1. The Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
2. Now at Solar-Terrestrial Environment Laboratory; Nagoya University; Nagoya Japan
3. Cooperative Institute for Research in Environmental Sciences; University of Colorado Boulder; Boulder Colorado USA
4. National Centers for Environmental Information; National Oceanic and Atmospheric Administration; Boulder Colorado USA
5. Institute of Geophysics and Planetary Physics; University of California; Los Angeles California USA