Dynamical Controls on Pacific-Origin Rossby Wave Propagation Across the North Atlantic–European Sector

Pacific-origin atmospheric teleconnections play a central role in shaping Northern Hemisphere summer circulation, yet their downstream expression over the North Atlantic–European sector varies substantially across models. Here, we assess the robustness, structure, and background-state dependence of these teleconnections using CMIP6 large ensembles together with idealized SST-perturbation experiments from the Decadal Climate Prediction Project (DCPP-C). The study focuses on Rossby Wave Sources (RWS) over the northeastern Pacific and the resulting wavetrain that propagates across North America, the Atlantic, and Eurasia during boreal summer.

All large ensembles reproduce a coherent circumglobal Rossby wave train associated with enhanced RWS in the northeastern Pacific. However, the degree of agreement deteriorates downstream, with the largest spread occurring over the North Atlantic and Europe. Model differences in upper-tropospheric jet strength and meridional position strongly modulate the phasing and amplitude of the wave train in this region. Models with small jet biases compared to the ERA5 reanalysis maintain a realistic sequence of alternating geopotential height anomalies, while stronger or latitudinally displaced jets distort or shift the European node of the teleconnection.

Idealized DCPP-C experiments reveal that the Pacific-Atlantic interaction is strongly state-dependent. Simulations with intensified RWS (negative IPV phase) produce a PDO-like surface cooling pattern in the northeastern Pacific and a robust cooling response in the North Atlantic, confirming a direct trans-basin link. Atlantic SST anomalies further modulate the downstream atmospheric response: a warm Atlantic suppresses the Pacific–Europe teleconnection, while a cold Atlantic allows for a strengthened and more coherent wave train. Additional experiments combining AMV and IPV phases demonstrate that the Pacific signal can be either reinforced or damped depending on the Atlantic background state.

These results highlight the joint role of northeastern Pacific RWS variability, upper-level jet biases, and Atlantic SST state in shaping the structure and persistence of Pacific-to-Europe summer teleconnections. Improving the representation of these elements is essential to reduce inter-model spread and enhance confidence in simulated boreal-summer circulation patterns.