Sunspots - the search for the missing link

For many years, before the role of scapegoat descended on El Nino, sunspots were a prime suspect for every kind of natural disaster…

For many years, before the role of scapegoat descended on El Nino, sunspots were a prime suspect for every kind of natural disaster.

These relatively dull areas on the solar disc, which increase and decrease in both size and number over a recurring cycle of about 11 years, reflect a cyclical variation in the radiant energy of the sun.

For many years there were, and indeed still are, continuing efforts to establish links between this solar cycle and weather happenings on Earth.

In the 1930s, for example, an otherwise eminent climatologist discovered that the level of the water in Lake Victoria in Africa varied directly with the sunspot cycle. That which had long been sought was thereby found: a link between sunspots and the weather!

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But alas, it was not so. His study related to the years from 1890 to 1920, and within that period the rise and fall of the lake water did indeed match the 11-year sunspot cycle - but further research showed that outside these years, there was no relationship at all.

More promising was the discovery in 1987 by a team of American meteorologists that a relationship appeared to exist between sunspot activity and the rise and fall of temperatures 15 miles or so above the polar ice-caps. Subsequent work uncovered similar temperature oscillations elsewhere in the upper atmosphere, and indeed, it appeared that here and there these temperature anomalies might percolate right down to ground level, causing an unseasonal chill in the southern states of the USA, for example, around the solar sunspot maximum.

Another team of scientists claimed to have found that in periods of high sunspot activity, depressions in the North Atlantic seemed to move on tracks slightly further north than usual.

On the troublesome question of the mechanism through which the solar influence might exert itself, it has been pointed out that cosmic radiation is modulated by the solar cycle, and suggested that this radiation may cause chemical changes in the upper atmosphere which affect its transparency - and thus the terrestrial ebb and flow of solar radiation. It is a link, a very tenuous link, between sunspots and the weather, but it is enough to whet the cerebral appetites of those who care about these things.

Of course, any such relationship has been disputed. Other scientists claim to have found that the atmosphere wobbles like a jelly with a natural frequency of about 10 years; they think it was this oscillation that their colleagues spotted, and that for the limited period on which these scientists based their calculations, the 10-year cycle happened, coincidentally, to be in phase with the sunspots.