On the energetics of a two-layer baroclinic flow

Abstract

The formation, evolution and co-existence of jets and vortices in turbulent planetary atmospheres is examined using a two-layer quasi-geostrophic β-channel shallow water model. The study in particular focuses on the vertical structure of jets. Following Panetta & Held (1988), a vertical shear arising from latitudinal heating variations is imposed on the flow and maintained by thermal damping. Idealised convection between the upper and lower layers is implemented by adding cyclonic/anti-cyclonic pairs, called hetons, to the flow, though the qualitative flow evolution is evidently not sensitive to this or other small-scale stochastic forcing. A very wide range of simulations have been conducted. A characteristic simulation which exhibits alternation between two different phases, quiescent and turbulent, is examined in detail. We study the energy transfers between different components and modes, and find the classical picture of barotropic/baroclinic energy transfers to be too simplistic. We also discuss the dependence on thermal damping and on the imposed vertical shear. Both have a strong influence on the flow evolution. Thermal damping is a major factor affecting the stability of the flow while vertical shear controls the number of jets in the domain, qualitatively through the Rhines scale L Rh = U/β.

Multistability and Rare Spontaneous Transitions in Barotropic β-Plane Turbulence

“…We will consider forced-dissipative barotropic turbulence on a beta plane, in which small-scale turbulence self-organizes into large-scale coherent structures, with upscale fluxes of energy. Although such a barotropic description of Jovian troposphere has long been used for theoretical studies (Galperin et al 2014), it has clearly some strong limitations as the energy transport through baroclinic instability is described only roughly by the stochastic forcing, as models with baroclinic instability may lead to dynamics with different qualitative aspects (Jougla and Dritschel 2017), and as the barotropic model does not contain vorticity stretching terms. It might be interesting to consider such a barotropic model for the evolution and stability of Jovian's interior jets, as first analyzed by Ingersoll and Pollard (1982) and more recently by Kaspi and Flierl (2007).…”