Disturbances in the Solar Wind

(Image courtesy of the National Aeronautics and Space Administration). About the Image: Artist's conception of an impending collision between a coronal mass ejection and the Earth's magnetosphere.

Hours to Days Later...

Disturbances in the solar wind arrive at the Earth within hours to days after a violent event on the Sun. The largest space weather disturbances at Earth are produced by coronal mass ejections and fast solar wind streams emanating from coronal holes. Coronal holes are the main source of recurrent solar activity.

Coronal mass ejections (CMEs) violently expell billions of tons of solar material into interplanetary space. They normally drive shocks ahead of them as they plow into the slower-moving solar wind streams. Vast quantities of high speed particles are born in these shock structures and speed ahead of the coronal mass ejection to impact the Earth before the CME itself makes an appearance. It is now believed that a large fraction of the solar energetic particles arriving at Earth were produced in these shocks rather than at flare sites on the Sun.

CMEs are difficult to detect and, in fact, were not observed until coronographs were build and flow in space. Many of the CMEs that are blown toward the Earth never actually directly hit us. They pass us by.