The mysterious “eclipse winds” — the sudden change in wind direction and speed that occurs when the moon blocks out the sun — have long baffled scientists. Now, in two separate studies published in the Philosophical Transactions of the Royal Society A, researchers have put forward an explanation for this mysterious phenomenon.
In order to study the effects of a solar eclipse on winds, researchers from the University of Reading sought the help of 4,500 citizen scientists around the U.K., who took part in the National Eclipse Weather Experiment during the partial eclipse in March last year. After analyzing the data collected, they found that not only did wind speeds drop by up to 4 knots (4.6 miles per hour) in parts of the U.K., temperatures also dropped by roughly 1 degree Celsius (1.8 degrees Fahrenheit) in parts of the country.
The researchers concluded that the wind change was caused by variations in the "boundary layer" — the area of air that separates high-level winds from those at the ground.
“There have been lots of theories about the eclipse wind over the years, but we think this is the most compelling explanation yet,” co-author Giles Harrison from the University of Reading said in a statement. “As the sun disappears behind the moon the ground suddenly cools, just like at sunset. This means warm air stops rising from the ground, causing a drop in wind speed and a shift in its direction, as the slowing of the air by the Earth’s surface changes.”
A second study of the event by researchers at the University of Sheffield also corroborated the observations. It found that during the eclipse, the average temperature dropped by 0.83 degree Celsius (1.5 degrees Fahrenheit), while the wind speed fell by 9 percent on average during the first half of the eclipse.
“A substantial solar eclipse, as occurred over Northwest Europe on 20 March 2015, provides an excellent opportunity for natural meteorological experiments, such as the ones reported here,” lead author Edward Hanna from University of Sheffield said in a statement. “However, there will not be another solar eclipse of comparable magnitude in the UK until 2026, so it is vital to take advantage of these relatively rare chances.”
Researchers in the U.S., though, will get another opportunity to verify the findings during next year’s total solar eclipse — an event that has already generated widespread interest.