Abstract
<title>Abstract</title> <p>Atmospheric teleconnections originating in the Pacific strongly influence Northern Hemisphere summer climate through Rossby wave trains, yet their downstream impact over Europe exhibits pronounced variability across time and models. Here, we investigate how Atlantic sea surface temperature (SST) anomalies modulate Pacific-origin Rossby wave teleconnections using CMIP6 large ensembles. Focusing on boreal summer, we diagnose Rossby Wave Sources (RWS) over the northeastern Pacific and track their associated circulation responses across the North Atlantic-European sector. CMIP6 large ensembles consistently reproduce a circumglobal Rossby wave train emanating from the northeastern Pacific; however, substantial inter-model spread emerges downstream over the North Atlantic and Europe, where the teleconnection is most sensitive to background flow conditions. We show that this spread is closely linked to biases in upper-tropospheric jet structure, which control both the amplitude and phase of Rossby wave propagation into Europe. Crucially, Atlantic SST anomalies regulate the efficiency of this trans-basin propagation: a cold Atlantic strengthens the upper-level waveguide and facilitates the eastward extension of the wave train into Europe, whereas a warm Atlantic weakens and disrupts this propagation. These results highlight the state-dependent nature of Pacific–Atlantic interactions and underscore the combined role of Atlantic SSTs and jet biases in shaping European summer predictability.</p>