\label{fig:rotation}
Atmospheric circulation at 500 hPa for a 30-day mean centered on 18 May 2006. The top panel shows the streamfunction anomaly plotted on a regular global grid (dashed contours indicate negative values and the contour interval is $3.0 \times 10^6 \: m^2 s^{-1}$), while the bottom panel shows the corresponding meridional wind anomaly on a rotated grid where the north pole is located at 20$^{\circ}$N, 260$^{\circ}$E. The solid green box is bounded by 10$^{\circ}$S to 10$^{\circ}$N and 115$^{\circ}$E to 235$^{\circ}$E on the rotated grid and corresponds to the search region of interest (or `PSA sector'), while the green dashed line corresponds to the equator on the rotated grid.