How Space Weather affects Earth

Magnetic field lines that twist up to generate solar flares occasionally become so warped that they break. Freed, a cloud of charged particles explodes into space as a coronal mass ejection (CME). It could take hours for such a CME to detach itself from the surface of the Sun, but once it does it races away at speeds as great as 1 000 km per second.

Scientists had the chance to study these powerful drivers of space weather using the first ever 3D images of the Sun and the heliosphere. The Solar Terrestrial Relations Observatory (STEREO) traced the flow of energy and matter from the Sun to Earth to reveal the mechanisms behind CME formation. A better understanding of what causes these explosions allowed them to improve theoretical models.

Specifically, within the context of the EU-funded project SEP (Study of solar eruptive phenomena: Understand their early phases and determine their arrival times to Earth), the scientists analysed observations at CME source region. High-resolution, multi-wavelength measurements of the coronal magnetic field from the Solar Dynamics Observatory (SDO) were combined with extreme ultraviolet (EUV) observations from STEREO.

The SEP study revealed the central role that a destabilisation of pre-existing magnetic flux ropes plays in great CME explosions. Significant research work was also devoted to the so-called EUV waves, bringing scientists closer to resolving the question of their nature. These brightness fronts propagate over the Sun's surface at speeds that reach hundreds of kilometres per second in the aftermath of CMEs and flares.

It takes light associated with a flare eight minutes to reach the terrestrial magnetosphere. But CMEs may take up to five days to travel the distance to our planet. The solar wind acts on these clouds of hot plasma like a current going against a boat, slowing down the faster ones. STEREO scientists found that shocks formed around the clouds need to be considered to more accurately 'predict' the arrival times.

From the constant stream of electrically charged particles in the form of solar wind to the unpredictable CMEs, Earth feels the impact of our stellar companion that is not limited to light and heat. The new view of the Sun offered by the STEREO and SDO missions aided SEP scientists to better understand solar physics and thereby improve space weather forecasting.