Historical Solar
Flare
On 1 September 1859, the Sun expelled huge quantities of high-energy protons in a 'superflare'. The event was seen on Earth by an observer who noticed a white spot on the Sun suddenly brighten for about five minutes.
When the magnetic storm struck Earth, fires started in telegraph stations due to electrical arcing in the telegraph wires. The northern lights, or aurorae borealis, were reportedly seen as far south as Florida in the US.
This flare released 6.5 times more energy than the largest solar flare of the satellite era, which occurred in 1989. That flare was strong enough to cause a power blackout in Quebec, Canada.
Now, scientists have calculated the ozone depletion from the 1859 solar flare for the first time by studying chemical deposits in Greenland ice cores.
Acid rain
The deposits were laid down after the flare set off a series of reactions in Earth's atmosphere. For roughly two days after the flare, high-energy protons entered the atmosphere through the polar regions, channelled there by the planet's magnetic field lines.
The protons ionised nitrogen and oxygen molecules in the atmosphere, which then formed nitrogen oxides. The nitrogen oxides in turn reacted with ozone – a molecule made up of three oxygen atoms, breaking it into oxygen molecules and atomic oxygen.
This breakdown caused global atmospheric ozone levels to drop by 5%. In comparison, chlorofluorocarbons (CFCs) and other chemicals have depleted the levels by about 3% in recent years, says team member Adrian Melott, a physicist at the University of Kansas in Lawrence, US.
However, unlike CFCs and other ozone-depleting chemicals, which can persist in the atmosphere for some time, the flare-induced ozone thinning probably lasted for just four years, the researchers report. That is because the nitrogen oxides that cause the depletion eventually rain down with water or ice. Indeed, it was this acid rain that was eventually recorded in the ice cores.