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Climatology Lecture 8

Climatology Lecture 8. Variability of the General Circulation. Richard Washington. Lecture Outline. El Nino - Southern Oscillation (ENSO): definition impacts on climate ways of measuring ENSO some past ENSO events North Atlantic Oscillation (NAO). Annual Average Rainfall mm/day.

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Climatology Lecture 8

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  1. Climatology Lecture 8 Variability of the General Circulation Richard Washington

  2. Lecture Outline • El Nino - Southern Oscillation (ENSO): • definition • impacts on climate • ways of measuring ENSO • some past ENSO events • North Atlantic Oscillation (NAO)

  3. Annual Average Rainfall mm/day

  4. Dec 82

  5. SEP 97

  6. Nov 88

  7. ENSO • Ocean - Atmosphere Interaction • Largest known source of climate variability • Global changes to rainfall, winds, pressure and temperature, especially in the tropics • Major El Nino event 1982/83 1997/98 • Sustained El Nino event 1991-1994

  8. Lecture Outline • El Nino - Southern Oscillation (ENSO): • definition • impacts on climate • ways of measuring ENSO • some past ENSO events • North Atlantic Oscillation (NAO)

  9. pressure higher (than normal) at Darwin pressure lower (than normal) in the C.Pacific westerlies (weak easterlies) across Pacific wet C.Pacificdry W.Pacific pressure lower (than normal) at Darwin pressure higher (than normal) in the C.Pacific strong easterlies across Pacific dry C.Pacificwet W.Pacific El NinoLa Nina

  10. WET East Africa (Oct-Dec) DRY southern Africa (Dec- March) DRY Sahel (July-Sep) DRY East Africa (Oct-Dec) WET southern Africa (Dec-March) WET Sahel (July-Sep) El NinoLa Nina

  11. Lecture Outline • El Nino - Southern Oscillation (ENSO): • definition • impacts on climate • ways of measuring ENSO • some past ENSO events • North Atlantic Oscillation (NAO)

  12. Southern Oscillation Index Centres Darwin Tahiti

  13. SEP 97

  14. http://www.pmel.noaa.gov/tao/realtime.html

  15. Lecture Outline • El Nino - Southern Oscillation (ENSO): • definition • impacts on climate • ways of measuring ENSO • some past ENSO events • North Atlantic Oscillation (NAO)

  16. INDEX CYCLE

  17. North Atlantic Oscillation • Pattern of Climate Variability that determines weather and climate in N.Atlantic • Controls much of the month to month variability of temerpature and rainfall in N.W. Europe

  18. North Atlantic Setting • High Pressure over the Azores • Low Pressure over Iceland • Westerly wind • low pressure systems (rain) travel in the westerlies

  19. North Atlantic Oscillation • Azores high and Icelandic Low are the centres • Azores high can weaken or strengthen • Icelandic low can weaken or strengthen

  20. High Phase Azores High strong Icelandic Low deep westerlies strong wind and rain mild conditions in UK dry conditions in Spain Low Phase Azores high weak Icelandic Low shallow westerlies weak clear and still cold and dry wet conditions in Spain North Atlantic Oscillation

  21. Temperature

  22. Rainfall

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