Solar activity predicted to increase next century

Press, 2 December 1987, Page 35

Solar activity predicted to increase next century

A Russian astronomer, V. F. Chistyakov, recently predicted that solar activity will be at high levels in the next century. This has important implications tor global weather patterns. Heinrich Schwabe, a German astronomer, found in 1843 that the interval between successive intervals of sunspot maxima was 10 years. Later it was ascertained that the average interval was actually 11 years. This interval is termed the sunspot or solar cycle. However, the interval of an individual cycle can vary between seven and 17 years. It is not only the sunspots that wax and wane in this period as all forms of solar activity conform to the same period. This cycle appears to be broken at long intervals during which activity seems almost to cease. This happened between 1645 and 1700 A.D. Such decreases in solar activity poses the question as to whether they have occurred in the distant past. If this happened did they coincide with any marked change in weather on the Earth? Large sunspots which usually occur during times of maximum activity can be seen with the naked eye provided the Sun is viewed through mist or haze so that the eye is not damaged. Observations of such events dating back 2000 years are found in the Chinese records as they kept careful records of all astronomical features that were visible without telescopic aid.

The Chinese also kept careful records of the ap-

pearances of aurora, which also vary in intensity with the 11-year solar cycle although their maxima lags behind that of sunspots.

Several Chinese scientists have investigated all the early records of both naked eye sunspots and aurora.. They have published a catalogue of such events in which they classified them according to their intensity and assigning them numbers according to this. Chistyakov has used this catalogue in his investigations into past solar and aurora activity. He found that there are cycles longer than that of 11 years. These occurs at intervals of 95 and 115 years and appear to alternate. He combined these records with those obtained from power spectra of the silt layers in Saki Lake in the Crimea. These covered the period between 2294 B.C. to 1894 A.D. He also used the records of tree rings of American sequoias from 1306 B.C. to 1914 A.D.

He found two deep minima of sunspot and aurora activity around 1000 B.C. and 1700 A.D. The radio carbon Cl 4 in the tree rings showed the same minima. He also claims that the silt deposits supported his results. He states that these times of very low activity coincide with little ice ages on the Earth.

It appears from this work that solar maxima are normally at a . high level as has been the case in the present century. However, this is destroyed from time to time by a marked decrease in solar activity even when it

should be at a peak. Such very much lower activity can last for three or four centuries. These are times in which little ice ages occur. Why such decreases occur is uncertain.

Chistyakov, on the basis of his investigations, believes that these declines in solar activity occur at intervals of nearly .2600 years. This leads him to predict that solar activity will be at a high level in the next century.

It is generally accepted that the amount of solar radiation reaching the Earth has profound effects on global weather. It is quite certain that magnetic storms and aurora are more frequent when the Sun is in an active state. The is however, no general agreement on exactly how solar activity affects our weather patterns.

Two Chinese astronomers also investigated the variability of sunspot activity before the seventeenth century. They used the catalogue of naked eye sunspots and gave each record a number, or weight, according to and descriptive differences in sunspot size, number and lasting period. They found that even allowing for the fact that sunspot records could not be successive the 11-year cycle persisted. They concluded that the times of prolonged minima of solar activity were the result of several long-term periods.

The Chinese results differ from those of Chistyakov inasmuch as they found that they times of weakest solar activity correspond to 400 and 1170 A.D. They then compared this result with the atmosphere curves of tempera-

tures of China and Greenland as’ well as the frequency curve of Oriental aurora. They found that these two epochs coincided with the lowest parts of these curves. They placed the long term of minimum solar activity at near 800 years. They conclude, however, that there is no threat of a little ice age in the near future.

Today there is concern that the “greenhouse effect” is incresing because of atmospheric pollution resulting in temperatures rising world wide. There is even greater concern at the depletion of the tropical rain forests, which it is estimated will have vanished within 30 years. All the factors outlined

in this article appear to indicate that there will be major climatic changes within the next few decades. Solar effects, atmospheric pollution and the lack of the tropical rain forests all combine to suggest that the present warming of the Earth will continue well into the next century. This can result in prolonged droughts over many parts of the globe as well as much melting of the polar ice caps resulting in a’ rise in sea-levels. The net result for the human race can be very serious. two naked eye planets will attract attention during December. Venus, because of its brightness, can be seen in evening twilight. It sets around 11

p.m.j, throughout the month.

Jupiter, in Pisces, will be in a very favourable position for viewing as it will be visible almost all night, setting around 3.40 a.m. on December 1 and at 2 a.m. on December 31. Saturn reaches conjunction with the Sun on December 16 and disappears from the evening sky. Mercury and Mars will both be too close to the Sun to be of interest.

Jupiter will be 4 deg north of the Moon at 11 p.m. on December 1. Exactly 48 hours later on December 3 Venus will be 2 deg south of Neptune. It can be used that evening to locate Neptune. Times quoted are Summer times.