1. PRACTICE QUIZ PARTS 1 & 2 Open Wednesday 16 Sept! Be sure to try BOTH PARTS of the practice quiz in VISTA! Go to either “Quizzes” from the homepage OR “Assessments” on the left panel. Opens Sept 16 th at 1 pm, and will remain open until October 21 st ALSO, the extra credit survey closes Sept 18 th ! (link in VISTA)

2. Rotating Earth. No continents. 0º0º 30º 60º 90º FROM what direction do the surface winds blow for the sailboat? FROM the… One more clicker question: A. north B. south C. northeast D. southwest E. southeast

3. Rotating Earth. No continents. 0º0º 30º 60º 90º Northeast Trades Southeast Trades Westerlies Polar easterlies

4. Coriolis Effect: last point ZERO at ZERO (the equator) Not much difference in circumference between these latitudes Large difference in circumference between these latitudes MAXIMUM at poles

5. Heat transport: redistribution

6. Summary: General Atmospheric Circulation Different latitudes receive and emit different amounts of energy due to Earth’s curvature & heat transfer processes Hot, wet air rises. Cold, dry air sinks. Objects in motion on this rotating planet tend to follow curved paths (Coriolis effect: to the RIGHT in the N. Hem. & to the LEFT in the S. Hem.) Differential heating, air rising and sinking, the Earth rotating, all lead to the general atmospheric circulation (which you can develop) Relevance: weather, climate, energy

7. Goals for Today 1.PREDICT atmospheric circulation, location of cloud formation and precipitation for today’s Earth with continents 2.EXPLAIN how a balance between atmospheric pressure differences and Coriolis results in geostrophic winds 3.APPLY geostrophic wind principles to storms and jet streams Atmosphere II: Continents, pressure gradients, geostrophic winds

8. To achieve these goals, you’ll need to… Explain why the distribution of continents matters –At present, there is more land mass in the northern hemisphere than in the southern hemisphere –Land heats up and cools off faster than oceans –Earth’s “thermal” equator is offset to the north, on average Use a logical sequence of events to deduce geostrophic flow –Air tends to move from high to low pressure, along any horizontal pressure gradient –As an object in motion on a rotating planet, moving wind is influenced by Coriolis –In cases where the horizontal pressure gradient force and the Coriolis force are balanced  geostrophic wind

9. RELEVANCE Storm behaviour Seasonal climate patterns Air travel Monsoon rains

10. An Earth with continents: Northern hemisphere Southern hemisphere

11. How easy is it to heat/cool land versus ocean water? Effect of HEAT CAPACITY Heat capacity of fresh water = 4.18 J/gK Heat capacity of seawater = 3.93 J/gK Heat capacity of granite = 0.79 J/gK Takes more energy to heat/cool Takes less energy to heat/cool

12. How easy is it to heat/cool land versus ocean water? Effects of CONVECTION, CONDUCTION & MIXING Energy (heat) RAPIDLY transferred downward by mixing Energy (heat) transferred down- ward SLOWLY by conduction

13. Our situation today: Northern hemisphere MORE LAND HEATS/COOLS more QUICKLY Southern hemisphere LESS LAND HEATS/COOLS more SLOWLY

14. For our water-covered earth (last class)… 0º0º 30º 60º 90º Warm, wet air rises at the equator. Surface winds blow toward the equator to replace the rising air. Surface winds CONVERGE at the equator ITCZ @ equator

15. Earth’s Thermal Equator, a.k.a., the INTERTROPICAL CONVERGENCE ZONE (ITCZ) Image: GFDL Geographic equator 0 ⁰ …on today’s Earth, with continents

16. ITCZ average location Tracer: ascent/descent of air Image: W.M. Connolley Blue = rising Red/pink = sinking Equator

17. NOAA, GOES satellite image Clicker question: Within the box, where is the ITCZ? A B C D E (this is a satellite image showing clouds)

18. Incoming/Outgoing energy distribution Top of Atmosphere Absorbed at Surface Energy Latitude 90°N0°90°S (after Gill, Figure 1.1) ITCZ

19. Cloud patterns in hurricanes: What’s the air doing in this picture? Hurricane Kate, 2003, NASA

20. The weather: A surface analysis map Environment Canada

21. High Pressure: Atmospheric Circulation H 1008 1004 1000 L L L L L L Direction of PRESSURE GRADIENT FORCE (NOT the wind!)

22. Horizontal Pressure Gradient: temperature WARM COLD 200 400 600 800 1000 400 200 400 600 800 1000 HPGForce Warm vs. cold air column Same number of air molecules (in this case, no pressure gradient at the surface. Pressure gradient aloft.) Notes

23. High Pressure: HPGF H L L P L Horizontal Pressure Gradient Force Horizontal Pressure Gradient Force

24. High Pressure: Circulation X H L HPGF Coriolis Geostrophic Flow: Coriolis = HPGF

25. Geostrophic Wind Development PGFGeostrophic WindCoriolis force Notes

26. Effect of Friction Notes

27. High Pressure: Circulation H 1008 1004 1000 L L L L L L Flow clockwise around a high (N. Hemisphere) Coriolis = HPGF HPGF = Coriolis

28. Low Pressure: Circulation L 1000 1004 1008 H H H H H H Flow counterclockwise around a low (N. Hem.) HPGF = Coriolis Notes

29. At a given altitude, air pressure over low latitude is greater than air pressure over high latitude. L  H Upper atmosphere: Geostrophic flow and jet streams Marshak, Figure 20.14a

30. Northern hemisphere jet streams

31. Clicker question: What about the southern hemisphere? What direction do the jet streams flow there? Marshak, Figure 20.14a South Pole A. West to east B. East to west C. North to south D. South to north

32. Natl. Weather Service

33. Surface Winds and Sea-level pressure January JANUARY Notes

34. JULY Surface Winds and Sea-level pressure Notes

35. Rotating Earth WITH continents.

36. The presence and distribution of continents influences the average position of the ITCZ, locations of cloud formation, and precipitation. Horizontal pressure gradients set air masses in motion. Once in motion, they are influenced by Coriolis. Geostrophic flow occurs when HPGF balances the Coriolis force. You can use knowledge of the geostrophic balance to figure out wind directions in different scenarios, e.g. hurricanes, jet streams Summary: Continents, pressure gradients, geostrophic winds Relevance: storms, seasonal climate, air travel

37. Extra slides below this one

38. OUTLINE An Earth with continents –The Intertropical Convergence Zone (ITCZ) –Differential heating of continents and oceans –Winds driven by atmospheric pressure gradients Monsoon circulation –Seasonal air movement –Seasonal precipitation patterns –The geologic record of monsoons

39. Clicker question: Where is the ITCZ?

40. NOAA, Natl. Weather Service At a given altitude, air pressure over low latitude is greater than air pressure over high latitude. L  H Upper atmosphere: Geostrophic flow and jet streams G 2-3