Phase-Locked Impact of the 11-Year Solar Cycle on Tropical Pacific Decadal Variability

As an important external forcing, the effect of the 11-yr solar cycle on the tropical Pacific decadal variability is an interesting question. Here, we systematically investigate the phase-locking of the atmosphere and ocean covariations to the solar cycle in the tropical Pacific and propose a new mechanism to explain these decadal covariations. In both observation/ reanalysis datasets and a solar cycle forced sensitivity experiment (named the SOL experiment), the ocean heat content anom-alies (OHCa; 300 m) resemble a La Nin similar to a-like pattern in the solar cycle ascending phase, and the Walker circulation shifts westward. In the declining phase, the opposite is true. The accumulative solar irradiation directly contributes to this coherent decadal variability via changing the warm water volume and the solar-related heat is redistributed by the ocean dynamic pro-cesses. During the 11-yr solar cycle, the Pacific Walker circulation anomalies maintain the OHCa in the western equatorial Pa-cific and work as negative feedback for the eastern Pacific to help the OHCa phase transition. In addition, oceanic meridional heat transport via the subtropical cells and the propagation of off-equatorial Rossby waves also provide a lagged negative feed-back to the OHCa phase transition according to the 11-yr solar cycle. The decadal coupled responses of the tropical Pacific cli-mate system are 2 years more lag in the SOL experiment than in the observation/reanalysis.

Automated summary

This study systematically investigates the response of the tropical Pacific to the 11-year solar activity cycle and proposes a new mechanism to explain the decadal variations. The solar radiation directly affects the warm water volume and redistributes the solar-related heat through ocean dynamic processes, leading to the maintenance of Pacific Walker circulation anomalies and a negative feedback to the transition of warm water volume in the eastern Pacific. Observations and experiments show a lagged response in the tropical Pacific climate system.