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Regional Oceanography III

Regional Oceanography III . OEAS 604. Lecture Outline Pacific Ocean circulation Climate cycles Atmosphere-ocean coupling Chapters 8,9 – Knauss Chapter 10 – Talley et al. Westerlies – 30-60 latitude Trade Winds – from east Intertropical Convergence Zone (Doldrums) .

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Regional Oceanography III

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  1. Regional Oceanography III OEAS 604 • Lecture Outline • PacificOcean circulation • Climate cycles • Atmosphere-ocean coupling • Chapters 8,9 – Knauss • Chapter 10– Talley et al.

  2. Westerlies – 30-60 latitude Trade Winds – from east Intertropical Convergence Zone (Doldrums) Annual Mean Wind Field

  3. East and west basins Connection to Arctic and Southern Ocean Arctic connection restricted by the Aleutian Islands and Bering Strait

  4. Bottom Water Pathways Different varieties along western and eastern sides of basin Limited across basin exchange No deep water formation in north Pacific

  5. PacificOcean Current Structure • Subtropical gyres in both hemispheres • Eastern and western boundary currents • Subpolar gyre in northern hemisphere • Equatorial current system • Connection to Arctic • Connection to Southern Ocean

  6. Western Boundary Currents Kuroshio, East Australia Current Eastern Boundary Currents California Current Peru/ChileCurrent Equatorial Current System North Equatorial Current Equatorial Countercurrent South Equatorial Current Subpolar Gyre North PacificCurrent Alaska Current/Stream Oyashio ME - Mindanao Eddy; HE- Halmahera Eddy

  7. EquatorialCurrent Structure Banded structure Undercurrent shallow Upwelling

  8. Temperature section alongEquator in PacificOcean Warm Pool Cold Tongue Thermocline slopes upward from west to east

  9. SST – Eastern Pacific Ocean Cold Tongue

  10. Kuroshio – sheds eddies as moves across Pacific

  11. Bering Sea – Current Pattern

  12. Climate Change is associated with changes in the air temperature of the Earth • Temperature changes are caused by • changes in heat input from the sun • exchange of heat between the ocean and atmosphere (mostly) • changes in the motion of heat through the ocean and atmosphere, and • changes in the radiation properties of the atmosphere • These changes lead to various physical, chemical and biological changes throughout the earth

  13. Milankovic cycles • Are variations in the orbit of the earth with times scales of 20,000 to 100,000 years • Changes in the orbit eccentricity, tilt of earth’s rotation axis, and precession of earth’s orbit • Affect the length of time for the various seasons • Length of the year remains constant • Affects the shortwave radiation to the earth

  14. Ocean-Atmosphere Coupling • Some variations are caused by internal feedbacks between the atmosphere and ocean or within the atmosphere • Many of these variations are described by indexes of various kinds • Best understood is the El Niño/Southern Oscillation (ENSO)

  15. ENSO • Associated with changes in the equatorial Pacific • Originally defined as a change of pressure difference between Darwin, Australia and Tahiti (southern oscillation index or SOI) • Change in strength of south Pacific Trade winds (east to west winds) • Winds cause water to move to the west leaving lower water off South America and higher water off South Asia • Low water off South America allows upwelling to bring cool, nutrient rich water to the surface • Reduced winds leaves warm water in the east, no nutrients upwelled, reduced productivity, and poor fish harvest (El Niño)

  16. Walker Circulation

  17. ENSO • Water temperature affects atmospheric convection which changes the air mass distribution (and pressure) • Warm ocean events are El Niño - associated with Christmas season off South America • Cold ocean events (La Niña, anti-El Niño, el viejo). • El Niño means cooler and wetter winters in the US SE • La Niña means dryer conditions in the US SE • Other influences around the world

  18. ENSO index based on ocean temperature in the central Pacific Ocean

  19. SOI Index – Atmospheric Pressure Difference

  20. Other Indexes • Annular Modes (Southern Annular mode, SAM) • Changes in North-South pressure • increase/decrease in winds • North Atlantic Oscillation (NAO) • Change in Azores-Iceland pressure difference • Changes in N Atlantic wind strength and storm track • Pacific Decadal Oscillation (PDO) • W Pacific cool SST, SE Pacific warm SST • 20 to 30 year period • all indexes are available at NOAA climate prediction center (www.cpc.ncep.noaa.gov)

  21. Southern Annular Mode (SAM) Southern Ocean

  22. Positive NAO Eastern US wetter and stronger winter storms Negative NAO Eastern US has drier and colder air

  23. Pacific Decadal Oscillation - PDO

  24. Atmospheric CO2 measurements Mauna Loa, Hawaii

  25. Gille, J Climate (2008) Temperature trends in Southern Ocean Top 1000 m

  26. Levitus GRL, 2005. Global ocean heat content change 1955 to 2003, 0-3000 m

  27. Sorkosz et al. (2012, J. Climate) IPCC (2007)

  28. Next Class • Ocean Waves • Chapter , Knauss • Quiz – Thursday, 14 November

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