[1] BACV Solut, Oak Ridge, TN 37830 USA
[2] Univ Alaska, Dept Phys, Coll Nat Sci & Math, Fairbanks, AK 99775 USA
[3] Univ Alaska, Inst Geophys, Fairbanks, AK 99775 USA
[4] Univ Carlos III Madrid, Dept Phys, Madrid, Spain
[5] Iowa State Univ, ECpE Dept, Ames, IA 50011 USA