SPECTRAL-ANALYSIS OF ANNUAL SUNSPOT SERIES - AN UPDATE

Maximum Entropy Spectral Analysis (MESA) of annual sunspot series for 1700-1987 (288 points) indicated the most prominent peak at T = 10.91 years, followed by T = 10.62, 10.00 and 103 years of comparable amplitudes and twelve others of smaller amplitudes, all significant at a 3-sigma a priori level. MACDONAND (1989) has suggested that the method of spectral analysis should depend upon the choice of the chosen model. However, our results compare well with his results from a periodogram study, indicating that the choice of the model, generally difficult in geophysical problems, is not vital. Since amplitude estimates in MESA are unreliable, our prescription is to use MESA only for detecting possible periodicities and then, estimate amplitudes and phases by a separate Multiple Regression Analysis.