1. Coriolis Effect Modifies Hadley Circulation

2. Modified Hadley Circulation Horizontal motions convergence: coming together divergence: spreading apart Vertical motions upwelling: rising air subsidence: sinking air *

3. “Seeing” Hadley Circulation Lines of constant pressure (isobars). More closely spaced lines: steeper change in pressure H H H HH H Mean Surface Pressure Contours

4. Announcements Posters: March 12 – 13 during lecture; buy one poster board (~ 4’x4’) per group –Groups to be solidified by next Friday –SEE WEBSITE FOR MORE DETAILS Office Hours today 4-5 pm (506 or 510 ATG) and 5-6 pm (406 ATG) Another problem set will be posted soon. Beware of quizzes in discussion sections…

5. This Week Finish Chapter 4 of text Regional Climates Continued –Midlatitude Circulation –Land/Ocean Contrasts Global Water Cycle

6. Hadley Circulation and Regional Climates World’s largest deserts Wet and dry seasons in the Tropics The Trade Winds

7. World’s Deserts Not shown: Polar Regions!

8. World’s Deserts Desert dust blows from W. Sahara and N. Morocco over Canary Islands. Desert dust is a source of nutrients to ocean and land biota (often a world away).

9. All desert areas (low annual precipitation) occur in regions of general subsidence 1.True 2.False

10. Suppose you wanted to the take Presidents’ Day vacation (Feb) in the sunny and warm tropics. Because you want sunny dry weather you choose 1.Costa Rica (NH) 2.Amazonia (SH)

11. Seasonal Shift in Hadley Circulation ITCZ location shifts N-S depending on season. Leads to wet and dry seasons in the tropics.

12. Surface Pressure and Winds Summary

13. Hadley Circulation Summary Low surface pressure near equator  convergence  ITCZ ITCZ: rainy!  location moves N or S with seasons causing WET and DRY seasons in the tropics High altitude branches WESTERLY @ 15 – 30 N/S due to Coriolis Force and PGF (geostrophic flow) Surface flow towards equator is northeasterly in NH and southeasterly in SH  TRADE WINDS Subsiding branches located around 30 o N and S  DESERTS and high surface pressure

14. Mid-latitude Circulation Westerly flow both NH and SH Strong temperature gradient gives rise cold/warm fronts (moving air masses) Cyclones and Anticyclones

15. Mid-latitude Westerlies

16. Warm/Cold Fronts Strong T gradients Higher P Lower P Subsiding Hadley Brach

17. Flow Around High and Low Pressure Centers Upper-level flow geostrophic: parallel to isobars. High Pressure CenterLow Pressure Center L H In NH flow counterclockwise around Low  cyclonic flow In NH flow clockwise around High  anticyclonic flow

18. Surface Flow Impacted by Friction High Pressure Low Pressure PGF Coriolis Actual Flow direction Friction Forces Friction causes flow to move away from high pressure, but towards low pressure.

19. Surface-level Flow affected by Friction Centers of low or high pressure at surface induce flow that spirals in or out, respectively. High Pressure CenterLow Pressure Center L H Convergence/uplift—StormyDivergence/Subsidence - Nice cyclones anticyclones

20. Tropical Cyclone—Hurricane Gordon

21. Midlatitude Cyclones

22. Midlatitude Average Circulation (Summary) Westerly flow 35 – 55 N/S Large latitudinal temperature gradients – warm and cold fronts induce storminess Low pressure centers are wet/rainy (storms) high pressure centers are dry/sunny

23. Where would you expect “continentality” to be greatest? 1.Northern Hemisphere 2.Southern Hemisphere

24. Continentality-Find the Continents Contours show annual temperature range: T summer - T winter 4 44 56

25. Diurnal (Daily) Sea Breeze Day Night

26. July January Similar to diurnal sea breeze but on larger spatial and temporal (seasonal) scales. Monsoonal Circulation H L

27. Atmospheric Circulation Summary Three major N – S circulation cells in each hemisphere (Hadley, Midlatitudes, Polar) Tropics: surface level easterlies (trades), ITCZ, and subsidence zones (30N/S) Midlatitudes: westerly flow, frontal storms Land/Ocean contrasts: monsoonal circulation, diurnal sea breeze, continentality

28. Ocean Circulation and Climate Reading: Chapter 5

29. Atmosphere-Ocean Couplings 1.Heat Exchange 2.Momentum Exchange (surface wind stress) 3.Moisture/Gas Exchange (water and carbon cycles)

30. Heat Transport by Ocean and Atmosphere TropicsMidlatitudesPolar regions

31. Key Ocean Properties Ocean water is salty ~ 30 g salt in 1 liter Ocean heated from above  warm surface water, cold deep ocean Vertical mixing determined by buoyancy –warm water less dense, saltier water more dense Vertical mixing suppressed: surface vs. deep circulation

32. Wind-driven Surface Ocean Circulation

33. Surface Ocean Circulation

34. Gulf Stream western branch of mid-Atlantic gyre AVHRR Satellite measurement of Sea Surface T

35. Convergence And Divergence Net convergence of surface water in center of gyres Net divergence at eastern ocean boundaries and equator Equator Wind Surface ocean

36. Divergence Causes Upwelling

37. Coastal Upwelling/Downwelling

38. Marine Stratus Clouds Eastern-boundary coastal upwelling  Cold water cools air  Cloud formation Surface winds Ocean surface flow

39. Where do you expect the coldest sea surface temperatures? 1.Eastern ocean boundaries 2.Western ocean boundaries

40. monthly mean SST animation 1.Latitudinal distribution of solar radiation 2.Heat exchange with atmosphere 3.Circulation patterns (e.g. upwelling) Sea Surface Temperatures Observe the following

41. Deep Ocean Circulation A SLOW process –Timescale to overturn ~ 1000 years –Lots of water (1.37x10 9 km 3 ) and suppressed vertical mixing Driven by formation of cold salty surface water

42. Physical Properties versus Depth

43. Salinity is measured in parts per thousand Salinity

44. Thermo-haline Circulation (temperature-salty) Mixed layer ~ 1 km deep Middle and deep ocean Lower latitudes High latitudes Net sinking: Deep Water formation Ocean-Atm heat transfer Sea ice Cold salty water

45. Reduces the influence of the winds Insulates the ocean (prevents heat loss) Rejects salt when it grows / Adds freshwater when it melts Sea ice influence on the ocean

46. Thermo-haline Circulation (THC)

47. Marine Chlorophyll From Space

48. Thermohaline Circulation Importance Deep ocean is an enormous reservoir for heat and dissolved gases like CO 2 Overturning brings nutrients up to surface biota  photosynthetic uptake of CO 2 Maintains transport of heat to higher latitudes, moderate latitudinal T gradients