Fig. 5

a Hovmoller diagram at the equator for thickness anomaly (color shading, normalized) with the blue and red lines indicating the phase speeds of equatorial Kelvin waves and long Rossby waves, respectively. b Hovmoller diagram at 2 °N for thickness anomaly (color shading, normalized) and the EPV-based streamfunction (contours, plotted as in the left panels of Fig. 4)