Potential Role of Inter-Basin Interactions in Eurasian Summer Blocking

Atmospheric blocking events are persistent tropospheric weather patterns that are associated with extreme events, such as heatwaves. In the summer, they primarily occur at high latitudes, e.g., over northern Eurasia. However, blocking frequency over these regions is underestimated in climate models, and often overestimated over the midlatitudes, while causes for such discrepancies remain elusive. To improve model representation of blocking frequency, it is important to understand different processes that affect it. Here, we explore blocking frequency in a reanalysis and experiments with an atmospheric general circulation model forced with different sea surface temperature (SSTs) profiles. The configurations range from an idealized no SST-front experiment and prescribing idealized SST-front in different regions to prescribing realistic climatological SSTs. Surprisingly, this reveals that more idealized (realistic) experiments lead to more (less) realistic blocking frequency. We find that weaker (less realistic) blocking frequency over northern Eurasia is primarily caused by the circulation changes related to SST gradients over the North Pacific. This suggests an important role of inter-basin interactions between the Atlantic and the Pacific. Additionally, tropical teleconnections can also play a role. This may suggest that models struggle with circulation response to SSTs in boreal summer, especially over the North Pacific. Thus, this work has implications for simulating (future) summer heat (and other) extremes over the high latitudes.