........ published in NEWSLETTER # 54
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........ published in NEWSLETTER # 54
THE SOLAR ENGINE AND ITS INFLUENCE ON THE TERRESTRIAL ATMOSPHERE AND CLIMATE
by Dr. E. Nesme_Ribes, Observatoire de Paris, Meudon (France)
No fully satisfactory explanation has ever been given for the many cold and warm fluctuations the earth has experienced in its geological past. What causes alterations of this kind, such as the present global warming?
Of the various factors that have been proposed as answers to this question, one of the most compelling is that the earth's climate may be altered by variations in the sun's energy output: the sun, contrary to common wisdom, is a variable star. It varies in a fairly regular cycle of 11 years on average; but it has also been known to behave much more erratically, with extended, deep lulls in activity stretching over several decades. Such has been the case several times over the past millenia, with the well_documented example of the Maunder minimum in the 17th century. Since these lulls seem to correspond to historic periods of cold on earth, the hint of a cause_and_ effect connection between the two was strong enough to attract a flock of scientists to this NATO workshop on solar climatic forcing.
The subjects discussed in the resulting volume (NATO ASI SERIES I25) range from the sun's interior to the earth's. The solar machinery is described first, emphasizing the dynamo of convective motions within the sun and how these generate a complex pattern of powerful magnetic fields that drive and control all the bright and dark objects visible on the sun's surface.
Then, drawing analogies from what is known of other solar_type stars in the universe, it is shown that the sun may very well spend a quarter of its time in an anomalous state with its brightness and energy output reduced by 0.25 to 1 %. While this may seem small, the earth's atmosphere probably magnifies any solar variation by a combination of intertropical stratospheric winds and planetary waves. So we looked for further historical confirmation that the solar variation actually does have some climatic forcing effect. The records are somewhat ambiguous here, but the ambiguities may be due rather to the spottiness of the records themselves.
An effort is made to fit a solar forcing parameter into atmospheric models of the earth's climate, to see if a solar minimum/earth Ice Age phenomenon could be simulated. The General Circulation Models (GCM) used here entail a number of simplifications and yet, when the solar forcing parameter is introduced, the GCM verdict is compatible with a little Ice Age.
Conclusion: There is compelling evidence that the sun plays a role in climatic fluctuations. There is other research underway on into the effects of volcanic activity, the circulation in the oceans and their interaction with the earth's atmosphere. Climatic models should consequently be developed to include a number of physical mechanisms that have been neglected so far, namely the sun's variable input to our complex environment.
Reference books: I25, C373