One plausible reason for the change in ENSO characteristics in the 2000s

Abstract

It is well known that El Ni{ñ}o Southern Oscillation (ENSO) causes floods, droughts and the collapse of fisheries, therefore forecasting of ENSO is an important task in climate researches. Variations in the equatorial warm water volume of the tropical Pacific and wind variability in the western equatorial Pacific has been considered to be a good 5 ENSO predictor. However, in the 2000s, the interrelationship between these two char-acteristics and ENSO onsets became weak. This article attempts to find some plausible explanation for this. The results presented here demonstrate a possible link between the variability of atmospheric conditions over the Southern Ocean and their impact on the ocean circu-10 lation leading to the amplifying/triggering of ENSO events. It is shown that the variabil-ity of the atmospheric conditions upstream of Drake Passage can strongly influence ENSO events. The interrelationship between ENSO and variability in the equatorial warm water volume of the equatorial Pacific, together with wind variability in the west-ern equatorial Pacific has recently weakened. It can be explained by the fact that the 15 process occurred in the Southern Ocean recently became a major contributor amplify-ing ENSO events (in comparison with the processes of interaction between the atmo-sphere and the ocean in the tropics of the Pacific). Likely it is due to a warmer ocean state observed from the end of the 1990s that led to smaller atmospheric variability in the tropics and insignificant their changes in the Southern Ocean.