Catching a glimpse of the northern lights is apparently the top experience for Britons compiling a “bucket list” of must-do experiences before they die. It’s not surprising, the aurora borealis is a breathtakingly beautiful natural phenomenon, but one that is seldom seen from the British Isles.
Nevertheless, on the morning of March 18, the British press were reporting a brilliant display of the northern lights the previous night. Social media was overflowing with photographic evidence of a display stretching from Scotland to Somerset. But what had brought the lights to the UK that night?
The story begins in the early hours of March 15, when a magnetically active region of the Sun’s surface crackled and erupted, hurling billions of tonnes of the solar atmosphere out into the solar system. Unless you have a keen interest in our local star, you were probably unaware this had happened. It didn’t make the news. But for scientists studying how solar activity affects the space environment surrounding our planet, it was the start of an interesting couple of days.
Within hours, the trajectory of this magnetised outpouring of subatomic particles had been modelled. The cloud, known as a coronal mass ejection (CME), was heading in our direction at about one million miles an hour. It looked like it would deliver a glancing blow to planet Earth some time on March 17, but what would happen if it did? Space weather forecasters the world over set to work.
A likely outcome in this scenario is that the arrival of the CME will trigger a geomagnetic storm. This occurs when the magnetic field within the CME couples with the Earth’s magnetic field, allowing energy and matter to transfer from the CME to the near-Earth space environment.
The most obvious symptom of a geomagnetic storm is more intense aurora borealis due to the increased inflow of electrically-charged particles to the Earth’s upper atmosphere. But less attractive side-effects include disruption to hi-tech navigation and communications systems, and the risk of damage to satellites and power grids. Space weather forecasting, while still in its infancy, is a serious business.
