A Nonlinear Full-Field Conceptual Model for ENSO Diversity

As the strongest year-to-year fl uctuation of the global climate system, El Ni & ntilde;o - Southern Oscillation (ENSO) exhibits spatial - temporal diversity, which challenges the classical ENSO theories that mainly focus on the canonical eastern Paci fi c (EP) type. Besides, the complicated interplay between the interannual anomaly fi elds and the decadally varying mean state is another dif fi culty in current ENSO theory. To better account for these issues, the nonlinear tworegion recharge paradigm model is extended to a three-region full- fi eld conceptual model to capture the physics in the western Paci fi c (WP), central Paci fi c (CP), and EP regions. The results show that the extended conceptual model displays a rich dynamical behavior as parameters setting the ef fi ciencies of upwelling and zonal advection are varied. The model can not only generate El Ni & ntilde;o bursting behavior but also simulate the statistical asymmetries between the two types of El Ni & ntilde;os and the warm and cold phases of ENSO. Finally, since both the anomaly fi elds and mean states are simulated by the model, it provides a simple tool to investigate their interactions. The strengthening of the upwelling ef fi ciency, which can be seen as an analogy to a cooling thermocline associated with the oceanic tunnel to the midlatitudes, will increase the zonal gradient of the mean state temperature between the WP and EP, i.e., resembling a negative Paci fi c decadal oscillation (PDO) pattern along the equatorial Paci fi c. The in fl uence of the zonal advection ef fi ciency is quite the opposite, i.e., its strengthening will reduce the zonal gradient of the mean state temperature along the equatorial Paci fi c.