(a) Grey points shows ap index values as a function of simultaneous am values for 1959–2017 (inclusive). Cyan points show the scatter plot of the corresponding 24-hour (8-point) running means, Am* and Ap*. The black points are means of ap (with error bars of plus and minus one standard deviation) as a function of means of am in am bins of width Δam = 10 nT (only means for bins containing six or more samples are shown). The mauve line is the ideal case for which ap = am. (b) and (c) Annual variations shown by means in fraction-of-year (F) bins of width ΔF = 0.05. (b) shows (in black) the annual variations of 〈am〉 and (in mauve) 〈ap〉 × η, where η is the ratio 〈am〉_all/〈ap〉_all for means taken over the whole dataset. (c) shows the annual variation of the ratio of ap/am. (d) and (e) Diurnal variations shown by means for the eight UT values of both indices using the same color coding as in (b) and (c).