Extended Data Figure 1 : Power spectrum of ENSO.

From: Evolution and forcing mechanisms of El Niño over the past 21,000 years

Extended Data Figure 1

Power spectra of Niño3.4 monthly SST variability in TRACE (after removing the annual cycle) in five 1,000-year windows: 1–2 kyr ago, 5–6 kyr ago, 10–11 kyr ago, 15–16 kyr ago and 19–20 kyr ago. The spectral peak remains at 2 years, but with a different intensity. For each spectrum, the 95% cut-off level and the corresponding red noise curve are also plotted (in dotted lines). The black bar at the bottom shows the 1.5–7-year band used for the calculation of ENSO variance.