Sun's impact on rainfall 'predictable'
The sun's magnetic fields may have an impact on weather conditions such as El Niño, and could be an effective tool in long-term rainfall predictions, an Australian geographer says.
In the latest issue of Geographical Research, Professor Robert Baker of the University of New England says there is a relationship between the sun's magnetic cycles and fluctuations in the Southern Oscillation Index (SOI).
The SOI is calculated from changes in the air pressure difference between Tahiti and Darwin.
Sustained negative values in the SOI indicate an El Niño episode, which are associated with drought and warmer weather in eastern and northern Australia.
Baker's study suggests that during periods of increased activity in the sun's magnetic field, "the more likely there will be positive SOI fluctuations".
A positive SOI means there is a higher chance for increased rainfall.
He suggests that increased activity in the sun's magnetic field impacts on the earth's magnetic field "opening the door" for solar winds to change atmospheric conditions.
Baker bases his analysis by matching solar cycles such as the 11-year Schwab cycle, the 22-year Hale cycle and the 88-year Gleissberg cycle with recorded SOI values.
"If solar cycles continue to show relational values to climate patterns there is potential for more accurate forecasting through to 2010 and possibly beyond," he says.
Baker says the SOI-solar relationship has been investigated recently due to increasing interest in the relationship between the sun's cycles and climate.
"Particular phases will have similar impacts, regularly, on atmospheric processes," he writes.
However Baker admits there is a "lot of research required to disentangle what appears to be a complex non-linear system".
"The aim here is to look at the overall pattern to ascertain whether there is scope to undertake more rigorous testing of the apparent relationships," he writes.
Dr Helen McGregor, at the University of Wollongong's Earth and Environmental Sciences, says it is an oversimplification to link solar cycles to rainfall in a specific location.
"For example the rainfall maps grouped with various solar phases in the Baker paper show differing spatial patterns of reduced rainfall for each year considered. That is the solar phase does not appear to give rise to a consistent pattern of rainfall," she says.
"This would limit the predictability of the method," she says, adding that the paper does not give a clear physical mechanism to explain how the solar variability is propagated through the climate system to influence rainfall.
McGregor says the paper only compares SOI data from the 130 years since 1876.
However, the 88-year Gleissberg cycle, Baker refers to would have only been realised 1.5 times in that period.
"Which is nowhere near enough to characterise its influence on climate," she says.
McGregor says climate skeptics should not jump on Baker's work to dismiss human-induced global warming.
"It is clear that global temperatures are rising. This temperature rise cannot be replicated with natural forces, for example solar and volcanic alone. CO2 emissions are part of the picture," she says.
"The earth's climate is extremely complicated and we must continue to work to understand all the factors controlling climate at a regional level."