Consider the following statements:
1. Southern Oscillation Index (SOI) is an index for gauging the strength of El Nino and La Nina
2. The index is best represented by monthly (or longer) averages
3. Sustained positive SOI values above about +8 indicate a La Nina event while sustained negative values below about –8 indicate an El Nino
Which of the above statements is/are correct?

Answer: [D] 1, 2 & 3

The Southern Oscillation Index (SOI) is a measure of the intensity or strength of the Walker Circulation. It is one of the key atmospheric indices for gauging the strength of El Niño and La Niña events and their potential impacts on the Australian region. The index is best represented by monthly (or longer) averages as daily or weekly SOI values can fluctuate markedly due to short-lived, day-to-day weather patterns, particularly if a tropical cyclone is present. Sustained positive SOI values above about +8 indicate a La Nina event while sustained negative values below about –8 indicate an El Nino.

This question is a part of GKToday's Integrated IAS General Studies Module