\label{fig:periodograms}
Temporal average (1979-2014) periodograms for the 500 hPa meridional wind at 54.75$^{\circ}$S. Panel (a) shows three different subsets of the 30-day running mean data (all data times, PWI greater than its 90th percentile, PWI less than its 10th percentile), while panel (b) includes all data times but varies the running mean (in days) applied to the data prior to the Fourier transform. The labels on the vertical axis correspond to Equation \ref{eq:variance_explained}. 