FY 2020

Uncoupled El Niño Warming

Hu, Z.-Z., M.J. McPhaden, A. Kumar, J.-Y. Yu, and N.C. Johnson

Geophys. Res. Lett., 47(7), e2020GL087621, doi: 10.1029/2020GL087621, View online (2020)

In light of a warming climate, the complexity of the El Niño/Southern Oscillation (ENSO) makes its prediction a challenge. In addition to various flavors of ENSO, oceanic warming in the central and eastern tropical Pacific is not always accompanied by corresponding atmospheric anomalies; that is, the atmosphere and ocean remain uncoupled. Such uncoupled warm events as happened in 1979, 2004, 2014, and 2018 are rare and represent an unusual form of ENSO diversity. A weaker zonal sea surface temperature anomaly gradient across the tropical Pacific compared to a conventional El Niño may partially account for the decoupling. Also, the uncoupled warm events typically start late in the calendar year, which raises the possible influence of seasonality in background conditions for the lack of coupling. Without coupling, the impact of the warming in the central and eastern tropical Pacific on extratropical climate is different from that of its coupled counterpart.

Plain Language Summary. In a warming climate, the features of the El Niño/Southern Oscillation seem to be changing. For example, during the El Niño events in 1979, 2004, 2014, and 2018, oceanic warming in the central and eastern tropical Pacific was not accompanied by corresponding atmospheric anomalies; that is, the atmosphere and ocean remained uncoupled. These uncoupled warming events were associated with a weaker east‐west contrast in sea surface temperature anomaly across the tropical Pacific compared to a conventional El Niño. Also, the uncoupled warm events typically start late in the calendar year, which raises the possible influence of seasonality in the background conditions for the lack of coupling. Without coupling, the impact of the warming in the central and eastern tropical Pacific on extratropical climate is different from that of the coupled counterpart, leading to different predictability of seasonal‐interannual climate in extratropical regions, such as the United States.