Triple-Dip La Niña in 2020-22: Impact of Annual Cycle in Tropical Pacific SST

The triple-dip La Niña in 2020-22 is characterized by persisting easterly and southeasterly wind anomalies over the tropical central and southeastern Pacific. Our results show that the wind anomalies are associated with two leading modes of the annual cycle (antisymmetric and symmetric modes) of sea surface temperature (SST). The first two modes account for 82.2% and 13.5% of total variances, linking to the seasonal swing of SST distribution in the northern and southern hemispheres and the temporal evolution of El Niño-Southern Oscillation (ENSO), respectively. The persistent negative phase of the symmetric mode enhances easterly wind, while the antisymmetric mode strengthens the southeasterly wind. The negative phase of the antisymmetric mode is regulated by the contrast of SST anomalies between the northern and southern hemispheres. Therefore, both the zonal and the meridional process associated with annual cycle anomalies may play an important role in the evolution of the triple-dip La Niña in 2020-22.