SEP

Study of Solar Eruptive Phenomena: Understand their Early Phases and Determine their Arrival Times to Earth

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 Obiettivo del progetto (Objective)

'Our Sun is a violent star. Frequently the solar atmosphere is the set of gigantic eruptions. These can be either confined (flares) or ejective (Coronal Mass Ejections; CMEs). Flares release huge amounts of energy while CMEs launch several billion tons of mass into the interplanetary space. Sometimes large scale coronal waves are observed in association with the above phenomena. Flares and CMEs represent the major drivers of intense Space Weather Phenomena, a number of phenomena in the Earth magnetic environment and upper atmosphere which can impact technological systems on Earth and in Space as well as humans in space. Currently, our understanding of these important solar phenomena is limited by the very nature of our observations which are taken from one viewpoint. This gives only 2D projections of intrinsically 3D objects. Moreover, single viewpoint observations could be always prone to projection effects which could mislead the analysis. The situation changed dramatically with the launch in late 2006 of the STEREO mission which supplies the first ever 3D views of the Sun and of the Heliosphere. STEREO consists of two identical satellites which observe the Sun and the Heliosphere from two distinct vantage points. Using the unique and novel 3D aspect of the STEREO data we will address (1) the genesis of CMEs, (2) the relationships between flares-CMEs-Coronal Waves and (3) more accurate determinations of CME arrival times to Earth. I'm a member of the US-based team of the main STEREO instrument and an expert in the analysis of STEREO imaging data. The proposed research will allow to decide between competing models/theories on CME initiation and determine what is the exact relationships between flares-CMES-Coronal Waves. It will also supply the basis of a space weather tool for predicting accurate CME arrival times to Earth. The proposal will enhance my chances of getting tenure and will help setting up a research center at my host.'

Introduzione (Teaser)

Occasionally, gigantic bubbles of magnetized gas billow away from the Sun and could trigger geomagnetic storms when they reach Earth. EU-funded scientists looked into magnetic field lines twisting up in our star's atmosphere to find how they are launched from the Sun'.

Descrizione progetto (Article)

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.