Fig. 7: Stratospheric polar vortex response to historical sea-ice loss.

a Wintertime (December–January–February) EP fluxes (purple arrows; scaled by air pressure; the vertical component is scaled by 10⁴ and the meridional component is scaled by 10⁶; m s⁻²) of zonal wave 1–2 and their divergence (shading; scaled by air pressure; s⁻²) regressed against early-winter BKS SIC, scaled by the early-winter BKS SIC difference between BKS low- and high-SIC years. b 200-year simulated differences of wintertime (December–January–February) EP fluxes (purple arrows; scaled by air pressure; the vertical component is scaled by 10⁴ and the meridional component is scaled by 10⁶; m s⁻²) of zonal wave 1–2 and their divergence (shading; scaled by air pressure; s⁻²) between the atmosphere-only historical BKS low- and high-SIC simulations (atm_lo minus atm_hi). c the same as (b), but for the coupled historical BKS low- and high-SIC simulations (cpl_lo minus cpl_hi). d–f are the same as (a–c), but for wintertime zonal-mean zonal wind (m/s). Purple contours denote the climatological mid-winter zonal-mean zonal wind derived from d ERA-5 reanalysis during 1979–2019, e atm_hi and f cpl_hi simulations, with solid/dashed lines denoting positive/negative values. Black stippling denotes the statistical significance at the 95% confidence level according to bootstrap resampling.