The Pacific breathes in, then out.
Before an El Niño, warm water piles up along the equator. The event then spends that heat, and the discharge sets up what comes next. Plot the heat store against Niño-3.4 and every event traces the same clockwise loop: recharge → El Niño → discharge → La Niña. Where the current event sits on the loop says a lot about how much fuel it has left.
Warm water volume against Niño-3.4, 1980 to now
Three-month running means, so each event reads as one loop. Grey: every month since 1980. Coloured: the great El Niños. Black: this event, month by month.
Reading the wheel
| Event | Heat store peak | Niño-3.4 peak | Lead |
|---|
Lead: months from the heat store's peak to Niño-3.4's peak within each event's window. The recharge oscillator (Jin 1997; Meinen and McPhaden 2000) expects the heat store to peak first. PMEL's anomalies are from a fixed climatology, so a warming ocean also lifts recent values.