1. Weather & Climate – MTDI 1200OL Plymouth State University
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 SURROUNDING AIR IS COOLED
THESE PROCESSES ALL TAKE ENERGY FROM SURROUNDING ENVIRONMENT AND “HIDE” IT IN THE WATER
SURROUNDING AIR IS COOLED

18. Liquid – Vapor Phase Changes SURROUNDING AIR IS WARMED
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. Freezing/melting temperature of water at sea level
Scales
Freezing/melting temperature of water at sea level

25. Boiling temperature of water at sea level
Scales
Boiling temperature of water at sea level

26. The temperature at which all molecular motion stops
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

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

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

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

42. AS TEMPERATURE INCREASES, OUTGOING RADIATION ALSO INCREASES
SUNRISE
AS TEMPERATURE INCREASES, OUTGOING RADIATION ALSO INCREASES

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

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

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

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

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

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

49. 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

50. 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 cooling of the surface

51. Nighttime Cooling
STUVE DIAGRAM

52. Nighttime Cooling
STUVE DIAGRAM
TEMPERATURE SCALE

53. Nighttime Cooling
STUVE DIAGRAM
PRESSURE SCALE

54. Nighttime Cooling PLOTTED VERTICAL TEMPERATURE PROFILE
TEMPERATURE USUALLY DECREASES WITH HEIGHT IN TROPOSPHERE

55. TEMPERATURE INVERSION
Nighttime Cooling
TEMPERATURE INVERSION
TEMPERATURE INCREASES WITH HEIGHT THROUGH LIMITED REGION OF TROPOSPHERE

56. Best conditions for radiation inversion
Clear
No clouds to radiate IR back to earth
Calm
No wind to mix warmer air down
Dry
Less cloudiness
No water vapor in the air to absorb heat
Allows IR radiation to escape
Long night
More time for ground to radiate IR away

57. How would the high temperature on a cloudy day compare to the high temperature on a clear day?
How would the low temperature on a cloudy night compare to the low temperature on a clear night?