The Evolutions of Single-Year and Multiyear El Niño from Preconditioning to Decay Stages: Direct Wind-Driven versus Boundary-Reflected Oceanic Responses
Journal
Journal of Climate
Journal Volume
38
Journal Issue
5
Start Page
1205
End Page
1220
ISSN
0894-8755
1520-0442
Date Issued
2025-03
Author(s)
Abstract
Advancing our understanding of single-year and multiyear El Niño events is essential for a better forecast of El Niños and assessment of their global socioeconomic impacts. Here, we compare these two types of El Niños in reanalysis and coupled model data. We further develop an approach in a linear continuously stratified ocean model to quantifying direct wind-driven (DWD) and boundary-reflected (BR) responses to wind stress forcing from the reanalysis and coupled model datasets. For single-year El Niños, the positive North Pacific meridional mode charges additional heat content to the tropical Pacific through DWD processes in year21 before the development year (year0), leading to the earlier event development. The subsequent discharge and zonal-advective reflective feedbacks by BR processes also start earlier and are intensified by wind anomalies of a more eastward fetch. Finally, during the mature boreal winter and decay spring in year1, the equatorial western Pacific winds turn into easterlies, terminating DWD downwelling Kelvin waves and the positive feedback. In contrast, multiyear El Niños feature a lower preconditioning recharge state in year21, later development and less eastward-extending wind and sea surface temperature anomalies in year0, and weaker delayed negative feedbacks and persistent western Pacific westerly winds in year1. The resultant insufficient BR negative feedbacks and lasting DWD downwelling Kelvin waves allow El Niño to continue into year1/year2. The approach developed here and the results that show the fundamental dynamic processes regulating El Niño’s duration should help in improving El Niño–Southern Oscillation (ENSO) seasonal forecasting.
Subjects
Atmosphere-ocean interaction
Climate variability
El Nino
ENSO
Publisher
American Meteorological Society
Type
journal article