The solar wind is the flow of gas and ionized particles resulting from the electromagnetic disturbances of the solar atmosphere, and emitted by the Sun into the interplanetary plasma. Magnetic arcs constantly intertwine and collide, creating gigantic explosions with the equivalent force of billions of atomic bombs.

The first sign of the violent encounter between the supersonic solar wind (travelling at about 400 km/s) and the Earth’s magnetic field is the bow shock that travels along the surface of the globe facing the Sun. This shock is comparable to the “sonic boom” produced by supersonic aircraft when they break through the sound barrier.

The strength of the Earth’s magnetic field protects the planet from these solar tornados and confines them to a buffer zone called the magnetosphere. Like an island in the stream, the magnetosphere deflects the flow of solar particles around the Earth. This buffer zone itself is significantly shaped by the pressure of the solar wind. Towards the Sun, it is flattened (daylight side), while it stretches away from the globe on the opposite hemisphere (night side).

Its outer boundary is referred to as the magnetopause. In particularly violent solar wind conditions, it can be pushed to within 35,000 km of the Earth’s surface. Closer to the Earth, the magnetosphere is bounded by the ionosphere, a partially ionized layer of gases from the atmosphere.

^{This diagram shows how the solar wind interacts with the Earth’s magnetosphere. Solar wind particles can leak into the magnetosphere at high-latitude regions known as the polar cusps.
Source : CNES}

Since 2000, Cluster has been producing real-time maps of certain key regions of the terrestrial magnetosphere. These include different zones whose composition and interactions are poorly understood. In spite of the results already obtained, scientists have not yet found an explanation for the slow evaporation of the solar wind within the magnetosphere.

The polar regions seem to be particularly vulnerable to solar tornados.