El Niño-Southern Oscillation

1. El Niño-Southern Oscillation • Current Weather • Air-Sea Interactions • ENSO • ENSO Impacts • Return Exam I • For Next Class: Read Moran Ch. 8 (pp. 265-276)

4. Driving Question • How do interactions between the ocean and atmosphere impact worldwide climate and short-term climate variability?

5. Air/Sea Interactions • Ocean and atmosphere are closely coupled • Variations in atmospheric conditions can impact temperatures and wind-driven currents • Ocean surface currents strongly influence climate • Broad scale patterns of sea-surface temperature strongly influence the location of major features of the atmosphere’s planetary scale circulation

6. Mean State of Ocean Circulation • Thermohaline Circulation • Deep-ocean circulation driven by variations in density • Caused by variations in temperature and salinity • Significant in the Earth system because • Contributes to poleward heat transport • Modifies climate

7. ENSO • What is ENSO and what are its three major phases? • Why is ENSO important?

8. El Niño-Southern Oscillation

9. ENSO • ENSO is a coupled phenomenon, depending on feedbacks between the ocean and the atmosphere. • Changes in the oceanic sea surface temperatures (SSTs) drive changes in atmospheric circulation which feedback and further alter the ocean.

10. Neutral Conditions in the Tropical Pacific Contrast between relatively high air pressure over the central and eastern tropical Pacific and relatively low air pressure over the western tropical Pacific ultimately drives the trade winds Walker Circulation: east-west oriented atmospheric circulation across the equatorial Pacific ENSO

12. Warm Phase With the onset of El Niño, air pressure falls over the eastern tropical Pacific and rises over the western tropical Pacific Trade winds slacken in the western and central equatorial Pacific Warm surface waters in the eastern tropical Pacific reduces upwelling ENSO

13. El Niño (Warm Phase ENSO)

15. 1997 e-mail from Anton Seimon in Peru

16. Cold Phase During La Niña, surface waters are colder than usual over the central and eastern tropical Pacific and somewhat warmer than usual over the western tropical Pacific Lower than usual SST in the east topical Pacific inhibit rainfall while higher than usual SST in the west enhance rainfall El Niño, La Niña, and the Southern Oscillation

18. El Niño, La Niña, and the Southern Oscillation • Frequency • Multivariate ESNO Index forms the basis for operational definitions of El Niño and La Niña • Based on six variables measured in the tropical Pacific • sea-level air pressure • zonal component of surface wind • meridional component of surface wind • surface air temperature • sky cloud cover • sea-surface temperature • ENSO Alert System launched in February 2009

20. 1982-83 El Niño 1997-98 El Niño 1998-99 La Niña

22. 18 Dec 2009 Warm-Phase ENSO (El Niño) and Negative Arctic Oscillation (AO) = Moist and Cold NCDC 2010

26. Francou et al. 2004

27. El Niño, La Niña, and the Southern Oscillation • Predicting and Monitoring ENSO • Atmosphere/ocean observational data from the tropical Pacific obtained using the ENSO Observing System • Consists of an array of moored and drifting instrumented buoys, island and coastal tide gauges, ship based measurements, and satellites

29. ENSO Links • http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml • http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

30. Exam I • A – 4 • B – 12 • C – 17 • D – 21 • F – 16 • Max – 96 • Mean – 69 • Min – 43