Fig. 2: Driving of northern hemisphere summer barotropic vorticity by SST on super-synoptic time-scales.

a–h Lead–lag correlation maps between weekly averaged values of SST and barotropic vorticity (vorticity averaged between 700 and 200 hPa). “SST lead1” refers to SST leading the barotropic vorticity by 1-week and so on. Dotted area represents regions significant above 95% CI based on the cutoff critical values for two-tail tests. The weekly data length spans from year 1982–2017.