Interesting to look at the SOI as a roiling and electrical change.
The recent negative values denote a west tropical Pacific increase in
conductivity brought about the roiling from the winds. What THEN
occurs is after some time that roiling reaches its potential of gas
exchange, and the warmer oceans there become less conductive, and the
pattern is set to possibly reverse. Induction is another factor of
impedance, where gas exchange is more about a varying resistance.
Induction comes from the straight line winds and current movements,
and can spell, along with biological feedbacks, the key mechanisms
toward sustaining an SOI which causes an El Nino or La Nina state.
Also note how near South America the winds have been anomaly strong
and that is consistant with the algae bloom off the west coast of