ИСТИНА

The El Niño–Southern Oscillation (ENSO) is tightly linked to the intraseasonal tropical variability (ITV) that contributes to energise the deterministic ocean dynamics during the development of El Niño. Meanwhile ENSO amplitude is modulated at decadal timescales, which, over the last decades, has been related to the low-frequency changes in the frequency of occurrence of the two types of El Niño events, that is the Eastern Pacific (EP) and Central Pacific (CP) El Niños. The ITV/ENSO relationship are revisited taking into account changes in ENSO properties over the last six decades. The focus is on two main components of ITV, the Madden–Julian Oscillation (MJO) and convectively coupled equatorial Rossby waves (ER). It is shown that the ITV/ENSO relationship exhibits a decadal modulation that is not related in a straight-forward manner to the change in occurrence of El Niño types and Pacific decadal modes. It is documented that the MJO/ENSO relationship is enhanced over period of strong EP El Niсo occurrence (80 and 90 s) and that of ER/ENSO is intensified in 1994–2006 and 1966–1980, which corresponds to periods over which a large number of CP El Niño events took place. The statistics of the MJO and ER activity is consistent with the hypothesis that they can be considered a state-dependent noise for ENSO linked to distinct lower frequency climate modes.