Abstract
Power spectral densities computed from low-latitude horizontal intensity of the Earth's magnetic field over two-year periods of declining phases of solar cycles 16 to 19 show a close relationship with the maximum relative sunspot number of the following solar cycles. The maximum sunspot number shows an exponential rise with the power density near 1/27 cd−1; maximum R z,however, increases linearly with power density near 1/14 cd−1. It is also shown that the rate of decline of sunspot number in a solar cycle is almost exactly related, linearly, to power spectral density for the preceding solar cycle. Power densities near 1/27 and 1/14 cd−1 in declining phase of solar cycle appear to be satisfactory indices for the maximum relative sunspot number of the following cycle and its rate of decline thereafter.
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Bhargava, B.N., Rangarajan, G.K. Recurrent magnetic activity, sunspot number and its rate of decline. Sol Phys 40, 235–239 (1975). https://doi.org/10.1007/BF00183166
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DOI: https://doi.org/10.1007/BF00183166