New discoveries about the interaction between the Sun and the Earth

The process that opens up the Earth's protective magnetic field to the solar wind is the subject of Lars-Goeran Westerberg's research project at Lulea University of Technology in Sweden.

The Sun and the Earth take part in continuous interaction in which the Sun's passing activity and moods dictate the agenda for the day.

One of the clearest proofs of the effect of solar activity is aurora borealis, the northern lights. They appear when particles in the electrically conductive gas (plasma) called the solar wind hit the Earth's atmosphere at an altitude of roughly 100 kilometres above the surface of the Earth.

The fact that our society is also affected by solar activity and solar wind was first observed by seafarers, who noticed that their compass navigation was sometimes unreliable. However, no one could explain then that this was the result of solar wind impacting the magnetic field.

Our Earth is surrounded by a protective package of magnetic field lines called the magnetosphere. The system can be likened to an onion, with the Earth as the centre and the many layers of peels representing different strata in the magnetosphere.

On planets and heavenly bodies that have no magnetic field, such as the moon and Venus, the solar wind particles hit the surface directly. This seriously reduces the chances of there being life there. Most of the solar wind that hits the Earth's magnetosphere goes past without coming into contact with the Earth, which in turn is of crucial importance to the evolution of life that took place and continues to take place.

Be that as it may, even though the magnetosphere constitutes an effective shield against solar wind, plasma can nevertheless penetrate the so-called magnetopause, the outer layer of the magnetosphere. By following the magnetic field lines, the charged particles make their way toward the Earth and the atmosphere, resulting in displays of northern lights, for one thing.

Solar wind can get through the magnetosphere in different ways. The dominant mechanism is called magnetic coupling. This means that the magnetic field stored in the solar wind interacts with the magnetic field of the Earth, with the two fields merging and thereby forming two new field configurations.

This converts magnetic energy in the solar wind into kinetic energy, which makes the plasma accelerate and flow into the Earth's magnetosphere via plasma rays. Magnetic coupling is a central process for converting magnetic energy to kinetic energy. It is involved in all space applications in which two magnetic fields cross each other, and the majority of the research into magnetic coupling targets the physics that underlies the process.

'The aim of my research project is to study the more global effects of magnetic coupling on the ambient plasma. When the process takes place, the structure and behaviour of the solar wind flow is radically altered around the area where the coupling takes place. This is reflected in the dynamics of the solar wind when it ultimately reaches the Earth's atmosphere,' says Lars-Goeran Westerberg.

In 'The Interaction of Solar Wind with the Earth's Magnetic Field,' Lars-Goeran Westerberg has applied newly developed theories together with computer simulations and measurements performed by the Cluster satellites. Cluster is a project involving the European and American space agencies, consisting of four satellites that circle the Earth in formation.

'The fact that there are four of them makes the measurements much more useful than any from a single satellite. With four satellites, it's possible to take measurements simultaneously from different places in an area where coupling is occurring. By studying how magnetic coupling impacts the local area, we gain enhanced knowledge of how the process is controlled by the behaviour of the prevailing solar wind and also what the consequences are in an area several Earth radii from the site where the coupling originates,' explains Lars-Goeran Westerberg.

An understanding of this process is also crucial because it represents a central mechanism for converting energy in space physics and, at the same time, is a direct result of Sun/Earth interaction that impacts the environment of the Earth.

Lars-Goeran Westerberg is involved in the Swedish national research school in space engineering that is coordinated by Lulea University of Technology.