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Sunspot cycles a key to drought prediction

July 05, 2006

sunspot.thumb.jpgNew discoveries linking rainfall patterns on Earth with the periodic twisting of the magnetic field within the Sun could provide a powerful tool in the prediction of drought.

Associate Professor Robert Baker from The University of New England outlined the results of his research yesterday at the Regional Congress of the International Geographical Union in Brisbane. He said his model could be used – in conjunction with other indicators such as the Southern Oscillation Index (SOI) – as a significant decision-making tool in agriculture and natural resource management. The paper he presented to the Congress was titled “Predicting drought in south-east Australia using solar cycles”.

Changing patterns of dark spots on the surface of the Sun are a visible indication of changes in the magnetic forces within. Dr Baker has correlated these sunspot patterns – which have been recorded since 1745 – with historical rainfall records in south-eastern Australia. The correlation shows that periods of high rainfall are associated with periods of increased sunspot activity.

The most well-known sunspot cycle is the 11-year cycle, which comprises alternating five-and-a-half-year periods of relatively high and low sunspot activity. Once every 11 years, too, there is a sudden reversal of the polarity of the Sun’s magnetic field, so that there is a complete magnetic cycle (the “Hale cycle” or “double sunspot cycle”) every 22 years. The 11-year sunspot cycle, however, is part of a more complex pattern that includes cycles of 500 and 1,500 years. (Some of the climatic effects of these longer cycles can be deduced from ice-core data and historical records.)

Dr Baker’s model, which incorporates all these factors, indicates that south-eastern Australia – much of it currently drought-affected – could be heading for a period of even lower rainfall. This is because of an imminent coincidence of several of the solar cycles. The sunspot minimum in the 11-year cycle due in August this year coincides with that phase of the Hale cycle in which the magnetic field lines emerge from the Sun’s south pole. Dr Baker said historical records showed that this coincidence was associated with reduced sunspot minima, and more severe droughts in eastern Australia. On top of this coincidence – and contributing to the potential for drought conditions – the Sun is entering a longer, 500-year period of reduced sunspot activity.

Dr Baker explained that the power of his predictive model lay in the fact that solar activity as a whole occurred in regular cycles. “In this respect,” he said, “the Sun is like a musical instrument – vibrating in a complex manner, but with all the components (like the ‘harmonics’ of music) related to a vast ‘fundamental’ vibration by simple numbers.” As he told the Congress: “This predictive potential of the sunspot cycle is available because much of solar behaviour is quasi-periodic, governed by the operation of the magnetic fields generated by a peculiar ‘dynamo’ in the Sun.”

A special feature of the Congress, which is continuing till Friday at Queensland University of Technology, is discussion on arid zones – particularly in Australia, New Zealand, South-east Asia, and the south-west Pacific.

PHOTO: NASA.


Media contact: Associate Professor Robert Baker, UNE, on (02) 6773 2884.

Posted by Jim Scanlan at July 5, 2006 04:20 PM