A Simple Multiscale Intermediate Coupled Stochastic Model for El Niño Diversity and Complexity

Abstract

El Niño-Southern Oscillation (ENSO) is the most prominent interannual climate variability in the tropics and exhibits diverse features in spatiotemporal patterns. In this paper, a simple multiscale intermediate coupled stochastic model is developed to capture the ENSO diversity and complexity. The model starts with a deterministic and linear coupled interannual atmosphere, ocean and sea surface temperature (SST) system. It can generate two distinct dominant linear solutions that represent the eastern Pacific (EP) and the central Pacific (CP) El Niños, respectively. In addition to adopting a stochastic model for characterizing the intraseasonal wind bursts, another simple stochastic process is developed to describe the decadal variation of the background Walker circulation. The latter links the two dominant modes in a simple nonlinear fashion and advances the modulation of the strength and occurrence frequency of the EP and the CP events. Finally, a cubic nonlinear damping is adopted to parameterize the relationship between subsurface temperature and thermocline depth. The model succeeds in reproducing the spatiotemporal dynamical evolution of different types of the ENSO events. It also accurately recovers the strongly non-Gaussian probability density function, the seasonal phase locking, the power spectrum and the temporal autocorrelation function of the SST anomalies in all the three Niño regions (3, 3.4 and 4) across the equatorial Pacific. Furthermore, both the composites of the SST anomalies for various ENSO events and the strength-location bivariate distribution of equatorial Pacific SST maxima for the El Niño events from the model simulation highly resemble those from the observations.

Strengthening ENSO amplitude asymmetry: historical trends and future projections in a warming climate

“…The ocean reanalysis datasets used in the study are from Simple Ocean Data Assimilation (SODA) version 2.2.4 for 1900-2010 with a resolution of 0.5° × 0.5°4 6 and extended from 2010 to 2020 with the Global Ocean Data Assimilation System (GODAS) with a 1°×1° grid 47 . We used the difference between GODAS and SODA2.2.4 during the overlay period 1980-2010 to calibrate the mean state of GODAS.…”

“…The El Niño-Southern Oscillation (ENSO) is the strongest interannual fluctuation of the global climate system, altering between warm El Niño phase and cold La Niña phase [1][2] . The occurrence of ENSO events is controlled by a variety of positive and negative coupled atmosphere-ocean feedback processes and noise forcing, resulting in complex properties of ENSO [3][4][5][6][7][8] . One well-known example of such ENSO complexity is that ENSO has several different types, which can be classified as the eastern Pacific (EP) type (or Cold Tongue type) and the central Pacific (CP) type (or Modoki type, Warm Pool type) [9][10][11][12] .…”

A Mechanism for the Generation of a Warm SST Anomaly in the Western Equatorial Pacific: A Pathway Perspective

“…Another important process affecting the onset of El Niño is the role played by stochastic wind forcing. WWBs over the western tropical Pacific are suggested to play a triggering role in the onset of El Niño (Chen et al., 2015; Chen & Fang, 2023; Fedorov et al., 2014; Hu et al., 2014; Lengaigne et al., 2004). But, analyses over the past 50 years indicate that their origins and causal relations with El Niño developments have proved elusive.…”