Winter-Spring Southern Oscillation Index (SOI)

  • Red bars indicate years when the winter-spring SOI was –10 or lower
  • Recognized El Niño years have their bars labelled
    Note that years marked with an asterisk (*) are ambiguous in that, depending on definitions, some scientists class these as El Niño years while others don't
  • A lack of data from the late 1800s and early 1900s makes it difficult to classify years during this period