ENSO Diversity in a tropical stochastic skeleton model for the MJO, El Nino, and dynamic walker circulation

摘要

El Nino-Southern Oscillation (ENSO) diversity has a significant impact on global climate and seasonal prediction. However, it is still a challenging problem for present-day global climate models to simulate different types of ENSO events with realistic features simultaneously. In this paper, a tropical stochastic skeleton model for the interactions among wind bursts and the Madden-Julian oscillation (MJO), the El Nino, and the Walker circulation is developed to reproduce both dynamical and statistical features of the ENSO diversity. In this model, the intraseasonal component with state-dependent noise captures general features of wind bursts and the MJO, both of which play important roles in triggering the El Nino. The thermocline feedback is the dominant mechanism for generating the eastern Pacific (EP) El Nino, while a nonlinear zonal advection is incorporated into the model that contributes to the central Pacific (CP) El Nino. Besides, a simple but effective stochastic process describing the multidecadal variation of the background Walker circulation modulates the spatial patterns and occurrence frequency of the EP and CP El Nino. This model succeeds in simulating the quasi-regular moderate EP El Nino, the super El Nino, and the CP El Nino as well as the La Nina simultaneously. It also captures the observed non-Gaussian characteristics of sea surface temperature anomalies in different Nino regions. Individual case studies highlight the outstanding skill of the model in reproducing the observed El Nino episodes and their underlying mechanisms.