ENSO Indices
 

 

Southern Oscillation Index (SOI)
standardized anomaly of the mean sea level pressure difference between Tahiti and Darwin

  • traditional ENSO index

  • correlates strongly with SST anomaly indices


NOAA Oceanic Niño Index (ONI)
sea surface temperature anomaly index for Niño 3.4 (5°N to 5°S, 170°W to 120°W)

  • onset of El Niño declared when Niño 3.4 anomaly exceeds +0.5°C for 3-month period

  • to be "full-fledged" El Niño (or La Niña), onset conditions must be met for 5 consecutive 3-month periods


Japanese Meteorological Agency ENSO Index (JMA)
sea surface temperature anomaly index for Niño 3 (4°N to 4°S, 150°W to 90°W)

  • less noisy than traditional SOI and more vigorous than NOAA ONI

  • anomalies must exceed 0.5°C for 6 consecutive 5-month periods


Multivariate ENSO Index (MEI)
weighted anomaly average of 6 meteorological variables in the tropical Pacific

  • sea surface temperature

  • sea level pressure

  • surface air temperature

  • components of surface wind

    • zonal component

    • meridional component

  • total cloudiness fraction of the sky



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