The role of the Aleutian Low in driving Pacific Decadal Variability

Variability in the Aleutian Low is a known contributor to North Pacific sea surface temperature (SST) variability, but its role in forcing the basin-wide SST anomalies that characterise Pacific Decadal Variability (PDV) is unclear owing to the difficulty of disentangling coupled atmosphere-ocean processes. Here we perform a large ensemble experiment with an intermediate complexity GCM where the winter-time Aleutian Low is nudged to an anomalously strong state during successive winters. This ensemble is compared to a free-running simulation to isolate the impacts of the anomalous Aleutian Low. The nudged experiment produces a basin-scale SST response that closely resembles PDV in the free running simulation, confirming that the Aleutian Low can force PDV-like variability. Tropical Pacific sea surface temperatures (SSTs) are significantly warmer in response to the strong Aleutian Low, demonstrating that extratropical atmospheric forcing can impart a signature in tropical SSTs. The largest tropical Pacific warming is manifest in the season following nudging (boreal spring), though anomalies persist year-round. We use the Bjerknes Stability Index to attribute the drivers of the tropical Pacific SST response and find that the thermocline feedback is key, which itself is most dominant in summer. The results lend new understanding to the potential for extratropical atmospheric forcing of tropical ocean variability.