The sun shines through smoke from forest fires near Las Conchas Los Alamos National Laboratory, Los Alamos, New Mexico, June 29, 2011.
A cyclical decline in solar radiation can lead to unusually cold winters in parts of North America and Europe, scientists say, a discovery that could improve long-term forecasts to help countries prepare for snowstorms.
Scientists have long known that the Sun has a cycle of 11 years during which the radiation measured by sunspots on the surface reaches a maximum and then falls. However, pointing a clear link with time became more difficult.
"Our research confirms the observed relationship between solar variability and regional winter weather," lead author Sarah Ineson the UK Met Office, told Reuters in an email. The study was published in the journal Nature Geoscience, said Monday.
His team focused on data from the recent solar minimum in 2008-10, a period of unusually calm for the intense sun and winters in the United States and parts of Europe, and companies stop flights disrupted .
The researchers found that a reduction in the ultraviolet (UV) rays can affect the wind patterns at high altitudes in the northern hemisphere, triggering cold winters.
"Although the levels of UV does not tell us what the weather is doing daily, offering exciting opportunities to improve weather and winter conditions for months and even years to come. These forecasts have an important role in long-term plans," Ineson, climatologist, said.
Ineson and colleagues at Imperial College London and Oxford University have used satellite data that more accurately measures ultraviolet radiation from the sun and found a much greater variation than previously thought .
They found that during the period of low activity, unusually cold air high in the atmosphere over the tropics. This causes a redistribution of heat in the atmosphere, triggering the easterly winds that bring cold and snow storms in Northern Europe and the United States, and warmer climate in Canada and the Mediterranean.
When solar UV radiation is stronger, the opposite occurs.
Ineson team used data from a complex computer model that simulates weather conditions over time. The model successfully reproduces what researchers have observed happening in the upper atmosphere from changes in solar radiation.
Further study is needed, however. A key uncertainty in the experiment is in the satellite data used, since it covers only a few years. "Many questions remain about the accuracy and also applicable to other solar cycles," he said.
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