Extended Data Fig. 1: Observed trends of equatorial wavenumber-frequency spectra.
From: Intensification of Pacific tropical instability waves over the recent three decades
1993–2021 trends (color shading) are superimposed with the mean states (contour, in log scale): a, SSTy variance spectrum, contour initiating from – 0.8 with interval of 0.2, (10−6 °C m−1)2; b, SST variance spectrum, contour initiating from – 2.6 with interval of 0.2, °C2; c, SSH-derived surface kinetic energy (KE) spectrum, contour initiating from – 0.2 with interval of 0.2, J m−3; d, SSH variance spectrum, contour initiating from – 1.4 with interval of 0.2, cm2. The period is shown on the y-axis in red text. Red dashed box represents the TIW spectral domain with westward wavelength ≤ 3000 km and period ≤ 40 days. Black dashed curves denote dispersion relations of free equatorial waves of the first baroclinic mode, with the phase velocity of long gravity wave at 2.8 m s−1: ‘R0’, ‘R1–3’ and ‘K’ denote the mixed Rossby-gravity, first–third meridional-mode Rossby, and Kelvin waves, respectively. The trends are based on the 9-year running average of the spectra that are calculated over 160°W–100°W at each year, then averaged between (1°S–1°N) / (2°S–2°N) for (a,c) / (b,d). Dotted regions pass the 95% confidence level based on the modified Mann–Kendall test.
