Fig. 5
From: A role for orbital eccentricity in Earth’s seasonal climate
Reproduced from Chiang et al. (2022), Fig. 3
Change in the cold tongue annual cycle with the longitude of perihelion and decomposition into contributions from the annual cycle from tilt, annual cycle from distance, and semiannual cycle from tilt as reported in Chiang et al. (2022). a Cold tongue SST (averaged over 6° S–6° N, 140–90° W) seasonal cycle for e = 0.04 with varying longitude of perihelion. The annual mean is removed from each annual cycle before plotting. b Least-square surface fit of the data in a, using Eq. (1) (see Sect. “Appendix” for details of the calculation). c Fitted coefficients of the distance effect amplitude (AD, black symbols) and the least-square linear fit to the data forced through the intercept (dashed line). The bars indicate the 95% confidence bounds for each AD fit. For comparison, the fitted coefficients of the tilt effect amplitude (AT) are shown in red. The green dot indicates the distance effect amplitude for eccentricity at pre-industrial (PI) level (e = 0.0167). d–f Contributions of the fit in b from tilt effect annual cycle, distance effect annual cycle, and tilt effect semiannual cycle, respectively. Note that the month axis for used in a, b, d, e, and f is such that 0 is the start of the year and 12 is the end; mid-January is thus 0.5.