1. Surface air temperature

2. Review of last lecture Earth’s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Earth’s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Atmospheric influences on radiation (3 ways) Atmospheric influences on radiation (3 ways) The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? What cause the greenhouse effect? What are the major greenhouse gases? Why is methane important? What cause the greenhouse effect? What are the major greenhouse gases? Why is methane important? Sensible heat flux (dry flux from warm to cold regions) and latent heat flux (wet flux from wet to dry regions) Sensible heat flux (dry flux from warm to cold regions) and latent heat flux (wet flux from wet to dry regions)

3. Temperature Basics Temperature – measure of average kinetic energy (motion) of individual molecules in matter Temperature – measure of average kinetic energy (motion) of individual molecules in matter Isotherms – maps, connect lines of equal temperature Isotherms – maps, connect lines of equal temperature

4. Different temperature scales (units) All scales are relative All scales are relative degrees F = 9 ⁄ 5 degrees C + 32 degrees F = 9 ⁄ 5 degrees C + 32 degrees K = degrees C + 273.15 degrees K = degrees C + 273.15

5. Measurement of Temperature Thermometers are used to measure temperature with either mercury or alcohol. A maximum thermometer is used to record daily temperature maximums while a minimum thermometer records minimums. Instrument Shelters Weather instruments require shelters that protect them from solar radiation. They are painted white to create a high albedo. Must be 5 ft from the ground /surface to reduce laminar layer bias.

6. Air Temperature and the Human Body Human comfort not only affected by temperature Human comfort not only affected by temperature Two important considerations  wind and humidity Two important considerations  wind and humidity Wind Chill Index Wind Chill Index –relates temperature and wind speed Heat Index Heat Index –relates temperature and humidity Wind Chill Index Heat Index

7. Video: The 1995 Chicago heat wave

8. Seasonal variation of surface air temperature

9. Principal Controls on Temperature Principal Controls on Temperature 1. Latitudinal variations in net radiation 2. Land-Water Contrasts 3. Atmospheric Circulation 4. Ocean Currents 5. Altitude 6. Local Effects

10. tropic-to-tropic – energy surplus poles – energy deficits ~ 38 o N/S – balance imbalance of net radiation at surface  Equator/Tropics vs. high latitudes drives global circulation agents: wind, ocean currents, weather systems Controls on temperature 1. Latitudinal Variations in Net Radiation

11. Daily/Seasonal Radiation Patterns insolation peak vs. temperature insolation peak vs. temperature daily lag daily lag seasonal lag seasonal lag Lag is function of type of surface, wetness, wind, etc Lag is function of type of surface, wetness, wind, etc

12. T decreases poleward larger T gradient in winter isotherms shift seasonally T over land > water in summer NH steeper T gradient Seasonal Temp Distributions

13. Controls on temperature 2. Land-water contrasts Surface influences heating Heat Capacity – water > land… (water takes longer heat/cool) Mixing – fluids can be physically mixed Transparency – greater penetration (distributed over greater volume) Evaporation – consumes large amount of energy – big over water

14. Temperature Ranges (Summer minus Winter) Large over land, small over ocean

15. large scale circulation patterns resulted from pressure differences (gradients) generates winds  move warm/cold air around  affects temperature influences cloud cover Controls on temperature 3. Atmospheric circulation

16. Controls on temperature 4. Ocean currents

17. Infrared Satellite image of the Gulf Stream Red/orange = 25-29 o C Yellow/green = 17-24 o C Blue = 10-16 o C Purple = 2-9 o C

18. Temperature decreases with increasing altitude  ground acts as heat source Controls on temperature 5. Altitude

19. slope orientation: North v. South-facing slopes  temperature/moisture regimes  vegetation Controls on temperature 6. Local effects

20. forested v. open fields

21. Summary Temperature, 3 units Temperature, 3 units 6 factors controlling temperature 6 factors controlling temperature