\label{fig:sf_composites}
Composite mean 500 hPa streamfunction anomaly for four different phase groupings: positive PSA pattern (4.5 to 19.5$^{\circ}$E), minima 1 (22.5 to 37.5$^{\circ}$E), negative PSA pattern (37.5 to 52.5$^{\circ}$E) and minima 2 (50.25 to 6.0$^{\circ}$E). Dashed contours indicate negative values and the contour interval is $1.5 \times 10^6 \: m^2 s^{-1}$.