Chapter 3: Air Temperature

1. Chapter 3: Air Temperature • Daily temperature variations • The controls of temperature • Air temperature data • Air temperature and human comfort • Measuring air temperature

2. Daily Temperature Variations Record high T: 58 C or 136 F (Libya) Record low T: -89 C or -129 F (Antarctic)

3. Daytime Warming • Thermals: calm wind condition • forced convection: strong wind • water vapor effects • Cumulus clouds are markers of convection.

4. Nighttime Cooling • radiational cooling • nocturnal inversions • Inversions tend to occur on clear, calm, dry nights: strong winds would mix air; clouds or water vapor would absorb longwave radiation

5. Stepped Art Fig. 3-2, p. 57

6. Fig. 3-5, p. 60

7. Cold Air Near the Surface • inversions • thermal belts • Drainage winds: cold air that slides downhill.

8. Protecting Crops from the Cold Night Air • orchard heaters • wind machines • Freeze: Ta below freezing for a long enough time • To protect small plants: Use straw, cloth, or plastic bag to cover

9. The Controls of Temperature

10. The Controls of Temperature • Latitude: control daylight period and solar radiation • land and water distribution: water moving • ocean currents • elevation • specific heat: energy needed to raise T of 1 kg air by 1 K • Average weather conditions in the interior of large continents are much different than average conditions in coastal areas.

11. January sea level Ta Fig. 3-8, p. 64

12. July sea level Ta Fig. 3-9, p. 64

13. Air Temperature Data

14. Daily, Monthly and Yearly Temperatures • diurnal temperatur range: Tmax – Tmin large range occurs for dry, clear sky over desert • clouds and humidity effects: reduce daytime T but increase nighttime T • proximity to large bodies of water • Urban heat island: • annual temperature range: max monthly T -- min monthly T

15. Fig. 3-11, p. 65

16. What is normal T (30-yr average) for a particular day (March 15 over southwestern U.S.)? Figure 2, p. 69

17. The Use of Temperature Data • heating degree-days: daily mean Tbelow 64oF • cooling degree-days: daily mean Tabove 65oF • growing degree-days: daily mean T 1 degree above base T

18. Air Temperature and Human Comfort • Human body stabilizes its T primarily by converting food • into heat (metabolism) • The stronger the wind, the faster the body’s heat loss • High winds in below-freezing air can remove heat from exposed • skin so quickly that the skin may actually freeze (called frostbite) • Dry heat: perspire to feel cool; heat and humidity: feel hotter

19. Air Temperature and Human Comfort • wind chill index Shaded area: frostbite could occur in 30 min or less

20. Measuring Air Temperature While T is as high as 500oC in the upper atmosphere of 300 km, astronauts still feel very cold. Why?

21. Measuring Air Temperature • liquid-in-glass thermometers: mercury or alcohol • maximum and minimum thermometers • Infrared sensor or radiometer • Electrical thermometers • instrument shelters

22. Precip, wind, T/Td, rain type, lightning, cloud base, freezing rain, visibility