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Announcements

Announcements. Exam THIS Friday in Discussion Section Review session Thursday during lecture Advanced notice is required if you know you will miss Fri’s exam (we only offer early exams) NO MAKEUP exams without official documentation of an unexpected emergency!. GHG Ranking Factors.

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Announcements

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  1. Announcements Exam THIS Friday in Discussion Section Review session Thursday during lecture Advanced notice is required if you know you will miss Fri’s exam (we only offer early exams) NO MAKEUP exams without official documentation of an unexpected emergency!

  2. GHG Ranking Factors • Amount: more there is, more radiation can be absorbed • Ability: depends on the wavelength • Location: both where in the atmosphere and where () in the outgoing radiation spectrum

  3. Absorptivity versus Amount “Absorptivity is saturating” 3 2 2 1 1 m m m1 m2 m3 1 A   1 (band saturation), increasing amount of GHG gives smaller and smaller increases in  e.g.: 2 << 1 Absorptivity () Amount of GHG (i.e. concentration)

  4. GHG Ranking: Wavelength Location Water Level ~ Ts Plug a small leak small increase in Ts Plug a big leak big increase in Ts

  5. GHG Ranking: “Emission Height” Tb4 Ta4 Emission to space from z1 carries much more energy than from z2 z2 Altitude (z) z1 Ts Temperature

  6. GHG Ranking: Emission Height (T) Tafter A GHG which causes a higher emission altitude is a larger constriction of energy flow out. Tbefore

  7. Doubling CO2 will basically double the amount of radiation absorbed by CO2. • True • False

  8. Water Vapor • The global warming skeptics’ favorite GHG Fact: The Greenhouse Effect is mostly due to absorption of OLR by water vapor Fiction: “Therefore, Earth’s surface T will only respond to changes in the amount of water vapor”

  9. Saturation Vapor Pressure of Water PH2O = 0 PH2O increases PH2O “saturates” H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas H2Ogas wait wait H2Oliq H2Oliq H2Oliq Start: H2Oliq w/dry air above Middle: net evaporation End: condensation equals evaporation “Equilibrium”

  10. Saturation Vapor Pressure of Water The maximum amount of water vapor air can hold increases exponentially with air T

  11. Suppose we stop emitting CO2 but emit more H2O vapor from our tail pipes in a H2-powered economy. Should we worry about continuing to enhance the GHE? • Yes • No

  12. The dependence of the saturation vapor pressure of water on T is a negative feedback on climate change • True • False

  13. Water Vapor as a GHG • Water vapor increases for an increase in T • Water vapor’s increase causes an additional change in T • An example of a positive feedback on climate

  14. What have we accomplished? Developed a physical basis of present day global climate Described the mechanisms that can cause globalclimate change. 1 2 Now know how changes in solar radiation, albedo, and, [GHGs] can/should alter global average T. 3

  15. This Week and Next: Regional Climates • Part 1 – Atmospheric Motions • Wet tropics, major deserts • Temperate but stormy mid-latitudes • Dry/Cold Poles • Continentality • Part 2 – Ocean Circulation

  16. Regional Climates • The average weather of a particular latitude and longitude zone

  17. Spatial Radiation Imbalance

  18. Spatial Radiation Imbalance 300 W/m2 EOUT (LW) EIN (SW) 100 W/m2

  19. Where on Earth receives the largest daily average solar flux • Equator • Mid-latitudes • Poles

  20. Today: Atmospheric Motions – Part 1 • Horizontal Motions: parallel to Earth’s surface (the everyday wind) • Vertical Motions: perpendicular to Earth’s surface (up/down)

  21. Important Concepts in Vertical Motions • An air parcel that rises  expands due to lower surrounding pressure • EXPANSION requires WORK by the air parcel • Air parcel doing WORK, loses Energy, temperature goes down.

  22. Day After Tomorrow

  23. In “Day After Tomorrow”, a super-storm with a very low pressure center draws very cold lower stratospheric air to the surface causing instant freezing. • Consistent with 1st Law • Violates 1st Law

  24. The movie’s science advisor, if there was one, should have his/her PhD revoked. • Yes • No

  25. Announcements • EXAM FRIDAY, Review session Thursday • Through yesterday: • i.e. T(z) = Tsurf –z*(10K/km) if dry • T(z) = Tsurf – z*(6.5K/km) if wet • Start forming a final project group (3-4), • see course website for project ideas • Use discussion board for finding group members

  26. What is Buoyancy? PGF PGF object (rob) Fluid (rf) Fg Fg Fbuoyancy = PGF – Fg 0 if obfluid

  27. Heating a Fluid From Below Warm surface air less dense “buoyant” rises Convection: transfer of heat via motions of a fluid

  28. Making Air Move Pressure Gradient Force Air/water will move from a region of high pressure to low pressure Fluid with horizontal pressure gradient

  29. Horizontal Pressure Gradients PGF The picture is roughly symmetric for the Southern Hemisphere (SH)

  30. General Circulation of the Atmosphere divergence subsidence subsidence Upwelling convergence Cold high lats Warm Tropics Cold high lats higher pressure Lower pressure higher pressure An early picture based on Hadley’s 1735 paper: Tropopause 90 45 0 -45 -90

  31. Phase Transitions in Rising/Sinking Air In subsiding air, condensation and precipitation suppressed. In rising air, condensation and precipitation more likely rising subsiding

  32. Intertropical Convergence Zone

  33. The (original) Hadley Circulation (1735) HOT COLD COLD Explains: Intertropical Convergence Zone (ITCZ) Wet Tropics Dry Poles But it has some problems.

  34. Earth Rotates from West to East Circumference decreases from equator to pole To complete a full rotation in 1 day, equator rotates faster than higher latitudes coriolis effect movie

  35. Coriolis Effect in Northern Hemisphere  so object curves to right of initial direction. Object moving from equator has greater easterly velocity than surface at northern latitudes

  36. Coriolis Cartoon Trajectory seen by thrower

  37. An object moving south from the equator curves to the ______ of its initial forward direction • Left • Right

  38. Coriolis/Centrifugal Effect Summary Applies to objects moving North or South relative to Earth’s surface A similar effect occurs for objects traveling in E-W directions (centrifugal force) Objects (air or water, e.g.) moving in the NH will curve to the right of their forward direction and to the left in SH.

  39. Suppose Earth were a cylinder. Where would there be a coriolis effect? • A only • B only • A and B A B

  40. Upper-level Flow Tends to be Geostrophic PGF Coriolis Flow direction Low Pressure Geostrophic Flow: When PGF balanced by Coriolis Effect High Pressure

  41. Coriolis Effect Modifies Hadley Circulation

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

  43. “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

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

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

  46. 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).

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