Fig. 1: El Niño–Southern Oscillation variability and periodicity.
From: Stronger and prolonged El Niño-Southern Oscillation in the Early Eocene warmth
a–d Standard deviation of sea surface temperature anomalies (SSTA, °C) in observation (ERSST), piControl, Early Eocene Climatic Optimum (EECO) 1xCO2, and 3xCO2 multi-model mean (MMM) simulations. The significant standard deviation difference in EECO simulations relative to piControl at the 5% level is stippled based on F-test. e SSTA standard deviation averaged over Niño3.4 region (5°S-5°N, 170°E-120°W) in observation and MMM (filled circle) with inter-model standard deviation (±σ) range shown in vertical bars; (f) peak frequency of Niño3.4 averaged SSTA in observation and MMM (filled circle). The vertical bars represent the inter-model ±σ range centered around the peak frequency; (g) autocorrelation of Niño3.4 averaged SSTA in Observation, piControl, 1xCO2, and 3xCO2 MMM simulations; (h) sensitivity of Recharge Oscillator model parameters to normalized changes in SSTA standard deviation (std(SSTA)) from piControl to 1xCO2 and from 1xCO2 to 3xCO2 simulations. Square markers denote the all-model mean values, while vertical bars represent inter-model ±σ range. A value of +1.0 indicates that the entire change in std(SSTA) is attributed to the given parameter, while −1.0 signifies an opposite influence. A value of 0.0 suggests no impact on std(SSTA).
