Abstract
AbstractMotions on planetary spatial scales in the atmosphere are governed by the planetary geostrophic equations. However, little attention has been paid to the interaction between the baroclinic and barotropic flows within the planetary geostrophic scaling. This is the focus of the present study, which utilizes planetary geostrophic equations for a Boussinesq fluid supplemented by a novel evolution equation for the barotropic flow. The latter is affected by meridional momentum flux due to baroclinic flow and drag by the surface wind. The barotropic wind, on the other hand, affects the baroclinic flow through buoyancy advection. Via a relaxation towards a prescribed buoyancy profile the model produces realistic major features of the zonally symmetric wind and temperature fields. We show that there is considerable cancellation between the barotropic and the baroclinic surface zonal mean zonal winds. Linear and nonlinear model responses to steady diabatic zonally asymmetric forcing are investigated, and the arising stationary waves are interpreted in terms of analytical solutions. We also study the problem of baroclinic instability on the sphere within the present model.
Highlights
Using scale considerations, Burger (1958) suggested that for atmospheric motions on planetary scales, that is, scales comparable with the radius of the Earth, the vorticity is quasi-stationary and the vorticity equation takes the form of a balance between the divergence of the horizontal wind and the advection of planetary vorticity
This is the focus of the present study, which utilizes planetary geostrophic equations for a Boussinesq fluid supplemented by a novel evolution equation for the barotropic flow
The latter is affected by meridional momentum flux due to baroclinic flow and drag by the surface wind
Summary
Using scale considerations, Burger (1958) suggested that for atmospheric motions on planetary scales, that is, scales comparable with the radius of the Earth, the vorticity is quasi-stationary and the vorticity equation takes the form of a balance between the divergence of the horizontal wind and the advection of planetary vorticity. The vertical velocity in the anelastic approximation of the PGEs results solely from variations of f and there is only one prognostic equation, namely for temperature Because of their reduced complexity the PGEs are part of the atmospheric module in some Earth system models of intermediate complexity (e.g., Petoukhov et al, 2000; Totz et al, 2018), allowing numerically efficient long-term climate simulations (for examples see Ganopolski and Rahmstorf, 2001; Claussen et al, 2002; Petoukhov et al, 2005).
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