Cause and impact of the record-breaking equatorial Pacific easterly anomalies in 2022

The tropical Pacific experienced a rare triple-dip La Niña event from 2020 to 2023. Extreme easterly wind stress anomalies were observed in the equatorial Pacific in 2022, yet the underlying dynamics causing the easterly anomalies remain unclear. Moreover, it was still under debate that easterly anomalies in which period played the dominant role in the development of the 2022 La Niña. Based on ERA5 reanalysis, we found that the annual-mean equatorial easterly wind stress anomalies in 2022 reached record highs since 1982, with the influence mainly from the strengthened trade winds over the past four decades (30.71%), cold sea surface temperature (SST) anomalies in the central equatorial Pacific (36.22%), cold SST anomalies in the southeastern tropical Pacific (21.26%), and two sets of easterly wind surges (EWSs) near the dateline (7.65%). A strong convective Madden-Julian Oscillation and a series of intense synoptic anticyclonic eddies in South Pacific were found as the main drivers of the EWSs. By forcing a coupled model with the equatorial zonal wind anomalies in different periods in 2022, we found that the easterly anomalies from January to mid-February and mid-March to mid-June played the critical role in the development of 2022 La Niña. While the two sets of EWSs cooled the equatorial central-eastern Pacific after their appearance, they did not significantly influence the intensity of 2022 La Niña in boreal winter. Our findings imply that multi-scale processes from synoptic to secular scales collectively contributed to the equatorial Pacific cooling in 2022 and further the genesis of the 2020-2023 triple-dip La Niña event.