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HEAT & TEMPERATURE Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University

HEAT & TEMPERATURE Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University. 1. Ahrens, Ch. 2 & Ch. 3. Heat. Weather is ultimately caused by the uneven heating of Earth’s surface

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HEAT & TEMPERATURE Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University

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  1. HEAT & TEMPERATURE Dr. Sam Miller Weather & Climate – MTDI 1200OL Plymouth State University 1

  2. Ahrens, Ch. 2 & Ch. 3

  3. Heat

  4. Weather is ultimately caused by the uneven heating of Earth’s surface • Temperature is a measure of the kinetic energy content of some object or fluid medium (like air) • Heat – energy transfer due to temperature differences • Temperature gradient – Temperature difference over a known distance

  5. Heat transfer mechanisms in the atmosphere • Radiation • Conduction • Convection • Latent heat

  6. Radiation Transfer of energy via electromagnetic wave Carries Sun’s energy to Earth 1350 Watts / m2 at top of atmosphere Heats surface of Earth Earth emits LW (IR) radiation IR is absorbed by greenhouse gases in atmosphere

  7. Conduction Transfer of energy across a temperature gradient Objects of two different temperatures must be in direct contact The greater the temperature gradient, the faster the flow of heat The atmosphere is a very poor conductor of heat Works best with solid objects

  8. Conduction Transfer of energy across a temperature gradient Objects of two different temperatures must be in direct contact The greater the temperature gradient, the faster the flow of heat The atmosphere is a very poor conductor of heat Works best with solid objects THE LOWEST FEW CENTIMETERS OF THE ATMOSPHERE ARE HEATED BY CONDUCTING HEAT FROM THE EARTH’S SURFACE

  9. Convection Transfer of energy by movement of a fluid medium, like air or water Very efficient process in the atmosphere

  10. Convection HEAT IS TRANSFERRED VERTICALLY TO GREAT HEIGHTS IN THERMALS HEAT IS TRANSFERRED HORIZONTALLY BY THE WIND (ADVECTION) Transfer of energy by movement of a fluid medium, like air or water Very efficient process in the atmosphere

  11. Latent Heat Latent means “hidden” Heat absorbed or released when medium changes phases In atmosphere, medium is water Three states (phases) of water in Earth system: Ice (solid) Liquid Vapor (gas)

  12. Phase Changes

  13. Solid – Vapor Phase Changes

  14. Solid – Vapor Phase Changes THESE PROCESSES USUALLY OCCUR VERY SLOWLY IN THE ATMOSPHERE

  15. Solid – Liquid Phase Changes THESE PROCESSES ORDINARILY OCCUR AT 0 CELSIUS (273 KELVINS)

  16. Liquid – Vapor Phase Changes THESE PROCESSES OCCUR AT ALL TEMPERATURES ABOVE FREEZING BOILING = VERY EFFICIENT FORM OF EVAPORATION AT 100 C (373 KELVINS)

  17. Liquid – Vapor Phase Changes THESE PROCESSES ALL TAKE ENERGY FROM SURROUNDING ENVIRONMENT AND “HIDE” IT IN THE WATER SURROUNDING AIR IS COOLED

  18. Liquid – Vapor Phase Changes THESE PROCESSES ALL TAKE HIDDEN ENERGY FROM WATER AND PUT IT BACK INTO ENVIRONMENT SURROUNDING AIR IS WARMED

  19. All Processes Together LATENT HEAT RADIATION CONDENSATION CONVECTION CONDUCTION

  20. Temperature

  21. Definition • Measure of the average kinetic energy of the molecules of a substance. • Hot substance – molecules move fast • Cold substance – molecules move slow

  22. Measuring Temperature • Thermometers are used to measure temperature • Usual units Fahrenheit and Celsius • Conversion

  23. Scales

  24. Scales Freezing/melting temperature of water at sea level

  25. Scales Boiling temperature of water at sea level

  26. Scales ABSOLUTE ZERO The temperature at which all molecular motion stops 0 Absolute (Kelvin) -273 Celsius -460 Fahrenheit

  27. Scales THERE ARE 100 DEGREES BETWEEN MELTING AND BOILING ON THE CELSIUS AND KELVIN SCALES Size of a degree

  28. Scales THERE ARE 180 DEGREES BETWEEN MELTING AND BOILING ON THE FAHRENHEIT SCALE Size of a degree

  29. Temperature Variations

  30. Types of Temperature Variations: • Diurnal (daily): Time of day • Annual: Time of year (seasonal) • Vertical: Temperature profiles of troposphere, stratosphere, etc. • Vertical: Terrain-induced variations • Horizontal: Latitude, surface type, wind direction, ocean currents, etc.

  31. Types of Temperature Variations: • Diurnal (daily): Time of day • Annual: Time of year (seasonal) • Vertical: Temperature profiles of troposphere, stratosphere, etc. • Vertical: Terrain-induced variations • Horizontal: Latitude, surface type, wind direction, ocean currents, etc.

  32. Daily Temperature Variations • In the course of a day, when are the highest temperatures? • But when is the strongest sunlight?

  33. Daily Temperature Variations • Maximum sunlight intensity is at local Solar noon • But maximum temperatures occur later • Sometime around 2 – 4 PM • Depending on location and conditions • Why not at noon?

  34. Daily Temperature Variations • Best explained by remembering radiation balance discussed earlier • Incoming energy = Sunlight • Outgoing energy = Terrestrial (IR) radiation • Weakest when surface is cold • Strongest when surface is hot

  35. If more energy is gained than is lost, temperature will increase • If more energy is lost than is gained, temperature will decrease

  36. OVERNIGHT SURFACE RADIATES INFRARED ALL NIGHT NO INCOMING RADIATION ALL RADIATION FLUX IS OUTWARD (LOSS) TEMPERATURE DROPS

  37. OVERNIGHT AS TEMPERATURE DROPS, OUTGOING RADIATION TERM ALSO DECREASES

  38. SUNRISE SUNLIGHT BEGINS INCREASING FROM ZERO INCOMING TERM QUICKLY BECOMES LARGER THAN OUTGOING TERM TEMPERATURE BEGINS TO INCREASE

  39. SUNRISE AS TEMPERATURE INCREASES, OUTGOING RADIATION ALSO INCREASES

  40. SOLAR NOON SUN AT ZENITH INCOMING TERM REACHES ITS MAXIMUM INCOMING RADIATION MUCH LARGER THAN OUTGOING RADIATION TEMPERATURE CONTINUES TO RISE

  41. SOLAR NOON OUTGOING RADIATION TERM CONTINUES TO INCREASE AS TEMPERATURE RISES

  42. MID-AFTERNOON INCOMING RADIATION TERM IS DECREASING TEMPERATURE CONTINUES TO RISE UNTIL OUTGOING TERRESTRIAL RADIATION IS LARGER THAN INCOMING SOLAR RADIATION

  43. LATE AFTERNOON INCOMING TERM IS DECREASING TEMPERATURE BEGINS TO FALL AS OUTGOING TERRESTRIAL RADIATION EXCEEDS INCOMING SOLAR RADIATION

  44. SUNSET INCOMING TERM GOES TO ZERO TEMPERATURE CONTINUES TO FALL AS TEMPERATURE FALLS, OUTGOING TERRESTRIAL RADIATION DECREASES

  45. EVENING INCOMING TERM IS ZERO TEMPERATURE CONTINUES TO FALL AS TEMPERATURE FALLS, OUTGOING TERRESTRIAL RADIATION DECREASES

  46. Daytime Warming • Maximum sunlight intensity is at noon • But maximum temperatures occur later • Sometime around 2 – 4 PM • Depending on location and conditions • The air temperature will keep increasing as long as the incoming Solar energy (gained) is greater than the outgoing IR energy (lost) by Earth’s surface

  47. Nighttime Cooling • No more solar energy, but Earth keeps radiating IR • Ground is better radiator than air • Temperature of air close to ground colder than air higher up • Radiation inversion– temperature just above the ground increases with height for a few hundred meters, then falls again • Formed through radiational coolingof the surface

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