1. NASA/Goddard Institute for Space Studies and Department of Applied Physics and Applied Mathematics, Columbia University, 2880 Broadway, New York, New York 10025, USA
2. Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 350, Campus d’Orsay F-91405, France
3. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487-0324, USA