\label{fig:psa-neg_seasonality}
Variability and trends in the negative phase of the PSA pattern. The total PSA-negative data times for each individual season are shown in panel (a), corresponding seasonal linear trends in panel (c) (black represents the annual trend) and monthly totals for the entire study period (1979--2014) in panel (b). To account for the fact that not all months have an equal number of days, the counts for each month are presented as a percentage of the total number of days for that month. Years in panel (a) are defined from December to November (e.g. the `year' 1980 spans December 1979 to November 1980) and trends that are statistically significant at the $p < 0.10$ and $p < 0.05$ level are indicated with a circle and star respectively.
