Fig. 1: Role of preceding strong El Niño in generating multi-year La Niña (LN).

a Evolution of Niño3.4 index for individual multi-year LN events during 1900‒2022. Each event year is depicted with a different color, corresponding to its specific evolution. b Scatter plot of Niño3.4 index values during the preceding winter against those during the second-winter for multi-year LN events with a preceding strong El Niño (myLN_wPrSEN, black dots with red outline) or without (myLN_w/oPrSEN, black dots with blue outline) and single-year LN events (syLN, gray dots). The black (gray) square represents the average for multi (single)-year LN events with error bars indicating ±1 s.d. c Composite evolution of Niño3.4 index for the three LN groups: myLN_wPrSEN (red curve), myLN_w/oPrSEN (blue curve), and syLN (gray curve). Shaded areas represent their ±1 s.d. d Same as (c) except for the ocean heat content (OHC) index. e Bar-charts displaying the OHC intensity during June⁰‒November⁰ for the three LN groups, with error bars indicating ±1 s.d. f Phase space diagram showing the Niño3.4 and OHC indices for myLN_wPrSEN (red curve), myLN_w/oPrSEN (blue curve), and syLN (gray curve) during the preceding (circle), first (square), and second (triangle) winters. The indices are smoothed with a 3-month running-mean filter.