Current Weather ENSO Terminology Neutral, Warm-Phase, and Cold-Phase ENSO Impacts For Next Class: Read Moran Ch. 8 (pp ) El Niño-Southern Oscillation

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

El Niño-Southern Oscillation

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. ENSO

Coupling of the ocean and atmosphere in the tropical Pacific Ocean El Niño (warm-phase of ENSO): above average sea-surface temperatures La Niña (cold-phase of ENSO): below average sea-surface temperatures La Nada (ENSO-neutral): average sea-surface temperatures El Niño-Southern Oscillation

© AMS6 ENSO  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 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 Walker Circulation: east-west oriented atmospheric circulation across the equatorial Pacific

© AMS8 ENSO  Warm Phase With the onset of El Niño, air pressure falls over the eastern tropical Pacific and rises over the western tropical Pacific 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 PacificTrade winds slacken in the western and central equatorial Pacific Warm surface waters in the eastern tropical Pacific reduces upwellingWarm surface waters in the eastern tropical Pacific reduces upwelling

El Niño (Warm Phase ENSO)

1997 from Anton Seimon in Peru

© AMS12 El Niño, La Niña, and the Southern Oscillation Cold Phase 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 PacificDuring 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 rainfallLower than usual SST in the east topical Pacific inhibit rainfall while higher than usual SST in the west enhance rainfall

© AMS14 El Niño, La Niña, and the Southern Oscillation Frequency Frequency Multivariate ESNO Index forms the basis for operational definitions of El Niño and La NiñaMultivariate ESNO Index forms the basis for operational definitions of El Niño and La Niña Based on six variables measured in the tropical Pacific Based on six variables measured in the tropical Pacific sea-level air pressuresea-level air pressure zonal component of surface windzonal component of surface wind meridional component of surface windmeridional component of surface wind surface air temperaturesurface air temperature sky cloud coversky cloud cover sea-surface temperaturesea-surface temperature ENSO Alert System launched in February 2009ENSO Alert System launched in February 2009

© AMS15

El Niño El Niño La Niña

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

Numerous stations set new records for days of snow cover. Boone NC: 71 days (mean: 26 days) Mt. LeConte, TN: 115 days (mean: 64 days) 66 days!

Would have missed another 5-10 days if the timing of the storms had been different (i.e., not over holidays or on weekends)

Nevado Chacaltaya (2003)

Nevado Chacaltaya (2015)

Francou et al. 2004

© AMS29 El Niño, La Niña, and the Southern Oscillation Predicting and Monitoring ENSO Predicting and Monitoring ENSO Atmosphere/ocean observational data from the tropical Pacific obtained using the ENSO Observing SystemAtmosphere/ocean observational data from the tropical Pacific obtained using the ENSO Observing System Consists of an array of moored and drifting instrumented buoys, island Consists of an array of moored and drifting instrumented buoys, island and coastal tide gauges, and coastal tide gauges, ship based measurements, ship based measurements, and satellites and satellites

© AMS30

ENSO Links is_monitoring/enso_update/sstanim.shtml is_monitoring/enso_update/sstanim.shtml is_monitoring/enso_update/sstanim.shtml is_monitoring/enso_update/sstanim.shtml is_monitoring/enso_advisory/ensodisc.html is_monitoring/enso_advisory/ensodisc.html is_monitoring/enso_advisory/ensodisc.html is_monitoring/enso_advisory/ensodisc.html