Space weather challenges of the polar cap ionosphere Jøran Moen, Kjellmar Oksavik, Lucilla Alfonsi, Yvonne Daabakk, Vineenzo Romano and Luca Spogli J. Space Weather Space Clim., 3 (2013) A02 Published online: 24 January 2013 DOI: 10.1051/swsc/2013025