ENSO(El Nino Southern Oscillation)

ENVS 110 10-12-2008

http://upload.wikimedia.org/wikipedia/commons/1/18/Wiki_plot_03.png

http://www.pmel.noaa.gov/pubs/outstand/kess2580/images/fig01.gif

http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/el-scans/el-nino1.jpg

http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/el-scans/walker.jpg

http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/el-scans/el-nino2.jpg

Normal Conditions: West Pacific Warm Pool

El Nino Conditions

http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/el-scans/catch.jpg

El Nino forecasting

• Careful monitoring of– Oceanic temperatures (satellites)– Strength of trade winds

sometimes it works – sometimes it doesn’t

How to measure sea surface temperatures (old school)• automated buoys (get spot measurement,

often temperature profile)→ buoy arrays

• temperature recorders in the water intakes of big ships→ variable locations, sampling depth might not be

constant (loaded vs. empty vessel) but greater geographical coverage

How to Measure Sea Surface Temperatures from Satellites?• infrared radiation

problem: cannot see through clouds, aerosols

• electromagnetic radiation at other wavelengths– microwave radiation (can see through clouds and

aerosols, but is scattered by raindrops)

http://www.sciencemag.org/cgi/content/full/288/5467/847

how to measure ocean temperature at depth ?• warm water is less dense → takes up more

space (floats on top of colder water)• sea surface rises• 50 m of 1C warmer water raises sea surface by

approximately 1 cm

• after lots of correlations, corrections and other trickery → get temperature distribution with depth

Historical variations

Red: El NinoBlue: La Nina

How can you Reconstruct ENSO Cycles ?• Expressed as:

– sea surface temperature anomalies– air temperature, atmospheric pressure anomalies

in Pacific– precipitation ?– economic effects ?

– climate effects outside equatorial Pacific?

Where is atmospheric pressure high, where is it low ?

source: http://www.worldatlas.com/webimage/countrys/islands/pacifics/tahiti.htm

Darwin Tahiti

The Southern Oscillation Index (SOI)

expresses difference in barometric pressure between Australia (Darwin) and Thaiti

several ways to calculate

Pdiff = MSLPThaiti - MSLPDarwin

sustained negative values: El Ninosustained positive values: La Nina

diff diff

diff

(p p )SOI 10*

(p )s

Source: Commonwealth of Australia 2006, Bureau of Meteorology (ABN 92 637 533 532)http://www.bom.gov.au/climate/current/soi2.shtml (accessed 3/13/06)

ENSO Cycles

• El Nino – La Nina phenomenon is cyclical• Note timescales involved

• How rapidly does atmosphere change ?• How rapidly do oceans change ?

• Oceans are a good place to look for drivers of short term climate change

http://www.sbg.ac.at/ipk/avstudio/pierofun/atmo/el-scans/rain.jpg