The Sun, on the whole, is a pretty neat thing to have around. After all, it’s responsible for sustaining life on Earth and making our planet hospitable. Sometimes, though, the Sun has altogether more nefarious effects. Case in point: When high-speed solar flares begin to whip up, their effect on Earth’s magnetosphere leads to an increase in lightning strikes, according to researchers at the University of Reading.

“Cosmic rays, tiny particles from across the Universe accelerated to close to the speed of light by exploding stars, have been thought to play a part in thundery weather down on Earth, but our work provides new evidence that similar, if lower energy, particles created by our own Sun also affect lightning,” said Dr. Chris Scott, the study’s lead author.

At least in Europe, the researchers found that the lightning effect can last for up to 40 days after solar winds bombard Earth. In their study, they found that there was an average of 422 lightning strikes across the UK in the following 40 days, compared to an average of 321 lightning strikes in the 40 days prior the arrival of the solar wind. The rate of lightning strikes peaked between 12 and 18 days after the arrival of the solar wind.

The findings shed new light on the effect of outer space on Earthly weather. Namely, it’s not just about cosmic rays anymore. Solar winds consist of a constant stream of energetic particles (mostly electrons and protons) propelled from the Sun’s atmosphere at incredible speeds. The streams of particles can vary in density, temperature and speed and sweep past Earth every 27 days or so, in line with the time it takes the Sun to make one complete rotation relative to Earth.

The fastest winds aren’t the problem, nor are the slow ones. In both instances, Earth’s magnetosphere does a good job of deflecting them and keeping them out of the atmosphere. The effects are most prominent when fast and slow winds collide, creating an enhancement and acceleration. In those cases, the particles are sometimes able to penetrate down to the cloud level, creating the observed effect on Earth’s weather.

Astute weather forecasters should take note of these findings – since solar streams rotate with the Sun, they sweep Earth at regular intervals. Though their effects might not be exactly predictable, it would make sense to allow for the chance of weather abnormalities during these periods.