1. Helmholtz Centre Potsdam, GFZ, German Research Centre for Geosciences; Potsdam Germany
2. Now at Korea Astronomy and Space Science Institute; Daejeon South Korea
3. Faculty of Science; University of Potsdam; Potsdam Germany
4. NASA Goddard Space Flight Center; Greenbelt Maryland USA
5. Swedish Institute of Space Physics; Uppsala Sweden
6. Center for Space Physics; Boston University; Boston Massachusetts USA