Zhang, Y., S. Yu, S.-P. Xie, D. J. Amaya, Q. Peng, Y. Kosaka, X.
Lin, J.-C. Yang, S. M. Larson,
A. J. Miller and
L. Fan, 2022:
Role of ocean dynamics in Equatorial Pacific decadal variability
Climate Dynamics, 59, 2517-2529.
Abstract.
The tropical Pacific exhibits decadal El Nino-Southern Oscillation (ENSO)-like
variability, characterized by meridionally broad sea surface temperature anomalies in the i
eastern Pacific. In this study, we focus on the variability in the equatorial Pacific band (5S-+5N),
termed equatorial Pacific decadal variability (EPDV). While it is known that ocean
dynamics plays an essential role in EPDV, the simulations by air-sea thermodynamically
coupled slab ocean models (SOM) obscure the nature of the role of ocean dynamics. To
confront this issue, we use a mechanically decoupled simulation, which isolates the effects of
thermodynamic coupling processes and mean ocean circulation on EPDV. Thus, by comparing
the simulation to a SOM, we investigate the role of mean ocean circulation and show that it
plays a role in damping EPDV, primarily through mean equatorial Pacific upwelling. By
comparing the simulation to a fully coupled dynamic ocean model (DOM), we examine the
role of anomalous wind-driven ocean circulation and demonstrate that it plays a role in
amplifying EPDV. Further, this amplification strength overwhelms the upwelling damping
effect, resulting in the anomalous wind-driven ocean circulation forcing EPDV. The forcing
process, however, is distinct between the central and eastern equatorial Pacific, with the former
dominated by zonal advective feedback and Ekman pumping feedback, while the latter
controlled by thermocline feedback. Taking the EPDV as an example, our study advances the
understanding on the two distinct dynamical systems (SOM and DOM), benefiting the physical
interpretation of other climate variabilities.
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