Met Office in the Media: Solar variability helps explain past cold winters

10 10 2011

There has been widespread coverage across the media today on research from the Met Office that has shed new light on a link between decadal solar variability and winter climate in the UK, northern Europe and parts of America.

The study, carried out by the Met Office with  Imperial College London and the University of Oxford, shows that low UV output from the sun can contribute to cold winters over parts of the northern hemisphere, such as recently seen in the UK. Years of higher UV have the opposite effect.

Some media coverage has suggested that this new research indicates that we are heading toward another cold winter this year or even a mini ice age. This is not the case as this research provides no information regarding an outlook for the coming winter months. In fact, levels of UV are now rising as part of the 11-year solar cycle.

Also, this research says nothing about entering a new ice age. Even if we did head in to low UV activity it is thought that this would not offset the temperature increases we have observed due to climate change.

Adam Scaife, one of the scientists involved in the research, said that new data from sensitive satellite equipment shows UV variability over the 11-year solar cycle may be much larger than previously thought and has been key to the research.

By using this information in the Met Office’s climate model, researchers were able to reproduce the effects of solar variability apparent in observed climate records.

In years of low UV activity unusually cold air forms over the tropics in the stratosphere, about 50km up. This is balanced by more easterly flow of air over the mid latitudes – a pattern which then ‘burrows’ its way down to the surface, bringing easterly winds and cold winters to northern Europe.

Low UV output from the sun leads to easterly winds and cold conditions in Europe and the US

Low UV output from the sun leads to easterly winds and cold conditions in Europe and the US

When solar UV output is higher than usual, the opposite occurs and there are strong westerlies which bring warm air and hence milder winters to Europe.

The Sun has recently been in a quiet phase of its regular 11-year cycle, which coincided with three years in which the UK, along with other places in northern Europe and parts of the US, experienced cold conditions unusual in the recent record. But unusually warm weather was felt both further south, around the Mediterranean Sea, and further north in Canada and Greenland.

“The key point is that this effect is a change in the circulation, moving air from one place to another, which is why some places get cold and others get warm. It’s a jigsaw puzzle, and when you average it up over the globe, there is no effect on global temperatures,” Adam Scaife told BBC News.

While UV levels won’t tell us what the day-to-day weather will do, they could be important in helping us develop improved forecasts for winter conditions for months or even a few years ahead and this is now being investigated.

You can read more about this research on the Met Office Research web pages


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