Fig. 5

Relative PG values compared to peak values during 10 min centered at the peak time for different PG peaks values for three different periods of a year. From top raw to fourth raw are negative peaks: a, e, i \(-\,1600< {\hbox {PG}}_{\mathrm{peak}} < -\,800\,\hbox {V/m}\), b, f, j \(-\,800< {\hbox {PG}}_{\mathrm{peak}} < -\,400\,\hbox {V/m}\), c, g, k \(-\,400< {\hbox {PG}}_{\mathrm{peak}} < -\,200\,\hbox {V/m}\), and d, h, l \(-\,200< {\hbox {PG}}_{\mathrm{peak}} < -\,100\,\hbox {V/m}\). The red-hatched area is range of standard deviation at each point of 2011 data. The bottom raw is for positive peaks from mid-March to April: m \(+\,400< {\hbox {PG}}_{\mathrm{peak}} < +\,800\,\hbox {V/m}\), n \(+\,200< {\hbox {PG}}_{\mathrm{peak}} < +\,400\,\hbox {V/m}\), and o \(+\,100< {\hbox {PG}}_{\mathrm{peak}} < +\,200\,\hbox {V/m}\). Numbers of data point of each minute are given at the top of each panel with red text for 2011 and blue text for the other years. Data point with six samples or more are plotted. In all panels, red crosses are for 2011, dashed lines are for the other years, and the thick line is for the average