Craig J Pollock, University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK, United States, James Burch, Southwest Research Institute, San Antonio, TX, United States, Barbara L Giles, NASA Goddard Space Flight Center, Greenbelt, MD, United States, William H Matthaeus, University of Delaware, Newark, DE, United States and Christopher T Russell, University of California Los Angeles, Department of Earth Planetary and Space Sciences, Los Angeles, CA, United States