Fig. 2: Effects of IO-PO coupling on each climate mode.

Seasonal changes in the standard deviation of the (a) IOB-M and (b) DMI in the control experiment (red line) and in the sensitivity experiment when the Pacific Ocean (PO) coupling effect on the Indian Ocean (IO) is turned off (cyan line, \({C}_{{PO}\to {IO}}=0\)). Panels c–f as a, b, but for the power spectra of each index in the two simulations. Panels g–l as a–f, but for when IO coupling effect on the PO is turned off (cyan line, \({C}_{{IO}\to {PO}}=0\)). Shading indicates a one-standard deviation inter-ensemble spread. The horizontal dotted line represents the significant level of each power spectrum. Panels show the standard deviations of the (m) Niño3.4, n IOB-M, and (o) DMI during their respective peak seasons: DJF, MAM, and SON. The black, red, magenta, and cyan bars represent the observation, control, \({C}_{{IO}\to {PO}}=0\), and \({C}_{{PO}\to {IO}}=0\) experiment, respectively.