What is the SOI (Southern Oscillation Index)?
It has been found that the cyclic warming and cooling of the eastern and central Pacific can be seen in the sea level pressure in the region. In particular, when the pressure measured at Darwin is compared with that measured at Tahiti, the differences between the two can be used to generate an “index” number. A positive number indicates La Nia (eastern tropical Pacific ocean cooling) and a negative number indicates El Nio (or ocean warming). Historical and recent values can be found at the Climate Prediction Center. PSD has a historical perspective on the SOI.
