1. Department of Mathematics and Statistics, University of Reading, Reading RG6 6AX, United Kingdom
2. Centre for the Mathematics of Planet Earth, University of Reading, Reading RG6 6AX, United Kingdom
3. Department of Earth and Planetary Sciences, Weizmann Institute, Rehovot 76100, Israel
4. Department of Atmospheric and Oceanic Sciences, University of California at Los Angeles, Los Angeles, California 90095, USA
5. Geosciences Department and Laboratoire de Météorologie Dynamique (CNRS and IPSL), Ecole Normale Supérieure and PSL University, Paris 75231, France
6. Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod 603950, Russia