Is ENSO a cycle or a series of events?

[1] After early ideas that saw El Ninos as isolated events, the advent of coupled models brought the conception of ENSO as a cycle in which each phase led to the next in a self-sustained oscillation. Twenty-two years of observations that represent the El Nino and La Nina peaks (east Pacific SST) and the memory of the system (zonal mean warm water volume) suggest a distinct break in the cycle, in which the coupled system is able to remain in a weak La Nina state for up to two years, so that memory of previous influences would be lost. Similarly, while the amplitude of anomalies persists from the onset of a warm event through its termination, there is no such persistence across the La Nina break. These observations suggest that El Ninos are in fact event-like disturbances to a stable basic state, requiring an initiating impulse not contained in the dynamics of the cycle itself.

[1]  D. E. Harrison,et al.  ENSO Warm (El Niño) and Cold (La Niña) Event Life Cycles: Ocean Surface Anomaly Patterns, Their Symmetries, Asymmetries, and Implications. , 2002 .

[2]  N. Mantua,et al.  Evidence for the Delayed Oscillator Mechanism for ENSO: The “Observed” Oceanic Kelvin Mode in the Far Western Pacific , 1994 .

[3]  N. Smith,et al.  An Improved System for Tropical Ocean Subsurface Temperature Analyses , 1995 .

[4]  D. Vimont,et al.  Footprinting: A seasonal connection between the tropics and mid‐latitudes , 2001 .

[5]  M. Mcphaden,et al.  Forcing of intraseasonal Kelvin waves in the equatorial Pacific , 1995 .

[6]  A. J. Clarke,et al.  On the Timing of Warm and Cold El Niño-Southern Oscillation Events , 1995 .

[7]  S. Manabe,et al.  Simulated ENSO in a Global Coupled Ocean–Atmosphere Model: Multidecadal Amplitude Modulation and CO2 Sensitivity , 1997 .

[8]  Michael J. McPhaden,et al.  Observations of Warm Water Volume Changes in the Equatorial Pacific and Their Relationship to El Niño and La Niña , 2000 .

[9]  Fei-Fei Jin,et al.  An Equatorial Ocean Recharge Paradigm for ENSO. Part II: A Stripped-Down Coupled Model , 1997 .

[10]  Max J. Suarez,et al.  Vacillations in a Coupled Ocean–Atmosphere Model , 1988 .

[11]  Anthony C. Hirst,et al.  Interannual variability in a tropical atmosphere−ocean model: influence of the basic state, ocean geometry and nonlinearity , 1989 .

[12]  K. Wyrtki,et al.  El Niño—The Dynamic Response of the Equatorial Pacific Oceanto Atmospheric Forcing , 1975 .

[13]  K. Wyrtki,et al.  Water displacements in the Pacific and the genesis of El Nino cycles , 1985 .

[14]  A. J. Clarke,et al.  An Examination of Some ENSO Mechanisms Using Interannual Sea Level at the Eastern and Western Equatorial Boundaries and the Zonally Averaged Equatorial Wind , 1994 .

[15]  M. Cane,et al.  A Model El Niñ–Southern Oscillation , 1987 .

[16]  D. Vimont,et al.  Pacific Interannual and Interdecadal Equatorial Variability in a 1000-Yr Simulation of the CSIRO Coupled General Circulation Model* , 2002 .

[17]  Max J. Suarez,et al.  A Delayed Action Oscillator for ENSO , 1988 .

[18]  M. Mcphaden,et al.  Genesis and evolution of the 1997-98 El Nino , 1999, Science.

[19]  Coupled atmosphere-ocean model simulations of El Nino/Southern Oscillation with and without an active Indian Ocean , 1995 .

[20]  Rong‐Hua Zhang,et al.  Role of off‐equatorial subsurface anomalies in initiating the 1991–1992 El Niño as revealed by the National Centers for Environmental Prediction ocean reanalysis data , 2000 .

[21]  Prashant D. Sardeshmukh,et al.  The Optimal Growth of Tropical Sea Surface Temperature Anomalies , 1995 .

[22]  D. Battisti,et al.  A Linear Stochastic Dynamical Model of ENSO. Part II: Analysis. , 2001 .

[23]  R. Weisberg,et al.  Slow Variability in the Equatorial West-Central Pacific in Relation to ENSO , 1997 .

[24]  D. E. Harrison,et al.  On the termination of El Niño , 1999 .

[25]  M. Mcphaden,et al.  Oceanic Equatorial Waves and the 1991–93 El Niño , 1995 .

[26]  J. David Neelin,et al.  ENSO theory , 1998 .

[27]  Mojib Latif,et al.  A review of the predictability and prediction of ENSO , 1998 .

[28]  J. McCreary,et al.  A Model of Tropical Ocean-Atmosphere Interaction , 1983 .

[29]  W. L. Culberson,et al.  Lichen biology: biology of lichenized fungi. , 1985, Science.

[30]  M. Mcphaden,et al.  Interannual Variability in Warm Water Volume Transports in the Equatorial Pacific during 1993–99* , 2001 .

[31]  Fei-Fei Jin,et al.  An Equatorial Ocean Recharge Paradigm for ENSO. Part I: Conceptual Model , 1997 .

[32]  J. Shukla,et al.  Annual Cycle and ENSO in a Coupled Ocean-Atmosphere General Circulation Model , 1997 .

[33]  M. Cane,et al.  A Theory for El Ni�o and the Southern Oscillation , 1985, Science.