A link between decadal solar variability and winter climate in the UK, northern Europe and parts of America has been demonstrated by scientists, according to a new study.
The findings are published in Nature Geoscience. The study was carried out by researchers in the Met Office, Imperial College London and the University of Oxford.
The study helps explain why the UK has been gripped by such cold winters over the last few years: the sun is just emerging from a so-called solar minimum, when solar activity is at its lowest. Our research establishes the link between the solar cycle and winter climate as more than just coincidence, says Dr. Adam Scaife from the UK's Met Office, one of the study's authors.
New satellite measurements from NASA's Solar Radiation and Climate Experiment (SORCE) have revealed that differences in the UV light reaching the Earth during the 11-year solar cycle are larger than previously thought. The satellite, launched in 2003, is the first ever to measure solar radiation across the entire UV spectrum. 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.
During years of low UV activity unusually cold air forms over the tropics in the stratosphere, about 50 km up. This is balanced by a more easterly flow of air over the midlatitudes – a pattern which then burrows its way down to the surface, bringing easterly winds and cold winters to northern Europe. 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.
While UV levels won't tell us what the day-to-day weather will do, they provide the exciting prospect of improved forecasts for winter conditions for months and even years ahead. These forecasts play an important role in long-term contingency planning, Ineson, a climate scientist, said.
At the same time the research team has noted that more study was needed since a main limitation in the experiment lay in the satellite data used, because it spans only a few years.