Pathways of Influence Between Northern Hemisphere Blocking and Stratospheric Polar Vortex Variability

We apply a causal inference-based framework to test and quantify previously suggested relationships between Northern Hemisphere blocking, upward wave-activity fluxes stratospheric polar vortex (SPV) variability using reanalysis data. show that the influence of blocking on is entirely mediated by fluxes, as classical view would suggest. However, pathway not completely straightforward. In contrast vortex-weakening effect European vortex-strengthening west Pacific lower only partially upper tropospheric fluxes. addition, two-thirds also sudden warmings are explainable in terms These findings help clarify pathways SPV variability.