1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2. Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, Alabama 35805, USA
3. Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia 22030, USA
4. Nordita, KTH Royal Institute of Technology and Stockholm University, 10691 Stockholm, Sweden