Illustration of a CME particle cloud blasted from the sun impacting Earth and creating aurora (in actual photo of aurora as taken by an astronaut on the space station). Courtesy of SOHO. Original image can be found at http://soho.nascom.nasa.gov/gallery/images/aurora01.html
Between May 10-12, 1999, the solar wind nearly vanished, causing Earth's magnetosphere to expand in volume by over 100 times!