The Spectrum of the Geomagnetic Activity Index Ap
STANFORD UNIV CA STANFORD ELECTRONICS LABS
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The ionospheric propagation of high-frequency radio waves is profoundly influenced by the variations of sunspot numbers and of geomagnetic activity. Thus, details of these variations, and of the relationship between them, has practical application. The variation of the geomagnetic activity index Ap over the 38-year interval January, 1932 through January, 1970 differs in several important characteristics from the variation of sunspot numbers over the same interval. A spectral analysis approach was used d to investigate this variation of AP, as well as its relation to the variation of sunspot numbers. The data analyzed consisted of the 457 monthly average AP indices AP for the interval and the corresponding observed monthly sunspot numbers. Several large samples of the original daily Ap indices were also analyzed. Two of the latter samples covered 11-year intervals April 1, 1944 - June 2, 1955 and June 1, 1956 - July 31, 1967 and the third covered a 23-year interval April 1, 1944 - December, 1967.
- Atmospheric Physics
- Radiofrequency Wave Propagation