Nonlin. Processes Geophys., 27, 147–173, 2020 https://doi.org/10.5194/npg-27-147-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Baroclinic and barotropic instabilities in planetary atmospheres: energetics, equilibration and adjustment Peter Read1,z, Daniel Kennedy2,1, Neil Lewis1, Hélène Scolan3,1, Fachreddin Tabataba-Vakili4,1, Yixiong Wang1, Susie Wright1, and Roland Young5,1 1Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK 2Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 3Laboratoire de Mécanique des Fluides et d’Acoustique, Université de Lyon, France 4Jet Propulsion Laboratory, Pasadena, California, USA 5Department of Physics & National Space Science and Technology Center, United Arab Emirates University, Al Ain, United Arab Emirates zInvited contribution by Peter Read, recipient of the EGU Lewis Fry Richardson Medal 2016. Correspondence: Peter Read (
[email protected]) Received: 3 October 2019 – Discussion started: 15 October 2019 Revised: 14 February 2020 – Accepted: 26 February 2020 – Published: 3 April 2020 Abstract. Baroclinic and barotropic instabilities are well stabilities may efficiently mix potential vorticity to result in known as the mechanisms responsible for the production of a flow configuration that is found to approach a marginally the dominant energy-containing eddies in the atmospheres of unstable state with respect to Arnol’d’s second stability theo- Earth and several other planets, as well as Earth’s oceans. rem. We discuss the implications of these findings and iden- Here we consider insights provided by both linear and non- tify some outstanding open questions. linear instability theories into the conditions under which such instabilities may occur, with reference to forced and dissipative flows obtainable in the laboratory, in simplified numerical atmospheric circulation models and in the plan- 1 Introduction ets of our solar system.