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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/npg-2019-53
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/npg-2019-53
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: review article 15 Oct 2019

Submitted as: review article | 15 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Nonlinear Processes in Geophysics (NPG).

Baroclinic and barotropic instabilities in planetary atmospheres - energetics, equilibration and adjustment

Peter Read1, Neil Lewis1, Daniel Kennedy1, Hélène Scolan2,1, Fachreddin Tabataba-Vakili3,1, Yixiong Wang1, Susie Wright1, and Roland Young4,1 Peter Read et al.
  • 1Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
  • 2Laboratoire de Mécanique des Fluides et d’Acoustique, Université Lyon, France
  • 3Jet Propulsion Laboratory, Pasadena, California, USA
  • 4Department of Physics & National Space Science and Technology Center, UAE University, Al Ain, United Arab Emirates

Abstract. Baroclinic and barotropic instabilities, are well known as the mechanisms responsible for the production of the dominant energy-containing eddies in the atmospheres of the Earth and several other planets, as well as the Earth's oceans. Here we consider insights provided by both linear and nonlinear 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 planets of our Solar System. The equilibration of such instabilities is also of great importance in understanding the structure and energetics of the observable circulation of atmospheres and oceans. Various ideas have been proposed concerning the ways in which baroclinic and barotropic instabilities grow to large amplitude and saturate, whilst also modifying their background flow and environment. This remains an area that continues to challenge theoreticians and observers, though some progress has been made. The notion that such instabilities may act under some conditions to adjust the background flow towards a critical state is explored here in the context of both laboratory systems and planetary atmospheres. Evidence for such adjustment processes is found relating to baroclinic instabilities under a range of conditions where the efficiency of eddy and zonal mean heat transport may mutually compensate to maintain a nearly invariant thermal structure in the zonal mean. In other systems, barotropic instabilities may efficiently mix potential vorticity to result in a flow configuration that is found to approach a marginally unstable state with respect to Arnol'd's second stability theorem. We discuss the implications of these findings and identify some outstanding open questions.

Peter Read et al.
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Data sets

Simulating Jupiter’s weather layer: Accompanying data for Parts I and II [data-set]. R. M. B. Young, P. L. Read, and Y. Wang https://doi.org/10.5287/bodleian:PyYbbxpk2

Peter Read et al.
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Short summary
Baroclinic and barotropic instabilities are well known as the processes responsible for the production of the most important energy-containing eddies in the atmospheres and oceans of the Earth and other planets. Linear and nonlinear instability theories provide insights into when such instabilities may occur, grow to large amplitude and saturate, with examples from the laboratory, simplified numerical models and planetary atmospheres. We conclude with a number of open issues for future research.
Baroclinic and barotropic instabilities are well known as the processes responsible for the...
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