Space weather starts at the sun. It begins with an eruption such as a huge burst of light and radiation called a solar flare or a gigantic cloud of solar material called a coronal mass ejection (CME). But the effects of those eruptions happen at Earth, or at least near-Earth space. Scientists monitor several kinds of space "weather" events geomagnetic storms, solar radiation storms, and radio blackouts all caused by these immense explosions on the sun.
One of the most common forms of space weather, a geomagnetic storm refers to any time Earth's magnetic environment, the magnetosphere, undergoes sudden and repeated change. This is a time when magnetic fields continually re-align and energy dances quickly from one area to another.
Geomagnetic storms occur when certain types of CMEs connect up with the outside of the magnetosphere for an extended period of time. The solar material in a CME travels with its own set of magnetic fields. If the fields point northward, they align with the magnetosphere's own fields and the energy and particles simply slide around Earth, causing little change. But if the magnetic fields point southward, in the opposite direction of Earth's fields, the effects can be dramatic. The sun's magnetic fields peel back the outermost layers of Earth's fields changing the whole shape of the magnetosphere. This is the initial phase of a geomagnetic storm.
The next phase, the main phase, can last hours to days, as charged particles sweeping into the magnetosphere accumulate more energy and more speed. These particles penetrate closer and closer to the planet. During this phase viewers on Earth may see bright aurora at lower latitudes than usual. The increase and lower altitude of radiation can also damage satellites traveling around Earth.