The El Nino-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 Nino and ~
subsequent La Nina is known to be dominated in the tropics by nonlinear physical interaction of wind with ~
the equatorial waveguide in ...
The El Nino-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 Nino and ~
subsequent La Nina 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.