1. Department of Earth, Atmospheric, and Planetary Sciences; Purdue University; West Lafayette Indiana USA
2. Department of Terrestrial Magnetism; Carnegie Institution of Washington; NW Washington DC USA
3. The Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
4. Lamont-Doherty Earth Observatory; Columbia University; Palisades New York USA
5. Department of Earth, Atmospheric, and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA