Radiation from atomic bomb tests during the Cold War era caused changes in the atmosphere that led to increased rainfall during that time, scientists have found.
Even though the detonations carried out in the 1950s and 1960s occurred in remote areas, the scientists said these tests resulted in changes to rainfall patterns in certain parts of the UK, despite being thousands of miles away from those sites.
A team of researchers from the universities of Reading, Bath and Bristol, looked at historic rainfall records between 1962-64 from research stations in London and Scotland.
They found clouds were “visibly thicker” and there was “24 per cent more rain on average” on the days when there was more radioactivity in the Shetland Isles.
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Giles Harrison, a professor of atmospheric physics at the University of Reading and lead author on the study, said: “By studying the radioactivity released from Cold War weapons tests, scientists at the time learnt about atmospheric circulation patterns. We have now reused this data to examine the effect on rainfall.
“The politically charged atmosphere of the Cold War led to a nuclear arms race and worldwide anxiety. Decades later, that global cloud has yielded a silver lining, in giving us a unique way to study how electric charge affects rain.”
Radioactivity is the emission of radiation originating from a nuclear reaction. It can also arise from the spontaneous decay of unstable atomic nuclei. The phenomenon can lead to an increase in air conductivity in the atmosphere through a process known as ionisation, releasing electric charge.
Scientists have long suspected electric charge in the air can affect the way water droplets combine in the clouds which, in turn, can influence rainfall. However, these changes have been difficult to observe from modern-day weather data.
So the team turned to the radioactive legacy of the Cold War nuclear arms race and combined bomb test data with historical weather records gathered from stations at Kew near London and Lerwick in the Shetland Isles.
Although thousands of miles away from the detonation sites in the US and around the world, rainfall patterns in the Shetlands showed “significant changes” during the test period as radioactive pollution spread widely throughout the atmosphere.
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The researchers wrote in their paper: “Significant changes occurred in daily rainfall distribution in the Shetland Islands, away from pollution. Daily rainfall changed by 24 per cent, and local cloud optically thickened, within the nuclear weapons test period.
“This supports expectations of electrically induced microphysical changes in liquid water clouds from additional ionisation.”
Scientists believe learning more about how electric charge affects rainfall will improve understanding of the weather processes and could help relieve droughts or prevent floods.
The findings are published in the journal Physical Review Letters.
Reader Q&A: Why do the British talk about the weather so much?
Asked by: Jules Weaver, via email
Brits really do like to talk about the weather: over 90 per cent admit to having done so in the previous six hours. But there’s always plenty to talk about, because our location means our weather is affected by six different air masses.
Southwesterly winds expose us to warm, moist tropical air from the Atlantic (tropical maritime), bringing rain and mild conditions, while Arctic air masses from the north (Arctic maritime) and northwest (polar maritime) can deliver cold, wet weather and potential blizzards in winter. Another air mass from the Arctic, travelling via the North Atlantic (returning polar maritime), delivers mild, cloudy weather.
Meanwhile, our summers can sizzle under the influence of hot, dry air from North Africa (tropical continental) or eastern air flows from the continent (polar continental) – which can also cause winter temperatures to plunge. Small wonder forecasting is so hard!