\label{fig:phase_distribution}
Phase distribution for all data times displaying PSA-like variability. The bars show the total count for each 0.75$^{\circ}$E interval over the period 1979--2014, while the lines represent kernel density estimates for a series of different time periods. Grey shading indicates the phase groupings taken to represent the positive (4.5 to 19.5$^{\circ}$E) and negative (37.5 to 52.5$^{\circ}$E) phase of the PSA pattern.