# LEGI - UMR 5519

Laboratoire des Écoulements Géophysiques et Industriels

## On the energetics of a two-layer baroclinic flow

21/09/2016

Thibault Jougla & David Dritschel

The formation, evolution and co-existence of jets and vortices in
turbulent planetary atmospheres is examined using a two-layer
quasi-geostrophic $\beta$-channel shallow water model. The study in
particular focuses on the vertical structure of jets. Following
Panetta (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. 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
$L_\mathsfRh=\sqrtU/\beta$.