Fig. 4

a Distribution of PG peak minute values during 50 days in the same season for 2006–2015. PG peaks are registered every 10 min, and numbers of these peaks within bins that are defined in logarithmic scale (20% stepping) are plotted, such that exponential distribution becomes a constant line, b 10-min averages for each bin of PG peaks. A larger difference means quick rise and/or quick decay from the peak values. In both panels, red crosses are for 2011, dashed lines are for the other years, and thick line is for the average