Understanding the evolution asymmetry between El Niño and La Niña events is challenging. Unlike El Niño, most La Niña events are characterised by a double-dip cooling (a.k.a. multi-year La Niña). Herein, we examined how single- and multi-year La Niña events differ by analysing observational and climate-model data sets. Single-year La Niña events tend to develop narrowly within the tropics from a central Pacific-type El Niño (Niño-4 > Niño-3), whereas multi-year La Niña events tend to originate from an eastern Pacific-type El Niño (Niño-3 > Niño-4) and are well-connected to mid-latitudes through the Pacific meridional mode, which leads to a meridionally wider response of the off-equatorial low-level atmospheric anti-cyclonic circulation. As the anti-cyclonic circulation controls the amount of equatorial upper-ocean heat recharge through Sverdrup transport, for single-year La Niña, efficient ocean recharging due to a narrower anti-cyclonic circulation causes a fast transition to an El Niño or a fast termination of a La Niña. In contrast, for multi-year La Niña, a weaker recharging causes surface cooling to persist, leading to another La Niña in the following year.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation (NRF) of Korea grant funded by the Korea government (MSIT) (NRF-2020R1C1C1006569 and NRF-2018R1A5A1024958). The SST data (Extended Reconstructed SST v3) and atmospheric data (National Centers for Environmental Prediction/National Center for Atmospheric Research) were downloaded from NOAA (https://www.esrl.noaa.gov/psd/data/). The oceanic data (Simple Ocean Data Assimilation v2.2.4) was downloaded from http://apdrc.soest.hawaii.edu/data/data.php. In this study, the Ncar-CCSM4 industrial run participated in the Coupled Model Inter-comparison Project Phase 5 (CMIP5), which was downloaded from its website (https://esgf-node.llnl.gov/projects/cmip5/).
All Science Journal Classification (ASJC) codes
- Atmospheric Science