Using the method of maximum entropy spectral analysis (MESA) by Burg and the least-squares linear prediction (lslp) (also calledFABNE) by Barrodale and Erickson, the spectra of geomagnetic indices Ap, AN, AS, AE, AU, AL, Dst and cosmic ray neutron intensity at Deep River are obtained for 1965 and 1969 from daily means and for longer periods from monthly means. A large number of peaks of periodicities from 2 days to several years is obtained, many of which are shown by all the indices. Some of these are probably harmonics of the 27 days solar rotation period and the 20–22 years double sunspot cycle period. Comparison is made with results of earlier workers who reported fewer peaks.

Using artificial samples, it is shown that, even for the method of maximum entropy spectral analysis (mesa) evolved by Burg, a presence of a linear trend gives distortions (frequency shifts) in the low frequency (high periodicity) region and hence, it is advisable to eliminate linear trends before attempting spectral analysis.

The effect of the presence of a non-zero mean is not very definite; but, very large mean values seem to reduce the sharpness of the peaks.

The implications of these findings for the results by Jin and Thomas for some geomagnetic parameters are discussed.

Association of ENSO (El Nino/southern oscillation) events with annual rainfalls in S. America, Africa, India, Australia and New Zealand was found to be poor except for India and Victoria. For these two regions the relationships were one-sided i.e. most of the ENSO were associated with droughts; but many droughts were not associated with ENSO. for some rainfall series, the relationships are significant and prominent periodicities existed in the long periodicity region.