They occur when the Sun gets a little rowdy, in the form of CMEs and solar winds, causing disruptions to Earth's magnetic field and upper atmosphere.
If the CME is oriented at Earth, the collision of the solar ejecta with Earth's magnetic field can cause a geomagnetic storm – also known as a solar storm.
A coronal hole fast wind may also affect the Earth on 27 and 28 September, although any effects from this wind are considered uncertain.
Any charged particles that collide with Earth's magnetic field are sent whizzing along the magnetic field lines towards the poles, where they rain down on Earth's upper atmosphere and collide with atmospheric molecules.During solar maximum, the solar magnetic field – which controls sunspots (temporary regions of strong magnetic fields), solar flares, and coronal mass ejections – is at its strongest, and so too is solar activity.