Ian Barnett explores the elusive northern lights

The strongest geomagnetic storm for seven years struck Earth this January, leading to spectacular shows of the aurora borealis, or northern lights, which were visible over vast regions of northern Britain. These storms are caused by coronal mass ejections from the surface of the sun releasing a cloud of billions of ions and electrons into space. These clouds of particles generally take a couple of days to reach Earth, where they interact with the magnetosphere, causing a geomagnetic storm.

The sun goes through a cycle of solar activity, with intense periods of magnetic activity occurring every eleven years. This most recent period of activity shows that the sun is approaching a maximum in its magnetic activity. The solar maximum is forecasted to occur in early 2013, when these coronal mass ejections will be at their most frequent: around five per day will come hurtling towards the Earth at almost a billion miles per hour. During this time more UV radiation will reach the surface of Earth and the northern lights will be visible further south; at the last solar maximum they were visible as far south as Spain.

In the northern hemisphere the aurora borealis (or aurora australis in the southern hemisphere) occur when gases in the atmosphere are bombarded with solar radiation. When oxygen or nitrogen molecules in the air absorb energy from radiation, they become ‘excited’. This is not a stable situation, so the energy is lost again, in the form of light: blue or red light from nitrogen and green or dark-red light from oxygen. This emission of light forms the aurorae. Charged particles are funnelled into the poles by the Earth’s magnetic field, hence this phenomenon can only be observed close to the extreme north or south of the planet.

When a geomagnetic storm hits the Earth, charged particles (including protons and electrons) cause its magnetic field to fluctuate. This can create problems with radio systems near the north pole, as well as for super-accurate GPS. In January, several flights were redirected from their usual routes over the north pole due to fears over communication problems and that passengers would have been exposed to excess radiation. Power distribution can also be disrupted during a geomagnetic storm, with large swathes of North America having been plunged into darkness in the past. However satellites are most likely to sustain damage from charged particles, and can even fall out of orbit during a geomagnetic storm.

While the geomagnetic storms which produce the northern lights trigger problems for some companies, others profit from them. In extreme northern countries, such as Norway, Sweden, Finland and Iceland, the extreme natural beauty of the northern lights can be observed almost daily. Holidays are available in these countries, which are tailored to provide tourists with a glimpse of the aurora borealis, combined with husky racing or a luxurious stay at Sweden’s Icehotel. However, not even the amazing Icehotel could surpass the multi-coloured magnificence of the awe-inspiring northern lights.

 

Ian Barnett

 

Image by Varjisakka