1. NATS 101 Lecture 8 Temperature Variations

2. Supplemental References for Today’s Lecture Wallace, J. M. and P. V. Hobbs, 1977: Atmospheric Science, An Introductory Survey. 467 pp. Academic Press. (ISBN 0-12-732950-1)

3. Review Seasons Due to Tilt of Earth’s Axis Affects Two Things: Solar Zenith Angle - Length of Day Differential Solar Heating and IR Cooling Cause of Atmospheric-Ocean Motions

4. Is Longest Day the Hottest Day? USA Today WWW Site Consider Average Daily Temperature for Chicago IL:

5. Annual Energy Balance Heat transfer done by winds and ocean currents Differential heating drives winds and currents We will examine later in course NHSH Radiative Warming Radiative Cooling Ahrens, Fig. 2.21

6. Temperature Questions What causes diurnal temperature variations? What physical processes can influence daily temperature variations? Why is MAX temperature after solar noon? Why is MIN temperature just after sunrise? What is Wind Chill Factor? (if time allows)

7. MAX Temperature near Surface Convection Conduction Solar SW Ahrens, Fig 3.1 Air at ground level is heated the most

8. MIN Temperature near Surface Ahrens, Fig 3.3 Outgoing Infrared Absorbed & Re-emitted Infrared Conduction INVERSION – Temp decreases w/height Air at ground level is cooled the most

9. Daily Range of Temperatures Ahrens, Fig 3.10 MAX-MIN difference decreases with height above ground

10. 12 and 00 UTC TUS Sounding MAX-MIN Range 12 o C at 925 mb 6 o C at 910 mb 2 o C at 800 mb 0 o C by 700 mb Range decreases with height isotherms isobars Diurnal Range Inversion

11. Temperature Height t1t1 t2t2 t3t3 Temperature Height t2t2 t3t3 t1t1 t4t4 Growth and Decay of Inversion Evening Morning t4t4 Cooled the most at the ground levelWarmed the most at the ground level

12. What Affects Inversion Strength? Cloud Cover Clear skies-strong inversion Cloudy skies-weak inversion Land Characteristics Snow cover-strong inversion Bare ground-weaker inversion Wind Speed Calm winds-strong inversion Strong winds-weak inversion Weak IRStrong IR Absorption Re-Emission Warm Cold Mixing with Fast Winds

13. Review: Is Longest Day the Hottest Day? USA Today WWW Site Average Daily Temperature for Chicago IL

14. When Does MAX-MIN Occur? When incoming SW exceeds outgoing IR Temperature rises When outgoing IR exceeds incoming SW Temperature falls When outgoing IR equals incoming SW Temp. is constant MAX occurs Late afternoon MIN occurs Just after sunrise Ahrens, Fig 3.2

15. Winter-Summer Temperature Variations at Sea Level Continents undergo larger changes than oceans High latitudes undergo larger changes than low latitudes Ahrens, Figs. 3.8, 3.9 100 o F 10 o F DJF JJA

16. Ahrens, Figs. 3.8, 3.9 100 o F 10 o F DJF JJA Winter-Summer Temperature Variations at Sea Level Continents undergo larger changes than oceans High latitudes undergo larger changes than low latitudes

17. Controls of Temperature Latitude Average temperatures in middle latitudes decrease by 5-10 o C every 10 o latitude Elevation Lapse rate in troposphere is 6.5 o C/km Tucson (2,500 ft)July Max - 100 o F Mt. Lemmon (8,500 ft) July Max - 76 o F

18. Controls of Temperature Ocean Currents and Prevailing Winds Warm-Gulf Stream Cold-California Current Land versus Water Heat capacity of water is 5X that of land Absorbed solar energy is distributed a greater depth in water than in land

19. Specific Heat Capacity Heat required to raise temperature of 1 gm of mass 1 o C. Rock has lower heat capacity than water Still water warms or cools very slowly compared to air and land

20. Water-Soil Heating Depth Deep Penetration Shallow Penetration Consider Incoming Solar Energy Penetrating Water-Soil Convective Mixing Small warming over great depthLarge warming in shallow layer Conduction No mixing Large Heat Capacity Small Heat Capacity

21. Wallace and Hobbs, p347 Soil Temperature

22. Wallace and Hobbs, p348 Ocean Temperature

23. Wallace and Hobbs, p348 Ice Formation

24. Wind Chill Still air is poor conductor; lack of wind allows insulating layer of still air to form near skin Wind blows insulating layer of air from skin Forced convection or heat transport by advection

25. Summary Balance between incoming and outgoing energy controls temperature rises and falls MAX late afternoon, MIN just after sunrise Diurnal temp. changes are largest at ground Affected by wind, cloud cover, land type Winter-Summer changes Largest over land, high latitudes Temperature Controls Latitude, Altitude, Land-Sea, Ocean Currents

26. Assignment Ahrens Atmospheric Moisture Pages 77-89, B: 430, D: 433-436 Problems 4.1, 4.2, 4.5, 4.6, 4.9, 4.10