There are some missing data for the period 1818 - 1849, and the data for SC10 - 11 are under revision, but all in all this graph conveys pretty well that - in general - a low
amplitude cycle is preceded by a solar cycle transition with a
high number of spotless
days, and vice versa.
These authors analyzed the relative deviations of TEC (rTEC) over Japan obtained in the years 2000 — 2008 and found that the correlation between rTEC and F10.7 is
highest during the maximum phase of solar activity, when the 27 -
day amplitude of rTEC is almost equal to its total deviation.