1986 Volume 38 Issue 6 Pages 551-572
By analyzing the values of whistler dispersion observed at Wakkanai (geomag. lat. 35.3°N) or Moshiri (geomag. lat. 34.0°N) during the period 1958-1982, the characteristics of the semi-annual and annual harmonic components included in their temporal variations have been revealed. By means of a pertinent statistical procedure, the most probable values of whistler dispersion of each month normalized to sunspot numbers 0, 50, 100, 150 and 200 have been derived. The results of harmonic analysis of these values made separately for each of five sunspot numbers show that the existence of the semi-annual component can be regarded as unquestionable from statistical consideration and its phase is very stable over day and night and the range of the sunspot numbers, maxima occurring around the middle of April and October. It is to be noted that, roughly at the same times as above, the semi-annual components included in the temporal variations in various geophysical phenomena take maximum values also. As regards the annual component of variation in whistler dispersion, the reality of its existence can be statistically confirmed for the cases of sunspot numbers 50, 100 and 150, but this is not always true in other cases. Maxima come about in the time interval from the beginning of July to the beginning of October, but this time interval is entirely different from the corresponding one of the non-seasonal variation in the peak electron density of the F2 layer, in disagreement with what we expect on the basis of a simple argument.