Correlation between Solar Activity and the Brightness of Jupiter's Great Red Spot

Abstract

IT may be interesting to note in connexion with the letter of Graf, Smith and McDevitt¹ discussing the correlation of solar activity and brightness of Jupiter's great red spot that the brightness of the Jovian spot seems to have two maxima for each single maximum of the Zurich sunspot number. It has been pointed out, particularly by Gnevyshev², that a number of aspects of the solar cycle behave in a similar manner. Perhaps the most striking of these is the incidence of proton flares (see especially Fig. 6 of Gnevyshev²) which clearly has two maxima per solar cycle with one maximum preceding the sunspot maximum by a slight amount and the other occurring during the declining phase of solar activity. Because the proton flares are known to have very important terrestrial effects, and because proton flares have the same double maxima behaviour as does the visibility of the Jovian red spot, it seems reasonable to suggest that perhaps the emission of solar particles may be a more relevant aspect of solar activity to associate with Jupiter's spot than the ultraviolet radiation suggested by Graf et al.¹.