**Alternating Jets in a Coupled Two-Layer Atmosphere-Interior Model of
the Extratropical Latitudes of a Gas-Giant Planet**

**T. E. Dowling (U. of Louisville), G. R. Flierl (MIT)**

We study the simplest possible coupled
atmosphere-interior model for a gas-giant planet. The model is
quasigeostrophic and consists of two active layers. Layer 1 models
the thin spherical-shell extratropical atmosphere and is
characterized by planetary-vorticity gradient .
Nondimensionalizing by the horizontal wind
speed, *U*, and the horizontal length scale, *L*, the
value for Jupiter is , which expresses the violation
of the sufficient barotropic shear-stability criterion
( ) found on Jupiter.
To capture the deep spherical geometry and Taylor-Proudman effect,
we follow Ingersoll and Pollard and examine
.
We study the linear stability problem, calculate growth rates for
unstable initial configurations, identify stable and marginally stable
configurations, and run fully nonlinear simulations of unstable
configurations. Two key parameters are the ratio of upper-layer to
lower-layer depth, , which is typically kept small, and the
inverse square of the upper-layer deformation radius, or Froude
number, . When initialized with random turbulence, the model
spontaneously forms alternating jets in the deep layer
that evolve to become
barotropically stable ( ), basically
following the Rhines scaling, and forms similar alternating jets in the
upper layer that violate the barotropic stability condition but are
nevertheless stable with respect to Arnol'd's 2nd stability criterion.
Isolated eddies tend to persist in the simulations after the jets have emerged,
which is characteristic of the gas-giant planets.
These results are
consistent with the Voyager data analysis and modeling of Dowling
(1993, *J. Atmos. Sci. * **50**: 14-22), and motivate full-scale
atmosphere-interior modeling efforts.