ИСТИНА

The El Niño-Southern Oscillation (ENSO) is the general mode of interannual climate variability. Intraseasonal tropical variability (ITV) is a major component of the tropical Pacific coupled system. The dominant intraseasonal mode in tropics is the Madden-Julian Oscillation (MJO) and convectively coupled equatorial Rossby waves (ER) were in particular shown to be tightly related to ENSO through their relationship to the episodes of westerlies that can trigger downwelling intraseasonal Kelvin waves, a precursor to El Niño onset. The ENSO / ITV does not only have a marked seasonal dependence, it is also sensitive to the state of the tropical Pacific, which has implication for ENSO seasonal forecasts. It raises concerns about how the ITV / ENSO relationship may change in the future climate. Here we use 23 CMIP5 coupled ocean-atmosphere general circulation models (CGCMs) to investigate the sensitivity of the ITV / ENSO seasonal dependence to global warming. As the first step, the models' skill in the simulating ENSO diversity is assessed, which indicates that few models are able to simulate realistically the statistics of the relative size of two types of El Niño. As a second step we tested the CGCMs' ability to correct the simulation of ITV components. Despite the ability of selected models to simulate relatively realistically both the ITV characteristics and the ENSO diversity, they exhibit limited skill in simulating the seasonal ENSO / ITV relationship. Eventually the five models (BNU-ESM, CCSM4, CMCC-CM, INMCM4 and MIROC5) simulate realistically some key aspects of ENSO/ITV relationship, in particular the phase lag between ITV and El Niño peak ITV and ENSO. These models are used to assess the change in the ITV / ENSO relationship in the warming climate based on the RCP 8.5 experiments. It was shown that the ITV / ENSO interactions are modulated at decadal timescales during the 21th century. Positive significant trend is observed for a predictable score of ER in order to CP El Niño and negative trend for ER to EP El Niño. Predictive score of MJO does not change significantly.