Solar activity geomagnetic field and terrestrial weather

Abstract

IT has long been known that geomagnetic disturbances tend to recur after ∼27 d (refs 1–4). More recently, this effect has been associated with the rotation of the interplanetary magnetic field^5–8, and some evidence for a relation between the interplanetary magnetic field and terrestrial weather has also been found^9,10. The interplanetary magnetic field is usually characterised by either two or four sectors, and this pattern rotates with a fairly well defined period of ∼27.1±0.1 d (ref. 7). Such a periodicity leads naturally to the use of spectral analysis as an independent test of the reported association between the interplanetary magnetic field structure and terrestrial weather. We have obtained data on the geomagnetic activity index A_p for the 1964–70 from the National Oceanic and Atmospheric Administration and the vorticity area index used by Wilcox and his colleagues in their analysis⁹ for the same interval. We wish to form spectra of both time series and examine the spectra for common features which may be associated with solar related phenomena. Specifically we look for peaks in the power spectra of both time series with periods near 27.1 d.