Extreme Zonal Dipole Pattern of January Blocking Days Between the Eastern North Atlantic and Ural in 2008: The Combined Impact of Sea Surface Temperature and Newly Formed Arctic Sea Ice Anomalies

Abstract A pronounced dipole anomaly of blocking days (BDD) between the eastern North Atlantic (ENA) and Ural occurred in January 2008, representing the strongest positive phase in recent decades, marked by considerably increased (decreased) Ural (ENA) blocking days. The background circulation exhibits a positive North Atlantic Oscillation phase, with diminished (strengthened) westerly winds and meridional potential vorticity gradients over Ural (ENA), which enhances (suppresses) blocking days. Under the combined anomalies of strong North Atlantic warming, robust La Niña and substantial Barents–Kara newly formed sea ice reduction, along with their joint effects inducing significant atmospheric wave responses, the notable BDD is facilitated. Over the North Atlantic, enhanced surface turbulent heat fluxes excite upward‐propagating Rossby waves and increase atmospheric baroclinicity, favoring local quasi‐barotropic low‐pressure anomalies that modulate background flow through downstream Rossby wave energy dispersion, thereby influencing the BDD. Over the Pacific, La Niña–associated cooling suppresses convection, triggering a Gill‐type response that strengthens anomalous easterly winds. In combination with reduced baroclinicity over the North Pacific, this enhances the subtropical anticyclone and initiates a downstream Rossby wave train that promotes the BDD. Moreover, declined Barents–Kara newly formed sea ice increases local turbulent heat fluxes and modulates mid‐to‐high‐latitude circulation over Eurasia through altered transient eddy activity and Rossby wave propagation, thus reinforcing the BDD. Numerical experiments using the ECHAM5 model and LBM simulations confirmed the atmospheric responses to these SST and sea ice anomalies. Additionally, BDD‐related circulation anomalies trigger widespread temperature and precipitation extremes and may contribute to compound extreme events.