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Coriolis Effect Modifies Hadley Circulation

Coriolis Effect Modifies Hadley Circulation. Modified Hadley Circulation. *. Vertical motions upwelling: rising air subsidence: sinking air. Horizontal motions convergence: coming together divergence: spreading apart. “Seeing” Hadley Circulation. H. H. H. H. H. H.

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Coriolis Effect Modifies Hadley Circulation

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  1. Coriolis Effect Modifies Hadley Circulation

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

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

  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 • True • 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 • Costa Rica (NH) • 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) Subsiding branches located around 30o N and S  DESERTS and high surface pressure Surface flow towards equator is northeasterly in NH and southeasterly in SH TRADE WINDS

  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 Subsiding Hadley Brach Strong T gradients Higher P Higher P Lower P

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

  18. Surface Flow Impacted by Friction Forces PGF Friction Coriolis Actual Flow direction Low Pressure High Pressure 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. Convergence/uplift—Stormy Divergence/Subsidence - Nice H L Low Pressure Center High Pressure Center anticyclones cyclones

  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? • Northern Hemisphere • Southern Hemisphere

  24. Continentality-Find the Continents 56 44 4 Contours show annual temperature range: Tsummer - Twinter

  25. Diurnal (Daily) Sea Breeze Day Night

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

  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 • Heat Exchange • Momentum Exchange (surface wind stress) • Moisture/Gas Exchange (water and carbon cycles)

  30. Heat Transport by Ocean and Atmosphere Tropics Midlatitudes Polar 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 Surface ocean Wind Equator

  36. Divergence Causes Upwelling

  37. Coastal Upwelling/Downwelling

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

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

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

  41. Deep Ocean Circulation • A SLOW process • Timescale to overturn ~ 1000 years • Lots of water (1.37x109 km3) and suppressed vertical mixing • Driven by formation of cold salty surface water

  42. Physical Properties versus Depth

  43. Salinity Salinity is measured in parts per thousand

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

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

  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 CO2 • Overturning brings nutrients up to surface biota  photosynthetic uptake of CO2 • Maintains transport of heat to higher latitudes, moderate latitudinal T gradients

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