The solar wind is responsible for the anti-sunward tails of comets and the shape of the magnetospheres (magnetic fields) around the planets, including our own planet Earth. The Earth has a relatively strong magnetic field and its magnetosphere forms a bubble around our planet that deflects the solar wind like water is deflected around the bow of a ship. The boundary between the magnetosphere and the solar wind is called the magnetopause. However, even though the magnetosphere shields the Earth from much of the solar wind, some of the solar plasma does penetrate the magnetopause and reach the planet via the magnetosphere. This is because of what is referred to as the interplanetary magnetic field’s Bz component.

The interplanetary magnetic field (IMF) has three directional components, two of which (Bx and By) are oriented parallel to the ecliptic, whilst the third component (Bz) is perpendicular to the ecliptic.

The Earth’s magnetic field points north at the magnetopause; but the IMF’s Bz, which is aligned with the Earth’s magnetic axis, can point either north or south, depending on the magnetic property of the solar wind at that moment.

If the IMF points south (i.e. a southward Bz) then it can partially cancel the Earth’s magnetic field at the point of contact, thereby opening a door through which magnetic and particle energy from the solar wind can reach the Earth’s atmosphere. In this way powerful geomagnetic activity such as geomagnetic storms are created, which can affect not only auroral activity but also radio communications, atmospheric drag on satellites, and power grids on Earth. The full effects of this plasma baptism of the Earth are not yet known to modern science.

© Peter Dawkins