current weather enso terminology neutral, warm-phase, and cold-phase enso impacts for next class:...
TRANSCRIPT
Current Weather
ENSO Terminology
Neutral, Warm-Phase, and Cold-Phase
ENSO Impacts
For Next Class: Read Moran Ch. 8 (pp. 265-276)
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
© AMS 6
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
Walker Circulation: east-west oriented atmospheric circulation across the equatorial Pacific
© AMS 8
ENSO
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
El Niño (Warm Phase ENSO)
1997 e-mail from Anton Seimon in Peru
© AMS 12
El Niño, La Niña, and the Southern Oscillation
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
14© AMS
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
15© AMS
1982-83 El Niño 1997-98 El Niño
1998-99 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
29© AMS
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
30© AMS
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