The F₂ Region as an Indicating Mechanism for Solar Activity

Abstract

THE fact that F₂ region critical frequencies and solar activity correlate in a general way is well known. Moreover, I have shown¹ that the effect of changes in ionization which occur throughout the year can be eliminated in such a way as to bring out a clear-cut correspondence between these critical frequencies and smoothed average sunspot numbers. In an effort to find a more sensitive index for correlation purposes, a study has been made using both whole disk and central zone character figures for calcium and hydrogen flocculi as well as relative sunspot numbers. It has been found that the central zone indexes are better than those for the whole disk. When the monthly averages of the character figures for calcium flocculi are used, it is found that no smoothing is necessary, provided the effect of changes that occur throughout the year is eliminated.