SUNSPOT CYCLES

Evening Post, Volume CVI, Issue 17, 21 July 1928, Page 17

SUNSPOT CYCLES

INFLUENCE ON WEATHER A KNOTTY PROBLEM ' Sunspot cycles and their possible effect on the weather was one of the subjects dealt with by Dr. E. Kidson, Government Meteorologist, in his lecture last night on "Some Periods in Australian aud New Zealand Weather," delivered to the Technological branch of the AVellington Philosophical Society. "For many years, but especially recently," said Dr..Kidson, "meteorologists aud mathematicians have searched • for periods in weather. The methods employed have been in many cases mechanical, some form of mathematical analysis being used. As a result, many periods have been found: in fact, most .meteorologists Jiave a few of their own, but most of them are not believed in by other meteorologists. Of all the periods advocated, those which receive the fullest support are one corresponding with the sunspot cycle and a shorter one ranging between 1.5 and 4 years, values about 3 years being very common. The number of spots on the sun, or the area of the sun's surface covered by spots, goes through a fairly regular cycle of variation. The length of the cycle varies, and may be anything between 9 aiid 13 years. Effects corresponding with the sunspot cycle, therefore, are of the kind which might easily fail to be exposed by a mathematical analysis of long records. In fact, the great defect of the mathematical method is that it is difficult to allow for possible yaria-j tions in the length of a period, or for interruptions or sudden, changes of phase in it." ■ ■ :.: ... ' At the beginning of the cycle, or sunspot minimum, comparatively few spots were to be seen on the sun's disc. The number then increased rapidly until the maximum, which occurred about four years later; then followed a gradual decrease until the next minimum. Some of the . variations in the earth's magnetism were very closely related to the number of sunspots, so that it was certain that there was a variation in some at least of the types of radiation coming from the. sun, of a similar nature to that of the number of sunspots. It was natural, therefore, to look for corresponding effects in the weather, and many such effects had been found, but the relationship was seldom close or the same over large portions of the earth's surface. In Europe scarcely any useful relationships had been found, and, since there was a concentration of meteorologists iv Europe, there had been a good deal, of scepticism regarding, the solar . effect. Australia, however,, offered a .more promising field than Europe, the elements showing the closest connection with sunspots being the range of north and south movement during the year of the mean monthly tracks of anticyclones. Observations of the upper clouds showed that the mean westerly component of cirrus velocity 'was high when sunspot numbers were low. The marked absence of westerly winds during last spring and summer was *due,. Dr. Kidson thought, to the fact that we are near a sunspot maximum. Slides were shown illustrating the variation of rainfall in New Zealand during the sunspot cycle. The mean for about nineteen stations situated in the North Islaud and in the Nelson province showed that at these stations the rainfall is higher the higher the number of sunspots. The connection was quite close except for a drop in the rainfall in the second year after sunspot maximum. Curves giving corresponding results for the rainfall at about an equal number of stations in Canterbury and Otago showed no useful relationship with sunspots, but it was interesting to note that in the seventh year, when the rainfall is low -at the northern stations, it is high at the southern ones. The' stations which show no direct relationship with sunspots arc those protected from westerly winds. It would seem, therefore, that the source of the ..sunspot effect is in tho north-westerly winds. Tho variations shown, said Dr. Kidsan in conclusion.'-are niuch smaller than the erratic variations in rainfall, and are of little use for seasonal forecasting. From a study of the two cycles, however, we might be helped to, understand the weather, processes, their study tending ultimately perhaps towards a means of issuing seasonal' forecasts.