Extreme Noise–Extreme El Niño: How State-Dependent Noise Forcing Creates El Niño–La Niña Asymmetry

A major open question about El Niño–Southern Oscillation (ENSO) is what causes ENSO amplitude asymmetry, with strong El Niños generally larger than strong La Niñas. The authors examine a leading hypothesis— that the ENSO state modifies the fetch and/or wind speed of westerly wind bursts (WWBs) that...

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Bibliographic Details
Published in:Journal of climate 2016-08, Vol.29 (15), p.5483-5499
Main Authors: Levine, Aaron, Jin, Fei Fei, McPhaden, Michael J.
Format: Article
Language:English
Subjects:
Archives & records
Asymmetry
Climate models
El Nino
El Nino events
El Nino forecasting
El Nino phenomena
El Nino-Southern Oscillation event
Growth rate
La Nina
Noise
Ocean currents
Simulation
Southern Oscillation
Standard deviation
Time series
Westerlies
Westerly wind bursts
Wind
Wind speed
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Summary:A major open question about El Niño–Southern Oscillation (ENSO) is what causes ENSO amplitude asymmetry, with strong El Niños generally larger than strong La Niñas. The authors examine a leading hypothesis— that the ENSO state modifies the fetch and/or wind speed of westerly wind bursts (WWBs) that create asymmetric forcing and an asymmetric ENSO response. Further, in El Niño forecasts, the number of WWBs expected increases in the month following a strong WWB when compared with the month preceding it. Using a conceptual model, a relationship is derived between the magnitude of the westerly wind burst state dependence on ENSO and ENSO asymmetry. It is found that this relationship between the magnitude of the state dependence and ENSO asymmetry holds in both the observations and 21 coupled climate models. Finally, it is found that because of state-dependent westerly wind burst forcing, extreme El Niño events tend to be of the eastern Pacific variety.
ISSN:0894-8755
1520-0442
DOI:10.1175/jcli-d-16-0091.1