Amazing aurora

15 April 2013 - This beautiful aurora illuminates the sky over the snow-clad landscape near Tromsø, Norway. These colourful displays are produced when electrically charged particles travelling from the Sun in the solar wind are channelled along Earth's magnetic field lines and strike atoms high in the atmosphere. Collisions with oxygen atoms typically generate green aurora, as seen here. The link between auroras and solar activity has been apparent for centuries, but only with the aid of satellites can scientists begin to decipher the physical mechanisms causing this spectacular phenomenon. ESA's Cluster quartet of satellites fly in formation around Earth, passing through its magnetic environment to explore the connection between the Sun and our home planet. In a new study , Cluster has investigated violent magnetic events called substorms, which result from variations in the stream of charged particles emitted in the solar wind colliding with Earth's magnetic shield - the magnetosphere. During a substorm, the tail of Earth's magnetosphere is compressed and blows powerful streams of high-energy plasma towards the planet at speeds that may reach a few thousand kilometres per second.