1. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095-1567, USA
2. Department of Earth and Space Sciences, UCLA, USA
3. Laboratoire de Physique de la Matière Condensée, CNRS UMR 6622, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice, France
4. Department of Atmospheric Sciences, UCLA, USA