Is there a standard way to classify SOI? I read that negative values of the SOI below −7 (-8) often indicate El Niño and positive values above +7(+8) are typical of a La Niña eposide (http://www.bom.gov.au/climate/glossary/soi.shtml#:~:text=The%20Southern%20Oscillation%20Index%2C%20or,often%20indicate%20El%20Ni%C3%B1o%20episodes.). However, other studies (https://doi.org/10.3390/ijgi9020073, https://doi.org/10.1080/02626667.2017.1296229 ) considered -1 instead of -7 and 1 instead of 8. How to explain this? Also, I am confused about Niño 3.4, AO, EAWR classification?