Recent amplification of the Siberian High decadal variability significantly influenced by anthropogenic aerosols in CanESM5

The Siberian High (SibH), a prominent feature of the Northern Hemisphere atmospheric circulation, exhibited enhanced interdecadal variability since 1970, characterized by a sharp decline from 1970 to 1990 followed by a steep recovery from 1990 to 2010. The factors underpinning these variations are unclear. Using the CanESM5 large ensemble, including the single forcing simulations, we find that anthropogenic aerosols played an important role in influencing the above SibH trends on top of pronounced internally-generated variations. Changes in the SibH during both periods are embedded in aerosol-induced upper-tropospheric mid-latitude wave trains propagating from upstream regions, with subsequent downward propagation of the signal to the surface via three-dimensional dynamical adjustments. Further insights into the physical mechanisms using regional aerosol perturbation experiments with CESM1 reveal a dominant role of decreased North American aerosol emissions in driving the atmospheric wave train through interaction with the North Atlantic jet during the first period. In the second period, European aerosol emissions, characterized by a large and extensive decrease, are crucial to explain the SibH recovery. A better understanding of the factors driving multidecadal variability of the SibH, and in particular of the interplay between internal variability and external forcing, is critical to reducing uncertainties in future projections of regional extremes, such as cold surges, which can cause large social and economic impacts on densely populated East Asia.