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Oceans and Climate

Oceans and Climate. 69EG5513 – Climate & Climate Change. Dr Mark Cresswell FOLLOWED BY: Sea-level Practical. Lecture Topics. Introduction to the World’s Oceans Interactions between Ocean/Atmosphere El Nino Southern Oscillation (ENSO) Measuring SSTs from Space Ocean-Climate Indices

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Oceans and Climate

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  1. Oceans and Climate 69EG5513 – Climate & Climate Change Dr Mark Cresswell FOLLOWED BY: Sea-level Practical

  2. Lecture Topics • Introduction to the World’s Oceans • Interactions between Ocean/Atmosphere • El Nino Southern Oscillation (ENSO) • Measuring SSTs from Space • Ocean-Climate Indices • Oceans & Climate Change

  3. Introduction • Most of planet Earth is covered with water (71%) or 361 million square km • Over 60% of global ocean surface is in the southern hemisphere • ¾ of the ocean is between 3 – 6km in depth • The deepest part of the oceans is the Mariana Trench – east of the Philippines at over 11km • The oceans are 96.5%, by volume, water • Remaining 3.5% is dissolved salts, particles, organic material and gases

  4. Introduction Thermohaline circulation

  5. Ocean-Atmosphere Interactions Reflectance of radiation from calm water (Bigg, 1996)

  6. Ocean-Atmosphere Interactions • Heat exchange between the oceans and atmosphere is mainly through radiation processes • Another dominant mechanism is latent heat transfer • Water evaporating from the ocean surface uses energy to allow them to free their bonds from liquid water below the surface • Condensation within clouds releases energy which increases cloud buoyancy • Latent heat flux (transfer) therefore contributes to energy recycling via ocean-atmosphere

  7. Ocean-Atmosphere Interactions • Direct physical contact between the atmosphere and oceans leads to energy being exchanged by conduction • This energy exchange is called sensible heat flux • Sensible heat flux causes heat to be transferred from warmer to cooler fluid • This process occurs at sea-surface and near-surface air • Turbulence and high wind speeds enhance sensible heat flux processes

  8. Ocean-Atmosphere Interactions • Five Basic forces within Ocean and Atmosphere: • Gravity • Pressure gradients (due to density/mass differences) • Drag (loss or gain across air/sea interface) • Coriolis force due to Earth rotation • Tidal motion due to Moon and Sun gravity

  9. El Nino Southern Oscillation • ENSO is an SST anomaly • Normally easterly trade winds prevents eastward movement of warm water from western Pacific to eastern Pacific • When trade winds weaken, warm water propagates eastward, the low pressure over Indonesia breaks down and so too does the Walker circulation • It is brought about by a change in circulation

  10. Read about Kelvin and Rossby waves

  11. El Nino Southern Oscillation TOPEX-POSEIDON • For much of our oceans, temperature is not measured directly – but by proxy • Warmer water expands – if surrounded by cooler water it rises. Its height is therefore an indication of its temperature

  12. El Nino Southern Oscillation • TOPEX is an altimetric satellite • Return time of pulses of energy sent by TOPEX to the ocean surface are measured • Distance between satellite and water surface can be accurately measured • TOPEX used to measure El Niño by proxy

  13. Ocean-Climate Indices • Southern Oscillation Index (SOI). The SOI is defined as the normalized pressure difference between Tahiti and Darwin

  14. Ocean-Climate Indices • North Atlantic Oscillation (NAO). Both phases of the NAO are associated with basin-wide changes in the intensity and location of the North Atlantic jet stream and storm track

  15. Ocean-Climate Indices • Pacific Decadal Oscillation (PDO). The Pacific Decadal Oscillation (PDO) is a long-lived El Niño-like pattern of Pacific climate variability

  16. Oceans & Climate Change Source: IPCC, 2007

  17. Oceans & Climate Change Southern Ocean region Source: IPCC, 2007

  18. Oceans & Climate Change Source: IPCC, 2007

  19. Oceans & Climate Change Source: IPCC, 2007

  20. Reading List Bigg G (1996). The oceans & climate. By Cambridge University Press Climate Research Unit (UEA):http://www.cru.uea.ac.uk/cru/data/soi.htm Univ. of Washington (PDO information): http://jisao.washington.edu/pdo/ Climate prediction Center: http://www.cpc.noaa.gov/data/teledoc/telecontents.shtml KNMI Data Explorer: http://climexp.knmi.nl/start.cgi?someone@somewhere IPCC: http://www.ipcc.ch

  21. Today’s Practical http://jcm.chooseclimate.org/

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