Northern lights lit up the sky all the way down to Southern Finland during Tuesday night and Wednesday morning. In terms of the large number and energy values of high-energy particles, this magnetic cloud can be considered the largest in ten years.
Image: Mikko Oksanen
At approximately 6:40 am on Tuesday morning, a geomagnetic storm began in the Sun, gaining moderate strength. The storm was caused by a coronal mass ejection from the Sun on Sunday, which reached the Earth earlier than predicted. The Finnish Meteorological Institute's magnetometers in Nurmijärvi and elsewhere in Finland already detected significant changes in the Earth's magnetic field in the early evening.
There is an active area on the surface of the Sun, which has produced a great deal of small and medium-sized flares during the past few days.
In terms of the large number and energy values of high-energy particles in the cloud, this magnetic cloud can be considered the largest in ten years. According to statistics, the number of nights of northern lights declines sharply from the north to the south. During the dark time of the year in Northern Lapland, three out of four nights are illuminated by northern lights. In Oulu, the frequency is approximately one in three nights, whereas in Helsinki it is approximately once a month. These are statistical averages, but the number of nights of northern lights varies from one year to the next.
In the long term, the amount of northern lights is determined by sunspots, and the 11-year rhythm of their appearance also affects the number of nights of northern lights. The number of sunspots was at its lowest at the end of 2008, after which their occurrence has increased.
Fluctuations in the Sun's activity affect the top layers of the Earth's atmosphere the most, from an altitude of 100 kilometres upwards. Particles erupting from the Sun ignite northern lights in the atmosphere and also cause other space weather disruptions. As they collide with the top layers of the atmosphere, particle torrents accelerated by reconnection may also disrupt radio communication and damage satellites. The last incidence of such considerable damage was in 2003. A solar storm may damage nearby satellites or disrupt communication on HF radio waves, but this week's storm did not cause damage to the electrical grid or any other terrestrial system.
Head of unit Minna Palmroth, FMI, tel. +358 40 5311 745, firstname.lastname@example.org
Researcher Tiera Laitinen, FMI, tel. +358 50 380 3279, email@example.com