Heartbeat of the Southern Oscillation explains ENSO climatic resonances. Issue 8 (28th August 2017)

• Record Type: Journal Article
• Authors: Bruun, John T.; Allen, J. Icarus; Smyth, Timothy J.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 8(2017)
• Page Start: 6746
• Page End: 6772
• Publication Date: 2017-08-28
• Subjects: SOI -- ENSO -- signal analysis -- extremes -- bifurcation -- prediction; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2017JC012892
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The El Niño‐Southern Oscillation (ENSO) nonlinear oscillator phenomenon has a far reaching influence on the climate and human activities. The up to 10 year quasi‐period cycle of the El Niño and subsequent La Niña is known to be dominated in the tropics by nonlinear physical interaction of wind with the equatorial waveguide in the Pacific. Long‐term cyclic phenomena do not feature in the current theory of the ENSO process. We update the theory by assessing low (>10 years) and high (<10 years) frequency coupling using evidence across tropical, extratropical, and Pacific basin scales. We analyze observations and model simulations with a highly accurate method called Dominant Frequency State Analysis (DFSA) to provide evidence of stable ENSO features. The observational data sets of the Southern Oscillation Index (SOI), North Pacific Index Anomaly, and ENSO Sea Surface Temperature Anomaly, as well as a theoretical model all confirm the existence of long‐term and short‐term climatic cycles of the ENSO process with resonance frequencies of {2.5, 3.8, 5, 12–14, 61–75, 180} years. This fundamental result shows long‐term and short‐term signal coupling with mode locking across the dominant ENSO dynamics. These dominant oscillation frequency dynamics, defined as ENSO frequency states, contain a stable attractor with three frequencies in resonance allowing us to coin the term Heartbeat of the Southern Oscillation due to its characteristic shape. We predict future ENSO states based on a stable hysteresis scenario of short‐term and long‐term ENSO oscillations over the next century. Plain Language Summary: The Pacific El Niño‐Southern Oscillation (ENSO) nonlinear oscillator phenomenon has a far reaching influence on the climate and our human activities. This work can help predict both long‐term and short‐term future ENSO events and to assess the risk of future climate hysteresis changes: is the elastic band that regulates the ENSO climate breaking? We update the current theory of the ENSO process with a sophisticated analysis approach (Dominant Frequency State Analysis) to include long‐term oscillations (up to 200 years) as well as tropical and extratropical interaction dynamics. The analysis uses instrumental and paleoproxy data records in combination with theoretical models of ENSO. This fundamental result that shows the ENSO phenomenon has a stable tropical Pacific attractor with El Niño and La Niña phases, tropical and extratropical coupling and an intermittency or longer‐term form of chaos. We call this attractor the Heartbeat of the Southern Oscillation as the phenomenon is measurable in the Southern Oscillation. We predict future ENSO states based on a stable hysteresis scenario of short‐term and long‐term ENSO oscillations over the next century. Key Points: The tropical ENSO system has a type of universal period doubling cascade route to chaos with low frequency modes and extratropical coupling The Heartbeat of the Southern Oscillation is the stable attractor for ENSO; frequency states of ENSO range from 2.5 to 180 years Prolonged El Niño (La Niña) period anticipated for 2050–2080 (2018–2026 and 2080–2100)