Rainfall in the Temperate Zone in Connection with the Sun-spot Cycle

Abstract

THIS month's number of the Nineteenth Century contains an article on the connection of rainfall with the eleven years' cycle of sun-spots. It takes a carefully-selected area in which such a coincidence, if it existed, would be well marked. The great tract of water spreading southwards from Asia to the southern pole affords an arena for the undisturbed play of solar activity. It may readily be understood that any excess of solar energy has a more direct and uniform influence upon the rainfall gathered from this vast aqueous expanse, than it would have upon smaller areas of water intermingled with tracts of land, and cut off from each other by ranges of mountains, as in the European and American continents. Other reasons exist which would render solar influence a more directly potent factor in the rainfall gathered from the Indian Ocean than in that of the temperate zone. Without doing more than alluding to the fact that sun-spot activity is confined to a belt of considerable thickness on either side of the sun's equator, there are several well-ascertained causes which would render an excess of solar activity more directly felt in the equatorial regions of our earth than in those nearer the poles. While, therefore, I believe that the coincidence of a rain cycle and of a cycle of wind disturbances with the eleven years' cycle of sum-spots, has now been established as regards the Indian Ocean and the Madras rainfall, I am anxious to guard against the conclusion being pushed too far. The article in the Nineteenth Century proves much, but it would be a misfortune at this still early stage of the inquiry, if wider inductions were drawn from it than are justified by the evidence which it brings forward.