Decadal Strengthening of the Siberian High–stratospheric Polar Vortex Coupling: a Direct Tropospheric Driver Independent of Ural Blocking

The troposphere-stratosphere coupling is a fundamental driver of winter atmospheric variability, yet the relative importance of different tropospheric precursors remains a subject of intense debate. This study identifies a significant decadal strengthening in the dynamical link between the December Siberian High (SH) and the January stratospheric polar vortex (SPV) over the past few decades. Our analysis reveals that the SH has emerged as a robust and independent precursor to SPV weakening, characterized by a marked increase in upward-propagating planetary wave activity. Notably, we find that this intensified SH-SPV coupling is decoupled from Ural Blocking (UB) activity, which has traditionally been considered the primary mediator of troposphere-stratosphere interactions. This direct SH-to-SPV pathway provides critical predictive skill for the intraseasonal reversal of East Asian surface temperatures. Our findings highlight the necessity of monitoring SH variability—beyond traditional blocking indices—to improve sub-seasonal forecasts of stratospheric disturbances and associated cold extremes.