and Micrometers Measure of length used to express length of short waves Millimeter = one-thousandth of a meter = mm Micrometer = one-millionth of a meter = µm = micron

21 Intensity of Light Versus Wavelength (µm) Temperature of the sun = 6000 K (10,500 F)

22 Comments Wavelengths with the greatest intensity are the visible ones. Some of the ultraviolet and infrared wavelengths are also intense.

23 The Sun s Emission Spectrum Versus Earth s

24 Q: Is the Atmosphere Transparent to this Radiation? That is, is the Atmosphere Like a Clear Window is to Visible Light?

25 A: Not Exactly Clear - Sort of Like of a Selectively Dirty Window

26 What Interferes with Transmission of Light Through the Atmosphere? Some gases called optically active gases. Different gases absorb different wavelengths Particles of dust natural and man-made made Clouds and fog

27 Absorption by Ozone and Water Vapor Percent Absorbed UV VIZ SUN IR Earth IR SUN UV VIZ IR Earth IR

28 ?

29 SUN UV VIS IR Earth IR Atm Window Percent Absorbed

30 Now That We Know How Heat is Transferred in the Atmosphere! Putting it All Together

31 The Atmospheric Energy Checkbook Balance Gains and Losses (On the Average)

32 Putting the Balance Under a Microscope

33 How the Warm Ground Heats the Air In Contact With It Convection Ground Conduction in lowest millimeter

34 The Diurnal and Seasonal Cycles of Heating Exist Because of the Earth- Sun Geometry

35 The Cycles Diurnal Rotation of Earth on axis every 24 h Annual or seasonal Revolution of Earth around the sun every days

36 Equinoxes: Points in Earth s orbit around the sun where the sun is directly over the equator (12 hrs light & 12 hrs of darkness). Solstice: Points in orbit where the sun is displaced farthest N or S.

37 Important Latitude Bands o Earth Equator: central latitude Tropics : (23.5 N&S) Latitudes of maximum displacement of the sun Tropic of Cancer: 23.5 N (Summer N. Hem.) Tropic of Capricorn: 23.5 S (Summer S. Hem.) Arctic/Antarctic Circles: 66.5 N&S Latitudes where there is 24 hrs of daylight(nighttime) at summer(winter) solstices

38 Another Look.

39 Tropic of Capricorn 23.5 S Arctic circle 66.5 N Tropic of Cancer 23.5 N Equator 0

40 Seasonal Cycle -Causes- The sun heats the ground less intensely when it is at a low angle in the sky (winter), and more intensely when it is at a high angle above the horizon. The suns heat the ground more when the daylight is longer (Summer).

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43 Average January Temperature Near Sea Level

44 Average July Air Temperature Near Sea Level

45 Something Peculiar So why isn t it (on a global average) hotter in January? Southern Hemisphere 81% ocean Northern Hemisphere 61% ocean

46 Daily Temperature Cycle Balance of Incoming Solar and Outgoing Infrared

47 Max

48 Temperature Profile Near The Ground DAY profile Note: Temperatures almost always decrease with height

49 NIGHT FROST Radiation Inversion: Temperatures increase with height

50 What Can Effect The Day- Night Temperature Change? Cloud cover reduces diurnal variability Terrain: surface type, mountains, canyons, Wind: causes turbulent mixing of the atmosphere which reduces diurnal variability Approaching weather systems: cold fronts, warm fronts, squall lines, hurricanes Humidity

51 Topographic Effects on Nighttime Temperature Cold air pooling

52 Factors That Cause Temperature Variation From Place to Place Latitude warmer to south Land and water distribution winter warmer near water summer cooler near water Ocean currents Warm currents generally on east side of continents, cold currents on the west side Elevation of the surface above sea level Temperature decreases with elevation

53 Surface type e.g., urban versus rural Surface wetness

54 Cooler of Higher Elev. Warmer Over Ocean in Winter Warmer to South - More Radiation

55 Two cities with the same mean annual temperature but with very different climates

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